Contralateral circling behavior induced by intranigral microinjections of taurine and GABA in rats.

Circling behavior induced by unilateral microinjections of taurine and gamma-aminobutyric acid (GABA) into the substantia nigra zona reticulata (SNR) was studied in rats. Both taurine (10-100 micrograms/rat) and GABA (30-300 micrograms/rat) induced the contralateral circling behavior in a dose-dependent manner when they were microinjected into the SNR. Neither compound induced ipsilateral circling. An ipsilateral injection of 6-hydroxydopamine (6-OHDA) into the nucleus caudatus putamen (CPU) caused a reduction of the dopamine (DA) content in the injected side and decreased the circling behavior induced by taurine but not GABA. Electrolesion of the ipsilateral nucleus ventromedialis thalami (VM) decreased both taurine- and GABA-induced circling. In contrast, only GABA-induced circling was reduced by the electrolesion of the ipsilateral nucleus parafascicularis thalami (PF). Electrolesion of the ipsilateral nucleus accumbens (ACB) did not modify the circling behavior induced by GABA, but did decrease the circling induced by taurine. Electrolesion of the ipsilateral globus pallidus (GP) or nucleus entopeduncularis (EP) did not attenuate the circling behavior induced by either taurine or GABA. These results suggest that taurine-induced circling behavior may be mediated by the nigrostriatal-nigrothalamic system, and the ACB. In contrast, the nigrothalamic system may play an important role in GABA-induced circling behavior.