Swim-stress-induced antinociception in young rats.
1. Opioid and non-opioid mechanisms have been implicated in the phenomenon of stress-induced antinociception in adult rodents. We have studied stress-induced antinociception in developing rats and characterized differences in the neurochemical basis of this effect in pre- and post-weanling animals. 2. Twenty and 25 day old rats were stressed using warm water (20 degrees C) swimming for 3 or 10 min periods and antinociception was assessed by the tail immersion test (50 degrees C). 3. A 3 min swim in 20 and 25 day old rats produced marked antinociception which was blocked by naloxone, Mr 1452, 16-methyl cyprenorphine and levallorphan but not Mr 1453 or N-methyl levallorphan. The delta-opioid receptor antagonist ICI 174,864 attenuated stress-induced antinociception in 25 day old rats but was without effect in 20 day old animals. 4. A 10 min swim in 25 day old rats produced antinociception which was non-opioid in nature. In contrast, antinociception was not observed in 20 day old rats after a 10 min swim-stress. 5. Pretreatment of animals with dexamethasone blocked 3 min swim-stress antinociception in 20 and 25 day old animals but had no effect on antinociception induced by a 10 min swim. 6. Swim-stress-induced antinociception can be observed in young rats and dissociated into opioid and non-opioid types dependent on the duration of swimming stress. The non-opioid type appears to develop more slowly and cannot be observed in preweanling rats. The opioid type is a predominantly mu-receptor phenomenon in preweanling animals but delta-receptor components are observable in postweanling rats.
Jackson
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HC
Department of Biochemistry, University of Surrey, Guildford.
Kitchen
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D000375:Aging / Q000378:metabolism; D000818:Animals; D000831:Animals, Newborn; D004743:Enkephalin, Leucine / Q000031:analogs & derivatives / Q000494:pharmacology; D005260:Female; D008297:Male; D009270:Naloxone / Q000494:pharmacology; D009292:Narcotic Antagonists / Q000494:pharmacology; D009619:Nociceptors / Q000502:physiology*; D051381:Rats; D011919:Rats, Inbred Strains; D013315:Stress, Psychological / Q000503:physiopathology*; D013550:Swimming
D009292:Narcotic Antagonists; D009270:Naloxone; D004743:Enkephalin, Leucine; C040643:N,N-diallyl-tyrosyl-alpha-aminoisobutyric acid-phenylalanyl-leucine