Systemic injections of gastro-intestinal peptides alter behavior in rats

Twenty-four male albino rats were given daily intraperitoneal injections of vasoactive intestinal polypeptide (VIP), motilin, human gastrin I (1-17) or the diluent control vehicle at a dose of 100 micrograms/kg for four consecutive days and food intake, water intake, body weight, and running wheel activity were determined every 24 hours. Animals injected with motilin or human gastrin I (1-17) exhibited decreased food intake relative to those injected with VIP or diluent, which did not differ from each other, although food intake increased reliably over days. The mean water consumption followed the same pattern as that of food intake. As expected from the above results, VIP produced weight gains as compared with rats injected with motilin or gastrin but not reliably more than after diluent. A reliable effect of trials for weight gain was the greatest on day three. Running wheel activity was not affected by injections of human gastrin I (1-17), motilin, or diluent but was reliably decreased by VIP. No significant differences existed across days. Although the results indicate that GI peptides may affect behavior when injected systemically and that like other peptides they have multiple effects, caution is urged in the interpretation of behavioral results at this time.