Hormonal tolerance to ethanol is associated with decreased expression of the GTP-binding protein, Gs alpha, and adenylyl cyclase activity in ethanol-treated LS mice

Behavioral Neuroadaptation to Alcohol: From Glucocorticoids to Histone Acetylation

A prime mechanism that contributes to the development and maintenance of alcoholism is the dysregulation of the hypothalamic-pituitary-adrenal axis activity and the release of glucocorticoids (cortisol in humans and primates, corticosterone in rodents) from the adrenal glands. In the brain, sustained, local elevation of glucocorticoid concentration even long after cessation of chronic alcohol consumption compromises functional integrity of a circuit, including the prefrontal cortex (PFC), the hippocampus (HPC), and the amygdala (AMG). These structures are implicated in learning and memory processes as well as in orchestrating neuroadaptive responses to stress and anxiety responses. Thus, potentiation of anxiety-related neuroadaptation by alcohol is characterized by an abnormally AMG hyperactivity coupled with a hypofunction of the PFC and the HPC. This review describes research on molecular and epigenetic mechanisms by which alcohol causes distinct region-specific adaptive changes in gene expression patterns and ultimately leads to a variety of cognitive and behavioral impairments on prefrontal- and hippocampal-based tasks. Alcohol-induced neuroadaptations involve the dysregulation of numerous signaling cascades, leading to long-term changes in transcriptional profiles of genes, through the actions of transcription factors such as [cAMP response element-binding protein (CREB)] and chromatin remodeling due to posttranslational modifications of histone proteins. We describe the role of prefrontal-HPC-AMG circuit in mediating the effects of acute and chronic alcohol on learning and memory, and region-specific molecular and epigenetic mechanisms involved in this process. This review first discusses the importance of brain region-specific dysregulation of glucocorticoid concentration in the development of alcohol dependence and describes how persistently increased glucocorticoid levels in PFC may be involved in mediating working memory impairments and neuroadaptive changes during withdrawal from chronic alcohol intake. It then highlights the role of cAMP-PKA-CREB signaling cascade and histone acetylation within the PFC and limbic structures in alcohol-induced anxiety and behavioral impairments, and how an understanding of functional alterations of these pathways might lead to better treatments for neuropsychiatric disorders.

A molecular pathway analysis of the glutamatergic-monoaminergic interplay serves to investigate the number of depressive records during citalopram treatment

The efficacy of current antidepressant (AD) drugs for the treatment of major depressive disorder (MDD) lays behind expectations. The correct genetic differentiation between severe and less severe cases before treatment may pave the way to the most correct clinical choices in clinical practice. Genetics may pave the way such identification, which in turns may provide perspectives for the synthesis of new ADs by correcting the molecular unbalances that differentiate severe and less severe depressive patients. We investigated 1,903 MDD patients from the STAR*D study. Outcome was the number of severe depressive records, defined as a Quick Inventory of Depressive Symptomatology (QIDS)-Clinician rated (C) total score >15, corrected for the number of observations for each patient during the first 14 weeks of citalopram treatment. Predictors were the genetic variations harbored by genes involved in the glutamatergic-monoaminergic interplay as defined in a previous work published by our group. Clinical and socio-demographic stratification factor analyses were taken in cases and controls. Covariated linear regression was the statistical model for the analysis. SNPs were analyzed in groups (molecular pathway analysis) testing the hypothesis that the distribution of significant (p < 0.05) associations between SNPs and the outcome segregates within each pathway/gene subset. The best associated results are relative to two signle SNPs, (rs7744492 in AKAP12 p = 0.0004 and rs17046113 in CAMK2D p = 0.0006) and a molecular pathway (cAMP biosynthetic process p = 0.005). After correction for multitesting, none of them resulted to be significantly associated. These results are consistent with previous findings in literature and further stress that the molecular mechanisms targeted by current ADs may not be the key biological variables that differentiate severe from mild depression.

Chronic alcohol consumption from adolescence-to-adulthood in mice--hypothalamic gene expression changes in the dilated cardiomyopathy signaling pathway

Background

Adolescence is a developmental stage vulnerable to alcohol drinking-related problems and the onset of alcoholism. Hypothalamus is a key brain region for food and water intake regulation, and is one of the alcohol-sensitive brain regions. However, it is not known what would be the alcohol effect on hypothalamus following adolescent alcohol intake, chronically over the adolescent development, at moderate levels.

Results

We employed a paradigm of chronic moderate alcohol intake from adolescence-to-adulthood in mice, and analyzed the alcohol effect on both behavioral and hypothalamic gene expression changes. A total of 751 genes were found and subjected to pathway analysis. The dilated cardiomyopathy (DCM) pathway was identified. The changes of ten genes under this pathway were further verified using RT-PCR. Chronic alcohol consumption during adolescence, even at moderate levels, led to a decrease of motor activity in mice, and also a concerted down regulation of signaling pathway initiating factor (SPIF) genes in the DCM signaling pathway, including β1-adrenergic receptor (Adrb1), Gs protein (Gnas), adenylyl cyclase 1 (Adcy1), and dihydropyridine receptor/L-type calcium channel (Cacna1d).

Conclusions

These findings suggest that adolescent alcohol intake may trigger gene expression changes in the CNS that parallel those found in the dilated cardiomyopathy signaling pathway. If such effects also take place in humans, our findings would serve as a warning against alcohol intake in youth, such as by teens and/or college students.

