(1) The effect of corticosterone on the extinction of a one-way active avoidance task was correlated with hypothalamic and mesencephalic serotonin (5-HT) content. (2) Corticosterone treatment in a daily dose of 1·0 and 5·0 mg/kg i.p. facilitated the extinction of active avoidance behaviour while doses of 10·0 mg/kg corticosterone delayed it. (3) 1·0 and 2·0 mg/kg corticosterone increased the hypothalamic 5-HT content in normal and adrenalectomized animals, 5·0 mg/kg failed to influence it, and 10·0 mg/kg decreased it. (4) After 1·0, 5·0 and 10·0 mg/kg corticosterone treatment, changes in mesencephalic 5-HT followed a pattern similar to that observed in the hypothalamus. (5) Adrenocorticotrophic hormone (ACTH), in doses of 2·0 and 4·0 i.u./animal, resulted in an increased hypothalamic and mesencephalic 5-HT content in intact animals; however, there were no changes in cerebral 5-HT levels in adrenalectomized rats. (6) Decreased brain 5-HT content, brought about by parachlorophenylalanine (PCPA) (300 mg/kg), was able to prevent the behavioural effect of 1·0 and 5·0 mg/kg corticosterone. (7) PCPA treatment alone given every 72 hr caused a transitory delay in extinction 24 and 48 hr after administration; however, the tendency for extinction to occur did not change. (8) Decreased 5-HT content caused by mesencephalic raphé lesions delayed extinction. (9) Nialamide treatment (125 mg/kg), which increased brain 5-HT content, counteracted the effect of 10·0 mg/kg corticosterone on extinction. (10) These data suggest that the action of corticosterone on active avoidance behaviour is mediated, at least in part, via changed 5-HT metabolism in the brain.
- avoidance behaviour
ASJC Scopus subject areas
- Endocrinology, Diabetes and Metabolism
- Endocrine and Autonomic Systems
- Psychiatry and Mental health
- Biological Psychiatry