title: Effects of morphine on thermal sensitivity in adult and aged rats.
abstract: There are contradictory data regarding older individuals' sensitivity to pain stimulation and opioid administration. Adult (12-16 months; n = 10) and aged (27-31 months; n = 7) male F344xBN rats were tested in a thermal sensitivity procedure where the animal chooses to remain in one of two compartments with floors maintained at various temperatures ranging from hot (45°C) through neutral (30°C) to cold (15°C). Effects of morphine were determined for three temperature comparisons (ie, hot/neutral, cold/neutral, and hot/cold). Aged rats were more sensitive to cold stimulation during baseline. Morphine produced antinociception during hot thermal stimulation, but had no effect on cold stimulation. The antinociceptive (and locomotor-altering) effects of morphine were attenuated in aged rats. These data demonstrate age-related differences in baseline thermal sensitivity and responsiveness to opioids. Based on behavioral and physiological requirements of this procedure, it is suggested that thermal sensitivity may provide a relevant animal model for the assessment of pain and antinociception.
authors.affiliation: Department of Psychiatry, University of Florida College of Medicine, Gainesville, FL 32610, USA. drakem@ufl.edu
authors.forename: Drake
authors.initials: D
authors.lastname: Morgan
authors.forename: Jeremiah D
authors.initials: JD
authors.lastname: Mitzelfelt
authors.forename: Lorraine M
authors.initials: LM
authors.lastname: Koerper
authors.forename: Christy S
authors.initials: CS
authors.lastname: Carter
mesh_terms: D000375:Aging / Q000502:physiology*; D000701:Analgesics, Opioid / Q000494:pharmacology*; D000818:Animals; D006358:Hot Temperature; D008297:Male; D009020:Morphine / Q000494:pharmacology*; D009043:Motor Activity; D051381:Rats; D011914:Rats, Inbred BN; D011916:Rats, Inbred F344; D011930:Reaction Time; D012684:Sensory Thresholds
chemical_list: D000701:Analgesics, Opioid; D009020:Morphine