Role of microglia in ethanol-induced neurodegenerative disease: Pathological and behavioral dysfunction at different developmental stages

Alcohol abuse can result in significant alterations to the structure of the brain and ultimately to behavioral dysfunctions. Epidemiological studies have shown that alcoholism is closely associated with impaired memory and judgment. However, the degree of deficit (brain injury) depends on factors such as the age of onset, duration of heavy drinking, continuous versus periodic (binge) drinking and the typical amount consumed per session. In recent years, neuroinflammation has been proposed as one of the alcoholism-induced neuropathological mechanisms, since increased levels of microglial markers are observed in the brains of both post-mortem human alcoholics and various alcohol-treated animals, from newborn or adolescent rodents to adult rodents. Many studies have investigated how microglia modulate alcohol-induced behavioral changes such as cognitive deficits, abnormal locomotor activity, motor impairment and mood disturbance. Importantly, we try to characterize and compare the distinct features in different ethanol (EtOH)-induced neurodegenerative disease (NDD) models. Moreover, mounting evidence indicates that in response to certain environmental toxins, microglia can become over-activated under oxidative stress, releasing pro-inflammatory mediators that cause central nervous system (CNS) disease. The molecular mechanisms involve free radical formation and the release of pro-inflammatory cytokines that are detrimental to neighboring neurons and interfere with the molecules regulating cell–cell interactions. The identification and understanding of the cellular and molecular mechanisms of microglial activation are described, as well as multiple downstream targets, in different alcohol-treated animal models. This review might contribute to the development of treatments and/or therapeutic agents that can reduce or eliminate the deleterious effects of alcohol-induced NDD.