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G Chevalier

Publications and source records attributed to G Chevalier.

At least 73 records · Page 4Linked to original sources
PubMed1984

Synaptic organization of the basal ganglia: an electroanatomical approach in the rat.

The physiological processes by which basal ganglia participate in the elaboration of movement are still poorly understood. In particular, lack of information about the synaptic organization of the output pathways of the basal ganglia impedes functional analysis of this system. To bridge this gap electroanatomical studies have been undertaken of one of the major output systems of the basal ganglia: the substantia nigra pars reticulata (SNr). This paper reviews recent results and proposes functional perspectives. The findings reported clearly establish that SNr exerts a tonic inhibitory influence on its collicular and thalamic targets. It is suggested that the striatum may achieve a complex-spatial pattern of facilitation in a large spectrum of structures related to ocular and cephalic motor activity by inhibiting the inhibitory nigrothalamic and nigrocollicular branched neurons.

Animals↗
PubMed1984

Inhibitory nigral influence on tectospinal neurons, a possible implication of basal ganglia in orienting behavior.

We have established in previous electrophysiological studies that the substantia nigra pars reticulata (SNr) exerts a potent inhibitory influence on cells located in the intermediate and deep tectal strata. The present study demonstrates that, in the rat, the tectospinal neurons constitute one of the cellular populations of the tectum on which the SN exerts its influence. Tectospinal neurons were identified using the antidromic activation method. Following SNr stimulation 17/37 (45%) of these cells showed a short-latency (1.5-2 ms) short-duration (7-15 ms) inhibition. This effect was revealed by a blockade of spontaneous and peripherally evoked discharges. Moreover, in some cases the nigral inhibition delayed the antidromic invasion of the somato-dendritic portion of the neuron. Tectospinal neurons have been considered as one of the neuronal substrate by which the superior colliculus (SC) can promote head orienting movements. The evidence that the SNr influences the responsiveness of these cells to their peripheral sensory inputs suggests that the basal ganglia and in particular the SNr are involved in the integrative sensorimotor processes underlying head orienting movements.

Afferent Pathways↗
PubMed1984

Pulmonary toxicity of aerosolized oil-formulated fenitrothion in rats.

To evaluate the potential risk of pulmonary damage due to aerial spraying of the insecticide fenitrothion, rat lungs were examined under light and electron microscopy at 3, 7, 21, and 60 days after exposure. Rats were exposed by a "nose-only" apparatus for 1 hr to 2 or 500 mg/m3 of aerosolized fenitrothion (15%) mixed with solvent Cyclosol 63 (35%) and diluent oil 585 (50%). Aerosol size particles were monitored by a light scattering apparatus. Only minor modifications of lung alveolar tissues were observed after exposure to the high concentration. At 3 days, discrete foci of mild inflammation were detected, including interstitial edema, cellular infiltration, and increased number of alveolar macrophages. At 7 days, signs of irritation were diminished while at 21 and 60 days alveolar tissues were essentially normal. Exposure to lower concentration induced more limited changes at 3 days; no modifications were seen at later periods. It is concluded that a single exposure to this fenitrothion mixture at 500 mg/m3 presents no serious hazard of pulmonary toxicity.

Aerosols↗
PubMed1984

Spatio-temporal organization of a branched tecto-spinal/tecto-diencephalic neuronal system.

The aim of the present study was to identify in the rat the diencephalic nuclei addressed by ascending collaterals of tecto-spinal neurons. For this purpose we made use of anterograde axonal transport method to determine the pattern of diencephalic projections arising from the lateral portion of the superior colliculus where most of tecto-spinal neurons are lying. Next, we used the antidromic activation method to analyse whether some of these colliculo-diencephalic projections were provided through collaterals of tecto-spinal neurons. Following injections of wheatgerm agglutinin, conjugated with horseradish peroxidase, in the lateral part of the superior colliculus, anterograde labelling was observed in: the contralateral superior colliculus, the ipsilateral pretectal nuclei, subthalamic area (zona incerta and Forel field) and thalamic structures namely: dorsal and ventral lateral geniculate, parafascicular, posterior nuclear group, reuniens nuclei and lateral portion of medio-dorsal nucleus. Moreover, bilateral projections were revealed in the following thalamic nuclei: lateral posterior, ventro-medial, paracentral and central-lateral. In the electrophysiological study we established that the thalamic nuclei medio-dorsal/central-lateral, paracentral, ventral-medial and the zona incerta receive ascending collaterals of the tecto-spinal neurons. In addition, an axonal branch to the contralateral superior colliculus was also revealed. The various ascending and descending collaterals of each branched neuron exhibited a similar conduction time for action potentials. It is thus likely that the tecto-spinal/tecto-diencephalic neurons provide a synchronized influence on their targets. The functional implication of such a branched collicular efferent pathway is discussed. Considering that tecto-spinal neurons are one of the collicular neuronal populations on which the substantia nigra exerts its influence, new perspectives in the analysis of basal ganglia collicular relationships are given.

