Inhibition of Platelet Aggregation by Ethanol in Vitro Shows Specificity for Aggregating Agent Used and Is Influenced by Platelet Lipid Composition

Ethanol at physiologically tolerable concentrations inhibited platelet aggregation in vitro in a relatively specific way, which may be influenced by platelet membrane lipid composition. Aggregation to collagen, calcium ionophore A23187 and thrombin (low doses) were often markedly inhibited by ethanol, adrenaline and ADP responses were little affected, and aggregation to exogenous arachidonic acid was actually potentiated by ethanol. Aggregation to collagen, thrombin and A23187 was inhibited more by ethanol in platelets enriched with saturated fatty acids than in those enriched with unsaturated fats. Platelets enriched with cholesterol showed increased sensitivity to ADP, arachidonate and adrenaline but this increase in cholesterol content did not appear to influence the inhibition by ethanol of platelet responses. The results suggest that ethanol may inhibit aggregation by an effect on membrane fluidity and/or calcium mobilization resulting in decreased activity of a membrane-bound phospholipase.

Target-directed discovery and production of pharmaceuticals in transgenic mutant plant cells

Plants are a source of complex bioactive compounds, with value as pharmaceuticals, or leads for synthetic modification. Many of these secondary metabolites have evolved as defenses against competing organisms and their pharmaceutical value is "accidental", resulting from homology between target proteins in these competitors, and human molecular therapeutic targets. Here we show that it is possible to use mutation and selection of plant cells to re-direct their "evolution" toward metabolites that interact with the therapeutic target proteins themselves. This is achieved by expressing the human target protein in plant cells, and selecting mutants for survival based on the interaction of their metabolome with this target. This report describes the successful evolution of hairy root cultures of a Lobelia species toward increased biosynthesis of metabolites that inhibit the human dopamine transporter protein. Many of the resulting selected mutants are overproducing the active metabolite found in the wild-type plant, but others overproduce active metabolites that are not readily detectable in non-mutants. This technology can access the whole genomic capability of a plant species to biosynthesize metabolites with a specific target. It has potential value as a novel platform for plant drug discovery and production, or as a means of optimizing the therapeutic value of medicinal plant extracts.

Animal Models for Medication Development and Application to Treat Fetal Alcohol Effects

Ethanol consumption during pregnancy can have lifelong consequences for the offspring, their family and society. Fetal alcohol spectrum disorders (FASD) include a range of physical and behavioral effects with the most significant impact occurring as a result of the effects of ethanol on the developing central nervous system (CNS). To date, there are no FDA approved drugs that have been tested that prevent/reduce or specifically treat the symptoms of FASD. There are several promising lines of research from rodent models aimed at reducing the neurotoxic effects of ethanol on the developing CNS or in treating the resulting behavioral impairments but these have not yet moved to clinical testing. The current review discusses some of the most promising targets for intervention and provides a review of the past and ongoing efforts to develop and screen pharmacological treatments for reducing the effects of prenatal ethanol exposure.

Natural Products Genomics: A novel approach for the discovery of anti-cancer therapeutics

Plants continue to retain some advantages over combinatorial chemistry as sources of novel compounds, for example, they can generate metabolites with a complexity beyond synthetic chemistry. However, this comes with its own problems in production and synthetic modification of these compounds. Natural Products Genomics (NPG) aims to access the plants own genomic capacity to increase yields, and modify complex bioactive metabolites, to alleviate these limitations. NPG uses a combination of gain of function mutagenesis and selection to a) mimic the evolution of novel compounds in plants, and b) to increase yields of known bioactive metabolites. This process is performed rapidly at the cell culture level in large populations of mutants. Two examples demonstrating proof of concept in Nicotiana tabacum (tobacco) and proof of application in the medicinal plant species Catharanthus roseus, are included to illustrate the feasibility of this approach. This biotechnology platform may alter the way in which plant drug discovery is perceived by the pharmaceutical industry, and provides an alternative to combinatorial chemistry for the discovery, modification and production of highly complex bioactive molecules.

Difluoromethylornithine decreases long-lasting protein oxidation induced by neonatal ethanol exposure in the hippocampus of adolescent rats

BACKGROUND

Ethanol exposure and withdrawal during central nervous system development can cause oxidative stress and produce severe and long-lasting behavioral and morphological alterations in which polyamines seem to play an important role. However, it is not known if early ethanol exposure causes long-lasting protein oxidative damage and if polyamines play a role in such a deleterious effect of ethanol.

METHODS

In this study we investigated the effects of early ethanol exposure (6 g/kg/d, by gavage), from postnatal day (PND) 1 to 8, and of the administration of difluoromethylornithine (DFMO, 500 mg/kg, i.p., on PND 8), a polyamine biosynthesis inhibitor, on the extent of oxidative modification of proteins. Indices of oxidative modification of proteins included protein carbonyls, 3-nitrotyrosine (3-NT), and protein bound 4-hydroxynonenal (HNE) in the hippocampus, cerebellum, hypothalamus, striatum, and cerebral cortex of Sprague-Dawley rats at PND 40.

RESULTS

Both ethanol and DFMO administration alone increased protein carbonyl immunoreactivity in the hippocampus at PND 40, but the combination of DFMO and ethanol resulted in no effect on protein carbonyl levels. No alterations in the content of protein-bound HNE, 3-NT, or carbonyl were found in any other cerebral structure.

CONCLUSIONS

These results suggest that the hippocampus is selectively affected by early ethanol exposure and by polyamine synthesis inhibition. In addition, the results suggest a role for polyamines in the long-lasting increase of protein carbonyls induced by ethanol exposure and withdrawal.

