Hippocampal and cerebellar beta-adrenergic receptors and adenylate cyclase are differentially altered by chronic ethanol ingestion

Cyclic nucleotide phosphodiesterases: potential therapeutic targets for alcohol use disorder

Alcohol use disorder (AUD), which combines the criteria of both alcohol abuse and dependence, contributes as an important causal factor to multiple health and social problems. Given the limitation of current treatments, novel medications for AUD are needed to better control alcohol consumption and maintain abstinence. It has been well established that the intracellular signal transduction mediated by the second messengers cyclic AMP (cAMP) and cyclic GMP (cGMP) crucially underlies the genetic predisposition, rewarding properties, relapsing features, and systemic toxicity of compulsive alcohol consumption. On this basis, the upstream modulators phosphodiesterases (PDEs), which critically control intracellular levels of cyclic nucleotides by catalyzing their degradation, are proposed to play a role in modulating alcohol abuse and dependent process. Here, we highlight existing evidence that correlates cAMP and cGMP signal cascades with the regulation of alcohol-drinking behavior and discuss the possibility that PDEs may become a novel class of therapeutic targets for AUD.

Targeting Phosphodiesterases in Pharmacotherapy for Substance Dependence

Substance dependence is a chronic relapsing brain disorder associated with adaptational changes in synaptic plasticity and neuronal functions. The high levels of substance consumption and relapse rate suggest more reliable medications are in need to better address the underlying causes of this disease. It has been well established that the intracellular second messengers cyclic AMP (cAMP) and cyclic GMP (cGMP) and their signaling systems play an important role in the molecular mechanisms of substance taking behaviors. On this basis, the phosphodiesterase (PDE) superfamily, which crucially controls cyclic nucleotide levels by catalyzing their hydrolysis, has been proposed as a novel class of therapeutic targets for substance use disorders. This chapter reviews the expression patterns of PDEs in the brain with regard to neural structures underlying the dependent process and highlights available evidence for a modulatory role of PDEs in substance dependence.

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.

Phosphodiesterase regulation of alcohol drinking in rodents

Alcohol use disorders are chronically relapsing conditions characterized by persistent drinking despite the negative impact on one's life. The difficulty of achieving and maintaining sobriety suggests that current treatments fail to fully address the underlying causes of alcohol use disorders. Identifying additional pathways controlling alcohol consumption may uncover novel targets for medication development to improve treatment options. One family of proteins recently implicated in the regulation of alcohol consumption is the cyclic nucleotide phosphodiesterases (PDEs). As an integral component in the regulation of the second messengers cyclic AMP and cyclic GMP, and thus their cognate signaling pathways, PDEs present intriguing targets for pharmacotherapies to combat alcohol use disorders. As activation of cAMP/cGMP-dependent signaling cascades can dampen alcohol intake, PDE inhibitors may provide a novel target for reducing excessive alcohol consumption, as has been proposed for PDE4 and PDE10A. This review highlights preclinical literature demonstrating the involvement of cyclic nucleotide-dependent signaling in neuronal and behavioral responses to alcohol, as well as detailing the capacity of various PDE inhibitors to modulate alcohol intake. Together these data provide a framework for evaluating the potential utility of PDE inhibitors as novel treatments for alcohol use disorders.

Effects of toluene exposure on signal transduction: toluene reduced the signaling via stimulation of human muscarinic acetylcholine receptor m2 subtypes in CHO cells

The organic solvent toluene is used widely in industry and is toxic to the central nervous system (CNS). To clarify the mechanisms of CNS toxicity following toluene exposure, especially with respect to the G protein-coupling of receptors, we determined the effects of toluene on the activation of Gi by stimulating human muscarinic acetylcholine receptor m2 subtypes (hm2 receptors) expressed in Chinese hamster ovary (CHO) cells. We first examined whether toluene affects the inhibition of adenylyl cyclase by Gi. The attenuation of forskolin-stimulated cAMP formation by the stimulation of hm2 receptors was reduced in a medium containing toluene. Next, we determined the effects of toluene on carbamylcholine-stimulated [35S]GTPgammaS binding using membrane fractions of CHO cell expressing hm2 receptors. Carbamylcholine-stimulated [35S]GTPgammaS binding activity was markedly reduced when assayed using reaction buffers containing toluene. However, carbamylcholine-stimulated [35S]GTPgammaS binding activity was essentially unchanged following pretreatment of the cells with a toluene-saturated medium prior to membrane isolation. Toluene pretreatment and the toluene itself did not alter the characteristics of the binding of carbamylcholine and [3H]N-methylscopolamine to hm2 receptors. On the contrary of the effect of toluene for [35S]GTPgammaS binding, the effect of toluene for attenuation of forskolin-stimulated cAMP formation by the stimulation of hm2 receptors was irreversible. These observations indicate that toluene acts as an inhibitor of the signal transduction via hm2 receptor stimulation in CHO cells, and at least two mechanisms exist in the inhibition mechanisms by toluene.

