Homo-and heteromeric complexes of KCNQ channel subunits are the molecular correlate of the M-current, a neuron-specific voltage-dependent K ϩ current with a well established role in control of neural excitability. We investigated the effect of KCNQ channel modulators on the activity of dopaminergic neurons in vitro and in vivo in the rat ventral mesencephalon. The firing of dopaminergic neurons recorded in mesencephalic slices was robustly inhibited in a concentration-dependent manner by the KCNQ channel opener N-(2-amino-4-(4-fluorobenzylamino)-phenyl) carbamic acid ethyl ester (retigabine). The effect of retigabine persisted in the presence of tetrodotoxin and simultaneous blockade of GABA A receptors, smallconductance calcium-activated K ϩ (SK) channels, and hyperpolarization-activated (I h ) channels, and it was potently reversed by the KCNQ channel blocker 4-pyridinylmethyl-9(10H)-anthracenone (XE991), indicating a direct effect on KCNQ channels. Likewise, in vivo single unit recordings from dopaminergic neurons revealed a prominent reduction in spike activity after systemic administration of retigabine. Furthermore, retigabine inhibited dopamine synthesis and c-Fos expression in the striatum under basal conditions. Retigabine completely blocked the excitatory effect of dopamine D 2 autoreceptor antagonists. Again, the in vitro and in vivo effects of retigabine were completely reversed by preadministration of XE991. Dual immunocytochemistry revealed that KCNQ4 is the major KCNQ channel subunit expressed in all dopaminergic neurons in the mesolimbic and nigrostriatal pathways. Collectively, these observations indicate that retigabine negatively modulates dopaminergic neurotransmission, likely originating from stimulation of mesencephalic KCNQ4 channels.KCNQ (also termed Kv7) channels are voltage-dependent potassium channels composed of homo-and heteromeric complexes of five different KCNQ subunits (KCNQ1-5, Kv7.1-Kv7.5). Unlike KCNQ1, all other KCNQ subunits (KCNQ2-5) are expressed in the CNS (Jentsch, 2000). Opening of KCNQ channels leads to neuronal hyperpolarization, thereby stabilizing the membrane potential and decreasing excitability. This makes them particularly interesting as targets in CNS diseases linked to hyperexcitability, including epilepsy, anxiety, pain, and migraine (Blackburn-Munro et al., 2005). The attractiveness of neuronal KCNQ channels in the treatment of such disease states is strongly supported by the identification of mutations within the human KCNQ genes. Thus, mutations in the KCNQ2 and KCNQ3 genes are associated with benign familial neonatal convulsions (Biervert et al., 1998), and certain mutations in the KCNQ4 gene result in progressive hearing loss (Kubisch et al., 1999). Several attempts have been made to find pharmacological KCNQ modulators. N-(2-Amino-4-(4-fluorobenzylamino)-This work was supported by the European Union 6th Framework Program (LSHM-CT-2004-503038) (to H.E.H., C.E., C.M., P.W., and L.C.R.) and by a grant from the Fonds National de la Recherche Scienti...