A major focus in development of novel therapies for Huntington's disease (HD) is identificati... more A major focus in development of novel therapies for Huntington's disease (HD) is identification of treatments that reduce the burden of mutant huntingtin (mHTT) protein in the brain. In order to identify and test the efficacy of such therapies, it is essential to have biomarkers that are sensitive to the effects of mHTT on brain function to determine whether the intervention has been effective at preventing toxicity in target brain systems before onset of clinical symptoms. Ideally, such biomarkers should have a plausible physiologic basis for detecting the effects of mHTT, be measureable both in preclinical models and human studies, be practical to measure serially in clinical trials, and be reliably measurable in HD gene expansion carriers (HDGECs), among other features. Quantitative electroencephalography (qEEG) fulfills many of these basic criteria of a "fit-for-purpose" biomarker. qEEG measures brain oscillatory activity that is regulated by the brain structures t...
724 Michael 5. Levine and Carlos Cepeda Using extracellular recording techniques, we found that b... more 724 Michael 5. Levine and Carlos Cepeda Using extracellular recording techniques, we found that brief trains of stimuli delivered to the amygdala facilitated PFC-evoked spiking as well; however, in this case, the facilitation occurred in a time-locked manner; that is, only ...
The results obtained by positron-emission tomography in an "in vivo" study on the baboo... more The results obtained by positron-emission tomography in an "in vivo" study on the baboon using a benzodiazepine (flunitrazepam) labeled with carbon-11 are presented. The specificity of "in vivo" binding of Flunitrazepam-11C was demonstrated by competition with Lorazepam in the brain, but it was not possible to verify the criterium of stereospecificity "in vivo". The preliminary results of a study carried out under the same conditions on RO 15 1788 11C show the interest of using this labeled antagonist as an "in vivo" ligand for the specific binding sites of benzodiazepines in positron-emission tomography.
Morphologically, gap junctions are intermembranous channels between cells thought to mediate elec... more Morphologically, gap junctions are intermembranous channels between cells thought to mediate electrotonic transmission and to serve as a passage for small molecules in the CNS (for a review see Sotelo and Korn, 1978). After the discovery that the fluorescent dye Lucifer yellow crosses gap junctions to label adjacent cells (Stewart, 1978), dye-coupling was used as indirect evidence for the presence of gap junctions. Dye-coupling occurs in several neural areas, including the hippocampus (Knowles et el., 1982; MacVicar et al., 1982), the neocortex (Connors et al., 1983; Gutnick and Prince, 1981) and the hypothalamus (Andrew et al., 1981; Hatton et al., 1987). In parallel ultrastructural studies, gap junctions have been shown to be present in some of these structures (Sloper and Powell, 1978; Sotelo and Korn, 1978).
Publisher Summary This chapter explores that the striatum is centrally located to receive a varie... more Publisher Summary This chapter explores that the striatum is centrally located to receive a variety of synaptic inputs that are integrated and distributed to appropriate output regions producing adaptive behaviors, through cortico-basal ganglia-thalamocortical loops. These functions are precisely regulated by the coordinated pre- and postsynaptic actions of dopamine (DA) modulating voltage- and ligand-gated conductances in medium-sized spiny neurons (MSNs), the principal cell type in striatum, as well as a variety of interneurons. Huntington's disease (HD) involves dysfunction and eventual degeneration of striatal and cortical neurons, whereas dysfunction and subsequent degeneration of DA neurons lead to Parkinson's disease (PD). The chapter reviews that with the introduction of animal models of HD and PD, it has become possible to study electrophysiological changes in basal ganglia neurons and, more specifically, alterations along the corticostriatal pathway in each of these disorders. It reviews that the role of changes in this pathway contributes to cognitive and motor disturbances in HD and PD models. It also focuses on alterations of the corticostriatal pathway in genetic mouse models.
