Chronic ethanol exposure alters dopaminergic signal transduction processes

Intracerebroventricular infusion of angiotensin II increases water and ethanol intake in rats

The influence of prolonged ingestion of ethanol on stimulation of water or ethanol intake by intracerebroventricular infusion of ANG II was evaluated in rats. Animals were maintained for 5-6 mo with either 10% ethanol solution or water as their only source of fluid. In both groups of rats, infusion of ANG II caused a large increase in water intake (7-fold) and a lesser increase in 10% ethanol intake (2-fold). The effect of ANG II on the volume of ethanol solution ingested, however, was inversely related to the concentration of the ethanol solution. As the concentration of ethanol solution was decreased, frequency and duration of drinking bouts increased. The intake of sweetened 10% ethanol solution or commercially produced wine during infusion of ANG II was similar to the intake of 10% ethanol and not related to taste preference. In conclusion, chronic consumption of ethanol solution did not appear to adversely effect ANG II stimulation of water intake. The intake of ethanol solution during infusion of ANG II was inhibited by a direct effect of ingested ethanol and/or by indirect effect from metabolized ethanol.

Alcohol and the brain: setting the benefit/risk balance

This article reviews the literature and presents some unpublished data on the CNS effects of alcohol at doses not producing tolerance and dependence. The available evidence indicates that the effect of low doses of ethanol may qualitatively differ from those produced in animal models mimicking alcoholism. For example, rats exposed for two months to alcohol in drinking water at a concentration (3%) not inducing tolerance or dependence, as assessed by lack of withdrawal signs upon treatment suspension, appear to be less stressed in the two-way avoidance-learning tests. Accordingly, the treated rats perform better and learn faster than sucrose-fed controls, while this behavior is disrupted by high levels of ethanol intake. These initial observations suggest that discontinuity may exist between the effects of low and high doses of this substance and underscore the need to expand research on the effects of alcohol on the CNS to include the bottom end of the dose-response curve.

Alcohol impairs age-dependent adaptation of human lymphocyte beta-adrenergic receptors

Lymphocyte beta-adrenergic receptor function and norepinephrine (NE) plasma concentration have been compared in normal subjects and in ethanol-addicted patients of different ages. Direct measurement of the density and properties of beta-adrenoceptors in membrane fractions was performed using the radioligand 125I-Iodocyanopindolol (ICYP). In normal subjects beta-receptor density decreased and norepinephrine plasma concentration increased with age. There was a statistically significant negative correlation between plasma norepinephrine and beta-receptor number. In ethanol-addicted patients the age-related modification in beta-receptor number and the correlation between plasma norepinephrine and beta-receptor density were lost, in spite of the fact that the increase of NE plasma concentration was still present. The ethanol-induced effects in lymphocyte beta-receptor may have consequences on immunological function and may be qualitatively similar to alterations in other tissues not routinely accessible in humans.

Altered calcium signal transduction after chronic ethanol consumption

Calcium and calcium-calmodulin dependent phosphorylation of several protein bands was found altered in synaptosomal membranes prepared from ethanol treated rats. The ethanol induced effect on Ca++ and Ca++-calmodulin phosphorylation presented regional differences. In particular 32P incorporation was lower in the striatum and cerebellum, higher in the hippocampus and unmodified in the cortex. Part of the phosphorylated bands had an apparent molecular weight similar to that of the phosphoproteins involved in neurotransmission. These results extend previous observations indicating that calcium movement control is modified during chronic ethanol consumption and suggest that ethanol may interfere at various steps in the calcium-promoted events.