Actions of κ-opioids on ventral tegmental area (VTA) dopamine neurons. A: (5α,7α,8α)-(+)-N-methyl-N-[7-(pyrrolidinly)-1-oxaspiro[4,5]dec-8-yl]-benzeneacatamide (U69593, 200 nM) inhibited D2 inhibitory postsynaptic currents (IPSCs) but had no effect on currents generated by the iontophoretic application of dopamine. B: dynorphin (Dyn, 200 nM) inhibited both the IPSC and the dopamine iontophoretic current. C and D: summary of the effects of U69593 and Dyn on VTA dopamine cells. Effects of U69593 and dynorphin were reversed by the opioid antagonist naloxone (NLX, 1 μM). E and F: Dyn produces a greater whole cell current than U69593 in VTA dopamine cells. Top traces: examples of the effects of U69593 and dynorphin on single cells. Bottom graphs: summarized data.