Midazolam-induced hyperphagia and FG 7142-induced anorexia: behavioural characteristics in the rat.

Non-deprived male rats, familiarized with a highly palatable diet, were treated with 0.3-10.0 mg/kg of the imidazobenzodiazepine midazolam. The increases in consumption of the food observed at larger doses of midazolam were due to increases in the duration of feeding, but not in the rate of eating. These, in turn, were due to increases in the duration of eating bouts, but not in their frequency. The beta-carboline FG 7142, a partial benzodiazepine receptor inverse agonist, reduced the consumption of the diet when it was injected at 10.0 and 15.0 mg/kg (IP). The overall duration of feeding was not affected at these doses in the 30 min test, but rate of eating was reduced. However, during the first 5 min interval of the test, when feeding behaviour was most motivated, FG 7142 did significantly reduce the duration of feeding. The effect depended upon a reduction in the duration of eating bouts, but not upon any change in their frequency. Hence, midazolam and FG 7142 had opposite effects on the duration of bouts of feeding. Both midazolam and FG 7142 reduced the frequencies of concurrent grooming, locomotor activity, and rearing in the test of palatable food consumption. Possible explanations for these effects are briefly considered.