Effects of short-term toluene exposure on ligand binding to muscarinic acetylcholine receptors in the rat frontal cortex and hippocampus

Changes in the binding affinity of the muscarinic acetylcholine receptor agonist carbamylcholine were determined in membranes isolated from the brains of rats exposed to toluene at concentrations of 500-2,000 ppm for 6 h. Membrane fractions of the frontal cortex and hippocampus were prepared and agonist-binding affinities were determined by measuring the displacement of [3H]N-methyl scopolamine-binding activity by carbamylcholine. In the frontal cortex, the affinity of high-affinity carbamylcholine binding was reduced following exposure to toluene at a concentration of 1000 ppm or higher. However, in the hippocampus, the affinity of high-affinity binding of carbamylcholine was increased following exposure to toluene. These observations suggest that toluene exposure affects binding affinity of carbamylcholine, and the effect differs by brain region.

Effect of chronic ethanol treatment of Ca2+-inhibited adenylyl cyclase in mouse striatum

In the present study, to investigate the possibility that chronic ethanol treatment might alter Ca2+-inhibited type 5 adenylyl cyclase (AC) activity, we examined the effect of chronic ethanol treatment on striatal dopaminergic signal transduction, especially the AC system, in mice. We fed male C57BL/6 mice for 7 days with a 5% ethanol-containing or control liquid diet. Basal and forskolin-stimulated AC activities were reduced in striatal membranes of ethanol-treated mice. 5'-guanylylimidodiphosphate-stimulated AC activity was also decreased in ethanol-treated mice. But no significant differences were observed in the levels of the guanine nucleotide binding protein subunits Gs alpha and Gi1alpha&2alpha, determined by immunoblotting, between ethanol-treated and control mice. These results indicated that the function of the catalytic subunit of AC was decreased in the straitum of chronically ethanol-treated mice. We further examined the inhibitory regulation of AC activity in the context of a change of type 5 AC. Inhibition of forskolin-stimulated AC activity by 10 microM free Ca2+ was smaller in ethanol-treated mice than in control mice. However, the protein level of type 5 AC in the striatum, determined by immunoblotting, was not significantly different between ethanol-treated and control mice. These findings suggest that Ca2+-inhibited, presumably type 5, AC activity is reduced in mouse striatum by chronic ethanol treatment, and that this reduction is not due to a decrease in type 5 AC expression.

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.

G-protein regulation of adenylate cyclase activity in rat prostatic membranes after chronic ethanol ingestion

BACKGROUND

The possibility that long-term ethanol ingestion might alter either vasoactive intestinal peptide (VIP) content, VIP binding to membrane receptors, G-protein levels or adenylate cyclase activity in rat prostate was tested, as ethanol produces serious alterations in the hypothalamic-pituitary-gonadal axis and several modifications on different elements on signal transduction pathways in other systems.

METHODS

Prostatic membranes from control and ethanol-treated (for 4 weeks) rats were used to study adenylate cyclase stimulation as well as for the immunodetection of stimulatory (alpha(s)) and inhibitory (alpha(i)1-2) G-protein subunits. Studies on VIP binding and cross-linking to receptors were performed using [125I]VIP. Prostatic VIP content was estimated by radioimmunoassay. GTPase activity was quantified by measuring the amount of 32Pi released from [gamma-32P]GTP.

