Subthalamic nucleus modulates burst firing of nigral dopamine neurones via NMDA receptors.

The role of the subthalamic nucleus in the burst firing of dopamine neurones of the substantia nigra was investigated using extracellular single unit recordings combined with pressure or iontophoretic micro-injections in anaesthetized rats. Inhibition of subthalamic neurones by pressure injection of gamma-aminobutyric acid (GABA) regularized the burst firing pattern in eight out of 17 dopamine neurones. Bicuculline injection near subthalamic neurones increased their firing rate and increased burst discharge in a subpopulation of dopamine neurones tested (34 out of 102). The increase was depressed by iontophoresis of the N-methyl-D-aspartate (NMDA) antagonist (+-)2-amino,5-phosphonopentanoic acid (AP-5), but not of the non-NMDA antagonist, 6-cyano,7-nitroquinoxaline-2,3-dione (CNQX). These data suggest that the subthalamic nucleus promotes burst discharge in a subpopulation of substantia nigra dopamine neurones via NMDA receptors.