Behavioural and adrenocortical responses to nicotine measured in rats with selective lesions of the 5-hydroxytryptaminergic fibres innervating the hippocampus.

The effects of acute and subchronic (7) injections of nicotine (0.4 mg kg-1, s.c.) and of selective lesions of the 5-hydroxytryptaminergic (5-HTergic) pathways innervating the hippocampus on the spontaneous behaviour of rats in an elevated X-maze composed of two open and two enclosed runways have been examined. Subchronic, but not acute, nicotine increased total spontaneous activity. Neither acute nor subchronic nicotine altered the ratio of open:closed runway entries. Destruction of the 5-HTergic pathways innervating the hippocampus with 5,7-dihydroxytryptamine caused a reduction in the ratio of open:enclosed runway entries. Acute, but not subchronic, nicotine caused a significant increase in plasma corticosterone. The lesion had no effects on the plasma levels of this hormone. No significant interactions between the lesion and the responses to nicotine were observed. The data failed to provide any evidence that hippocampal 5-HTergic systems may be implicated in the effects of nicotine on the spontaneous behaviour of the rat.