The effects of intoxicating doses of ethanol upon intermediary metabolism in rat brain

Effects of ethanol on brain metabolism

The influence of acute or chronic ethanol administration on the biochemical processes in brain and cerebral metabolic pathways has been discussed. Ethanol seems to affect cerebral carbohydrate metabolism mainly through increased glycogenolysis, although the possibility of decreased cerebral glucose utilization remains eminent. Ethanol affects the consumption of oxygen by the brain tissue presumably through alterations in the brain cell membranes. Inhibition of Na+-K+-ATP-ase observed during ethanol intoxication is suspected to result in alterations in the membranes of the nerve cells. Isotope studies in addition to total respiratory carbon dioxide production strongly suggest the inhibition of citric acid cycle function during ethanol metabolism. Although synthetic pathways for lipids do not seem to be affected by ethanol, lipid oxidation in the cerebral tissue is significantly inhibited. In addition to above mentioned alterations in the cerebral metabolic processes, ethanol also affects ionic transport processes, adenine nucleotides, and amino acid and protein metabolism. The metabolic consequences of such effects of ethanol have been discussed.

Metabolic correlates of ethanol, acetaldehyde, acetate and methanol in humans and animals

Following the administration of alcoholic beverages, ethanol exerts a number of direct and indirect effects on the body and in turn, ethanol is itself metabolized. Liver and brain are twomajor organs which are immediately concerned with the effects of ethanol. Ethanol acts as CNS depressant and as a source of energy. Since the metabolism of ethain the liver proceeds at a constant rate until completion,acetate is produced regardless of energy requirements of the body. Thus, ethanol plays the role of an aberrant nutrient. Although ethanol has no effect on oxygen consumption in the liver, it severely suppresses the productionof carbon dioxide in the Krebs cycle resulting in the corresponding suppressionof respiratory quotient. This indicates that ethanol diverts the utilizationof oxygen for the oxidationof reducing, equivalents which accumulate as a consequence of increased formation of NADH. This is reflected in the shift from the oxidative to reductive components of a number of oxido-reductive couples, e.g.: pyruvate-lactate, oxaloacetate-malate and acetoacetate-beta-hydroxybutyrate. These actions of ethanol are exarcerbated by the fact that the metabolism of ethanol is also associated with the diversion of the availability of a number of enzymes and coenzymes from the metabolism of endogenous substrates towards the metabolism of metabolites of ethanol, thus resulting in the competitive inhibitionof a number of enzyme catalyzed reactions, e.g., inhibition of methanol metabolism during long-term consumption resulting in the acumulation of methanol in body fluids; shift in the peripheral metabolism of biogenic amines from oxidative to reductive pathways; and formation of aberrant neurotransmitters (in vitro); inhibition of the oxidation of fatty acids in the liver...

Induction of physical dependence on alcohol in rodents

An ethanol withdrawal syndrome consisting of tremors and seizures can be induced in rats and mice. This syndrome closely resembles the physical signs observed in human patients during alcohol withdrawal. The criteria for an animal model of a human disease appear to be fulfilled regarding the etiological agent, course of illness, the similarity of physical and electrophysiological manifestations and response to therapeutic agents. Therefore these models should lend themselves for the elucidation of the pathogenesis at the molecular level of biological organization and for the development of new therapeutic approaches. Criteria for an optimal animal model of ethanol dependence are outlined. Withdrawal signs are classified into minor (startle threshold and exploratory behavior) and major types (tremors and seizures). Methods for quantification of tremors and seizures are described. The procedures for induction of the major withdrawal signs are classified according to the mode of ethanol administration designed to circumvent the animal's inherent aversion to the taste of ethanol: Oral (free feeding, behavioral modifications of free feeding and force feeding), parenteral and inhalation. Auxiliary procedures consist of pyrazole administration and weight reduction resulting in a decreased rate of ethanol metabolism. Exposure to low environmental temperatures increases consumption of ethanol containing diets without proportionately increasing the rate of ethanol metabolism. Auxiliary procedures for the induction of seizures during withdrawal consist of handling the animals and audiogenic stimuli. Advantages and limitations of various rodent models are evaluated in terms of the procedures (practicability, compounding variables) and their results (reproducibility, severity and yield of major withdrawal signs, objective quantification). It is concluded that none of the current methods fulfill all requisites for all types of experiments. The selection of methods best suited for a particular experiment depend upon its objectives.