. Intracellular stores release Ca 2/ Asaf Keller. Distribution and activation of intracellular Ca... more . Intracellular stores release Ca 2/ Asaf Keller. Distribution and activation of intracellular Ca 2/ stores through at least two pathways, each mediated by a specific in cultured olfactory bulb neurons. J. Neurophysiol. 78: 2176family of receptors. In one pathway, Ca 2/ entry through 2185, 1997. The presence and distribution of intracellular Ca 2/ the plasma membrane activates r yanodine receptors in the release pathways in olfactory bulb neurons were studied in dissoci-ER that mediate Ca 2/ release from this organelle ( Galione ated cell cultures. Histochemical techniques and imaging of Ca 2/ 1992 ) . This process often is referred to as Ca 2/ -induced fluxes were used to identify two major intracellular Ca 2/ release Ca 2/ release ( CICR ) ( Ehrlich et al. 1994; Henzi and mechanisms: inositol 1,4,5-triphosphate receptor (IP 3 R)-mediated MacDermott 1992; Irving et al. 1992; ) . release, and ryanodine receptor-mediated release. Cultured neurons The other pathway involves activation of plasma membrane were identified by immunocytochemistry for the neuron-specific marker b-tubulin III. Morphometric analyses and immunocyto-receptors -such as the glutamate-sensitive metabotropic chemistry for glutamic acid-decarboxylase revealed a heterogereceptors -that activate, through intermediary G proteins, neous population of cultured neurons with phenotypes correphospholipase C, leading to the generation of inositol 1,4,5sponding to both projection ( mitral / tufted ) and intrinsic ( peritriphosphate ( IP 3 ). IP 3 then binds to an IP 3 receptor-Ca 2/ glomerular / granule ) neurons of the in vivo olfactory bulb. channel complex on the ER, inducing Ca 2/ release ( Putney Immunocytochemistry for the IP 3 R, and labeling with fluorescent-1990; . tagged ryanodine, revealed that, irrespective of cell type, almost Although modulation of [Ca 2/ ] i in general has been all cultured neurons express IP 3 R and ryanodine binding sites shown to regulate numerous neuronal functions, in some in both somata and dendrites. Functional imaging revealed that cases, these activities may be specifically dependent on Ca 2/ intracellular Ca 2/ fluxes can be generated in the absence of exterrelease from intracellular stores (reviewed in: Simpson et al. nal Ca 2/ , using agonists specific to each of the intracellular release pathways. Local pressure application of glutamate or quis-1995). These include the modulation of neuronal excitability qualate evoked Ca 2/ fluxes in both somata and dendrites in nomi- ; Kawai and nally Ca 2/ free extracellular solutions, suggesting the presence Watanabe 1989), presynaptic transmitter release (Blaustein of IP 3 -dependent Ca 2/ release. These fluxes were blocked by Peng 1996), long-term depression and potentiapreincubation with thapsigargin and persisted in the presence of tion (Behnisch and Reymann 1995; Kasono and Hirano the glutamate receptor antagonist 6-cyano-7-nitroquinoxaline-1995; , and 2,3-dione. Local application of caffeine, a ryanodine receptor neuronal development agonist, also evoked intracellular Ca 2/ fluxes in the absence of 1995). Therefore, studies of Ca 2/ -dependent phenomena in extracellular Ca 2/ . These Ca 2/ fluxes were suppressed by preinneurons must consider the presence of intracellular release cubation with ryanodine. In all neurons, both IP 3 -and ryanodinepathways. dependent release pathways coexisted, suggesting that they interact to modulate intracellular Ca 2/ concentrations. The present study was designed to identify the types of intracellular Ca 2/ release mechanisms in cultured neurons of the rat olfactory bulb. Functional imaging of Ca 2/ fluxes I N T R O D U C T I O N and immunocytochemical techniques revealed that both IP 3and ryanodine-dependent release mechanisms are expressed Neuronal mechanisms controlling cytoplasmic calcium in a heterogeneous population of these neurons. Some of concentrations ( [ Ca 2/ ] i ) modulate a number of neuronal these results were published previously in abstract form activities, including neurotransmitter release ( Katz 1969. control of membrane excitability ( Llinás 1990 ) and receptor function ( Jaffe et al. 1994 ) , differential gene expression M E T H O D S ( Sheng and Greenberg 1990 ) , and neuronal migration and growth ( Komuro and Rakic 1995 ) . Increases in [ Ca 2/ ] i Cell cultures occur by extracellular Ca 2/ influx through transmembrane Dissociated cell cultures were prepared from 3-day-old Wistar channels and intracellular release of Ca 2/ sequestered in rat pups. Olfactory bulbs were dissected into culture medium conintracellular organelles. Because intracellular stores, such taining minimal essential medium supplemented with L-alanyl-Las the endoplasmic reticulum ( ER ) , can sequester high glutamine (MEM a medium, GIBCO), 10% fetal calf serum concentrations of Ca 2/ , these stores serve not only to buffer (GIBCO), 5% horse serum (GIBCO), and 0.6% glucose. The free intracellular Ca 2/ , but can produce rapid, local Ca 2/ meninges were removed, and the bulbs were dissociated both enzymatically (papain; 20 U/ml, Worthington) and by gentle mechani-transients in response to specific stimuli 2176 0022-3077/97 $5.00
1. Intracellular recordings were obtained from neurons in the motor cortex (MCx), in which excita... more 1. Intracellular recordings were obtained from neurons in the motor cortex (MCx), in which excitatory postsynaptic potentials (EPSPs) were evoked by microstimulation of the somatosensory cortex (SCx) and the ventrolateral nucleus (VL) of the thalamus. The effects of combined tetanic stimulation of SCx and VL on the amplitudes of these EPSPs were studied. 2. Amplitudes of both corticocortical (CC) and thalamocortical (TC) EPSPs were potentiated after combined tetanic stimulation. This potentiation occurred exclusively in neurons that were located in the superficial layers (II/III) and that received direct input from both the SCx and VL, with both inputs synapsing in close proximity to each other. In all cases, the potentiation lasted until the electrode went out of the cell (21 +/- 25 min, mean +/- SD) the longest being 90 min. We therefore refer to this potentiation as long-term potentiation (LTP). 3. Tetanic stimulation of the thalamus only did not produce LTP in neurons receiving direct input from the VL. 4. LTP was not induced in either CC or TC EPSPs in neurons located in layer V and/or in neurons receiving long-latency CC EPSPs. 5. It is concluded that TC input from the VL to the MCx is potentiated only when coactivated with the CC input from the SCx.
