〔Abstract〕 Objective To investigate the effect of Arginine Vasopressin(AVP) on the median preoptic glutamatergic(MnPOVglut2) neurons and its mechanism. Methods Brain slices were prepared from male Vglut2-tdTomatomice. MnPOVglut2neurons expressing red fluorescent protein were located by using fluorescence microscope. Whole-cell patch clamp technique was used to observe the effect of AVP on the firing frequency of MnPOVglut2neurons, the effect of synaptic transmission blockers(STBs) on the AVP-induced change in the firing frequency of MnPOVglut2neurons, and the effect of AVP V1a receptor antagonist on the AVP-induced change in the firing frequency of MnPOVglut2neurons. Results The mean firing frequency of MnPOVglut2neurons increased during perfusion with artificial cerebrospinal fluid(ACSF) and AVP compared with that during perfusion with ACSF(P<0.01), indicating that AVP excited the MnPOVglut2neurons. The mean firing frequency of MnPOVglut2neurons still increased during perfusion with ACSF, STBs, and AVP compared with that during perfusion with ACSF and STBs(P<0.001); moreover, the magnitude of AVP-induced increase in firing frequency didn′t change significantly during perfusion with ACSF, STBs, and AVP compared with that during perfusion with ACSF and AVP(P>0.05), suggesting that AVP excited the MnPOVglut2neurons directly in a postsynaptic manner. The magnitude of AVP-induced increase in the firing frequency of MnPOVglut2neurons declined during perfusion with ACSF, STBs, AVP, and V1a receptor antagonist compared with that during perfusion with ACSF, STBs, and AVP(P<0.01), suggesting that AVP excited MnPOVglut2neurons directlyviaV1a receptor. Conclusion AVP can excite MnPOVglut2neuronsviaV1a receptor directly in a postsynaptic manner. This study reveals the molecular marker of MnPO neurons which AVP act on.