Circling behavior in rodents following an imbalance of basal ganglia GABA concentrations.

Unilateral focal injection of the GABA - transaminase inhibitor, ethanolamine O-sulphate, into one substantia nigra or globus pallidus of rats or the striatum of mice induces spontaneous and drug-induced circling behaviour. Circling parallels the imbalance of GABA concentrations between the injected and the noninjected side of the brain, being most striking on Day 1 and 3, and non-existent by Day 7. Increases in GABA concentration were demonstrated in areas distant from the injection site, on both the injected and noninjected side of the brain presumably due to diffusion of the ethanolamine O-sulphate. This diffusional effect made it impossible to define the exact site of GABA and dopamine interaction.