The purpose of this study was to determine whether long-term changes in synaptic efficacy can be ... more The purpose of this study was to determine whether long-term changes in synaptic efficacy can be induced in the pyramidal tract (PT). Tetanic stimulation of the PT induced long-term facilitation of PT input to spinal cord neurons. In contrast, tetanic stimulation of the pyramidal tract did not alter the efficacy of synaptic inputs of PT cells' intracortical axon collaterals to other cortical neurons. These findings suggest that the PT participates in motor learning by modulating the excitability of spinal cord neurons. The results also indicate that induction of LTP in the PT is dependent on postsynaptic mechanisms.
1. Intracellular recordings were obtained from neurons in the motor cortex (MCx), in which excita... more 1. Intracellular recordings were obtained from neurons in the motor cortex (MCx), in which excitatory postsynaptic potentials (EPSPs) were evoked by microstimulation of the somatosensory cortex (SCx) and the ventrolateral nucleus (VL) of the thalamus. The effects of combined tetanic stimulation of SCx and VL on the amplitudes of these EPSPs were studied. 2. Amplitudes of both corticocortical (CC) and thalamocortical (TC) EPSPs were potentiated after combined tetanic stimulation. This potentiation occurred exclusively in neurons that were located in the superficial layers (II/III) and that received direct input from both the SCx and VL, with both inputs synapsing in close proximity to each other. In all cases, the potentiation lasted until the electrode went out of the cell (21 +/- 25 min, mean +/- SD) the longest being 90 min. We therefore refer to this potentiation as long-term potentiation (LTP). 3. Tetanic stimulation of the thalamus only did not produce LTP in neurons receiving direct input from the VL. 4. LTP was not induced in either CC or TC EPSPs in neurons located in layer V and/or in neurons receiving long-latency CC EPSPs. 5. It is concluded that TC input from the VL to the MCx is potentiated only when coactivated with the CC input from the SCx.
Our aim was to investigate the patterns of functional inputs and outputs from individual barrels ... more Our aim was to investigate the patterns of functional inputs and outputs from individual barrels in the mouse somatosensory cortex, and to test the hypothesis that individual barrels in layer IV are functionally independent of direct inputs from neighboring barrels. In a mouse in vitro slice preparation of the barrel cortex, we recorded voltage-sensitive dye signals evoked in response to microstimulation of a single barrel. Activity propagated from the stimulated barrel to the supragranular layers, where it spread to activate several barrel columns. However, in no instance did activity propagate directly from the stimulated barrel to neighboring barrels. Neither suppression of GABAergic inhibition, nor activation of N-methyl-D-aspartate receptors, revealed direct interbarrel interactions. By contrast, microstimulation in the supra-or infragranular layers resulted in direct propagation of activity to neighboring barrel columns. We conclude that the neurons within individual barrels are functionally independent of direct inputs from neighboring barrels. This suggests that the response properties of layer IV barrel neurons are shaped primarily by their presynaptic thalamic afferents and by intrabarrel interactions, and that these responses are independent of direct inputs from neighboring barrels.
The posterior thalamic nucleus (PO) is a higher order nucleus heavily implicated in the processin... more The posterior thalamic nucleus (PO) is a higher order nucleus heavily implicated in the processing of somatosensory information. We have previously shown in rodent models that activity in PO is tightly regulated by inhibitory inputs from a GABAergic nucleus known as the zona incerta (ZI). The level of incertal inhibition varies under both physiological and pathological conditions, leading to concomitant changes in PO activity. These changes are causally linked to variety of phenomena from altered sensory perception to pathological pain. ZI regulation of PO is mediated by GABAA and GABAB receptors (GABAAR and GABABR) that differ in their binding kinetics and their electrophysiological properties, suggesting that each may have distinct roles in incerto-thalamic regulation. We developed a computational model to test this hypothesis. We created a two-cell Hodgkin-Huxley model representing PO and ZI with kinetically realistic GABAAR- and GABABR-mediated synapses. We simulated spontaneous...
1. Intracellular recordings were obtained from neurons in the motor cortex (MCx), in which excita... more 1. Intracellular recordings were obtained from neurons in the motor cortex (MCx), in which excitatory postsynaptic potentials (EPSPs) were evoked by microstimulation of the somatosensory cortex (SCx) and the ventrolateral nucleus (VL) of the thalamus. The effects of combined tetanic stimulation of SCx and VL on the amplitudes of these EPSPs were studied. 2. Amplitudes of both corticocortical (CC) and thalamocortical (TC) EPSPs were potentiated after combined tetanic stimulation. This potentiation occurred exclusively in neurons that were located in the superficial layers (II/III) and that received direct input from both the SCx and VL, with both inputs synapsing in close proximity to each other. In all cases, the potentiation lasted until the electrode went out of the cell (21 +/- 25 min, mean +/- SD) the longest being 90 min. We therefore refer to this potentiation as long-term potentiation (LTP). 3. Tetanic stimulation of the thalamus only did not produce LTP in neurons receiving ...
