Gabaergic

Balanced control of neuronal activity is central in maintaining function and viability of neuronal circuits. The endocannabinoid system tightly controls neuronal excitability. Here, we show that endocannabinoids directly target hippocampal glutamatergic neurons to provide protection against acute epileptiform seizures in mice. Functional CB1 cannabinoid receptors are present on glutamatergic terminals of the hippocampal formation, colocalizing with vesicular glutamate transporter 1 (VGluT1). Conditional deletion of the CB1 gene either in cortical glutamatergic neurons or in forebrain GABAergic neurons, as well as virally induced deletion of the CB1 gene in the hippocampus, demonstrate that the presence of CB1 receptors in glutamatergic hippocampal neurons is both necessary and sufficient to provide substantial endogenous protection against kainic acid (KA)-induced seizures. The direct endocannabinoid-mediated control of hippocampal glutamatergic neurotransmission may constitute a promising therapeutic target for the treatment of disorders associated with excessive excitatory neuronal activity.

The basal forebrain (BF) plays crucial roles in arousal, attention, and memory, and its impairment is associated with a variety of cognitive deficits. The BF consists of cholinergic, GABAergic, and glutamatergic neurons. Electrical or optogenetic stimulation of BF cholinergic neurons enhances cortical processing and behavioral performance, but the natural activity of these cells during behavior is only beginning to be characterized. Even less is known about GABAergic and glutamatergic neurons. Here, we performed microendoscopic calcium imaging of BF neurons as mice engaged in spontaneous behaviors in their home cages (innate) or performed a go/no-go auditory discrimination task (learned). Cholinergic neurons were consistently excited during movement, including running and licking, but GABAergic and glutamatergic neurons exhibited diverse responses. All cell types were activated by overt punishment, either inside or outside of the discrimination task. These findings reveal functional...

The dorsal pons has long been implicated in the generation of rapid eye movement (REM) sleep, but the underlying circuit mechanisms remain poorly understood. Using cell-type-specific microendoscopic Ca2+ imaging in and near the laterodorsal tegmental nucleus, we found that many glutamatergic neurons are maximally active during REM sleep (REM-max), while the majority of GABAergic neurons are maximally active during wakefulness (wake-max). Furthermore, the activity of glutamatergic neurons exhibits a medio-lateral spatial gradient, with medially located neurons more selectively active during REM sleep.

The forkhead box O (FoxO) proteins regulate processes ranging from cell longevity to cell apoptosis and function as transcription factors. FoxO3a is expressed throughout the brain including the hippocampus. In the present study, we investigated the changes in FoxO3a immunoreactivity and its protein levels in the gerbil hippocampal CA1 region after 5 min of transient global cerebral ischemia. FoxO3a immunoreactivity and protein levels in the ischemic CA1 region, which is very vulnerable to ischemic damage, were slightly decreased from 3 h after ischemia-reperfusion (I-R) and maintained until 12 h after I-R. One and 2 days after I-R, FoxO3a immunoreactivity and protein levels were similar to those in the sham-operated group. At 3 days after I-R, FoxO3a immunoreactivity and protein levels were markedly increased in the CA1 region. FoxO3a immunoreactivity was hardly detected in pyramidal neurons from 5 days after I-R; however, at 5 days after I-R, FoxO3a immunoreactivity was detected in astrocytes and GABAergic interneurons of the ischemic CA1 region. These results indicate that both FoxO3a immunoreactivity and protein levels are distinctively altered in the ischemic CA1 region after transient cerebral ischemia, and that the changes in FoxO3a expression may be related to the ischemia-induced delayed neuronal death.

Gamma-aminobutyric acid (GABA) is the prevalent inhibitory neurotransmitter in nervous systems promoting sleep in both mammals and insects. In the Madeira cockroach, sleep-wake cycles are controlled by a circadian clock network in the brain's optic lobes, centered in the accessory medulla (AME) with its innervating pigment-dispersing factor (PDF) expressing clock neurons at the anterior-ventral rim of the medulla. GABA is present in cell clusters that innervate different circuits of the cockroach's AME clock, without colocalizing in PDF clock neurons. Physiological, immunohistochemical, and behavioral assays provided evidence for a role of GABA in light entrainment, possibly via the distal tract that connects the AME's glomeruli to the medulla. Furthermore, GABA was implemented in clock outputs to multiple effector systems in optic lobe and midbrain. Here, GABAergic brain circuits were analyzed further, focusing on the circadian system in search for sleep/wake controlling brain circuits. All GABAimmunoreactive neurons of the cockroach brain were also stained with an antiserum against the GABA-synthesizing enzyme glutamic acid decarboxylase. We found strong overlap of the distribution of GABA-immunoreactive networks with PDF clock networks in optic lobes and midbrain. Neurons in five of the six soma groups that innervate the clock exhibited GABA immunoreactivity. The intensity of GABA immunoreactivity in the distal tract showed daily fluctuations with maximum staining intensity in the middle of the day and weakest staining at the end of the day. Quantification via enzyme-linked immunosorbent assay and quantitative liquid chromatography coupled to electrospray ionization tandem mass spectrometry, likewise, showed higher GABA levels in the optic lobe during the inactivity phase of the cockroach during the day and lower levels during its activity phase at dusk. Our data further support the hypothesis that light-and PDF-dependently the circadian clock network of the cockroach controls GABA levels and thereby promotes sleep during the day.

We have used specific antisera against proteinconjugated 7-aminobutyric acid (GABA) in immunocytochemical preparations to investigate the distribution of putatively GABAergic neurons in the brain and suboesophageal ganglion of the sphinx moth Manduca sexta. About 20000 neurons per brain hemisphere exhibit GABA-immunoreactivity. Most of these are optic-lobe interneurons, especially morphologically centrifugal neurons of the lamina and tangential neurons that innervate the medulla or the lobula complex. Many GABA-immunoreactive neurons, among them giant fibers of the lobula plate, project into the median protocerebrum. Among prominent GABAimmunoreactive neurons of the median protocerebrum are about 150 putatively negative-feedback fibers of the mushroom body, innervating both the calyces and lobes, and a group of large, fan-shaped neurons of the lower division of the central body. Several commissures in the supra-and suboesophageal ganglion exhibit GABA-immunoreactivity. In the suboesophageal ganglion, a group of contralaterally descending neurons shows GABA-Iike immunoreactivity. The frontal ganglion is innervated by immunoreactive processes from the tritocerebrum but does not contain GABAimmunoreactive somata. With few exceptions the brain nerves do not contain GABA-immunoreactive fibers.

