Switch to glutamate receptor 2-lacking AMPA receptors increases neuronal excitability in hypothalamus and sympathetic drive in hypertension.

Glutamatergic synaptic input in the hypothalamic paraventricular nucleus (PVN) plays a critical role in regulating sympathetic outflow in hypertension. GluR2-lacking AMPA receptors (AMPARs) are permeable to Ca(2+), and their currents show unique inward rectification. However, little is known about changes in the AMPAR composition and its functional significance in hypertension. In this study, we found that AMPAR-mediated EPSCs (AMPAR-EPSCs) of retrogradely labeled spinally projecting PVN neurons exhibited a linear current-voltage relationship in Wistar-Kyoto (WKY) rats. However, AMPAR-EPSCs of labeled PVN neurons in spontaneously hypertensive rats (SHR) displayed inward rectification at positive holding potentials, which were not altered by lowering blood pressure with celiac ganglionectomy. Blocking GluR2-lacking AMPARs with 1-naphthyl acetyl spermine (NAS) caused a greater reduction in the AMPAR-EPSC amplitude and firing activity of PVN neurons in SHR than in WKY rats. Furthermore, blocking NMDA receptors and inhibition of calpain or calcineurin abolished inward rectification of AMPAR-EPSCs of PVN neurons in SHR. The GluR2 protein level was significantly less in the plasma membrane but greater in the cytosolic vesicle fraction in SHR than in WKY rats. In addition, microinjection of NAS into the PVN decreased blood pressure and lumbar sympathetic nerve activity in SHR but not in WKY rats. Our study reveals that increased GluR2-lacking AMPAR activity of PVN neurons results from GluR2 internalization through NMDA receptor-calpain-calcineurin signaling in hypertension. This phenotype switch in synaptic AMPARs contributes to increased excitability of PVN presympathetic neurons and sympathetic vasomotor tone in hypertension.