INFREQUENT CELLULAR COEXISTENCE OF NADPH-DIAPHORASE AND CALRETININ INTHE NEUROSECRETORY NUCLEI AND ADJACENT AREAS OF THE RAT HYPOTHALAMUS

Colocalization of the, calcium-binding protein calretinin and NADPH-di aphorase activity at the cellular level was studied in the magnocellul ar secretory nuclei of the rat hypothalamus using sequential immunocyt ochemical and histochemical staining of the same sections. A low degre e of colocalization of these markers was observed in certain cellular subpopulations within all-the areas considered (supraoptic, paraventri cular, 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 di fferent neuronal populations, the coexistence was almost non-existent in some subdivisions of this nucleus. This rare coexistence strongly s uggests that NADPH-diaphorase and calretinin are related to different functions shared by restricted hypothalamic neuronal populations.