Biomedical subjects

A Jobert

Publications and source records attributed to A Jobert.

At least 55 records · Page 3Linked to original sources

PubMed1985

[Properties of thalamocortical cells identified by antidromic stimulation in the ventrolateral and ventrobasal thalamic nuclei in rats].

The physiological and pharmacological properties of thalamocortical neurons, identified by electrical antidromic stimulation of the frontoparietal cortex, were studied in the ventrobasal and ventrolateral thalamic nuclei in urethane anaesthetized rats. The spontaneous activity and conduction velocity of these neurons were similar in both nuclei. At both sites, thalamocortical neurons could be excited through iontophoretic application of acetylcholine and muscarinic or nicotinic agonists. Despite the known differences in thalamic organization of the two species, these properties are quite similar to those described in cat by other authors.

Acetylcholine↗

PubMed1984

Septo-hippocampal and other medial septum-diagonal band neurons: electrophysiological and pharmacological properties.

Neurons located in the medial septum-nucleus of the diagonal band (vertical limb) area and antidromically activated by electrical stimulation of the fimbria were recorded in urethane anesthetized rats. Forty-five percent of these septo-hippocampal neurons (SHNs) discharged rhythmically in short bursts (mean burst frequency, 4 Hz). They were antidromically driven at short latencies from the fimbria. SHNs driven at long latencies (above 5 ms) were never bursting neurons. Fimbria stimulation also had a powerful inhibitory effect on the spontaneous activity of SHNs. The vast majority of the septo-hippocampal neurons were excited by the iontophoretic application of acetylcholine or cholinergic agonists, carbachol being the most effective. The acetylcholine-induced excitations were readily abolished by atropine. In contrast hexamethonium and mecamylamine were less effective. The rhythmic bursting activity could not be consistently altered by the iontophoretic application of cholinergic agonists or antagonists or of divalent cations. SHNs were also sensitive to various other putative neurotransmitters (substance P, GABA) known to play a role in the medial septal area. Bursting neurons and ACh-sensitive neurons were less frequent among unidentified medial septal neurons. The regulation of the septo-hippocampal cholinergic pathway is therefore not likely to be due to a direct feedback inhibition by locally released acetylcholine. However a strong inhibitory feedback could be exerted by the hippocampo-septal pathway impinging directly or indirectly on septo-hippocampal neurons.

Animals↗

PubMed1984

Cortical projections of the nucleus of the diagonal band of Broca and of the substantia innominata in the rat: an anatomical study using the anterograde transport of a conjugate of wheat germ agglutinin and horseradish peroxidase.

The projections of the nucleus of the diagonal band of Broca and of the substantia innominata to the cerebral cortex were studied in the rat, using the anterograde transport of wheat germ agglutinin conjugated with horseradish peroxidase. Following diagonal band injections, fibers were observed ascending in the septum and reaching the cingulate cortex. They had a rostrocaudal, horizontal direction, mostly in layer VI and could be followed over long distances on sagittal sections. The fibers gave off collaterals which were seen ascending in the cerebral cortex and reaching more superficial layers. Following substantia innominata injections, fibers were observed to take two routes: the first one identical to the one described above and a second through the caudate-putamen reaching the temporo-insular cortex. Terminal fields had a more diffuse distribution following substantia innominata than following diagonal band injections. No clear laminar pattern of termination was observed. However the density of terminals was higher in layers IV, V and VI than in layers I, II and III. Since the conjugate used is not taken up by fibers of passage, this pattern of connection is believed to reflect the organization of the projection of the nucleus of the diagonal band and of the substantia innominata to the cerebral cortex.

Animals↗

PubMed1983

Acetylcholine excites identified septo-hippocampal neurons in the rat.

Neurons of the medial septum-nucleus of the diagonal band of Broca (vertical limb) area were identified as septo-hippocampal neurons by antidromic electrical activation in anesthetized rats. A large majority of these presumably cholinergic neurons could be excited by the iontophoretic application of acetylcholine or cholinergic agonists such as carbachol. The acetylcholine-induced excitations were readily antagonized by atropine. These results suggest that cholinergic neurons can be excited by their own transmitter, i.e. acetylcholine.

Acetylcholine↗

PubMed1983

A comparative study of two populations of acetylcholine-sensitive neurons in rat somatosensory cortex.

