Differential effects of colchicine on the induction of nitric oxide synthase in neurons containing progesterone receptors of the guinea pig hypothalamus.

Using nicotinamide-adenine-dinucleotide-phosphate-diaphorase (NADPHd) histochemistry, we analyzed the effects of an intracerebroventricular injection of colchicine on the activity of neuronal nitric oxide synthase in the hypothalamic nuclei of intact and ovariectomized estradiol-primed guinea pigs. We also examined the effects of colchicine on the immunocytochemical colocalization of nitric oxide synthase with the progesterone receptor in the ventrolateral nucleus, a key region in the control of sexual behavior. Treatment with colchicine resulted in a significant increase in the number of NADPHd-positive neurons in the ventrolateral nucleus in intact as well as in ovariectomized estradiol-primed animals, whereas in the other hypothalamic regions analyzed (preoptic area, paraventricular nucleus and posterior arcuate nucleus), the enzymatic activity remained unchanged. Quantitative analysis showed a significantly greater number of NADPHd-positive cells in the medial and the posterior aspects of the ventrolateral nucleus of colchicine-treated guinea pigs compared to the control group. In the caudal subdivision of this nucleus, colchicine induced nitric oxide synthase in the target cells for progesterone. These results suggest that neuronal nitric oxide synthase activity in the hypothalamus is affected by colchicine in a region-specific manner and especially in the ventrolateral nucleus, which is involved in progesterone-facilitated lordosis.