Behavioral effects of pentobarbital, lorazepam, ethanol and chlorpromazine substitution in pentobarbital-dependent baboons.

Baboons were given continuous intragastric infusions of 100 mg/kg/day of pentobarbital before and during these experiments. The baboons responded under a fixed-ratio (FR) 30-response schedule of food presentation from 10:00 A.M. of one day to 8:00 A.M. of the next day. Terminating pentobarbital administration (i.e., substituting water for pentobarbital) from 8:00 A.M. of one day to 8:00 A.M. of the next day produced large decreases in the number of pellets earned. Repeated 24-h terminations of pentobarbital administration at 1-week intervals produced similar decreases in the pellets earned. In another experiment, the effects of terminating pentobarbital administration for several days were examined. The number of pellets earned decreased within 2 h of terminating pentobarbital administration was maximally suppressed during the first day, and recovered over 3 to 5 days. When different doses of pentobarbital were substituted for 24 h, the disruption of responding seen after pentobarbital termination was attenuated in a dose-dependent manner. In another experiment, the effects of substituting lorazepam, ethanol or chlorpromazine for pentobarbital for 24 h were examined. Lorazepam produced a dose-dependent attenuation of the effects of pentobarbital termination, whereas ethanol did not. Chlorpromazine did not attenuate the effects of pentobarbital termination in two of the three baboons tested, and produced erratic results in the third.