title: Neonatal treatment with naloxone causes permanent hyperalgesia in rats.
abstract: The effect of treatment with naloxone early in life on pain responsiveness was studied in Wistar rats. Litters of six rats were divided equally into groups of 3 pups receiving daily naloxone (50 mg/kg, sc) and 3 pups receiving saline from the 3rd to 18th day of life. On days 30, 50, 70 and 90, one group of animals previously injected during suckling with naloxone (N = 21) and another with saline (N = 21) were submitted to the hot-plate test to measure the latency to paw licking. Other groups of rats also treated during suckling with naloxone (N = 13) and saline (N = 14) were assessed for the antinociceptive effect of morphine (10 mg/kg,sc). The naloxone group displayed a lower latency than the saline group in all test sessions and a diminished analgesic response to morphine. The results indicate that the use of naloxone (an antagonist opioid) during suckling, the brain growth spurt period, facilitates a long-lasting increased pain responsiveness and alters antialgesic mechanisms. In this respect, the opioid and non-opioid effects of naloxone on the ontogeny of neural systems should be taken into account.
authors.affiliation: Departamento de Nutricão, Universidade Federal de Pernambuco, Recife, Brasil.
authors.forename: R M
authors.initials: RM
authors.lastname: de-Castro
authors.forename: J E
authors.initials: JE
authors.lastname: Cabral-Filho
authors.forename: J A
authors.initials: JA
authors.lastname: Costa
authors.forename: F B
authors.initials: FB
authors.lastname: Costa
authors.forename: M A
authors.initials: MA
authors.lastname: Gallindo
authors.forename: C A
authors.initials: CA
authors.lastname: Hecksher
mesh_terms: D000818:Animals; D000831:Animals, Newborn; D000833:Animals, Suckling; D006930:Hyperalgesia / Q000139:chemically induced / Q000503:physiopathology*; D008297:Male; D009020:Morphine / Q000494:pharmacology; D009270:Naloxone / Q000494:pharmacology*; D009619:Nociceptors / Q000187:drug effects; D051381:Rats; D011930:Reaction Time / Q000187:drug effects
chemical_list: D009270:Naloxone; D009020:Morphine