Studies on the possible role of brain 5-HT systems and adrenocortical activity in behavioural responses to nicotine and diazepam in an elevated X-maze

Abstract

Subchronic (6 days) but not acute injections of nicotine (0.4 mg/kg SC) increased spontaneous activity (P less than 0.01) in an elevated X-maze composed of two open and two enclosed runways. Neither acute nor subchronic nicotine altered significantly the ratio of open:enclosed runway entries (O/E ratio). Diazepam (5 mg/kg PO) had no significant effects on spontaneous activity but increased the O/E ratio (P less than 0.05). Acute nicotine increased (P less than 0.01) whereas subchronic nicotine caused a small decrease (P less than 0.05) in the plasma corticosterone concentration. Both acute and subchronic diazepam decreased the levels of the hormone (P less than 0.01 and P less than 0.05, respectively) although the reduction elicited by chronic diazepam was less than that caused by acute diazepam (P less than 0.05). In the experiments with diazepam the plasma corticosterone concentration correlated negatively with the O/E ratio (r = -0.58; P less than 0.05), whereas in the experiments with nicotine plasma corticosterone correlated negatively (r = -0.46; P less than 0.05) with enclosed runway entries. Nicotine injections were associated with a regionally-selective reduction in the 5-hydroxyindole acetic acid (5-HIAA) concentration in the hippocampus (P less than 0.05) and a reduction in hippocampal 5-hydroxytryptamine (5-HT) which approached statistical significance. Chronic, but not acute, diazepam increased (P less than 0.01) hypothalamic 5-HT. The changes in 5-HT and 5-HIAA did not appear to be directly related to the behavioural or adrenocortical responses to either of the drugs.

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

“…However, since consistent reductions in 5-HIAA were observed in both hypothalamus and cerebral cortex of lesioned rats, it is perhaps more likely that, in these rats at least, the loss of 5-HT secreting terminals in the hippocampus may have been associated with reduced 5-HT secretion in these other two brain regions. The data reported here for the effects of nicotine on the behaviour of the rats in the maze are in very good agreement with the results of previous studies with unoperated rats in this maze (Balfour et al, 1986). Specifically both this and the earlier study have shown the subchronic, but not acute, licotine causes a stimulation of spontaneous activity while having no effect on the O/E ratio.…”

“…Previous studies (Balfour et al, 1986) have shown that the increase in O/E ratio observed in rats given diazepam appears to be associated with a reduction in the plasma corticosterone concentration. These earlier experiments also showed that the increased plasma corticosterone levels observed in rats given acute nicotine were not associated with a decrease in the ratio.…”

Nicotinic systems and cognitive function

“…In addition, nicotine effects on serotonin and somatostatin innervation of the hippocampus have been documented (Balfour et al 1986;Barrios et al 1990). The behavioral significance of these interactions with nicotine effects on memory function is currently unclear.…”

Utility of an elevated plus-maze for the evaluation of memory in mice: effects of nootropics, scopolamine and electroconvulsive shock

“…The elevated plus-maze, consisting of two open and two enclosed arms, is based on the apparent natural aversion of rodents to open and high spaces, and is used for measurement of anxiety (Pellow et al 1985;Balfour et al 1986;Pellow and File 1986;Lister 1987). Animals spend more time in the enclosed arms than the open Offprint requests to."…”