Animals↗
PubMed1984

Growth-related enzymatic control of glycogen metabolism in cultured human tumor cells.

The activities of glycogen synthase and phosphorylase were measured and compared to the growth-related variations of glycogen accumulation in three cultured human tumor cell lines: HT-29 (colon carcinoma); MeWo (malignant melanoma); and RT-4 (carcinoma of the urinary bladder). A similar pattern of variations in the enzyme activities was found in the three cell lines. The activities of the a + b forms of glycogen phosphorylase increased throughout the culture period. Maximal activity of phosphorylase a coincided with low intracellular concentrations of glycogen during the period of exponential growth. When the rate of cell division decreased, phosphorylase a activity also decreased while the glycogen levels increased. Glycogen synthase was almost entirely in b form during the entire culture period, i.e., in both the exponential and the stationary phases. In vitro incubation of the cellular extracts without NaF showed, however, that the enzyme could be partially converted to the a form by the endogenous phosphatases. The A0.5 values of the enzyme for glucose-6-phosphate (Glc-6-P) were of the same order of magnitude as the intracellular Glc-6-P concentrations which ranged from 2.2 to 5.4 mM (almost 10 times those reported in normal cells). Similar Glc-6-P values were obtained by two different extraction methods controlled by the intracellular ATP and ADP concentrations. The Km values for uridine-5'-diphosphoglucose were always 2 to 3 times lower than the intracellular uridine-5'-diphosphoglucose concentrations. These results suggest that: (a) in these tumor cells, glycogen is essentially synthesized by glycogen synthase b via an allosteric activation by intracellular Glc-6-P; (b) there is no obvious growth-related control of glycogen synthase activity; and (c) the activity of glycogen phosphorylase seems to be growth dependent with maximal phosphorylase a activities associated with the period of high division rate.

Adenosine Diphosphate↗
PubMed1983

Diencephalic and mesencephalic efferents of the medial prefrontal cortex in the rat: electrophysiological evidence for the existence of branched axons.

Efferents originating from the rat medial prefrontal cortex and projecting to diencephalic and mesencephalic structures were analyzed electrophysiologically. The antidromic activation technique was used in order to identify cortical neurons which innervate the medio-dorsal nucleus of the thalamus (MD), lateral habenula, ventro-medial mesencephalic tegmentum (VMT), substantia nigra (SN), superior colliculus (SC) and central gray (CG). Corresponding cortical neurons, found mainly in layers V and VI, were distributed in the rostro-caudal extension of the medial prefrontal cortex. Their conduction velocities were relatively slow and ranged between 0.4 and 5.5 m/s. The reciprocal collision test allowed us to determine whether a given cortical neuron innervated only one structure or whether it sent axon collaterals to other subcortical areas. Twelve patterns of axonal branching were established: MD-VMT, MD-SN, MD-SC, VMT-SN, VMT-SC, VMT-CG, SN-SC, habenula-VMT, habenula-CG, MD-SN-SC, VMT-SN-SC and VMT-habenula-CG. Finally, it was estimated that a large proportion of the prefrontal cells which project to a given subcortical structure also innervate one or two other subcortical areas. Results are discussed in the light of anatomical data and their functional significance.

Animals↗
PubMed1982

Inhibitory nigral influence on cerebellar evoked responses in the rat ventromedial thalamic nucleus.

The ventral medial nucleus of the thalamus (VM) has been shown in rats and cats to constitute a common target for nigro- and cerebello-thalamic pathways. In the present study the responses of VM neurons to ipsilateral substantia nigra (SN) and contralateral cerebellar nuclei stimulation were analyzed in the rat. The typical response of VM neurons to SN stimulation consisted of a pure short-latency (1.1-3 ms), short-duration (7-17 ms) IPSP. Latencies of these responses were accorded well with the conduction velocity of the nigro-thalamic fibers as measured on the basis of antidromic activation of this pathway. A high percentage (58%) of the thalamic neurons receiving the inhibitory nigral effect were also affected by cerebellar stimulation. The cerebellar effect consisted of a short-latency depolarizing potential which could trigger an action potential. These responses were invariably blocked during the course of SN evoked inhibition. Such convergence was found with fastigial as well as interpositus/dentatus evoked responses. The demonstration of an interaction between the processing of SN and cerebellar output at thalamic level provides an important clue for the understanding of the neurophysiologic mechanisms by which SN acts on motor behavior.

