Figure 1.
Dynorphin inhibits hypocretin neurons: mechanisms. A, A typical hypocretin neuron showing that flow-pipe application of dynorphin (10 μm) decreased spike frequency. B, Dynorphin decreased spike frequency in a dose-dependent manner. Dynorphin (0.01, 0.1, 1, and 10 μm) was applied by flow pipe. C, nor-BNI (1 μm) blocked dynorphin-induced hyperpolarization. Top, Dynorphin hyperpolarized membrane potential. Bottom, Pretreatment with κ-receptor antagonist nor-BNI blocked the dynorphin-mediated hyperpolarization. MP, Membrane potential. D, Dynorphin (10 μm) inhibited spikes of hypocretin neurons in the presence of μ receptor antagonist CTAP (1 μm), suggesting that μ receptors are not responsible for actions of dynorphin on hypocretin cells. E, Dynorphin decreases input resistance. F, Dynorphin-activated GIRK. Representative current induced by ramp pulse before and during dynorphin application. External potassium concentration was 16 mm. G, The net dynorphin-induced current was potassium and GDP-β-S dependent. The approximate reversal potential was −90, −60, and −40 mV when external potassium concentration was 3, 16, and 30 mm, respectively. H, A typical cell showing that dynorphin (10 μm) depressed and Cd2+ (200 μm) blocked the Ca2+ current. The letters a–d refer to the order of application and proceed in alphabetical order. I, A bar graph showing that dynorphin (10 μm) decreased Cd2+-blockable Ca2+ current. DYN, Dynorphin; W/O, washout; Ctrl, control. J, κ receptor antagonist nor-BNI (1 μm) increased spike frequency.