Adaptation of cyclic AMP generating system in rat cerebral cortical slices during chronic ethanol treatment and withdrawal

Recent Advances in Pharmacological Research on Alcohol

Alcohol dependence is a major public health problem. Studies have shown that a person dependent on alcohol often coabuses other substances, such as cocaine. Cocaine is a powerful stimulant whereas ethanol is generally considered to be a depressant, with some stimulating properties. The subjective effects of these two substances in a dependent individual may often appear to be more similar than they are different. Animals also self-administer both substances. Basically, although both substances have anesthetic properties and both act to functionally increase catecholaminergic function, especially that of dopamine, there are some differences in their actions. Both alcohol and cocaine have various effects on several neurotransmitters and systems, which ultimately interact to produce the feeling of well-being avidly sought by many individuals today. This drive often eventually produces a dependence which has associated social and medical consequences. It seems likely that the neurochemical changes that ensue following abuse of these substances underlie the phenomena of dependence, tolerance, and subsequent withdrawal. The apparent similarities and differences between these two substances will be reviewed in this chapter.

The effects of maternal ethanol exposure on neurotransmission and second messenger systems: a quantitative autoradiographic study in the rat brain

The effects of maternal ethanol exposure on neurotransmission and second messenger systems were examined in rats using histochemistry and in vitro autoradiography. Thirty % ethanol was administered to pregnant rats from gestational day 7 to the day of delivery. Quantitative autoradiography was used to map muscarinic cholinergic, dopamine D2, adenosine A1, and inositol 1,4,5-trisphosphate binding sites, as well as to localize adenylate cyclase and protein kinase C. We found no difference in the patterns of staining with acetylcholinesterase and Timm's stain between control and prenatally ethanol-exposed rats on postnatal day (PN) 30. In the ethanol-exposed rats, [3H]forskolin binding sites were increased during early development in the CA1 subfield of the hippocampus and the occipital cortex; [3H]phorbol ester binding sites were increased in the cortex, striatum, and hippocampus; hippocampal muscarinic cholinergic sites were increased on PN4 and 30; adenosine A1 binding was reduced on PN10 in most regions examined, but was increased in the CA1 subfield on PN30; dopamine D2 receptor levels were significantly reduced on PN30 in the striatum; and IP3 receptors were decreased in most regions studied, but particularly in the cerebellum. Thus, some of these changes were transient and others were long-lasting. Although histopathological abnormalities were minimal, the alterations of binding sites in the cerebellum (the coordination center) and in the hippocampus (related to memory and learning) that were detected may contribute to the behavioral and mental deterioration seen in the fetal alcohol syndrome.

Differential response of adenylate cyclase and ATPase activities after chronic ethanol exposure of PC12 cells

The direct effects of chronic ethanol administration on adenylate cyclase, Na,K-ATPase, and Mg-ATPase activities in a cell containing neuronal characteristics were investigated using PC12 pheochromocytoma cells. Exposure of PC12 cells to 0, 75, and 150 mM ethanol for 4 days caused a dose-dependent increase in the stimulation of adenylate cyclase by in vitro ethanol without altering activation of the enzyme by GTP, NaF, MnCl2, or 2-chloroadenosine. Conversely, a 4-day treatment with 150 mM ethanol increased Na,K-ATPase and Mg-ATPase activities without altering the inhibitory effects of in vitro ethanol. The increase in Na,K-ATPase activity was associated with an increase in Vmax without any change in the Km for KCl. Chronic ethanol exposure also increased the amount of [3H]ouabain specifically bound to PC12 cell membranes. Except for the increase in Mg-ATPase activity, the above results were also observed when chronic ethanol treatment was carried out in the presence of pyrazole. Although ethanol slowed PC12 cell growth, observed changes were not due to an ethanol-induced reduction in cellular density. A 4-day exposure of a nonneuronal cell line (Madin Darby canine kidney cell) to 150 mM ethanol did not alter adenylate cyclase or ATPase activities. The present study indicates that the direct effects of chronic ethanol exposure of a neuronal-like cell involve an increase in the density of sodium pumps per cell and an enhanced sensitivity of adenylate cyclase to activation by ethanol.

Chronic in vivo ethanol administration alters the sensitivity of adenylate cyclase coupling in homogenates of rat brain

The high activities of adenylate cyclase, phosphodiesterase and protein kinases in the synaptic terminals of the central nervous system makes these enzymes prime candidates for the in vivo actions of ethanol. Adult female rats were fed a liquid diet containing ethanol as 35% of the available calories for 6 days. This resulted in a decrease (22-45%) in the basal activity of adenylate cyclase, as determined by cyclic 3',5'-adenosine monophosphate (cAMP) production, in homogenates of all brain areas tested. In these homogenates the ability of guanosine triphosphate and noradrenaline to stimulate basal cyclase activity was severely reduced. These results suggest that ethanol administration causes an uncoupling of the beta-receptor/adenylate cyclase cascade and an interruption of the control of the synthesis of cAMP.

Biochemical basis of alcoholism: statements and hypotheses of present research

Experimental results and theoretical considerations on the biology of alcoholism are devoted to the following topics: genetically determined differences in metabolic tolerance; participation of the alternative alcohol metabolizing systems in chronic alcohol intake; genetically determined differences in functional tolerance of the CNS to the hypnotic effect of alcohol; cross tolerance between alcohol and centrally active drugs; dissociation of tolerance and cross tolerance from physical dependence; permanent effect of uncontrolled drinking behavior induced by alkaloid metabolites in the CNS; genetically determined alterations in the function of opiate receptors; and genetic predisposition to addiction due to innate endorphin deficiency. For the purpose of introducing the most important research teams and their main work, statements from selected publications of individual groups have been classified as to subject matter and summarized. Although the number for summary-quotations had to be restricted, the criterion for selection was the relevance to the etiology of alcoholism rather than consequences of alcohol drinking.

Alterations in brain lipid composition of mice made physically dependent to ethanol

The ability of chronic ethanol treatment to alter CNS membrane lipids was tested. Adult C57/BL6 mice were given a liquid diet containing ethanol for eight days. This regimen produced strong physical dependence as judged by withdrawal seizures, tremors and concomitant hypothermia. Analyses were performed on cholesterol, total phospholipid content and total phospholipid acyl composition of myelin, crude (P2), light and heavy synaptosomes as well as synaptosomal plasma membranes. Chronic ethanol treatment had no effect on total phospholipid levels nor phospholipid acyl composition in any of the above subcellular fractions. In ethanol dependent mice, significant increases in cholesterol content and cholesterol/phospholipid ratios were observed in synaptosomal plasma membranes.