ABSTRACT
The globus pallidus occupies a critical position in the indirect pathway of the basal ganglia circuit, which regulates movement under both normal and pathological conditions. Previous studies have shown that the globus pallidus receives dopaminergic innervation from the axonal collaterals of nigrostriatal fibers. Both dopamine Dand Dlike receptors are expressed in the globus pallidus. The present study was aimed to investigate the direct in vivo electrophysiological effects of dopamine Dlike receptors in the globus pallidus of both normal and parkinsonian rats. Extracellular recordings of multi-barreled microelectrode were used in the present study. In normal rats, micro-pressure ejection of dopamine Dlike receptor agonist quinpirole induced different effects on the firing rate of globus pallidus neurons. In 24 out of the 61 pallidal neurons, quinpirole significantly increased the firing rate by (62.7 ± 11.2)%. In another 16 neurons, quinpirole decreased the spontaneous firing rate by (37.5 ± 2.9)%. Furthermore, co-application of dopamine Dlike receptor antagonist, sulpride, blocked quinpirole-induced modulation of the firing rate of pallidal neurons. On the 6-hydroxydopamine (6-OHDA) lesioned side of parkinsonian rats, quinpirole increased the firing rate in 25 out of the 47 pallidal neurons by (64.2 ± 10.1)%, while decreased the firing rate in 11 neurons by (51.9 ± 6.2)%. Our findings suggest that activation of pallidal dopamine Dlike receptors may bidirectionally modulate the spontaneous firing of globus pallidus neurons in both normal and parkinsonian rats.