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

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Abstract
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 vericosities of various hypothalamic nuclei, as well as within an ependymally associated network of fibers. Pharmacological administration of the serotoninprecursor, 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 regulation of hypothalamically mediated endocrine function due to their neuroanatomical placement in the medial basal hypothalamus.