Galanin-positive nerves of trigeminal origin innervate rat cerebral vessels

(GAL)-positive nerve fibers in rat cerebral vessels were demonstrated by immunohistochemistry, and their origin in the trigeminal ganglia and pathway in the nasociliary nerve to the vessels was shown by retrograde tracer technique and nerve transection. Some fibres in the vertebrobasilar system appear to originate in extracranial sources. With the antiserum used only few GAL fibers could be seen in the vessels, mostly in the vertebrobasilar system. In neonatally sympathectomized animals a rich network could be visualized in most pial arteries - still particularly in the vertebrobasilar system - probably as a result of a diminished competition for nerve growth factor. No vasomotor effect of GAL could be detected in isolated segments of pial arteries, neither in normal nor in sympathectomized animals, which rules out a direct postsynaptic effect on vascular tone. GAL did not display prejunctional modulatory action on the adrenergic nerves present in the vascular preparations. A sensory function of GAL is discussed.