Hyperphagic effect of B-HT 920 in a modified X-maze test

The influence on rat-feeding behavior of B-HT 920 (a selective agonist of D2DA receptors at low doses, but also a potent stimulant of alpha 2-adrenoceptors at high doses) was examined using a new experimental model. The apparatus adopted was an X-maze with alternate open and covered arms, each baited with two food-pellets. Individual rats were placed in the apparatus and observed for 5 min. Two essential aspects of rat behavior in the presence of food were considered: tasting and feeding. A number of parameters were recorded: latency to tasting and feeding; interval between tasting and feeding; total feeding time. We also took into account the type of arm in which the rats indulged in their first bout of tasting and feeding. In the first series of experiments, B-HT 920 was injected intraperitoneally (0.1, 1, 2 and 3 mg/kg) into fed and fasted rats; in the second series, the drug was injected intracerebroventricularly (10, 20 and 80 micrograms/rat) into fasted rats. In both experimental conditions, the drug significantly modified the animals' feeding behavior and affected their natural preference for the closed arms as places of choice in which to feed. Comparison of the results with those obtained using norepinephrine (20 micrograms/rat, intracerebroventricularly), a well-known hyperphagic agent, shows that B-HT 920 strongly stimulates feeding. Also, the results of the intracerebroventricular experiments confirm that the effect on feeding appears at doses that are active both on alpha 2-adrenoceptors and on D2DA receptors, as can be deduced from penile erection and stretching and yawning elicited in rats by the same D2DA stimulant doses. The involvement of the latter receptors in feeding has been investigated by means of a new series of experiments with rats treated with the D2DA antagonist sulpiride, before B-HT 920 at 100 micrograms/kg. The possible mechanisms underlying B-HT 920-hyperphagic effects and the value of the X-maze feeding test as a simple procedure indicative of changes in rat feeding and emotionality are discussed in the light of these latest findings.