Role of 5-HT1A and 5-HT1B receptors in the hypophagic effect of 5-HT on the structure of feeding behavior.

Background: Feeding behavior is deeply affected by serotonergic neurotransmission. This regulatory activity is mediated mainly by specific 5-HT1/2 receptors, and the paraventricular nucleus (PVN) plays a key role in this phenomena. In order to reveal the involvement of 5-HT1A and 5-HT1B receptors in the paraventricular nucleus of the hypothalamus (PVN) on serotonin-induced hypophagia, we examined the effects of intra-PVN injections of serotonin in WAY 100635 or SB 216641-pretreated rats on the structure of feeding behavior.

Material/methods: Male Wistar rats were kept at 21+/-1 degrees C with a 12 h light /dark cycle on a self-selection feeding paradigm, provided with freely available and separate sources of protein, carbohydrate, fat and water. Blockade of 5-HT1A or 5-HT1B receptors in the paraventricular nucleus was effected by WAY 100635 (2 microg) or SB-216641 (2 microg) pretreatment; ten minutes later, 5-HT (2 microg) was applied into the same nucleus, then food intake and meal patterns were measured in a 30-minute period. The behavioral test was conducted at the beginning of the dark phase.

Results: The suppressive effect of 5-HT on carbohydrate intake was blocked by both WAY 100635 and SB 216641 at the beginning of the active (dark) feeding period.

Conclusions: The hypophagic effect induced by 5-HT requires activation of 5-HT1A and 5-HT1B receptors, and the specific contribution of these subtype receptors is different, since the 5-HT1A subtype showed higher behavioral selectivity.