Neurotherapeutics : the journal of the American Society for Experimental NeuroTherapeutics, 2013
Spinal cord injury (SCI) causes not only sensorimotor and cognitive deficits, but frequently also... more Spinal cord injury (SCI) causes not only sensorimotor and cognitive deficits, but frequently also severe chronic pain that is difficult to treat (SCI pain). We previously showed that hyperesthesia, as well as spontaneous pain induced by electrolytic lesions in the rat spinothalamic tract, is associated with increased spontaneous and sensory-evoked activity in the posterior thalamic nucleus (PO). We have also demonstrated that rodent impact SCI increases cell cycle activation (CCA) in the injury region and that post-traumatic treatment with cyclin dependent kinase inhibitors reduces lesion volume and motor dysfunction. Here we examined whether CCA contributes to neuronal hyperexcitability of PO and hyperpathia after rat contusion SCI, as well as to microglial and astroglial activation (gliopathy) that has been implicated in delayed SCI pain. Trauma caused enhanced pain sensitivity, which developed weeks after injury and was correlated with increased PO neuronal activity. Increased CC...
The superior colliculus, usually considered a visuomotor structure, is anatomically positioned to... more The superior colliculus, usually considered a visuomotor structure, is anatomically positioned to perform sensorimotor transformations in other modalities. While there is evidence for its potential participation in sensorimotor loops of the rodent vibrissa system, little is known about its functional role in vibrissa sensation or movement. In anesthetized rats, we characterized extracellularly recorded responses of collicular neurons to different types of vibrissa stimuli. Collicular neurons had large receptive fields (median = 14.5 vibrissae). Single units displayed responses with short latencies (5.6 +/- 0.2 msec, median = 5.5) and relatively large magnitudes (1.2 +/- 0.1 spikes/stimulus, median = 1.2). Individual neurons could entrain to repetitive vibrissa stimuli delivered at < or = 20 Hz, with little reduction in phase locking, even when response magnitude was decreased. Neurons responded preferentially to vibrissa deflections at particular angles, with 43% of the cells hav...
The Journal of neuroscience : the official journal of the Society for Neuroscience, Jan 15, 2001
Ephaptic coupling refers to interactions between neurons mediated by current flow through the ext... more Ephaptic coupling refers to interactions between neurons mediated by current flow through the extracellular space. Ephaptic interactions between axons are considered negligible, because of the relatively large extracellular space and the layers of myelin that separate most axons. By contrast, olfactory nerve axons are unmyelinated and arranged in tightly packed bundles, features that may enhance ephaptic coupling. We tested the hypothesis that ephaptic interactions occur in the mammalian olfactory nerve with the use of a computational approach. Numerical solutions of models of axon fascicles show that significant ephaptic interactions occur for a range of physiologically relevant parameters. An action potential in a single axon can evoke action potentials in all other axons in the fascicle. Ephaptic interactions can also lead to synchronized firing of independently stimulated axons. Our findings suggest that ephaptic interactions may be significant determinants of the olfactory code...
The Journal of neuroscience : the official journal of the Society for Neuroscience, Jan 15, 2001
Whole-cell patch-clamp recordings were used to investigate the electrophysiological properties of... more Whole-cell patch-clamp recordings were used to investigate the electrophysiological properties of mitral cells in rat main olfactory bulb brain slice preparations. The majority of mitral cells are bistable. These cells spontaneously alternate between two membrane potentials, separated by approximately 10 mV: a relatively depolarized potential (upstate), which is perithreshold for spike generation, and a relatively hyperpolarized potential (downstate), in which spikes do not occur. Bistability occurs spontaneously in the absence of ionotropic excitatory or inhibitory synaptic inputs. Bistability is voltage dependent; transition from the downstate to the upstate is a regenerative event activated by brief depolarization. A brief hyperpolarization can switch the membrane potential from the upstate to the downstate. In response to olfactory nerve (ON) stimulation, mitral cells in the upstate are more likely to fire an action potential than are those in the downstate. ON stimulation can s...
The Journal of neuroscience : the official journal of the Society for Neuroscience, 2000
We investigated the mechanisms of long-lasting depolarizing potentials (LLDs) generated in mitral... more We investigated the mechanisms of long-lasting depolarizing potentials (LLDs) generated in mitral cells with whole-cell patch recordings in the rat olfactory bulb slice. LLDs occur spontaneously and are evoked by either orthodromic stimulation of the olfactory nerve or antidromic stimulation of mitral and tufted (M/T) cells. LLDs are followed by a long refractory period, limiting LLD generation to approximately 1 Hz. LLD production does not appear to involve either intrinsic voltage-activated or metabotropic mechanisms. The initiation of LLDs requires activation of non-NMDA but not NMDA receptors. Dual recordings from the apical dendrites and somata of mitral cells show that LLDs are generated in the distal portion of the apical dendrite, most likely in the glomerulus. The rising phase of LLDs shows characteristics of polyneuronal input, including a high variability and sensitivity to charge screening. Paired recordings from adjacent mitral cells suggest that LLDs occur synchronousl...
