This study tested the effect of brain serotonin (5-HT) depletion on the secretion of oxytocin (OT), vasopressin (VP), and adrenocorticotropin (ACTH) due to an osmotic load. The 5-HT neurotoxin 5,7-dihydroxytryptamine (5,7-DHT) was used to deplete brain 5-HT. The OT, VP, and ACTH osmotic sensitivity (slope of Δ[OT]/Δ[Osm]) and the osmotic threshold (X intercept of Δ[OT]/Δ[Osm]) were evaluated. Depletion of brain 5-HT decreased the OT osmotic sensitivity by >80% (p < 0.001) without changing the OT osmotic threshold. Brain 5-HT depletion had no effect on the VP osmotic sensitivity and increased the VP osmotic threshold from 287.8 ± 1.5 to 293.1 ± 2.0 mOsm/kg (p < 0.05). The plasma ACTH increase due to infusion of hypertonic saline was not affected 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%, respectively, without changing ACTH content. These results provide evidence for a functional role of serotonergic neurons in osmoregulation of plasma and pituitary concentration of OT and VP, but not ACTH. © 1993.
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