Loss of Rhythmically Bursting Neurons in Rat Medial Septum Following Selective Lesion of Septohippocampal Cholinergic System

Emmanuelle Apartis 1 , 2 , Frederique R. Poindessous-Jazat 1 , Yvon A. Lamour 1 , 2 , , and Marie H. Bassant 1 1  Unité de Recherches de Physiopharmacologie du Système Nerveux, Institut National de la Santé et de la Recherche Médicale U 161, 75014 Paris; and 2  Service d'Explorations Fonctionne...

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Published in:Journal of neurophysiology 1998-04, Vol.79 (4), p.1633-1642
Main Authors: Apartis, Emmanuelle, Poindessous-Jazat, Frederique R, Lamour, Yvon A, Bassant, Marie H
Format: Article
Language:English
Subjects:
Acetylcholine - physiology
Acetylcholinesterase - analysis
Anesthetics
Animals
Hippocampus - physiology
Histocytochemistry
Male
Neurons - physiology
Rats
Rats, Sprague-Dawley
Respiratory Burst - physiology
Septum Pellucidum - physiology
Theta Rhythm
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Summary:Emmanuelle Apartis 1 , 2 , Frederique R. Poindessous-Jazat 1 , Yvon A. Lamour 1 , 2 , , and Marie H. Bassant 1 1  Unité de Recherches de Physiopharmacologie du Système Nerveux, Institut National de la Santé et de la Recherche Médicale U 161, 75014 Paris; and 2  Service d'Explorations Fonctionnelles du Système Nerveux, Hopital Lariboisière, 75010 Paris, France Apartis, Emmanuelle, Frederique R. Poindessous-Jazat, Yvon A. Lamour, and Marie H. Bassant. Loss of rhythmically bursting neurons in rat medial septum following selective lesion of septohippocampal cholinergic system. J. Neurophysiol. 79: 1633-1642, 1998. The medial septum contains cholinergic and GABAergic neurons that project to the hippocampal formation. A significant proportion of the septohippocampal neurons (SHN) exhibit a rhythmically bursting (RB) activity that is involved in the generation of the hippocampal theta rhythm. The neurochemical nature of septal RB neurons is not firmly established. To address this question, the septal unit activity has been recorded in rats after selective destruction of the cholinergic septal neurons by the immunotoxin 192 IgG-saporin. Experiments have been performed in urethan-anesthetized and unanesthetized rats, 14-21 days after lesion. Acetylcholinesterase (AChE) histochemistry revealed a near-complete loss of cholinergic septal neurons and of cholinergic fibers in the hippocampus. The recorded neurons were located in the medial septum-diagonal band of Broca area. A number of these neurons were identified as projecting to the hippocampus (SHN) by their antidromic response to the electrical stimulation of the fimbria-fornix. In urethan-anesthetized lesioned rats, the percentage of RB neurons decreased significantly as compared with controls (17 vs. 41% for SHNs and 5 vs. 19% for unidentified septal neurons). The axonal conduction velocity and the burst frequency of the SHNs that retained a RB activity were higher in lesioned as compared with control rats. The number of spikes per burst was lower and the burst duration was shorter in lesioned rats as compared with controls. The urethan-resistant hippocampal theta was altered both in terms of frequency and amplitude. In unanesthetized lesioned rats, no RB septal neurons were found during arousal, as compared with 25% in controls. Their number was also markedly reduced during paradoxical sleep (9.7 vs. 38.5%). Histochemistry in 192 IgG-saporin-treated rats showed that RB neurons were found in areas devoid of AChE
ISSN:0022-3077
1522-1598
DOI:10.1152/jn.1998.79.4.1633