Intraneuronal Acidification with Acetic Acid, an Ethanol Metabolite, Increases Excitability of Central Nucleus of Amygdala Neurons with Axon Projecting to Rostral Ventrolateral Medulla (CeA‐RVLM)

We have reported that activation of central nucleus of amygdala (CeA) is involved in the in vivo sympathoexcitatory and pressor responses to acute local challenge of acetate, the ethanol metabolite. However, the underlying neural mechanisms have not been determined. Evidence indicates weak organic acids are capable of decreasing intracellular pH due to intracellular transport of the organic acid and alternating neuronal activity. Recently, we have found that bath application of acetate caused a dose dependent increase in the in vitro excitability of CeA neurons with axon projecting to rostral ventrolateral medulla (CeA‐RVLM), which may underlie the mechanisms of increased sympathetic outflow in response to acetate challenge. We hypothesized that intraneuronal acidification due to intracellular transport of acetic acid may be a contributing factor. The role of intraneuronal acidification with the ethanol metabolite acetic acid was investigated under brain slice preparation. Specifically, we compared the action potential firing rate, depolarizing input resistance (R input ), and voltage threshold (V t ) for firing action potentials between control intracellular recording solution (pH = 7.35) and 7.5 mM acetic acid loaded intracellular recording solution (pH = 5.20). In current‐clamp recordings, graded current injections evoked graded increases in discharge frequency among neurons from both groups. Maximum discharge evoked by +250 pA current injection in the 7.5 mM acetic acid loaded (pH = 5.20) group was 31 ± 1 Hz (n=6), which was significantly greater (P < 0.05) than that of controls group (pH = 7.35, 19 ± 1 Hz, n=7). Intraneuronal acidification with 7.5 mM acetic acid significantly (p < 0.05) increased R input of CeA‐RVLM neurons (731 ± 64 MΩ) compared to control (531 ± 48 MΩ). Likewise, 7.5 mM acetic acid caused a significant (p < 0.05) hyperpolarizing shift in V t (−49.28 ± 1.37 mV) compared to control neurons (−43.83 ± 1.76 mV). In cultured neurons incubated with a pH sensitive probe, increases in bath application of acetate (7.5 mM) significantly (p < 0.05) increased the corrected fluorescence intensity of the neurons compared to control, indicative of a decrease in intraneuronal pH. This data suggests that extracellular acetate leads to intraneuronal acidification via transport of acetic acid which has profound effects on CeA‐RVLM membrane properties that enhance neuronal excitability and may contribute to the mechanism underlying alcohol associated sympathetic activation and hypertension. Support or Funding Information 11SDG7420029 (ZYS) and R15‐HL122952 (QHC)