Interneurons are GABAergic neurons responsible for inhibitory activity in the adult hippocampus, thereby controlling the activity of principal excitatory cells through the activation of postsynaptic GABAA receptors. Subgroups of GABAergic neurons innervate specific parts of excitatory neurons. This specificity indicates that particular interneuron subgroups are able to recognize molecules segregated on the membrane of the pyramidal neuron. Once these specific connections are established, a quantitative regulation of their strength must be performed to achieve the proper balance of excitation and inhibition. We will review when and where interneurons are generated. We will then detail their migration toward and within the hippocampus, and the maturation of their morphological and neurochemical characteristics. We will finally review potential mechanisms underlying the development of GABAergic interneurons. V

g-Amino butyric acid (GABA) is an ubiquitous neurotransmitter in the central nervous system and it is also present in non-neuronal cells. In this study we investigated the presence of neuronal components of the GABAergic system in lymphocytes and its functional significance. By using RT-PCR we detected mRNA expression of different components of the GABAergic system in resting and mitogen-activated lymphocytes: i) GAD67, an isoform of the enzyme that synthetizes GABA; ii) VIAAT, the vesicular protein involved in GABA storage; iii) GABA transporters (GAT-1 and GAT-2); iv) GABA-T, the enzyme that catabolizes GABA; and v) subunits that conform ionotropic GABA receptors. The presence of VIAAT protein in resting and activated cells was confirmed by immunocytochemistry. The functionality of GABA transporters was evaluated by measuring the uptake of radioactive GABA. The results show that [ 3 H]GABA uptake is 5-fold higher in activated than in resting lymphocytes. To determine if GABA subunits assemble into functional channels, we performed whole-cell recordings in activated lymphocytes. GABA and muscimol, a specific agonist of ionotropic GABA receptors, elicit macroscopic currents in about 10e15% of the cells. Finally, by using [ 3 H]thymidine incorporation assays, we determined that the presence of agonists of GABA receptor during activation inhibits lymphocyte proliferation. Our results reveal that lymphocytes have a functional GABAergic system, similar to the neuronal one, which may operate as a modulator of T-cell activation. Pharmacological modulation of this system may provide new approaches for regulation of T-cell response.

GABA A receptors (GABA A R) mediate inhibitory neurotransmission in the human brain. Neurons modify subunit expression, cellular distribution and function of GABA A R in response to different stimuli, a process named plasticity. Human lymphocytes have a functional neuronal-like GABAergic system with GABA A R acting as inhibitors of proliferation. We here explore if receptor plasticity occurs in lymphocytes. To this end, we analyzed human T lymphocyte Jurkat cells exposed to different physiological stimuli shown to mediate plasticity in neurons: GABA, progesterone and insulin. The exposure to 100 mM GABA differently affected the expression of GABA A R subunits measured at both the mRNA and protein level, showing an increase of a1, b3, and g2 subunits but no changes in d subunit. Exposure of Jurkat cells to different stimuli produced different changes in subunit expression: 0.1 mM progesterone decreased d and 0.5 mM insulin increased b3 subunits. To identify the mechanisms underlying plasticity, we evaluated the Akt pathway, which is involved in the phosphorylation of b subunits and receptor translocation to the membrane. A significant increase of phosphorylated Akt and on the expression of b3 subunit in membrane occurred in cells exposed 15 h to GABA. To determine if plastic changes are translated into functional changes, we performed whole cell recordings. After 15 h GABA-exposure, a significantly higher percentage of cells responded to GABA application when compared to 0 and 40 h exposure, thus indicating that the detected plastic changes may have a role in GABA-modulated lymphocyte function. Our results reveal that lymphocyte GABA A R are modified by different stimuli similarly and by similar mechanisms to those in neurons. This property is of significance for the development of future therapies involving pharmacological modulation of the immune response.

Hippocampal theta rhythm (HPC) may be important for various phenomena, including attention and acquisition of sensory information. Two types of HPC (types I and II) exist based on pharmacological, behavioral, and electrophysiological characteristics. Both types occur during locomotion, whereas only type II (atropine-sensitive) is present under urethane anesthesia. The circuit of HPC synchronization includes the medial septum-diagonal band of Broca (MSDB), with cholinergic and ␥-aminobutyric acid (GABA)ergic neurons comprising the two main projections from MSDB to HPC. The primary aim of the present study was to assess the effects of GABAergic MSDB lesions on urethane-and locomotion-related HPC, and compare these effects to those of cholinergic MSDB lesions. Saline, kainic acid (KA), or 192 IgG-saporin (SAP) was injected into MSDB before recording. KA preferentially destroys GABAergic MSDB neurons, whereas SAP selectively eliminates cholinergic MSDB neurons. A fixed recording electrode was placed in the dentate midmolecular layer, and stimulating electrodes were placed in the posterior hypothalamus (PH), and medial perforant path (PP). Under urethane anesthesia, HPC was induced by tail pinch, PH stimulation, and systemic physostigmine; none of the rats with KA or SAP showed HPC in any of these conditions. During locomotion, HPC was attenuated, but not eliminated, in rats with KA or SAP lesions. Intraseptal KA in combination with either intraseptal SAP or PP lesions reduced locomotion-related HPC beyond that observed with each lesion alone, virtually eliminating HPC. In contrast, intraseptal SAP combined with PP lesions did not reduce HPC beyond the effect of each lesion alone. We conclude that both GABAergic and cholinergic MSDB neurons are necessary for HPC under urethane, and that each of these septohippocampal projections contributes to HPC during locomotion.

The perifornical area in the posterior lateral hypothalamus (PeFLH) has been implicated in several physiological functions including the sleep-wakefulness regulation. The PeFLH area contains several cell types including those expressing orexins (Orx; also known as hypocretins), mainly located in the PeF nucleus. The aim of the present study was to elucidate the synaptic interactions between Orx neurons located in the PeFLH area and different brainstem neurons involved in the generation of wakefulness and sleep stages such as the locus coeruleus (LC) nucleus (contributing to wakefulness) and the oral pontine reticular nucleus (PnO) nucleus (contributing to REM sleep). Anatomical data demonstrated the existence of a neuronal network involving the PeFLH area, LC, and the PnO nuclei that would control the sleep-wake cycle. Electrophysiological experiments indicated that PeFLH area had an excitatory effect on LC neurons. PeFLH stimulation increased the firing rate of LC neurons and induced an activation of the EEG. The excitatory effect evoked by PeFLH stimulation in LC neurons was blocked by the injection of the Orx-1 receptor antagonist SB-334867 into the LC. Similar electrical stimulation of the PeFLH area evoked an inhibition of PnO neurons by activation of GABAergic receptors because the effect was blocked by bicuculline application into the PnO. Our data also revealed that the LC and PnO nuclei exerted a feedback control on neuronal activity of PeFLH area. Electrical stimulation of LC facilitated firing activity of PeFLH neurons by activation of catecholaminergic receptors whereas PnO stimulation inhibited PeFLH neurons by activation of GABAergic receptors. In conclusion, Orx neurons of the PeFLH area seem to be an important organizer of the wakefulness and sleep stages in order to maintain a normal succession of stages during the sleep-wakefulness cycle.