The Journal of neuroscience : the official journal of the Society for Neuroscience, Jan 15, 2000
We used optical imaging of voltage-sensitive dye signals to study the spatiotemporal spread of ac... more We used optical imaging of voltage-sensitive dye signals to study the spatiotemporal spread of activity in the mouse barrel cortex, evoked by stimulation of thalamocortical afferents in an in vitro slice preparation. Stimulation of the thalamus, at low current intensity, results in activity largely restricted to a single barrel, and to the border between layers Vb and VI. Low concentrations of the GABA(A) receptor antagonist bicuculline increase the amplitude of the optical signals, without affecting their spatiotemporal propagation. Higher concentrations of bicuculline result in paroxysmal activity, which propagates via intracolumnar and intercolumnar excitatory pathways. Enhancing the activity of NMDA receptors, by removing Mg(2+) from the extracellular solution, dramatically alters the spatiotemporal pattern of excitation: activity spreads to supragranular and infragranular layers and adjacent barrel columns. This enhanced propagation is suppressed by the NMDA receptor antagonist...
The presence and distribution of intracellular Ca2+ release pathways in olfactory bulb neurons we... more The presence and distribution of intracellular Ca2+ release pathways in olfactory bulb neurons were studied in dissociated cell cultures. Histochemical techniques and imaging of Ca2+ fluxes were used to identify two major intracellular Ca2+ release mechanisms: inositol 1, 4,5-triphosphate receptor (IP3R)-mediated release, and ryanodine receptor-mediated release. Cultured neurons were identified by immunocytochemistry for the neuron-specificmarker beta-tubulin III. Morphometric analyses and immunocytochemistry for glutamic acid-decarboxylase revealed a heterogeneous population of cultured neurons with phenotypes corresponding to both projection (mitral/tufted) and intrinsic (periglomerular/granule) neurons of the in vivo olfactory bulb. Immunocytochemistry for the IP3R, and labeling with fluorescent-tagged ryanodine, revealed that, irrespective of cell type, almost all cultured neurons express IP3R and ryanodine binding sites in both somata and dendrites. Functional imaging revealed ...
1. The laminar distribution of synaptic activity in the primary motor cortex, elicited by stimula... more 1. The laminar distribution of synaptic activity in the primary motor cortex, elicited by stimulation of intracortical, horizontal afferents, was studied in young (12-17 days old) and adult rats using the in vitro brain slice preparation. Connectivity patterns were deduced from current-source density (CSD) analyses of field potential depth profiles and were confirmed by anatomic data of retrograde cell labeling after focal injections of a fluorescent tracer. 2. According to the CSD distributions, horizontal axons in layer II/III provide strong monosynaptic input to dendrites of layer II and III pyramidal cells in a distant column, and weaker monosynaptic input to layer V and VI cells by synapsing on dendritic fields at the border of layer III and V and in deep layer V. When these pathways are activated, layer II/III cells may relay excitatory activity to upper and deep layer V, as well as to other cells in layer II/III of the same column. Axons arising from layer V provide monosynap...
Marijuana use in adolescence, but not adulthood, may permanently impair cognitive functioning and... more Marijuana use in adolescence, but not adulthood, may permanently impair cognitive functioning and increase the risk of developing schizophrenia. Cortical oscillations are patterns of neural network activity implicated in cognitive processing, and are abnormal in patients with schizophrenia. We have recently reported that cortical oscillations are suppressed in adult mice that were treated with the cannabinoids WIN55,212-2 (WIN) or Δ(9)tetrahydrocannabinol (THC) in adolescence, but not adulthood. WIN and THC are cannabinoid-1 (CB1R) and CB2R agonists, and also have activity at non-cannabinoid receptor targets. However, as acute WIN and THC administration can suppress oscillations through CB1Rs, we hypothesize that a similar mechanism underlies the permanent suppression of oscillations by repeated cannabinoid exposure in adolescence. Here we test the prediction that cannabinoid exposure in adolescence permanently suppresses cortical oscillations by acting through CB1Rs, and that these suppressive effects can be antagonized by a CB1R antagonist. We treated adolescent mice with various cannabinoid compounds, and pharmacologically-evoked oscillations in local field potentials (LFPs) in vitro in adults. We find that WIN exposure for six days in early adolescence suppresses oscillations preferentially in adult medial prefrontal cortex (mPFC) via CB1Rs, and that a similar CB1R mechanism accounts for the suppressive effects of long-term (20 day) adolescent THC in adult somatosensory cortex (SCx). Unexpectedly, we also find that CB2Rs may be involved in the suppression of oscillations in both mPFC and SCx by long-term adolescent cannabinoid exposure, and that non-cannabinoid receptors may also contribute to oscillation suppression in adult mPFC. These findings represent a novel attempt to antagonize the effects of adolescent cannabinoid exposure on neural network activity, and reveal the contribution of non-CB1R targets to the suppression of cortical oscillations.
... to their dense terminations within barrel hollows, afferents from the VB branch and form term... more ... to their dense terminations within barrel hollows, afferents from the VB branch and form terminal clusters in layers Vb and VIa, below a barrel hollow, and a few afferents project to and terminate in layer IIII (Bernardo and Woolsey, 1987; Jensen and Killackey, 1987; Keller et al ...
Neural mechanisms subserving the acquisition of new motor skills are discussed in this article. M... more Neural mechanisms subserving the acquisition of new motor skills are discussed in this article. Motor learning is defined, in this context, as the acquisition of novel motor skills. It is proposed that complex motor skills are acquired through a process of segmental motor learning, in which movement segments are formed, and retrieved for the execution of the learned skill. Individual movement segments are created by modulating neural activity in loop circuits that link the motor cortex and the periphery. This neural modulation occurs through synaptic plasticity in the motor cortex. Increase of synaptic efficacy in existing neural circuits, in the form of long-term potentiation (LTP), is proposed to be involved in earlier stages of motor learning. It is suggested that the retention of motor skills involves formation of new synapses.