Increased expression of G11α in osteoblastic cells enhances parathyroid hormone activation of phospholipase C and AP-1 regulation of matrix metalloproteinase-13 mRNA

In osteoblasts parathyroid hormone (PTH) stimulates the PTH/PTH-related peptide (PTHrP) receptor (PTH1R) that couples via G(s) to adenylyl cyclase stimulation and via G(11) to phospholipase C (PLC) stimulation. We have investigated the effect of increasing G(11)alpha levels in UMR 106-01 osteoblastic cells by transient transfection with cDNA encoding G(11)alpha on PTH stimulation of PLC and protein kinase C (PKC) as well as PTH regulation of mRNA encoding matrix metalloproteinase-13 (MMP-13). Transfection with G(11)alpha cDNA resulted in a 5-fold increase in PTH-stimulated PLC activity with no change in PTH-stimulated adenylyl cyclase. PTH-induced translocation of PKC-betaI, -delta, and -zeta to the cell membrane and PKC-zeta to the nucleus was also increased. Increased G(11)alpha protein resulted in increased stimulation of MMP-13 mRNA levels at all doses of PTH. There was a 2.5 +/- 0.35 fold increase in maximal PTH-stimulation of c-jun mRNA and smaller but significant increases in c-fos accompanied by increased basal and PTH-stimulated AP-1 binding in cells expressing increased G(11)alpha. Runx-2 mRNA and protein levels were not significantly increased by increased G(11)alpha expression. The increase in PTH stimulation of c-jun, c-fos, and MMP-13 in G(11)alpha-transfected cells were all blocked by bisindolylmaleimide I, a selective inhibitor of PKC. These results demonstrate that regulation of the PLC pathway through the PTH1R is significantly increased by elevating expression of G(11)alpha in osteoblastic cells. This leads to increased PTH stimulation of MMP-13 expression by increased stimulation of AP-1 factors c-jun and c-fos.

The gene transcription factor cyclic AMP-responsive element binding protein: role in positive and negative affective states of alcohol addiction

The gene transcription factor cyclic adenosine monophosphate (cAMP)-responsive element binding (CREB) protein is a nuclear protein that regulates synaptic plasticity via modulating the expression of several (cAMP)-inducible genes. Alcohol addiction is a complex psychiatric disorder and is characterized by a compulsive and uncontrolled pattern of alcohol drinking by an individual in spite of the adverse consequences of its abuse. Ethanol produces both euphoric (reward and reinforcing) and dysphoric (negative withdrawal reactions) effects and these are most likely involved in the initiation and maintenance of alcohol use and abuse. Several neurotransmitter systems in the brain might be involved in the effects of alcohol but the exact molecular mechanisms of both the positive and negative affective states of alcohol abuse are still unclear. Recent research in molecular neurosciences using animal models have identified the role of extended amygdaloid (shell structures of nucleus accumbens [NAc] and central and medial amygdaloid nuclei) CREB signaling in positive and negative affective states of alcohol drinking behaviors. This review article highlights the current findings on the role of nucleus accumbal and amygdaloid CREB signaling in behavioral consequences of alcohol use and abuse.

Ethanol inhibits palmitoylation of G protein Gαs

Neurobiological actions of ethanol have been linked to perturbations in cyclic AMP (cAMP)-dependent signaling processes. Chronic ethanol exposure leads to desensitization of cAMP production in response to physiological ligands (heterologous desensitization). Ethanol-induced alterations in neuronal expression of G proteins G(s) and G(i) have been invoked as a cause of heterologous desensitization. However, effects of ethanol on G protein expression vary considerably among different experimental protocols, various brain regions and diverse neuronal cell types. Dynamic palmitoylation of G protein alpha subunits is critical for membrane localization and protein-protein interactions, and represents a regulatory feature of G protein function. We studied the effect of ethanol on G alpha(s) palmitoylation. In NG108-15 rat neuroblastoma x glioma hybrid cells, acute exposure to pharmacologically relevant concentrations of ethanol (25-100 mm) inhibited basal and prostaglandin E1-stimulated incorporation of palmitate into G alpha(s). Exposure of NG108-15 cells to ethanol for 72 h induced a shift in G alpha(s) to its non-palmitoylated state, coincident with an inhibition of prostaglandin E1-induced cAMP production. Both parameters were restored following 24 h of ethanol withdrawal. Chronic ethanol exposure also induced the depalmitoylation of G alpha(s) in human embryonic kidney (HEK)293 cells that overexpress wild-type G alpha(s) and caused heterologous desensitization of adenylyl cyclase. By contrast, HEK293 cells that express a non-palmitoylated mutant of G alpha(s) were insensitive to heterologous desensitization after chronic ethanol exposure. In summary, the findings identify a novel effect of ethanol on post-translational lipid modification of G alpha(s), and represent a mechanism by which ethanol might affect adenylyl cyclase activity.