The neuropeptide PACAP, acting as a co-transmitter, increases neuronal excitability, which may enhance anxiety and arousal associated with threat conveyed by multiple sensory modalities. The distribution of neurons expressing PACAP and its receptor, PAC1, throughout the mouse nervous system was determined, in register with expression of glutamatergic and GABAergic neuronal markers, to develop a coherent chemoanatomical picture of PACAP role in brain motor responses to sensory input. A circuit role for PACAP was tested by observing Fos activation of brain neurons after olfactory threat cue in wild-type and PACAP knockout mice. Neuronal activation and behavioral response, were blunted in PACAP knockout mice, accompanied by sharply downregulated vesicular transporter expression in both GABAergic and glutamatergic neurons expressing PACAP and its receptor. This report signals a new perspective on the role of neuropeptide signaling in supporting excitatory and inhibitory neurotransmission in the nervous system within functionally coherent polysynaptic circuits.

Calbindin cells represent a major interneuron subtype of the cortical/pallial regions, such as the basolateral amygdala, which are often analyzed in studies of tangential migration of interneurons from the subpallial ganglionic eminences to the pallium/cortex. However, previous evidence suggests that during development the calbindin cells may include more than one of the interneuron subtypes found in the adult pallium/cortex. Furthermore, in the adult basolateral amygdala, calbindin cells include a subpopulation of non-GABAergic (non-interneuron) cells. To better characterize these cells throughout development, in the present study we investigated the colocalization of calbindin, parvalbumin and GABA in cells of the mouse basolateral amygdala during late embryonic (E16.5) and several postnatal ages from birth until 4 weeks after birth (P0, P10 and P28). Our results indicate that CB, PV and GABA show a dynamic pattern of colocalization in cells of the mouse basolateral amygdalar nucleus throughout development. From E16.5 through P28, the majority of CB+ neurons and virtually all PV+ neurons are GABAergic. However, after P10, the percentage of GABAergic CB+ cells decline from 96% to 70%. Furthermore, while only 9% of CB+ neurons are PV+ at P10, this percentage raises to 42% at P28. At all postnatal ages studied, the majority of the PV+ cells are CB+, suggesting that PV+ interneurons develop postnatally mainly as a subpopulation within the CB+ cells of the basolateral amygdalar nucleus. These results are important for interpreting data from interneuron migration.

M. C. DfAZ AND D. P. CARDINALI. GABA as a presumprive pcmcrine signal in rhe pined gland. Evidence on nn intrapineal GABAergic system. BRAIN RES BULL 25(2) 339-344. 1990.-CiABA is present in the pineal gland of several mammals, where it is synthesized in situ as well as taken up from the circulation. This article reviews available information suggesting a local, physiological role of pineal GABA. Both the pinealocytes and the glial pineal cells have the capacity to take up GABA from the extracellular space. The GABA synthesizing enzyme glutamic decarboxylase (GAD) is detectable in the pineal gland; in the bovine pineal GAD exhibits "neuronal-like" properties. By employing a specific antibody against GABA, about 15% of pinealocytes gave a positive reaction in bovine pineal glands. After a depolarizing stimulus, GABA was released from bovine and rat pineal glands by both Ca'+-dependent and Ca'+-independent p recesses. By employing neuronal and glial GABA uptake inhibitors, most %GABA release in bovine pineal gland could be attributed to a "neuronal" (presumably pinealocyte) compartment. Several components of the GABA type A receptor supramolecular complex (i.e., GABA binding sites. central-type benzodiazepine binding sites, Cl-ionophore), as well as a minor population of GABA type B receptor sites, were detected in bovine and human pineal glands. In the rat pineals, GABA is released by norepinephrine (NE) acting through alpha,-adrenoceptors. Physiological concentrations of GABA, by its effect on type A receptor sites, impaired NE-induced melatonin release; by acting on GABA type B receptors, it decreased NE release. Another presumable presynaptic effect of GABA (i.e., to augment maximal velocity and to decrease affinity of NE uptake) was mediated by type A receptor sites. It is proposed that pre-and postsynaptic activity of GABA in the pineal does not differ from that found for GABA interneurons in local circuits of the brain. GABA Pineal gland Paracrine relations GABA receptors Benzodiazepine receptors Cl ionophore Glutamic acid decarboxylase Glial uptake Alpha,-adrenoceptors Norepinephtine uptake and release Melatonin release GABAergic interneurons GABA immunohistochemistry

Umbilical cord blood contains a population of non-hematopoietic multipotent stem cells that are capable of neuronal differentiation in-vitro. These cells have shown great potential as a therapeutic tool for central nervous system diseases and disorders. However whether these cells are able to produce neurons with similar developmental and functional characteristics to indigenous neurons within the brain remains poorly investigated. In this study, we used purified umbilical cord blood non-hematopoietic stem cells to produced GABAergic neurons with similar developmental and functional characteristics to cortical GABAergic neurons. We analyzed the expression of transcription factors MASH1, DLX1 and DLX2 throughout the 24 days of a sequential neuronal induction protocol and found that their expression patterns resembled those reported in the developing human cortex. The derived neurons also expressed components of GABAergic neurotransmission including GABA regulatory enzymes, GABA recep...

The hippocampus, a key structure in learning and memory processes, receives a powerful cholinergic innervation from the septum and contains nicotinic acetylcholine receptors (nAChRs). Early in postnatal development, activation of nAChRs by nicotine or endogenous acetylcholine contributes to enhance synaptic signalling. Here, the patch‐clamp technique was used to assess the contribution of α7 and β2‐containing (α7* and β2*) nAChRs to nicotine‐elicited modulation of GABAergic and glutamatergic activity at the network and single‐cell level in the immature hippocampus of wild‐type (WT), α7−/− and β2−/− mice. We found that α7* and β2* nAChRs were sufficient to modulate nicotine‐induced increase in frequency of spontaneously occurring giant depolarizing potentials (GDPs), which are generated at the network level by the synergistic action of glutamate and depolarizing GABA, and thought to play a crucial role in neuronal wiring. However, α7* but not β2* receptors were essential in nicotine‐...

In the immature hippocampus, the so-called 'giant depolarizing potentials' (GDPs) are network-driven synaptic events generated by the synergistic action of glutamate and GABA. Here we tested the hypothesis that ATP, a widely distributed neurotransmitter, directly contributes to the network activity during the first postnatal week. We found that in CA3 pyramidal cells, in the presence of the adenosine antagonist 8-cyclopentyl-1,3-dipropylxanthine (DPCPX), ATP produced a transient facilitation of GDPs followed by a depressant effect. A similar biphasic effect was produced by blockade of the ectoATPase activity with 6-N,N-diethyl-D-beta,gamma-dibromomethylene ATP (ARL-67156). The effects of exogenous and endogenous ATP on GDPs were prevented by the P2X receptor antagonist pyridoxal phosphate-6-azophenyl-2',4'-disulphonic acid (PPADS). On pyramidal cells, ATP upregulated spontaneous action-potential-dependent GABA(A)-mediated synaptic events (GABA-SPSPs), suggesting a ne...

