Evidence that the parafascicular projection to the subthalamic nucleus is glutamatergic

The parafascicular nucleus projection to the subthalamic neurones has an excitatory synaptic effect. We have examined the possible glutamatergic mediation of this pathway. The initial excitatory response elicited by electrical stimulation of the parafascicular neurones was inhibited by a microinjection of excitatory amino acid receptor antagonists into the subthalamic nucleus. The antagonists were the broad spectrum kynurenic acid, the NMDA selective antagonist d-AP-5 and the AMPA antagonist CNQX. Their effects were dose-dependent and reversible. The results suggest that the excitatory effect of the parafascicular neurones is mediated by AMPA and NMDA receptors.