The regulation of GABA release from the inhibitory input to dopamine cells in the substantia nigra pars compacta (SNc) plays a key role in different reward-related behaviors. Gamma-hydroxybutyrate (GHB) has therapeutical properties in various psychiatric disorders, especially in alcohol abuse. GHB is also used as a drug of abuse, which induces sedation and euphoria. Using whole-cell patch-clamp recordings, we studied the effects of GHB on GABA release in the SNc by recording spontaneous inhibitory postsynaptic currents (sIPSCs) in brain slices of 21- to 25-day-old rats. We found that GHB depressed the frequency and amplitude of sIPSCs, while the frequency and the amplitude of miniature inhibitory postsynaptic currents (mIPSCs), recorded in the presence of TTX, were not affected. However, in the presence of high extracellular potassium (15 mM), which increases the contribution of voltage-dependent calcium channels, GHB induced a reduction in the frequency of the mIPSCs without any effect on their amplitude. All of these effects were GABA(B)-independent and they were blocked by the GHB receptor antagonist NCS-382. The present results indicate that GHB inhibits spontaneous inhibitory synaptic transmission recorded from dopaminergic neurons in the SNc likely by reducing voltage-dependent calcium influx involved in presynaptic GABA release.