. Intracellular stores release Ca 2/ Asaf Keller. Distribution and activation of intracellular Ca... more . Intracellular stores release Ca 2/ Asaf Keller. Distribution and activation of intracellular Ca 2/ stores through at least two pathways, each mediated by a specific in cultured olfactory bulb neurons. J. Neurophysiol. 78: 2176family of receptors. In one pathway, Ca 2/ entry through 2185, 1997. The presence and distribution of intracellular Ca 2/ the plasma membrane activates r yanodine receptors in the release pathways in olfactory bulb neurons were studied in dissoci-ER that mediate Ca 2/ release from this organelle ( Galione ated cell cultures. Histochemical techniques and imaging of Ca 2/ 1992 ) . This process often is referred to as Ca 2/ -induced fluxes were used to identify two major intracellular Ca 2/ release Ca 2/ release ( CICR ) ( Ehrlich et al. 1994; Henzi and mechanisms: inositol 1,4,5-triphosphate receptor (IP 3 R)-mediated MacDermott 1992; Irving et al. 1992; ) . release, and ryanodine receptor-mediated release. Cultured neurons The other pathway involves activation of plasma membrane were identified by immunocytochemistry for the neuron-specific marker b-tubulin III. Morphometric analyses and immunocyto-receptors -such as the glutamate-sensitive metabotropic chemistry for glutamic acid-decarboxylase revealed a heterogereceptors -that activate, through intermediary G proteins, neous population of cultured neurons with phenotypes correphospholipase C, leading to the generation of inositol 1,4,5sponding to both projection ( mitral / tufted ) and intrinsic ( peritriphosphate ( IP 3 ). IP 3 then binds to an IP 3 receptor-Ca 2/ glomerular / granule ) neurons of the in vivo olfactory bulb. channel complex on the ER, inducing Ca 2/ release ( Putney Immunocytochemistry for the IP 3 R, and labeling with fluorescent-1990; . tagged ryanodine, revealed that, irrespective of cell type, almost Although modulation of [Ca 2/ ] i in general has been all cultured neurons express IP 3 R and ryanodine binding sites shown to regulate numerous neuronal functions, in some in both somata and dendrites. Functional imaging revealed that cases, these activities may be specifically dependent on Ca 2/ intracellular Ca 2/ fluxes can be generated in the absence of exterrelease from intracellular stores (reviewed in: Simpson et al. nal Ca 2/ , using agonists specific to each of the intracellular release pathways. Local pressure application of glutamate or quis-1995). These include the modulation of neuronal excitability qualate evoked Ca 2/ fluxes in both somata and dendrites in nomi- ; Kawai and nally Ca 2/ free extracellular solutions, suggesting the presence Watanabe 1989), presynaptic transmitter release (Blaustein of IP 3 -dependent Ca 2/ release. These fluxes were blocked by Peng 1996), long-term depression and potentiapreincubation with thapsigargin and persisted in the presence of tion (Behnisch and Reymann 1995; Kasono and Hirano the glutamate receptor antagonist 6-cyano-7-nitroquinoxaline-1995; , and 2,3-dione. Local application of caffeine, a ryanodine receptor neuronal development agonist, also evoked intracellular Ca 2/ fluxes in the absence of 1995). Therefore, studies of Ca 2/ -dependent phenomena in extracellular Ca 2/ . These Ca 2/ fluxes were suppressed by preinneurons must consider the presence of intracellular release cubation with ryanodine. In all neurons, both IP 3 -and ryanodinepathways. dependent release pathways coexisted, suggesting that they interact to modulate intracellular Ca 2/ concentrations. The present study was designed to identify the types of intracellular Ca 2/ release mechanisms in cultured neurons of the rat olfactory bulb. Functional imaging of Ca 2/ fluxes I N T R O D U C T I O N and immunocytochemical techniques revealed that both IP 3and ryanodine-dependent release mechanisms are expressed Neuronal mechanisms controlling cytoplasmic calcium in a heterogeneous population of these neurons. Some of concentrations ( [ Ca 2/ ] i ) modulate a number of neuronal these results were published previously in abstract form activities, including neurotransmitter release ( Katz 1969. control of membrane excitability ( Llinás 1990 ) and receptor function ( Jaffe et al. 1994 ) , differential gene expression M E T H O D S ( Sheng and Greenberg 1990 ) , and neuronal migration and growth ( Komuro and Rakic 1995 ) . Increases in [ Ca 2/ ] i Cell cultures occur by extracellular Ca 2/ influx through transmembrane Dissociated cell cultures were prepared from 3-day-old Wistar channels and intracellular release of Ca 2/ sequestered in rat pups. Olfactory bulbs were dissected into culture medium conintracellular organelles. Because intracellular stores, such taining minimal essential medium supplemented with L-alanyl-Las the endoplasmic reticulum ( ER ) , can sequester high glutamine (MEM a medium, GIBCO), 10% fetal calf serum concentrations of Ca 2/ , these stores serve not only to buffer (GIBCO), 5% horse serum (GIBCO), and 0.6% glucose. The free intracellular Ca 2/ , but can produce rapid, local Ca 2/ meninges were removed, and the bulbs were dissociated both enzymatically (papain; 20 U/ml, Worthington) and by gentle mechani-transients in response to specific stimuli 2176 0022-3077/97 $5.00
1. Intracellular recordings were obtained from neurons in the motor cortex (MCx), in which excita... more 1. Intracellular recordings were obtained from neurons in the motor cortex (MCx), in which excitatory postsynaptic potentials (EPSPs) were evoked by microstimulation of the somatosensory cortex (SCx) and the ventrolateral nucleus (VL) of the thalamus. The effects of combined tetanic stimulation of SCx and VL on the amplitudes of these EPSPs were studied. 2. Amplitudes of both corticocortical (CC) and thalamocortical (TC) EPSPs were potentiated after combined tetanic stimulation. This potentiation occurred exclusively in neurons that were located in the superficial layers (II/III) and that received direct input from both the SCx and VL, with both inputs synapsing in close proximity to each other. In all cases, the potentiation lasted until the electrode went out of the cell (21 +/- 25 min, mean +/- SD) the longest being 90 min. We therefore refer to this potentiation as long-term potentiation (LTP). 3. Tetanic stimulation of the thalamus only did not produce LTP in neurons receiving direct input from the VL. 4. LTP was not induced in either CC or TC EPSPs in neurons located in layer V and/or in neurons receiving long-latency CC EPSPs. 5. It is concluded that TC input from the VL to the MCx is potentiated only when coactivated with the CC input from the SCx.