In the adult rat hippocampus, granule cell mossy fibers (MFs) form excitatory glutamatergic synapses with CA3 principal cells and local inhibitory interneurons. However, evidence has been provided that, in young animals and after seizures, the same fibers can release in addition to glutamate GABA. Here we show that, during the first postnatal week, stimulation of granule cells in the dentate gyrus gave rise to monosynaptic GABAA-mediated responses in principal cells and in interneurons. These synapses were indeed made by MFs because they exhibited strong paired-pulse facilitation, high sensitivity to the metabotropic glutamate receptor agonistl-AP-4, and short-term frequency-dependent facilitation. MF responses were potentiated by blocking the plasma membrane GABA transporter GAT-1 with NO-711 or by allosterically modulating GABAAreceptors with flurazepam. Chemical stimulation of granule cell dendrites with glutamate induced barrages of GABAA-mediated postsynaptic currents into targ...

Early in postnatal life γ-aminobutyric acid (GABA), the primary inhibitory transmitter in adults, excites targeted neurons by an outwardly directed flux of chloride which results from the unbalance between the cation-chloride cotransporters NKCC1 and KCC2, involved in chloride uptake and extrusion, respectively. This effect contributes to generate synchronized network activity or giant depolarizing potentials (GDPs) in the developing hippocampus. Here, we review some recent data concerning the mechanisms by which GDPs are generated and their functional role in enhancing synaptic efficacy at poorly developed GABAergic and glutamatergic synapses. In adulthood, reshaping neuronal circuits due to changes in chloride homeostasis and to the shift of GABA from hyperpolarizing to depolarizing, has been implicated in several neurological disorders, including epilepsy. Evidence has been recently provided that in chronically nerve growth factor-deprived mice expressing a progressive agedependent neurodegenerative pathology resembling that observed in patients with Alzheimer's disease, the reduced expression of mRNA encoding for the Kcc2 gene and the depolarizing action of GABA lead to the reorganization of the neuronal hippocampal network. This may represent a novel mechanism by which GABAergic signaling counterbalances the loss of synaptic activity in neurodegenerative diseases.

Adenosine is a widespread neuromodulator that can be directly released in the extracellular space during sustained network activity or can be generated as the breakdown product of adenosine triphosphate (ATP). Whole cell patch-clamp recordings were performed from CA3 principal cells and interneurons in hippocampal slices obtained from P2–P7 neonatal rats to study the modulatory effects of adenosine on giant depolarizing potentials (GDPs) that constitute the hallmark of developmental networks. We found that GDPs were extremely sensitive to the inhibitory action of adenosine (IC50 = 0.52 μM). Adenosine also contributed to the depressant effect of ATP as indicated by DPCPX-sensitive changes of ATP-induced reduction of GDP frequency. Similarly, adenosine exerted a strong inhibitory action on spontaneous glutamatergic synaptic events recorded from GABAergic interneurons and on interictal bursts that developed in CA3 principal cells after blockade of γ-aminobutyric acid type A (GABAA) rec...

Reactive oxygen species (ROS) constitute important signaling molecules in the central nervous system. They regulate a number of different functions both under physiological conditions and under pathological conditions. Here we tested the hypothesis that in the immature hippocampus ATP, the most diffuse neurotransmitter in the brain, modulates synaptic transmission via ROS. We show that ATP, acting on metabotropic P2Y 1 receptors, increased the frequency of GABA A-mediated spontaneous postsynaptic currents (SPSCs) in CA3 principal cells, an effect that was prevented by the antioxidant N-acetyl-cysteine or by catalase, an enzyme that breaks down H 2 O 2. The effect of ATP on SPSCs was mimicked by H 2 O 2 or by the pro-oxidant, Fe 2؉ , which, through the Fentol reaction, catalyzes the conversion of H 2 O 2 into highly reactive hydroxyl radicals. MRS-2179, a P2Y 1 receptor antagonist, removed the facilitatory action of Fe 2؉ on SPSCs, suggesting that endogenous ATP acting on P2Y 1 receptors is involved in Fe 2؉-induced modulation of synaptic transmission. Imaging ROS with the H 2 O 2-sensitive dye DCF revealed that ATP induces generation of peroxide in astrocytes via activation of P2Y 1 receptors coupled to intracellular calcium rise. Neither N-acetyl-cysteine nor catalase prevented Ca 2؉ transients induced by ATP in astrocytes. Since a single hippocampal astrocyte can contact many neurons, ATP-induced ROS signaling may control thousands of synapses. This may be crucial for information processing in the immature brain when GABAergic activity is essential for the proper wiring of the hippocampal network.

In this review some of the recent work carried out in our laboratory concerning the functional role of GABAergic signalling at immature mossy fi bres (MF)-CA3 principal cell synapses has been highlighted. While in adulthood MF, the axons of dentate gyrus granule cells release onto CA3 principal cells and interneurons glutamate, early in postnatal life they release GABA, which exerts into targeted cells a depolarizing and excitatory action. We found that GABA Amediated postsynaptic currents (MF-GPSCs) exhibited a very low probability of release, were sensitive to L-AP4, a group III metabotropic glutamate receptor agonist, and revealed short-term frequency-dependent facilitation. Moreover, MF-GPSCs were down regulated by presynaptic GABA B and kainate receptors, activated by spillover of GABA from MF terminals and by glutamate present in the extracellular medium, respectively. Activation of these receptors contributed to the low release probability and in some cases to synapses silencing. By pairing calcium transients, associated with network-driven giant depolarizing potentials or GDPs (a hallmark of developmental networks thought to represent a primordial form of synchrony between neurons), generated by the synergistic action of glutamate and GABA with MF activation increased the probability of GABA release and caused the conversion of silent synapses into conductive ones suggesting that GDPs act as coincident detector signals for enhancing synaptic effi cacy. Finally, to compare the relative strength of CA3 pyramidal cell output in relation to their MF glutamatergic or GABAergic inputs in adulthood or in postnatal development, respectively, a realistic model was constructed taking into account different biophysical properties of these synapses.

Cortical oscillations in the beta band (13-35 Hz) are known to be modulated by the GABAergic agonist benzodiazepine. To investigate the mechanisms generating the å20-Hz oscillations in the human cortex, we administered benzodiazepines to healthy adults and monitored cortical oscillatory activity by means of magnetoencephalography. Benzodiazepine increased the power and decreased the frequency of beta oscillations over rolandic areas. Minimum current estimates indicated the effect to take place around the hand area of the primary sensorimotor cortex. Given that previous research has identified sources of the beta rhythm in the motor cortex, our results suggest that these same motor-cortex beta sources are modulated by benzodiazepine. To explore the mechanisms underlying the increase in beta power with GABAergic inhibition, we simulated a conductancebased neuronal network comprising excitatory and inhibitory neurons. The model accounts for the increase in the beta power, the widening of the spectral peak, and the slowing down of the rhythms with benzodiazepines, implemented as an increase in GABAergic conductance. We found that an increase in IPSCs onto inhibitory neurons was more important for generating neuronal synchronization in the beta band than an increase in IPSCs onto excitatory pyramidal cells.

