Acetate is an Active Metabolite of Ethanol: Increases Firing and Evokes Inward Currents through Activation of NMDA Receptors in RVLM Projecting CeA Neurons

Abstract

We have recently reported that activation of central nucleus of amygdala (CeA) is involved in the in vivo sympathoexcitatory and pressor responses to acute challenge of acetate, the ethanol metabolite. However, the underlying neural mechanisms have not been determined. Here we investigated the role of acetate in regulating the in vitro excitability of CeA neurons with axon projecting to rostral ventrolateral medulla (CeA‐RVLM) under brain slice preparation. In current‐clamp recordings, graded current injections evoked graded increases in spike frequency. Maximum discharge was evoked by +250 pA injections and averaged 19 ± 1 Hz (n=8). Bath application of acetate (0, 7.5, 37.5 and 75 mM) increased the excitability of CeA‐RVLM neurons in a dose‐dependent manner. Maximum spike discharge in the presence of acetate (75 mM) was 44 ± 5 Hz (n=7). Pre‐treatment with AP5 (60 µM, n=7), the NMDA receptor competitive blocker or memantine (30 µM, n=9) a NMDA receptor channel pore blocker, significantly attenuated the increased excitability elicited by acetate (34 ± 4 Hz for AP5 and 20 ± 5 Hz for memantine respectively, p<0.05 vs 75 mM acetate alone). AP5 or memantine alone did not alter baseline excitability. In voltage‐clamp recordings, acetate application produced inward currents (22.4 ± 2 pA, n=6) which were completely abolished by pre‐treatment with AP5 (n=4) or memantine (n=6). Immunohistochemistry study demonstrates expression of NMDA NR1 in CeA‐RVLM neurons. Our data indicate that activation of NMDA receptors by acetate contributes to the increased excitability of CeA‐RVLM neurons, which may underlie the mechanism of sympathoexcitation and pressor response in vivo. AHA2640130 (QHC)