We assessed changes in neuronal circuitry following NMDA-induced activation of the ventral pallidum (VP) and how these changes are altered in a rat model of Parkinson’s disease (PD). The model was created by a unilateral injection of 6-OHDA into the substantia nigra (SN) of rats which caused a 95% reduction in ipsilateral striatal dopamine (DA) 21- 27 days later. We previously showed that intra-VP NMDA (0.45μg/0.5μl PBS) increased the number of Fos-immunoreactive (ir) neurons in the VP and medial subthalamic nucleus (mSTN) in non-lesioned rats. This enhancement was reduced in the mSTN of the lesioned hemisphere in the PD model (SFN Abstr. 27: 430.13, 2001). The present study compared several limbic and basal ganglia outputs of the VP and the medial and lateral subfields of the STN. Intra-VP NMDA elevated the number of Fos-ir cells in the frontal (motor) cortex and the medial substantia nigra pars reticulata (mSNpr) as well as the mSTN. This occurred in unlesioned control rats as well as in the hemisphere c...