Intracerebroventricular injection of senktide-induced Fos expression in vasopressin-containing hypothalamic neurons in the rat.

Intracerebroventricular injection of senktide, a selective agonist for neurokinin B receptor (NK3), induced Fos expression in many neurons of the rat hypothalamus. Fos-positive neurons were predominantly present in the supraoptic and paraventricular hypothalamic nuclei, and some of them were seen in the lateral preoptic area, lateral hypothalamic area, arcuate nucleus, perifornical region, posterior hypothalamic area, circular nucleus, and along relatively large blood vessels (lateral hypothalamic perivascular nucleus) in the anterior hypothalamus. A double labeling study was performed to examine if vasopressin-containing neurons in the hypothalamus could be activated by the treatment. Neurons with both Fos-like immunoreactivity (-LI) and vasopressin-LI were found in the paraventricular nucleus, supraoptic nucleus, circular nucleus and lateral hypothalamic perivascular nucleus. In the supraoptic nucleus, about 87% of vasopressin-containing neurons exhibited Fos-LI, which corresponded to about 64% of Fos-positive neurons in the nucleus. In the paraventricular nucleus, about 80% of vasopressin-like immunoreactive neurons exhibited Fos-LI, which constituted about 51% of the total population of Fos-positive neurons in the region. The results suggest that NK3 receptor may be involved in the modulation of release of vasopressin from the hypothalamus in the rat.