Effect of hypertonic saline on rat hypothalamic paraventricular nucleus parvocellular neurons in vitro

The effects of hypertonic saline on hypothalamic paraventricular nucleus (PVN) parvocellular neurons were examined using whole-cell patch-clamp technique. Under current-clamp, 50% (41/82) of parvocellular neurons were depolarized than the predicted values by hypertonic saline, and associated with increasing action potential frequency. Under voltage-clamp, unless hypertonic saline induced a shift of reverse potential to more positive values, neither mannitol nor hypertonic saline obviously increased the conductance in parvocellular neurons. Moreover, spontaneous excitatory postsynaptic currents (sEPSCs) were increased by isotonic increases in [Na+]o in the parvocellular neurons. Bath application AMPA receptor antagonist CNQX or non-selective glutamate antagonist kynurenic acid almost completely blocked the sEPSCs. Extracellular application of gadolinium (Gd3+) blocked the hypertonic saline-induced response. These results suggested that subpopulation of PVN parvocellular neurons are selectively sensitive to NaCl. Hypertonic saline excited the PVN parvocellular neurons through Na+-detection and the excitatory glutamatergic synaptic input.