Corticosterone and dexamethasone potentiate cytotoxicity associated with oxygen-glucose deprivation in organotypic cerebellar slice cultures

Many patients display elevated levels of serum cortisol following acute ischemic stroke. Given that glucocorticoids may potentiate some forms of insult, these studies examined the effects of corticosterone or dexamethasone exposure on cytotoxicity following oxygen-glucose deprivation in the cerebellum, a brain region susceptible to stroke. In organotypic cerebellar slice cultures prepared from neonatal rat pups, 90-min of oxygen-glucose deprivation at 15 days in vitro resulted in significant cytotoxicity at 24-, 48-, and 72-h post-oxygen-glucose deprivation, as measured by uptake of propidium iodide. Exposure of cultures following oxygen-glucose deprivation to the antioxidant trolox (500 microM), but not to the glucocorticoid receptor antagonist RU486 (10 microM), completely blocked oxygen-glucose deprivation-induced cytotoxicity. Corticosterone (1 microM) or dexamethasone (10 microM) exposure alone did not significantly increase propidium iodide uptake above levels observed in control cultures. However, corticosterone or dexamethasone exposure after oxygen-glucose deprivation potentiated oxygen-glucose deprivation-mediated propidium iodide uptake at each time point. Trolox, as well as RU486, co-exposure of cultures to corticosterone or dexamethasone after oxygen-glucose deprivation abolished all cytotoxicity. In conclusion, these data demonstrated that glucocorticoid exposure modulated oxygen-glucose deprivation-mediated propidium iodide uptake, which likely involved glucocorticoid receptor activation and pro-oxidant effects.

Thiamine deficiency in the pathogenesis of chronic ethanol-associated cerebellar damage in vitro

Nutritional deficiencies associated with long-term ethanol consumption may cause neuronal damage in ethanol-dependent individuals. Thiamine deficiency, in particular, is thought to contribute to ethanol-associated cerebellar degeneration, although damage may occur in adequately nourished alcoholics. Thus, the present study examined the effects of thiamine depletion and ethanol exposure on cytotoxicity in rat cerebellum. Organotypic cerebellar slice cultures were treated starting at 25 days in vitro with 100 mM ethanol for 11 days or 10 days followed by a 24-h withdrawal period. This exposure paradigm has previously been shown in hippocampal slice cultures to result in spontaneous cytotoxicity upon ethanol withdrawal. Additional cerebellar cultures were exposed to the thiamine depleting agent pyrithiamine (10-500 microM) for 10 or 11 days, some in the presence of ethanol exposure or withdrawal. Other cultures were co-exposed to thiamine (1-100 microM), 500 microM pyrithiamine, and ethanol for 10 or 11 days. The results demonstrated that neither 11-day ethanol treatment nor withdrawal from 10-day exposure significantly increased cerebellar cytotoxicity, as measured by propidium iodide fluorescence. The 11-day treatment with 100 or 500 microM pyrithiamine significantly increased propidium iodide fluorescence approximately 21% above levels observed in control tissue. Cultures treated with both ethanol (11 days or 10 days plus withdrawal) and 500 microM pyrithiamine displayed a marked increase in cytotoxicity approximately 60-90% above levels observed in control cultures. Pyrithiamine and ethanol-induced cytotoxicity was prevented in cultures co-exposed to thiamine (10-100 microM) for the duration of pyrithiamine treatment. Findings from this report suggest that the cerebellum may be more sensitive to the toxic effects of thiamine deficiency, as compared with alcohol withdrawal, associated with alcohol dependence.

Hippocampal CA1 region neurodegeneration produced by ethanol withdrawal requires activation of intrinsic polysynaptic hippocampal pathways and function of N-methyl-D-aspartate receptors

Long-term intake of ethanol produces adaptive alterations in multiple transmitter systems in the hippocampal formation that likely contribute to ethanol withdrawal-induced seizure and excitotoxicity. The present studies were designed to examine the role of N-methyl-d-aspartate receptor activation and cytosolic Ca(2+) accumulation in the neurotoxic effects of ethanol withdrawal. Further, these studies investigated the role of hippocampal network excitation in promoting both Ca(2+) accumulation and neurotoxicity during ethanol withdrawal. Chronic, continuous (11 day) exposure to ethanol (91 mM starting concentration) did not produce neurotoxicity in any region of organotypic hippocampal explants, as measured by uptake of the non-vital fluorescent marker propidium iodide. Withdrawal from chronic (10 day) ethanol exposure was associated with rapid (30 min) and significant increases in intracellular Ca(2+), assessed by visualization of Calcium-Orange fluorescence, in each region of hippocampal explants. However, neurotoxicity was observed 24 h after initiation of withdrawal and was only seen in the cornu ammonis 1 (CA1) region. Exposure to MK-801 (20 microM) at the start of ethanol withdrawal markedly attenuated Ca(2+) entry in all regions, as well as, CA1 region neurodegeneration. Further, treatment of explants with tetrodotoxin (500 nM) as well as surgical transection of mossy fiber or Schaffer collateral projections immediately prior to ethanol withdrawal blocked both regional increases in Ca(2+) accumulation and CA1 neurotoxicity. These data suggest that neurodegeneration observed during ethanol withdrawal is dependent upon polysynaptic propagation of action potentials ("network excitation") and whole-hippocampal excitation of glutamatergic systems.

(−)-nicotine ameliorates corticosterone's potentiation of N-methyl-d-aspartate receptor-mediated cornu ammonis 1 toxicity