Since the identification of the gene responsible for HD (Huntington's disease), many genetic ... more Since the identification of the gene responsible for HD (Huntington's disease), many genetic mouse models have been generated. Each employs a unique approach for delivery of the mutated gene and has a different CAG repeat length and background strain. The resultant diversity in the genetic context and phenotypes of these models has led to extensive debate regarding the relevance of each model to the human disorder. Here, we compare and contrast the striatal synaptic phenotypes of two models of HD, namely the YAC128 mouse, which carries the full-length huntingtin gene on a yeast artificial chromosome, and the CAG140 KI*** (knock-in) mouse, which carries a human/mouse chimaeric gene that is expressed in the context of the mouse genome, with our previously published data obtained from the R6/2 mouse, which is transgenic for exon 1 mutant huntingtin. We show that striatal MSNs (medium-sized spiny neurons) in YAC128 and CAG140 KI mice have similar electrophysiological phenotypes to t...
Dopamine (DA), a prominent neuromodulator in the brain, regulates neuronal excitability and synap... more Dopamine (DA), a prominent neuromodulator in the brain, regulates neuronal excitability and synaptic transmission. These actions are effected through diverse DA receptor subtypes whose effects vary as a function of a number of factors including pre- or postsynaptic localization and the intracellular signaling cascades they activate. We have chosen the corticostriatal synapse as a model to study the interactions between
Electroencephalography and Clinical Neurophysiology, 1983
... and EMG jerks, resembling the human adversive seizures presumably originating from the inter-... more ... and EMG jerks, resembling the human adversive seizures presumably originating from the inter-mediate frontal cortex (Penfield and Jasper 1954). ... Cepeda, C., Pacheco, MT, Cruz, ML, Almanza, X. and Velasco, M. Phasic paradoxical sleep precipitates focal mo-tor and limbic ...
Genetic mouse models based on identification of genes that cause Huntington's and Parkinson's dis... more Genetic mouse models based on identification of genes that cause Huntington's and Parkinson's diseases have revolutionized understanding of the mechanistic pathophysiological progression of these disorders. These models allow the earliest manifestations of the diseases to be identified, and they display behavioral, neuropathological and electrophysiological deficits that can be followed over time in mechanistic and drug studies. An intriguing feature is that they do not reproduce the relatively selective and massive cell loss characterizing the human diseases. There is more information on Huntington's disease models because the disorder involves a single gene that was identified over ten years ago; genetic mutations causing Parkinson's disease are rare and were discovered more recently, and models of the disease have been generated only within the past few years.
7-OH-DPAT has been shown to exhibit selectivity between Dz and D3 dopamine receptors in a variety... more 7-OH-DPAT has been shown to exhibit selectivity between Dz and D3 dopamine receptors in a variety of in vitro assay systems. Although the drug has been used in a variety of studies to evaluate the behavioral effects of D3 receptor stimulation, the in vivo Dz/D3 selectivity of the compound has not been determined. In this study, protection against inactivation by EEDQ was used as a measure of in vivo occupancy of D2 receptors by behaviorally relevant doses of 7-OH-DPAT (0.03-10 mg/kg, s.c.) in adult, male Sprague-Dawley rats. Ex vivo [3Hlspiperone binding was then determined in striatal membranes. 7-OH-DPAT protected against inactivation of Dz receptors with an EDSo value of 11 mg/kg. Significant protection of Dz receptors was observed at doses of 1 mgkg and above. These data suggest that stimulation of Dz receptors contributes to the pharmacological effects of 7-OH-DPAT when administered at doses above 0.3 mg/ kg (s.c.). o 1996 Wiley-Liss, Inc.
The responses of human neocortical neurons to iontophoretic application of excitatory amino acids... more The responses of human neocortical neurons to iontophoretic application of excitatory amino acids and their modulation by dopamine (DA) were studied in vitro. Brain slices were obtained from children undergoing surgery for intractable epilepsy. Application of N-methyl-D-aspartate (NMDA) to the slices induced slow depolarizations accompanied by decreased input conductances and sustained action potentials in cortical neurons. Glutamate produced rapid depolarizations and firing with few changes in input conductances. Quisqualate also induced depolarization and firing, but input conductances increased during the rising phase of the membrane depolarization. Iontophoretic application of DA alone produced no change in membrane potential or input conductance. However, when DA was applied in conjunction with the excitatory amino acids, it produced contrasting effects. With either bath application of DA or when iontophoresis of DA preceded application of NMDA, the amplitude of the membrane depolarizations and the number of action potentials were increased, whereas the latency of these responses decreased. In contrast, DA decreased the amplitude of the depolarizations and the number of action potentials evoked by glutamate or quisqualate. The fact that DA affects responses to NMDA and glutamate or quisqualate in opposite directions is of considerable importance to the understanding of cellular mechanisms of neuromodulation and the role of DA in cognitive processing and in epilepsy. o 1992 Wiley-Liss, Inc.
