Ethanol's effects on cortical adenylate cyclase activity

Ethanol and acetaldehyde action on central dopamine systems: mechanisms, modulation, and relationship to stress

There has been a great deal of activity in recent years in the study of the direct effects of ethanol on the dopamine reward system originating in the ventral tegmental area (VTA). In addition, recent evidence suggests that acetaldehyde formed from ethanol in the brain or periphery may be a crucial factor in the central effects of ethanol. This critical review examines the actions of ethanol and acetaldehyde on neurons of the VTA and the possible interactions with stress, with a focus on electrophysiological studies in vivo and in vitro. Ethanol has specific effects on dopamine neurons and there is recent evidence that some of the in vivo and in vitro effects of ethanol are mediated by acetaldehyde. Stress has some analogous actions on neuronal activity in the VTA, and the interactions between the effects of stress and alcohol on VTA neurons may be a factor in ethanol-seeking behavior. Taken together, the evidence suggests that stress may contribute to the activating effects of ethanol on dopamine VTA neurons, that at least some actions of ethanol on dopamine VTA neurons are mediated by acetaldehyde, and that the interaction between stress and alcohol could play a role in susceptibility to alcoholism. The link between acetaldehyde and ethanol actions on brain reward pathways may provide a new avenue for the development of agents to reduce alcohol craving.

Ethanol enhances both action potential-dependent and action potential-independent GABAergic transmission onto cerebellar Purkinje cells

Ethanol (EtOH) modulates synaptic efficacy in various brain areas, including the cerebellum, which plays a role in motor coordination. Previous studies have shown that EtOH enhances tonic inhibition of cerebellar granule cells, which is one of the possible reasons for the alcohol-induced motor impairment. However, the effects of EtOH on molecular layer interneurons (MLIs) in the mouse cerebellum have remained unknown. Here we found that MLIs were depolarized by EtOH through enhancement of hyperpolarization-activated cationic currents (I(h)). Under physiological conditions, a low EtOH concentration (3-50 mM) caused a small increase in the firing rate of MLIs, whereas, in the presence of blockers for ionotropic glutamate and GABA receptors, EtOH (>or=10 mM) robustly enhanced MLI firing, suggesting that synaptic inputs, which seem to serve as the phasic inhibition, could suppress the EtOH-mediated excitation of MLIs and Purkinje cells (PCs). Even in the absence of synaptic blockers, a high EtOH concentration (100 mM) markedly increased the firing rate of MLIs to enhance GABAergic transmission. Furthermore, 100 mM EtOH-facilitated miniature IPSCs via a mechanism that depended on intracellular cyclic AMP, voltage-dependent Ca(2+) channels, and intracellular Ca(2+) stores, but was independent of I(h) or PKA. The two distinct effects of a high EtOH concentration (>or=100 mM), however, failed to attenuate the EtOH-induced strong depolarization of MLIs. These results suggest that acute exposure to a low EtOH concentration (<or=50 mM) enhanced GABAergic synaptic transmission, which suppressed the EtOH-evoked excitation of MLIs and PCs, thereby maintaining precise synaptic integration of PCs.

Effect of ethanol on follicle stimulating hormone-induced steroidogenic acute regulatory protein (StAR) in cultured rat granulosa cells

Steroidogenic acute regulatory protein (StAR) plays a critical role in trophic hormone-stimulated steroid biosynthesis by facilitating the transfer of cholesterol across the mitochondrial membrane, where the cytochrome P450scc enzyme resides to initiate steroid hormone biosynthesis. Because follicle stimulating hormone (FSH) is a critically important regulator of estradiol (E2) synthesis in granulosa cells and because ethanol is known to suppress gonadotropin-stimulated ovarian steroidogenesis, we evaluated the effects of ethanol on FSH-stimulated StAR in ovarian granulosa cells. Granulosa cells from immature rats pretreated with pregnant mare serum gonadotropin were cultured for 24 h in serum-free medium, either alone (medium only) or with FSH (25 ng/ml) in the presence or absence of ethanol (50 mM). Real-time polymerase chain reaction (PCR) analysis showed increased (p < 0.01) expression of the StAR transcript in FSH-treated cells, when compared with cells that received medium only. The FSH stimulation of StAR transcript was blocked (p < 0.01) by the presence of ethanol. This effect coincided with a decrease in E2 secretion into the culture medium. We also examined whether ethanol could affect the production of cyclic AMP (cAMP), the main second messenger that mediates gonadotropin action within the ovary. FSH treatment of granulosa cells markedly increased (p < 0.001) cAMP levels, an effect that was not altered by ethanol. Importantly, FSH induced an increase (p < 0.01) in the release of prostaglandin E2 (PGE2), an effect that was blocked by ethanol. Real-time PCR analysis showed that ethanol had no effect on the expression of cyclooxygenase-1 (COX-1), but blocked (p < 0.01) FSH-stimulated expression of COX-2. These results demonstrate that ethanol is capable of inhibiting FSH-induced ovarian StAR and thus, contributing to suppressed E2 secretion, at least in part, through an inhibitory action on the COX-2-PGE2 pathway.

Vasoactive intestinal peptide and corticotropin-releasing hormone increase beta-endorphin release and proopiomelanocortin messenger RNA levels in primary cultures of hypothalamic cells: effects of acute and chronic ethanol treatment

BACKGROUND

beta-Endorphin (beta-EP) neurons are involved in ethanol's action on a variety of brain functions, including positive reinforcement. These neurons are innervated by vasoactive intestinal peptide (VIP)-containing and corticotropin-releasing hormone (CRH)-containing neurons in the hypothalamus. Whether these neuropeptides affect beta-EP neuronal function in the presence or absence of ethanol has not previously been determined.