Hypercortisolemia, long-term exposure of the brain to high concentrations of stress hormones (i.e. cortisol), may occur in patients suffering from depression, alcoholism, and other disorders. This has been suggested to produce neuropathological effects, in part, via increased function or sensitivity of N-methyl-d-aspartate (NMDA)-type glutamate receptors. Given that cigarette smoking is highly prevalent in some of these patient groups and nicotine has been shown to reduce toxic consequences of NMDA receptor function, it may be suggested that nicotine intake may attenuate the neurotoxic effects of hypercortisolemia. To investigate this possibility, organotypic hippocampal slice cultures derived from rat were pre-treated with corticosterone (0.001-1 microM) alone or in combination with selective glucocorticoid receptor antagonists for 72-h prior to a brief (1-h) NMDA exposure (5 microM). Pre-treatment with corticosterone (0.001-1 microM) alone did not cause hippocampal damage, while NMDA exposure produced significant cellular damage in the cornu ammonis (CA)1 subregion. No significant damage was observed in the dentate gyrus or CA3 regions following NMDA exposure. Pre-treatment of cultures with corticosterone (0.1-1 microM) markedly exacerbated NMDA-induced CA1 and dentate gyrus region damage. This effect in the CA1 region was prevented by co-administration of the glucocorticoid receptor antagonist RU486 (>or=1 microM), but not spironolactone (1-10 microM), a mineralocorticoid receptor antagonist. In a second series of studies, both acute and pre-exposure of cultures to (-)-nicotine (1-10 microM) significantly reduced NMDA toxicity in the CA1 region. Co-administration of cultures to (-)-nicotine (1-10 microM) with 100 nM corticosterone prevented corticosterone's exacerbation of subsequent CA1 insult. This protective effect of (-)-nicotine was not altered by co-exposure of cultures to 10 microM dihydro-beta-erythroidine but was blocked by co-exposure to 100 nM methyllycaconitine, suggesting the involvement of nicotinic acetylcholine receptors possessing the alpha7* subunit. The present studies suggest a role for hypercortisolemia in sensitizing the hippocampal NMDA receptor system to pathological activation and indicate that prolonged nicotine exposure attenuates this sensitization. Thus, it is possible that one consequence of heavy smoking in those suffering from hypercortisolemia may be a reduction of neuronal injury and sparing of cellular function.

Nicotine exposure reduces N-methyl-D-aspartate toxicity in the hippocampus: relation to distribution of the alpha7 nicotinic acetylcholine receptor subunit

BACKGROUND

Exposure to nicotine has been shown to promote neuronal survival after excitotoxic insult to the brain. The role of specific nicotinic acetylcholine receptors (nAChRs) subtypes in mediating this effect is not well understood, however. Examination of distinct receptor subtypes in promoting neuronal survival is of importance not only in understanding the regulation of necrotic cell death but potentially in the development of novel pharmacological therapies that may reduce this form of neurodegeneration.

MATERIAL AND METHODS

The present studies examined the relationship between distribution of alpha7 subunit-bearing nAChRs, using autoradiographic imaging of [125I]alpha-bungarotoxin binding, and protective effects of nicotine against excitotoxic damage. Organotypic cultures of rat hippocampus were exposed to N-methyl-D-aspartate (NMDA; 200 microM) for 1 hour with or without (-)-nicotine (0.1-10 microM) and the alpha7 nAChR antagonist methyllycaconitine (MLA; 100 nM). Neuronal damage was assayed 24 hours later by observation of uptake of the non-vital fluorescent marker propidium iodide.

RESULTS

NMDA exposure produced significant neurotoxicity, particularly in pyramidal cell layers of CA3 and CA1, that was prevented by co-exposure to MK-801 (10 microM). Localization of the alpha7 subunit was varied with no binding observed in the dentate gyrus, low density in the CA3 and CA1 regions, and dense binding in the hilus. In all regions, co-exposure to (-)-nicotine (0.1-10.0 microM) significantly reduced (>30%) the cytotoxic consequences of NMDA insult. This protective effect was inhibited by co-exposure to MLA in the dentate and CA3, and to a lesser extent, CA1 regions.

CONCLUSIONS

The neuroprotective effect of nicotine against excitotoxicity, then, is not directly related to alpha7 subunit localization in the hippocampus.

Chronic nicotine exposure reduces N-methyl-D-aspartate receptor-mediated damage in the hippocampus without altering calcium accumulation or extrusion: evidence of calbindin-D28K overexpression

Neuronal accumulation of excess Ca2+ has been implicated in cellular death following several forms of physical and chemotoxic insult. Recent studies have suggested that exposure to agonists at brain nicotinic acetylcholine receptors reduces cytotoxic consequences of increased intracellular Ca2+ following some insults. In the present study, the ability of chronic exposure to (-)-nicotine to reduce cytotoxicity and attenuate increases in intracellular Ca2+ caused by exposure to N-methyl-D-aspartate were examined in organotypic cultures of rat hippocampus. Cultures were exposed to nicotine (0.1-10.0 microM) for five days prior to excitotoxic insult with N-methyl-D-aspartate. Exposure to N-methyl-D-aspartate produced concentration-dependent increases in both accumulation of 45Ca and in early and delayed cell death in the CA1, CA3 and dentate gyrus regions of cultures. The CA1 region of the hippocampus displayed the greatest sensitivity to cytotoxic effects of N-methyl-D-aspartate exposure; however, this regional difference was not associated with increased accumulation of 45Ca. Prior exposure to nicotine markedly attenuated N-methyl-D-aspartate-induced early and delayed cell death in each hippocampal region at concentrations as low as 0.1microM. However, nicotine did not alter the initial N-methyl-D-aspartate-stimulated influx of 45Ca or enhance extrusion of accumulated 45Ca measured at several time-points after insult. Five days of exposure to nicotine markedly increased immunoreactivity of the Ca2+ binding protein calbindin-D28K in each region of hippocampal cultures, effects reduced by mecamylamine co-exposure. These findings suggest that the potent protective effects of chronic nicotine exposure against neuronal overexcitation are not likely attributable to attenuations of Ca2+ accumulation, but are likely related to increased buffering of accumulated Ca2+.

Role of polyamines and NMDA receptors in ethanol dependence and withdrawal

This article represents the proceedings of a symposium at the 2000 ISBRA Meeting in Yokohama, Japan. The chair was John M. Littleton. The presentations were (1) Examination of ethanol spermine and acamprosate actions on native and recombinant NMDA receptors, by David Lovinger; (2) Ethanol inhibition of NMDA neurotoxicity on the polyamine site in cerebellar granule cells, by Sture Liljequist; (3) Alterations in expression of NMDA receptor subunits during ethanol exposure and withdrawal, by Raj Ticku; (4) Alterations in polyamine synthesis and release as a potential mechanism for ethanol dependence and withdrawal, by Izuru Matsumoto; (5) The role of polyamines in neurotoxicity induced by alcohol withdrawal in vitro, by John Littleton; and (6) Agmatine reduces some of the effects of "third trimester" alcohol exposure using a rodent model, by Susan Barron.