RESULTS

Chronic ethanol ingestion resulted in an increased presence of VIP in the rat prostate without any change on the VIP receptor/effector system in this gland. By contrast, the basal adenylate cyclase activity as well as the dose-dependent stimulation of this enzyme by either the nonhydrolyzable GTP analogue Gpp(NH)p or the beta-adrenergic agonist isoproterenol were enhanced in prostatic membranes after ethanol intake. Moreover, an increase in the content of G-protein subunits (alpha(S) and alpha(i)1-2) was observed without any change in GTPase activity in this condition. These modifications were accompanied by a significant decrease in rat prostate weight and, consequently, the height of the secretory epithelium in this gland.

CONCLUSIONS

Considering the role of VIP in the mechanisms of secretion and cell proliferation in the prostate, the observed increases in the prostatic content of VIP and G-protein subunits make conceivable that VIP and cAMP signal transduction could be involved in the atrophy of the rat prostate and in the alterations in the composition of seminal fluid that appear in the alcoholic syndrome.

Positron emission tomographic studies of cerebral benzodiazepine-receptor binding in chronic alcoholics

Positron emission tomography was used with [11C]flumazenil (FMZ) and [18F]fluorodeoxyglucose to study GABA type A/benzodiazepine (GA-BA-A/BDZ) receptors and cerebral metabolic rates for glucose (1CMRg1c) in 17 male patients with severe chronic alcoholism (ALC), 8 with (ACD) and 9 without alcoholic cerebellar degeneration (non-ACD). In comparison with male normal controls of similar ages, the ALC group had significantly reduced FMZ ligand influx (K1), FMZ distribution volume (DV), and 1CMRg1c bilaterally in the medial frontal lobes, including superior frontal gyrus and rostral cingulate gyrus; the ACD group had significant reductions of K1, DV, and 1CMRg1c bilaterally in the same distribution, and also in the superior cerebellar vermis; and the non-ACD group had significant reductions of K1, DV, and 1CMRg1c bilaterally in the same regions of the frontal lobes but not in the superior cerebellar vermis. When compared with the non-ACD group, the ACD group had significant reductions of K1, and DV bilaterally in the superior cerebellar vermis. The results suggest that severe chronic alcoholism damages neurons containing GA-BA-A/BDZ receptors in the superior medial aspects of the frontal lobes, and in patients with clinical signs of ACD, neurons containing GABA-A/BDZ receptors in the superior cerebellar vermis.

8-Bromo-cAMP mimics beta-adrenergic sensitization of GABA responses to ethanol in cerebellar Purkinje neurons in vivo

Previous studies in our laboratory indicated that electrophysiological responses of cerebellar Purkinje neurons to GABA were not routinely potentiated by ethanol (EtOH), and the potentiation was not large when it occurred. In the presence of beta-adrenergic agonists, such as isoproterenol, however, GABA inhibitions became sensitive to potentiation by EtOH in nearly every Purkinje neuron tested. beta-adrenergic receptor activation alone also modulates (potentiates) GABA responses on Purkinje neurons, and this has been reported to be mediated by a cAMP second messenger system. Herein, we report that the membrane-permeable cAMP analog, 8-bromoadenosine-3',5'-cyclic monophosphate (8-Br-cAMP), but not the membrane-impermeable cAMP, can also modulate GABA responses and that EtOH potentiates this facilitatory action of 8-Br-cAMP. These effects are not likely caused by adenosine receptor mechanisms, because this 8-bromoadenosine mediated modulation and sensitization was observed in the presence of systemic theophylline. These data suggest that the beta-adrenergic modulation and sensitization to EtOH of cerebellar Purkinje neuron GABA responses occur via a cAMP second messenger mechanism.

Site-specificity of ethanol-induced dephosphorylation of rat hepatocyte keratins 8 and 18: A 31P NMR study

