Development of dispositional tolerance to phencyclidine by osmotic minipump in the mouse

Development of tolerance to phencyclidine (PCP) was assessed in male ICR mice, using motor incoordination as a parameter. The implantation of a PCP (1-3 mg/ day/mouse for 1-5 days)-containing osmotic minipump, induced tolerance, as evidenced by a gradual reduction of the duration of motor incoordination. The degree of tolerance exhibited dose and time dependency. Even after the removal of the PCP pump (1 mg/day/mouse for 5 days), the tolerance remained to the same degree for at least 4 days. The hepatic microsomal cytochrome P-450, cytochrome b₅ and nicotinamide adenine dinucleotide phosphatase (NADPH)-cyctochrome c reductase activities were found to be elevated in tolerant mice (2 mg/ day/mouse for 5 days). The half-life of PCP in the brains of tolerant mice was likewise decreased. These data indicate a dispositional tolerance for PCP. It appears that the administration of PCP by the osmotic minipump offers a convenient method for inducing PCP tolerance.