THE EFFECT OF CARBACHOL ON HIPPOCAMPAL THETA IN CARBENOXOLONE PRETREATED RATS

Among the number of the mechanisms of signal transmission evolved in biological systems, a distinctive feature of gap-junction coupling is ability of direct high-speed information spreading over the space of coupled cells. It is performed on cytoplasmic tracks provided by the channel structure of gap junction assemblies (electrical synapses). In the nervous system this high-speed pathway is considered as a promoter of neuronal synchrony, and so - an underground for oscillatory events. On the other hand, it is well known that to produce oscillations, the brain tissue needs qualitatively and quantitatively balanced neurotransmitter input feeding the oscillation-generating networks. The question arise what is the real contribution of the two signalling systems: electrical and chemical to oscillatory activity. Hippocampal formation (HPC) theta rhythm is one of the best synchronized brain oscillations. Our earlier experiments demonstrted that the cessation of gap junction coupling had a spectacular effect on HPC spontaneous theta rhythm. HPC administrations of carbenoxolone (CBX), a gap junction blocker, produced progressive impairment of theta oscillations up to their abolition. In order to estimate if high-level enhancement of chemical transmission is capable of counteracting the gap junction blockage, in the present work car-bachol, a cholinergic agonist, was injected into CBX pretreated hippocampus. Under CBX-blockage no effect of carbachol was noticed.