By using an experimental model with either mouse organotypic spinal cultures or isolated spinal cord preparations, the present study examined the role of the ERG current (I(K(ERG))), a potassium conductance expressed by developing, GABA-immunoreactive spinal neurons. In organotypic cultures, only ventral interneurons with fast adaptation and GABA immunoreactivity, and only after 1 week in culture, were transformed into high-frequency bursters by E4031, a selective inhibitor of I(K(ERG)) that also prolonged and made more regular spontaneous bursts. In the isolated spinal cord in which GABA immunoreactivity and m-erg mRNA were colocalized in interneurons, ventral root rhythms evoked by NMDA plus 5-hydroxytryptamine were stabilized and synchronized by E4031.