Biochemical, behavioral, and electrophysiologic actions of the selective sigma receptor ligand (+)-pentazocine

Research on the sigma receptor, a binding site associated with drug-induced psychotomimetic behaviors, has been hampered because most sigma agonists also interact with the phencyclidine (PCP) receptor. (+)-Pentazocine, a human psychotogen, is a selective sigma receptor ligand. To demonstrate sigma receptor activities, we studied the behavioral and electrophysiologic actions for (+)-pentazocine. In the behavioral drug discrimination procedure in which rats were trained to discriminate between 2.0 mg/kg (5.59 mumol/kg) (+)-pentazocine and saline, (+)-pentazocine produced dose-related increases in the percentage of trials completed on the (+)-pentazocine lever. At a dose of 1.0 mg/kg (3.29 mumol/kg) (+)-N-allylnormetazocine generalized completely to (+)-pentazocine. By contrast, PCP only partially generalized. In the visual evoked potential test, these compounds produced a significant dose-dependent slowing of the N2 latency. This response was prevented by haloperidol pretreatment. These results demonstrate pharmacologic actions for the selective sigma receptor ligand (+)-pentazocine and suggest some overlapping pharmacologic properties of the sigma and PCP receptor sites despite differences in central nervous system distribution.