EFFECTS OF MODERATE ALCOHOL-CONSUMPTION ON THE CENTRAL-NERVOUS-SYSTEM

The concept of moderate consumption of ethanol (beverage alcohol) has evolved over time from considering this level of intake to he nonintox icating and noninjurious, to encompassing levels defined as ''statisti cally'' normal in particular populations, and the public health-driven concepts that define moderate drinking as the level corresponding to the lowest overall rate of morbidity or mortality in a population. The various approaches to defining moderate consumption of ethanol provid e for a range of intakes that can result in blood ethanol concentratio ns ranging from 5 to 6 mg/dl, to levels of over 90 mg/dl (i.e., simila r to 20 mM). This review summarizes available information regarding th e effects of moderate consumption of ethanol on the adult and the deve loping nervous systems. The metabolism of ethanol in the human is revi ewed to allow for proper appreciation of the important variables that interact to influence the level of exposure of the brain to ethanol on ce ethanol is orally consumed. At the neurochemical level, the moderat e consumption of ethanol selectively affects the function of GABA, glu tamatergic, serotonergic, dopaminergic, cholinergic, and opioid neuron al systems. Ethanol can affect these systems directly, and/or the inte ractions between and among these systems become important in the expre ssion of ethanol's actions. The behavioral consequences of ethanol's a ctions on brain neurochemistry, and the neurochemical effects themselv es, are very much dose- and time-related, and the collage of ethanol's actions can change significantly even on the rising and falling phase s of the blood ethanol curve. The behavioral effects of moderate ethan ol intake can encompass events that the human or other animal can perc eive as reinforcing through either positive (e.g., pleasurable, activa ting) or negative (e.g., anxiolysis, stress reduction) reinforcement m echanisms. Genetic factors and gender play an important role in the me tabolism and behavioral actions of ethanol, and doses of ethanol produ cing pleasurable feelings, activation, and reduction of anxiety in som e humans/animals can have aversive, sedative, or no effect in others. Research on the cognitive effects of acute and chronic moderate intake of ethanol is reviewed, and although a number of studies have noted a measurable diminution in neuropsychologic parameters in habitual cons umers of moderate amounts of ethanol, others have not found such chang es. Recent studies have also noted some positive effects of moderate e thanol consumption on cognitive performance in the aging human. The mo derate consumption of ethanol by pregnant women can have significant c onsequences on the developing nervous system of the fetus. Consumption of ethanol during pregnancy at levels considered to be in the moderat e range can generate fetal alcohol effects (behavioral, cognitive anom alies) in the offspring. A number of factors-including gestational per iod, the periodicity of the mother's drinking, genetic factors, etc.-p lay important roles in determining the effect of ethanol on the develo ping central nervous system. A series of recommendations for future re search endeavors, at all levels, is included with this review as part of the assessment of the effects of moderate ethanol consumption on th e central nervous system.