Mitochondria influence NMDA‐induced calcium dynamics in hypothalamic magnocellular neurosecretary cells (686.28)

The spatiotemporal characteristics of NMDA receptor‐mediated changes in intracellular calcium ([Ca2+]i) (NMDAR‐[Ca2+]i) is critical in determining the strength of NMDA effects on neuronal excitability. Here we investigated the role mitochondria in shaping NMDAR‐[Ca2+]i dynamics. We activated NMDARs before and after the mitochondrial uncoupler CCCP (10µM for 10 sec), which prevents [Ca2+]i uptake by disruption of the proton gradient across the mitochondrial inner membrane. In both, identified and non‐identified eGFP‐VP SON neurons, focal application of NMDA (10µM for 1 sec) following CCCP resulted in a significantly larger and slower Δ[Ca2+]i response both in soma and dendrites, and a more robust membrane depolarization and firing discharge compared to the control application. Conversely, a similar underlying NMDAR‐mediated current (INMDA) was observed. Direct depolarization of SON neurons by current injection (0.15 nA for 2 sec) was used to evoke a similar number of action potentials and associated increase in [Ca2+]I as those evoked NMDAR activation. In this condition however, CCCP failed to potentiate the action potential‐evoked Δ[Ca2+]i response. Moreover In slices preincubated with Ru360 (10 µM, 30 min), a selective and potent inhibitor of the mitochondrial Ca2+ uptake uniporter, subsequent application of CCCP failed to potentiate the NMDA‐[Ca2+]i response. Taken together, our study support the hypothesis that mitochondria play a critical role in regulating NMDA‐[Ca2+]i dynamics, and therefore, the degree of membrane excitability and firing activity of MNC neurons following NMDAR activation. Grant Funding Source : NIH HL090948‐2