METHODS

The authors determined the effects of VIP and CRH on gene expression and peptide release from beta-EP neurons in primary cultures of mediobasal hypothalamic cells. The effects of receptor antagonists on VIP- and CRH-induced beta-EP release was determined. Furthermore, the authors studied the effects of acute and chronic treatment with ethanol on the response of beta-EP neurons to VIP and CRH. Real-time reverse-transcription polymerase chain reaction was used for messenger RNA (mRNA) detection, and radioimmunoassay was used for hormone measurements.

RESULTS

We show that beta-EP neurons responded concentration dependently to VIP and CRH treatments by increasing both beta-EP release and proopiomelanocortin mRNA expression. Simultaneous treatment with a nonspecific receptor antagonist reduced the ability of CRH or VIP to induce beta-EP release from mediobasal hypothalamic cells. Acute treatment with ethanol increased beta-EP neuronal gene expression and the secretory response to CRH and VIP. However, previous exposure to chronic ethanol reduced the CRH and VIP responses of these neurons.

CONCLUSIONS

These results indicate that VIP and CRH stimulate beta-EP release from hypothalamic cells in primary cultures and that the stimulatory and adaptive responses of beta-EP neurons to ethanol may involve alteration in the responsiveness of beta-EP-secreting neurons to CRH and VIP.

Pharmacogenomic analysis of mechanisms mediating ethanol regulation of dopamine beta-hydroxylase

We previously showed that ethanol regulates dopamine beta-hydroxylase (DBH) mRNA and protein levels in human neuroblastoma cells (Thibault, C., Lai, C., Wilke, N., Duong, B., Olive, M. F., Rahman, S., Dong, H., Hodge, C. W., Lockhart, D. J., and Miles, M. F. (2000) Mol. Pharmacol. 58, 1593-1600). DBH catalyzes norepinephrine synthesis, and several studies have suggested a role for norepinephrine in ethanol-mediated behaviors. Here, we performed a detailed analysis of mechanism(s) underlying ethanol regulation of DBH expression in SH-SY5Y cells. Transient transfection analysis showed that ethanol (25-200 mM) caused concentration- and time-dependent increases in DBH gene transcription. Progressive deletions identified ethanol-responsive sequences in the -262 to -142 bp region of the DBH gene promoter. Mutagenesis of cAMP-response element (CRE) sequences in this region abolished ethanol responsiveness while maintaining responsiveness to phorbol esters. Coexpression of dominant-negative CRE-binding protein greatly reduced ethanol induction of DBH. Inhibitors of protein kinase A, casein kinase II, and MAPK reduced ethanol induction of DBH promoter activity. Pharmacogenomic studies with microarrays showed that protein kinase A, MEK, and casein kinase II inhibitors blocked induction of DBH and a large subset of ethanol-responsive genes. These genes had diverse functional groupings, including multiple members of the MAPK and phosphatidylinositol signaling cascades. Real-time PCR analysis validated select microarray results. Taken together, these results suggest that ethanol regulation of DBH requires a functional CRE and its binding protein and may require interaction of multiple kinase pathways. This mechanism may also mediate ethanol responsiveness of a complex subset of genes in neural cells. These studies may have implications for behavioral responses to ethanol or mechanisms underlying ethanol-related neurological disease.

Isoform-specific regulation of adenylyl cyclase: a potential target in future pharmacotherapy

Adenylyl cyclase (AC) is a target enzyme of multiple G-protein-coupled receptors (GPCRs). In the past decade, the cloning, structure and biochemical properties of nine AC isoforms were reported, and each isoform of AC shows distinct patterns of tissue distribution and biochemical/pharmacological properties. In addition to the conventional regulators of this enzyme, such as calmodulin (CaM) or PKC, novel regulators, for example, caveolin, have been identified. Most importantly, these regulators work on AC in an isoform dependent manner. Recent studies have demonstrated that certain classic AC inhibitors, i.e., P-site inhibitors, show an isoform-dependent inhibition of AC. The side chain modifications of forskolin, a diterpene extract from Coleus forskolii, markedly enhance its isoform selectivity. When taken together, these findings suggest that it is feasible to develop new pharmacotherapeutic agents that target AC isoforms to regulate various neurohormonal signals in a highly tissue-/organ-specific manner.

Ethanol-induced phosphorylation and potentiation of the activity of type 7 adenylyl cyclase. Involvement of protein kinase C delta

Ethanol can enhance G(salpha)-stimulated adenylyl cyclase (AC) activity. Of the nine isoforms of AC, type 7 (AC7) is the most sensitive to ethanol. The potentiation of AC7 by ethanol is dependent on protein kinase C (PKC). We designed studies to determine which PKC isotype(s) are involved in the potentiation of Galpha(s)-activated AC7 activity by ethanol and to investigate the direct phosphorylation of AC7 by PKC. AC7 was phosphorylated in vitro by the catalytic subunits of PKCs. The addition of ethanol to AC7-transfected HEK 293 cells increased the endogenous phosphorylation of AC7, as indicated by a decreased "back-phosphorylation" of AC7 by PKC in vitro. The potentiation of Galpha(s)-stimulated AC7 activity by either phorbol 12,13-dibutyrate or ethanol, in HEL cells endogenously expressing AC7, was not through the Ca(2+)-sensitive conventional PKCs. However, the potentiation of AC7 activity by ethanol or phorbol 12,13-dibutyrate was found to be reduced by the selective inhibitor of PKCdelta (rottlerin), a PKCdelta-specific inhibitory peptide (deltaV1-1), and the expression of the dominant negative form of PKCdelta. Immunoprecipitation data indicated that PKCdelta could bind and directly phosphorylate AC7. The results indicate that the potentiation of AC7 activity by ethanol involves phosphorylation of AC7 that is mediated by PKCdelta.

