LESIONS OF THE PEDUNCULOPONTINE TEGMENTAL NUCLEUS BLOCK DRUG-INDUCED REINFORCEMENT BUT NOT AMPHETAMINE-INDUCED LOCOMOTION

It has been proposed that the positive reinforcing and motor stimulati ng effects of drugs involve the activation of a common neural substrat e. Reinforcing effects of food, drugs and brain stimulation are blocke d by lesions of the pedunculopontine tegmental nucleus (PPTg), which i s a component of the mesencephalic locomotor region. This has suggeste d that the PPTg may be involved in both positive reinforcement and for ward locomotion. In four separate experiments, rats were prepared with NMDA (0.5 mu l of 0.1 M solution) or sham lesions of the PPTg. Animal s in the first two experiments were tested for the development of a co nditioned place preference (CPP) to morphine (2 mg/kg X 3 pairings) or amphetamine (1.5 mg/kg X 3 pairings). Ten days later, spontaneous mot or activity (SMA) was assessed in these animals following a subcutaneo us injection of saline or amphetamine (1.5 mg/kg). In two further expe riments, drug-naive lesioned and control animals were tested for SMA o nly (saline or 1.5 mg/kg amphetamine in Experiment 3, and saline, 0.5 mg/kg, or 3 mg/kg amphetamine in Experiment 4). Lesions of the PPTg bl ocked the development of a CPP to both morphine and amphetamine. In co ntrast, lesions had no effect on saline or amphetamine-stimulated SMA. The PPTg, therefore, appears to be involved in the reinforcing effect s of amphetamine and morphine, but is not necessary for the expression of amphetamine-induced activity.