LAUSR

OBJECTIVE Melatonin (MT) is a hormone mainly produced by the pineal gland. It may be involved in the regulation of nociception, the mechanisms of which remain unclear. In the present study, electrophysiological effects of MT on neurons were studied. MATERIALS AND METHODS The cultured neurons were isolated from Sprague-Dawley rats trigeminal ganglia (TG). The neuron was voltage clamped using the whole cell patch clamp technique. We recorded resting membrane potential, action potential threshold and number, action potential duration and GABA-activated inward currents in the presence of 0.01 μM, 10 μM MT, and in the absence of MT. RESULTS In the presence of high concentration of MT, the spontaneous action potential disappeared and action potential threshold was significantly increased. GABA-activated inward currents were recorded and blocked by GABAA receptor antagonist, bicuculline, in the majority of TG neurons (91% 40/44). Continuous perfusion of MT could cause a decrease of GABA-activated currents. The inhibiting effect was dose-dependent and irreversible. CONCLUSIONS The results suggest that MT has several electrophysiological effects on TG neurons, which may be involved in the peripheral mechanisms of orofacial pain.