Dynorphin B is present in sensory and parasympathetic nerves innervating pial arteries

Dynorphin B (dyn B) in trigeminal ganglion cells and in perivascular nerve fibers in pial arteries was demonstrated in rat, guinea-pig, and monkey by immunohistochemistry. The pathway from the trigeminal ganglion, which runs via the nasociliary nerve and ethmoidal foramen to the pial arteries, was shown in rat by retrograde tracer technique and nerve section. In the guinea-pig the peptide was demonstrated to coexist with substance P and calcitonin gene-related peptide in neurons of the trigeminal ganglion and pial nerve fibers, i.e., it was present in cerebrovascular sensory nerves with primarily nociceptive function. Another finding in guinea-pig was a coexistence of dyn B with vasoactive intestinal polypeptide in the pial nerve fibers and neurons of the sphenopalatine ganglion, indicating a presence also in parasympathetic nerves to the cerebral vessels. No vasomotor effect of dyn B could be detected in isolated segments of rat pial arteries, which rules out a direct postsynaptic effect on vascular tone. The peptide did not display a prejunctional modulatory action on the adrenergic nerves present in the vessels. The function of dyn B in the cerebrovascular nerves is discussed.