The effect of some drugs on hippocampal arousal

Abstract

The electrical activity of the neocortex and ventral hippocampus has been described in the encéphale isolé preparation of the cat, during the behavioural states of wakefulness and sleep. It was observed that the desynchronisation of cortical activity in the state of wakefulness was accompanied by synchronised activity in the hippocampus and that behavioural and electrocortical arousal was not instantaneously accompanied by changes in hippocampal activity. The results of previous investigations have been confirmed but the significance of certain variations in the present and previous studies has been discussed. The changes induced in the electrical activity of the hippocampus by some drugs have been studied and it was observed that amphetamine and pentobarbitone induced changes in the hippocampal activity which were correlated with the states of wakefulness and sleep, whereas atropine and physostigmine induced changes which were not correlated with the behaviour of the animal. It is suggested that the inverse relationship between the electrical activity of the hippocampus and neocortex may be due to an inhibitory control of hippocampal neurones by the midbrain limbic area. The synchronous activity observed in the state of wakefulness and following the administration of amphetamine may be due to the activation of an inhibitory reticular control exerted by the mid-brain limbic area. In a similar manner the changes in the electrical activity of the hippocampus following the administration of pentobarbitone may be due to the depressant action of this drug on the mid-brain limbic area, although with this drug a direct effect on the hippocampal neurones or an effect mediated by a forebrain neural system may also be involved. It is also considered unlikely that changes in hippocampal activity associated with arousal are mediated by a predominantly cholinergic system.