Hippocampal fear engrams modulate ethanol-induced maladaptive contextual generalization in mice.

The compounding symptomatology of comorbid alcohol use disorder (AUD) and post-traumatic stress disorder (PTSD) gives rise to an interaction of maladaptive neurobiological processes, the etiology of which remains elusive. Here, we devised an optogenetic strategy aimed at rescuing maladaptive responses to fearful stimuli in male c57BL/6 mice following chronic ethanol administration and forced abstinence. In the first experiment, we confirmed that fear acquisition and maladaptive contextual generalization was potentiated in ethanol-exposed mice during fear conditioning and exposure to a novel environment, respectively. In the second experiment, using an activity-dependent tet-tag system, we labeled and artificially inhibited the neural ensemble selectively activated by contextual fear conditioning in the dorsal hippocampus to attenuate behavioral dysfunctions resulting from ethanol exposure. We found that acute optogenetic inhibition during exposure to a novel environment suppressed maladaptive generalization in ethanol-exposed mice. These results provide further evidence for a crucial link between ethanol exposure and impaired fear memory processing by providing cellular and behavioral insights into the neural circuitry underlying AUD and PTSD comorbidity.