The membrane properties and synaptic physiology of developing cat substantia nigra (SN) neurons w... more The membrane properties and synaptic physiology of developing cat substantia nigra (SN) neurons were studied in in vitro slice preparations. Stable intracellular recordings were obtained from 46 neurons in 20 kittens ranging in age from fetal day (F) 51 to postnatal day (P) 120. Only two of these properties changed with development. The percentage of cells displaying inward rectification and the percentage of cells that generated low-threshold Ca++ spikes increased with age. Properties that did not change included resting membrane potentials, action potential amplitudes and durations, and input resistances. At all ages locally evoked synaptic responses consisted of sequences of excitatory postsynaptic potentials followed by inhibitory postsynaptic potentials. Most of the cells recorded had the electrophysiological properties which have been attributed to SN dopamine-containing neurons. To identify neurons morphologically, and verify the recording site, cells were filled with Lucifer yellow at the end of each experiment. Somatic shapes varied widely from oval to fusiform to triangular. Somatic diameters and dendritic length increased with development. Filopodial processes and growth cones were present up to the first postnatal month. Dye-coupling occurred only in the fetal group. These results indicate that cat SN neurons have many mature physiological properties during late fetal and early postnatal development. This contrasts with the significant maturation that occurs in cat caudate neurons during the same developmental period (Cepeda et al.,
This report represents a detailed description of experiments designed to replicate and extend the... more This report represents a detailed description of experiments designed to replicate and extend the findings of a published study on the effects of treating the R6/2 Huntington's disease (HD) mouse model with ~300 CAG repeats using the pimelic diphenylamide histone deacetylase (HDAC) inhibitor, HDACi 4b (Thomas et al., 2008). In addition to testing the R6/2 mice, similar experiments examined the effects of the drug on a second transgenic HD mouse model, the N171-82Q mice. As in the original study, the drug was delivered in the drinking water. In the present study we tested larger groups of mice than in the original study. The results indicated that we were unable to replicate the significant behavioral effects of oral HDACi 4b treatment in the R6/2 mice. There were however, non-significant trends for the treated R6/2 mice to be less affected on some of the measures and there were instances of phenotype progression being delayed in these treated mice. In contrast, we did replicate the protection from striatal atrophy in the R6/2 mice. We also did not observe any beneficial effects of HDACi 4b treatment in the N171-82Q mice. Although the behavioral procedures were replicated and an automated activity assessment was added, there were several unexpected complications in terms of solubility of the drug, CAG repeat length differences and gender differences in progression of the phenotype that could have affected outcomes. Clearly more studies will have to be performed using other methods of delivery as well as assessing effects in more slowly progressing HD models to better evaluate the effects of this HDAC inhibitor.
prominent example of such a proposed circuit is suggested for the dopaminergic regulation of volu... more prominent example of such a proposed circuit is suggested for the dopaminergic regulation of voluntary motor learning. The basic "striatal microcircuit" (Figure 1A
Abnormally enhanced N-methyl-D-aspartate (NMDA) receptor function is implicated in Huntington's d... more Abnormally enhanced N-methyl-D-aspartate (NMDA) receptor function is implicated in Huntington's disease (HD). In this issue of Neuron and a recent issue of Nature Medicine, an abnormal balance between the activity of NMDA receptors at synaptic (prosurvival) and extrasynaptic (proapoptotic) sites has been uncovered in a cellular and a mouse model of HD.