Neuronal signaling systems and ethanol dependence

In recent years there have been remarkable developments toward the understanding of the molecular and/or cellular changes in the neuronal second-messenger pathways during ethanol dependence. In general, it is believed that the cyclic adenosine 3',5'-monophosphate (cAMP) and the phosphoinositide (PI) signal-transduction pathways may be the intracellular targets that mediate the action of ethanol and ultimately contribute to the molecular events involved in the development of ethanol tolerance and dependence. Several laboratories have demonstrated that acute ethanol exposure increases, whereas protracted ethanol exposure decreases, agonist-stimulated adenylate cyclase activity in a variety of cell systems, including the rodent brain. Recent studies indicate that various postreceptor events of the cAMP signal transduction cascade (i.e., Gs protein, protein kinase A [PKA], and cAMP-responsive element binding protein [CREB]) in the rodent brain are also modulated by chronic ethanol exposure. The PI signal-transduction cascade represents another important second-messenger system that is modulated by both acute and chronic ethanol exposure in a variety of cell systems. It has been shown that protracted ethanol exposure significantly decreases phospholipase C (PLC) activity in the cerebral cortex of mice and rats. The decreased PLC activity during chronic ethanol exposure may be caused by a decrease in the protein levels of the PLC-beta 1 isozyme but not of PLC-delta 1 or PLC-gamma 1 isozymes in the rat cerebral cortex. Protein kinase C (PKC), which is a key step in the PI-signaling cascade, has been shown to be altered in a variety of cell systems by acute or chronic ethanol exposure. It appears from the literature that PKC plays an important role in the modulation of the function of various neurotransmitter receptors (e.g., gamma-aminobutyrate type A [GABAA], N-methyl-D-aspartate [NMDA], serotonin2A [5-HT2A], and 5-HT2C, and muscarinic [m1] receptors) resulting from ethanol exposure. The findings described in this review article indicate that neuronal-signaling proteins represent a molecular locus for the action of ethanol and are possibly involved in the neuro-adaptational mechanisms to protracted ethanol exposure. These findings support the notion that alterations in the cAMP and the PI-signaling cascades during chronic ethanol exposure could be the critical molecular events associated with the development of ethanol dependence.

The combined effects of chronic ethanol/desipramine treatment on beta-adrenoceptor density and coupling efficiency in rat brain

Both ethanol and desipramine influence beta-adrenoceptor regulation. We reported previously that ethanol partially counteracted desipramine's effects on beta-adrenoceptor. Previous studies utilized beta-adrenoceptor radioligands that also bind to 5-HT1B receptors, thus, changes in 5-HT1B receptors could have confounded the results. The effects of chronic ethanol, desipramine and ethanol/desipramine treatment on beta-adrenoceptor coupling efficiency to Gs protein in rat brain were examined using 125I-iodocyanopindolol after blocking binding to 5-HT1B receptors. In the frontal cortex, ethanol uncoupled beta-adrenoceptor from GS. Desipramine decreased beta-adrenoceptor density, particularly in the high-conformational state, with no effect on coupling. In combined treatment, desipramine prevented ethanol-induced uncoupling. In the hippocampus, desipramine enhanced beta-adrenoceptor coupling, but ethanol had no effect. In combination with desipramine, ethanol enhanced desipramine-induced decrease in beta-adrenoceptor density in the high-conformational state, but uncoupled beta-adrenoceptors, an effect not observed with ethanol alone. These results suggest a complex interplay between ethanol and antidepressants in modulating beta-adrenoceptor function.

Reduced immunoreactivity of type I adenylyl cyclase in the postmortem brains of alcoholics

Reduced adenylyl cyclase activity after chronic ethanol exposure has been reported. In this study, we investigated by immunoblotting whether quantitative changes of adenylyl cyclase isoforms (type I, type II, and type V/VI adenylyl cyclases) exist in membrane preparations of the temporal cortex obtained from six alcoholics and six age-matched controls. The immunoreactivity of type I adenylyl cyclase decreased significantly in the temporal cortex of alcoholics when compared with controls (p < 0.05), whereas those of type II and type V/VI adenylyl cyclases showed no changes between the groups. These findings suggest that these isoform-specific afterations in the adenylyl cyclase system may be involved in the pathophysiology of alcoholism.

Effect of mu opioid receptor blockade on alcohol intake in rats bred for high alcohol drinking

Beta-funaltrexamine (beta-FNA), a selective mu opioid receptor antagonist, when administered in doses of 10.0, 15.0, and 20.0 mg/kg b.wt., decreased alcohol but not water intake in a dose-dependent manner in rats selectively bred for high alcohol intake (HAD line). Beta-FNA also suppressed the intake of a saccharin solution containing alcohol without altering the intake of a similar solution without alcohol. The results suggest that beta-FNA may prove useful as a pharmacotherapeutic agent for the treatment of alcohol dependence. In a second study, pituitary beta-endorphin gene expression (proopiomelanocortin or POMC messenger ribonucleic acid-mRNA) was compared in another pair of rat lines selectively bred for high or low alcohol intake (alcohol-preferring or P and alcohol-nonpreferring or NP lines). A repeated alcohol challenge (1.0 g/kg b.wt./day, IP for 4 days) produced a greater increase in POMC mRNA in the anterior and neurointermediate lobes of the pituitary of P rats compared with NP rats. The results suggest that a genetic predisposition toward high alcohol drinking may be associated with increased responsiveness of the opioid system to alcohol.

Altered cyclic AMP-dependent human chorionic gonadotropin production in cultured human placental trophoblasts exposed to ethanol

Chronic ethanol abuse during pregnancy can cause fetal injury, including the fetal alcohol syndrome (FAS). A contributing factor in this fetal injury may be the effect of ethanol on placental function. Previous studies have shown that ethanol treatment increases human chorionic gonadotropin (hCG) production by cultured human placental trophoblasts. In this study, we demonstrated that the stimulation of hCG production correlates with the ethanol concentration. Ethanol treatment enhanced intracellular adenosine 3':5'-cyclic monophosphate (cAMP) levels in response to either cholera toxin (CTX) or forskolin (FSK). Moreover, basal (i.e. unstimulated) cAMP levels were increased at 2 hr of ethanol exposure. However, this effect did not persist throughout the 24-hr incubation period. Therefore, ethanol treatment appears to induce increased hCG production, secondary to enhanced basal or stimulated cAMP production. The effect of ethanol was not associated with changes in Gs or Gi2 expression, as determined by northern blot and western blot analyses. In plasma membrane preparations from ethanol-treated cells, cAMP production was higher in response to Mn2+, a direct stimulator of adenylyl cyclase. Inclusion of Rp-cAMP, a protein kinase A inhibitor, eliminated the ethanol effect on hCG production. Treatment of cells with 8-Br-cAMP stimulated hCG production, but there was no difference between the ethanol-naive control and the ethanol-treated cells. These data suggest that ethanol treatment increases in vitro hCG production in human placental trophoblasts by enhancing cAMP production. Ethanol treatment appears to increase trophoblast adenylyl cyclase activity.