Selective vulnerability is an enigmatic feature of neurodegenerative diseases (NDs), whereby a widely expressed protein causes lesions in specific brain regions and cell types. This selectivity may arise from cells possessing varying capacities to regain proteostasis when stressed by cytotoxic protein conformers. Using the RiboTag method in mice, translational responses of five neural subtypes to acquired prion disease (PrD) were measured. Pre-onset and disease onset timepoints were chosen based on longitudinal electroencephalography (EEG) that revealed a gradual increase in theta power between 10- and 18-weeks after prion injection, resembling a clinical feature of human PrD. At disease onset, marked by significantly increased theta power and histopathological lesions, mice had pronounced translatome changes in all five cell types despite having a normal outward appearance. Remarkably, at a pre-onset stage, prior to EEG and neuropathological changes, we found that 1) translatomes o...

Inputs from GABAergic and glutamatergic neurons are suspected to play an important role in regulating the activity of the gonadotropin-releasing hormone (GnRH) neurons. The GnRH neurons exhibit marked plasticity to control the ovarian cycle with circulating estradiol concentrations having profound "feedback" effects on their activity. This includes "negative feedback" responsible for suppressing GnRH neuron activity and "positive feedback" that occurs at mid-cycle to activate the GnRH neurons to generate the preovulatory luteinizing hormone surge. In the present study, we employed brain slice electrophysiology to question whether synaptic ionotropic GABA and glutamate receptor signaling at the GnRH neuron changed at times of negative and positive feedback. We used a well characterized estradiol (E)-treated ovariectomized (OVX) mouse model to replicate negative and positive feedback. Miniature and spontaneous postsynaptic currents (mPSCs and sPSCs) attributable to GABA A and glutamatergic receptor signaling were recorded from GnRH neurons obtained from intact diestrous, OVX, OVX ϩ E (negative feedback), and OVX ϩ EϩE (positive feedback) female mice. Approximately 90% of GnRH neurons exhibited spontaneous GABA A-mPSCs in all groups but no significant differences in the frequency or kinetics of mPSCs were found at the times of negative or positive feedback. Approximately 50% of GnRH neurons exhibited spontaneous glutamate mPSCs but again no differences were detected. The same was true for spontaneous PSCs in all cases. These observations indicate that the kinetics of ionotropic GABA and glutamate receptor synaptic transmission to GnRH neurons remain stable across the different estrogen feedback states.

The amino acid transmitter γ-aminobutyric acid (GABA) is suspected to play an important role in regulating the activity of the gonadotropinreleasing hormone (GnRH) neurons controlling fertility. Rodent GnRH neurons have a novel dendritic compartment termed the "distal dendron" through which action potentials pass to the axon terminals and where inputs from the kisspeptin pulse generator drive pulsatile GnRH secretion. Combining Gnrh1-Cre mice with the Cre-dependent calcium sensor GCaMP6 and confocal imaging of acute brain slices, we examined whether GABA regulated intracellular calcium concentrations ([Ca 2+ ]) in the GnRH neuron distal dendron. Short puffs of GABA on the dendron evoked either a monophasic sustained suppression of [Ca 2+ ] or a biphasic acute elevation in [Ca 2+ ] followed by the sustained suppression. Application of muscimol to the dendron replicated the acute elevation in [Ca 2+ ] while baclofen generated the sustained suppression. Robust GABA B receptor-mediated inhibition was observed in 80% to 100% of dendrons recorded from females across the estrous cycle and from approximately 70% of dendrons in males. In contrast, the GABA A receptor-mediated excitation was rare in males and varied across the estrous cycle, being most prominent at proestrus. The activation of GABA B receptors potently suppressed the stimulatory effect of kisspeptin on the dendron. These observations demonstrate that the great majority of GnRH neuron distal dendrons are regulated by GABAergic inputs in a sex-and estrous cycle-dependent manner, with robust GABA B receptor-mediated inhibition being the primary mode of signaling. This provides a new, kisspeptin-independent, pathway for the regulation of pulsatile and surge modes of GnRH secretion in the rodent.

The amino acid transmitter γ-aminobutyric acid (GABA) is suspected to play an important role in regulating the activity of the gonadotropin-releasing hormone (GnRH) neurons controlling fertility. Rodent GnRH neurons have a novel dendritic compartment termed the “distal dendron” through which action potentials pass to the axon terminals and where inputs from the kisspeptin pulse generator drive pulsatile GnRH secretion. Combining Gnrh1-Cre mice with the Cre-dependent calcium sensor GCaMP6 and confocal imaging of acute brain slices, we examined whether GABA regulated intracellular calcium concentrations ([Ca2+]) in the GnRH neuron distal dendron. Short puffs of GABA on the dendron evoked either a monophasic sustained suppression of [Ca2+] or a biphasic acute elevation in [Ca2+] followed by the sustained suppression. Application of muscimol to the dendron replicated the acute elevation in [Ca2+] while baclofen generated the sustained suppression. Robust GABAB receptor-mediated inhibiti...

Inputs from GABAergic and glutamatergic neurons are suspected to play an important role in regulating the activity of the gonadotropin-releasing hormone (GnRH) neurons. The GnRH neurons exhibit marked plasticity to control the ovarian cycle with circulating estradiol concentrations having profound "feedback" effects on their activity. This includes "negative feedback" responsible for suppressing GnRH neuron activity and "positive feedback" that occurs at mid-cycle to activate the GnRH neurons to generate the preovulatory luteinizing hormone surge. In the present study, we employed brain slice electrophysiology to question whether synaptic ionotropic GABA and glutamate receptor signaling at the GnRH neuron changed at times of negative and positive feedback. We used a well characterized estradiol (E)-treated ovariectomized (OVX) mouse model to replicate negative and positive feedback. Miniature and spontaneous postsynaptic currents (mPSCs and sPSCs) attri...

Dorsomedial hypothalamus (DMH) plays a key role in the organization of functional responses to stress. Microinjection of GABA A antagonist bicuculline methiodide (BMI) into DMH evokes cardiovascular and neuroendocrine changes typically seen in experimental emotional stress. The aim of the present study was to investigate the peripheral metabolism of glucose following microinjection of BMI, (10pmol / 100nl) or vehicle (NaCl 0.9%-100nl) into DMH. Male wistar rats were anesthetized and a guide cannula was set into DMH. The jejunal loop was isolated and perfused with Tyrode solution. Blood samples were taken 15 and 40 minutes after the beginning of experimental period. When compared to vehicle, BMI into DMH increased plasma insulin (0.22±0.04 vs. 0.34±0.04 ng/ml; P<0.05), decreased glucose-6-phosphate in the liver (0.012±0.003 vs. 0.004±0.002 mol/g tissue; P<0.05) and increased this same metabolite in muscle (0.14±0.05 vs. 0.43±0.10 mol/g tissue; P<0.05). We found that DMH activation caused changes in plasma insulin and intermediate metabolite of glycolitic pathways.

