Excessive ethanol consumption, characteristic of alcohol use disorders (AUDs), is associated with widespread neurodegeneration and cognitive and behavioral impairments that may contribute to the chronic and relapsing nature of alcoholism. Therefore, identifying novel targets that can afford neuroprotection will undoubtedly aid current treatment strategies for AUDs. The cannabinoids have been shown to provide neuroprotection in a variety of preclinical models of neurodegeneration; however minimal data is available regarding the use of cannabinoid-based pharmacotherapies for treating ethanol-induced neurodegeneration. Therefore, the current dissertation examined the overarching hypothesis: the cannabinoids are a therapeutic strategy to afford neuroprotection in the context of ethanol-induced neurodegeneration. Importantly, this overarching hypothesis was approached with translational considerations in mind. Specifically, the use of many cannabinoids in the clinic is hindered due to multiple unfavorable pharmacokinetic/pharmacodynamic profiles, including high first pass metabolism and untoward psychoactivity. Therefore, the studies herein were designed to circumvent these PK/PD obstacles. The first set of studies examined whether transdermal delivery of the phytocannabinoid, cannabidiol (CBD), could attenuate binge ethanol induced neurodegeneration. Transdermal CBD afforded neuroprotection in the entorhinal cortex and neuroprotection was similar in magnitude as intraperitoneal administration. The second set of studies found that binge ethanol treatment transiently down-regulated the main CNS cannabinoid receptor, CB1R. Interestingly, these changes were not accompanied by alterations in one of the major endogenous ligands, anandamide (AEA), or other related n-acylethanolamides (NAEs). The latter finding is in contrast to other literature reports demonstrating that endocannabinoid content is substantially elevated in response to a CNS insult. Nevertheless, studies were carried out to determine if administration of the AEA and NAE catabolism inhibitor, URB597, could attenuate binge ethanol induced neurodegeneration. URB597 failed to produce neuroprotection in the entorhinal cortex and dentate gyrus of the hippocampus. However, additional studies found that URB597 failed to elevate AEA in the entorhinal cortex, and in general the biological activity of URB597 was impaired by ethanol exposure. Therefore, with further drug discovery/development efforts, it may be feasible to optimize such treatment strategies. In conclusion, the studies within the current dissertation demonstrated the feasibility of using some cannabinoid-based agents to prevent ethanol-induced neurodegeneration.

Chronic ethanol exposure results in neuroadaptations that drive the progression of an alcohol use disorder (AUD). One such driving force is alcohol-induced neurodegeneration. Neuroinflammation has been proposed as a mechanism underlying this damage. Although neuroinflammation is a physiological response to damage, overactivation of its pathways can lead to neurodegeneration. A hallmark indicator of neuroinflammation is microglial activation, but microglial activation is a heterogeneous continuum of phenotypes that can promote or inhibit neuroinflammation. Furthermore acute microglial activation is necessary to restore homeostasis, but prolonged activation can exacerbate damage. The diversity of microglia makes both the level and timecourse of activation vital to understanding their role in damage and/or recovery. The current set of experiments examines the effects of ethanol on microglia within the hippocampus and entorhinal cortex in a binge model of alcohol-induced neurodegeneration. In the first set of experiments, the phenotype of microglia activation was assessed using Raivich’s 5-stages of activation that separates pro- and anti-inflammatory forms of microglia. Morphological and functional assessments suggest that ethanol does not elicit classical microglial activation but instead induces partially activated microglia. In the second set of experiments, the earliest signs of microglial activation were determined to understand the initiation of microglial activation. Experiments indicated that activation occurred subsequent to previous evidence of neuronal damage; however, activation was accompanied by a loss of microglia and the discovery of dystrophic microglia. The final set of experiments examined whether alcohol-induced partial activation of microglia would show a differential response with further alcohol exposure. Experiments showed that animals previously exposed to ethanol showed a greater response to a second ethanol insult. Overall, these studies suggest that although alcohol may initially interrupt the normal microglia response, during abstinence from ethanol a partial activation phenotype appears that may contribute to recovery. Once activated, however, data suggest that these microglia are primed and upon subsequent exposure show an increased response. This heterogeneous microglial response with respect to time does not necessarily reflect a neuroinflammatory response that would be neurodegenerative but does imply that chronic ethanol consumption affects the normal neuroimmune system.