Endogenous indoles as novel polyamine site ligands at the N-methyl-D-aspartate receptor complex

High-throughput ligand displacement screens of a series of endogenous indoles revealed that tryptamine, serotonin and 5-methoxytryptamine readily displace [3H]spermidine and [3H]MK-801 from their respective binding sites in rat brain homogenate. These data, coupled with their potent inhibition of spermidine-potentiated [3H]MK-801 binding, suggest that certain endogenous indoles may act as ligands to one or more polyamine binding sites in the brain, including those on the N-methyl-D-aspartate receptor complex.

Aminoanthraquinones as novel ligands at the polyamine binding site on the N-methyl-D-aspartate receptor complex

As part of a drug discovery program using high-throughput radioligand-binding assays, aminoanthraquinones were identified as potential modulators of N-methyl-D-aspartate (NMDA) receptor function. Aminoanthraquinones may represent a novel class of polyamine binding site ligands with a unique pharmacophore and may facilitate the rational design of novel NMDA-receptor modulators.

In vitro effects of ethanol withdrawal and spermidine on viability of hippocampus from male and female rat

BACKGROUND

Long-term ethanol dependence results in neuronal adaptation that likely contributes to ethanol withdrawal-induced central nervous system excitability and, potentially, neurotoxicity. This has been suggested to result, in part, from increased release of or response to endogenous polyamines. Furthermore, it has been reported that neurological difficulties related to ethanol dependence and withdrawal may be more severe in female than in male alcoholics. Thus, we designed this study to examine effects of the polyamine spermidine on neurotoxicity associated with withdrawal from long-term ethanol exposure by using organotypic hippocampal slice cultures derived from male and female rats.

METHODS AND RESULTS

Twenty-four hours of withdrawal after continuous 10 day ethanol exposure (100 mM in culture medium) resulted in cytotoxicity in hippocampal slice explants obtained from both sexes. This was most evident in pyramidal cell layers of the CA1 region, and no sex differences were observed in the severity of damage. Exposure of explants from both sexes to the NMDA blocker MK-801 during ethanol withdrawal significantly reduced this toxicity. In control cultures, exposure to spermidine (100 microM) alone produced significant and similar cytotoxicity in hippocampal explants of male and female rats. Exposure to spermidine (100 microM) during ethanol withdrawal significantly increased cytotoxicity in all regions of explants. In the CA3 region, spermidine-potentiation of ethanol withdrawal damage was significantly greater in explants from female rats compared with those from male rats.

CONCLUSIONS

These data demonstrate the presence of significant hippocampal neurotoxicity during withdrawal from long-term ethanol exposure that is mediated, in part, by overactivation of NMDA receptors. Furthermore, these findings suggest that the central nervous system of females may be more susceptible than that of males to polyamine-mediated neuronal damage during withdrawal from long-term ethanol exposure.

Chronic, but not acute, nicotine exposure attenuates ethanol withdrawal-induced hippocampal damage in vitro

BACKGROUND

Long-term ethanol use and long-term tobacco use frequently occur together, which suggests concurrent dependence on ethanol and nicotine. Consequences of this form of polydrug dependence are not well understood, however. Previous evidence suggests detrimental effects of long-term ethanol and beneficial effects of nicotine exposure on neuronal viability. Thus, the present study was designed to use an organotypic hippocampal slice culture model to examine the ability of chronic and acute nicotine exposure to reduce neurotoxicity associated with withdrawal from long-term ethanol exposure.

METHODS AND RESULTS

Twenty-four hours of withdrawal after continuous 10 day ethanol exposure (50 or 100 mM in culture medium) resulted in cytotoxicity in hippocampal slice explants obtained from neonatal rat, most notably in pyramidal cell layers of the CA1 region. Exposure of slices to the N-methyl-D-aspartate receptor blocker MK-801 during ethanol withdrawal significantly reduced this toxicity. Exposure of slices to nicotine (0.1-10.0 microM) during the 24 hr withdrawal period did not reduce hippocampal damage. However, treatment of slices with nicotine (0.1-10.0 microM) during 10 days of ethanol exposure was associated with significant reductions in subsequent withdrawal-induced cytotoxicity, an effect reduced by mecamylamine coexposure with nicotine and ethanol.

CONCLUSIONS

These findings indicate the development of marked hippocampal neurotoxicity during withdrawal from long-term ethanol exposure that is mediated, in part, by overactivation of N-methyl-D-aspartate receptors. Furthermore, these data suggest that one consequence of concurrent dependence on ethanol and nicotine may be reduced neurological damage associated with ethanol withdrawal.

Acamprosate, but not naltrexone, inhibits conditioned abstinence behaviour associated with repeated ethanol administration and exposure to a plus-maze

RATIONALE

Drugs that reduce relapse in alcoholics are thought to inhibit either positive reinforcement for drinking (e.g. naltrexone) or negative reinforcement (e.g. acamprosate), and may reduce the impact of conditioned stimuli associated with previous alcohol use. We have developed a model for such conditioning by repeatedly pairing ethanol administration with plus-maze exposure. Substitution of saline for ethanol greatly increased stretched-attend postures and time in the central square, conditioned to the environment.

OBJECTIVE

To test the hypothesis that if this behaviour indicates a negative affective state caused by the expectation of ethanol, it should be inhibited by drugs that reduce negative, but not positive, reinforcement.

METHODS

The effects of naltrexone and acamprosate on alcohol-conditioned abstinence behaviour were compared.

RESULTS

Acute administration of either drug alone produced no significant effects on plus-maze behaviour in naive mice. Naltrexone had no significant effect on the alcohol-conditioned abstinence behaviour, but acamprosate reduced the incidence of stretched-attend postures.

CONCLUSIONS

The experiments replicated previous findings for alcohol/environment conditioned behaviour, and demonstrated, as predicted, that this was decreased by acamprosate but not by naltrexone. Effects of acamprosate on conditioned negative reinforcement may be the cause of this effect, but more work is required to establish the usefulness of this model in evaluation of anti-relapse drugs.

