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R Gardette

Publications and source records attributed to R Gardette.

30 records · Page 2Linked to original sources
PubMed1985

Electrophysiological studies on the postnatal development of intracerebellar nuclei neurons in rat cerebellar slices maintained in vitro. I. Postsynaptic potentials.

The development of the synaptic responses of intracerebellar nuclei neurons was studied in the rat by the use of thick sagittal cerebellar slices maintained in vitro. It has been shown that functional excitatory synapses are present on these neurons from birth, probably due to climbing and/or mossy fiber collaterals; functional inhibitory synapses, due to monosynaptic projections of Purkinje cell axons onto intracerebellar nuclei, are present as early as postnatal day 2; and a more complex pattern of synaptic responses, including short latency excitatory postsynaptic potentials (EPSPs) and inhibitory postsynaptic potentials (IPSPs), longer latency IPSPs, and late depolarizing responses, can be elicited in nuclear neurons as early as postnatal day 3, indicating an early development of some complete functional cerebellar circuits involving the intracerebellar nuclei.

Animals↗
PubMed1984

Effect of excitatory amino acids on Purkinje cell dendrites in cerebellar slices from normal and staggerer mice.

The sensitivity of Purkinje cells to short pulse applications of L-aspartate, L-glutamate and related derivatives in their dendritic fields was tested in normal and staggerer mutant mice using cerebellar slices maintained in vitro. In normal mice, the response of Purkinje cells to L-aspartate and L-glutamate consisted of a transient and dose-dependent increase of their firing of simple spikes. The potency of L-aspartate in exciting Purkinje cells was lower than that of L-glutamate when the two drugs were released from adjacent barrels of the same iontophoretic electrode. Quisqualate was an even more potent excitant of these cells than L-aspartate and L-glutamate, whereas N-methyl-DL-aspartate had little or no effect. In staggerer mutant mice, the sensitivity of Purkinje cells to L-aspartate, L-glutamate and quisqualate was not significantly altered. On the contrary, N-methyl-DL-aspartate had a much stronger potency than normal in exciting Purkinje cells although this was still smaller than that of the other agonists tested. These results suggest that the sensitivity of Purkinje cells to L-aspartate and L-glutamate, i.e. the putative neurotransmitters of the climbing and parallel fibers respectively, remains largely normal in staggerer mice. In contrast, in the mutant, N-methyl-D-aspartate receptors are likely to be much more developed than normal.

Amino Acids↗
PubMed1984

Selective absence of calcium spikes in Purkinje cells of staggerer mutant mice in cerebellar slices maintained in vitro.

The bioelectrical properties of Purkinje cells (intrasomatic recordings) were studied in sagittal cerebellar slices of both adult staggerer and control mice. Mean input resistances of Purkinje cells were 25 +/- 4 M omega and 48 +/- 7 M omega in normal and staggerer mice respectively. In both groups, time-dependent inward rectifications were apparent in the hyperpolarizing voltage-responses. In normal mice, tetrodotoxin (TTX)-sensitive simple spikes and slower-rising multiphasic spikes, abolished when Ca was replaced by Cd in the bath, spontaneously occurred in Purkinje cells. These Na- and Ca-dependent spikes were also elicited by depolarizing current pulses. In the mutant, Ca spikes were never observed, even in strongly depolarized cells. On the contrary, TTX-sensitive simple spikes occurred spontaneously or were elicited by depolarizing current pulses. When Ca was replaced by Ba in the bath, the Ca spikes evoked in normal Purkinje cells by direct stimulation were first enhanced and then replaced by prolonged action potentials (1-6 s in duration) which were TTX-resistant and Cd-sensitive. These (Ba) action potentials were also triggered by climbing fibre activation of the cells. In staggerer mice, Ca spikes were never elicited by direct stimulation in Ba-containing medium, although in a few cells prolonged action potentials were occasionally elicited by depolarizing current pulses. However, this latter type of response was never evoked by climbing fibre activation of Purkinje cells. In the mutant, extracellular application of tetraethylammonium (TEA) generated prolonged action potentials, the plateaux of depolarization of which were less positive than those elicited by Ba in control mice. These plateaux were abolished by TTX and left unaffected by the substitution of Ca by Cd in the bath, suggesting that they were due to a non-inactivating Na conductance. On the whole, the present study strongly suggests that voltage-dependent Ca channels are missing in most staggerer Purkinje cells or at least that their characteristics and/or distribution are such that they cannot be activated. Na channels appear unaffected.

Action Potentials↗
PubMed1983

Voltage clamp analysis of the effect of excitatory amino acids and derivatives on Purkinje cell dendrites in rat cerebellar slices maintained in vitro.

A voltage clamp analysis of the effects of L-aspartate, L-glutamate and related derivatives on Purkinje cell dendrites was performed in rat cerebellar slices maintained in vitro. Short iontophoretic pulse applications of L-aspartate and L-glutamate in the dendritic field of Purkinje cells induced dose-dependent inward currents with fast onset and recovery. Quisqualate application also gave rise to well developed inward currents with fast onset and slow recovery, whereas N-methyl-D,L-aspartate had no or little effect on Purkinje cell membranes unless prolonged (several seconds) applications were used. Steady applications of low doses of N-methyl-D,L-aspartate much more severely depressed L-aspartate than L-glutamate mediated responses, whereas inward currents due to quisqualate were unaffected. Inward currents due to quisqualate were often more reduced than those due to L-aspartate by steady applications of 2-amino-5-phosphonovalerate, and the antagonistic action of this drug on responses due to L-glutamate was very weak. These results suggest that receptors of Purkinje cells for glutamate and aspartate are different, and are also different from N-methyl-D-aspartate and quisqualate receptors.

