S. Charpier - Academia.edu (original) (raw)
Papers by S. Charpier
Journal of Neurophysiology, 1994
1. Presynaptic activity in the inhibitory network impinging on the Mauthner (M-) cell was investi... more 1. Presynaptic activity in the inhibitory network impinging on the Mauthner (M-) cell was investigated in the goldfish medulla in vivo using extra- and intracellular recordings. The inhibitory presynaptic volley elicited by stimulation of the contralateral vestibular nerve consisted of multiple successive peaks at high frequency (up to 1,000 Hz). Less pronounced multicomponent responses were recorded after antidromic activation of the M-cell. Such high-frequency “oscillatory” field potentials also occurred spontaneously. 2. In intracellular recordings, a subset of inhibitory interneurons showed evoked and spontaneous burst discharge. Burst action potentials were correlated with the peaks in the extracellular volley, suggesting that repetitive firing of these cells is synchronized. Nonbursting cells, on the other hand, fired single action potentials in response to vestibular stimuli and were not activated via the M-cell collateral network. 3. Bursting cells were determined morphologi...
Journal of Neurophysiology, 1995
1. Tetanizing protocols were used to test whether glycinergic inhibition undergoes long-term plas... more 1. Tetanizing protocols were used to test whether glycinergic inhibition undergoes long-term plasticity in vivo. For this purpose we studied the inhibition evoked disynaptically in the teleost Mauthner (M) cell by stimulation of the posterior branch of the contralateral VIIIth nerve. The advantage of this experimental design is that the inhibition, which is mediated by identified second-order commissural interneurons, is not contaminated by parallel excitation. 2. The VIIIth-nerve-evoked inhibitory postsynaptic potentials (IPSPs), which are generated at the level of the soma, are depolarizing in Cl(-)-loaded M cells. After VIIIth nerve tetanization, these IPSPs exhibited potentiation lasting > 30 min in 23 of 31 cells. The maximum enhancement measured 5-10 min after the onset of the tetanization averaged 100 +/- 19% (mean +/- SE). In contrast, the non-"tetanized" collateral IPSP induced by antidromic stimulation of the M axon did not increase significantly suggesting sy...
Proceedings of the National Academy of Sciences, 1995
Simultaneous pre- and postsynaptic recordings from identified glycinergic inhibitory interneurons... more Simultaneous pre- and postsynaptic recordings from identified glycinergic inhibitory interneurons and the Mauthner cell showed that 25% of the afferents produced no or extremely small postsynaptic responses. Morphological determination of the number of contacts made by these cells on the Mauthner cell revealed a connectivity similar to that of functional neurons which always produce clear inhibitory postsynaptic potentials, suggesting that most of the endings, made by weak interneurons are silent. Intraaxonal injection of 4-aminopyridine or Ca2+ greatly enhanced transmission at functional connections but did not modify those which were ineffective. However, after eighth nerve tetanic stimuli, transmission at the weak connections was unmasked or enhanced for prolonged periods and was twice as likely to be potentiated, with a 6-fold greater mean enhancement than the potent ones. This result provides additional support for long-term potentiation of inhibitory synapses. Furthermore, wea...
The Journal of Physiology, 1998
In vivo extracellular and intracellular recordings were performed from thalamocortical (TC) neuro... more In vivo extracellular and intracellular recordings were performed from thalamocortical (TC) neurones in a genetic model of absence epilepsy (genetic absence epilepsy rats from Strasbourg) during spontaneous spike and wave discharges (SWDs). Extracellularly recorded single units (n= 14) fired either a single action potential or a high frequency burst of up to three action potentials, concomitantly with the spike component of the spike‐wave complex. Three main events characterized the intracellular activity of twenty‐six out of twenty‐eight TC neurones during SWDs: a small amplitude tonic hyperpolarization that was present throughout the SWD, rhythmic sequences of EPSP/IPSPs occurring concomitantly with the spike‐wave complexes, and a small tonic depolarization at the end of the SWD. The rhythmic IPSPs, but not the tonic hyperpolarization, were mediated by activation of GABAA receptors since they reversed in polarity at ‐68 mV and appeared as depolarizing events when recording with KC...
