Repeated withdrawal from ethanol spares contextual fear conditioning and spatial learning but impairs negative patterning and induces over-responding: evidence for effect on frontal cortical but not hippocampal function?

Abstract

Repeated exposure of rats to withdrawal from chronic ethanol reduces hippocampal long-term potentiation and gives rise to epileptiform-like activity in hippocampus. We investigated whether such withdrawal experience also affects learning in tasks thought to be sensitive to hippocampal damage. Rats fed an ethanol-containing diet for 24 days with two intermediate 3-day withdrawal episodes, resulting in intakes of 13-14 g/kg ethanol per day, showed impaired negative patterning discrimination compared with controls and animals that had continuous 24-day ethanol treatment, but did not differ from these animals in the degree of contextual freezing 24 h after training or in spatial learning in the Barnes maze. Repeatedly withdrawn animals also showed increased numbers of responses in the period immediately before reinforcement became available in an operant task employing a fixed-interval schedule although overall temporal organization of responding was unimpaired. Thus, in our model of repeated withdrawal from ethanol, previously observed changes in hippocampal function did not manifest at the behavioural level in the tests employed. The deficit seen after repeated withdrawal in the negative patterning discrimination and over-responding in the fixed-interval paradigm might be related to the changes in the functioning of the cortex after withdrawal