Occurrence and distribution of substance P receptors in the cerebral blood vessels of the rat

The distribution of immunoreactivity to the receptor for substance P was examined in the cerebral blood vessels of the rat. Substance P immunoreactivity has been demonstrated in the nerve fibers of the cerebral blood vessels. Recently, the production of substance P receptor specific antibody has enabled the detection of localization of the substance P receptor in the central nervous system. In this study, we examined the existence of nerve fibers with substance P receptor immunoreactivity in the cerebral blood vessels and the cranial ganglia innervating the cerebral blood vessels. Sprague-Dawley rats were perfused with fixative and the pial arteries and the cranial ganglia known to innervate the cerebral blood vessels, i.e., trigeminal, sphenopalatine, internal carotid, otic and superior cervical ganglia, were dissected. All specimens were incubated with anti-substance P receptor IgG, then stained by the avidin-biotin-peroxidase complex method. Numerous nerve fibers with varicosities forming plexuses, with substance P receptor immunoreactivity were observed on the walls of the major extracerebral arteries forming the circle of Willis and its branches. Substance P receptor immunoreactivity was also detected in the endothelium of the cerebral arteries. Substance P receptor immunoreactivity was positive in many neurons of the sphenopalatine ganglion, otic ganglion, trigeminal ganglion, superior cervical ganglion and internal carotid ganglion. The present study demonstrated the existence of nerve fibers with substance P receptor immunoreactivity in the cerebral blood vessels and the cranial ganglia that innervate the cerebral blood vessels. These findings are important in understanding the responsiveness of the cerebral blood vessels to substance P.