Proceedings of the National Academy of Sciences, 1997
The purpose of the present study was to investigate in vivo the activity-dependent plasticity of ... more The purpose of the present study was to investigate in vivo the activity-dependent plasticity of glutamatergic cortico-striatal synapses. Electrical stimuli were applied in the facial motor cortex and intracellular recordings were performed in the ipsilateral striatal projection field of this cortical area. Recorded cells exhibited the typical intrinsic membrane properties of striatal output neurons and were identified morphologically as medium spiny type I neurons. Subthreshold cortical tetanization produced either shortterm posttetanic potentiation or short-term depression of cortically-evoked excitatory postsynaptic potentials. When coupled with a postsynaptic depolarization leading the membrane potential to a suprathreshold level, the tetanus induced long-term potentiation (LTP) of cortico-striatal synaptic transmission. Induction of striatal LTP was prevented by intracellular injection of a calcium chelator suggesting that this synaptic plasticity involves an increase of postsynaptic free calcium concentration. Contrasting with previous in vitro studies our findings demonstrate that LTP constitutes the normal form of use-dependent plasticity at cortico-striatal synapses. Since excitation of striatal neurons produces a disinhibition of premotor networks, LTP at excitatory striatal inputs should favor the initiation of movements and therefore could be critical for the functions of basal ganglia in motor learning.
Neuropharmacology, 1999
Cortical and thalamic neurones play a major role in the generation/expression of spike and wave d... more Cortical and thalamic neurones play a major role in the generation/expression of spike and wave discharges (SWDs), the main electroencephalographic (EEG) feature of absence seizures. The detailed mechanisms leading to this paroxysmal EEG activity, however, are still poorly understood. We have now made in vivo intracellular recordings from layer V cortical neurones of the facial motor cortex and from thalamocortical (TC) neurones of the ventroposteromedial and ventroposterolateral nuclei in a well established model of this disease: the Genetic Absence Epilepsy Rats from Strasbourg (GAERS). The main feature of the intracellularly recorded activity of TC neurones during spontaneous SWDs was the presence of rhythmic sequences of synaptic potentials consisting of an EPSP closely followed by 2-6 IPSPs. These rhythmic sequences were superimposed on a small tonic hyperpolarization that lasted for the whole duration of the SWD and was still present at potentials close to −85 mV. The rhythmic IPSPs, on the other hand, had a reversal potential of −68 mV, and always appeared as depolarizing events when recording with KCl-filled electrodes at − 55 mV. Low frequency electrical stimulation of the corresponding cortical area evoked in TC neurones a short and a long lasting IPSP, whose waveforms were reminiscent of a GABA A and a GABA B IPSP, respectively. The main feature of the intracellular activity recorded in cortical neurones during spontaneous SWDs was the presence of rhythmic depolarizations. Their frequency was similar to the one of SWDs in the EEG, and was not affected by DC injection. The amplitude of the rhythmic depolarizations, however, increased following steady hyperpolarization of the neurone by DC injection. An increase in the apparent input resistance of cortical neurones was observed during SWDs compared to the inter-SWDs periods. Low frequency electrical stimulation of the contralateral striatum evoked in cortical neurones a short and a long lasting IPSP, whose waveforms were reminiscent of a GABA A and a GABA B IPSP, respectively. Our data indicate that there are no rhythmic GABA B IPSPs and low threshold Ca 2 + potentials in GAERS TC neurones during SWDs, but rhythmic sequences of EPSP/IPSPs superimposed on a tonic hyperpolarization that might represent a long lasting GABA B IPSP. Further experiments are required to clarify the nature of the voltage waveform and the increase in input resistance observed in cortical neurones during spontaneous SWDs in GAERS.
