Autoradiographic localization of substance P receptors in rat medulla: effect of vagotomy and nodose ganglionectomy.

Light microscopic autoradiography of [125I]Bolton-Hunter substance P binding sites was used to study the localization and denervation-induced changes in substance P receptors in the medulla oblongata. Substance P binding sites were widely distributed. The highest density was in the rostral nucleus ambiguus, dorsal motor nucleus of the vagus, nucleus of the solitary tract, hypoglossal nucleus, spinal trigeminal nucleus and inferior olive. Moderate density was apparent in the commissural nucleus of the solitary tract, area postrema, parvocellular reticular nucleus, medial vestibular nucleus and facial nucleus. The remainder of the medullary nuclei contained few or no specific substance P binding sites. Specific binding was inhibited by the addition of unlabeled substance P (1 microM). The association of substance P binding sites with the spinal trigeminal nucleus and with several nuclei involved in autonomic function suggest a role for substance P receptor activation in nociceptive and autonomic regulation, respectively. To study the influence of afferent and efferent denervation, the substance P binding sites in the medulla of sham operated rats were compared with those of both unilateral nodose ganglionectomized and cervical vagotomized rats. Substance P binding was unilaterally reduced in the rostral nucleus ambiguus and the rostral dorsal motor nucleus of the vagus with either surgical procedure. No changes in substance P binding were detected in other medullary nuclei, including the nucleus of the solitary tract, the site of termination of afferent vagal fibers.(ABSTRACT TRUNCATED AT 250 WORDS)