Scopolamine impairs information processing in the hippocampus and performance of a learned eyeblink response in alert cats

The object of this work was to determine whether the changes in field activ ity and neuronal excitability recorded in the hippocampus during eyeblink c lassical conditioning are induced by the cholinergic input, and their relat ionships with the conditioned response performance. The pyramidal layer fie ld activity, its response to fornix stimulation and eyelid responses were r ecorded during paired tone-air puff presentations, under scopolamine (25, 5 0 and 100 mu g/kg) or saline administration, following well-established eye blink conditioning in a trace paradigm in cats. Scopolamine impaired behavi oral performance, and, in the hippocampus, disrupted conditioned stimulus-e voked field potential, high frequency shift in field activity, and paired p resentation-induced hyperexcitability. These findings indicate that the cho linergic input participates in hippocampal information processing in a way that allows precise conditioned response performance and memory trace forma tion. (C) 2000 Elsevier Science Ireland Ltd. AII rights reserved.