Although endocannabinoids have emerged as essential retrograde messengers in several forms of synaptic plasticity, it remains controversial whether they mediate long-term depression (LTD) of glutamatergic synapses onto excitatory and inhibitory neurons in the hippocampus. Here, we show that parvalbumin-and somatostatin/metabotropic glutamate receptor 1 a (mGlu 1a)-positive GABAergic interneurons express diacylglycerol lipase-␣ (DGL-␣), a synthesizing enzyme of the endocannabinoid 2-arachidonoylglycerol (2-AG), albeit at lower levels than principal cells. Moreover, this lipase accumulates postsynaptically around afferent excitatory synapses in all three cell types. To address the role of retrograde 2-AG signaling in LTD, we investigated two forms: (1) produced by postsynaptic spiking paired with subsequent presynaptic stimulation or (2) induced by group I mGlu activation by (S)-3,5-dihydroxyphenylglycine (DHPG). Neither form of LTD was evoked in the presence of the mGlu 5 antagonist MPEP [2-methyl-6-(phenylethynyl)-pyridine], the DGL inhibitor THL [N-formyl-L-leucine (1S)-1-[[(2S,3S)-3-hexyl-4oxo-2-oxetanyl]methyl]dodecyl ester], or the intracellularly applied Ca 2ϩ chelator BAPTA in CA1 pyramidal cells, fast-spiking interneurons (representing parvalbumin-containing cells) and interneurons projecting to stratum lacunosum-moleculare (representing somatostatin/ mGlu 1a-expressing interneurons). Both forms of LTD were completely absent in CB 1 cannabinoid receptor knockout mice, whereas pharmacological blockade of CB 1 led to inconsistent results. Notably, in accordance with their lower DGL-␣ level, a higher stimulation frequency or higher DHPG concentration was required for LTD induction in interneurons compared with pyramidal cells. These findings demonstrate that hippocampal principal cells and interneurons produce endocannabinoids to mediate LTD in a qualitatively similar, but quantitatively different manner. The shifted induction threshold implies that endocannabinoid-LTD contributes to cortical information processing during distinct network activity patterns in a cell type-specific manner.

Objectives: Alexithymia is a multicomponent personality construct that could occur in up to 53% of patients with multiple sclerosis (MS), with recent works proposing higher rates of alexithymia in progressive MS. Among the available models of alexithymia, some propose a deficient interhemispheric communication and an aberrant GABAergic transmission at its origin. However, no single study has addressed the underlying mechanism of alexithymia in MS. The aim of this work was to assess the relationship between GABAergic neurotransmission and alexithymia in progressive MS by means of transcranial magnetic stimulation (TMS). Methods: Twelve patients with high alexithymia and fifteen patients with low alexithymia were included based on Toronto Alexithymia Scale (TAS). Sociodemographic, clinical and neuropsychological data were recorded. The following corticospinal excitability measures were obtained: resting motor threshold, cortical silent period (CSP which reflects cortical GABAergic function), and interhemispheric inhibition (i.e., GABAergic function mediated by interhemispheric fibers). Results: No significant group differences were observed regarding sociodemographic, clinical or neuropsychological variables. Patients with high alexithymia scores exhibited shorter CSP than those with low alexithymia scores (81.87 ± 45.72 ms vs. 145.27 ± 77.26 ms, respectively, p<0.05). A significant inverse correlation was also found between TAS scores and CSP duration (r=-0.59, p<0.05). Conclusion: This study offers insights into the neurophysiological mechanisms of alexithymia in MS. Reduced GABAergic transmission, as reflected by short CSP, seems to be associated with alexithymia in this population. Future studies would benefit from a more comprehensive evaluation of cortical and interhemispheric mechanisms in MS patients with alexithymia.

Eating addiction is the primary cause of modern obesity. Although the causal role of the lateral hypothalamic area (LHA) for eating is demonstrated in rodents, there is no evidence in primates regarding naturalistic eating behaviors. We investigated the role of LHA GABAergic (LHAGABA) neurons in eating by chemogenetics in three macaques. LHAGABAneuron activation significantly increased naturalistic goal-directed behaviors and food motivation, which was specific for palatable food. PET and MRS validated the chemogenetic activation. Rs-fMRI result revealed that functional connectivity (FC) between the LHA and frontal areas was increased, while the FC between the frontal cortices was decreased after the LHAGABAneuron activation. Thus, our study elucidates the role of LHAGABAneurons in eating and obesity therapeutics for primates and humans.

Neocortical neurons expressing the serotonin 5-HT 3 receptor (5-HT 3 R) were characterized in rat acute slices by using patchclamp recordings combined with single-cell RT-PCR and histochemical labeling. The 5-HT 3A receptor subunit was expressed selectively in a subset of GABAergic interneurons coexpressing cholecystokinin (CCK) and vasoactive intestinal peptide (VIP). The 5-HT 3B subunit was never detected, indicating that 5-HT 3 Rs expressed by neocortical interneurons did not contain this subunit. In 5-HT 3A-expressing VIP/CCK interneurons, serotonin induced fast membrane potential depolarizations by activating an inward current that was blocked by the selective 5-HT 3 R antagonist tropisetron. Furthermore, we observed close appositions between serotonergic fibers and the dendrites and somata of 5-HT 3 R-expressing neurons, suggestive of possible synaptic contacts. Indeed, in interneurons exhibiting rapid excitation by serotonin, local electrical stimulations evoked fast EPSCs of large amplitude that were blocked by tropisetron. Finally, 5-HT 3 R-expressing neurons were also excited by a nicotinic agonist, indicating that serotonergic and cholinergic fast synaptic transmission could converge onto VIP/CCK interneurons. Our results establish a clear correlation between the presence of the 5-HT 3A receptor subunit in neocortical VIP/CCK GABAergic interneurons, its functional expression, and its synaptic activation by serotonergic afferent fibers from the brainstem raphe nuclei.

Chandelier (or axo-axonic) cells are one of the most distinctive GABAergic interneurons in the brain. Their exquisite target specificity for the axon initial segment of pyramidal neurons, together with their GABAergic nature, long suggested the possibility that they provide the ultimate inhibitory control of pyramidal neuron output. Recent findings indicate that their function may be more complicated, and perhaps more interesting, than initially believed. Here we review these recent developments and their implications. We focus in particular on whether chandelier cells may provide a depolarizing, excitatory effect on pyramidal neuron output, in addition to a powerful inhibition.

