EFFECTS OF FOOD-DEPRIVATION ON MIDBRAIN 5-HT1A AUTORECEPTORS IN LEWISAND SHR RATS

Food deprivation stimulates the activity of the hypothalamo-pituitary- adrenal axis and brain serotonin (5-hydroxytryptamine, 5-HT) synthesis . Because midbrain somato-dendritic 5-HT1A autoreceptors may obey homo logous and heterologous (e.g. by glucocorticoids) down-regulation, we have analyzed whether 24 hr of fasting affects midbrain 5-HT1A recepto r binding and sensitivity in Lewis and SHR rats (i.e. strains that dif fer in behavioral/neuroendocrine responses to stressors). Fasting affe cted neither [H-3]8-hydroxy-2-(di-N-propylamino)tetralin ([H-3]8-OH-DP AT) binding at 5-HT1A autoreceptors nor 8-OH-DPAT-induced inhibition o f midbrain 5-HT synthesis (an index of 5-HT1A autoreceptor sensitivity ). Because fasting increased 5-HT precursor (tryptophan) levels to sim ilar extents in the midbrains of saline- and 8-OH-DPAT-treated rats, w e conclude that food deprivation does not affect 5-HT1A autoreceptors. In turn, our results suggest that the differential effects of 5-HT1A receptor agonists on food intake, in fed and fasted rats map be indepe ndent from 5-HT1A autoreceptors. (C) 1997 Elsevier Science Ltd.