Ontogeny of behavioral sensitization in the rat: effects of direct and indirect dopamine agonists.
In the present study, the abilities of NPA (a direct DA receptor agonist) and amphetamine (an indirect DA receptor agonist) to induce short- and long-term behavioral sensitization were assessed in 11- and 17-day-old rats (age at initial injection). Rats were injected on 4 consecutive days with amphetamine (1.0, 2.5, or 5.0 mg/kg), NPA (1.0 mg/kg), or saline. A final test day occurred either 2 days (experiment 1) or 8 days (experiment 2) later. On the test day, rats given successive agonist injections received a single injection of the same agonist again; whereas rats given successive saline injections received either amphetamine or NPA for the first time. Five minutes after injection, locomotor activity (line-crosses), stereotyped sniffing, and vertical activity were measured during a 30-min testing session. The results showed that 11- and 17-day-old rats exhibited behavioral sensitization when tested with NPA or amphetamine after a 2-day interval. In contrast, neither NPA nor amphetamine was able to sensitize the behaviors of preweanling rats when measured 8 days after initial drug treatments. Therefore, these results show that both direct and indirect DA agonists are able to induce short-term behavioral sensitization in preweanling rats, but that the mechanisms responsible for mediating long-term behavioral sensitization have not yet matured.
McDougall
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SA
Department of Psychology, California State University, San Bernardino 92407.
Duke
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MA
Bolanos
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CA
Crawford
C A
CA
D000375:Aging / Q000523:psychology*; D000661:Amphetamine / Q000494:pharmacology; D000818:Animals; D001058:Apomorphine / Q000031:analogs & derivatives / Q000494:pharmacology; D001522:Behavior, Animal / Q000187:drug effects*; D018491:Dopamine Agonists / Q000494:pharmacology*; D005260:Female; D008297:Male; D009043:Motor Activity / Q000187:drug effects; D051381:Rats; D017207:Rats, Sprague-Dawley; D013239:Stereotyped Behavior / Q000187:drug effects
D018491:Dopamine Agonists; C009074:N-n-propylnorapomorphine; D000661:Amphetamine; D001058:Apomorphine