Intravenous GABA agonist administration stimulates firing of A10 dopaminergic neurons

Increasing intravenous doses of two γ-aminobutyric acid (GABA) agonists, muscimol and 4,5,6,7-tetrahydro-isoxazolo-[5,4-c]pyridin-3-ol (THIP), caused dose-related increases in extracellular, single unit activity of A₁₀ dopaminergic neurons of the ventral tegmental area. Muscimol, the more potent of the two compounds, stimulated firing at doses approximately 15–20 times lower than the doses of THIP required to elicit equivalent excitatory effects. The maximum stimulation achieved was approximately 150 and 140% of the baseline firing rate for muscimol and THIP, respectively.