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P Monmaur

Publications and source records attributed to P Monmaur.

At least 19 recordsLinked to original sources
PubMed1992

Changes in hippocampal acetylcholine and glutamate extracellular levels during soman-induced seizures: influence of septal cholinoceptive cells.

The changes in extracellular acetylcholine and glutamate levels were determined, during the course of seizures induced by soman, an irreversible inhibitor of acetylcholinesterase, in the CA1 hippocampal area of rats previously injected with atropine or normal saline into septum. The marked increases observed in soman-treated animals were abolished in rats receiving atropine. These data strongly suggest that, during soman intoxication, septal cholinoceptive cells play a key role in controlling the release of acetylcholine and glutamate in hippocampus. The mechanisms underlying this phenomenon are discussed.

Acetylcholine↗
PubMed1991

Elicitation of hippocampal theta by intraseptal carbachol injection in freely moving rats.

Following infusion into the septum of carbachol, a powerful muscarinic agonist, a theta (theta) rhythm was emitted during complete relaxed immobility as well as during automatic movements. This was not seen following administration of the drug within the caudate/putamen, which is rich in muscarinic receptors but which is not believed to be involved in hippocampal theta generation. Local administration of atropine abolished carbachol-induced theta but did not suppress the theta which normally occurs during voluntary movements. These findings clearly demonstrate that at least a component of the hippocampal theta may be manipulated by intraseptal administration of muscarinic agents, thus supporting our previous assumption that, in theta generation, the septum may be a sensitive site of action for exogenously administered cholinomimetic drugs. They also raise the possibility that the activity of the well identified septohippocampal system involved in the presumed cholinergic hippocampal theta generation is regulated trans-synaptically by acetylcholine at the septal level. Finally, our micropharmacological approach, by suggesting the carbachol-responding septohippocampal cells pacing theta rhythm which is correlated to important functional states, such as attentive waking and active sleep, provides a potential powerful tool for clarifying the neurobiological function of the septohippocampal pathway.

Analysis of Variance↗
PubMed1990

Effects of transient cerebral ischemia on the hippocampal dentate theta (theta) profile in the acute rat: a study 4-5 months following recirculation.

This study mainly describes the long-term effects of 20 min of cerebral ischemia on the profile of the presumed cholinergic theta rhythm in the rat dorsal hippocampal formation during ether anesthesia and injection of the muscarinic agonist agent arecoline. The experimental data were collected 4-5 months after ischemia. They show that ischemia results in a statistically significant reduction in both superficial and deep theta recorded from the CA1 area of the hippocampus and the dentate gyrus, respectively. Amplitude reduction is similar for both rhythms and co-varies positively with the extent of CA1 stratum pyramidale damage which, from light microscope observation, appeared to be the major neuroanatomical consequence of ischemic insult in the dorsal hippocampal formation. The medial septal nucleus-diagonal band of Broca complex involved in theta generation did not suffer visible anatomical damage. Moreover, no significant alteration in the spatial distribution and the density of hippocampal dentate acetylcholinesterase reaction product was seen in ischemic animals. These histological data were statistically confirmed by computerized image analysis. Finally, this is the first investigation to show that transient interruption of cerebral blood flow results in a long-lasting alteration of theta rhythm which is probably the major aspect of the basic activity of the hippocampal formation. Thus, the present findings obtained in the acute rat at 4-5 months postischemia confirm and extend, in most respects, our previous results collected in the chronic animal 2-29 days following 4-vessel occlusion. Possible significance of these findings for the hypothesis of the dependent generation sites of superficial and deep thetas in the hippocampus assumed to be crucial in learning and memory, is discussed.

Acetylcholinesterase↗
PubMed1988

Effects of unilateral cerebral ischemia on the hippocampal theta depth profile in the ether-anesthetized Mongolian gerbil.

In gerbils (Meriones unguiculatus) unilateral cerebral ischemia of 5 to 15 min resulted in selective destruction of the ipsilateral hippocampal CA1 stratum pyramidale. It also produced an obvious amplitude reduction in both superficial and deep theta rhythms recorded from damaged hippocampal formation. The presence of normal theta in the left normoxic hemisphere showed that the septohippocampal projections, integrity of which is essential for theta appearance, were spared by ischemia. These data have implications in relation to the two generators hypothesis of theta.

Anesthesia↗
PubMed1987

Effects of selective lesions of fimbria-fornix on learning set in the rat.

The effects of selective partial lesions of the Fimbria-Fornix (FiFx) on reversal and place learning sets were investigated in rats by using a T-maze and a semi-circular multiple discrimination apparatus. Lesions restricted to the Fimbria (Fi) produced a significant deficit in reversal and place learning set, whereas lesions to the Fornix (Fx) only disturbed the learning set based on a reversal procedure. Combined Fi + Fx lesions resulted in impairment in the retention of spatial discrimination tested in the two mazes. Ventral Hippocampal Commissure (vhc) had no significant effect on reversal learning set. These results confirm previous data that the hippocampal formation is involved in learning transfer, and suggest that the Fi and the Fx may play a role in learning set. Our data also confirm previous demonstrations of the ability of rats to rapidly acquire place learning set.

