Circadian Mechanisms in Alcohol Use Disorder and Tissue Injury

Heavy use of alcohol can lead to addictive behaviors and to eventual alcohol‐related tissue damage. While increased consumption of alcohol has been attributed to various factors including level of alcohol exposure and environmental factors such as stress, data from behavioral scientists and physiological researchers are revealing roles for the circadian rhythm in mediating the development of behaviors associated with alcohol use disorder as well as the tissue damage that drives physiological disease. In this work, we compile recent work on the complex mutually influential relationship that exists between the core circadian rhythm and the pharmacodynamics of alcohol. As we do so, we highlight implications of the relationship between alcohol and common circadian mechanisms of effected organs on alcohol consumption, metabolism, toxicity, and pathology.     

Effects of Ethanol on Glucose Transporter Expression in Cultured Hippocampal Neurons

Glucose transport was studied in primary hippocampal neuron cultures exposed to ethanol. Immunofluorescent staining with antibodies against neuron-specific enolase and glial fibrillary acidic protein identified ∼95% of the cultured cells as neurons. Western blot analysis was conducted with polyclonal antisera to glucose transporter isoforms GLUT1 and GLUT3. As previously seen in astrocytes, GLUT1 protein was regulated by the culture medium glucose content. Exposure to 50 and 100 mM of ethanol for 5 hr induced dose-dependent reductions in GLUT1 and GLUT3 protein. In contrast, GLUT1 mRNA abundance was increased relative to controls under the same conditions. Glucose uptake, measured with the nonmetabolized analog, 2-deoxy- d -glucose, was reduced by 50 and 100 mM of ethanol in four experiments. These results indicate a direct effect of ethanol on neuronal glucose transporter expression, which may play a role in the neurotoxic effects of alcohol.     

Alcohol Withdrawal in Rats Is Associated with a Marked Fall in Extraneuronal Dopamine

Withdrawal of rats from chronic ethanol (2-5 g/kg, every 6 hr for 6 days) resulted in withdrawal symptomatology and dramatic fall in extracellular dopamine (DA) in the ventral striatum as measured by microdialysis. The changes in DA output paralleled the withdrawal symptomatology and both phenomena were reversed by a challenge ethanol dose (5 g/kg orally). The results suggest that the decrease in DA output may be responsible for the aversive symptoms of withdrawal.     

Ethanol Inhibition of AMPA and Kainate Receptor-Mediated Depolarizations of Hippocampal Area CA1

Longitudinal hippocampal slices were prepared from adult female rats. The excitatory amino acids, α-amino-3-hydroxy-5-methyl-4-isoxazole propionate (AMPA) and kainic acid, were applied to area CA1, and the resulting depolarizations were measured using the grease-gap electrophysiological technique. Agonist dose-response curves were generated in the presence and absence of various concentrations of ethanol. Ethanol (25–200 mM) significantly attenuated the depolarizations that were produced by each agonist. In addition, we found that ethanol potently antagonized kainate-induced depolarizations across the agonist concentration-response curve, whereas it significantly suppressed only AMPA responses that were induced with moderate-to-high agonist concentrations.
These results indicate that ethanol has potent antagonist actions against non- N -methyl- d -aspartate (NMDA) excitatory amino acid-induced neuronal depolarizations in hippocampal area CA1. Moreover, the relative potency of ethanol depends on the specific excitatory agonist tested and the concentration of that agonist. This suggests that, in addition to the known effects of ethanol on NMDA receptor-mediated activity, it may also potently attenuate ongoing "fast" glutamatergic synaptic activity in the hippocampus.     

Repeated Ethanol Withdrawal Delays Development of Focal Seizures in Hippocampal Kindling

Clinical studies report an increase in the prevalence of alcohol withdrawal-related seizures in patients with a history of multiple detoxifications. In order to investigate the alcohol withdrawal-related alterations in neural activity that lead to this increase in seizure propensity, basic researchers have examined both spontaneous and elicited seizures in animals undergoing withdrawal from chronic ethanol. This study was designed to further examine alcohol withdrawal-related seizure activity in a rodent model by assessing the development of electrical kindling after chronic ethanol exposure administered in multiple or single treatment episodes. Laboratory rats were exposed to either five periods of 3 days of ethanol, one 15-day period of continuous ethanol, or a period of control handling with no ethanol exposure. Ten days after a final withdrawal episode, all animals were surgically prepared with recording and stimulating electrodes. Twenty days after final withdrawal from ethanol or an equivalent period of similar handling, daily electrical stimulation of hippocampal area CA3 was initiated. Animals exposed to ethanol required more daily stimulations to become fully kindled than did ethanol-naive controls, with those animals experiencing five withdrawals requiring the most stimulations overall and more stimulations to progress from focal to generalized seizure behaviors. These results indicate that chronic ethanol exposure and withdrawal alter neuronal mechanisms important for hippocampal kindling in a manner that persists long after cessation of ethanol exposure, and they indicate that this effect is increased by exposure to repeated withdrawal episodes.     

Low Doses of Ethanol Impair Spatial Working Memory and Reduce Hippocampal Theta Activity

Low doses of ethanol can alter neural activity in the septohippocampal pathway, a pathway critical for spatial working memory. The present study was designed to determine whether acute ethanol induces impairments in working memory and disrupts septohippocampal function as measured by the hippocampal theta rhythm. Rats were preoperatively trained on delayed alternation. A within-subject design was used to evaluate the effects of ethanol (0.25,0.5, 0.75 and 1.0 g/kg, intraperitoneally) on performance 10 min and 90 min after injection as compared with preinjection baseline. Ethanol produced dose-, delay-, and time-dependent impairments in working memory as indicated by a change in choice accuracy in the delayed alternation task. Ethanol did not affect performance time, the ability to complete the task, or response bias. Thus, the impairment does not appear to result from a decrement in general performance, but rather from an impairment in spatial working memory. Hippocampal theta activity was suppressed by ethanol at the same doses, 0.75 g/kg and 1.0 g/kg, that impaired working memory. The interaction of ethanol with functions of the septohippocampal pathway are discussed.