Tuberous sclerosis complex (TSC) and cortical dysplasia Type IIB (CDIIB) share histopathologic fe... more Tuberous sclerosis complex (TSC) and cortical dysplasia Type IIB (CDIIB) share histopathologic features that suggest similar epileptogenic mechanisms. This study compared the morphological and electrophysiological properties of cortical cells in tissue from pediatric TSC (n=20) and CDIIB (n=20) patients using whole-cell patch clamp recordings and biocytin staining. Cell types were normal-appearing and dysmorphiccytomegalic pyramidal neurons, interneurons, and giant/ balloon cells, including intermediate neuronal-glial cells. In the cortical mantle, giant/balloon cells occurred more frequently in TSC than in CDIIB cases, whereas cytomegalic pyramidal neurons were found more frequently in CDIIB. Cell morphology and membrane properties were similar in TSC and CDIIB cases. Except for giant/balloon and intermediate cells, all neuronal cell types fired action potentials and displayed spontaneous postsynaptic currents. However, the frequency of spontaneous glutamatergic postsynaptic currents in normal pyramidal neurons and interneurons was significantly lower in CDIIB compared with TSC cases and GABAergic activity was higher in all neuronal cell types in CDIIB. Further, acutely dissociated pyramidal neurons displayed higher sensitivity to exogenous application of GABA in CDIIB compared with TSC cases. These results indicate that, in spite of similar histopathologic features and basic cell membrane properties, TSC and CDIIB display differences in the topography of abnormal cells, excitatory and inhibitory synaptic network properties, and GABA A receptor sensitivity. These differences support the notion that the mechanisms of epileptogenesis could differ in patients with TSC and CDIIB. Consequently, pharmacologic therapies should take these findings into consideration.
Overexpression or mutation of α-synuclein (α-Syn), a protein associated with presynaptic vesicles... more Overexpression or mutation of α-synuclein (α-Syn), a protein associated with presynaptic vesicles, causes familial forms of Parkinson's disease in humans and is also associated with sporadic forms of the disease. We used in vivo microdialysis, tissue content analysis, behavioral assessment, and whole-cell patch clamp recordings from striatal medium-sized spiny neurons (MSSNs) in slices to examine dopamine transmission and dopaminergic modulation of corticostriatal synaptic function in mice overexpressing human wild-type α-Syn under the Thy1 promoter (α-Syn mice). Tonic striatal extracellular dopamine and 3-methoxytyramine levels were elevated in α-Syn mice at 6 months of age, prior to any reduction in total striatal tissue content, and were accompanied by an increase in open-field activity. Dopamine clearance and amphetamine-induced dopamine efflux were unchanged. The frequency of MSSN spontaneous excitatory postsynaptic currents (sEPSCs) was lower in α-Syn mice. Amphetamine reduced sEPSC frequency in wild types (WTs) but produced no effect in α-Syn mice. Furthermore,
We used two mouse models of Huntington's disease (HD) to examine changes in gluta... more We used two mouse models of Huntington's disease (HD) to examine changes in glutamate receptor sensitivity and striatal electrophysiology. One model, a transgenic, consisted of mice expressing exon 1 of the human HD gene and carrying 141-157 CAG repeat sequences (R6/2 line). The second model, a CAG repeat "knockin," consisted of mice with different lengths of CAG repeats (CAG71 and CAG94 repeats). The effects of glutamate receptor activation were examined by visualizing neurons in brain slices with infrared videomicroscopy and differential interference contrast optics to determine changes in somatic area (cell swelling). Striatal and cortical neurons in both models (R6/2 and CAG94) displayed more rapid and increased swelling to N-methyl-D-aspartate (NMDA) than those in controls. This effect was specific as there were no consistent group differences after exposure to alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid (AMPA) or kainate (KA). Intracellular recordings revealed that resting membrane potentials (RMPs) in the R6/2 transgenics were significantly more depolarized than those in their respective controls. RMPs in CAG94 mice also were more depolarized than those in CAG71 mice or their controls in a subset of striatal neurons. Confirming previous results, R6/2 mice expressed behavioral abnormalities and nuclear inclusions. However, CAG71 and CAG94 knockins did not, suggesting that increased sensitivity to NMDA may occur early in the disease process. These findings imply that NMDA antagonists or compounds that alter sensitivity of NMDA receptors may be useful in the treatment of HD.