Changes in Ca2+-dependent protein kinase C isoforms induced by chronic ethanol treatment in mice

Protein kinase C (PKC) has been shown to regulate ethanol sensitivity. The goal of the present study was to ascertain whether chronic in vivo ethanol treatment could affect PKC isoforms in the mouse brain. We measured the protein level of membrane-bound PKC isoforms following chronic ethanol treatment using Western blotting. The protein level of membrane-bound PKCalpha and PKCgamma isoforms, which are defined as Ca2+-dependent PKC isoforms (cPKC), in the limbic forebrain during chronic ethanol treatment was significantly increased, whereas the levels of both were significantly decreased in the frontal cortex. By contrast, there was no change in PKCepsilon, a Ca2+-independent PKC isoform, in both areas. These findings suggest that the change in membrane-bound cPKC in the limbic forebrain and frontal cortex may play substantial roles for the development of ethanol dependence.

Regulation and role of adenylyl cyclase isoforms

At least nine closely related isoforms of adenylyl cyclases (ACs), the enzymes responsible for the synthesis of cyclic AMP (cAMP) from ATP, have been cloned and characterized in mammals. Depending on the properties and the relative levels of the isoforms expressed in a tissue or a cell type at a specific time, extracellular signals received through the G-protein-coupled receptors can be differentially integrated. The present review deals with various aspects of such regulations, emphasizing the role of calcium/calmodulin in activating AC1 and AC8 in the central nervous system, the potential inhibitory effect of calcium on AC5 and AC6, and the changes in the expression pattern of the isoforms during development. A particular emphasis is given to the role of cAMP during drug and ethanol dependency and to some experimental limitations (pitfalls in the interpretation of cellular transfection, scarcity of the invalidation models, existence of complex macromolecular structures, etc).

Increased levels of calcium-sensitive adenylyl cyclase subtypes in the limbic system of alcoholics: evidence for a specific role of cAMP signaling in the human addictive brain

We examined the amounts of several adenylyl cyclase (AC) isoforms and of cAMP-response element binding protein (CREB) in alcoholic and control brains. Immunoreactivity of type I AC was significantly increased in alcoholic nucleus accumbens and corpus amygdaloideum. Immunoreactivity of type VIII AC was also increased in alcoholic corpus amygdaloideum and hippocampus. CREB immunoreactivities were unchanged. These findings indicate that the brain-region specific increase of Ca(2+)-sensitive AC may contribute to the pathophysiology of alcoholism.

Phosphorylation cascades control the actions of ethanol on cell cAMP signalling

Our studies indicate that, in the presence of particular isoforms of adenylyl cyclase (i.e., type 7 AC), moderately intoxicating concentrations of ethanol will significantly potentiate transmitter-mediated activation of the cAMP signaling cascade. Activation of this signaling cascade may have important implications for the mechanisms by which ethanol produces intoxication, and/or for the mechanisms of neuroadaptation leading to tolerance to, and physical dependence on, ethanol. We initiated a series of studies to investigate the phosphorylation of AC7 by PKC, the role of this phosphorylation in modulating the sensitivity of AC7 to activation by Gsalpha, and the PKC isotype(s) involved in the phosphorylation of AC7. The T7 epitope-tagged AC7 expressed in Sf9 and HEK293 cells was found to be phosphorylated in vitro by the catalytic subunit of PKC. Treatment of AC7-transfected HEK293 cells with phorbol dibutyrate (PDBu) or ethanol increased the phosphorylation of AC7 and its responsiveness to Gsalpha. In human erythroleukemia (HEL) cells, which endogeneously express AC7, ethanol and PDBu increased AC activity stimulated by PGE(1). The potentiation by both PDBu and ethanol was found to be sensitive to the PKC delta-selective inhibitor, rottlerin. The potentiation of AC activity by ethanol in HEL cells was also selectively attenuated by the RACK inhibitory peptide specific for PKC delta, and by expression of the dominant negative, catalytically inactive, form of PKC delta. These data demonstrate that AC7 can be phosphorylated by PKC, leading to an increase in functional activity, and ethanol can potentiate AC7 activity through a PKC delta-mediated phosphorylation of AC7.

Uncoupling of betaIIPKC from its targeting protein RACK1 in response to ethanol in cultured cells and mouse brain

Protein kinase C (PKC) is involved in many neuroadaptive responses to ethanol in the nervous system. PKC activation results in translocation of the enzyme from one intracellular site to another. Compartmentalization of PKC isozymes is regulated by targeting proteins such as receptors for activated C kinase (RACKs). It is possible, therefore, that ethanol-induced changes in the function and compartmentalization of PKC isozymes could be due to changes in PKC targeting proteins. Here we study the response of the targeting protein RACK1 and its corresponding kinase betaIIPKC to ethanol, and propose a novel mechanism to explain how ethanol modulates signaling cascades. In cultured cells, ethanol induces movement of RACK1 to the nucleus without affecting the compartmentalization of betaIIPKC. Ethanol also inhibits betaIIPKC translocation in response to activation. These results suggest that ethanol inhibition of betaIIPKC translocation is due to miscompartmentalization of the targeting protein RACK1. Similar events occurred in mouse brain. In vivo exposure to ethanol caused RACK1 to localize to nuclei in specific brain regions, but did not affect the compartmentalization of betaIIPKC. Thus, some of the cellular and neuroadaptive responses to ethanol may be related to ethanol-induced movement of RACK1 to the nucleus, thereby preventing the translocation and corresponding function of betaIIPKC.