The properties of two populations of acetylcholine-sensitive neurons, defined by their different laminar distribution (group A, layers V and upper VIa; group B, layer VIb and underlying white matter) were studied in the SmI cortex of urethane-anesthetized rats. The spontaneous activity of group B neurons was significantly lower than in group A. The proportion of neurons excited by iontophoretic acetylcholine, the duration and the pharmacological properties of the excitations were the same in both groups. The dose-response curves obtained for sets of neurons of both groups, recorded with the same electrode, had comparable slopes. Carbachol had a greater potency than acetylcholine in both groups. In contrast, the latency of the response to acetylcholine was significantly shorter in group B. The amount of current required to increase the spontaneous discharge rate of a given neuron by 200% was lower in group B than in group A. These data suggest that the relative change in firing frequency induced by a given cholinergic input is likely to be larger in group B than in group A. Finally, neuronal excitations could still be obtained in both groups when acetylcholine was applied 300 micron, but not 600 micron, from the cell body, suggesting that the spatial distribution of acetylcholine receptors is similar in groups A and B.

Acetylcholine↗

PubMed1983

Effects of neuropeptides on rat cortical neurons: laminar distribution and interaction with the effect of acetylcholine.

The effects of the microiontophoretic application of five different peptides (cholecystokinin octapeptide sulfated form, cholecystokinin octapeptide non-sulfated form, vasoactive intestinal polypeptide, angiotensin-II and substance P) on cortical neurons were studied in rats anaesthetized with urethane. Vertical electrode penetrations were made in the first somatic sensory cortex and the laminar position of the neurons determined by the reconstruction of the tracks based on extracellular dye deposits. The first type of effect observed was an excitation of some cortical neurons. These neurons were mostly found in infragranular layers, specially in layer Vb. Pyramidal tract neurons were more often excited by peptides than the cortical population taken as a whole. Substance P excited the largest percentage of neurons, followed by vasoactive intestinal polypeptide and cholecystokinin octapeptide sulfated form, whereas angiotensin II and cholecystokinin octapeptide non-sulfated form were the least potent in terms of frequency of neurons excited as well as of amplitude of the responses. The vast majority of the neurons excited by a peptide could also be excited by acetylcholine. A second and independent effect of peptides was observed: the neuronal excitation induced by acetylcholine could be depressed by the simultaneous application of peptide. This depressing effect was also the most frequently observed with substance P, followed by cholecystokinin and vasoactive intestinal polypeptide.

Acetylcholine↗

PubMed1983

[Comparison of 2 groups of neurons sensitive to the excitatory effect of acetylcholine in the cerebral cortex of the rat].

Two groups of neurons which are excited by the iontophoretic application of acetylcholine were described in the primary somatosensory cortex of the Rat. The first one is located in the middle part (group A) and the second one in the deepest part of the cortex (group B). Group A neurons had a higher average spontaneous activity than group B neurons. The latency of group A neurons responses to the iontophoretic application of acetylcholine was longer. The amount of iontophoretic current required to increase the discharge rate of the neuron by 200% was higher in group A than in group B. In contrast the average slope of the regression lines calculated from dose-response curves was not different between the two groups.

Acetylcholine↗

PubMed1983

[Physiological and pharmacological properties of septohippocampal neurons identified by antidromic simulation in rats].

The physiological and pharmacological properties of septo-hippocampal neurons (identified through antidromic stimulation of the fimbria) were studied in the Rat under urethane anaesthesia. Half of these neurons (located in the medial septum and the nucleus of the diagonal band of Broca) displayed a rhythmic, bursting activity at about 4/s. A large majority of these neurons (bursting as well as non-bursting) could be excited through iontophoretic application of acetylcholine or carbachol.

Acetylcholine↗

PubMed1982

Topographic organization of basal forebrain neurons projecting to the rat cerebral cortex.

The topographic organization of basal forebrain neurons projecting to the rat cerebral cortex was investigated using the retrograde transport of horseradish peroxidase (HRP). HRP injections in cingulate and occipital cortices labeled neurons in the nucleus of the diagonal band of Broca. In contrast, injections in the frontal cortex labeled mostly neurons in the substantia innominata, and injections in the temporal and parietal cortices labeled neurons in the medial and ventral boundaries of the globus pallidus. These results suggest that the basal forebrain projection to the cerebral cortex is topographically organized.

Animals↗

PubMed1982

Spread of acetylcholine sensitivity in the neocortex following lesion of the nucleus basalis.

