Tolerance and Physical Dependence on Alcohol at the Level of Synaptic Membranes: A Review

Association between CANCA1C gene rs1034936 polymorphism and alcohol dependence in bipolar disorder

INTRODUCTION

Bipolar disorder (BD) is a highly heritable and disabling mental illness, commonly associated with substance abuse, being alcohol abuse the most frequent. Comorbid BD and substance abuse disorders are often associated with high levels of health service utilization and destabilization of the course of illness resulting in poor treatment outcomes. Although recent genome-wide association studies have detected a number of risk genes for BD, the data is still sparse and inconclusive for those genes that may contribute to the increased risk of comorbid alcohol abuse (AA) in BD. The primary aim of the present study was to investigate the effects of 46 single-nucleotide polymorphisms (SNPs) within eight genes on different phenotypes of BD patients, such as comorbid alcohol abuse. We further assessed clinical variables associated with AA.

METHODS

One-hundred fifty-eight BD I and II patients were enrolled in a naturalistic cohort study. Genomic DNA of 92 patients was extracted from whole blood using standard procedures and 46 tag SNPs in eight genes of interest (ANK, CACNA1C, CACNB2, FKBP5, GRM7, ITIH3, SYNE1 and TCF4) were genotyped.

RESULTS

Seventy-one patients out of 158 (45%) satisfied diagnostic criteria for comorbid AA. Among 46 SNPs analyzed, the only SNP associated with comorbid AA was rs1034936 polymorphism in the CANCA1C gene. This polymorphism was also associated with lifetime cocaine abuse, manic switch and current atypical antipsychotics.

CONCLUSIONS

Our findings suggest a role of rs1034936 CACNA1C gene variant in BD-AA group. Despite their preliminary nature, the present results may provide new insight on mechanisms underlying AA in BD.

Changes in adipose tissue hormone-sensitive lipase activity and cAMP during ethanol withdrawal

The time course of the effects of ethanol withdrawal on brown and white adipose tissue hormone-sensitive lipase, cAMP production, and phosphodiesterase have been investigated after chronic drinking or liquid diet schedules. Chronic drinking significantly reduced brown adipose tissue hormone-sensitive lipase activity and cAMP levels from control. During withdrawal, there was a rebound increase to 200% control, peaking 9 h into withdrawal. White adipose tissue hormone-sensitive lipase activity and cAMP accumulation were significantly raised by both treatment schedules. Ethanol liquid diet produced a significant fall in adipose tissue hormone-sensitive lipase activity and cAMP accumulation. In brown fat, there was a rebound increase in hormone-sensitive lipase activity and cAMP; in white fat, no rebound was observed. In brown fat, the reductions in hormone-sensitive lipase activity and cAMP accumulation after chronic drinking coincided with an increase in phosphodiesterase activity. In white fat, the rise in cAMP and hormone-sensitive lipase activation coincided with a decrease in phosphodiesterase activity. We conclude that the effects of chronic ethanol on hormone-sensitive lipase activity are cAMP-dependent and mediated via alterations in phosphodiesterase activity.

Chronic exposure to ethanol alters GABA(A) receptor-mediated responses of layer II pyramidal cells in adult rat piriform cortex

This study examined the effect of chronic exposure to ethanol on gamma-aminobutyric acid type-A (GABA(A)) receptor-mediated responses of layer II pyramidal neurons of the piriform cortex. Slices containing the piriform cortex were derived from pair-fed adult rats maintained on ethanol-supplemented or control liquid diet for 30 days. Responses of identified layer II pyramidal neurons to exogenously applied GABA were monitored by whole-cell patch-clamp recording. Chronic exposure to ethanol resulted in a rightward shift in the EC(50) of GABA and a decrease in the amplitude of maximal GABA response. GABA-induced responses were modulated by acutely applied ethanol (10-100 mM) in both chronic ethanol-treated and control groups. No significant difference was found in the average change in GABA response, suggesting that tolerance to acute ethanol exposure did not develop. When the modulatory responses of individual cells were classified and grouped as either being attenuating, potentiating, or having no effect, the incidence of potentiation in the ethanol-treated group was significantly higher. Consistent with the absence of tolerance to acute ethanol, cross-tolerance to diazepam was not observed following 30 days of treatment with ethanol. These results are discussed in light of regionally specific effects of chronic ethanol treatment on GABA(A) receptor-mediated responses of layer II piriform cortical neurons.

