Design of a phencyclidine implantation pellet; suitable for tolerance development.

When using laboratory animals (e.g., mice) for phencyclidine (PCP) tolerance studies, an essential part of the procedure is to administer the PCP in such a way that the animals received adequate doses of the drug at frequent enough intervals to reach and maintain the desired levels of tolerance or employ a osmotic minipump which is either suitable or convenient to develop a high degree of tolerance to PCP in a large number of animals in a short period. However, these methods are unfit for routine work because of repeated daily injections consume too much time and osmotic minipump comes expensive. Therefore, in this paper we attempted to develop PCP pellet suitable for tolerance development. The s.c. implantation of a 10 or 20 mg PCP pellet in the back of a conscious mouse resulted in a much more rapid development of tolerance to PCP than that produced in mice receiving daily i.p. injection of, 10 or 20 mg/kg, PCP-HCl. Assessment of and degree of tolerance to PCP by PCP pellet implantation and daily injection of PCP-HCl were evidenced by a degree of decrease in the duration of motor incoordination after the challenge with, 20 mg/kg, PCP-HCl 24 h after removal of PCP pellets or a last injection of PCP-HCl. These studies may demonstrate a substantial methodological improvement in producing a high degree of tolerance to PCP in a short period of time by means of the s.c. pellet implantation technique.