INDUCING GLUTAMATE CO-RELEASE FROM SNR GABAERGIC NEURONS RESCUES MOTOR SYMPTOMS IN THE 6-OHDA HEMIPARKINSONIAN MOUSE MODEL

Parkinson's disease motor symptoms arise from degeneration of dopaminergic neurons in the substantia nigra pars compacta (SNc), producing basal ganglia imbalance and excessive inhibitory output from the substantia nigra pars reticulata (SNr). This heightened gamma-aminobutyric acid (GABA)-ergic tone suppresses thalamic activity and impairs voluntary movement. We tested whether reprogramming SNr GABAergic neurons to co-release glutamate could counteract this pathological inhibition and restore motor function. Using the unilateral 6-hydroxydopamine mouse model, we induced dopamine depletion by lesioning the medial forebrain bundle, followed four weeks later by Cre-dependent viral delivery of vesicular glutamate transporter 2 (VGLUT2) into the SNr. Electrophysiological recordings in SNr projection targets confirmed glutamate/GABA co-release, with glutamatergic currents selectively abolished by 6,7-dinitroquinoxaline-2,3-dione, demonstrating that VGLUT2 expression is necessary and sufficient to enable co-glutamate release. Across multiple behavioral assays—including open field, apomorphine-induced rotation, cylinder, and pole tests—VGLUT2-treated lesioned mice showed motor recovery. Stereological analysis confirmed substantial SNc dopamine neuron loss from the lesion but no additional toxicity following VGLUT2 overexpression. Neuron specific nuclear protein analysis in the SNr, ventromedial thalamus, and superior colliculus showed no VGLUT2-related neurodegeneration. These results demonstrate that inducing glutamate co-release in SNr neurons reduces their net inhibitory output, rebalances basal ganglia microcircuit activity, and rescues Parkinsonian motor deficits.