Effect of serotonergic agents on regional concentrations of somatostatin- and neuropeptide Y-like immunoreactivities in rat brain.

A possible role for neuropeptides in affective disorders is suggested by many investigators. Somatostatin-like immunoreactivity (SS-LI) and neuropeptide Y-like immunoreactivity (NPY-LI) concentrations are demonstrated to be reduced in cerebrospinal fluid from depressed patients. We have shown that long-term treatment with serotonin uptake inhibitors, clomipramine and zimelidine, reduce brain SS-LI concentrations in the rat. We have studied the effect of serotonergic agents on regional brain SS-LI and NPY-LI concentrations in rats. Long-term treatment with 5-hydroxytryptamine (5-HTP), a serotonin precursor, caused reductions in SS- and NPY-LI levels in the hypothalamus. SS- and NPY-LI concentrations in the brain were markedly elevated by treatment with p-chlorophenylalanine, a serotonin synthesis inhibitor. Intracerebroventricular administration of 5,7-dihydroxytryptamine, a serotonin neurotoxin, resulted in elevations of both peptides in the brain. These results suggest a inhibitory role for the serotonergic system in the brain in the regulation of SS and NPY.