Opioid peptides costored with glutamate have emerged as powerful regulators of long-term potentiation (LTP) induction in several hippocampal pathways. The objectives of the present study were twofold: (1) to identify which opioid receptor types (mu, delta, or kappa) regulate LTP induction at lateral perforant path-granule cell synapses and (2) to test the hypothesis that endogenous opioids regulate LTP induction via modulation of GABAergic inhibition. LTP of lateral perforant path-evoked field EPSPs was induced selectively by high-frequency stimulation applied to the outer third of the molecular layer of the dentate gyrus of rat hippocampal slices. No changes in medial perforant path responses occurred. LTP was blocked when high-frequency stimulation was applied in the presence of the mu receptor antagonist CTAP, the selective delta-1 receptor antagonist BNTX, or the delta-1 and delta-2 receptor antagonist naltrindole. By contrast, the kappa-1 opioid receptor antagonist NBNI had no effect on LTP induction. The role of GABAergic inhibition was investigated by comparing the effect of naloxone on LTP induction in slices maintained in standard buffer and picrotoxin-containing buffer. Naloxone blocked LTP in standard buffer, whereas normal LTP was induced in picrotoxin-treated, disinhibited slices. Finally, NMDA receptor blockade completely inhibited LTP in both standard and disinhibited slices. The results show that mu and delta-1 opioid receptors regulate LTP induction and that this mechanism critically depends on GABAergic inhibition. A key issue then becomes how endogenous opioids fine-tune the activity of intact inhibitory networks in the dentate gyrus, effectively gating synaptic plasticity in specific dendritic strata.

The nucleus accumbens (NAc) is a critical brain region involved in many reward-related behaviors. The NAc comprises major compartments the core and the shell, which encompass several subterritories. GABAergic medium-sized spiny neurons (MSNs) constitute the output neurons of the NAc core and shell. While the functional organization of the NAc core outputs resembles the one described for the dorsal striatum, a simple classification of the NAc shell neurons has been difficult to define due to the complexity of the compartmental segregation of cells. We used a variety of BAC transgenic mice expressing enhanced green fluorescence (EGFP) or the Cre-recombinase (Cre) under the control of the promoter of dopamine D1, D2, and D3 receptors and of adenosine A2a receptor to dissect the microanatomy of the NAc. Moreover, using various immunological markers we characterized in detail the distribution of MSNs in the mouse NAc. In addition, cell-type specific extracellular signal-regulated kinase (ERK) phosphorylation in the NAc subterritories was analyzed following acute administration of SKF81297 (a D1R-like agonist), quinpirole (a D2 receptors (D2R)-like agonist), apomorphine (a non-selective DA receptor agonist), raclopride (a D2R-like antagonist), and psychostimulant drugs, including cocaine and d-amphetamine. Each drug generated a unique topography and cell-type specific activation of ERK in the NAc. Our results show the existence of marked differences in the receptor expression pattern and functional activation of MSNs within the shell subterritories. This study emphasizes the anatomical and functional heterogeneity of the NAc, which will have to be considered in its further study.

Molecular processes in GABAergic local circuit neurons critically contribute to information processing in the hippocampus and to stress-induced activation of the amygdala. In the current study, we determined expression changes in GABA-related factors induced in subregions of the dorsal hippocampus as well as in the BLA of rats 5 h after spatial learning in a Morris water maze (MWM), using laser microdissection and quantitative real-time PCR. Spatial learning resulted in highly selective pattern of changes in hippocampal subregions: gene expression levels of neuropeptide Y (NPY) were reduced in the hilus of the dentate gyrus (DG), whereas somatostatin (SST) was increased in the stratum oriens (SO) of CA3. The GABA-synthesizing enzymes GAD65 and GAD67 as well as the neuropeptide cholecystokinin (CCK) were reduced in SO of CA1. In the BLA, expression of GAD65 and GAD67 were reduced compared to a handled Control group. These expression patterns were further compared to alterations in a ...

All dendritic spines of the inferior olive receive a combined inhibitory and excitatory input, which is critical for regulation of temporal control during sensorimotor coordination. Yet, some sources of GABAergic input to specific parts of the olive remain to be identified. While completing the map of inhibitory inputs, we establish here that part of the caudal medial accessory olive receives a GABAergic input from neurons in the contralateral superior colliculus that receive a direct input from the cerebellar nuclei. Interestingly, the laterality of this disynaptic projection is unique among olivocerebellar modules, highlighting a potential push-pull mechanism in directional gaze control.

Recent work has shown that most cells in the rostral, gustatory portion of the nucleus tractus solitarius (rNTS) in awake, freely licking rats show lick-related firing. However, the relationship between taste-related and lick-related activity in rNTS remains unclear. Here, we tested if GABA-derived inhibitory activity regulates the balance of lick-and taste-driven neuronal activity. Combinatorial viral tools were used to restrict expression of ChR2-EYFP to GAD1+ GABAergic neurons. Viral infusions were bilateral in rNTS. 2-4wks later, an optical fiber attached to 8-16 drivable microwires was implanted into the rNTS. After recovery, waterdeprived rats were presented with taste stimuli in an experimental chamber. Trials were 5 consecutive taste licks [NaCl, KCl, NH4Cl, sucrose, MSG/IMP, citric acid, quinine, or artificial saliva (AS)] separated by 5 AS licks on a VR5 schedule. Each taste lick triggered a 1s train of laser light (25Hz; 473nm; 8-10mW) in a random half of the trials. In all, 113 cells were recorded

Background: Although it is well recognized that anesthetics modulate the central control of cardiorespiratory homeostasis, the cellular mechanisms by which anesthetics alter cardiac parasympathetic activity are poorly understood. One common site of action of anesthetics is inhibitory neurotransmission. This study investigates the effect of propofol on ␥-aminobutyric acid-mediated (GABAergic) and glycinergic neurotransmission to cardiac parasympathetic neurons. Methods: Cardiac parasympathetic neurons were identified in vitro by the presence of a retrograde fluorescent tracer, and spontaneous GABAergic and glycinergic synaptic currents were examined using whole cell patch clamp techniques. Results: Propofol at concentrations of 1.0 M and greater significantly (P < 0.05) increased the duration and decay time of spontaneous GABAergic inhibitory postsynaptic currents. To determine whether the action of propofol was at presynaptic or postsynaptic sites, tetrodotoxin was applied to isolate miniature inhibitory postsynaptic currents. Propofol at concentrations of 1.0 M and greater significantly (P < 0.05) prolonged the decay time and duration of miniature inhibitory postsynaptic currents, indicating that propofol directly alters GABAergic neurotransmission at a postsynaptic site. Propofol at high concentrations (> 50 M) also inhibited the frequency of both GABAergic inhibitory postsynaptic currents and miniature inhibitory postsynaptic currents. Propofol at concentrations up to 50 M had no effect on glycinergic neurotransmission. Conclusions: Propofol may vary heart rate by modulating GABAergic neurotransmission to cardiac parasympathetic neurons. At clinically relevant concentrations (> 1.0 M), propofol facilitated GABAergic responses in cardiac vagal neurons by increasing decay time, which would increase inhibition of cardioinhibitory cardiac vagal neurons and evoke an increase in heart rate. At higher supraclinical concentrations (> 50 M), propofol inhibits GABAergic neurotransmission to cardiac vagal neurons, which would evoke a decrease in heart rate.