The purpose of this study was to determine whether long-term changes in synaptic efficacy can be ... more The purpose of this study was to determine whether long-term changes in synaptic efficacy can be induced in the pyramidal tract (PT). Tetanic stimulation of the PT induced long-term facilitation of PT input to spinal cord neurons. In contrast, tetanic stimulation of the pyramidal tract did not alter the efficacy of synaptic inputs of PT cells&amp;amp;#39; intracortical axon collaterals to other cortical neurons. These findings suggest that the PT participates in motor learning by modulating the excitability of spinal cord neurons. The results also indicate that induction of LTP in the PT is dependent on postsynaptic mechanisms.
1. Intracellular recordings were obtained from neurons in the motor cortex (MCx), in which excita... more 1. Intracellular recordings were obtained from neurons in the motor cortex (MCx), in which excitatory postsynaptic potentials (EPSPs) were evoked by microstimulation of the somatosensory cortex (SCx) and the ventrolateral nucleus (VL) of the thalamus. The effects of combined tetanic stimulation of SCx and VL on the amplitudes of these EPSPs were studied. 2. Amplitudes of both corticocortical (CC) and thalamocortical (TC) EPSPs were potentiated after combined tetanic stimulation. This potentiation occurred exclusively in neurons that were located in the superficial layers (II/III) and that received direct input from both the SCx and VL, with both inputs synapsing in close proximity to each other. In all cases, the potentiation lasted until the electrode went out of the cell (21 +/- 25 min, mean +/- SD) the longest being 90 min. We therefore refer to this potentiation as long-term potentiation (LTP). 3. Tetanic stimulation of the thalamus only did not produce LTP in neurons receiving direct input from the VL. 4. LTP was not induced in either CC or TC EPSPs in neurons located in layer V and/or in neurons receiving long-latency CC EPSPs. 5. It is concluded that TC input from the VL to the MCx is potentiated only when coactivated with the CC input from the SCx.
Our aim was to investigate the patterns of functional inputs and outputs from individual barrels ... more Our aim was to investigate the patterns of functional inputs and outputs from individual barrels in the mouse somatosensory cortex, and to test the hypothesis that individual barrels in layer IV are functionally independent of direct inputs from neighboring barrels. In a mouse in vitro slice preparation of the barrel cortex, we recorded voltage-sensitive dye signals evoked in response to microstimulation of a single barrel. Activity propagated from the stimulated barrel to the supragranular layers, where it spread to activate several barrel columns. However, in no instance did activity propagate directly from the stimulated barrel to neighboring barrels. Neither suppression of GABAergic inhibition, nor activation of N-methyl-D-aspartate receptors, revealed direct interbarrel interactions. By contrast, microstimulation in the supra-or infragranular layers resulted in direct propagation of activity to neighboring barrel columns. We conclude that the neurons within individual barrels are functionally independent of direct inputs from neighboring barrels. This suggests that the response properties of layer IV barrel neurons are shaped primarily by their presynaptic thalamic afferents and by intrabarrel interactions, and that these responses are independent of direct inputs from neighboring barrels.
The posterior thalamic nucleus (PO) is a higher order nucleus heavily implicated in the processin... more The posterior thalamic nucleus (PO) is a higher order nucleus heavily implicated in the processing of somatosensory information. We have previously shown in rodent models that activity in PO is tightly regulated by inhibitory inputs from a GABAergic nucleus known as the zona incerta (ZI). The level of incertal inhibition varies under both physiological and pathological conditions, leading to concomitant changes in PO activity. These changes are causally linked to variety of phenomena from altered sensory perception to pathological pain. ZI regulation of PO is mediated by GABAA and GABAB receptors (GABAAR and GABABR) that differ in their binding kinetics and their electrophysiological properties, suggesting that each may have distinct roles in incerto-thalamic regulation. We developed a computational model to test this hypothesis. We created a two-cell Hodgkin-Huxley model representing PO and ZI with kinetically realistic GABAAR- and GABABR-mediated synapses. We simulated spontaneous...
1. Intracellular recordings were obtained from neurons in the motor cortex (MCx), in which excita... more 1. Intracellular recordings were obtained from neurons in the motor cortex (MCx), in which excitatory postsynaptic potentials (EPSPs) were evoked by microstimulation of the somatosensory cortex (SCx) and the ventrolateral nucleus (VL) of the thalamus. The effects of combined tetanic stimulation of SCx and VL on the amplitudes of these EPSPs were studied. 2. Amplitudes of both corticocortical (CC) and thalamocortical (TC) EPSPs were potentiated after combined tetanic stimulation. This potentiation occurred exclusively in neurons that were located in the superficial layers (II/III) and that received direct input from both the SCx and VL, with both inputs synapsing in close proximity to each other. In all cases, the potentiation lasted until the electrode went out of the cell (21 +/- 25 min, mean +/- SD) the longest being 90 min. We therefore refer to this potentiation as long-term potentiation (LTP). 3. Tetanic stimulation of the thalamus only did not produce LTP in neurons receiving ...
