Local Metabolism of Ethanol to Acetic Acid/Acetate in the Central Nucleus of Amygdala Elicits Sympathoexcitatory Responses through Activation of NMDAR in Sprague Dawley Rats
Authors: Chapp Andrew D. , Huber Michael J. , Collins Andréa R. , Driscoll Kyle M. , Behnke Jessica E. , Larson Robert A. , Shan Zhiying , Zhang Li. , Chen Qing-Hui 
Published: July 2020

Binge alcohol consumption elicits robust sympathoexcitation and excitatory neuronal output. However, the central mechanism that mediates these effects remains elusive. We investigated the effects of ethanol metabolism within the central nucleus of the amygdala (CeA) on sympathoexcitation, and elucidated the role of acetate in these excitatory responses.In vivoarterial blood pressure, heart rate and sympathetic nerve activity responses to CeA microinjected ethanol or acetate with appropriate inhibitors/antagonists were tracked.In vitrowhole-cell electrophysiology recording responses to acetate in CeA neurons with axon projecting to the rostral ventrolateral medulla (CeA-RVLM) were investigated, and cytosolic calcium responses in primary neuronal cultures were quantified. We demonstrate that in Sprague Dawley rats, local brain metabolism of ethanol in the CeA to acetic acid/acetate elicits sympathoexcitatory responsesin vivothrough activation of NMDA receptor (NMDAR). Alcohol dehydrogenase or aldehyde dehydrogenase inhibition using fomepizole or cyanamide and NMDAR antagonism using AP5 or memantine blunted these effects. Whole-cell patch-clamp recordings in brain slices containing autonomic CeA-RVLM neurons revealed a dose-dependent increase in neuronal excitability in response to acetate. NMDAR antagonists suppressed the acetate-induced increase in CeA-RVLM neuronal excitability, and memantine suppressed the direct activation of NMDAR-mediated inward currents by acetate in brain slices. We observed that acetate increased cytosolic Ca2+in a time-dependent manner in primary neuronal cell cultures. The acetate enhancement of calcium signaling was abolished by memantine. These findings suggest that within the CeA, ethanol is sympathoexcitatory through local brain metabolism, which generates acetic acid/acetate leading to activation of NMDAR.

NEW AND NOTEWORTHY

Brain ethanol metabolism to acetic acid (vinegar)/acetate causes activation of N-methyl-D-aspartate receptors (NMDARs) in the central nucleus of the amygdala and elicits sympathoexcitatory responses. This excitatory mechanism is opposite to the inhibitory effects of ethanol at NMDAR. Understanding the active compounds that arise from ethanol metabolism, and the molecular mechanisms by which they influence alcohol reward and cardiovascular function, may be beneficial in developing targeted intervention strategies for both alcohol use disorder and its cardiovascular sequelae.

Graphical Figure

Proposed mechanisms for ethanol and acetate induced increases in sympathoexcitation within the central nucleus of the amygdala (CeA). Abbreviations: Acetic acid (HOAc), acetate (-OAc), ADH (alcohol dehydrogenase), ALDH (aldehyde dehydrogenase), BBB (blood brain barrier), FOM (fomepizole), CYAN (cyanamide), CYP450 (cytochrome P450), IML (intermediolateral nucleus), RVLM (rostral ventrolateral medulla), SNA (sympathetic nerve activity).