NO is involved in the neural control of heart rate, and NO synthase expressing neurons and terminals have been localized in the nucleus ambiguus where parasympathetic cardiac vagal preganglionic neurons are located; however, little is known about the mechanisms by which NO alters the activity of premotor cardiac vagal neurons. This study examines whether the NO donor sodium nitroprusside ([SNP] 100 mol/L) and precursor, L-arginine (10 mmol/L), modulate excitatory and inhibitory synaptic neurotransmission to cardiac vagal preganglionic neurons. Glutamatergic, GABAergic, and glycinergic activity to cardiac vagal neurons was examined using whole-cell patch-clamp recordings in an in vitro brain slice preparation in rats. Both SNP, as well as L-arginine, increased the frequency of GABAergic neurotransmission to cardiac vagal preganglionic neurons but decreased the amplitude of GABAergic inhibitory postsynaptic currents. In contrast, both L-arginine and SNP inhibited the frequency of glutamatergic and glycinergic synaptic events in cardiac vagal preganglionic neurons. SNP and L-arginine also decreased glycinergic inhibitory postsynaptic current amplitude, and this response persisted in the presence of tetrodotoxin. Inclusion of the NO synthase inhibitor 7-nitroindazole (100 mol/L) prevented the L-arginine-evoked responses. These results demonstrate that NO differentially regulates excitatory and inhibitory neurotransmission, facilitating GABAergic and diminishing glutamatergic and glycinergic neurotransmission to cardiac vagal neurons.

This study examined whether adenosine 5'-triphosphate (ATP) modulated inhibitory glycinergic and GABAergic neurotransmission to cardiac vagal neurons. Inhibitory activity to cardiac vagal neurons was isolated and examined using whole-cell patch-clamp recordings in an in vitro brain slice preparation in rats. ATP (100 µM) evoked increases in the frequency of glycinergic and GABAergic miniature inhibitory postsynaptic currents (mIPSCs) in cardiac vagal neurons which were blocked by the broad P2 receptor antagonist pyridoxal-phosphate-6-azophenyl-2',4'-disulphonic acid (100 µM). Application of the P2Y agonists uridine triphosphate (15 µM) and adenosine 5'-0-(Zthiodiphosphate) (60 µM) did not enhance inhibitory neurotransmission to cardiac vagal neurons however, application of the selective P2X receptor agonist, α, β-methylene ATP (100 µM), increased glycinergic and GABAergic mIPSC neurotransmission to cardiac vagal neurons. The increase in inhibitory neurotransmission evoked by α, β-methylene ATP was abolished by the selective P2X receptor antagonist 2',3'-O-(2,4,6-Trinitrophenyl) adenosine 5'-triphosphate (100 µM) indicating P2X receptors enhance the release of inhibitory neurotransmitters to cardiac neurons. The voltage gated calcium channel blocker cadmium chloride did not alter the evoked increase in inhibitory mIPSCs. This work demonstrates that P2X receptor activation enhances inhibitory neurotransmission to parasympathetic cardiac vagal neurons and demonstrates an important functional role for ATP mediated purinergic signaling to cardiac vagal neurons.

The heart rate increases during inspiration and decreases during expiration. This respiratory sinus arrhythmia (RSA) occurs by modulation of premotor cardioinhibitory parasympathetic neuron (CPN) activity. However, RSA has not been fully characterized in rats, and despite the critical role of CPNs in the generation of RSA, little is known about the mechanisms that mediate this cardiorespiratory interaction. This study demonstrates that RSA in conscious rats is similar to that in other species. The mechanism of RSA was then examined in vitro. Rhythmic inspiratory-related activity was recorded from the hypoglossal rootlet of 700-to 800-m medullary sections. CPNs were identified by retrograde fluorescent labeling, and neurotransmission to CPNs was examined using patch-clamp electrophysiological techniques. During inspiratory bursts, the frequency of both spontaneous ␥-aminobutyric acidergic (GABAergic) and spontaneous glycinergic synaptic events in CPNs was significantly increased. Focal application of the nicotinic antagonist dihydro-␤-erythroidine in an ␣ 4 ␤ 2-selective concentration (3 mol/L) abolished the respiratory-evoked increase in GABAergic frequency. In contrast, the increase in glycinergic frequency during inspiration was not altered by nicotinic antagonists. Prenatal nicotine exposure exaggerated the increase in GABAergic frequency during inspiration and enhanced GABAergic synaptic amplitude both between and during inspiratory events. Glycinergic synaptic frequency and amplitude were unchanged by prenatal nicotine exposure. This study establishes a neurochemical link between neurons essential for respiration and CPNs, reveals a functional role for endogenous acetylcholine release and the activation of nicotinic receptors in the generation of RSA, and demonstrates that this cardiorespiratory interaction is exaggerated in rats prenatally exposed to nicotine.

The basolateral amygdala (BL) is a putative site for regulating anxiety, where inhibition and excitation respectively lead to decreases and increases in anxiety-like behaviors. The BL contains local networks of GABAergic interneurons that are subdivided into classes based on neurochemical content, and are hypothesized to regulate unique functional responses of local glutamatergic projection neurons. Recently it was demonstrated that lesioning a portion of the BL interneuronal population, those interneurons that express neurokinin1 receptors (NK 1r), resulted in anxiety-like behavior. In the current study, these NK 1r expressing cells of the BL are further phenotypically characterized, demonstrating approximately 80% co-expression with GABA thus confirming them as GABAergic interneurons. These NK 1r interneurons also co localize with two distinct populations of BL interneurons as defined by the neuropeptide content. 41.8% of the NK 1r positive cells are also positive for neuropeptide Y (NPY) and 39.7% of the NK 1r positive cells are also positive for cholecystokinin (CCK). In addition to enhancing the phenotypic characterization, the extent to which the NK 1r cells of amygdala nuclei contribute to anxiety-like responses was also investigated. Lesioning the NK 1r expressing interneurons, with a stable form of substance P (SSP; the natural ligand for NK 1r) coupled to the targeted toxin saporin (SAP), in the anterior and posterior divisions of the BL was correlated to increased anxiety-like behaviors compared to baseline and control treated rats. Furthermore the phenotypic and regional selectivity of the lesions was also confirmed.

Seizures and epilepsy are some of the most common serious neurological disorders, with approximately 80% of patients living in developing/underdeveloped countries. However, about one in three patients do not respond to currently available pharmacological treatments, indicating the need for research into new anticonvulsant drugs (ACDs). The GABAergic system is the main inhibitory system of the brain and has a central role in seizures and the screening of new ACD candidates. It has been demonstrated that the action of agents on endocannabinoid receptors modulates the balance between excitatory and inhibitory neurotransmitters; however, studies on the anticonvulsant properties of endocannabinoids from plant oils are relatively scarce. The Amazon region is an important source of plant oils that can be used for the synthesis of new fatty acid amides, which are compounds analogous to endocannabinoids. The synthesis of such compounds represents an important approach for the development of ...