Chronic feeding of ethanol to rats results in disorganization of the keratin intermediate filament network within hepatocytes. Previous studies from this laboratory have shown that intermediate filament organization in cultured cells is related to the phosphorylation state of the proteins. Therefore, we have examined the phosphorylation state of hepatocyte keratins from control and ethanol-fed rats. Feeding ethanol to rats results in dephosphorylation of one site on keratin 8 and one site on keratin 18 at all time points beginning with 6 weeks of ethanol treatment. Dephosphorylation was detected by phosphate analysis and by two-dimensional electrophoresis in which a change in isoelectric point of keratins from ethanol-fed rats was observed. These observations indicate that dephosphorylation of keratins in ethanol-fed animals may be an early step in alcoholic hepatitis which has occurred by 6 weeks of ethanol treatment. To further characterize keratin dephosphorylation in ethanol-fed rats, we used 31P NMR spectroscopy to classify the dephosphorylation site(s). Hepatocyte keratins were purified and solubilized in 9.5 M urea, 10 mM Tris-Cl, pH 8.1. 31P NMR spectra were obtained at 109 MHz, in 10 mm tubes at 30 degrees C. Samples of hepatocyte keratins were phosphorylated with A-kinase, protein kinase C, casein kinase II or Ca/CAM kinase and these samples were analyzed by 31P NMR spectroscopy. The resulting spectra were used as standards to compare the 31P chemical shifts of the resonances produced by these kinases with the phosphorus resonances of control and experimental samples. The 31P NMR spectrum of control hepatocyte keratins shows three resonances at 0.7, 4 and 5 ppm. In vitro phosphorylation by A-kinase produces a resonance at 4 ppm which is distinctly different from the resonance produced by each of the other kinases. In hepatocyte keratins from ethanol-fed animals, the resonance at 4 ppm was missing from the spectrum. These observations indicate that the keratin site that is dephosphorylated in ethanol-fed rats is characterized by the same 31P chemical shift as the keratin site that is phosphorylated by A-kinase.

Biochemical actions of chronic ethanol exposure in the mesolimbic dopamine system

In previous studies, we have demonstrated that chronic administration of morphine or cocaine produces some common biochemical adaptations in the ventral tegmental area (VTA) and nucleus accumbens (NAc), components of the mesolimbic dopamine system implicated in the reinforcing actions of these and other drugs of abuse. Since this neural pathway is also implicated in the reinforcing actions of ethanol, it was of interest to determine whether chronic ethanol exposure results in similar biochemical adaptations. Indeed, as seen for chronic morphine and cocaine treatments, we show here that chronic ethanol treatment increased levels of tyrosine hydroxylase and glial fibrillary acidic protein immunoreactivity, and decreases levels of neurofilament protein immunoreactivity, in the VTA. Also like morphine and cocaine, ethanol increases levels of cyclic AMP-dependent protein kinase activity in the NAc. These actions of ethanol required long-term exposure to the drug, and were in most cases not seen in the substantia nigra or caudateputamen, components of the nigrostriatal dopamine system studied for comparison. Altered levels of tyrosine hydroxylase in catecholaminergic cells frequently reflect altered states of activation of the cells. Moreover, increasing evidence indicates that ethanol produces many of its acute effects on the brain by regulating NMDA glutamate and GABAA receptors. We therefore examined the influence of chronic ethanol treatment on levels of expression of specific glutamate and GABA receptor subunits in the VTA. It was found that long-term, but not short-term, ethanol exposure increased levels of immunoreactivity of the NMDAR1 subunit, an obligatory component of NMDA glutamate receptors, and of the GluR1 subunit, a component of many AMPA glutamate receptors; but at the same time, long-term ethanol exposure decreased immunoreactivity levels of the alpha 1 subunit of the GABAA receptor complex. These changes are consistent with an increased state of activation of VTA neurons inferred from the observed increase in tyrosine hydroxylase (TH) expression. These results demonstrate that chronic ethanol exposure results in several biochemical adaptations in the mesolimbic dopamine system, which may underlie prominent changes in the structural and functional properties of this neural pathway related to alcohol abuse and alcoholism.

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)

Adaptation of signal transduction in brain

Cell culture models were used to study the effects of long-term ethanol exposure on neuronal cells. Effects on phospholipase C and phospholipase D mediated signal transduction were investigated by assaying receptor-binding, G protein function, activities of lipases, formation of second messengers and c-fos mRNA. The signal transduction cascades displayed abnormal activities from 2 to 7 days of exposure which differed from the acute effects. Phosphatidylethanol formed by phospholipase D is an abnormal lipid that may harmfully affect nerve cell function.

