Time-dependent changes in amphetamine self-administration following frontal cortex ablations in rats.

Rats were trained to intravenously self-administer d-amphetamine (.01 mg/kg/reward infusion) during daily 1-hr. testing sessions. Following removal of frontal cortex, rates of d-amphetamine self-administration were higher at early (3-5 days) postoperative intervals but lower at later (2-4 wk.) postoperative intervals. These and other results indicated that, as a function of time after surgery, frontal rats are first hyposensitive and then become increasingly hypersensitive to the rewarding effect of d-amphetamine.