Histochemical, pharmacological and microspectrofluorometric analysis of new sites of serotonin localization in the rat hypothalamus.

Histopharmacological and microspectrofluorometric analysis was applied to the rat hypothalamus for the identification of serotonin. Neuronal perikarya, especially certain of those of the endocrinologically important arcuate nucleus, were seen to contain a yellow histofluorescence which possessed spectral characteristics consistent with the serotonin fluorophor. Serotonin was localized also within varicosities of various hypothalamic nuclei, as well as within an ependymally associated network of fibers. Pharmacological administration of the serotonin precursor, tryptophan, resulted in the identification of serotonin histofluorescence and spectra within hypothalamic neurons yielding evidence that these neurons possess the capacity to synthesize serotonin. These newly described cells may be of importance to the regulatin of hypothalamically mediated endocrine function due to their neuroanatomical placement in the medical basal hypothalamus.