Role of extracellular adenosine in ethanol-induced desensitization of cyclic AMP production

The decrease in receptor-stimulated cyclic AMP production after chronic ethanol exposure was suggested previously to be secondary to an ethanol-induced increase in extracellular adenosine. The present study was undertaken to ascertain whether a similar mechanism was responsible for the ethanol-induced desensitization of cyclic AMP production in PC12 pheochromocytoma cells. The acute addition of ethanol in vitro significantly increased both basal cyclic AMP content and extracellular levels of adenosine. A 4-day exposure to ethanol decreased basal as well as 2-chloroadenosine- and forskolin-stimulated cyclic AMP contents. No change in cyclic AMP content was observed after a 2-day exposure of PC12 cells to ethanol. Inclusion of adenosine deaminase during the chronic ethanol treatment significantly decreased extracellular levels of adenosine, yet the percentage decrease in 2-chloroadenosine- and forskolin-stimulated cyclic AMP levels after chronic ethanol exposure was not changed by the inclusion of the adenosine deaminase. Similar results were obtained when the chronic treatment was carried out with serum-free defined media. The ethanol-induced desensitization could not be mimicked by chronic exposure of PC12 cells to adenosine analogues. A 24-h exposure of PC12 cells to 2-chloroadenosine resulted in a decrease in the subsequent ability of this adenosine analogue to stimulate cyclic AMP content, but basal and forskolin-stimulated cyclic AMP levels were increased. Similar results were obtained after a 4-day exposure of PC12 cells to 2-chloroadenosine or 5'-N-ethylcarboxamido-adenosine. The present results indicate that the ethanol-induced decrease in receptor-stimulated cyclic AMP content in PC12 cells is not due to an increase in extracellular adenosine.

Surface exposure of synaptosomal gangliosides from long-sleep and short-sleep mice

A galactose oxidase/NaB[3H]4 technique was used to examine the relative surface exposure of gangliosides from whole brain synaptosomes of long-sleep (LS) and short-sleep (SS) mice. The surface exposure of the monosialoganglioside, GM1, did not differ between the two lines. Surface exposure of the polysialogangliosides GD1a, GD1b, and GT1b, however, was significantly greater in LS synaptosomes than in SS. Hydrolysis of the polysialogangliosides by neuraminidase to the end-product, GM1, at early time periods occurred more rapidly in LS than in SS synaptosomes. Upon exposure to either 250 mM or 50 mM ethanol, LS synaptosomal ganglioside surface exposure was decreased, but that of SS was increased. Pairwise comparisons of the individual ganglioside classes indicated that the decrease in LS synaptosomal ganglioside surface exposure was attributable to decreases in the polysialogangliosides, compared with controls. The ethanol-induced increase in SS synaptosomal ganglioside surface exposure, however, was mainly due to an increased surface exposure of only GD1a. These results suggest that intrinsic differences in the surface exposure of gangliosides and/or the magnitude and direction of ethanol-induced changes in ganglioside surface distribution may reflect biophysical or modulatory mechanisms by which this class of compounds modifies membrane sensitivity to ethanol. These results suggest that further studies should be performed to determine whether gangliosides are factors in genetically determined sensitivity to ethanol.

Ceramide composition of whole brain synaptosomal gangliosides from mice genetically bred for divergent ethanol sensitivities

A comparison of the two major ceramide molecular species (d18:1-C18:0 and d20:1-C18:0) of synaptosomal gangliosides GM1, GD1a+GT1a, GD1b, GT1b, revealed a difference between the ceramide composition of ethanol-sensitive LS and ethanol-insensitive SS whole brain synaptosomal gangliosides. In all comparisons, the ratio of the two major molecular species, (d18:1-C18:0/d20:1-C18:0) was less for LS than for SS mice.

Ethanol has no effect on cAMP-dependent protein kinase-, protein kinase C-, or Ca(2+)-calmodulin-dependent protein kinase II-stimulated phosphorylation of highly purified substrates in vitro

The actions of ethanol on kinase stimulated phosphorylation were examined using highly purified protein kinases and a variety of purified substrates. Ethanol (25-200 mM) failed to alter the phosphorylation of histone IIa and histone IIIs by cAMP-dependent protein kinase (PKA) and protein kinase C (PKC), respectively. Moreover, ethanol (25-200 mM) did not affect the phosphorylation of synapsin I by Ca(2+)-calmodulin-dependent protein kinase II (CAM kinase II). Finally, neither PKA nor PKC stimulated phosphorylation of the GABAA receptor (GABAA-R) was modulated by ethanol at any concentration of ethanol tested. These results suggest that ethanol, in pharmacological concentrations, has no direct actions on the ability of these kinases to catalyze the phosphorylation of specific substrate proteins. In particular, ethanol does not appear to directly influence GABAA-R phosphorylation by either PKA or PKC.

