Calcitonin gene-related peptide and vasodilator nerves in large cerebral arteries of cats.

Calcitonin gene-related peptide's (CGRP) role(s) was examined in the transmural nerve stimulation (TNS)-induced vasodilator response of the large cerebral arteries of the cat in vitro. Numerous CGRP-like immunoreactive nerves were demonstrated to be present in the adventitial layer of the middle cerebral, anterior communicating and basilar arteries of the cat. An electron microscopic study revealed that immunoreactive material was contained in not only nerve axons but also in the button-like structures, i.e., varicosities, which were located close to smooth muscle cells. Exogenously applied CGRP induced a dose-dependent vasodilator response which was independent of the presence of endothelial cells and of nerve components. Nerve stimulation elicited transient hyperpolarization, i.e., inhibitory junction potential, which was of nonadrenergic, noncholinergic origin. Likewise, CGRP produced hyperpolarization of smooth muscle cells. After incubation of the tissue with capsaicin in vitro, the intensity of the CGRP-like immunoreactivity diminished greatly. The TNS-induced vasodilator response and inhibitory junction potentials were also attenuated after the incubation with capsaicin. These results suggest that CGRP is involved in the TNS-induced vasodilator response of the large cerebral arteries of the cat.