COLOCALIZATION OF NADPH-DIAPHORASE AND ESTROGEN-RECEPTOR IMMUNOREACTIVITY IN THE RAT VENTROMEDIAL HYPOTHALAMIC NUCLEUS - STIMULATORY EFFECTOF ESTROGEN ON NADPH-DIAPHORASE ACTIVITY

NADPH-diaphorase (NADPH-d) histochemistry was combined with estrogen r eceptor (ER) immunohistochemistry in order to study effect of estrogen on NADPH-d activity and establish an anatomical relationship between NADPH-d and ER-immunoreactivity (ir) containing neurons in the ventrom edial hypothalamic nucleus (VMN). Gonadectomized female and male rats received either oil (control group) or 10 mu g of estradiol benzoate ( EB) for two successive days and were sacrificed on day 4. While NADPH- d histochemistry stained a specific subpopulation of neurons in the ve ntrolateral portion of the VMN of all groups, there was a marked sex d ifference in the effect of EB treatment. EB elevated the number of NAD PH-d positive neurons in females but had no significant effect in male s. Double-labeling histochemistry revealed that more than 70% of the N ADPH-d positive neurons contained ER-ir in the VMN of all groups, with EB-treated females having a significantly higher frequency than all o ther groups. Since neuronal NADPH-d is nitric oxide synthase (NOS), th ese results provide anatomical evidence for an association of estrogen with NOS in the rat VMN and suggest that NOS activity can be modulate d by estradiol in estrogen sensitive neurons.