PRESYNAPTIC EFFECT OF THE ATP-SENSITIVE POTASSIUM CHANNEL OPENER DIAZOXIDE ON RAT SUBSTANTIA-NIGRA PARS RETICULATA NEURONS

Spontaneous synaptic currents were recorded from visually identified s ubstantia nigra pars reticulata (SNR) neurons in the rat brain slice p reparation by whole-cell patch clamp technique. GABA neurons were dist inguished from dopamine neurons by their electrophysiological characte ristics. In the presence of 20 mu M AP5 and CNQX, the spontaneous syna ptic currents recorded from GABA neurons were sensitive to bicuculline and reversed polarity at a potential close to the equilibrium potenti al of Cl-, indicating that they were mediated by GABA(A) receptors. TT X at 1 mu M eliminated action potential-dependent release of GABA from nerve terminals, revealing the miniature inhibitory post-synaptic cur rents (mIPSCs). The ATP-sensitive potassium channel (K-ATP channel) op ener diazoxide (30-300 mu M) significantly reduced the frequency of th e mIPSCs in a dose-dependent manner. However, diazoxide did not affect the average value and the distribution of the mIPSC amplitudes. Thus, this effect of diazoxide was pre-synaptic in nature. The K-ATP channe l blocker glibenclamide (300 mu M) was able to restore the frequency o f the mIPSCs. These data suggest that the striatonigral projection, wh ich represents the major inhibitory input controlling SNR GABA neuron activities, possesses presynaptic K-ATP channels on the nerve terminal s. (C) 1997 Elsevier Science B.V.