- activated ion currents triggered by ryanodine receptor - mediated 1 Ca 2 + release control the firing of inhibitory neurons in the prepositus

35 Spontaneous miniature outward currents (SMOCs) are known to exist in smooth 36 muscles and peripheral neurons, and evidence for the presence of SMOCs in central 37 neurons has been accumulating. SMOCs in central neurons are induced through 38 Ca-activated K (KCa) channels, which are activated through Ca-induced Ca 39 release from the endoplasmic reticulum via ryanodine receptors (RyRs). Previously, 40 we found that some neurons in the prepositus hypoglossi nucleus (PHN) showed 41 spontaneous outward currents (SOCs). In the present study, we used whole-cell 42 recordings in slice preparations of the rat brainstem to investigate the following: 1) the 43 ionic mechanisms of SOCs, 2) the types of neurons exhibiting frequent SOCs, and 3) 44 the effect of Ca-activated conductance on neuronal firing. Pharmacological analyses 45 revealed that SOCs were induced via the activation of small conductance-type KCa 46 channels (SK channels) and RyRs, indicating that SOCs correspond to SMOCs. An 47 analysis of the voltage responses to current pulses of the fluorescence-expressing 48 inhibitory neurons of transgenic rats revealed that inhibitory neurons frequently 49 exhibited SOCs. The abolition of SOCs via the blockade of SK channels enhanced the 50 frequency of the spontaneous firing of inhibitory PHN neurons. However, the 51 abolition of SOCs via the blockade of RyRs reduced the firing frequency and 52