Adolescent ethanol exposure decreases cholinergic markers, blunts behaviorally-evoked acetylcholine and increases in apical dendritic branching within the orbital frontal cortex

Kipp, BT; Nunes, PT; Galaj, E; Hitchcock, B; Nasra, T; Poynor, KR; Heide, SK; Reitz, NL; Savage, LM

During adolescence, heavy binge-like ethanol consumption can lead to frontocortical structural and functional impairments. These impairments are likely driven by adolescence being a critical time point for maturation of brain regions associated with higher-order cognitive functioning. Rodent models of heavy binge-like ethanol exposure show consistent disruptions to the typical development of the prefrontal cortex (PFC). All deep cortical layers receive cholinergic projections that originate from the Nucleus basalis of Meynert (NbM) complex. These cholinergic projections are highly involved in learning, memory, and attention. Adolescent intermittent ethanol exposure (AIE) induces cholinergic dysfunction as a result of an epigenetic suppression of the genes that drive the cholinergic phenotype. The current study used a model of AIE to assess structural and functional changes to the frontal cortex and NbM following binge-like ethanol exposure in adolescence. Western blot analysis revealed long-term disruptions of the cholinergic circuit following AIE: choline acetyltransferase (ChAT) was suppressed in the NbM and vesicular acetylcholine transporter (VAChT) was suppressed in the orbitofrontal cortex (OFC). In vivo microdialysis for acetylcholine efflux during a spatial memory task determined changes in cholinergic modulation within the PFC following AIE. However, AIE spared performance on the spatial memory task and on an operant reversal task. In a second study, Golgi-Cox staining determined that AIE increased apical dendritic complexity in the OFC, with sex influencing whether the increase in branching occurred near or away from the soma. Spine density or maturity was not affected, likely compensating for a disruption in neurotransmitter function following AIE. Significance Statement Adolescent ethanol exposure decreases cholinergic markers in the basal forebrain to orbital frontal cortical circuit, which lead to a massive suppression of behaviorally-activated tonic release acetylcholine and sex-dependent increases in dendritic branching. We concluded that cholinergic dysfunction is a contributor to cognitive impairments associated with heavy alcohol exposure during adolescence. Data Sharing The data that support the findings of this study are available from the corresponding author upon reasonable request.