PSD95 Coupling of NMDA Receptor Activation and Nitric Oxide Activity in the Hypothalamic PVN

Abstract

PVN regulation of sympathetic nerve activity (SNA) and mean arterial pressure (MAP) strongly depends on the balance of glutamatergic excitation by NMDAR and GABAergic inhibition facilitated by nitric oxide (NO). The adaptor protein PSD95 regulates NO production by tethering nNOS to Ca2+‐permeable GluN2B‐containing NMDA receptors. To determine the importance of PSD95 in NMDA‐NO auto‐inhibitory feedback in PVN, lentivirus encoding PSD95 shRNA or scrambled shRNA (control) was injected into PVN (400 nL/side) of male rats. Rats were anesthetized 3‐4 weeks later and NMDA was injected into PVN. Consistent with diminished NMDA‐mediated stimulation of NO in LV‐PSD95‐shRNA rats, PVN NMDA evoked greater increases of renal SNA (PSD95 shRNA: 80±15% vs control: 28±5%) and MAP (PSD95 shRNA: 13±3 mmHg vs control: 10±1 mmHg) compared to controls. Whereas the non‐selective NOS inhibitor L‐NAME in PVN had no effect on baseline renal SNA or MAP, it reduced PVN NO as measured in controls by amperometry. During L‐NAME suppression of NO in controls, PVN NMDA caused greater increases of renal SNA (NMDA: 28±5% vs NMDA+L‐NAME: 70±12%) and MAP (NMDA: 10±1 mmHg vs NMDA+L‐NAME: 21±1 mmHg). Consistent with reduced capacity for NMDA stimulation of NO in LV‐PSD95‐shRNA rats, PVN L‐NAME did not enhance renal SNA (NMDA: 62±16% vs NMDA+L‐NAME: 59±13%) or MAP (NMDA: 13±1 mmHg vs NMDA+L‐NAME: 13±1 mmHg) responses to NMDA. Results indicate that PVN PSD95 couples NMDAR activation to NO production, which restrains NMDAR driven responses. In the context of neurogenic cardiovascular diseases, decreased PVN PSD95 expression/function could contribute to loss of NO inhibition and to exaggerated glutamatergic/NMDAR driven SNA. HL 088052 & 102310 (GMT), T32 07446 (MEB)