The seven members of Shaker-related K(+) channel family, which are known to regulate membrane excitability and transmitter release, have been identified in the CNS. It is known that the substantia nigra pars reticulata (SNr) receives GABAergic inputs mainly from the striatum and sends GABAergic outputs to the thalamus. An immunohistochemical study shows that the Kv1 family, particularly Kv1.4, is expressed in the SNr, while it is reported that Kv1.2 mRNA is detected in the striatal neurons. Therefore, which Kv channels may be involved in the release of GABA in the SNr remains still controversial. To address this issue, we tested the effects of various K(+) channel blockers on the synaptic transmission using mechanically dissociated SNr neurons known as "synaptic bouton preparation", that retained functional presynaptic nerve terminals which enable us to examine miniature inhibitory postsynaptic currents (mIPSCs) by conventional whole-cell patch clamp recordings. Based on the sensitivities of mIPSCs to the Kv channel blockers, we concluded that Kv channels, in particular Kv1.2 subunit play the most significant role in the release of GABA at the presynaptic terminals projecting to the SNr neurons.