Effects of (-)-epigallocatechin-3-gallate on the activity of substantia nigra dopaminergic neurons

Despite many studies on the biological and pharmacological properties of (-)-epigallocatechin-3-gallate (EGCG), an active component of green tea, information on neuronal modulation by EGCG is limited. This study was designed to investigate the effects of EGCG on the electrical activity of rat substantia nigra dopaminergic neurons using whole-cell patch clamp recordings. The spike frequency was increased to 6.33 +/- 0.23 (p < 0.05) and 7.15 +/- 0.29 (p < 0.05) by 5 and 10 mu M EGCG, respectively, from the control level of 5.49 +/- 0.19 spikes/second, respectively (n=18). The resting membrane potential of the cells was decreased to -45.66 +/- 0.45 and -43.99 +/- 0.87 (p < 0.05), by 5 and 10 mu M EGCG, respectively, from -47.82 +/- 0.57 mV. The amplitude of afterhyperpolarization was decreased to 12.73 +/- 0.45 (p < 0.05) and 11.60 +/- 0.57 (p < 0.05) by 5 and 10 mu M EGCG, respectively, from 13.80 +/- 0.31 mV. The neuronal activity of dopaminergic neurons is closely linked to dopamine release. When neurons switch from a single-spike firing to bursts of action potentials, the release of dopamine increases. The above experimental results suggest that EGCG increases the neuronal activity via inhibition of calcium-dependent potassium currents underlying the afterhyperpolarization, and it could act as a facilitating factor that elicits NMDA-dependent bursts of action potentials like apamin or bicuculline methiodide. (c) 2006 Elsevier B.V. All rights reserved.