Neurokinin B receptor (NK3)-containing neurons in the paraventricular and supraoptic nuclei of the rat hypothalamus synthesize vasopressin and express Fos following intravenous injection of hypertonic saline.

Subnuclear localization of neurokinin B receptor (NK3) in the paraventricular and supraoptic nuclei of the hypothalamus was immunohistochemically investigated in the rat. In the paraventricular hypothalamic nucleus, intense neurokinin B receptor-like immunoreactivity was found in the posterior magnocellular part, moderate to weak neurokinin B receptor-like immunoreactivity was seen in the other parts. In the supraoptic nucleus, intense neurokinin B receptor-like immunoreactivity was distributed in its principal part, and a few neurons with neurokinin B receptor-like immunoreactivity were found in the retrochiasmatic part. Co-localization of neurokinin B receptor-like immunoreactivity with vasopressin-like immunoreactivity was examined through serial adjacent sections. Neurons with both neurokinin B receptor-like immunoreactivity and vasopressin-like immunoreactivity were primarily found in the supraoptic nucleus and posterior magnocellular part of the pavaventricular nucleus. A small number of neurons with neurokinin B receptor-like immunoreactivity and vasopressin-like immunoreactivity were also seen in the circular nucleus and the region surrounding blood vessel in the anterior hypothalamus. Many neurokinin B receptor-containing neurons in the paraventricular and supraoptic nuclei, as well as in circular nucleus and the region surrounding the blood vessel, expressed Fos-like immunoreactivity after intravenous injection of hypertonic saline. The present study demonstrated that a large proportion of neurokinin B receptor-like immunoreactive neurons in the paraventricular hypothalamic and supraoptic nuclei contained vasopressin-like immunoreactivity, and expressed Fos-like immunoreactivity after intravenous administration of hypertonic saline. The results suggest that neurokinin B receptor in the two nuclei may be involved in modulation of the release of vasopressin when the internal environment is disturbed.