A major focus in development of novel therapies for Huntington's disease (HD) is identificati... more A major focus in development of novel therapies for Huntington's disease (HD) is identification of treatments that reduce the burden of mutant huntingtin (mHTT) protein in the brain. In order to identify and test the efficacy of such therapies, it is essential to have biomarkers that are sensitive to the effects of mHTT on brain function to determine whether the intervention has been effective at preventing toxicity in target brain systems before onset of clinical symptoms. Ideally, such biomarkers should have a plausible physiologic basis for detecting the effects of mHTT, be measureable both in preclinical models and human studies, be practical to measure serially in clinical trials, and be reliably measurable in HD gene expansion carriers (HDGECs), among other features. Quantitative electroencephalography (qEEG) fulfills many of these basic criteria of a "fit-for-purpose" biomarker. qEEG measures brain oscillatory activity that is regulated by the brain structures t...
724 Michael 5. Levine and Carlos Cepeda Using extracellular recording techniques, we found that b... more 724 Michael 5. Levine and Carlos Cepeda Using extracellular recording techniques, we found that brief trains of stimuli delivered to the amygdala facilitated PFC-evoked spiking as well; however, in this case, the facilitation occurred in a time-locked manner; that is, only ...
The results obtained by positron-emission tomography in an "in vivo" study on the baboo... more The results obtained by positron-emission tomography in an "in vivo" study on the baboon using a benzodiazepine (flunitrazepam) labeled with carbon-11 are presented. The specificity of "in vivo" binding of Flunitrazepam-11C was demonstrated by competition with Lorazepam in the brain, but it was not possible to verify the criterium of stereospecificity "in vivo". The preliminary results of a study carried out under the same conditions on RO 15 1788 11C show the interest of using this labeled antagonist as an "in vivo" ligand for the specific binding sites of benzodiazepines in positron-emission tomography.
Morphologically, gap junctions are intermembranous channels between cells thought to mediate elec... more Morphologically, gap junctions are intermembranous channels between cells thought to mediate electrotonic transmission and to serve as a passage for small molecules in the CNS (for a review see Sotelo and Korn, 1978). After the discovery that the fluorescent dye Lucifer yellow crosses gap junctions to label adjacent cells (Stewart, 1978), dye-coupling was used as indirect evidence for the presence of gap junctions. Dye-coupling occurs in several neural areas, including the hippocampus (Knowles et el., 1982; MacVicar et al., 1982), the neocortex (Connors et al., 1983; Gutnick and Prince, 1981) and the hypothalamus (Andrew et al., 1981; Hatton et al., 1987). In parallel ultrastructural studies, gap junctions have been shown to be present in some of these structures (Sloper and Powell, 1978; Sotelo and Korn, 1978).
Publisher Summary This chapter explores that the striatum is centrally located to receive a varie... more Publisher Summary This chapter explores that the striatum is centrally located to receive a variety of synaptic inputs that are integrated and distributed to appropriate output regions producing adaptive behaviors, through cortico-basal ganglia-thalamocortical loops. These functions are precisely regulated by the coordinated pre- and postsynaptic actions of dopamine (DA) modulating voltage- and ligand-gated conductances in medium-sized spiny neurons (MSNs), the principal cell type in striatum, as well as a variety of interneurons. Huntington's disease (HD) involves dysfunction and eventual degeneration of striatal and cortical neurons, whereas dysfunction and subsequent degeneration of DA neurons lead to Parkinson's disease (PD). The chapter reviews that with the introduction of animal models of HD and PD, it has become possible to study electrophysiological changes in basal ganglia neurons and, more specifically, alterations along the corticostriatal pathway in each of these disorders. It reviews that the role of changes in this pathway contributes to cognitive and motor disturbances in HD and PD models. It also focuses on alterations of the corticostriatal pathway in genetic mouse models.
