Changes in Locomotor Activity, Core Temperature, and Heart Rate in Response to Repeated Cocaine Administration

The effects of daily single injections of 20 mg/kg cocaine on locomotor activity, core temperature, and heart rate were determined by radiotelemetry. There was a progressive increase in locomotor activity over the 30-day treatment period. Cocaine-induced activity was 9-12-fold greater than that of saline-treated animals. Cocaine also caused increases in core temperature and heart rate. Tolerance did not develop to the locomotor, hyperthermic, and tachycardic responses resulting from repeated cocaine administration. Comparison of the time-course of the cocaine-induced responses revealed that, on Day 1 and 3, the peak locomotor activity was observed 15 min after cocaine administration, whereas the hyperthermic response peaked at 95 min on those days. The fact that the peak locomotor activity and the hyperthermic response occurred at different times suggests that different processes acting independently or interacting may be involved in these actions of cocaine.