RESUMO
In the present study, interactions of dopamine receptor agonists and antagonists with water swimming stress [WSS] on naloxone-induced jumping in morphine-dependent mice were examined. Mice were rendered dependent as described in the methods section. The opioid receptor antagonist, naloxone [1 mg/kg], was injected to elicit jumping [as a withdrawal sign]. The first group exposed to WSS in the presence or absence of dopamine receptor drugs, before naloxone injection, in order to test the interaction of dopamine receptor mechanisms with WSS on expression of jumping behavior. When the animals were exposed to WSS for periods of 0.5, 1 or 3 min, 15 min prior to naloxone injection, WSS administration for a period of 3 min decreased the expression of jumping, but not diarrhea induced by naloxone. The Dl receptor agonist, SKF38393 [l-phenyl-7,8-dihydroxy-2,3,4,5-tetrahydro-lH-3-benzazepine hydrochloride; 8 and 16 mg/kg], Dl receptor antagonist, SCH 23390 [R-[+]-8-chloro-2,3,4,5-tetrahydro-3-methyl-5-phenyl-lHbenzazepine=7-ol maleate; 0.0025 and 0.005 mg/kg], D2 receptor agonist, quinpirole [0.3 and 0.5 mg/kg] and D2 receptor antagonist, sulpiride [50 mg/kg], potentiated the inhibition of jumping induced by WSS. Quinpirole, but not other dopamine receptor agents, increased diarrhea. In the second group of animals, effects of the dopamine receptor drugs; during development of morphine dependence, in the presence of WSS administration were tested. Administration of apomorphine [1 and 2 mg/kg] or SKF 38393 [8 mg/kg] in the presence of WSS, during the development of morphine dependence increased jumping, while quinpirole [0.5 mg/kg] decreased diarrhea. In contrary, neither sulpiride nor SCH 23390 did not alter jumping or diarrhea induced by naloxone. It could be concluded that dopamine receptor mechanism[s] and/or WSS could be related the development of morphine dependency