Application of fixed-interval schedules to intracranial self-stimulation for assessing psychomotor stimulants

Rats were implanted with stimulating electrodes aimed at the medial forebrain bundlelateral hypothalamus (MFB‐LH) and were trained to lever‐press for brain stimulation on a fixed‐interval 15‐sec schedule of reinforcement. When behavior had stabilized, the animals were tested with graded doses of d‐amphetamine (0.1–1.0 mg/kg), cocaine (3.0–30 mg/kg), and nomifensine (1.0–10 mg/kg). Separate groups of animals were tested in a locomotor activity procedure over the same dose ranges. All three drugs produced graded increases in rates of responding which ranged from 180–295% of saline control levels following the highest dose of each drug. In contrast, there were no significant changes in numbers of reinforcements at any of the doses used. When tested in a locomotor activity device, all three drugs produced similar increases in activity with increasing dosage. Although currently little used, the fixed‐interval schedule of brain self‐stimulation can be helpful in making comparisons of the stimulant properties of abused drugs, such as amphetamine and cocaine, and less well‐known drugs with abuse potential such as nomifensine. © 1992 Wiley‐Liss, Inc.