Adenylyl cyclase signal transduction and alcohol-induced sedation

This study examined adenylyl cyclase (AC) signal transduction in alcohol-sensitive brain regions of rats selectively bred for high (HAD) and low (LAD) alcohol drinking and correlated these findings with differences in sensitivity and tolerance to alcohol-induced sedation found within these lines. LAD rats were more sensitive to the sedative effects of alcohol than were HAD rats as evidenced by a shorter latency to lose the righting response (RR) after a single alcohol challenge. When time to recover the RR was compared after each of two alcohol challenges, HAD rats recovered the RR more rapidly following the second challenge compared to the first, indicating that the HAD rats rapidly developed tolerance to the sedative effects of alcohol. Tolerance did not develop in rats of the LAD line. Two months after completion of behavioral testing, adenylyl cyclase (AC) signal transduction was examined in alcohol-sensitive brain regions of rats from both lines. Immunoblot analyses indicated that LAD rats had greater Gs alpha expression in the frontal cortex (FC) and hippocampus (HIP) compared to HAD rats. Rats with the highest HIP and FC Gs alpha levels were more rapidly affected by the sedative properties of alcohol than were rats with lower Gs alpha levels. G protein expression and AC activity in the FC, HIP, cerebellum (CERE), and nucleus accumbens (ACB) were also correlated with sensitivity to the sedative properties of alcohol and with the rapid development of tolerance to this alcohol effect. The results suggest that sensitivity and tolerance to alcohol-induced sedation may be mediated in part through AC signal transduction.

No allelic association of an exon 13 polymorphism of the Gsα gene to alcohol and/or drug dependence

The adenylyl cyclase signal transduction system, a ubiquitous second messenger system, has been identified as a potential marker for genetic risk of alcohol and drug dependence. Using the polymerase chain reaction (PCR) to amplify exon 13 of the Gsα gene, two alleles were distinguished by denaturing gradient gel electrophoresis. One allele, designed A, contained the previously published C in the codon for asparagine 371, while the second allele, designated A, contains a C-T transition that conserves the asparagine residue at codon 371. The neutral polymorphism eliminates a Fok I restriction enzyme cleavage site, allowing use of restriction fragment length polymorphisms of PCR products to determine allelic frequency in 235 subjects with alcohol and/or drug dependence and in 85 control subjects. Since allele frequencies differ significantly by race, comparisons between affected individuals and controls were conducted separately for white and black groups. Within race, there were no significant differences in the frequency of the A allele among alcoholics, subjects dependent on cocaine or opioids, subjects dependent on these drugs and alcohol, and controls. We conclude that there is no association between alcohol and/or drug dependence and alleles of an exon 13 polymorphism of the Gsα gene in either black or white individuals.

Increased expression of Gs(alpha) enhances activation of the adenylyl cyclase signal transduction cascade

Expression of the stimulatory G protein, G(S)alpha, can vary over a 3-fold range in human tissues and in rodent central nervous system. In fact, the offspring of alcoholics have higher levels of G(S)alpha expression in certain tissues compared with the offspring of nonalcoholics. The aim of this research was to test the hypothesis that a causal relationship exists between the level of expression of G(S)alpha and induction of the adenylyl cyclase (AC) cascade. The methodology employed transient transfection of HEK 293 cells with a cDNA for the 52-kDa form of G(S)alpha under regulation by inducible metallothionein promoters. Transfectants were exposed to varying concentrations (0-125 microM) of zinc sulfate that produced a 3-fold range of membrane G(S)alpha expression. The range of G(S)alpha expression produced was found to mimic a physiologically relevant spectrum of G(S)alpha expression in membranes derived from human tissues and rat brain. It was observed that induction of G(S)alpha expression increased constitutive as well as stimulated cAMP accumulation. Moreover, induction of G(S)alpha expression increased events distal to the accumulation of cAMP including the phosphorylation of the transcription factor, cAMP response element binding protein and transcriptional activation of cAMP-dependent reporter genes. In summary, these studies show that the amount of G(S)alpha expression has a marked impact on the level of activity of the AC cascade from the membrane through to the nucleus. It is hypothesized that individuals who differ in G(S)alpha expression may also differ in the expression of certain cAMP-dependent genes.

Confirmation of quantitative trait loci for ethanol sensitivity in long-sleep and short-sleep mice

Initial insensitivity to alcohol is a strong predictor of human alcoholism, a widespread and heritable health problem. The Long Sleep and Short Sleep lines of mice were developed by genetic selection for high or low alcohol sensitivity. We have identified seven quantitative trait loci (QTLs) specifying differences in alcohol sensitivity using intercross progeny from these selected strains. These QTLs (Lorel-Lore7) together account for approximately 60% of the total genetic variance for this trait. This represents the first report of linkages for genes influencing alcohol action in any mammalian system using stringent, genome-wide mapping criteria.

