Age-related changes in body temperature responses to morphine in rats

Abstract

Body temperature responses to morphine were studied in rats of thr three age groups: young (3–5 months old), mature (10–12 months old), and senescent (26–28 months old). A low dose of morphine (5 mg/kg s.c.) produced hyperthermia in all three age groups, but the senescent rats displayed the greates increase in body temperature. In contrast, the senescent rats displayed the least hypothermic response to a high dose of morphine (25 mg/kg s.c.). The age-related differences in response to morphine were specific since all age groups responded similarly to ethanol (1.5 g/kg i.p.). In response to thermic stress, senescent rats developed exaggerated hyperthermia during heat stress and hypothermia during cold stress, indicating no peripheral impairment of ability to conserve or dissipate heat. Age-related differences in response to morphine appear to result from alterations in central thermoregulatory mechanisms.