Partial rescue of ethanol-induced neuronal apoptosis by growth factor activation of phosphoinositol-3-kinase

BACKGROUND

Ethanol inhibition of insulin signaling pathways may contribute to impaired central nervous system (CNS) development in the fetal alcohol syndrome and brain atrophy associated with alcoholic neurodegeneration. Previous studies demonstrated ethanol inhibition of insulin-stimulated growth in PNET2 CNS-derived proliferative (immature) neuronal cells. We now provide evidence that the growth-inhibitory effect of ethanol in insulin-stimulated PNET2 cells is partly due to apoptosis.

METHODS

Control and ethanol-treated PNET2 cells were stimulated with insulin and analyzed for viability, apoptosis, activation of pro-apoptosis and survival gene expression and signaling pathways, and evidence of caspase activation.

RESULTS

Ethanol-treated PNET2 neuronal cells exhibited increased apoptosis mediated by increased levels of p53 and phospho-amino-terminal c-jun kinase (phospho-JNK), and reduced levels of Bcl-2, phosphoinositol 3-kinase (PI3 K), and intact (approximately 116 kD) poly (ADP ribose) polymerase (PARP), a deoxyribonucleic acid repair enzyme and important substrate for caspase 3. Partial rescue from ethanol-induced neuronal cell death was effected by culturing the cells in medium that contained 2% fetal calf serum instead of insulin, or insulin plus either insulin-like growth factor type 1 or nerve growth factor. The resulting enhanced viability was associated with reduced levels of p53 and phospho-JNK and increased levels of PI3 K and intact PARP.

CONCLUSIONS

The findings suggest that ethanol-induced apoptosis of insulin-stimulated neuronal cells can be reduced by activating PI3 K and inhibiting pro-apoptosis gene expression and intracellular signaling through non-insulin-dependent pathways.

Ethanol-induced translocation of cAMP-dependent protein kinase to the nucleus. Mechanism and functional consequences

Ethanol induces translocation of the catalytic subunit (Calpha) of cAMP-dependent protein kinase (PKA) from the Golgi area to the nucleus in NG108-15 cells. Ethanol also induces translocation of the RIIbeta regulatory subunit of PKA to the nucleus; RI and Cbeta are not translocated. Nuclear PKA activity in ethanol-treated cells is no longer regulated by cAMP. Gel filtration and immunoprecipitation analysis confirm that ethanol blocks the reassociation of Calpha with RII but does not induce dissociation of these subunits. Ethanol also reduces inhibition of Calpha by the PKA inhibitor PKI. Pre-incubation of Calpha with ethanol decreases phosphorylation of Leu-Arg-Arg-Ala-Ser-Leu-Gly (Kemptide) and casein but has no effect on the phosphorylation of highly charged molecules such as histone H1 or protamine. cAMP-response element-binding protein (CREB) phosphorylation by Calpha is also increased in ethanol-treated cells. This increase in CREB phosphorylation is inhibited by the PKA antagonist (R(p))-cAMPS and by an adenosine receptor antagonist. These results suggest that ethanol affects a cascade of events allowing for sustained nuclear localization of Calpha and prolonged CREB phosphorylation. These events may account for ethanol-induced changes in cAMP-dependent gene expression.

Quantitative reduction of type I adenylyl cyclase in human alcoholics

The amounts of adenylyl cyclase type I (AC I) were examined in various parts of the postmortem brains from alcoholics who prior to death had been abstinent from alcohol for at least 6 months and compared with controls using immunoblot analysis with anti-AC I specific antibody. It was revealed that a significant reduction of AC I was observed in both frontal and temporal cortices. On the other hand, in other areas (occipital cortex, caudate nucleus, putamen, and hippocampus) the amounts were comparable between alcoholics and controls. In the next step, we examined two subtypes of human AC mRNA levels (AC I and AC VIII) in blood cells by quantitative RT-PCR using [alpha-32P]dCTP with two sets of the synthetic oligonucleotide primers based on the DNA sequences reported elsewhere (Villacres, E.C. et al., Genomics 16 (1993) 473-478; J. Parma et al., Biochem. Biophys. Res. Commun. 179 (1991) 455-462). The amounts of amplified DNAs of both AC I and AC VIII were significantly smaller in alcoholics than in controls. On the other hand, the amounts of amplified DNA of beta-actin DNA were almost equal between alcoholics and controls. It appears from these results that a reduction in the amount of AC subtypes may be a biological marker for alcoholics.

Effects of ethanol on basal and adenosine-induced increases in beta-endorphin release and intracellular cAMP levels in hypothalamic cells

Recently we have shown that the cAMP system is involved in ethanol-regulated beta-endorphin (beta-EP) release from rat hypothalamic neurons in primary cultures. The cascade of events that leads to activation of cAMP following ethanol treatment in hypothalamic beta-EP neurons is not apparent. In this study the role of adenosine, a cAMP regulator, in ethanol-regulated beta-EP release was determined by measuring the cellular incorporation of [3H]adenosine, intracellular cAMP levels and media immunoreactive (IR) beta-EP levels in cultures of rat hypothalamic cells following ethanol treatments in the presence and absence of an adenosine agonist and antagonist. Acute exposure to a 50 mM dose of ethanol for a period of 1 h increased media levels of IR-beta-EP and cellular contents of cAMP, but the ethanol treatment decreased [3H]adenosine uptake. Constant exposure to a 50 mM dose of ethanol for a period of 48 h, failed to alter media levels of IR-beta-EP, cell content of cAMP and [3H]adenosine uptake. The media level of IR-beta-EP was elevated following treatment with adenosine receptor agonist phenyl-isopropyl adenosine (PIA) and was reduced following treatment with adenosine receptor antagonist isobutylmethylxanthine (IBMX) or with adenosine uptake inhibitor adenosine deaminase. The level of cellular cAMP was also increased by PIA but was decreased by IBMX and adenosine deaminase. The stimulatory actions of the adenosine agonist PIA on IR-beta-EP release and on cAMP production were potentiated by simultaneous incubation with ethanol for 1 h. However, chronic ethanol exposure reduced PIA-induced IR-beta-EP release and cAMP production. Additionally, both IBMX and adenosine deaminase reduced ethanol-induced IR-beta-EP release and cAMP levels. These results suggest that ethanol inhibits adenosine uptake in IR-beta-EP neurons in the hypothalamus, thereby increasing extracellular levels of adenosine and leading to activation of membrane adenosine receptors, cAMP production and IR-beta-EP secretion from these neurons. Chronic ethanol desensitizes the adenosine-regulated cAMP production and IR-beta-EP release from hypothalamic neurons.

