TIPEPIDINE ACTIVATES VTA DOPAMINE NEURON VIA INHIBITING DOPAMINE D2 RECEPTOR-MEDIATED INWARD RECTIFYING K+ CURRENT

We previously reported that the novel antidepressant-like effect of tipepidine may be produced at least partly through the activation of mesolimbic dopamine (DA) neurons via inhibiting G protein-coupled inwardly rectifying potassium (GIRK) channels. In this study, we investigated the action of tipepidine on DA D-2 receptor-mediated GIRK currents (I-DA(GIRK)) and membrane excitability in DA neurons using the voltage clamp and current clamp modes of the patch-clamp techniques, respectively. DA neurons were acutely dissociated from the ventral tegmental area (VTA) in rats and identified by the presence of the hyperpolarization-activated currents. Tipepidine reversibly inhibited I-DA(GIRK) with IC50 7.0 mu M and also abolished I-DA(GIRK) irreversibly activated in the presence of intracellular GTP gamma S. Then tipepidine depolarized membrane potential and generated action potentials in the neurons current-clamped. Furthermore, the drug at 40 mg/kg, i.p. increased the number of cells immunopositive both for c-Fos and tyrosine hydroxylase (TH) in the VTA. These results suggest that tipepidine may activate DA neurons in VTA through the inhibition of GIRK channel-activated currents. (C) 2013 IBRO. Published by Elsevier Ltd. All rights reserved.