Suckling-induced changes in responsivity to the hypoalgesic effect of morphine.
The hypoalgesic effect of morphine in lactating rats was assessed using the hot-plate test. At midlactation (days 12 and 18 postpartum) females nursing litters of 8 pups were less responsive to the hypoalgesic effect of morphine than ovariectomised or cycling females and females on days 6 or 24 of lactation. Subsequent studies showed that the hypoalgesic response to morphine was inhibited in lactating rats at a number of time points after drug administration and across a variety of doses. This effect was not dependent on milk delivery but was dependent on the hormonal state of the female since separation of dams and their litters for 96 h was sufficient to reinstate the response to morphine if it resulted in a reappearance of vaginal estrus.
Woodside
Barbara C
BC
Center for Studies in Behavioral Neurobiology, Department of Psychology, Concordia University, Montreal, Quebec H4B 1R6 Canada Department of Psychiatry, Douglas Hospital Research Center, McGill University, Montreal, Quebec H4H 1R3 Canada.
Lee
Belinda A
BA
Rochford
Joseph
J
D000700:Analgesics / Q000494:pharmacology*; D000818:Animals; D004305:Dose-Response Relationship, Drug; D005260:Female; D007774:Lactation / Q000502:physiology*; D008321:Mammary Glands, Animal / Q000502:physiology; D008425:Maternal Behavior; D009020:Morphine / Q000494:pharmacology*; D010147:Pain Measurement / Q000187:drug effects; D011247:Pregnancy; D051381:Rats; D017208:Rats, Wistar
D000700:Analgesics; D009020:Morphine