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.

Blood ethanol levels and adenylyl cyclase activity in lymphocytes of alcoholic patients

BACKGROUND

The adenylyl cyclase (AC) signal transduction pathway is a target of acute and chronic ethanol actions. This study examined whether AC activity in lymphocyte membranes of male alcoholic patients correlated with blood concentrations of ethanol.

METHODS

Patients (n = 13; mean age: 40 +/- 8 years) were studied on the day of admission (day 0) and 2 days later under detoxification. Moreover, 13 age-matched male healthy controls (mean age 40 +/- 9 years) were included. Lymphocyte membranes were prepared by differential centrifugation whereby blood ethanol was washed out. As a measure of AC activity the formation of cyclic adenosine monophosphate (cAMP) from adenosine triphosphate was determined without (basal activity) and with stimulation of the second messenger system by the guanosine triphosphate (GTP) analogue GTP gamma S (20 mumol/L) via the G-protein or by forskolin (100 mumol/L) acting directly on the AC enzyme.

RESULTS

On day 0, when ethanol blood concentrations were 38-100 mmol/L, we found a significant negative correlation between ethanol blood levels and stimulated AC activities. On day 2, the negative correlation with blood ethanol levels of day 0 had disappeared.

CONCLUSIONS

The consumption of ethanol affects the AC system in lymphocytes of alcohol-dependent patients by a persistent effect on the cAMP forming enzyme.

Enhanced Gi-protein-mediated mitogenesis following chronic ethanol exposure in a rat model of experimental hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is associated with increased expression and function of inhibitory guanine nucleotide regulatory proteins (Gi-proteins). This study addresses the effects of chronic ethanol exposure on the expression and function of adenylyl cyclase (AC)-linked G-proteins (Gs and Gi) and growth in experimental HCC. G-protein expression and function was determined by immunoblot in the hepatic tumorigenic H4IIE cell line and isolated cultured hepatocytes in the absence or presence of ethanol (5-100 mmol/L). Chronic exposure (24 hours) to ethanol dose-dependently increased Gialpha1/2 expression in the H4IIE cell line, but not in cultured hepatocytes. Gsalpha-protein expression remained unchanged in both H4IIE cells and cultured hepatocytes following ethanol treatment. In addition, ethanol directly activated a Gi-protein, because pertussis toxin (PTx)-catalyzed, adenosine diphosphate (ADP)-dependent ribosylation of Gialpha substrates decreased following ethanol treatment. The increased functional activity of Gialpha1/2-protein expression was confirmed by demonstrating that ethanol dose-dependently inhibited basal and stimulated AC activity in H4IIE cells, while not significantly altering basal AC activity in isolated cultured hepatocytes. Furthermore, while ethanol had no significant effect on basal mitogenesis in H4IIE cells or hepatocytes, increased mitogenesis caused by direct Gialpha-protein stimulation (mastoparan M7; 10-5,000 nmol/L) was further enhanced in the presence of ethanol, an effect that was completely blocked following Gi-protein inhibition (PTx; 100 ng/mL). In contrast, activation of Gi-proteins using M7 failed to alter cellular mitogenesis in isolated cultured hepatocytes, whether in the absence or presence of ethanol. Finally, analysis of mitogen-activated protein kinase (MAPK) activity demonstrated that chronic ethanol treatment further enhanced Gi-protein-stimulated MAPK activity in hepatic tumorigenic cells. In conclusion, these data demonstrate that ethanol enhances cellular mitogenesis in experimental HCC as a result of, at least in part, a Gi-MAPK-dependent pathway. Furthermore, this effect may be caused by ethanol's direct up-regulation of the expression and activity of Gi-proteins in HCC.

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.

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.

Effects of ethanol and nomifensine on NE clearance in the cerebellum of young and aged Fischer 344 rats

Rapid chronoamperometric recordings coupled with local application of drugs by pressure ejection were used to investigate the effects of nomifensine and ethanol (EtOH) on exogenous norepinephrine (NE) clearance in the cerebellum of young (5-month-old) and aged (24-26-month-old) male Fischer 344 rats. In the young rats, local nomifensine application prolonged exogenous NE clearance, indicating transporter mediated uptake inhibition. NE clearance was modestly but significantly prolonged in the aged rats as compared to the young rats, suggesting less efficient uptake. Consistent with this, there was little effect of nomifensine on NE clearance in the aged rats. In contrast to the effect of nomifensine, EtOH inhibited NE clearance in both young and aged rats. These data further support the hypothesis that one effect of EtOH in cerebellar NE systems is inhibition of NE uptake into NE-containing nerve terminals, and they also demonstrate that the effect of nomifensine on exogenous NE clearance in vivo in the cerebellum is altered by the aging process, while the effect of EtOH is not.

