Target-related patterns of co-existence of neuropeptide Y, vasoactive intestinal peptide, enkephalin and substance P in cranial parasympathetic neurons innervating the facial skin and exocrine glands of guinea-pigs.

The patterns of co-existence of neuropeptides in cranial autonomic neurons of guinea-pigs have been examined with quantitative double-labelling immunofluorescence and retrograde axonal tracing using Fast Blue. Within the sphenopalatine, otic, sublingual and submandibular ganglia, and a prominent intracranial ganglion associated with the glossopharyngeal nerve, most neurons contained immunoreactivity of vasoactive intestinal peptide, neuropeptide Y, enkephalin and substance P in combinations that were correlated with their projections. Hair follicles in the facial skin formed a major target of sphenopalatine ganglion cells. The combinations of peptides co-existing in these neurons depended upon the region of the skin where the follicles were located. The parotid gland was innervated by neurons with cell bodies in the otic ganglion or the intracranial ganglion. Most of these neurons contained immunoreactivity to all four peptides. The sublingual gland was innervated by local ganglion cells usually containing immunoreactivity to neuropeptide Y, vasoactive intestinal peptide and substance P. The submandibular gland was innervated by local ganglion cells containing enkephalin immunoreactivity and low levels of immunoreactivity to neuropeptide Y. Presumptive vasodilator neurons, containing immunoreactivity to vasoactive intestinal peptide but no other peptide examined here, comprised less than 10% of cranial autonomic ganglion cells. These results demonstrate that the patterns of co-existence of neuropeptides in cranial autonomic neurons show a high degree of target specificity. The discovery that hair follicles form a major parasympathetic target implies a broader range of actions of cranial autonomic neurons than has been suspected until now.