The effects of methamphetamine on core body temperature in the rat—PART 1: chronic treatment and ambient temperature
- First Online:
- Cite this article as:
- Myles, B.J., Jarrett, L.A., Broom, S.L. et al. Psychopharmacology (2008) 198: 301. doi:10.1007/s00213-007-1061-z
Stimulants such as methamphetamine (METH) alter core temperature in a manner that is dependent on ambient temperature and that shows tolerance after chronic use. Our objectives were to (1) determine whether tolerance to METH-induced hyperthermia was a consequence of neurotoxicity to dopamine or serotonin and (2) determine the relationship between ambient temperature and chronic treatment on the METH-induced temperature response.
Materials and methods
Rats were treated with 1.0, 5.0, or 10.0 mg/kg METH at 24°C (experiment 1) or treated with 5.0 mg/kg METH at 20°C, 24°C, or 28°C (experiment 2). Treatment occurred for 12 days, and temperature measurements were made once per minute telemetrically during 7-h sessions in computer-regulated environments.
Peak increases in core temperature occurred at 60 min post-treatment for the 1.0 and 10.0 mg/kg doses, and at 180 min for the 5.0 mg/kg dose. Tolerance-like effects were seen with chronic 5.0 (mixed results) and 10.0 mg/kg METH in the absence of dopamine or serotonin depletions measured 2 weeks after the completion of treatment. After 5.0 mg/kg METH, variations in ambient temperature resulted in an early flexible change in core temperature (phase 1) (hyperthermia at 28° and hypothermia at 20°) and a later inflexible hyperthermia (phase 2).
The results suggest that (1) the peak effect of different doses of METH occurs at different times (24°), (2) the diminished temperature response with chronic METH treatment was not associated with long-term dopamine and serotonin depletions, and (3) a two-phase temperature response to METH may reflect two independent mechanisms.