Journal of Neurophysiology, 1994
1. Presynaptic activity in the inhibitory network impinging on the Mauthner (M-) cell was investi... more 1. Presynaptic activity in the inhibitory network impinging on the Mauthner (M-) cell was investigated in the goldfish medulla in vivo using extra- and intracellular recordings. The inhibitory presynaptic volley elicited by stimulation of the contralateral vestibular nerve consisted of multiple successive peaks at high frequency (up to 1,000 Hz). Less pronounced multicomponent responses were recorded after antidromic activation of the M-cell. Such high-frequency “oscillatory” field potentials also occurred spontaneously. 2. In intracellular recordings, a subset of inhibitory interneurons showed evoked and spontaneous burst discharge. Burst action potentials were correlated with the peaks in the extracellular volley, suggesting that repetitive firing of these cells is synchronized. Nonbursting cells, on the other hand, fired single action potentials in response to vestibular stimuli and were not activated via the M-cell collateral network. 3. Bursting cells were determined morphologi...
Journal of Neurophysiology, 1995
1. Tetanizing protocols were used to test whether glycinergic inhibition undergoes long-term plas... more 1. Tetanizing protocols were used to test whether glycinergic inhibition undergoes long-term plasticity in vivo. For this purpose we studied the inhibition evoked disynaptically in the teleost Mauthner (M) cell by stimulation of the posterior branch of the contralateral VIIIth nerve. The advantage of this experimental design is that the inhibition, which is mediated by identified second-order commissural interneurons, is not contaminated by parallel excitation. 2. The VIIIth-nerve-evoked inhibitory postsynaptic potentials (IPSPs), which are generated at the level of the soma, are depolarizing in Cl(-)-loaded M cells. After VIIIth nerve tetanization, these IPSPs exhibited potentiation lasting > 30 min in 23 of 31 cells. The maximum enhancement measured 5-10 min after the onset of the tetanization averaged 100 +/- 19% (mean +/- SE). In contrast, the non-"tetanized" collateral IPSP induced by antidromic stimulation of the M axon did not increase significantly suggesting sy...
Proceedings of the National Academy of Sciences, 1995
Simultaneous pre- and postsynaptic recordings from identified glycinergic inhibitory interneurons... more Simultaneous pre- and postsynaptic recordings from identified glycinergic inhibitory interneurons and the Mauthner cell showed that 25% of the afferents produced no or extremely small postsynaptic responses. Morphological determination of the number of contacts made by these cells on the Mauthner cell revealed a connectivity similar to that of functional neurons which always produce clear inhibitory postsynaptic potentials, suggesting that most of the endings, made by weak interneurons are silent. Intraaxonal injection of 4-aminopyridine or Ca2+ greatly enhanced transmission at functional connections but did not modify those which were ineffective. However, after eighth nerve tetanic stimuli, transmission at the weak connections was unmasked or enhanced for prolonged periods and was twice as likely to be potentiated, with a 6-fold greater mean enhancement than the potent ones. This result provides additional support for long-term potentiation of inhibitory synapses. Furthermore, wea...
The Journal of Physiology, 1998
In vivo extracellular and intracellular recordings were performed from thalamocortical (TC) neuro... more In vivo extracellular and intracellular recordings were performed from thalamocortical (TC) neurones in a genetic model of absence epilepsy (genetic absence epilepsy rats from Strasbourg) during spontaneous spike and wave discharges (SWDs). Extracellularly recorded single units (n= 14) fired either a single action potential or a high frequency burst of up to three action potentials, concomitantly with the spike component of the spike‐wave complex. Three main events characterized the intracellular activity of twenty‐six out of twenty‐eight TC neurones during SWDs: a small amplitude tonic hyperpolarization that was present throughout the SWD, rhythmic sequences of EPSP/IPSPs occurring concomitantly with the spike‐wave complexes, and a small tonic depolarization at the end of the SWD. The rhythmic IPSPs, but not the tonic hyperpolarization, were mediated by activation of GABAA receptors since they reversed in polarity at ‐68 mV and appeared as depolarizing events when recording with KC...