Neuronal responses to the iontophoretic application of acetylcholine, carbachol and nicotine were studied in rats, 2 or 3 weeks following bilateral lesions of the nucleus basalis region, and compared to those obtained in normal animals. The percentage of cortical neurons excited by acetylcholine and their individual sensitivity were higher in lesioned animals. Furthermore, the laminar distribution of the responses to acetylcholine and the proportion of responses to carbachol and nicotine were also modified.

Acetylcholine↗

PubMed1982

[Excitatory effects of 2 peptides on rat cortical neurons: laminar distribution and correlation with the effect of acetylcholine].

The most frequent effect observed following iontophoretic application of cholecystokinin or vasoactive intestinal polypeptide on Rat SI cortical neurons was an excitation. Most of the peptide-sensitive neurons were located in infragranular layers of the cortex. In most instances these neurons could also be excited by acetylcholine. These results suggest that some neuropeptides and acetylcholine might share common mechanisms of action on cortical neurons.

Acetylcholine↗

PubMed1982

[Physiologic and pharmacologic differences in 3 types of pyramidal cells identified by antidromic stimulation in the primary somatosensory cortex of the rat].

The physiological and pharmacological properties of three types of pyramidal neurons (pyramidal tract neurons, cortico-thalamic neurons and commissural neurons) identified by electrical antidromic stimulation were studied in the first somatic sensory cortex of the Rat. The laminar distribution of these neurons (as determined through histological reconstruction of the electrode tracks), their axonal conduction velocity, their sensitivity to iontophoretically applied acetylcholine and their ability to be driven by the stimulation of a peripheral somatic receptive field were shown to be different in the three groups. Some hypotheses are discussed, which could explain such differences.

Acetylcholine↗

PubMed1982

Excitatory effect of acetylcholine on different types of neurons in the first somatosensory neocortex of the rat: laminar distribution and pharmacological characteristics.

In rats anaesthetized with either urethane, pentobarbital or fluothane the effects of acetylcholine, cholinergic agonists and antagonists (applied by iontophoresis) were studied on single cortical neurons of first somatosensory region. The laminar distribution of the neurons excited by acetylcholine was determined by the reconstruction of each electrode track based on a dye-deposit made at the last recording site. Neurons were identified using antidromic stimulation of the pyramidal tract, the ventrobasal thalamus and the corpus callosum. Neurons excited by acetylcholine could be segregated into two groups: one encompassing layer Vb and the upper part of layer VI, the other more deeply located at the limit between the cerebral cortex and the subjacent white matter. Neuronal responses to glutamate and nicotine, unlike those to actylcholine were evenly distributed in the cortex. Pyramidal tract neurons had corticothalamic neurons were frequently excited by acetylcholine and were shown to be located with the first group of acetylcholine sensitive neurons. Commissural neurons were rarely excited by acetylcholine and were not restricted to either group. The analysis of neuronal responses to acetylcholine and various agonists (carbachol, nicotine, acetyl-beta-methylcholine, carbamyl-beta-methylcholine, butyrylcholine) and antagonists (atropine, mecamylamine) revealed a prominent but not exclusive muscarine character. It is included (i) that cortical neurons of first somatosensory cortex which are excited by acetylcholine belong to two populations, one consisting, at least in part, of projection neurons (upper group) and the other of interneurons (lower group); (ii) that cortical acetylcholine receptors are of a 'mixed' type strongly weighted toward the muscarinic side.

Acetylcholine↗

PubMed1982

Laminar distribution and convergence of deep and superficial peripheral inputs in the forelimb representation of rat SI somatosensory cortex.

The laminar distribution of single unit responses to stimulation of peripheral nerves (deep and superficial radial nerves) or to stimulation of peripheral receptive fields has been studied in the forelimb representation of the first somatic sensory cortex (SI) of the rat. 1. Under both conditions the majority of the responding units was located in layers IV, V and VI of the cortical area containing dense neuronal aggregates in layer IV. 2. Following electrical stimulation of the deep radial nerve (DRN) and of the superficial radial nerve (SRN), 18.9% of the neurons were observed to receive convergent inputs from both nerves. 3. Following natural stimulation of the forelimb, no evidence of convergent inputs on single neurons was obtained. 4. There was no clear submodality segregation in the receptive fields observed during vertical penetration.

Animals↗

PubMed1981

[Laminar distribution of excitatory responses to acetylcholine in rat somatic sensory cortex: a microionophoretic study].