Ethanol causes translocation of cAMP-dependent protein kinase catalytic subunit to the nucleus

Short- and long-term ethanol exposures have been shown to alter cellular levels of cAMP, but little is known about the effects of ethanol on cAMP-dependent protein kinase (PKA). When cAMP levels increase, the catalytic subunit of PKA (C alpha) is released from the regulatory subunit, phosphorylates nearby proteins, and then translocates to the nucleus, where it regulates gene expression. Altered localization of C alpha would have profound effects on multiple cellular functions. Therefore, we investigated whether ethanol alters intracellular localization of C alpha. NG108-15 cells were incubated in the presence or absence of ethanol for as long as 48 h, and localization of PKA subunits was determined by immunocytochemistry. We found that ethanol exposure produced a significant translocation of C alpha from the Golgi area to the nucleus. C alpha remained in the nucleus as long as ethanol was present. There was no effect of ethanol on localization of the type I regulatory subunit of PKA. Ethanol also caused a 43% decrease in the amount of type I regulatory subunit but had no effect on the amount of C alpha as determined by Western blot. These data suggest that ethanol-induced translocation of C alpha to the nucleus may account, in part, for diverse changes in cellular function and gene expression produced by alcohol.

Defective calcium increase and inositol phosphate production in anti-CD3-stimulated lymphocytes of alcoholics without progressive liver disease

Intracellular free calcium concentration, phosphoinositide turnover, and inositol phosphate production were analyzed in peripheral blood lymphocytes from seven well-nourished alcoholic patients without severe acute or chronic liver disease, before and after stimulation with anti-CD3 antibody. Seven comparable nondrinkers were studied as controls. A lower increase in intracellular free calcium concentration was detected in alcoholics, after anti-CD3 stimulation of lymphocytes, than in control subjects. Lymphocyte activation generated inositol phosphates in both controls and alcoholics, but inositol phosphate production was significantly lower in alcoholics. The agreement between these findings indicates that the reduction in inositol phosphates is one of the most important events in the early phases of lymphocyte activation in alcoholics.

Evidence for prolonged recovery of dopaminergic transmission after detoxification in alcoholics with poor treatment outcome

It has been hypothesized that dysfunction of dopaminergic neurotransmission is involved in the pathogenesis of alcohol addiction. Therefore, peripheral dopamine levels, sensitivity of central dopamine receptors (apomorphine-induced Growth Hormone (GH) secretion), and the inhibitory efficacy of G-proteins on adenylyl cyclase activity (as an indicator for dopamine D2-receptor coupled second messenger mechanisms) were measured in 45 alcohol-dependent patients before and after detoxification and in 10 healthy controls. The time needed to adjust to abstinence conditions differed between patients with good and poor treatment outcome. In subsequent abstainers, effects of alcohol withdrawal were already found during the first 24 hours of abstinence (normalisation of GH response, increases in dopamine levels and the inhibitory efficacy of G-proteins). During the next 7 days of abstinence, no more significant changes were observed in the assessed variables. In subsequent relapsers, no significant effect of acute ethanol withdrawal on the same measures was found. However, at day 8 of abstinence, increases in apomorphine-induced GH secretion (towards normalisation), in dopamine plasma levels, and in the inhibitory efficacy of G-proteins (towards above-normal levels) were observed. This retarded adjustment of dopaminergic signal transduction seems to reflect the relapse risk of treatment nonresponders.

Quantitative changes in G proteins do not mediate ethanol-induced downregulation of adenylyl cyclase in mouse cerebral cortex

Our prior work, and the work of others, demonstrated that chronic administration of ethanol to cells in culture or to mice resulted in decreased responsiveness of adenylyl cyclase (EC4.6.1.1) to a number of stimulatory agents. In this study, we substantiated the ethanol-induced changes in cerebral cortical adenylyl cyclase activity in alcohol-tolerant and alcohol-dependent mice, and we examined whether chronic ethanol treatment of mice altered the quantity of heterotrimeric guanine nucleotide-binding regulatory proteins (G proteins) in cerebral cortex and other mouse brain areas. Amounts of various G protein subunits--including the alpha subunits of GS (GS alpha), Gi alpha 1-3, G(o) alpha, and beta subunits--were examined by Western blot analysis. There was no change in quantity of these G protein subunits in cerebral cortex, hippocampus, or cerebellum of ethanol-fed mice, compared with controls. In striatum of ethanol-fed mice, small increases in Gi alpha 1 and G(o) alpha were observed, but these changes could not explain the ethanol-induced desensitization of adenylyl cyclase in brain areas such as the cerebral cortex. Forskolin activation of cerebral cortical adenylyl cyclase activity showed two components of activation, with high and low "affinity" for forskolin. Ethanol treatment caused a decrease in the efficacy of forskolin for both components, whereas the EC50 of forskolin for each component did not change. Adenylyl cyclase activity measured in the presence of manganese was also diminished in cortical membranes of ethanol-treated mice.(ABSTRACT TRUNCATED AT 250 WORDS)

Ethanol-induced reduction of the amount of stimulatory GTP-binding regulatory protein, Gs, in wild-type S49 murine lymphoma cells: effect of cycloheximide and puromycin

The activity and the amount of Gs in wild-type S49 murine lymphoma cells decreased by 16-18% and by 29%, respectively, after 24 h treatment of the cells with 50 mM ethanol, through a transient increase of the Gs activity with no alteration in its content after 4 and 8 h treatment. No decrease of the Gs activity was noted when membranes from S49 cells were treated with 50-500 mM ethanol. To study the role of protein metabolism in the ethanol-induced reduction in the amount of Gs, S49 cells were treated with ethanol for 24 h in the presence of inhibitor of protein synthesis. Cycloheximide at concentrations of 0.05-0.15 micrograms/ml and puromycin at 0.15-0.60 micrograms/ml caused a dose-dependent inhibition of cell division in S49 cells to a similar degree. The ethanol-induced reduction of the activity and the amount of Gs was completely abolished by those concentrations of cycloheximide, but not by puromycin. Cycloheximide itself caused no alteration in the Gs activity of S49 cell membranes. These results indicate that the process of the ethanol-induced event of Gs involves cycloheximide-sensitive protein synthesis.

