Analysis of thirst mechanisms: osmosis and sodium sensing

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Thirst sensation is induced by stimulating the thirst center, including the circumventricular organs. The electrical activities were recorded from mouse slice preparation, by using patch clam recordings. SFO neurons were depolarized by hypertonic stimulation, under current clamp mode. The depolarization amplitude in the 30 mM NaC1 stimulation was large than that in the 60 mM mannitol stimulation. The same stimuli induced inward currents under voltage clamp mode. The inward currents were also larger in the NaC1 than mannitol. As for postsynaptic currents, the frequencies of EPSCs were increased and those of IPSCs were decreased by the same hypertonic stimuli. The increment and decrement in synaptic currents were also larger in the NaC1 than mannitol. The amplitude of their synaptic currents was unaffected. There suggest that SFO neurons sense to both hypertonicity and sodium ions and the sodium sensing is superior to the osmotic perception.