Effects of diazepam and pentobarbital on discrete lever-press avoidance response in mice: baseline-dependent changes.

Effects of diazepam (0.5, 1, 2 and 4 mg/kg, sc) and pentobarbital (5, 10, 20 and 30 mg/kg, sc) on discrete lever-press avoidance response in the dd strain mice were investigated in consideration of the baseline avoidance levels. The dose-effect relations were obtained with 4 groups of mice showing the baseline avoidance rates of 0-24% (Group 1), 25-49% (Group 2), 50-74% (Group 3) and 75-100% (Group 4). In Group 1, both diazepam (0.5-2 mg/kg) and pentobarbital (5-20 mg/kg) increased the avoidance rate without a marked change in the response rate (frequency of lever-pressings). A significant increase in the avoidance rate was observed when 1 mg/kg of diazepam and 10 mg/kg of pentobarbital were administered. In contrast, both diazepam and pentobarbital decreased the response and avoidance rates in Groups 2-4. These results suggest that the effects of diazepam and pentobarbital on the avoidance response in mice vary depending on the baseline avoidance levels.