Damaging effects of the calcium paradox are reduced in isolated hearts from ethanol-dependent rats: paradoxic effects of dihydropyridine drugs

Previous experiments showed that isolated hearts from ethanol-exposed rats show a marked increase in sensitivity to anoxic myocardial damage, and we suggested that this may be due to excess calcium entry through L-type voltage-operated calcium channels (L-VOCCs). To challenge this hypothesis, we investigated the effect of ethanol treatment ex vivo on a damaging stimulus, the "calcium paradox," which is associated with removal of calcium from the perfusate. Adult male Sprague-Dawley rats were exposed to intoxicating concentrations of ethanol for 6-10 days by inhalation. Isolated hearts from these animals were perfused with Krebs-Henseleit buffer by using a modified Langendorff technique, and the calcium paradox induced by a 10-min period of perfusion with calcium-free buffer, followed by reperfusion with calcium-containing buffer. Compared with controls, hearts from ethanol-exposed rats were significantly protected against myocardial damage, as shown by a marked reduction in release of intracellular proteins (lactate dehydrogenase, creatine phosphokinase, and myoglobin) during the reperfusion phase. These indices of myocardial damage were modified by the presence of the dihydropyridine (DHP) calcium channel antagonist nitrendipine (10(-6) M) and the DHP L-VOCC activator Bay K 8644 (10(-7) M) in the perfusate during the calcium paradox. Paradoxically, both drugs appeared to increase the damaging effects of calcium-free perfusion, with this effect being generally greater in the preparations from ethanol-exposed rats. As a result, the difference between these hearts and those from control rats was reduced, although a significant degree of protection against the calcium paradox remained. The results support the hypothesis that long-term exposure to ethanol in vivo produces marked alterations in the toxic effects of changes in myocardial calcium concentration. The increased sensitivity to DHP drugs of isolated hearts from ethanol-treated rats is consistent with previous experiments showing increased DHP radioligand-binding sites in these tissues.

Increased sensitivity to damaging effects of hypoxia and anoxia of isolated hearts from rats after prolonged exposure to ethanol: apparent protection by nitrendipine

The studies described here investigate whether pathologic states that are thought to cause myocardial damage through excess calcium entry (i.e., hypoxia and anoxia) indeed cause greater damage in hearts from ethanol-exposed animals, and whether L-type voltage-operated calcium channels (L-VOCCs) are implicated. Adult male Sprague-Dawley rats were exposed to intoxicating concentrations of ethanol vapor for 6-10 days, and their isolated hearts compared with those of control animals in a Langendorff perfusion system. Hypoxia was induced by perfusion with Krebs-Henseleit buffer, which had not previously been bubbled with oxygen; anoxia was produced by perfusion with buffer bubbled with nitrogen. On reperfusion with oxygenated buffer, evidence of myocardial damage during the hypoxic/anoxic period was obtained by the release of intracellular proteins into the perfusate. After hypoxia, release of myoglobin (MYO) was significantly greater from hearts from ethanol-exposed rats than from controls; other indices of myocardial damage also were increased by hypoxia but did not differ significantly between treatment groups. After anoxic perfusion, release of lactate dehydrogenase (LDH) and creatine phosphokinase (CPK) as well as MYO were all markedly and significantly increased from ethanol-exposed hearts compared with those from control rats. The role of L-VOCCs in this damage was assessed with the calcium channel antagonist nitrendipine (10(-6) M) present in the perfusing buffer immediately before and during the anoxic stimulus. This completely reversed the situation so that preparations from ethanol-exposed rats now showed a reduced release of intracellular proteins compared with hearts from controls. Comparisons with absolute values from the previous experiments suggest that nitrendipine increased release of LDH and CPK from control hearts with little effect on these indices from ethanol-exposed hearts. However, in the case of anoxia-induced MYO release, nitrendipine markedly and significantly reduced this in hearts from ethanol-treated rats but had only a very small effect on the same parameter in controls. The results strongly suggest increased pathologic effects of hypoxia/anoxia in hearts from ethanol-exposed rats. This increased sensitivity may be at least partly a consequence of increased numbers of L-VOCCs in this tissue.

Effect of calcium, Bay K 8644, and reduced perfusion on basic indices of myocardial function in isolated hearts from rats after prolonged exposure to ethanol

We previously reported findings consistent with a marked upregulation in functional L-type voltage-operated calcium channels (L-VOCCs) in hearts obtained from rats exposed over the long term to ethanol. These experiments were undertaken to establish whether detrimental effects on cardiac function were associated with excess calcium entry into the myocardium in these hearts. Isolated hearts from adult male Sprague-Dawley rats received intoxicating concentrations of ethanol for 6-10 days by inhalation, were perfused with Krebs-Henseleit buffer by a modified Langendorff technique, and several functional parameters were assessed continuously. In some experiments, the calcium concentration in the perfusate was first reduced from the physiologic range (1.2 mM) to 0.15 mM and then increased in a step-wise fashion to 4 mM. In other experiments, hearts were exposed to buffer containing concentrations of the L-VOCC activator, (+/-)Bay K 8644, increasing from 10(-9) to 10(-6) M. These perfusion protocols were repeated in hearts from treated animals subject to reduced coronary flow because of induction of partial left ventricular ischemia. There were some close similarities in the effects of these different stimuli. When the calcium concentration in the perfusate exceeded a physiologic level, there were signs of decreased function relative to controls in the hearts from ethanol-exposed rats. Thus R-wave amplitude and systolic pressure were lower, diastolic pressure also was reduced, but heart rate was elevated above that of controls. Similarly the presence of (+/-)Bay K 8644 in the perfusate caused a decrease in systolic and diastolic pressure and an increase in heart rate in hearts from ethanol-exposed rats. When cardiac perfusion was reduced in vitro by inflation of a balloon in the left ventricle, some of the effects of excess calcium and (+/-)Bay K 8644 were reproduced in control hearts. However, imposition of this "ischemic" stress did not appear to exacerbate the effects of prior exposure to ethanol. In general, in control hearts, indices of contractility were increased across the range of calcium concentration or by perfusing with (+/-)Bay K 8644. Hearts from ethanol-exposed rats, however, showed no further increase in these parameters once physiologic levels of calcium were exceeded, or showed inhibition of contractility in the presence of (+/-)Bay K 8644. The results are consistent with calcium entry through L-VOCCs in hearts from ethanol-exposed animals having detrimental effects on cardiac function once physiologic levels are exceeded. However, it is possible that these channels also may be involved in maintenance of cardiac function at hypocalcemic levels.

