Hippocampal electrical activity in relation to behavior following ethylcholine aziridinium ion (AF64A) treatment

The effects of intracerebroventricular (ICV) injections of ethylcholine aziridinium ion (AF64A; 3 nmol/3 microliters/side) on the pattern of hippocampal electrical activity were studied in freely moving and urethane anesthetized rats. AF64A treated rats showed a significantly smaller increase in 6-12 Hz hippocampal rhythmical slow activity (RSA) with struggling in the no drug condition in comparison to the vehicle injected rats. However, neither AF64A treatment nor a control injection abolished the presumed cholinergic form of RSA that is present during urethane anesthesia. Systemic injection of atropine in waking rats did not significantly alter RSA in either the AF64A or vehicle injected rats. Analysis of histological brain sections revealed extensive damage to the fimbria-fornix, CA3 of the hippocampus, corpus callosum, neocortex and striatum. Acetylcholinesterase staining of the remaining hippocampus appeared normal in the AF64a treated rats. The data indicate that the depletion of cholinergic markers in the hippocampus following ICV administration of AF64A is not sufficient to disrupt the cholinergic form of RSA. Further, the question is discussed as to whether AF64A produces its cholinoselective effects via a specific pharmacological action or through a nonspecific destruction of the fimbria-fornix.