Cross-sensitization between phencyclidine and (-) but not (+) pentazocine.

Repeated administration of psychomotor stimulants such as amphetamine and cocaine, and psychotomimetics such as phencyclidine, produce progressively enhanced behavioral effects, a phenomenon known as behavioral sensitization. Little is known about the effects of repeated treatment with sigma ligands on locomotor activity. The present research determined the psychomotor stimulant effects of the sigma ligand (+)pentazocine and its enantiomer; and investigated whether reciprocal cross-sensitization occurs between them and PCP-induced locomotor activity and ambulation. Adult female Sprague-Dawley rats were used. Total locomotor activity and ambulation were assessed with an automated photoelectric system. Acute (+) or (-)pentazocine given IP produced slight but insignificant locomotor stimulant effects. Repeated administration of (+)pentazocine failed to produce behavioral sensitization. However, four repeated injections of (-)pentazocine or PCP produced behavioral sensitization. (-)Pentazocine sensitized rats showed cross-sensitization to PCP-induced locomotion and ambulation. Furthermore, PCP sensitized rats showed cross-sensitization to (-)pentazocine-induced locomotion and ambulation. These findings suggest that (+) and (-)pentazocine act at different receptor sites. (-)Pentazocine is more similar to PCP in producing locomotor stimulant effects.