Effects of prolonged exposure to ethanol in vivo on functional parameters and sensitivity to nitrendipine in the isolated rat heart

This study investigated the possibility that previously reported marked upregulation of binding sites for the dihydropyridine calcium channel antagonist nitrendipine in heart tissue during the development of ethanol dependence in the rat may represent functional L-type voltage-operated calcium channels (L-VOCCs). Isolated hearts obtained from adult Sprague-Dawley rats, which received intoxicating concentrations of ethanol for 6-10 days, by inhalation, were perfused with Krebs-Henseleit solution in the Langendorff mode. Basic measurements of cardiac function were compared with hearts from control rats not exposed to ethanol vapor. In another study, concentration-response curves were constructed for nitrendipine at concentrations in the range of 10(-10)-10(-6) M for hearts obtained from control and ethanol-exposed animals. Changes in measured cardiac parameters such as R-wave amplitude, heart rate, diastolic and systolic pressure, and (+)dP/dt(max) and coronary flow were recorded. All comparisons were made between preparations set to a similar left ventricular end-diastolic pressure. Under these conditions, there were no significant differences in R-wave amplitude, but isolated hearts from ethanol-dependent rats showed significantly greater indices of myocardial contraction than did controls. These included increased systolic and developed ventricular pressure and increased (+)dP/dt(max). Coronary flow also was significantly greater in hearts from ethanol-dependent rats compared with controls. Heart rate was higher in the alcohol-exposed group, but this difference did not achieve significance. When nitrendipine was added to the perfusate at concentrations between 10(-10) and 10(-6) M, hearts from ethanol-dependent animals showed a greater sensitivity to the effects of the drug on heart rate and systolic pressure. Effects on R-wave amplitude and (+)dP/dt(max) were less clear but also suggested a greater sensitivity to nitrendipine in hearts from ethanol-exposed rats. Effects on coronary flow were small and did not differ significantly between preparations from control and ethanol-dependent rats. The results suggest that the increase in Bmax of DHP binding previously observed in hearts from ethanol-dependent animals might represent an increase in L-VOCCs, which alters physiologic function, and pharmacologic responses in the isolated heart. These changes may represent the exposure of an adaptive mechanism designed to overcome the generally depressant effects of ethanol on cardiac function in vivo.

Effects of repeated ethanol administration in the plus maze; a simple model for conditioned abstinence behaviour

Classical conditioning is considered to be an important factor in drug dependence. Exposure to an environment in which alcohol has been repeatedly consumed may produce feelings of anxiety and dysphoria in a currently abstinent patient, and may precipitate relapse drinking. The present study modeled this process, by repeatedly exposing mice to an elevated plus maze after ethanol administration. When ethanol injections and maze exposure were repeated for 9 days, and the ethanol injections replaced by saline on the tenth day, mice consistently exhibited a characteristic behaviour pattern, with increased stretched attend postures and proportion of time spent in the central square. This behaviour was different from that previously seen during withdrawal from ethanol, and was not observed when repeated injections of ethanol were given either without, or after, maze exposure. Thus the characteristic behaviour pattern appeared to be contingent on the animals being repeatedly exposed to the maze environment while under the influence of ethanol. In particular, the reduction in stretched attend postures produced by acute ethanol, the tolerance to this behaviour seen after repeated ethanol and the increase in it after replacement of ethanol by saline, are consistent with the pattern predicted for a behavioural response to the absence of ethanol, conditioned to the environment of the maze.

Expression of c-Fos protein immunoreactivity in rat brain during ethanol withdrawal is prevented by nifedipine

Male rats were made physically dependent on ethanol by inhalation of the vapour for 10 days, and c-Fos protein-like immunoreactivity was visualised in the brain of these animals after various periods of ethanol withdrawal. Immunostaining for c-Fos appeared 2 h after ethanol withdrawal, the number of cells increased significantly at 8 h, but c-Fos had returned to basal level after 24 h. Immunoreactive cells were distributed throughout the brain but were concentrated in cerebral cortex, striatum, and hippocampus. Intraperitoneal injection of the calcium channel antagonist nifedipine (3 x 100 mg/kg) prior to, and during ethanol withdrawal totally prevented c-Fos protein-like expression. These results suggest that the superinduction of c-Fos protein in the brain of rats undergoing ethanol withdrawal is induced by calcium influx into neuronal cells, and may be related to previously reported increases in L-type voltage-operated calcium channels in the brain associated with ethanol dependence.

Time course and genetic variation in the regulation of calcium channel antagonist binding sites in rodent tissues during the induction of ethanol physical dependence and withdrawal

Physical dependence was induced by ethanol inhalation in male Sprague-Dawley rats and, in parallel experiments, in two lines of mice (WSR and WSP) genetically selected for differential severity of ethanol withdrawal. In dependent rats [3H]nitrendipine binding sites were significantly increased in cerebral cortex, cardiac and smooth muscle (vas deferens). Cerebral cortical membranes were the first to show an increase, the Bmax for nitrendipine binding rising sharply after 3-4 days of ethanol administration, whereas binding sites in the other tissues increased after 5-6 days. Nitrendipine binding affinity in all tissues was consistently reduced immediately preceding the rise in Bmax to a new steady state, but then returned to control values. Between 6 and 10 days of ethanol exposure there was no further increase in the Bmax for nitrendipine binding, and on removal of ethanol, the numbers of nitrendipine binding sites fell precipitously to control levels within 24 h of withdrawal. In the genetically selected mice, the up-regulation of nitrendipine binding sites in cardiac membranes was significantly greater in the WSP line. This correlates with severity of physical signs of withdrawal and parallels previous results obtained in brain. The results are consistent with an increase in the synthesis and membrane insertion of dihydropyridine sensitive calcium channel proteins in several tissues during the induction of ethanol dependence and suggest that in the brain this change may play a role in the ethanol withdrawal syndrome.