Since the identification of the gene responsible for HD (Huntington's disease), many genetic ... more Since the identification of the gene responsible for HD (Huntington's disease), many genetic mouse models have been generated. Each employs a unique approach for delivery of the mutated gene and has a different CAG repeat length and background strain. The resultant diversity in the genetic context and phenotypes of these models has led to extensive debate regarding the relevance of each model to the human disorder. Here, we compare and contrast the striatal synaptic phenotypes of two models of HD, namely the YAC128 mouse, which carries the full-length huntingtin gene on a yeast artificial chromosome, and the CAG140 KI*** (knock-in) mouse, which carries a human/mouse chimaeric gene that is expressed in the context of the mouse genome, with our previously published data obtained from the R6/2 mouse, which is transgenic for exon 1 mutant huntingtin. We show that striatal MSNs (medium-sized spiny neurons) in YAC128 and CAG140 KI mice have similar electrophysiological phenotypes to t...
Dopamine (DA), a prominent neuromodulator in the brain, regulates neuronal excitability and synap... more Dopamine (DA), a prominent neuromodulator in the brain, regulates neuronal excitability and synaptic transmission. These actions are effected through diverse DA receptor subtypes whose effects vary as a function of a number of factors including pre- or postsynaptic localization and the intracellular signaling cascades they activate. We have chosen the corticostriatal synapse as a model to study the interactions between
Electroencephalography and Clinical Neurophysiology, 1983
... and EMG jerks, resembling the human adversive seizures presumably originating from the inter-... more ... and EMG jerks, resembling the human adversive seizures presumably originating from the inter-mediate frontal cortex (Penfield and Jasper 1954). ... Cepeda, C., Pacheco, MT, Cruz, ML, Almanza, X. and Velasco, M. Phasic paradoxical sleep precipitates focal mo-tor and limbic ...
Genetic mouse models based on identification of genes that cause Huntington's and Parkinson's dis... more Genetic mouse models based on identification of genes that cause Huntington's and Parkinson's diseases have revolutionized understanding of the mechanistic pathophysiological progression of these disorders. These models allow the earliest manifestations of the diseases to be identified, and they display behavioral, neuropathological and electrophysiological deficits that can be followed over time in mechanistic and drug studies. An intriguing feature is that they do not reproduce the relatively selective and massive cell loss characterizing the human diseases. There is more information on Huntington's disease models because the disorder involves a single gene that was identified over ten years ago; genetic mutations causing Parkinson's disease are rare and were discovered more recently, and models of the disease have been generated only within the past few years.
7-OH-DPAT has been shown to exhibit selectivity between Dz and D3 dopamine receptors in a variety... more 7-OH-DPAT has been shown to exhibit selectivity between Dz and D3 dopamine receptors in a variety of in vitro assay systems. Although the drug has been used in a variety of studies to evaluate the behavioral effects of D3 receptor stimulation, the in vivo Dz/D3 selectivity of the compound has not been determined. In this study, protection against inactivation by EEDQ was used as a measure of in vivo occupancy of D2 receptors by behaviorally relevant doses of 7-OH-DPAT (0.03-10 mg/kg, s.c.) in adult, male Sprague-Dawley rats. Ex vivo [3Hlspiperone binding was then determined in striatal membranes. 7-OH-DPAT protected against inactivation of Dz receptors with an EDSo value of 11 mg/kg. Significant protection of Dz receptors was observed at doses of 1 mgkg and above. These data suggest that stimulation of Dz receptors contributes to the pharmacological effects of 7-OH-DPAT when administered at doses above 0.3 mg/ kg (s.c.). o 1996 Wiley-Liss, Inc.
The responses of human neocortical neurons to iontophoretic application of excitatory amino acids... more The responses of human neocortical neurons to iontophoretic application of excitatory amino acids and their modulation by dopamine (DA) were studied in vitro. Brain slices were obtained from children undergoing surgery for intractable epilepsy. Application of N-methyl-D-aspartate (NMDA) to the slices induced slow depolarizations accompanied by decreased input conductances and sustained action potentials in cortical neurons. Glutamate produced rapid depolarizations and firing with few changes in input conductances. Quisqualate also induced depolarization and firing, but input conductances increased during the rising phase of the membrane depolarization. Iontophoretic application of DA alone produced no change in membrane potential or input conductance. However, when DA was applied in conjunction with the excitatory amino acids, it produced contrasting effects. With either bath application of DA or when iontophoresis of DA preceded application of NMDA, the amplitude of the membrane depolarizations and the number of action potentials were increased, whereas the latency of these responses decreased. In contrast, DA decreased the amplitude of the depolarizations and the number of action potentials evoked by glutamate or quisqualate. The fact that DA affects responses to NMDA and glutamate or quisqualate in opposite directions is of considerable importance to the understanding of cellular mechanisms of neuromodulation and the role of DA in cognitive processing and in epilepsy. o 1992 Wiley-Liss, Inc.