Alcohol-induced bone disease: impact of ethanol on osteoblast proliferation

The habitual consumption of even moderate quantities of alcohol (1 to 2 drinks/day) is clearly linked with reduced bone mass (osteopenia). Biochemical and histological evaluation of patients with alcoholic bone disease reveal a marked impairment in bone formation in the face of relatively normal bone resorption. Experiments using well-defined osteoblastic model systems indicate that the observed reductions in bone formation result from a direct, antiproliferative effect of ethanol on the osteoblast itself. As bone remodeling and mineralization are dependent on osteoblasts, it follows that the deleterious effect of alcohol on these cells would result in slowed bone formation, aberrant remodeling of skeletal tissue and, ultimately, osteopenia and fractures. The skeletal consequences of alcohol intake during adolescence, when the rapid skeletal growth ultimately responsible for achieving peak bone mass is occurring, may be especially harmful. The specific subcellular mechanisms whereby ethanol inhibits cell proliferation are, as yet, unknown. During the last few years, attention has shifted from nonspecific membrane perturbation effects to actions on certain signaling proteins. Specifically, there is increasing evidence that ethanol may exert significant effects on transmembrane signal transduction processes that constitute major branches of cellular control mechanisms. At present, abstinence is the only effective therapy for alcohol-induced bone disease. An improved understanding of the pathogenesis of alcohol-induced bone disease may eventually result in alternative therapeutic avenues for those who are unable to abstain.

Involvement of metabotropic glutamate receptors in Gi- and Gs-dependent modulation of adenylate cyclase activity induced by a novel cognition enhancer NS-105 in rat brain

The effect of a novel cognition enhancer [(+)-5-oxo-D-prolinepiperidinamide monohydrate] (NS-105) on cAMP formation was investigated in both slices and membranes of the rat cerebral cortex. NS-105 (10(-8)-10(-6) M) inhibited forskolin-stimulated cAMP formation in membranes, however, the compound significantly enhanced the cAMP formation in pertussis toxin-pre-treated membranes, an action that was abolished by cholera toxin. In contrast, in digitonin-permeabilized membranes, NS-105 had no influence on Mn2+-stimulated cAMP formation. Both of the inhibitory and facilitatory actions of NS-105 on cAMP formation were mimicked by a metabotropic glutamate receptor (mGluR) agonist (1S,3R)-1-aminocyclopentane-1,3-dicarboxylic acid (1S,3R-ACPD) and an adrenergic alpha2 agonist UK-14,304, and blocked by a mGluR antagonist 2-amino-3-phosphonopropanoate but not by an alpha2 antagonist yohimbine. In cortical slices, NS-105 (10(-8)-10(-7) M) inhibited forskolin-stimulated cAMP accumulation but enhanced isoproterenol-stimulated cAMP accumulation, as did by a GABA(B) agonist (-)baclofen. On the other hand, (-)baclofen, while it significantly inhibited cAMP accumulation in slices, did no longer inhibit cAMP accumulation, when treated with NS-105 (10(-8)-10(-5) M). Similarly, (-)baclofen-induced inhibition of the cAMP accumulation was reversed by 1S,3R-ACPD and UK-14,304. NS-105 (10(-6)) increased [35S]GTPgammaS binding in the intact but not digitonin-permeabilized cortical membranes, as produced by UK-14,304, although the compound (10(-9)-10(-3) M) had no influence on various neurotransmitter receptor bindings, including alpha2 receptors. These results suggest that NS-105 modulates adenylate cyclase activity by stimulating mGluRs which might coupled to both Gi/Go and Gs.

Decreased inositol 1,4,5-trisphosphate-specific binding in platelets from alcoholic subjects

We measured the degree of inositol 1,4,5-triphosphate (IP3)-specific binding in platelets from alcoholic and nonalcoholic subjects. IP3-specific binding in alcoholic subjects was 45% less than that in nonalcoholic subjects. There was no significant difference in the number of IP3 receptors as detected immunologically in the platelet membrane fractions from alcoholic and nonalcoholic subjects. These results indicate that the decrease in IP3-specific binding in alcoholic subjects may have been due to a decreased affinity, but not number of IP3 binding sites. In contrast to the decrease in IP3 receptor binding, there were no significant changes in phospholipase-C activity or immunoreactivity of phospholipase C-beta 1 in platelet membranes from alcoholic subjects. The decreased IP3-specific binding in platelets may allow for the development of biological markers for alcoholism.

Effects of ceruletide on perioral movements and the dopamine receptor-adenylate cyclase system in rats chronically treated with fluphenazine

The effects of repeated administration of ceruletide (100 micrograms/kg/perday, i.p. for 3 days) on perioral movements and the striatal dopamine receptor adenylate cyclase system were examined in rats chronically treated with fluphenazine enanthate (FPZ) (25 mg/kg i.m. every 3 weeks for 30 weeks) and sesame oil-treated (control) rats. After the tenth injection of fluphenazine, the rats started to display five types of perioral movements (teeth chattering, chewing, tongue protrusion, mouth opening and perioral tremors). Moreover, increases in SCH23390 binding and spiperone binding to striatal membranes, were found in the FPZ-treated rats. Furthermore, dopamine receptor-coupled adenylate cyclase activity was potentiated in striatal membranes. High amplitude EMG discharges (8-10 Hz), recorded from the masseter in the FPZ-treated rats occurred concurrently with perioral tremors. Repeated ceruletide (CLT) injections abolished perioral movements, and reversed both the elevated SCH23390 binding and the dopamine stimulated adenylate cyclase (AC) activity to the control level. The effect of CLT on perioral movements, D1 receptors and dopamine-stimulated AC activity continued for 6 days after the final CLT injection. These findings suggest that systemically administered CLT affects the D1 receptor adenylate cyclase system and that an increase of the D1 receptor mechanism may play an important role in the pathogenesis of tardive dyskinesia.

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.

