THE ROLE OF SEROTONERGIC NEURONS IN INTRAVENOUS HYPERTONIC SALINE-INDUCED SECRETION OF VASOPRESSIN, OXYTOCIN, AND ACTH

This study tested the effect of brain serotonin (5-HT) depletion on th e secretion of oxytocin (OT), vasopressin (VP), and adrenocorticotropi n (ACTH) due to an osmotic load. The 5-HT neurotoxin 5,7-dihydroxytryp tamine (5,7-DHT) was used to deplete brain 5-HT. The OT, VP, and ACTH osmotic sensitivity (slope of DELTA[OT]/DELTA[Osm]) and the osmotic th reshold (X intercept of DELTA[OT]/DELTA[Osm]) were evaluated. Depletio n of brain 5-HT decreased the OT osmotic sensitivity by > 80% (p < 0.0 0 1) without changing the OT osmotic threshold. Brain 5-HT depletion h ad no effect on the VP osmotic sensitivity and increased the VP osmoti c threshold from 287.8 +/- 1.5 to 293.1 +/- 2.0 mOsm/kg (p < 0.05). Th e plasma ACTH increase due to infusion of hypertonic saline was not af fected by brain 5-HT depletion. Brain 5-HT depletion significantly (p < 0.01) decreased the pituitary content of OT and VP by 38 and 32%, re spectively, without changing ACTH content. These results provide evide nce for a functional role of serotonergic neurons in osmoregulation of plasma and pituitary concentration of OT and VP, but not ACTH.