Differences in the properties of ionotropic glutamate synaptic currents inoxytocin and vasopressin neuroendocrine neurons

Oxytocin (OT) and vasopressin (VP) hormone release from neurohypophysial te rminals is controlled by the firing pattern of neurosecretory cells located in the hypothalamic supraoptic (SON) and paraventricular nuclei. Although glutamate is a key modulator of the electrical activity of both OT and VP n eurons, a differential contribution of AMPA receptors (AMPARs) and NMDA rec eptors (NMDARs) has been proposed to mediate glutamatergic influences on th ese neurons, In the present study we examined the distribution and function al properties of synaptic currents mediated by AMPARs and NMDARs in immunoi dentified SON neurons. Our results suggest that the properties of AMPA-medi ated currents in SON neurons are controlled in a cell type-specific manner. OT neurons displayed AMPA-mediated miniature EPSCs (mEPSCs) with larger am plitude and faster decay kinetics than VP neurons, Furthermore, a peak-scal ed nonstationary noise analysis of mEPSCs revealed a larger estimated singl e-channel conductance of AMPARs expressed in OT neurons. High-frequency sum mation of AM PA-mediated excitatory postsynaptic potentials was smaller in OT neurons. In both cell types, AMPA-mediated synaptic currents showed inwa rd rectification, which was more pronounced in OT neurons, and displayed Ca 2+ permeability. On the other hand, NMDA-mediated mEPSCs of both cell types had similar amplitude and kinetic properties. The cell type-specific expre ssion of functionally different AMPARs can contribute to the adoption of di fferent firing patterns by these neuroendocrine neurons in response to phys iological stimuli.