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The status of serotonin as a putative neurotransmitter involved in the control of the secretion of corticotrophin-releasing activity from the rat hypothalamus has been further investigated. The experimental model used for the investigation was the rat hypothalamus incubated in vitro. It was confirmed that serotonin causes a dose-related release of corticotrophin-releasing activity from the tissue and it was shown that this effect was mimicked by the addition to the tissue of chlorimipramine or d-fenfluramine, two drugs expected to cause an increase in the concentration of serotonin in the synaptic cleft. The effect of the latter drug was greatly reduced by the simultaneous addition of either methysergide or metergoline.

Destruction of serotonin-containing nerve terminals in the hypothalamus was caused by the intraventricular administration of the neurotoxic drug 5,7-dihydroxytryptamine. This treatment resulted in an 84% reduction of the serotonin concentration in the hypothalamus 12 days later. Hypothalami taken from animals 12 days after treatment with the drug secreted corticotrophin-releasing activity in basal amounts equal to those found in tissues taken from control rats, but showed supersensitivity in response to added serotonin. No such supersensitivity was seen in response to d-fenfluramine and a diminished response to chlorimipramine was noted. Despite its intraventricular route of administration, 5,7dihydroxytryptamine was found to increase the sensitivity of segments of anterior pituitary gland in vitro to low doses of preparations containing corticotrophin releasing factor.

These results are consistent with the view that endogenous serotonin can act as a stimulator of the secretion of corticotrophin-releasing activity from the rat hypothalamus. They also suggest that conclusions about the control of the release of this trophic material inferred from measurements of corticotrophin or corticosterone in the circulation must be viewed with caution when the drug 5,7-dihydroxytryptamine has been used, because of the development of supersensitivity both in the hypothalamus and in the anterior pituitary gland.

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				H. K. Manji, J. K. Hsiao, E. D. Risby, O. T. Osman, M. V. Rudorfer, and W. Z. Potter ECT treatment does not enhance neuroendocrine responses to serotonergic challenge J Psychopharmacol, January 1, 1992; 6(4): 501 - 508. [Abstract] [PDF]