Some cholecystokinin-8 immunoreactive fibers in large pial arteries originate from trigeminal ganglion.

Cholecystokinin-8 immunoreactive (CCK8I) nerve fibers were demonstrated in whole mount preparations and cross-sections of pial blood vessels in the cat, guinea pig and rat using a specific antiserum and the avidin-biotin-peroxidase complex method. Positive fibers were present in nearly all pial arteries examined, and were located in the adventitial layer and at the junction of the adventitia and media. In general, CCK8I fibers were less abundant than substance P immunoreactive (SPI) fibers visualized in the same vessels. A marked depletion of CCK8I was noted in large cerebral arteries following treatment of adult guinea pigs with capsaicin, a drug shown previously to deplete CCK8 in some primary sensory neurons. The density of CCK8I-containing fibers was also decreased in the ipsilateral vessels of the cat circle of Willis following unilateral trigeminal ganglionectomies. These results indicate that CCK8I is contained in afferent fibers within large pial arteries of Willis' circle which project from neurons in the ipsilateral trigeminal ganglion. Whether CCK8 coexists with SP in these fibers remains to be determined.