SUBTHALAMIC NUCLEUS MODULATES BURST FIRING OF NIGRAL DOPAMINE NEURONSVIA NMDA RECEPTORS

THE role of the subthalamic nucleus in the burst firing of dopamine ne urones of the substantia nigra was investigated using extracellular si ngle unit recordings combined with pressure or iontophoretic micro-inj ections in anaesthetized rats. Inhibition of subthalamic neurones by p ressure injection of gamma-aminobutyric acid (GABA) regularized the bu rst firing pattern in eight out of 17 dopamine neurones. Bicuculline i njection near subthalamic neurones increased their firing rate and inc reased 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-nitroquino xaline-2,3-dione (CNQX). These data suggest that the subthalamic nucle us promotes burst discharge in a subpopulation of substantia nigra dop amine neurones via NMDA receptors.