Lack of interaction between alpha 2-adrenoceptors and dopamine D2-receptors in mediating their inhibitory effects on [3H]dopamine release from rat nucleus accumbens slices.

The alpha 2-adrenoceptor agonist, UK14304, dose-dependently inhibited the electrically stimulated release of dopamine (DA) from rat nucleus accumbens slices. This effect was antagonized by idazoxan, confirming that it was an alpha 2-adrenoceptor mediated effect. There was no evidence of endogenous activation of noradrenergic receptors suggesting that the alpha 2-adrenoceptor agonist was not acting presynaptically to inhibit noradrenaline release. An in vitro superfusion technique was used to investigate whether there was any interaction between alpha 2-adrenoceptors and DA D2-receptors in mediating their inhibitory effects on [3H]DA release from rat nucleus accumbens slices. alpha 2-Adrenoceptors and DA D2-receptors interact with similar second messenger systems and it was considered that they may compete for a common pool of G-proteins. The inhibitory effects of the alpha 2-adrenoceptor agonist, UK14304, and the DA receptor agonists, quinpirole, apomorphine and pergolide were not independent. However, there was no evidence of any interaction between UK14304 and the DA D2-receptor antagonists, sulpiride or haloperidol, suggesting that the two receptors do not compete for a common pool of G-proteins in mediating their inhibitory effects on DA release.