Neurotherapeutics : the journal of the American Society for Experimental NeuroTherapeutics, 2013
Spinal cord injury (SCI) causes not only sensorimotor and cognitive deficits, but frequently also... more Spinal cord injury (SCI) causes not only sensorimotor and cognitive deficits, but frequently also severe chronic pain that is difficult to treat (SCI pain). We previously showed that hyperesthesia, as well as spontaneous pain induced by electrolytic lesions in the rat spinothalamic tract, is associated with increased spontaneous and sensory-evoked activity in the posterior thalamic nucleus (PO). We have also demonstrated that rodent impact SCI increases cell cycle activation (CCA) in the injury region and that post-traumatic treatment with cyclin dependent kinase inhibitors reduces lesion volume and motor dysfunction. Here we examined whether CCA contributes to neuronal hyperexcitability of PO and hyperpathia after rat contusion SCI, as well as to microglial and astroglial activation (gliopathy) that has been implicated in delayed SCI pain. Trauma caused enhanced pain sensitivity, which developed weeks after injury and was correlated with increased PO neuronal activity. Increased CC...
The superior colliculus, usually considered a visuomotor structure, is anatomically positioned to... more The superior colliculus, usually considered a visuomotor structure, is anatomically positioned to perform sensorimotor transformations in other modalities. While there is evidence for its potential participation in sensorimotor loops of the rodent vibrissa system, little is known about its functional role in vibrissa sensation or movement. In anesthetized rats, we characterized extracellularly recorded responses of collicular neurons to different types of vibrissa stimuli. Collicular neurons had large receptive fields (median = 14.5 vibrissae). Single units displayed responses with short latencies (5.6 +/- 0.2 msec, median = 5.5) and relatively large magnitudes (1.2 +/- 0.1 spikes/stimulus, median = 1.2). Individual neurons could entrain to repetitive vibrissa stimuli delivered at < or = 20 Hz, with little reduction in phase locking, even when response magnitude was decreased. Neurons responded preferentially to vibrissa deflections at particular angles, with 43% of the cells hav...
The Journal of neuroscience : the official journal of the Society for Neuroscience, Jan 15, 2001
Ephaptic coupling refers to interactions between neurons mediated by current flow through the ext... more Ephaptic coupling refers to interactions between neurons mediated by current flow through the extracellular space. Ephaptic interactions between axons are considered negligible, because of the relatively large extracellular space and the layers of myelin that separate most axons. By contrast, olfactory nerve axons are unmyelinated and arranged in tightly packed bundles, features that may enhance ephaptic coupling. We tested the hypothesis that ephaptic interactions occur in the mammalian olfactory nerve with the use of a computational approach. Numerical solutions of models of axon fascicles show that significant ephaptic interactions occur for a range of physiologically relevant parameters. An action potential in a single axon can evoke action potentials in all other axons in the fascicle. Ephaptic interactions can also lead to synchronized firing of independently stimulated axons. Our findings suggest that ephaptic interactions may be significant determinants of the olfactory code...
The Journal of neuroscience : the official journal of the Society for Neuroscience, Jan 15, 2001
Whole-cell patch-clamp recordings were used to investigate the electrophysiological properties of... more Whole-cell patch-clamp recordings were used to investigate the electrophysiological properties of mitral cells in rat main olfactory bulb brain slice preparations. The majority of mitral cells are bistable. These cells spontaneously alternate between two membrane potentials, separated by approximately 10 mV: a relatively depolarized potential (upstate), which is perithreshold for spike generation, and a relatively hyperpolarized potential (downstate), in which spikes do not occur. Bistability occurs spontaneously in the absence of ionotropic excitatory or inhibitory synaptic inputs. Bistability is voltage dependent; transition from the downstate to the upstate is a regenerative event activated by brief depolarization. A brief hyperpolarization can switch the membrane potential from the upstate to the downstate. In response to olfactory nerve (ON) stimulation, mitral cells in the upstate are more likely to fire an action potential than are those in the downstate. ON stimulation can s...
The Journal of neuroscience : the official journal of the Society for Neuroscience, 2000
We investigated the mechanisms of long-lasting depolarizing potentials (LLDs) generated in mitral... more We investigated the mechanisms of long-lasting depolarizing potentials (LLDs) generated in mitral cells with whole-cell patch recordings in the rat olfactory bulb slice. LLDs occur spontaneously and are evoked by either orthodromic stimulation of the olfactory nerve or antidromic stimulation of mitral and tufted (M/T) cells. LLDs are followed by a long refractory period, limiting LLD generation to approximately 1 Hz. LLD production does not appear to involve either intrinsic voltage-activated or metabotropic mechanisms. The initiation of LLDs requires activation of non-NMDA but not NMDA receptors. Dual recordings from the apical dendrites and somata of mitral cells show that LLDs are generated in the distal portion of the apical dendrite, most likely in the glomerulus. The rising phase of LLDs shows characteristics of polyneuronal input, including a high variability and sensitivity to charge screening. Paired recordings from adjacent mitral cells suggest that LLDs occur synchronousl...
