Cocaine and body temperature in the rat: effects of exercise and age

The laboratory rat is being used to determine if abuse of cocaine is a risk factor in the pathogenesis of exercise-induced heatstroke. The effect of running on a treadmill on the core temperature (Tc) has been studied in two groups of rats: animals approximately 20 weeks old ('young rats') and animals approximately 52 weeks old ('old rats'). During 60 min running the Tc increased to a steady level, within 15-30 min, which was higher in the old than in the young animals at environmental temperatures (Ta) of 25 and 30 degrees C. A significantly greater rise occurred in both groups of animals at Ta of 30 compared to 25 degrees C. Injection of cocaine (20 mg/kg) was without effect on the rise in Tc in young animals running at a Ta of 25 degrees C but significantly increased the hyperthermia in the old rats. It is suggested that the rise in the thermoregulatory set point induced by muscle exercise is greater with advancing age. Also in older animals, the effect of cocaine on the central nervous system may be enhanced.