The membrane properties and synaptic physiology of developing cat substantia nigra (SN) neurons w... more The membrane properties and synaptic physiology of developing cat substantia nigra (SN) neurons were studied in in vitro slice preparations. Stable intracellular recordings were obtained from 46 neurons in 20 kittens ranging in age from fetal day (F) 51 to postnatal day (P) 120. Only two of these properties changed with development. The percentage of cells displaying inward rectification and the percentage of cells that generated low-threshold Ca++ spikes increased with age. Properties that did not change included resting membrane potentials, action potential amplitudes and durations, and input resistances. At all ages locally evoked synaptic responses consisted of sequences of excitatory postsynaptic potentials followed by inhibitory postsynaptic potentials. Most of the cells recorded had the electrophysiological properties which have been attributed to SN dopamine-containing neurons. To identify neurons morphologically, and verify the recording site, cells were filled with Lucifer yellow at the end of each experiment. Somatic shapes varied widely from oval to fusiform to triangular. Somatic diameters and dendritic length increased with development. Filopodial processes and growth cones were present up to the first postnatal month. Dye-coupling occurred only in the fetal group. These results indicate that cat SN neurons have many mature physiological properties during late fetal and early postnatal development. This contrasts with the significant maturation that occurs in cat caudate neurons during the same developmental period (Cepeda et al.,
This report represents a detailed description of experiments designed to replicate and extend the... more This report represents a detailed description of experiments designed to replicate and extend the findings of a published study on the effects of treating the R6/2 Huntington's disease (HD) mouse model with ~300 CAG repeats using the pimelic diphenylamide histone deacetylase (HDAC) inhibitor, HDACi 4b (Thomas et al., 2008). In addition to testing the R6/2 mice, similar experiments examined the effects of the drug on a second transgenic HD mouse model, the N171-82Q mice. As in the original study, the drug was delivered in the drinking water. In the present study we tested larger groups of mice than in the original study. The results indicated that we were unable to replicate the significant behavioral effects of oral HDACi 4b treatment in the R6/2 mice. There were however, non-significant trends for the treated R6/2 mice to be less affected on some of the measures and there were instances of phenotype progression being delayed in these treated mice. In contrast, we did replicate the protection from striatal atrophy in the R6/2 mice. We also did not observe any beneficial effects of HDACi 4b treatment in the N171-82Q mice. Although the behavioral procedures were replicated and an automated activity assessment was added, there were several unexpected complications in terms of solubility of the drug, CAG repeat length differences and gender differences in progression of the phenotype that could have affected outcomes. Clearly more studies will have to be performed using other methods of delivery as well as assessing effects in more slowly progressing HD models to better evaluate the effects of this HDAC inhibitor.
prominent example of such a proposed circuit is suggested for the dopaminergic regulation of volu... more prominent example of such a proposed circuit is suggested for the dopaminergic regulation of voluntary motor learning. The basic "striatal microcircuit" (Figure 1A
Abnormally enhanced N-methyl-D-aspartate (NMDA) receptor function is implicated in Huntington's d... more Abnormally enhanced N-methyl-D-aspartate (NMDA) receptor function is implicated in Huntington's disease (HD). In this issue of Neuron and a recent issue of Nature Medicine, an abnormal balance between the activity of NMDA receptors at synaptic (prosurvival) and extrasynaptic (proapoptotic) sites has been uncovered in a cellular and a mouse model of HD.
