Evidence for substance P, serotonin and oxytocin input to medullary catecholamine neurons with diencephalic...

Using the retrograde transport of horseradish peroxidase (HRP) in combination with two-color immunoperoxidase staining, boutons stained with antisera to substance P (SP), serotonin (5HT) and oxytocin (OX) have been observed in contiguity with neurons in the rostral and caudal medulla that showed immunoreactivity for phenylethanolamine N-methyl transferase (PNMT) and tyrosine hydroxylase (TH), respectively, and which were backfilled with HRP injected into the diencephalon. The juxtaposition of these immunostained structures indicates that SP, 5HT and OX released from fibers in the medulla may affect the activity of adrenergic and noradrenergic medullary neurons that project to the diencephalon. Moreover, the presence of 5HT- and OX-immunoreactive processes in contiguity with medullary CA cells that send fibers to the diencephalon indicates that the raphe nuclei and the paraventricular nucleus of the hypothalamus can directly influence ascending pathways that are known to innervate the hypothalamus and appear to effect changes in vasopressin release.