Morphine hyperalgesic effects on developmental changes in thermal nociception and respiration in domestic fowl (Gallus gallus).
Domestic fowl tested at 3, 5, and 7 days posthatch jumped from a heated grid more rapidly than animals tested at 14 days posthatch. Morphine (2.5 mg/kg) decreased jump latency in 14-day-old chicks but did not significantly affect jump latency in younger chicks. Respiration was lower in 3-day-old chicks than in the older groups but morphine depressed respiration at each age. In a second experiment morphine significantly decreased jump response latency in 5-day-old chicks when thermal stimulus intensity was lowered and morphine dose increased (5 mg/kg). Posttest respiration rate was depressed by morphine. Morphine hyperalgesia and respiratory depression were reversed by naloxone (5 mg/kg). However, naloxone alone increased jump response latency. Young domestic fowl are more sensitive and/or reactive to a noxious thermal stimulus and are less sensitive to morphine than 14-day-old chicks but morphine hyperalgesia was evident in both 5- and 14-day-old chicks. These hyperalgesic chicks may be tolerant at birth to morphine hypoalgesic effects on nociception.
Hughes
R A
RA
Department of Psychology, Iowa State University, Ames 50011-3180.
Bowes
M
M
Sufka
K J
KJ
D000375:Aging / Q000502:physiology*; D000818:Animals; D002645:Chickens / Q000502:physiology*; D006358:Hot Temperature; D008297:Male; D009020:Morphine / Q000037:antagonists & inhibitors / Q000494:pharmacology*; D009270:Naloxone / Q000494:pharmacology; D009619:Nociceptors / Q000187:drug effects*; D010147:Pain Measurement; D012119:Respiration / Q000187:drug effects*
D009270:Naloxone; D009020:Morphine