Tuberous sclerosis complex (TSC) and cortical dysplasia Type IIB (CDIIB) share histopathologic fe... more Tuberous sclerosis complex (TSC) and cortical dysplasia Type IIB (CDIIB) share histopathologic features that suggest similar epileptogenic mechanisms. This study compared the morphological and electrophysiological properties of cortical cells in tissue from pediatric TSC (n=20) and CDIIB (n=20) patients using whole-cell patch clamp recordings and biocytin staining. Cell types were normal-appearing and dysmorphiccytomegalic pyramidal neurons, interneurons, and giant/ balloon cells, including intermediate neuronal-glial cells. In the cortical mantle, giant/balloon cells occurred more frequently in TSC than in CDIIB cases, whereas cytomegalic pyramidal neurons were found more frequently in CDIIB. Cell morphology and membrane properties were similar in TSC and CDIIB cases. Except for giant/balloon and intermediate cells, all neuronal cell types fired action potentials and displayed spontaneous postsynaptic currents. However, the frequency of spontaneous glutamatergic postsynaptic currents in normal pyramidal neurons and interneurons was significantly lower in CDIIB compared with TSC cases and GABAergic activity was higher in all neuronal cell types in CDIIB. Further, acutely dissociated pyramidal neurons displayed higher sensitivity to exogenous application of GABA in CDIIB compared with TSC cases. These results indicate that, in spite of similar histopathologic features and basic cell membrane properties, TSC and CDIIB display differences in the topography of abnormal cells, excitatory and inhibitory synaptic network properties, and GABA A receptor sensitivity. These differences support the notion that the mechanisms of epileptogenesis could differ in patients with TSC and CDIIB. Consequently, pharmacologic therapies should take these findings into consideration.
Overexpression or mutation of α-synuclein (α-Syn), a protein associated with presynaptic vesicles... more Overexpression or mutation of α-synuclein (α-Syn), a protein associated with presynaptic vesicles, causes familial forms of Parkinson's disease in humans and is also associated with sporadic forms of the disease. We used in vivo microdialysis, tissue content analysis, behavioral assessment, and whole-cell patch clamp recordings from striatal medium-sized spiny neurons (MSSNs) in slices to examine dopamine transmission and dopaminergic modulation of corticostriatal synaptic function in mice overexpressing human wild-type α-Syn under the Thy1 promoter (α-Syn mice). Tonic striatal extracellular dopamine and 3-methoxytyramine levels were elevated in α-Syn mice at 6 months of age, prior to any reduction in total striatal tissue content, and were accompanied by an increase in open-field activity. Dopamine clearance and amphetamine-induced dopamine efflux were unchanged. The frequency of MSSN spontaneous excitatory postsynaptic currents (sEPSCs) was lower in α-Syn mice. Amphetamine reduced sEPSC frequency in wild types (WTs) but produced no effect in α-Syn mice. Furthermore,
We used two mouse models of Huntington's disease (HD) to examine changes in gluta... more We used two mouse models of Huntington's disease (HD) to examine changes in glutamate receptor sensitivity and striatal electrophysiology. One model, a transgenic, consisted of mice expressing exon 1 of the human HD gene and carrying 141-157 CAG repeat sequences (R6/2 line). The second model, a CAG repeat "knockin," consisted of mice with different lengths of CAG repeats (CAG71 and CAG94 repeats). The effects of glutamate receptor activation were examined by visualizing neurons in brain slices with infrared videomicroscopy and differential interference contrast optics to determine changes in somatic area (cell swelling). Striatal and cortical neurons in both models (R6/2 and CAG94) displayed more rapid and increased swelling to N-methyl-D-aspartate (NMDA) than those in controls. This effect was specific as there were no consistent group differences after exposure to alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid (AMPA) or kainate (KA). Intracellular recordings revealed that resting membrane potentials (RMPs) in the R6/2 transgenics were significantly more depolarized than those in their respective controls. RMPs in CAG94 mice also were more depolarized than those in CAG71 mice or their controls in a subset of striatal neurons. Confirming previous results, R6/2 mice expressed behavioral abnormalities and nuclear inclusions. However, CAG71 and CAG94 knockins did not, suggesting that increased sensitivity to NMDA may occur early in the disease process. These findings imply that NMDA antagonists or compounds that alter sensitivity of NMDA receptors may be useful in the treatment of HD.
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Papers by Carlos Cepeda