Animals↗
PubMed1986

Temporal changes in hippocampal theta activity following twenty minutes of forebrain ischemia in the chronic rat.

The present study was designed to examine the temporal changes in the theta (theta) rhythm recorded from the dorsal hippocampal formation of the chronic rat following 20 min of cerebral ischemia. Recordings were made during both wakefulness and paradoxical sleep. The experimental results show that ischemia resulted in a drastic amplitude reduction in both superficial and deep theta. Amplitude reduction occurred between days 1 and 4 postischemia and was maintained across the subsequent survival period. This EEG alteration was associated with an excessive loss of pyramidal cells in the hippocampal CA1 area, as observed by light microscopy. The above data strongly support our previous conclusions that neural components of the CA1 area may be of fundamental importance for the appearance and the maintenance of not only superficial theta but also deep theta. Moreover, they suggest that the preparation used in the present study may be a useful model for investigations on the neuroanatomophysiological effects of transient cerebral ischemia.

Animals↗
PubMed1986

Spatial distribution of hippocampal-dentate theta rhythm following colchicine injection into the hippocampal formation of the rat.

This investigation confronts the basic question of dentate granule cell participation in the generation of superficial and/or deep theta recorded from the dorsal hippocampal formation in the ether-anesthetized rat. Granular cells were destroyed unilaterally by local injection of 2 micrograms of colchicine (COL) dissolved in 0.2 microliter of distilled water. Hippocampal EEG was recorded 8 days after the neurotoxin injection. The COL injection which destroyed most dentate granular cells but left nearby pyramidal cells of the hippocampal CA1 area virtually unaffected, failed to disrupt significantly either superficial or deep theta. In contrast, the COL injection which destroyed most dentate granular cells and, also, caused some damage to the nearby pyramidal cells of the CA1 area, resulted in a sharp alteration of both theta. These data strongly suggest that granular cells of the dentate gyrus may not be critically involved in theta production, at least in the ether-anesthetized rat. They also confirm a previous conclusion that the neuroanatomical integrity of the CA1 area of the dorsal hippocampus is necessary for the normal appearance and maintenance of both superficial and deep theta. These data are discussed in the context of the generally accepted notion that superficial and deep theta are produced by the rhythmic activity of CA1 pyramidal cells and dentate granular neurons respectively.

Animals↗
PubMed1985

Hippocampal-dentate theta disturbance after selective CA1 pyramidal cell damage in the rat.

The contribution of the CA1 area of the dorsal hippocampus to both superficial and deep theta recorded from the dorsal hippocampal formation was assessed in rats anesthetized with ether. CA1 area cells were destroyed unilaterally by local injection of 2 micrograms of ibotenic acid dissolved in 0.1 microliters of phosphate buffer. Limited destruction of CA1 resulted in partial suppression of both superficial and deep theta, whereas extensive destruction resulted in almost total suppression of both theta's. A good correlation was found between the extent of the lesion and the theta disruption. Control preparations involving destructions by means of this neurotoxin of the hippocampal CA3 area or lower blade of the dentate gyrus failed to alter either superficial or deep theta. These data suggest that neuroanatomical integrity of the CA1 area of the dorsal hippocampus is a necessary condition for the normal appearance and maintenance of both superficial and deep theta as recorded from the dorsal hippocampal formation of the ether-anesthetized rat.

Animals↗
PubMed1985

Selective lesions of the fimbria and the fornix in the rat: differential effects on CA1 and dentate theta.

The effects of electrolytic lesions of the dorsal fornix and the dorsomedial fimbria on the CA1 and the dentate theta rhythms (theta s) recorded from the dorsal hippocampal formation were investigated in the ether-anesthetized rat. The results showed that (i) fornix lesions mainly affected CA1 theta, (ii) fimbrial lesions mainly affected dentate theta, and (iii) combined fornix-fimbria lesions suppressed both CA1 and dentate theta s. When considered in connection with other observations, these data suggest that the septal projections pacing the CA1 theta may course essentially within the dorsomedial fornix whereas those pacing the dentate theta may pass essentially within the dorsomedial fimbria. Moreover, our data provide new support for the hypothesis that at least two septohippocampal neural systems are anatomically and functionally independent and capable of controlling the theta activity of the dorsal hippocampal formation of the anesthetized rat.

Animals↗
PubMed1985

Influence of female odors on lateral hypothalamus in the male rat. Semiquantitative deoxyglucose analysis.

The uptake of 14C deoxyglucose (2DG) has been studied in various hypothalamic and limbic structures of male rats exposed to female odors. Uptake differences were visualized by image processing and quantified by measurement of optical density ratios. With respect to the control group, an increase in uptake was observed in the lateral hypothalamic area (LHA), not only in the olfactory bundle, but also, and more obviously, in the parafornical part. This 2DG response is not a result of an odor-induced general motor activation, although it seems to depend on the behavioral reaction of the animal towards the odor. A similar correspondence was not observed for the 2DG response to odor in the ventromedial hypothalamus. Observations in the medial preoptic area, in the corticomedial amygdala, in the lateral septum, or in the dorsomedial hypothalamus did not reveal any significant change in 2DG uptake.

