Cholinergic and glutaminergic control of hippocampal RSA during behavior in rabbits

An experimental model, with novel environmental stimuli, has been used in order to study the effects of cholinergic and glutaminergic modulation on hippocampal electrical activity and behavior. The test consisted in the introduction of a rabbit in an experimental cage in the absence of external stimuli (neutral environment) followed by the introduction into the cage of a novel object containing odorous vegetable branches, a stuffed sparrow-hawk and a live cat. The effects of drug treatments on hippocampal rhythmic slow activity (RSA) parameters (total amount, episode durations and frequency) were studied. Physostigmine (0.1 mg/kg) increased RSA amount both during immobility and movements and was effective only on the frequency of the immobility related RSA. Scopolamine (0.4 mg/kg) reduced the percentage of RSA occurring during immobility and movements and the frequency of the movement related RSA. Glutamic acid diethyl ester (GDEE) (400 micrograms), injected into the dorsal hippocampus, had qualitative effects similar to those obtained with scopolamine, but, quantitatively, they were less pronounced. The combination between GDEE and scopolamine potentiated the effects of the two drugs. Results support the assumption that cholinergic septal input is responsible for hippocampal RSA and the glutaminergic entorhinal input to the hippocampus modulates RSA, probably under cholinergic control.