CARDIOVASCULAR, THERMAL AND BEHAVIORAL SENSITIZATION TO METHAMPHETAMINE IN FREELY MOVING RATS

Mean arterial blood pressure (MAP), heart rate (HR), body temperature (BT) and locomotive activity (LA) were measured simultaneously after i .p. or i.c.v. injection of methamphetamine (MAH) using a biotelemetric system. The system enabled us to observe the parameters in freely mov ing rats under minimum stress. MAH (1 mg/kg) given by i.p. injection s ignificantly increased MAP, HR, BT and LA, as compared with the saline -control. MAH (5, 50 mug) administered by i.c.v. injection stimulated responses of HR, BT and LA. After the i.p. injections of MAH (1 mg/kg) on days 1, 4, 8, 11 and 15, MAH was administered either through i.p. (1 mg/kg) or i.c.v. (50 mug) route on day 18. In addition to the LA se nsitization induced by i.p. and i.c.v. administration of MAH, it was f ound for the first time, to our knowledge, that the repeated i.p. inje ctions potentiated the responses of MAP and BT to the subsequent injec tion of MAH through i.p., but not i.c.v., route. The latter finding su ggests that the sensitization, produced by the repeated i.p. injection s, affected responses that MAH induced either peripherally or centrall y through a peripheral humoral factor or an afferent nervous system.