Effects of chronic alcohol consumption and aging on dopamine D2 receptors in Fischer 344 rats

Aging and chronic alcohol consumption are each accompanied by significant changes in dopamine and dopamine receptors. This study extended previous work by investigating the combined effects of chronic alcoholism and aging on total dopamine D2 receptors in brain areas associated with the nigrostriatal and mesocorticolimbic systems. In addition, the effects of chronic alcohol consumption and aging on the high-affinity state of D2 receptors and their conversion to the low-affinity form is included. Quantitative autoradiography was used to assess [3H]spiperone-labeled D2 receptors in tissue sections from 5- to 14- and 24-month Fischer 344 rats that were pair-fed a control or 6.6% (v/v) ethanol-containing liquid diet for 6 weeks. In addition, D2 receptors were determined in rats given the control liquid diet ad libitum. The results of these experiments demonstrated age-related changes in the nigrostriatal system. There was an age-related loss of total dopamine D2 receptors in the rostral and caudal striatum (approximately 25% decrease in Bmax). This decline in D2 receptors may be associated with changes in motor function. Despite the age-related decline in D2 receptors, there were no significant differences in the proportion of striatal receptors in the high-affinity form or in their conversion to the low-affinity state. Both aging and chronic alcohol consumption produced significant changes in the concentration of D2 receptors in brain areas associated with the mesocorticolimbic system. That is, the specific binding of [3H]spiperone was decreased in the frontal cortex of aged rats. In addition, chronic alcoholism was associated with a significant increase (approximately 20%) in the Bmax for D2 receptors in the nucleus accumbens. Nonetheless, neither age nor chronic alcohol consumption altered the proportion of high-affinity D2 receptors in the nucleus accumbens or their conversion to the lower affinity state. The observed changes in D2 receptors in the frontal cortex and nucleus accumbens are of interest because of the involvement of the mesocorticolimbic dopamine areas in the rewarding properties of alcohol and other drugs of abuse. Although aging and chronic alcoholism both produced significant changes in dopamine D2 receptor concentrations, alcohol did not accentuate the age-related loss of D2 receptors. We cannot eliminate the possibility that a more prolonged exposure of higher ethanol dose may potentiate age-related changes in the dopaminergic system.

Selective effects of ethanol on the generation of cAMP by particular members of the adenylyl cyclase family

A selective action of ethanol on major signal transduction proteins, such as adenylyl cyclase, has been considered to be important for certain actions of ethanol, and alcoholics have been demonstrated to differ from controls in measures of platelet adenylyl cyclase activity. Recent advances in identification and characterization of isoforms of adenylyl cyclase have demonstrated that there exists at least eight different forms of this enzyme. To examine whether the effect of ethanol on generation of cAMP is modified by the presence of particular isoforms of adenylyl cyclase within a cell, we transiently expressed each of six adenylyl cyclases in human embryonic kidney (HEK293) cells and measured cAMP accumulation in whole cells in the presence and absence of ethanol. The treatment of cells expressing the various adenylyl cyclases with ethanol alone did not enhance cAMP generation. In the presence of prostaglandin E1, cAMP generation by type I and type III adenylyl cyclases was insensitive to ethanol. cAMP accumulation generated by the other adenylyl cyclases was, however, increased by incubation of cells with ethanol in the presence of stimulatory agonists (e.g., prostaglandin E1). Stimulation by ethanol of cAMP generation by type VII adenylyl cyclase was 2- to 3-fold greater than that seen with the other tested adenylyl cyclases. The noted stimulation of cAMP generation by ethanol was dose-dependent and required concurrent activation of adenylyl cyclase through the stimulatory G protein. The effects of ethanol were reversible and mimicked by butanol but not by chloroform.

Effects of chronic alcohol consumption and aging on dopamine D1 receptors in Fischer 344 rats

The present study examined the hypothesis that chronic alcoholism augments the age-related loss of dopamine D1 receptors. This hypothesis was investigated because previous studies reported that both aging and chronic alcoholism produce significant changes in dopaminergic systems, and because chronic alcoholism potentiates some age-related CNS losses. In addition, this study investigated the effects of aging on D1 receptors in animals 1 and 7 days after withdrawal from chronic ethanol. Quantitative autoradiography was used to measure [3H]SCH 23390 binding to D1 receptors in brain areas associated with both the nigrostriatal and mesocorticolimbic dopamine systems. Receptors were assessed in 5-, 14-, and 24-month-old male Fischer 344 rats that were pair-fed a control or 6.6% (v/v) ethanol-containing liquid diet for 6 weeks. The results of these studies demonstrated that aging is associated with a significant decline in D1 receptors in the rostral and caudal striatum, and substantia nigra of both control and ethanol-fed rats. These receptor changes in the nigrostriatal system may be associated with motor abnormalities. In addition, there was an age-related decline in D1 receptors in two brain areas of the mesocorticolimbic system: the nucleus accumbens and frontal cortex. The latter findings may be important because of the involvement of this system with the rewarding properties of ethanol and other drugs of abuse. There were no age-related differences in the response of D1 receptors to ethanol withdrawal in the caudal and rostral striatum, substantia nigra, and nucleus accumbens.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of systemic and local ethanol on responses of rat cerebellar Purkinje neurons to iontophoretically applied norepinephrine and gamma-aminobutyric acid

