PROPERTIES OF CARBACHOL-INDUCED OSCILLATORY ACTIVITY IN RAT HIPPOCAMPUS

Citation
Jh. Williams et Ja. Kauer, PROPERTIES OF CARBACHOL-INDUCED OSCILLATORY ACTIVITY IN RAT HIPPOCAMPUS, Journal of neurophysiology, 78(5), 1997, pp. 2631-2640
Citations number
62
Categorie Soggetti
Neurosciences,Physiology
Journal title
ISSN journal
00223077
Volume
78
Issue
5
Year of publication
1997
Pages
2631 - 2640
Database
ISI
SICI code
0022-3077(1997)78:5<2631:POCOAI>2.0.ZU;2-Z
Abstract
The recent resurgence of interest in carbachol oscillations as an in v itro model of theta rhythm in the hippocampus prompted us to evaluate the circuit mechanisms involved. In extracellular recordings, a regula rly spaced bursting pattern of field potentials was observed in both C A3 and CAI subfields in the presence of carbachol. Removal of the CA3 region abolished oscillatory activity observed in CAI, suggesting that the oscillatory generator is located in CA3. An lpha-amino-3-hydroxy- 5-methyl-4-isoxazolepropionic acid (AMPA) receptor antagonist, 6, 7-di nitroquinoxaline-2, 3-dione (DNQX), blocked carbachol oscillations, in dicating that AMPA receptor-mediated synaptic currents are necessary f or the population oscillation. Moreover, the spread of oscillatory act ivity into CAI required intact N-methyl-D-aspartate receptors. These d ata are mole consistent with epileptiform bursting than with theta rhy thm described in vivo. In the presence of carbachol, individual CA3 py ramidal cells exhibited a slow, rhythmic intrinsic oscillation that wa s not blocked by DNQX and that was enhanced by membrane hyperpolarizat ion. We hypothesize that this slower oscillation is the fundamental os cillator that participates in triggering the population oscillation by exciting multiple synaptically connected CA3 neurons. gamma-aminobuty ric acid-A (GABA(A)) receptors are not necessary for carbachol to elic it synchronous CA3 field events but are essential to the bursting patt ern observed. Neither GABAB nor metabotropic glutamate receptors appea r to be necessary for carbachol oscillations. However, both nicotinic and M1 and M3 muscarinic cholinergic receptors contribute to the gener ation of this activity. These results establish the local circuit elem ents and neurotransmitter receptors that contribute to carbachol-induc ed oscillations and indicate that carbachol-induced oscillations are f undamentally distinct from theta rhythm in vivo.