Opioid involvement in alcohol drinking

A large body of evidence indicates that the endogenous opioid system plays an important role in maintaining alcohol drinking behavior. Evidence is reviewed that indicates that the reinforcing properties of alcohol that lead to continued and repeated bouts of drinking may be due, in part, to alcohol-induced activation of the endogenous opioid system. Much of this evidence is pharmacologic in nature. Blocking the action of endogenous opioid peptides via administration of opioid antagonists significantly attenuates alcohol consumption in animals under a variety of experimental conditions. In clinical trials, opioid receptor antagonists decrease alcohol consumption, relapse rates, subjective high, and alcohol craving in outpatient alcoholics. The potential clinical utility of opioid receptor antagonists in the treatment of alcoholism and alcohol dependence is discussed.

Ethanol enhancement of ligand-stimulated cAMP production by cultured human placental trophoblasts

Chronic ethanol (EtOH) use during pregnancy can be associated with fetal injury including the fetal alcohol syndrome (FAS). A contributing factor in this fetal injury may be the effect of EtOH on the placenta. In this study, we have examined the effect of in vitro EtOH treatment on adenosine 3':5'-cyclic monophosphate (cAMP) production by cultured trophoblasts, in response to various ligands. Epinephrine (10(-6) M) rapidly stimulated cAMP with a peak between 2.5 and 5 min, which gradually returned to basal levels over 3-4 hr. EtOH treatment for > 16 hr resulted in an up-regulation of epinephrine-stimulated cAMP production. Inhibition of phosphodiesterase with Rolipram enhanced the effect of EtOH on cAMP production, suggesting that the effect of EtOH treatment was not due to phosphodiesterase inhibition. In cultured trophoblasts, EtOH treatment increased both epinephrine and 16,16'-dimethylprostaglandin E2 (dm-PGE2)-dependent cAMP production at varying ligand concentrations, suggesting an increased capacity to respond. When trophoblasts were treated with forskolin, a stimulator of adenylyl cyclase, cAMP production was enhanced in EtOH-treated cells. This suggests that EtOH treatment enhances adenylyl cyclase activity in these intact, cultured cells. Unlike trophoblasts from term human placenta, JAR choriocarcinoma cells did not respond to epinephrine, adenosine, or dm-PGE2. The choriocarcinoma cells appeared to have lost the ability to respond to these ligands. Although the JAR cell adenylyl cyclase was stimulated by forskolin, EtOH treatment did not alter forskolin-stimulated cAMP production. In summary, EtOH-induced up-regulation of cAMP production appears to be cell specific, being present in normal human trophoblasts but not in undifferentiated choriocarcinoma cells.

Differential expression of guanosine triphosphate binding proteins in men at high and low risk for the future development of alcoholism

We evaluated G-proteins that are components of adenylyl cyclase (AC) signal transduction in erythrocyte and lymphocyte membranes from 26 family history positive (FHP) non-alcoholic and 26 family history negative (FHN) nonalcoholic subjects. Subjects were classified as FHP if their father met criteria for alcohol dependence; as FHN, if there was no history of alcoholism in any first or second degree relatives. Immunoblot analysis indicated that levels of erythrocyte membrane Gs alpha from FHP subjects were greater than levels in FHN subjects (171 +/- 11 vs 100 +/- 6, P < 0.001). To confirm the results of the immunoblot analysis, Gs alpha was quantitated by cholera toxin-dependent [32P]ADP-ribosylation. Levels of erythrocyte [32P]ADP-ribose-Gs alpha from FHP subjects were greater than levels in FHN subjects (236 +/- 28 vs 100 +/- 14, P < 0.001). Gs alpha levels did not correlate with age or alcohol consumption. By contrast to differences in Gs alpha, immunoblot analysis showed similar levels of Gi(2)alpha and Gi(3)alpha in erythrocyte membranes of FHP and FHN subjects. Pertussis toxin-catalyzed [32P]ADP-ribosylation of Gi-like G-proteins confirmed the immunoblot observations. Lastly, compared to FHN subjects, FHP subjects had enhanced Gs alpha expression in lymphocyte membranes as well (138 +/- 11 vs 100 +/- 5.5; P < 0.02). In summary, compared to FHN nonalcoholic men, FHP nonalcoholic men had greater levels of the stimulatory G-protein, Gs alpha, in erythrocyte and lymphocyte membranes. Enhanced expression of Gs alpha may be a marker of increased risk for the future development of alcoholism.