Effects of chronic ethanol exposure on cardiac receptor-adenylyl cyclase coupling: studies in cultured embryonic chick myocytes and ethanol fed rats

Ethanol effects in the brain appear to be mediated at least in part by an alteration in receptor-effector coupling via guanine nucleotide-binding regulatory proteins (G proteins). To test the hypothesis that a similar pathway participates in the cardiotoxic effects of ethanol, we assessed the effects of chronic ethanol on two commonly used experimental models: embryonic chick myocytes in culture and ventricular myocardium from chronically fed rats. Ethanol had no effect on either the function or quantity of G proteins as assessed by effector-stimulated adenylyl cyclase activity and the levels of ADP-ribosylation substrates. In contrast, effector-stimulated adenylyl cyclase activity was significantly altered in the liver of ethanol-fed rats. These results suggest that receptor-effector coupling via G proteins in our two cardiac models is insensitive to ethanol and that ethanol effects may be species or organ specific.

Pharmacotherapies for alcoholism: promising agents and clinical issues

The past 10 years have witnessed important advances in research on pharmacotherapy for alcoholism. Promising drugs are discussed under six headings: agents to treat alcohol withdrawal; anticraving agents; agents that make drinking an aversive experience; agents to alleviate concomitant psychiatric problems; agents to treat concurrent drug abuse; and amethystic ("sobering-up") agents. Research on the drug classes is summarized and clinical issues surrounding specific agents and alcoholism pharmacotherapy in general are discussed. Finally, long-range therapeutic implications of recent findings on the actions of alcohol on basic mechanisms of the brain are offered.

G proteins coupled to phospholipase C: molecular targets of long-term ethanol exposure

Long-term ethanol exposure is known to inhibit bradykinin-stimulated phosphoinositide hydrolysis in cultures of neuroblastoma x glioma 108-15 cells. In the present study, [3H]bradykinin binding, GTP-binding protein function, and phospholipase C activity were assayed in cells grown for 4 days in 100 mM ethanol with the aim of elucidating the molecular target of ethanol on signal transduction coupled to inositol trisphosphate and diacylglycerol formation. Ethanol exposure reduced guanosine 5'-O-(3-thiotriphosphate) [GTP(S)]- and, to a lesser extent, NaF/AlCl3-stimulated phosphoinositide hydrolysis, whereas it had no effect on the enzymatic activity of a phosphatidylinositol 4,5-bisphosphate-specific phospholipase C. [3H]Bradykinin binding in the absence of GTP(S) was not influenced by ethanol exposure. However, the reduction in [3H]bradykinin binding seen in control cells after addition of GTP analogue was inhibited in cells grown in ethanol-containing medium. The results indicate that long-term ethanol exposure exerts its effects on receptor-stimulated phosphoinositide hydrolysis primarily at the level of the GTP-binding protein.

Neuroadaptive responses to chronic ethanol

Cellular responses of neuronal tissue to chronic ethanol exposure are reviewed. Evidence for adaptive responses to the acute actions of ethanol is available for five systems: GABA-activated chloride channels, voltage-sensitive calcium channels, NMDA-activated cation channels, receptors coupled through stimulatory guanine nucleotide binding proteins, and membrane lipid order. We suggest that at least some of these adaptive responses occur because of ethanol actions at the level of gene expression.

The molecular biology of addictive drugs

The additive drugs alcohol, morphine, cocaine, and amphetamine are each associated with the development of tolerance and physical dependence. Changes in gene expression occur in cell culture and in vivo with the administration of these centrally-acting drugs. This article reviews those experiments that have studied drug-induced alterations in gene transcription. Ethanol has diverse effects on the amounts of messenger RNA molecules within the central nervous system. Ion channels, neuropeptides, membrane receptors, and immediate early genes represent several regulated mRNAs. The effects are selective, however, as many other specific products are not altered. Evidence for a genetic predisposition to ethanol use reinforces the importance of the genotype. Opioids, cocaine, and amphetamine also affect gene transcription. Messenger RNAs studied have included many of those demonstrated to be altered by alcohol use. Interestingly, use of any of these drugs alters the expression of immediate early genes. These genes may represent an initial step in the pathway that leads to drug addiction. The composite of drug-induced changes in gene expression results in the cellular responses of tolerance and dependence. The characterization of these changes should provide a better understanding of the molecular mechanisms of drug addiction.