Animals↗
PubMed1984

Decrease in both choline acetyltransferase activity and EEG patterns in the hippocampal formation of the rat following septal macroelectrode implantation.

A decrease in both choline acetyltransferase (CAT) activity and theta (theta) rhythm were observed in the hippocampal formation of rats implanted with a macroelectrode in the dorsomedial part of the septum. The decrease in CAT activity and in theta occurred simultaneously and in parallel, and there was no instance where the two parameters were uncoupled. These observations suggest that a common neurophysiological mechanism is involved in both CAT activity control and theta rhythm production in the hippocampal formation. From a methodological point of view, these observations should be borne in mind in septohippocampal investigations using septal electrode implantation procedures.

Animals↗
PubMed1983

Topographic organization of septal cells innervating the dorsal hippocampal formation of the rat: special reference to both the CA1 and dentate theta generators.

We determined the topographic organization of septal cells innervating monosynaptically the two generators of theta rhythm of the rostral hippocampal formation of the rat. Under ether anesthesia, horseradish peroxidase (HRP) was injected into the dorsal CA 1 region close to the corpus callosum, the ventral part of CA 1 region close to the hippocampal fissure, and the dentate hilus. The HRP micropipet tip was positioned in these hippocampal-dentate sites by recording the hippocampal EEG through the micropipet itself before HRP injection. The major findings were: (i) Injection of HRP in the superficial part of the dorsal CA 1 region (i.e., the septal pole) resulted in labeling of neurons situated mainly in the diagonal band of Broca, ipsilateral to the injection site. (ii) Injection of HRP in the deep part of the dorsal CA 1 region resulted in the labeling of a few cells scattered in the septal region ipsilateral to the injection site. (iii) After injection of HRP in the dentate hilus, labeled cells were selectively detected in the rostral half of the medial septal nucleus mainly ipsilateral to the injection site. A high degree of organization was revealed in the connections between the septal region and the rostral hippocampal formation of the rat, two cerebral regions critically involved in theta production. The results are relevant to the two-generator hypothesis of theta.

Animals↗
PubMed1982

Radioautographic analysis of [14C]2-deoxyglucose uptake in hippocampal formation of the rat during enforced locomotor activity-induced theta.

The [14C]2-deoxyglucose ( [14C]2-DG) uptake in the hippocampal formation of the rat was studied following enforced locomotor activity-induced theta (M theta). M theta was found to be essentially associated with an increase in 2-DG uptake in the stratum oriens of the hippocampal CA1-CA2 areas. These data contrast with our previous findings that physostigmine-induced theta (I theta) is specifically associated with a decrease in 2-DG uptake in the stratum lacunosum moleculare of hippocampal CA1-CA2 areas. When both of our sets of radioautographic data are considered together, M theta and I theta appear to have a distinct neurophysiological basis.

Animals↗
PubMed1982

The neocortex of rats behaving in a driven rotating wheel shows a band characterized by preferential uptake of deoxyglucose.

In comparison with control rats placed in a glass chamber, the neocortex of experimental rats performing in a motor-driven activity wheel shows a limited region of high metabolic activity, as revealed by the deoxyglucose radioautographic method. This region consists of a bilateral band located in the somesthetic area SI. An overlap of this labeling with the sensory and/or motor cortical representation of the head, and especially a correlation with head posture and movements, is discussed.

Animals↗
PubMed1982

Hippocampal theta rhythms from CA1 and dentate generators during paradoxical sleep of the rat: differential alterations after septal lesion.

Hippocampal theta (theta) rhythm was recorded from CA1 and dentate generators respectively, before and after septal lesion in the freely moving rat. It was observed that theta recorded from CA1 generator and theta recorded from dentate generator can be differentially affected by the lesion. In agreement with our previous data, these findings strongly support the hypothesis that CA1 and dentate generators producing the hippocampal theta are functionally independent. The existence of two independent septo-hippocampal neural systems which might mediate theta CA1 and theta dentate separately is discussed.

Animals↗
PubMed1981

Phasic hippocampal activity during paradoxical sleep in the rat: selective suppression after diazepam administration.

The effects of diazepam on tonic (T theta) and phasic (P theta) components of the paradoxical-sleep hippocampal theta rhythm were studied in the rat. Results show that diazepam, a benzodiazepine analogue known to interfere with the putative neurotransmitter gamma-aminobutyric acid (GABA) in the mammalian central nervous system, selectively abolishes P theta. They confirm previous data according to which sedative/anaesthetic drugs cause an apparent dissociation of T theta and P theta of the paradoxical-sleep hippocampal theta rhythm. Moreover, they suggest a possible involvement of GABA in the neurochemical mechanisms underlying P theta in the rat.

Animals↗