Morphine tolerance offers protection from radiogenic performance deficits.
When rats are exposed to a sufficiently large dose of ionizing radiation they exhibit lethargy, hypokinesia, and deficits in performance. These and other behavioral changes parallel those often observed in this species after a large dose of morphine. Since the release of endogenous opiates has been implicated in some stress reactions, we sought to determine if they might play a part in radiogenic behavioral deficits. Rats were trained to criterion on a signaled avoidance task. Some subjects were then implanted with a pellet containing 75 mg of morphine. Other animals received placebo implants. Over a number of days, morphine tolerance was evaluated by measurement of body temperature changes. Prior to 2500 rad 60Co exposure or sham irradiation, morphine (or placebo) pellets were removed. Twenty-four hours later rats were retested to assess their performance on the avoidance task. Morphine-tolerant subjects performed significantly better than the irradiated placebo-implanted group and no differently than morphine-tolerant/sham-irradiated animals. Morphine tolerance seems to provide a degree of behavioral radiation resistance. These data are consistent with the hypothesis that endogenous opiate hyperexcretion may play some part in the behavioral deficits often observed after irradiation.
D000818:Animals; D001522:Behavior, Animal / Q000187:drug effects* / Q000528:radiation effects; D001831:Body Temperature / Q000187:drug effects / Q000528:radiation effects; D004343:Drug Implants; D004361:Drug Tolerance; D005334:Fever / Q000139:chemically induced; D008297:Male; D009020:Morphine / Q000008:administration & dosage / Q000494:pharmacology*; D011837:Radiation-Protective Agents / Q000494:pharmacology*; D051381:Rats; D011919:Rats, Inbred Strains; D013997:Time Factors
D004343:Drug Implants; D011837:Radiation-Protective Agents; D009020:Morphine