Role of cerebellar dopamine D3 receptors in modulating exploratory locomotion and cataleptogenicity in rats

Dopamine D3 receptors are highly expressed in the cerebellum; however, their pathophysiological functions are not fully understood. Here, we conducted microinjection studies to clarify the role of cerebellar D3 receptors in modulating locomotion and cataleptogenicity in rats. Microinjection of the preferential D3 agonist 7-hydroxy-N,N-di-n-propyl-2-aminotetralin (7-OH-DPAT) into lobe 9 of the cerebellum significantly reduced spontaneous locomotor activity with a U-shaped dose-response curve. The intracerebellar microinjection of 7-OH-DPAT did not elicit catalepsy by itself, but markedly potentiated catalepsy induction with a low dose (0.3 mg/kg) of haloperidol. The catalepsy enhancement by 7-OH-DPAT occurred in a dose-dependent manner and was not associated with the locomotor inhibition. U-99194A (a selective D3 antagonist) or AD-6048 (a preferential D3 vs. D2 antagonist) antagonized both the catalepsy enhancement and the locomotor inhibition with 7-OH-DPAT. In addition, U-99194A and AD-6048 per se significantly alleviated catalepsy induced by a high dose (0.5 mg/kg) of haloperidol. Furthermore, microinjection of 7-OH-DPAT into the nucleus accumbens or the dorsolateral striatum neither affected spontaneous locomotor activity nor haloperidol (0.3 mg/kg)-induced catalepsy. The present results illustrate for the first time the role of cerebellar D3 receptors in modulating cataleptogenicity of antipsychotic agents, implying that blockade of cerebellar D3 receptors contributes to the reduction of extrapyramidal side effects.