Alterations of fast-reacting sulfhydryl groups of rat brain microsomes by ethanol

The neurotoxicity of ethanol

Alterations in nervous system functioning following acute and chronic ethanol exposure have been studied in a great number of experimental investigations. Results from many of these investigations can be difficult to interpret, particularly since a variety of techniques and exposure models are employed. This review emphasizes those studies which, in the opinion of the author, fit into a pattern where results from studying one function of the nervous system is in accordance with results from studying another. Thus, the fluidizing effect of ethanol on the neuronal membrane - an effect which ethanol shares with anaesthetics - leads to a change in protein function which in turn affects ion transport such as Na+ and Ca++ across the membrane due to changes in the ion channels. Cation influx is probably directly coupled to neurotransmitter release which is in agreement with the finding that ethanol exposure results in inhibition of Na+ and Ca++ current as well as acetylcholine release. The sensitization of the dopaminergic system after ethanol exposure may also be related to the changes in cation flux, and the changes in this system probably play a crucial rôle in the development of tolerance and withdrawal symptoms. Other aspects such as impairment of protein synthesis, altered GABA function of impairment of neuron excitability and conduction are more difficult to place in proper perspective. The rôle of acetaldehyde in acute as well as chronic ethanol intoxication also remains a controversy. These may, however, be secondary phenomena to primary changes in different part of the nervous system not necessarily important in the clinical situation. Behavioural and anatomical studies particularly from recent years have shown that experimental animals develop memory disturbances following chronic exposure even when kept on sufficient diet. These findings argue strongly for a direct toxic effect of ethanol, and are furthermore compatible with behavioural changes in chronic alcoholics, dominated by memory impairment. Since it has been argued that the cholinergic system plays a significant rôle for memory function, a possible explanation for some of the psychological and anatomical deficits caused by ethanol is thus the changes in the function of the cholinergic system particularly in the hippocampal regions.

Ethanol causes increases in excitation and inhibition in area CA3 of the dorsal hippocampus

The effects of ethanol on synaptic transmission in hippocampus were studied by changes in the response of CA3 pyramidal cells to stimulation of two afferent pathways, the dentate (mossy fiber) pathway, and the commissural pathway. Both sources produce an excitatory response as measured either by single unit spiking or by population spike followed by a period of post-stimulus inhibition (PSI). After the injection of 3 g/kg ethanol (i.p.), both the excitatory responses and the duration of PSI are significantly increased. Because these changes occur in both afferent pathways, they are not pathway specific, but may be the result of the local microcircuitry in area CA3. Although the change in excitatory and inhibitory responses can occur simultaneously, detailed statistical analyses show that neither the magnitude nor onset times are correlated. Thus, the two responses are functionally separable. In addition, the increase in the duration of PSI is related to the rate of rise of blood ethanol level and shows short-term tolerance. The maximum change in the PSI occurs after blood ethanol levels plateau suggesting a secondary process is necessary before neurophysiological effects are apparent.

Alcohol abuse, anaesthesia, and intensive care

The biochemistry, pharmaco-kinetics, and pathophysiology of alcohol and alcoholism are reviewed and approaches to the clinical management of coma, alcohol withdrawal, and anaesthesin are considered.

Role of calcium in ethanol-membrane interactions: a model for tolerance and dependence

The calcium content of membranes may regulate a number of key neuronal processes. Studies are described in which acute and chronic administration of ethanol was shown to alter calcium binding to synaptosomal plasma membranes.