Tolerance and withdrawal to chronic morphine treatment in the week-old rat pup.
Chronic treatment of adult animals with morphine results in tolerance but there are fewer reports on the effects of chronic opiates during ontogeny. The present experiments assessed the development of morphine-induced tolerance and withdrawal in infant rats. Pups were injected with morphine twice daily from ages 1-7 days and then tested on day 7 for morphine-induced analgesia in a hot-water immersion test, and separation-induced ultrasonic vocalizations in response to isolation from the dam and littermates at 7 and 10 days of age. Tolerance occurred to the analgesic effects of morphine but not to its suppression of ultrasonic vocalizations. Separation-induced vocalizations were greatly increased in chronic morphine-treated pups following naltrexone-precipitated withdrawal at 7 days of age. The increase in ultrasonic vocalizations following naltrexone treatment in morphine exposed pups may be a developmentally unique sign of opiate withdrawal.
Barr
G A
GA
Department of Developmental Psychobiology, New York State Psychiatric Institute, Columbia University College of Physicians and Surgeons, New York 10032.
Wang
S
S
D000698:Analgesia; D000704:Analysis of Variance; D000818:Animals; D000831:Animals, Newborn / Q000502:physiology*; D001522:Behavior, Animal / Q000187:drug effects; D001835:Body Weight / Q000187:drug effects; D004361:Drug Tolerance; D005260:Female; D008297:Male; D009020:Morphine / Q000009:adverse effects*; D051381:Rats; D011919:Rats, Inbred Strains; D013375:Substance Withdrawal Syndrome / Q000209:etiology*; D013997:Time Factors; D014828:Vocalization, Animal / Q000187:drug effects
D009020:Morphine