Effects of ethanol on cAMP production in murine embryonic palate mesenchymal cells

Ethanol affected the ability of murine embryonic palate mesenchymal (MEPM) cells to produce cAMP in response to hormone treatment. Acute exposure to ethanol resulted in an increase in hormone-stimulated cAMP levels, while chronic ethanol treatment led to decreased sensitivity to hormone. Forskolin-stimulated cAMP levels were decreased by both acute and chronic ethanol treatment, while the cells' response to cholera toxin was unchanged by ethanol treatment. The lack of sensitivity of the cholera toxin response to ethanol suggests that, in contrast to what has been observed in other systems, ethanol does not affect the production or activity of G alpha s in MEPM cells. These results suggest a possible explanation for the molecular basis for the craniofacial abnormalities observed in the fetal alcohol syndrome.

Effects of chronic exposure to ethanol alone and in combination with desipramine on beta-adrenoceptors of rat brain

The effect of chronic ethanol exposure alone or in combination with desipramine on agonist and antagonist binding to beta-adrenoceptors was studied in membrane preparations from rat frontal cortex and hippocampus. Ten day exposure of animals to ethanol vapor (25 mg/l) in inhalation chambers had no effect on binding properties of antagonist iodocyanopindolol (ICYP) in either brain region. However, ethanol in combination with chronic desipramine treatment prevented the reduction of beta-adrenoceptor density in frontal cortex produced by desipramine administration. Similar to its effects on antagonist binding, chronic ethanol exposure did not change the agonist isoproterenol binding characteristics measured in membranes from either rat frontal cortex or hippocampus. However, the combination of ethanol plus desipramine reduced the dissociation constant of the low affinity state of the receptor (KL) in frontal cortex from 23.1 +/- 3.7 microM in controls to 11.2 +/- 1.7 microM. Moreover, ethanol plus desipramine produced a greater decrease in the percentage of cortical receptors in the high affinity state for agonist (%RH) than did desipramine alone. This suggests that ethanol enhances desipramine-induced desensitization of beta-adrenoceptors in frontal cortex in spite of the prevention of reduction in density of the receptors. In hippocampal membranes, ethanol together with desipramine prevented desipramine-induced changes in agonist binding characteristics, i.e. the decrease in KH (dissociation constant from high affinity state of the receptor) and the consequent enhancement in KL/KH ratio. Thus, chronic exposure to relatively low concentrations of ethanol partially prevents effects of desipramine on beta-adrenoceptors.

Brain forskolin binding in mice dependent on and tolerant to ethanol

Chronic ethanol ingestion by mice was previously shown to result in decreased activation of adenylate cyclase by guanine nucleotides and beta-adrenergic agonists, and in the loss of the high affinity beta-adrenergic agonist binding site in frontal cortex and hippocampus but not in cerebellum. These results indicate a regional specificity of ethanol's actions on beta-adrenergic receptors, the guanine nucleotide binding protein (Gs) and/or adenylate cyclase. To further detail the anatomical specificity of the effects of ethanol ingestion on receptor-coupled adenylate cyclase (AC) systems we have quantified the binding of [3H]forskolin to brain sections of control and ethanol-fed mice. High-affinity forskolin binding, thought to represent the complex of the alpha-subunit of Gs (as) and AC, was decreased in several brain areas including frontal cortex and hippocampus, but not in cerebellum, nucleus accumbens and certain other brain areas of ethanol-fed mice. Guanine nucleotides, such as Gpp(NH)p, generally enhanced forskolin binding in control animals. In ethanol-fed mice, however, Gpp(NH)p failed to enhance forskolin binding in most brain regions. These findings suggest that chronic ethanol ingestion may decrease the amount or function of as-AC in certain brain regions. Moreover, the regulation of the formation of this complex in different brain regions may affect responses to ethanol ingestion in mice.