Binding characteristics of the calcium channel antagonist [3H]-nitrendipine in tissues from ethanol-dependent rats

Male Sprague-Dawley rats were made physically dependent on ethanol by exposure to ethanol vapour in inhalation chambers for 6-10 days. Animals were sacrificed immediately after removal from the chambers. After sacrifice, membrane preparations from cerebral cortex, heart, vas deferens and thigh skeletal muscle were prepared and studied to determine the characteristics of [3H]-nitrendipine binding. In membranes from cerebral cortex, the number of binding sites (Bmax) was increased 40% in preparations from ethanol-dependent rats compared to controls. Similar results were obtained in heart (Bmax increased 125%), vas deferens (Bmax increased 50%) and skeletal muscle (Bmax increased 33%). Binding affinity (Kd) in all these tissues was unchanged. Membranes from cortex and heart were studied more extensively. Displacement studies using other dihydropyridines and the effects of ionic composition on [3H]-nitrendipine binding provided no evidence to suppose that the binding sites induced by the development of ethanol dependence were from a population different from those in control tissues. The results suggest a generalised 'up-regulation' of the dihydropyridine-sensitive subclass of voltage operated calcium channels in excitable tissues from ethanol-dependent rats.

Chronic exposure to anxiolytic drugs, working by different mechanisms causes up-regulation of dihydropyridine binding sites on cultured bovine adrenal chromaffin cells

Exposure of bovine adrenal chromaffin cells to ethanol [50 mM], alprazolam [10(-7) M] and buspirone [10(-7) M] inhibited basal and carbachol-induced release of catecholamines from these cells. The inhibition produced by alprazolam was prevented, and that produced by ethanol inhibited, by the presence of the benzodiazepine receptor antagonist, flumazenil [10(-8) M]. The inhibition produced by buspirone was unaffected by flumazenil, but was mimicked by the selective 5-HT1A receptor agonist, 8-OH DPAT and prevented by the 5-HT receptor antagonist spiperone [10(-6) M]. These results suggest that bovine adrenal chromaffin cells express GABAA receptors, containing a benzodiazepine recognition site and also 5-HT1A receptors. Ethanol and alprazolam appear to inhibit the excitability of bovine adrenal chromaffin cells by an action related to the former, while buspirone probably inhibits these cells through the latter. Maintaining bovine adrenal chromaffin cells for several days in culture medium, containing inhibitory concentrations of ethanol alprazolam or buspirone, produced a marked increase in binding sites for a [3H]dihydropyridine [DHP] calcium channel antagonist, on cell membranes. The increase in binding sites produced by alprazolam was greater than that produced by the other two agents and was almost completely prevented by the concomitant presence of flumazenil. The effects of ethanol and buspirone on the binding of DHP were not prevented by flumazenil. The results suggest that drugs which decrease excitability of bovine adrenal chromaffin cells by different mechanisms, may evoke a similar adaptive response involving an increase in DHP-sensitive calcium channels.

Development of tolerance to ethanol in cultured adrenal chromaffin cells

Dissociated bovine adrenal chromaffin cells in culture were utilized to study the mechanisms for development of cellular tolerance to ethanol. Three days after plating, cells were grown in either control medium or medium containing 200 mM ethanol for periods up to 6 days. Catecholamine release induced by carbachol, 80 mM K+, BAY K 8644, and veratrine was studied in ethanol-treated and untreated cultures. The presence of ethanol in vitro was inhibitory to all these stimuli in untreated cell cultures, carbachol-induced release being most sensitive (IC50 approximately 30 mM). After growth in ethanol for 6 days, carbachol-induced catecholamine release was completely resistant to the inhibitory effects of ethanol. The resistance to ethanol of carbachol-induced catecholamine release from cells grown in medium containing ethanol also extended to the inhibitory effects of butanol. The results show some similarities with changes observed in the central nervous system during the development of ethanol tolerance, and it is suggested that this model system may be useful in examining the mechanisms by which tolerance occurs.

Second messengers involved in genetic regulation of the number of calcium channels in bovine adrenal chromaffin cells in culture

Bovine adrenal chromaffin cells in culture show an increased formation of [3H]inositol phosphates (after preloading with [3H]inositol) on depolarisation with increased extracellular K+. This increased breakdown of inositol lipid is further increased by the dihydropyridine Ca2+ channel activator BAY K 8644 at nM concentrations, implying that proteins which bind dihydropyridines are involved in this mechanism. Further, pretreatment of adrenal cells with pertussis toxin (100 ng ml-1) prevented the K(+)-induced breakdown of inositol lipids, arguing the involvement of a pertussis toxin-sensitive G protein in the effect. Chronic exposure of bovine adrenal chromaffin cells to a concentration of ethanol which inhibits K(+)-induced breakdown of inositol phospholipid, caused a 70-100% increase in the binding of [3H]DHP sites. In these experiments it was found that excess extracellular Ca2+ would considerably reduce this up-regulation, whereas growth of cells in pertussis toxin closely mimicked the up-regulation obtained by growth of cells in ethanol. These experiments suggest that inhibition of membrane Ca2+ flux, through a G protein-associated channel, is closely involved in the ethanol-induced regulation of [3H]dihydropyridine binding sites. The inositol lipid-protein kinase C second messenger system is also implicated in this regulation, by experiments in which inhibitors of protein kinase C (chronic treatment with phorbol myristyl acetate, or with sphingosine) up-regulated binding sites for [3H]dihydropyridine to a similar extent as that seen with growth in ethanol.

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

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

Effects of dihydropyridine calcium channel antagonists in ethanol withdrawal; doses required, stereospecificity and actions of Bay K 8644

The effects of dihydropyridine calcium channel antagonists, and the calcium channel activator, Bay K 8644, were examined on the convulsive behaviour induced by handling in mice following withdrawal from chronic ethanol inhalation. Nimodipine and nitrendipine and PN 200-110 significantly decreased the convulsive behaviour, after intraperitoneal doses of the same order of magnitude as have been found by others to be required for displacement of radiolabelled dihydropyridine in the CNS. The (+) isomer of PN 200-110 was effective, but the (-) isomer, which is ineffective in vitro, had no significant action. Bay K 8644 prevented the actions of nimodipine against the ethanol withdrawal syndrome. The behavioural ratings after nimodipine plus Bay K 8644 were significantly higher than after vehicle treatment. Bay K 8644 alone, when given to naive mice, caused convulsive behaviour resembling that seen in withdrawal from chronic ethanol treatment, but when given during ethanol withdrawal did not significantly increase the behavioural signs.

