Blockade of median raphe nucleus α1-adrenoceptor subtypes increases food intake in rats

Abstract Previous studies have shown that the blockade of α 1 -adrenoceptors in the median raphe nucleus (MnR) of free-feeding animals increases food intake. Since there is evidence for the presence of α 1A -, α 1B - and α 1D -adrenoceptors in the MnR of rats, this study investigated the involvement of MnR α 1 -adrenoceptor subtypes in the control of feeding behavior, looking for possible differences on the role of each α 1 -adrenoceptor in feeding. Male adult rats weighing 280–300 g with guide cannulae chronically implanted above the MnR were injected with antagonists of α 1A - (RS100329, 0, 2, 4 or 20 nmol), α 1B - (Rec 15/2615, 0, 2, 4 or 20 nmol) or α 1D -adrenoceptor (BMY 7378, 0, 2, 4 or 20 nmol). Subsequently, behavioral evaluation of ingestive and non-ingestive parameters was monitored for 1 h and the amount of food and water ingested was assessed for 4 h. The highest dose (20 nmol) of RS100329 and BMY 7378 increased food intake, feeding duration and frequency, and decreased the latency to start feeding. During the second hour 2 nmol dose of Rec 15/2615 increased food intake and all doses of BMY 7378 decreased water intake. No behavioral alterations were observed during the fourth hour. The results corroborate previous work from our lab in which we describe the involvement of α 1 -adrenoceptors of MnR on food intake control. Moreover, we show evidence that α 1A - and α 1D -adrenoceptors mediate feeding responses to adrenaline injections and that the behavioral modifications are of considerable duration, persisting up to 2 h after injection of the antagonists.