The laminar distribution of excitatory responses to iontophoretically applied acetylcholine (ACh) was studied in the first somatic sensory cortex (SI) of the Rat, using extracellular dye deposits for reconstruction of the electrode tracks. Most of the responses were recorded from neurons located in the lower half of the cortex, namely in layers V and VI. ACh sensitive neurons were found in two locations: one encompassing layer V and upper part of VI and the other at the border between cortex and white matter. The functional significance of this distribution is discussed.

Acetylcholine↗

PubMed1981

Serotoninergic control of punished behavior: effects of intra-raphe microinjections of chlordiazepoxide, GABA and 5-HT on behavioral suppression in rats.

The effects of intra dorsalis raphe microinjections of chlordiazepoxide, GABA and 5-HT were studied on a model of behavioral suppression in rats. The suppression of responding for food was elicited by a 10 min presentation of a signal previously associated with the delivery of electric foot shocks. Microinjections of chlordiazepoxide, GABA and 5-HT (0.2 microliters) performed in awake hand-held rats reduced the behavioral suppression. Chlordiazepoxide and 5-HT acted in a synergistic way, while such a synergy could not be obtained when chlordiazepoxide and GABA were coadministered. Moreover, the effects of intra-raphe chloridazepoxide no longer appeared in rats given intra dorsalis raphe 5-7 dihydroxytryptamine (3 micrograms in 0.4 microliters) 3 weeks before testing. All these results further support the hypothesis of the involvement of 5-HT neurons both in punishment-induced inhibition and in the antipunishment activity of benzodiazepines. No evidence was obtained suggesting a GABAergic mediation for the functional interaction of chlordiazepoxide with 5-HT neurons in this experimental model. Since high 3H-flunitrazepam binding was found at the raphe dorsalis level, and since a 30% decrease in the number of intra-raphe 3H-flunitrazepam binding sites was detected after intra-raphe 5-7 dihydroxytryptamine, it is possible that intra-raphe chlordiazepoxide controls 5-HT neurons partly through some benzodiazepine binding sites located on 5-HT cells.

5,7-Dihydroxytryptamine↗

PubMed1980

Decreased convulsant potency of picrotoxin and pentetrazol and enhanced [3H]flunitrazepam cortical binding following stressful manipulations in rats.

Various stressful manipulations in rats (cold-water swim, electric foot-shock administration, imparied access to food reward) were found to reduce the convulsant potency of drugs which interfere with GABA or benzodiazepine central processes. The convulsant threshold dosages of picrotoxin (0.4 mg/ml) or pentetrazol (10 mg/ml) administered after the stress by infusion (0.2 ml/min) via a vein of the tail were enhanced. The onset of generalized seizures induced by isoniazid (800 mg/kg) or by thiosemicarbazide (64 mg/kg) i.p. was delayed after cold-water swim. However, convulsant threshold dosages of bemegride or strychnine perfused at 2 and 0.2 mg/ml respectively were not changed by stress. Cold-water swim increased the number of cortical (but not cerebellar) [3H]flunitrazepam binding sites (+ 24%) but failed to alter cortical [3H]muscimol binding. This post-stress enhancement of binding sties, although suppressed by bicuculline (10(-4) M) seems not to be dependent on GABAergic mechanisms. Indeed cold-water stress did not reduce the ability of muscimol (10(-6) and 10(-5) M) and GABA (5 x 10(-6) and 5 x 10(-5) M) to increase flunitrazepam binding. Finally, this post-stress enhancement of benzodiazepine binding was not found to be paralleled by changes in the protective effects of diazepam against picrotoxin- or pentetrazol-induced seizures.

Animals↗

PubMed1980

Differential effects on naloxone against the diazepam-induced release of behavior in rats in three aversive situations.

The effects of naloxone on diazepam-induced release of behavior in aversive situations were investigated in rats. Naloxone (0.5 and 1 mg/kg-1) suppressed diazepam-induced eating in an unfamiliar situation and reduced (1 mg/kg-1) spontaneous food intake. Naloxone (1 mg/kg-1) canceled the increased lever pressing produced by diazepam in a conflict procedure in which one electric shock was delivered at each seventh press. Naloxone (1 mg/kg-1) failed to reverse the enhanced responding for food induced by diazepam in the presence of a signal previously paired with electric foot shocks. In this situation, naloxone alone reinforced the behavioral suppression. These results suggest that transmission mediated by opiate peptides may be involved in only some 'disinhibitory' effects of benzodiazepines. In addition, such a peptidergic transmission may play a role in the control of stress-induced behavioral suppression.

Animals↗