Amino Acids↗
PubMed1983

Bioelectrical properties of cerebellar Purkinje cells in reeler mutant mice.

Electroresponsive properties of intracellularly recorded Purkinje cells (PCs) in reeler mice were studied by using sagittal cerebellar slices maintained in vitro. In normally as well as in abnormally located PCs, fast spikes and slower rising multiphasic spikes were elicited by depolarizing currents, and they were abolished by tetrodotoxin and by cadmium respectively. This demonstrates that these neurons, as PCs in normal animals, do have sodium- and calcium-dependent spikes, thus indicating that these bioelectrical properties do not depend on the connectivity of PCs.

Action Potentials↗
PubMed1983

Olivocerebellar projections in control and staggerer mutant mice. An autoradiographic study.

Olivocerebellar projections were studied in normal and in staggerer mutant mice by means of autoradiographic methods following [3H]leucine injections in the inferior olivary complex. In normal mice, a sagittal banding pattern of labeled climbing fibers was apparent in the contralateral cerebellar cortex, thus confirming previous observations in rodents. In staggerer mice, olivocerebellar projections also displayed a clear sagittal zonation, thus indicating that this organization may be achieved in the mutant, in spite of pronounced abnormalities of the cerebellar cortex.

Animals↗
PubMed1983

[Development of synaptic responses and membrane conductances of neurons of intracerebellar nuclei in the rat].

A study of synaptic responses and membrane conductances of intracerebellar nuclei neurones, from thick sagittal cerebellar slices maintained in vitro, has shown that 1) functional excitatory synapses are present on these neurones from birth, probably due to climbing and/or mossy fibre collaterals; 2) functional inhibitory synapses, due to monosynaptic projections of Purkinje cell axons onto intracerebellar nuclei, are present as early as postnatal day 2; 3) immature nuclear neurones display not only fast sodium conductances, but also slow calcium conductances which persist until weaning time together with fast sodium spikes.

Action Potentials↗
PubMed1982

A standardized automatic procedure to evaluate cell numbers in low cell density tissues by image analysis: application to the Staggerer mutant mouse cerebellum.

To obtain a reliable and fast quantification in low cell density tissues, we have developed a standardized procedure based on image analysis. The successive steps of quantification, starting with the necessary histological procedure and ending with the desired quantitative parameters, are described. Excepting the histological procedure, we have attempted to automate all the subsequent steps of the experiment, especially the acquisition of the data by an image analyser TAS (Leitz), and the storage and the analysis of these data by a PDP 11-34 computer. The final parameters calculated by such a method are the total number of cells and the cell density within the organ under study, either for all the cells, or for different cellular categories. This procedure has been applied to the quantitative study of cerebellar cells of an adult Staggerer mutant mouse and the results obtained are presented.

Animals↗
PubMed1982

Prenatal development of mouse central nervous structures: time of neuron origin and gradients of neuronal production. A radioautographic study.

In order to obtain an overall view of neurogenesis in the main central nervous structures of the mouse, we have undertaken a systematic study of the time of neuron origin and of the gradients of neuronal production. The animals were the offspring of pregnant females given a pulse label of 3H-thymidine on selected days after conception. These days were chosen to cover the principal brain development stages: E10.5, E11.5, E12.5, E13.5, E14.5, E15.5, E16.5, E17.5 and E18.5. The offspring were sacrificed during the fourth postnatal week and labeling indices were calculated in the different brain structures. The study of labeling indices as a function of the day of injection and of the brain level studied provided us with information on the major periods of neuronal proliferation in these structures and allowed us to analyse the formation gradients inside a given nervous structure. As a whole, for a majority of nervous structures (olfactory, cortical, septal, hippocampal, preoptic, thalamic, epithalamic, hypothalamic and cerebellar structures), our results are in good agreement with the already published observations. However, we outlined two major phenomena apparently unobserved until now in the mouse: the first is a rostrocaudal gradient of neuronal production in the inferior colliculi, and the second is the long period of neuronal proliferation in the caudate nucleus lasting from E11.5 to E18.5, along a complex inside-out and mediolateral gradient.

Animals↗
PubMed1981

Automatic recognition of nervous structures by image analysis. A pattern recognition method applied to the study of mouse cerebellum.

An automatic image pattern analysis method based on differential densitometry is presented. It is applied to histological sections of mouse cerebellum. This method allows an automatic recognition of any cerebellar microscopic field. After recognition, histological images are decomposed into homogeneous parts with respect to cerebellar cellular layers, and both densitometric patterns and partial areas of each of these layers are estimated. This method is accurate to within 94% for a learning sample and 75% for a test sample. This score can be improved by adjunct algorithms presently under study.

Animals↗