Enhanced activity of the brain beta-endorphin system by free-choice ethanol drinking in C57BL/6 but not DBA/2 mice

The objective of the present studies was to investigate the effect of voluntary ethanol consumption for 21 days on the brain beta-endorphin system of C57BL/6 (alcohol-preferring) and DBA/2 (alcohol-avoiding) strains of mice. As expected, C57BL/6 mice consumed a significantly higher quantity of the 10% ethanol solution than the DBA/2 mice. Under basal conditions the content of beta-endorphin like peptides differed only in the nucleus accumbens, higher levels being found in the DBA/2 mice. Voluntary ethanol consumption induced an increase in the hypothalamic content of mRNA coding for proopiomelanocortin, associated with a significant increase in the tissue content of beta-endorphin-like peptides in the arcuate nucleus and septum of the C57BL/6 mice, but did not alter the activity of the brain beta-endorphin system of the DBA/2 mice. Since voluntary ethanol consumption was not associated with nutritional deficits and stress, the ethanol-induced enhanced activity of the brain beta-endorphin system of the C57BL/6 mice must be a direct effect of ethanol and may be important in controlling the voluntary ethanol consumption by this strain of mice.

Genetics of alcoholism: role of the endogenous opioid system

At the present time alcoholism is recognized as a metabolic disease exhibiting the clinical features of craving for alcohol, loss of control over drinking, tolerance and physical dependence on alcohol, while both epidemiological and experimental studies have demonstrated that genetic factors may be important in determining whether an individual has a high or low vulnerability to develop alcoholism. Evidence also indicates that alcoholism is not characterized by a single gene single allele inheritance. Instead it seems that multiple genes and environmental factors interact to increase or decrease an individual's vulnerability to become an alcoholic. Current research is aimed at investigating whether certain behavioral, physiological and biochemical markers are highly associated with the incidence of alcoholism. Among the biochemical markers currently under investigation is the endogenous opioid system and its implication in mediating the reinforcing effects of ethanol. It is the objective of this manuscript to review current research on: (a) the interactions of ethanol with the endogenous opioid system at the molecular level; (b) the existence of genetically determined differences in the response of the endogenous opioid system to ethanol between subjects at high and low risk for excessive ethanol consumption, as well as between lines of animals showing preference or aversion for ethanol solutions; (c) the decrease of alcohol consumption following pretreatment with opioid antagonists; and (d) the possible use of specific opioid receptor antagonists together with behavioral therapy to modify drinking behavior, to control craving and to prevent relapse.

Genotype regulates the development of tolerance to ethanol and cross-tolerance to nicotine

The long-sleep (LS) and short-sleep (SS) mouse lines were selectively bred for differential sensitivity to the anesthetic actions of ethanol, but they also differ in sensitivity to nicotine. A recent study suggested that the LS mice develop more tolerance to ethanol and cross-tolerance to nicotine than do the SS following chronic ethanol treatment. The studies reported here expand on these previous studies by assessing potential tolerance to ethanol and cross-tolerance to nicotine using additional behavioral and physiological measures. In addition, the effects of chronic ethanol treatment on ethanol and nicotine metabolism were measured. The LS mice developed tolerance to ethanol as measured by effects on open-field activity, body temperature, and sleep time, whereas the SS mice did not develop consistent tolerance to ethanol's effects on any of these measures. Cross-tolerance to nicotine's effects on open-field activity and body temperature developed, but only in the LS mice. The ethanol tolerance is likely due to changes in CNS sensitivity to ethanol, but altered elimination of nicotine may explain much of the cross-tolerance to nicotine seen in chronic ethanol-treated LS mice.

Signal-transducing G proteins: basic and clinical implications

The pivotal role that G proteins play in transmembrane signal transduction is highlighted by the rapidly expanding list of receptors and effector molecules that are coupled through G proteins. G proteins are poised to allow discrimination and diversification of cellular signals into the cytosolic milieu. The utilization of an evolutionarily conserved "GTPase clock" by G proteins, offers insight into the fundamental role these proteins play in biology. Knowledge of the implication of altered expression or function of G proteins in human disease is now emerging. It is not surprising that deficiency or expression of altered forms of these important proteins can lead to global or restricted metabolic disturbances, depending upon the distribution and role of the G protein. Human disorders, including heart failure, alcoholism, endocrine abnormalities, and neoplasia, are now recognized as due in part to altered expression or function of G proteins.

Phosducin-like protein: an ethanol-responsive potential modulator of guanine nucleotide-binding protein function

Acute and chronic exposure to ethanol produces specific changes in several signal transduction cascades. Such alterations in signaling are thought to be a crucial aspect of the central nervous system's adaptive response, which occurs with chronic exposure to ethanol. We have recently identified and isolated several genes whose expression is specifically induced by ethanol in neural cell cultures. The product of one of these genes has extensive sequence homology to phosducin, a phosphoprotein expressed in retina and pineal gland that modulates trimeric guanine nucleotide-binding protein (G protein) function by binding to G-protein beta gamma subunits. We identified from a rat brain cDNA library an isolate encoding the phosducin-like protein (PhLP), which has 41% identity and 65% amino acid homology to phosducin. PhLP cDNA is expressed in all tissues screened by RNA blot-hybridization analysis and shows marked evolutionary conservation on Southern hybridization. We have identified four forms of PhLP cDNA varying only in their 5' ends, probably due to alternative splicing. This 5'-end variation generates two predicted forms of PhLP protein that differ by 79 aa at the NH2 terminus. Treatment of NG108-15 cells for 24 hr with concentrations of ethanol seen in actively drinking alcoholics (25-100 mM) causes up to a 3-fold increase in PhLP mRNA levels. Induction of PhLP by ethanol could account for at least some of the widespread alterations in signal transduction and G-protein function that are known to occur with chronic exposure to ethanol.

