Gastrin-releasing peptide (GRP) was demonstrated by immunohistochemistry and high-performance liquid chromatography to be present in the great majority of neurons in the geniculate ganglion of rat and man. This was in contrast to findings in the sphenopalatine ganglion of rat, where only little GRP was found, and in the otic, trigeminal, glossopharyngeal-vagal and internal carotid ganglia, where no GRP-containing cells could be demonstrated. The peptide was not detected by immunohistochemistry in nerve fibers within structures innervated from the ganglion (tongue, soft palate, retroauricular skin and facial musculature). The retrograde axonal tracer True blue accumulated in these neurons of rat after application not only in the tongue and soft palate but also in the retroauricular skin.
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