Adolescent alcohol exposure produces long-lasting alterations in neuroimmune signaling that bias the brain toward a proinflammatory state that persists into adulthood. Adolescent intermittent ethanol (AIE) exposure leads to sustained astrocyte and microglial activation in the frontal cortex, mediated through the release of HMGB1 (Cullen and Halliday, 1994; Marshall et al., 2020; Crews et al., 2025). HMGB1 is a damage-associated molecular pattern (DAMP) that activates innate immune responses. This persistent neuroinflammation is linked to cognitive deficits and increased risk for substance use disorder later in adulthood (Crews et al., 2015; Coleman et al., 2018). Glycyrrhizic acid, an FDA approved food additive derived from licorice root, binds HMGB1 and inhibits its proinflammatory signaling (Mollica et al., 2007). We hypothesized that AIE would result in tolerance-like behavior and elevate neuroimmune cell density and HMGB1 expression, and both changes would be reversed by glycyrrhizic acid treatment. Male and female Wistar rats were randomly assigned to AIE or control groups, receiving ethanol or water on a 2-day-on/2-day-off schedule from PND 25-54. Post alcohol exposure, rats received glycyrrhizic acid (1.0 g/L) or vehicle with water from PND 56-95. Within the female cohorts specifically, ethanol response battery (ERB) was performed to assess ethanol sensitivity and tolerance. Through this behavioral testing, measures taken included behavioral intoxication, body temperature (hypothermia), blood ethanol concentration, tilting plane balance, loss of righting reflex (LORR), and baseline HMGB1 plasma levels. Following behavioral assessment, immunohistochemistry was performed for HMGB1, GFAP, an astrocytic activation marker, and CD11b, a microglial activation marker, in the frontal cortex with analysis specifically in the anterior insula and orbitofrontal cortex subregions. Glycyrrhizic acid administration following AIE exposure reversed tolerance-like behaviors to control levels in female Wistar rats. Additionally, the AIE paradigm resulted in increased HMGB1 expression along with astrocyte and microglial activity across subregions of the prefrontal cortex with no significant difference between sexes. This increase in HMGB1 expression and neuroinflammation was reversed with glycyrrhizic acid treatment. AIE caused a persistent tolerance-like phenotype and cortical neuroimmune activation. Administration of glycyrrhizic acid will suppress HMGB1 signaling and reduce microglial and astrocyte activation in the frontal cortex, and reverse alcohol tolerance in adulthood. These findings support the role of HMGB1 as a therapeutic target for alcohol-induced neuroimmune dysfunction.
Kaitlyn Campbell (Wed,) studied this question.