Chronic ethanol exposure potentiates muscarinic receptor and alpha 2-adrenoceptor-mediated inhibition of cAMP accumulation in PC 12 cells

The effects of ethanol on receptor-mediated inhibition of cAMP production were investigated in PC 12 cells. The in vitro addition of ethanol enhanced N-ethylcarboxyadenosine (NECA)-stimulated cAMP production without altering the inhibitory action of carbachol or epinephrine. A 4 day exposure of PC 12 cells to ethanol decreased the stimulation of cAMP production by NECA, but increased the inhibition of NECA-stimulated cAMP production by carbachol and epinephrine.

Alterations of guanine nucleotide-binding proteins in post-mortem human brain in alcoholics

Qualitative and quantitative alterations of G proteins in membrane preparations from parietal and temporal cortex regions in post-mortem brains obtained from alcoholics and controls matched with respect to age and post-mortem delay were investigated by Western-blotting with polyclonal antibodies against specific G protein subunits and functional photoaffinity GTP binding. Quantitative immunoblotting showed that only Gs alpha (52 kDa species) in temporal cortex was significantly decreased (30%, P < 0.05) in alcoholics compared with controls. Moreover, ethanol-stimulated photoaffinity GTP labeling of Gs alpha and Gi/o alpha was decreased in alcoholics in both cortex regions. These results suggest that disturbances of G protein-mediated signal transduction may be involved in the pathophysiology of alcoholics.

Enhanced expression of the inhibitory protein Gi2 alpha and decreased activity of adenylyl cyclase in lymphocytes of abstinent alcoholics

Ethanol exposure alters signal transduction through the adenylyl cyclase (AC) system. To elucidate the basis for this effect, we investigated the AC system in peripheral lymphocytes from abstinent alcoholic men (n = 22), actively drinking alcoholic men (n = 41), and nonalcoholic control men (n = 16). Immunoblot analysis of lymphocyte membranes from abstinent alcoholics demonstrated a 3.0-fold increase in the level of Gi2 alpha protein (p < 0.05) compared with controls. However, levels of Gs alpha protein were similar in both groups. Abstinent alcoholics had a 2.9-fold increase in Gi2 alpha mRNA (p < 0.001) and a 2.7-fold increase in Gs alpha mRNA (p < 0.03) compared with lymphocytes from control subjects. Actively drinking alcoholics, in contrast, had unaltered Gs alpha protein, Gi2 alpha protein, and Gi2 alpha mRNA levels compared with control subjects, but did have a 1.8-fold increase (p < 0.01) in Gs alpha mRNA. Consistent with enhanced Gi2 alpha expression, lymphocyte membranes from abstinent alcoholics had decreased basal, prostaglandin E1-, guanosine 5'-0-(3-thiotriphosphate)-gamma S-, and forskolin-stimulated AC activity compared with both controls and actively drinking alcoholics (p < 0.05). We conclude that lymphocyte AC is reduced during abstinence from alcohol and enhanced expression of the inhibitory G-protein, Gi2 alpha, may account for this change.

Selective breeding for initial sensitivity to ethanol

Selective breeding for initial sensitivity to ethanol has been carried out by a number of investigators in order to investigate the mechanisms by which ethanol brings about a myriad of effects on the mammalian central nervous system. In addition the availability of these selectively bred animals provides clues to the causes of the genetic predisposition of humans to alcoholism. Eventually it is envisioned that the synteny between the mouse and human genomes will allow identification of specific genes responsible for acute effects of ethanol in both species as well as clues as to how alcoholism in humans can be better identified, prevented, and treated.

Proopiomelanocortin messenger RNA is decreased in the mediobasal hypothalamus of rats made dependent on ethanol

It is thought that certain actions of ethanol involve an interaction with endogenous opioids, including proopiomelanocortin-derived peptides such as beta-endorphin. To examine this possibility, we used a sensitive and specific assay for proopiomelanocortin mRNA to obtain an estimate of the activity of the endorphinergic system in the mediobasal hypothalamus and the pituitary of rats exposed for 10 days in an inhalation chamber to either ethanol or water. This protocol causes dependence in the ethanol-exposed group, as demonstrated by the presence of withdrawal seizures after cessation of treatment. While ethanol treatment did not affect proopiomelanocortin mRNA levels in the pituitary, the level in hypothalamus was significantly lower in the ethanol-treated animals than in controls. These results suggest that some effect of ethanol may involve the hypothalamic endorphinergic system.

Differential expression of guanine nucleotide-binding proteins enhances cAMP synthesis in regenerating rat liver

Events leading to cAMP accumulation after partial hepatectomy (PH) and effects of cAMP on hormonal induction of DNA synthesis in hepatocytes were characterized. Hepatic cAMP peaked biphasically post-PH and paralleled changes in adenylyl cyclase activity. Fluctuations in cyclase activity were not explained by variations in glucagon receptor kinetics, but reflected altered G-protein expression. Membrane levels of the stimulatory G-protein, Gs alpha, increased early after PH and were sustained. Levels of the inhibitory G-protein, Gi2 alpha, increased more slowly, peaked later, and quickly fell. Levels of both G-proteins correlated poorly with levels of their mRNAs, suggesting posttranscriptional factors modify their membrane concentrations. When growth factor-induced DNA synthesis was compared in hepatocyte cultures grown with or without agents that increase intracellular cAMP, DNA synthesis was inhibited by sustained high levels of cAMP but was enhanced when high cAMP levels fell. In both regenerating liver and hepatocyte cultures, the expression of a "differentiated" hepatocyte gene, phosphoenolpyruvate carboxykinase, correlated with elevated cAMP levels. These data suggest that the differential expression of G-proteins integrates signals initiated by several growth factors so that the accumulation of cAMP is tightly regulated post-PH. The ensuing variations in cAMP levels modulate both growth and differentiated functions during liver regeneration.