Infrequent cellular coexistence of NADPH-diaphorase and calretinin in the neurosecretory nuclei and adjacent areas of the rat hypothalamus.

Colocalization of the calcium-binding protein calretinin and NADPH-diaphorase activity at the cellular level was studied in the magnocellular secretory nuclei of the rat hypothalamus using sequential immunocytochemical and histochemical staining of the same sections. A low degree of colocalization of these markers was observed in certain cellular subpopulations within all the areas considered (supra-optic, paraventricular, circular and both fornicals nuclei and in the hypothalamic area located between the supraoptic and paraventricular nuclei). However, since in the paraventricular nucleus both markers were expressed by different neuronal populations, the coexistence was almost non-existent in some subdivisions of this nucleus. This rare coexistence strongly suggests that NADPH-diaphorase and calretinin are related to different functions shared by restricted hypothalamic neuronal populations.