Effect of Different Dopaminergic Agonists on the Activity of Pallidal Neurons in the Normal Monkey

Abstract

The classic schema of Alexander and Crutcher (1990) proposes that cortical information is processed by basal ganglia throughout the direct and indirect pathways, which are respectively modulated by D1 and D2 dopamine receptors. The effect of dopaminergic manipulations on the electrophysiological activity of the entire pallidum, both external (GPe) and internal (GPi), remains, however, subject to debate. We tested the effects of three different dopaminergic agonists (apomorphine, piribedil, and SKF 38393) on the pallidal neuronal activity of two calm awake monkeys (Macaca fascicularis). Extracellular unit recordings gave data on firing frequency and firing pattern for the GPe and GPi neurons. The effects of drug administration were diverse. The D1/D2 agonist apomorphine and the D2 agonist piribedil decreased the firing rate of both GPe and GPi neurons but only modified the pattern of GPi neurons. The D1 agonist SKF-38393 modified the firing pattern of both GPe and GPi neurons but only decreased the firing rate of GPi neurons. These results provide considerable interest since GPe does not appeared as important that predicted by the proposal of Delong’s team.