Hippocampal Physiological and Behavioral Deficits Related to Alcohol‐induced Disruption of Local Blood Perfusion

Abstract

Despite preventative education, moderate‐heavy episodic alcohol (ethanol; EtOH) intake, such as in “binge” drinking, remains a major public health problem. Binge drinking, can lead to blood ethanol levels above legal intoxication and cause alcohol‐induced blackouts (AIB), a form of amnesia linked to dysfunction of the hippocampal CA1 region. The neurobiological bases of AIB, however, remain largely unknown. It is noteworthy that proper function of neurons in the brain, including the CA1 region, critically depends on aerobic metabolism and optimal blood flow (BF). Using rodent models, we previously showed that EtOH at intoxicating concentrations constricted cerebral arteries independently of circulatory, metabolic, and endothelial factors, but due to drug inhibition of large conductance Ca2+‐ and voltage‐gated K+ (BK) channels present in vascular smooth muscle. Using behavioral modeling of contextual fear conditioning with miniscope technology, the present study tests the hypothesis that EtOH‐induced anterograde memory dysfunction is coincidental to EtOH‐induced reduction in local blood flow and reduced neuronal activity in the CA1 region. Thus, we used Ca2+‐release imaging to map single neuron activity in combination with dynamic local BF recordings in awake and freely moving mice to simultaneously determine vascular, neurophysiological and behavioral effects of EtOH in a mouse model of AIB. Ca2+ imaging was conducted using GCaMP6, which provided a blue fluorescent light when neurons released Ca2+, indicating action potentials, while rhodamine dextran dye provided a red label for the vasculature within the CA1. AIB was modeled via contextual fear conditioning, in which mice were exposed to electric shocks after receiving intraperitoneal injections (IP) of saline or EtOH. Twenty‐four hours later, animals were placed into the same boxes, and their freezing behavior was recorded. Data revealed that IP injection of 2 mg/kg EtOH evoked a robust (>50%) decrease in Ca2+ fluorescence which was coincidental to an 18% decrease in cerebral artery diameter. Reductions in neuronal activity and cerebral artery diameter were, indeed, accompanied by a 42.3% reduction in freezing behavior (P>0.05). Thus, this study identifies both vascular and neurophysiological components of EtOH action on the hippocampus CA1 region in a behavioral model of AIB. More generally, our study is the first to investigate the simultaneous effects of EtOH on behavior, including anterograde memory, neuronal activity, and local BF dynamics in the brain.