THE ROLE OF DOPAMINE IN THE EXPRESSION OF MORPHINE-WITHDRAWAL

1. Both L-dopa and low doses of apomorphine potentiated withdrawal sym ptoms such as jumping, ''wet dog'' shakes and burrows. L-dopa reduced hypothermia and potentiated body weight loss, whereas apomorphine prod uced opposite effects. 2. Higher doses of apomorphine attenuated jumpi ng and burrows but had no effect on ''wet dog'' shakes. On the other h and, and with the exception of sulpiride, all other dopamine (DA) anta gonists produced effects opposite those of the agonists with regard to jumping, ''wet dog'' shakes and burrows. 3. In addition, DA antagonis ts reduced hypothermia and body weight loss. The effects of DA agonist s and antagonists were investigated in mice injected with 6-hydroxydop amine (6-OHDA) intracerebrally to examine whether DA mediated effects are somehow linked to noradrenergic pathways. 4. Mice pretreated with 6-OHDA developed a higher degree of naloxone induced withdrawal jump i ng than did untreated mice. 6-OHDA reversed the effects of apomorphine on ''wet dog'' shakes and burrows while abolishing those of L-dopa on all withdrawal symptoms, the only exception being jumping, which rema ined unchanged. 5. 6-OHDA also reversed the effects of sulpiride on al l withdrawal symptoms while reversing the effects of pimozide on jumpi ng, and it abolished its effect on hypothermia. 6. These findings prov ide evidence suggesting that the effects of DA agonists and antagonist s are dependent at least partly on intact noradrenergic pathways. (C) 1998 Elsevier Science Inc.