Effects of drugs on behavior before and during chronic diazepam administration

The effects of diazepam, pentobarbital, and phencyclidine (PCP) were studied on punished and unpunished responding maintained by fixed-interval schedules before and during chronic administration of diazepam. Before chronic diazepam administration, increasing doses of diazepam and PCP increased and then decreased rates of both punished and unpunished responding. Increases in punished responding were larger than increases in unpunished responding. Pentobarbital only increased punished responding, while higher doses decreased both rates of punished and unpunished responding. During chronic diazepam administration, rates of punished and unpunished responding showed further increases with all three drugs and the dose-effect curves also shifted to the right. Analysis of local rates of responding within fixed-interval components suggested that increases in low rates early in the interval were responsible for the rate increases produced by these drugs before chronic diazepam administration. During chronic diazepam administration low rates early in the interval showed greater increases after all three drugs and their ability to produce rate-increasing effects extended further into the interval. The similar effects of these drugs before and during chronic diazepam administration suggests a similar mechanism despite the widely recognized differences in their interaction with receptors. This common mechanism may relate to rate-increasing effects more than to specific effects on punished responding.