Intrapallidal D₂ dopamine receptors control globus pallidus neuron activity in the rat

Because activation of D₂ dopamine receptors inhibits γ-aminobutyric acid (GABA) release from intrapallidal nerve terminals, we measured the effects of modifiers of dopamine D₂ receptors on the firing rate of single neurons in the globus pallidus (GP) of the anesthetized rat. The predominant effect of intrapallidal administration of the selective D₂ agonist quinpirole was an increase in the rate of spontaneous firing while the D₂ blocker sulpiride caused a decrease. The spontaneous firing of GP neurons is inhibited by stimulation of the GABAergic striatopallidal projection. We therefore measured the effects of modifiers of D₂ receptors on striatal inhibition of GP neurons and found that intrapallidal quinpirole blocked the inhibitory effects of striatal stimulation while sulpiride enhanced them. These experiments show that both the spontaneous rate of firing of pallidal neurons and its modification by striatopallidal inputs is controlled by intrapallidal dopamine D₂ receptors. In addition, taken together with other findings in the literature, our results suggest that activation of dopamine D₂ receptors within the globus pallidus leads to inhibition of GABA release from presynaptic terminals.