Locally‐generated acetaldehyde contributes to the effects of ethanol on neurosteroids and long‐term potentiation in the hippocampus

Aim As severe alcohol intoxication impairs memory function, a high concentration of ethanol (60 mmol L−1) acutely inhibits long-term potentiation (LTP), a cellular model of learning and memory, in rat hippocampal slices. Neurosteroids are involved in this LTP inhibition. We recently reported that the inhibitory effects of 60 mmol L−1 ethanol are blocked by 4-methylpyrazole (4MP), an inhibitor of alcohol dehydrogenase, suggesting that acetaldehyde locally generated within the hippocampus participates in LTP inhibition. We investigated whether acetaldehyde generated by ethanol metabolism contributes to neurosteroidogenesis and LTP inhibition. Results Like 60 mmol L−1 ethanol, we found that exogenous acetaldehyde enhanced neurosteroid immunostaining in CA1 pyramidal neurons, and that augmented neurosteroid immunostaining by high ethanol alone was blocked by 4MP, but not by inhibitors of other ethanol metabolism pathways. The inhibitory effects of 60 mmol L−1 ethanol on LTP were mimicked by a lower concentration of ethanol (20 mmol L−1) plus acetaldehyde (60 μmol L−1), although neither agent alone was effective at these concentrations, suggesting that 60 mmol L−1 ethanol inhibits LTP through multiple actions, one of which involves acetaldehyde and the other of which requires just 20 mmol L−1 ethanol. The effects of ethanol and acetaldehyde on neurosteroid staining and LTP were overcome by inhibition of neurosteroid synthesis and by blockade of N-methyl-D-aspartate receptors (NMDAR). Conclusion These observations show that acetaldehyde generated by local ethanol metabolism within the hippocampus serves as a signal for neurosteroid synthesis in pyramidal neurons, and participates in the synaptic dysfunction associated with severe alcohol intoxication.