Studies on D1 and D2 dopamine receptor involvement in conditioned taste aversions

This series of studies investigated the ability of compounds selective for either the D1 or D2 dopamine receptor to induce a conditioned taste aversion (CTA) in thirsty rats. Neither the D1 antagonist SCH23390 (0.12-0.60 mg/kg) nor the D2 antagonist haloperidol (0.125-0.375 mg/kg) were able to induce CTAs to a saccharin solution. In contrast, the D1 agonist SKF38393 produced a dose-dependent taste aversion which was stereoselective to the (R-) enantiomer. The aversion to (R,S)-SKF38393 was not blocked by pretreatment with either SCH23390 or haloperidol, suggesting that the aversion is not mediated through stimulation of either dopamine receptor subtype. The D2 dopamine receptor agonist quinpirole was also found to produce a dose-dependent CTA. This aversion was blocked by injections of haloperidol and was attenuated following injections of domperidone, suggesting involvement of peripheral dopamine receptors in the aversion. Pretreatment with SCH23390 failed to affect the quinpirole-induced CTA, providing additional evidence that the D1 and D2 dopamine receptor subtypes can function independently of one another in the control of behavior. Finally, it does not appear that the area postrema is importantly involved in these taste aversions since lesions of this brain region did not affect the CTAs induced by either SKF38393 or quinpirole.