Proceedings of the National Academy of Sciences, 1997
The purpose of the present study was to investigate in vivo the activity-dependent plasticity of ... more The purpose of the present study was to investigate in vivo the activity-dependent plasticity of glutamatergic cortico-striatal synapses. Electrical stimuli were applied in the facial motor cortex and intracellular recordings were performed in the ipsilateral striatal projection field of this cortical area. Recorded cells exhibited the typical intrinsic membrane properties of striatal output neurons and were identified morphologically as medium spiny type I neurons. Subthreshold cortical tetanization produced either shortterm posttetanic potentiation or short-term depression of cortically-evoked excitatory postsynaptic potentials. When coupled with a postsynaptic depolarization leading the membrane potential to a suprathreshold level, the tetanus induced long-term potentiation (LTP) of cortico-striatal synaptic transmission. Induction of striatal LTP was prevented by intracellular injection of a calcium chelator suggesting that this synaptic plasticity involves an increase of postsynaptic free calcium concentration. Contrasting with previous in vitro studies our findings demonstrate that LTP constitutes the normal form of use-dependent plasticity at cortico-striatal synapses. Since excitation of striatal neurons produces a disinhibition of premotor networks, LTP at excitatory striatal inputs should favor the initiation of movements and therefore could be critical for the functions of basal ganglia in motor learning.
Neuropharmacology, 1999
Cortical and thalamic neurones play a major role in the generation/expression of spike and wave d... more Cortical and thalamic neurones play a major role in the generation/expression of spike and wave discharges (SWDs), the main electroencephalographic (EEG) feature of absence seizures. The detailed mechanisms leading to this paroxysmal EEG activity, however, are still poorly understood. We have now made in vivo intracellular recordings from layer V cortical neurones of the facial motor cortex and from thalamocortical (TC) neurones of the ventroposteromedial and ventroposterolateral nuclei in a well established model of this disease: the Genetic Absence Epilepsy Rats from Strasbourg (GAERS). The main feature of the intracellularly recorded activity of TC neurones during spontaneous SWDs was the presence of rhythmic sequences of synaptic potentials consisting of an EPSP closely followed by 2-6 IPSPs. These rhythmic sequences were superimposed on a small tonic hyperpolarization that lasted for the whole duration of the SWD and was still present at potentials close to −85 mV. The rhythmic IPSPs, on the other hand, had a reversal potential of −68 mV, and always appeared as depolarizing events when recording with KCl-filled electrodes at − 55 mV. Low frequency electrical stimulation of the corresponding cortical area evoked in TC neurones a short and a long lasting IPSP, whose waveforms were reminiscent of a GABA A and a GABA B IPSP, respectively. The main feature of the intracellular activity recorded in cortical neurones during spontaneous SWDs was the presence of rhythmic depolarizations. Their frequency was similar to the one of SWDs in the EEG, and was not affected by DC injection. The amplitude of the rhythmic depolarizations, however, increased following steady hyperpolarization of the neurone by DC injection. An increase in the apparent input resistance of cortical neurones was observed during SWDs compared to the inter-SWDs periods. Low frequency electrical stimulation of the contralateral striatum evoked in cortical neurones a short and a long lasting IPSP, whose waveforms were reminiscent of a GABA A and a GABA B IPSP, respectively. Our data indicate that there are no rhythmic GABA B IPSPs and low threshold Ca 2 + potentials in GAERS TC neurones during SWDs, but rhythmic sequences of EPSP/IPSPs superimposed on a tonic hyperpolarization that might represent a long lasting GABA B IPSP. Further experiments are required to clarify the nature of the voltage waveform and the increase in input resistance observed in cortical neurones during spontaneous SWDs in GAERS.