Jh. Williams et Ja. Kauer, PROPERTIES OF CARBACHOL-INDUCED OSCILLATORY ACTIVITY IN RAT HIPPOCAMPUS, Journal of neurophysiology, 78(5), 1997, pp. 2631-2640
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.