The Journal of neuroscience : the official journal of the Society for Neuroscience, Jan 15, 2000
We used optical imaging of voltage-sensitive dye signals to study the spatiotemporal spread of ac... more We used optical imaging of voltage-sensitive dye signals to study the spatiotemporal spread of activity in the mouse barrel cortex, evoked by stimulation of thalamocortical afferents in an in vitro slice preparation. Stimulation of the thalamus, at low current intensity, results in activity largely restricted to a single barrel, and to the border between layers Vb and VI. Low concentrations of the GABA(A) receptor antagonist bicuculline increase the amplitude of the optical signals, without affecting their spatiotemporal propagation. Higher concentrations of bicuculline result in paroxysmal activity, which propagates via intracolumnar and intercolumnar excitatory pathways. Enhancing the activity of NMDA receptors, by removing Mg(2+) from the extracellular solution, dramatically alters the spatiotemporal pattern of excitation: activity spreads to supragranular and infragranular layers and adjacent barrel columns. This enhanced propagation is suppressed by the NMDA receptor antagonist...
The presence and distribution of intracellular Ca2+ release pathways in olfactory bulb neurons we... more The presence and distribution of intracellular Ca2+ release pathways in olfactory bulb neurons were studied in dissociated cell cultures. Histochemical techniques and imaging of Ca2+ fluxes were used to identify two major intracellular Ca2+ release mechanisms: inositol 1, 4,5-triphosphate receptor (IP3R)-mediated release, and ryanodine receptor-mediated release. Cultured neurons were identified by immunocytochemistry for the neuron-specificmarker beta-tubulin III. Morphometric analyses and immunocytochemistry for glutamic acid-decarboxylase revealed a heterogeneous population of cultured neurons with phenotypes corresponding to both projection (mitral/tufted) and intrinsic (periglomerular/granule) neurons of the in vivo olfactory bulb. Immunocytochemistry for the IP3R, and labeling with fluorescent-tagged ryanodine, revealed that, irrespective of cell type, almost all cultured neurons express IP3R and ryanodine binding sites in both somata and dendrites. Functional imaging revealed ...
1. The laminar distribution of synaptic activity in the primary motor cortex, elicited by stimula... more 1. The laminar distribution of synaptic activity in the primary motor cortex, elicited by stimulation of intracortical, horizontal afferents, was studied in young (12-17 days old) and adult rats using the in vitro brain slice preparation. Connectivity patterns were deduced from current-source density (CSD) analyses of field potential depth profiles and were confirmed by anatomic data of retrograde cell labeling after focal injections of a fluorescent tracer. 2. According to the CSD distributions, horizontal axons in layer II/III provide strong monosynaptic input to dendrites of layer II and III pyramidal cells in a distant column, and weaker monosynaptic input to layer V and VI cells by synapsing on dendritic fields at the border of layer III and V and in deep layer V. When these pathways are activated, layer II/III cells may relay excitatory activity to upper and deep layer V, as well as to other cells in layer II/III of the same column. Axons arising from layer V provide monosynap...
Marijuana use in adolescence, but not adulthood, may permanently impair cognitive functioning and... more Marijuana use in adolescence, but not adulthood, may permanently impair cognitive functioning and increase the risk of developing schizophrenia. Cortical oscillations are patterns of neural network activity implicated in cognitive processing, and are abnormal in patients with schizophrenia. We have recently reported that cortical oscillations are suppressed in adult mice that were treated with the cannabinoids WIN55,212-2 (WIN) or Δ(9)tetrahydrocannabinol (THC) in adolescence, but not adulthood. WIN and THC are cannabinoid-1 (CB1R) and CB2R agonists, and also have activity at non-cannabinoid receptor targets. However, as acute WIN and THC administration can suppress oscillations through CB1Rs, we hypothesize that a similar mechanism underlies the permanent suppression of oscillations by repeated cannabinoid exposure in adolescence. Here we test the prediction that cannabinoid exposure in adolescence permanently suppresses cortical oscillations by acting through CB1Rs, and that these suppressive effects can be antagonized by a CB1R antagonist. We treated adolescent mice with various cannabinoid compounds, and pharmacologically-evoked oscillations in local field potentials (LFPs) in vitro in adults. We find that WIN exposure for six days in early adolescence suppresses oscillations preferentially in adult medial prefrontal cortex (mPFC) via CB1Rs, and that a similar CB1R mechanism accounts for the suppressive effects of long-term (20 day) adolescent THC in adult somatosensory cortex (SCx). Unexpectedly, we also find that CB2Rs may be involved in the suppression of oscillations in both mPFC and SCx by long-term adolescent cannabinoid exposure, and that non-cannabinoid receptors may also contribute to oscillation suppression in adult mPFC. These findings represent a novel attempt to antagonize the effects of adolescent cannabinoid exposure on neural network activity, and reveal the contribution of non-CB1R targets to the suppression of cortical oscillations.
... to their dense terminations within barrel hollows, afferents from the VB branch and form term... more ... to their dense terminations within barrel hollows, afferents from the VB branch and form terminal clusters in layers Vb and VIa, below a barrel hollow, and a few afferents project to and terminate in layer IIII (Bernardo and Woolsey, 1987; Jensen and Killackey, 1987; Keller et al ...
Neural mechanisms subserving the acquisition of new motor skills are discussed in this article. M... more Neural mechanisms subserving the acquisition of new motor skills are discussed in this article. Motor learning is defined, in this context, as the acquisition of novel motor skills. It is proposed that complex motor skills are acquired through a process of segmental motor learning, in which movement segments are formed, and retrieved for the execution of the learned skill. Individual movement segments are created by modulating neural activity in loop circuits that link the motor cortex and the periphery. This neural modulation occurs through synaptic plasticity in the motor cortex. Increase of synaptic efficacy in existing neural circuits, in the form of long-term potentiation (LTP), is proposed to be involved in earlier stages of motor learning. It is suggested that the retention of motor skills involves formation of new synapses.
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Papers by Asaf Keller