GLUTAMATERGIC SYNAPTIC INPUTS TO MOUSE SUPRAOPTIC NEURONS IN CALCIUM-FREE MEDIUM IN-VITRO

The effects of Ca2+-free perfusion medium on excitatory postsynaptic c urrents (EPSCs) and potentials (EPSPs) were studied by whole-cell reco rdings from neurons of the supraoptic nucleus (SON) in trimmed slice p reparations of mouse hypothalamus, EPSCs evoked with either focal stim ulation to the SON or perfusion of slices with high K+-medium, spontan eous EPSCs (sEPSCs) and miniature EPSCs (mEPSCs) recorded from neurons of the SON were blocked by the glutamate receptor antagonist kynureni c acid (1 mM), While EPSCs evoked by focal stimulation were abolished in the presence of Ca2+-free perfusion medium; sEPSCs and mEPSCs remai ned, Neither the frequency nor the amplitude of the sEPSCs and mEPSCs significantly changed during the application of Ca2+-free perfusion me dium, Perfusion of slices with high K+-medium increased the mEPSC freq uency compared with that recorded in normal Ca2+-containing perfusion medium, In contrast, mEPSC frequency did not change during perfusion w ith Ca2+-free high K+-medium, In current-clamp mode sEPSPs were observ ed during the perfusion with Ca2+-free medium. Some sEPSPs recorded in Ca2+-free medium were sufficiently large to evoke action potentials, These results imply that spontaneous glutamatergic synaptic inputs to the hypothalamic neurosecretory cells exist in Ca2+-free perfusion med ium, Thus, the present study suggests that Ca2+-free medium does not a lways block the synaptic transmission in hypothalamic slice preparatio ns.