The goal of the present study was to determine the effect of acute ethanol (ETOH), administered intraperitoneally or electro-osmotically, on norepinephrine (NE) induced increases in gamma-aminobutyric acid (GABA) mediated inhibition of single cerebellar Purkinje neurons (P-cells). Male Sprague-Dawley rats (230-370g) were anesthetized with halothane and implanted with an intraperitoneal catheter for systemic administration of ETOH (1.0-1.5 g/kg) prior to the recording session. Extracellular activity of single P-cells was recorded before and after iontophoresis of GABA and NE using five-barrel glass micropipettes. GABA was administered at the recording site by microiontophoretic pulses before, during and after continuous iontophoretic application of NE. Spontaneous discharge, GABA responses and NE-GABA interactions in P-cells were monitored for each experiment before and 1-1.5 h following systemic administration of ETOH. As in our previous reports administration of NE, at low ejection currents (10-60 nA), augmented GABA mediated suppression of P-cell spontaneous discharge. Between 10 and 60 min after injection of ETOH, this NE induced augmentation of GABA inhibition was further potentiated. This potentiation involved increases in both the magnitude and the duration of the GABA inhibition observed after NE alone. NE-induced augmentation of GABA inhibition persisted for 2-13 min longer after ETOH administration than in the pre-ETOH control period. Local electro-osmotic application of ETOH, which resulted in strong depression of spontaneous activity and caused small increases in GABA-mediated inhibition, did not directly potentiate NE-induced augmentation of GABA action. These results indicate that NE-mediated augmentation of GABA inhibition of P-cell activity is potentiated following systemic, but not local, ETOH administration.

Prenatal alcohol exposure and pineal response to isoproterenol, vasoactive intestinal polypeptide, and desmethylimipramine

Pineals from neonatal rats born to alcohol-fed mothers had lower unstimulated serotonin-N-acetyltransferase activity (NAT) and responded less to isoproterenol, vasoactive intestinal polypeptide, or desmethylimipramine challenge than did pineals from pups born to normal or pair-fed mothers. Group differences disappeared after the first week of life. Reduced NAT activity is coincident with elevated glucocorticoids in these pups. In contrast to these effects of chronic in utero ethanol exposure, acute ethanol addition to normal adult pineals in organ culture enhanced ISO but not VIP stimulation of NAT activity. The results suggest that the neonatal pineal is more affected by ethanol-induced activation of the adrenocortical axis during gestation than by the direct effect of ethanol on membrane fluidity.

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)

Role of adenosine A1 receptors in inhibition of receptor-stimulated cyclic AMP production by ethanol in hepatocytes

Brief exposure of primary cultures of hepatocytes to ethanol had a biphasic effect on glucagon receptor-dependent cyclic AMP (cAMP) production: 25-50 mM ethanol decreased cAMP levels, whereas treatment with 100-200 mM ethanol increased cAMP. This biphasic effect was also observed after pretreatment with 10 microM 4-methylpyrazole, an inhibitor of alcohol dehydrogenase. Adenosine A1 and A2 receptors in primary cultures of rat hepatocytes are coupled to inhibition and stimulation of adenylyl cyclase, respectively. Since primary cultures of hepatocytes release adenosine into their extracellular media, we tested whether the acute effects of ethanol on cAMP were mediated by extracellular adenosine. Co-incubation with 2 U/mL adenosine deaminase prevented inhibition of cAMP production by 25-50 mM ethanol, but had no effect on stimulation by 100-200 mM ethanol. Pretreatment of hepatocytes with 110 nM 8-cyclopentyl-1,3-dimethylxanthine, an adenosine A1 receptor antagonist, also completely blocked the inhibitory effects of ethanol on cAMP production. Low concentrations of ethanol enhanced the inhibitory effects of R(-)N6-(2-phenylisopropyl)adenosine, an A1 receptor agonist, on cAMP production in cells pretreated with adenosine deaminase to remove endogenous adenosine. These data suggest that endogenously produced adenosine can be an important modulator of the effects of ethanol on receptor-stimulated cAMP production in primary cultures of rat hepatocytes.

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.

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.

Ethanol inhibits the uptake of exogenous norepinephrine from the extracellular space of the rat cerebellum

Rapid chronoamperometric recordings using nafion-coated carbon fiber electrodes coupled with pressure-ejection of drugs were used to investigate the effects of ethanol on norepinephrine (NE)-containing nerve terminals in the urethane-anesthetized Fischer 344 rat. Local application of ethanol from a double-barrel micropipette did not produce detectable changes in extracellular levels of NE in the rat cerebellar cortex. However, when ethanol was applied prior to local application of NE, it was seen to inhibit the uptake of NE from the extracellular space. These results were compared to the effects seen from the local application of a known high-affinity uptake inhibitor, nomifensine. Nomifensine was found to inhibit the extracellular uptake of NE in rat cerebeller cortex similar to ethanol. Our results support the hypothesis that one effect of ethanol on the noradrenergic system of the rat cerebellum is an alteration in the uptake of NE into NE-containing nerve endings. In addition, the present data concerning ethanol-induced inhibition of NE clearance or uptake support our previous electrophysiological studies in which we found that ethanol can potentiate the modulatory effects of beta-agonists on GABA responses of cerebellar Purkinje neurons.

Norepinephrine metabolite in CSF correlates with ethanol consumption and heredity in humans

Previous studies showed that in cerebrospinal fluid (CSF) the concentration of 3-methoxy-4-hydroxy-phenylglycol (MHPG), the main metabolite of norepinephrine (NE), was positively correlated with blood ethanol concentrations in both healthy volunteers and in alcoholics. In this preliminary study we have extended those results by correlating MHPG concentrations in CSF with reported ethanol consumption and other indices of alcohol problems before and after consumption of 60-120 g of ethanol. MHPG in CSF correlates negatively with reported ethanol consumption, presence of first-degree relatives with alcohol problems, and presence of memory lapses, and correlates positively with age and the amount of ethanol consumed in the experiment. These results suggest that MHPG may indicate not only a high alcohol consumption but also a familial or genetic predisposition for alcoholism.

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.