Animals↗
PubMed1982

In vivo incorporation of 3H-choline in alveolar type-II pneumocytes in mice treated with butylated hydroxytoluene (BHT).

Butylated hydroxytoluene has been previously shown to damage alveolar type-I cells followed by proliferation of type-II pneumocytes which then redifferentiate into intermediate and newly formed type-I epithelial cells. In relation to this transformation process, in vivo incorporation of H3-choline, a precursor of the main component of lung surfactant, was studied in type-II cells of BHT-treated mice by electron microscopic radioautography. The labeling density was reduced in some type-II cells at 2, 3 and 5 days after a single injection of BHT. Cellular compartment analysis indicated that the transformation of type-II cells is accompanied by a notable loss of their lamellar body component as well as a decreased radioautographic labeling associated with this cell type, possible in relation with modified synthesis of phospholipid material of surfactant.

Animals↗
PubMed1982

Variations of glycogen level and alpha-glucosidase activity in human malignant epithelial cell lines in culture.

1. Acid lysosomal and neutral alpha-glucosidase activities are measured during the culture of five human malignant epithelial cell lines, as a function of the growth-related glycogen accumulation. 2. Neutral alpha-glucosidase is found to be active mainly during the exponential phase of cell culture, which could be related to an enhancement of glycosylated compound synthesis. 3. The latent activity of the acid lysosomal alpha-glucosidase increases during the course of cell culture and especially when glycogen accumulates, suggesting that this enzyme could be involved in the control of the polysaccharide storage within the cell.

Cell Division↗
PubMed1981

The nigro-tectal pathway. An electrophysiological reinvestigation in the rat.

Controversial data have been reported concerning the effect induced by stimulation of substantia nigra (SN) on the cells of the ipsilateral superior colliculus (SC) in the rat. Stimulation applied within SN activates not only the nigral neurons but also fibers passing through and in the vicinity of SN, especially those of cerebral peduncle (Ped) and optic tract (OT). The effect of SN stimulation has therefore been reinvestigated on two types of preparation: firstly in animals whose Ped--OT fibers were transected rostral to SN; and secondly in rats whose nigral cells destroyed by kainic acid injection. In normal animals, SN stimulation induced both inhibitory and excitatory responses in SC cells. After transection of Ped--OT fibers, SN stimulation no longer induced excitatory but only inhibitory effects. This observation clearly demonstrates that the nigro-tectal pathway is inhibitory. The excitatory responses observed in normal rats are related to activation of Ped--OT fibers at the level of SN. Indeed these excitations induced by SN stimulation still persist in kainic acid lesioned animals. Moreover, stimulation of Ped--OT fibers applied rostral to SN also produce these excitatory effects on SC cells. On the other hand, Ped--OT stimulation not only induces excitations but also inhibitory responses. These latter effects can still be evoked by SN stimulation after kainic acid induced loss of nigral cells. In conclusion the SC receives both excitatory and inhibitory input from Ped--OT fibers and only inhibitory input from nigral cells. This inhibitory nigral control is mainly exerted on cells of intermediate and deep collicular layers.

Animals↗
PubMed1981

Evidence for a GABAergic inhibitory nigrotectal pathway in the rat.

The aim of the present study was to test the GABAergic nature of the inhibitory projection from substantia nigra, pars reticulata (SNr) to superior colliculus (SC) in the rat, through the use of extracellular recordings and microiontophoresis. The effect of SN stimulation on the spontaneous or glutamate-evoked firing of SC units was analyzed. Among 28 SC cells inhibited by SNr stimulation, 27 decreased their firing rate following iontophoretic application of either GABA or glycine. The effect of the iontophoretic administration of bicuculline on SN4-evoked inhibition was studied on 14 of these GABA- and glycine-sensitive neurons. Bicuculline reversibly blocked nigral inhibition on 12 neurons, with iontophoretic current which did not affect glycine depression. These results are consistent with the hypothesis that GABA is the inhibitory transmitter of the nigrotectal projection.

Animals↗