Activation of hypothalamic insulin by serotonin is the primary event of the insulin-serotonin interaction involved in the control of feeding.

摘要

In previous experiments, we reported a close parallelism in the responses of both serotonin (5-HT) and insulin in the hypothalamic PVN-VMH region of freely-moving rats during feeding. Thus, hypothalamic 5-HT and insulin may participate, independently or in interaction, in the control of carbohydrate and fat ingestion. The precedence of the activation of one or the other substance remained to be investigated. In adult male Wistar rats, (a) dexfenfluramine was administered to the PVN-VMH region by reverse microdialysis (80 &mgr;M for 10 min) while local insulin was assessed; (b) insulin was locally infused (400 mU for 10 min) through the tip of the dialysis probe while 5-HT was measured. Dexfenfluramine immediately increased 5-HT release, and also extracellular insulin levels (+102%). This activation of insulin by serotonin is actually a central effect since neither insulinemia nor glycemia were affected. Conversely, insulin enhanced 5-HT release (+81%), but only 45 min after the beginning of its infusion. Noradrenaline, dopamine and metabolites were slightly or not at all modified by insulin. These data demonstrate that an interaction does exist between insulin and 5-HT in the VMH-PVN area. Because of the delay of 5-HT response to insulin, an activation of the serotonergic system would be the causal event acting immediately on insulin, and not the contrary. Whatever the exact mechanism of this interaction, it seems to be a link in a larger cascade of events involving numerous neurotransmitters and peptides leading to the regulation of feeding.