Prolonged changes in neurochemistry of dopamine neurones after chronic ethanol consumption

The effects of 3 weeks of chronic ethanol consumption in mice on brain concentrations and turnover of monamine transmitters was examined. The measurements were made at 24 h, 6 days and 2 months after cessation of the ethanol intake to examine changes that might be relevant to relapse drinking. Increases in noradrenaline and dopamine concentrations, and decreases in the ratios of dopamine metabolites to dopamine, were seen in ventral tegmental tissue at 24 h after alcohol consumption. Increased noradrenaline was also evident at the 6-day interval, but no other changes were seen at this time. At the 2-month interval, the ventral tegmentum from ethanol-treated animals showed decreases in metabolite/dopamine ratios. No changes were seen in 5-hydroxytryptamine or its metabolite. In striatal tissue, none of these changes were seen, but at 24 h decreases occurred in the content of dopamine and its metabolites and a decrease in 5-hydroxyindoleacetic acid. The results indicate changes occur in monoamine turnover in the VTA as long as 2 months after cessation of chronic ethanol consumption; such changes may be related to the prolonged nature of alcohol dependence.

Genetic regulation of dihydropyridine-sensitive calcium channels in brain may determine susceptibility to physical dependence on alcohol

Experiments utilising rodents in vivo and cultures of adrenal cells in vitro have suggested that genetic regulation of dihydropyridine-sensitive calcium channels may be involved in dependence on alcohol. Selection of mouse lines for either a very severe ethanol-withdrawal syndrome (withdrawal seizure prone) or a very mild syndrome (withdrawal seizure resistant), has produced lines which differ very markedly in these characteristics. In these experiments, mice bred selectively for these symptoms for 26 generations, were compared for the severity of withdrawal from alcohol after inhalation of ethanol (plus injections of pyrazole) for 3 days. A proportion of animals from each line was killed before withdrawal and membranes from whole brain were analysed by radioligand binding for binding sites for [3H] nitrendipine. Mice which were withdrawal seizure prone showed a markedly greater severity of the ethanol-withdrawal syndrome, and also showed a significantly greater up-regulation of binding sites for [3H]nitrendipine with no significant difference in binding affinity. The results suggest a relationship between genetic susceptibility to dependence on alcohol and genetic regulation of neuronal calcium channels in brain.

Alterations in synaptic membrane molecular order associated with alcoholization and protein deficiency in rats

The effects of chronic alcoholization and protein deficiency on synaptic membrane characteristics were studied in rats fed the following four liquid diets for 4 weeks: a protein-deficient diet containing alcohol, a protein-deficient diet containing no alcohol, a non-protein-deficient diet containing alcohol and a non-protein-deficient diet containing no alcohol. A fluorescent probe, diphenylhexatriene (DPH), was used to estimate the fluidity of synaptic membranes and their sensitivity to the fluidizing effect of ethanol added in vitro, in concentrations ranging from 50 mM to 800 mM. Prior to in vitro addition of ethanol, the difference between the fluidity of synaptic membranes of alcoholized and non-alcoholized animals was significant for the two groups of protein-deficient animals but not for the two groups of non-protein-deficient animals. After in vitro addition of ethanol, the differences between the fluidity of synaptic membranes of the alcoholized and non-alcoholized animals were larger and more frequently significant for the protein-deficient animals than for the non-protein-deficient animals. In view of previous observations that rats fed a protein-deficient diet experience more severe withdrawal symptoms following alcoholization than rats fed a nutritionally adequate diet, the results of the present experiment lend additional support to the hypothesis that tolerance and dependence may be mediated by alterations in biomembrane characteristics.

Three-dimensional mapping of local cerebral perfusion in alcoholic encephalopathy with and without Wernicke-Korsakoff syndrome

Seventeen severe chronic alcoholic patients with and without Wernicke-Korsakoff syndrome (WKS) were examined prospectively after being treated by withdrawal from alcohol. The WKS patients also received thiamine supplements. Three-dimensional measurements of local cerebral blood flow (LCBF) and local partition coefficients (L lambda) were made utilizing xenon contrast computed tomography (Xe CT-CBF). Results were displayed as color-coded brain maps before and after treatment and these were correlated with neurological and cognitive examinations. Before treatment chronic alcoholics without WKS (n = 10) showed diffuse reductions of LCBF values throughout all gray matter including hypothalamus, vicinity of nucleus basalis of Meynert, thalamus, and basal ganglia. Similar, but more severe, reductions were seen in patients with WKS (n = 7), however, white matter perfusion was also reduced. In WKS, most prominent reductions of LCBF were also seen in hypothalamus and basal forebrain nuclei but thalamus, basal ganglia, and limbic systems were severely reduced. After treatment, both groups with alcoholic encephalopathy showed marked clinical improvement and cerebral perfusion was restored toward normal. Chronic alcohol abuse, in the absence of thiamine deficiency, reduces CBF by direct neurotoxic effects. If thiamine deficiency is also present, more severe and localized hemodynamic reductions are superimposed.