Effect of MK-801 on endogenous dopamine release in vivo.

The effect of MK-801 on striatal dopamine (DA) release was investigated by using an in vivo microdialysis technique in the freely moving rat. Systemic injection of MK-801 (0.25, 0.5, 1, 2 mg/kg, i.p.) reduced the extracellular level of DA significantly and produced no change in the level of 3,4-dihydroxyphenylacetic acid. The behavioral observation, recorded simultaneously, revealed that MK-801, with smaller doses, produced ipsilateral circling toward the side with the dialysis probe. At larger doses, MK-801 predominantly evoked ataxia. These findings indicate that the behavioral effect of MK-801 may not be mediated via the release of DA.