Membrane receptors, involved in up-regulation of calcium channels in bovine adrenal chromaffin cells, chronically exposed to ethanol

Release of catecholamines, induced by carbachol, from bovine adrenal chromaffin cells, maintained in culture, is potently inhibited by the presence of ethanol (50 mM). This inhibition is prevented by the concomitant presence of bicuculline (1 microM) or by the inverse agonist at the benzodiazepine receptor, Ro 15 4513 (50 nM), arguing that the effect of ethanol is, at least, partly due to potentiation of endogenous GABA at the GABAA receptor sites on these cells. Exposing cells to medium containing ethanol (200 mM) for 4 days results in an approximately 100% increase in binding sites for [3H]dihydropyridine on membranes of adrenal chromaffin cells. This increase in binding sites was largely prevented by the presence in the culture medium of Ro 15 4513 (50 nM), the dihydropyridine calcium channel agonist BAY K 8644 (50 nM) or the calcium channel antagonist, nitrendipine (50 nM). The results strongly suggest that the increase in binding sites for [3H]dihydropyridine represents an adaptation of cells to overcome the inhibitory effect of ethanol on the excitability of cells (which is, at least partly, due to some action at the GABAA receptor). The protein containing the receptor site for dihydropyridine drugs is clearly also involved in controlling its up-regulation by ethanol, but this is probably not directly related to its channel function, since both activators and inhibitors of the dihydropyridine-sensitive channel prevented ethanol-induced up-regulation of binding sites for [3H]dihydropyridine.

Genetic up-regulation of calcium channels in a cellular model of ethanol dependence

Bovine adrenal chromaffin cells were maintained in culture medium containing ethanol (200 mM) for 6 days. Cultures maintained in ethanol were viable and were morphologically similar to controls. There was a greater than 100% increase in the number of [3H]dihydropyridine calcium channel antagonist binding sites on the cell membranes from ethanol-treated cultures, which could be prevented by concomitant exposure to cycloheximide (5 micrograms.ml-1) and the mRNA synthesis inhibitor, anisomycin (10 micrograms.ml-1) implicating de novo synthesis of protein and genetic regulation, respectively. Release of catecholamines, induced by 18 mM K+, from cultures grown in ethanol was enhanced. The increased release of catecholamines was inhibited by nM concentrations of dihydropyridine calcium channel antagonists, implying that an increase in the number of dihydropyridine-sensitive calcium channels accounts for this functional alteration.

Altered characteristics of [3H]dopamine release from superfused slices of corpus striatum obtained from rats receiving ethanol in vivo

Ethanol, 50 mM, in vitro inhibited the release of [3H]dopamine ([3H]DA) induced by depolarisation with 40 mM K+ from slices of corpus striatum of the rat. In contrast, the release of [3H]DA induced by the Ca2+ ionophore (A23187) was enhanced by the presence of ethanol in vitro. When similar preparations were obtained from brains of rats which had received ethanol in vivo chronically by inhalation for 5-7 days the characteristics of release of [3H]DA were altered. Thus, the inhibitory effect of ethanol in vitro on release induced by K+-depolarisation was lost, as was the enhancing effect of ethanol on the release induced by A23187. When release of [3H]DA was studied in the absence of added ethanol the fraction of stored 3H released either by K+-depolarisation or by A23187 was increased in the preparations from animals which had received ethanol in vivo. Similar changes in release induced by A23187, though of lesser magnitude, could be seen in rats which had received ethanol acutely (3 g kg-1 i.p.; 30 min). An even greater fraction of [3H]DA was released by A23187 in preparations from rats which had been made physically dependent on ethanol. These changes in the release characteristics of [3H]DA were still apparent in animals undergoing a physical syndrome of withdrawal from ethanol. The results are discussed in relation to the cellular basis for the development of tolerance to and dependence on ethanol.

Increased activity of Ca2+-dependent enzymes of membrane lipid metabolism in synaptosomal preparations from ethanol-dependent rats

In synaptosomal fractions of rat brain the activities of phospholipase A2 and the phospholipid base-exchange enzymes are highly dependent on external Ca2+ concentrations. Their activity is inhibited by the presence of 50 mM ethanol in vitro. Administration of ethanol to rats by inhalation causes a progressive increase in the activity of these enzymes in synaptosomal preparations at all Ca2+ concentrations studied. The increased activity of these enzymes persists in preparations from rats undergoing a physical syndrome of withdrawal from ethanol. The addition of ethanol in vitro to preparations from animals that had received ethanol in vivo had no significant effect on enzyme activity. The results are discussed in relation to the possible roles of membrane lipid metabolism and synaptic Ca2+ sensitivity in ethanol tolerance and physical dependence.

Effect of ethanol on thrombin-induced platelet phospholipid breakdown and release of [3H]-5-hydroxytryptamine

Ethanol has been reported previously to inhibit chemically-induced platelet aggregation and the release of platelet contents. In platelet suspensions the mechanical stimulus of stirring can induce slow aggregation and the loss of endogenous arachidonic acid from phospholipids by activation of platelet phospholipases. These changes are prevented by the presence of ethanol 20-100 mM, whereas, in unstirred suspensions, ethanol alone has no effect on platelet phospholipids. Under similar conditions of reduced platelet: platelet contact, chemical stimuli, such as thrombi, although unable to produce visible aggregation, still cause the release of [3H]-5-hydroxytryptamine from platelets and also initiate the breakdown of platelet phospholipids. Ethanol does not now inhibit the thrombin-induced release of platelet contents and has little effect on phosphatidylinositol breakdown, though it inhibits phosphatidylcholine breakdown. Ethanol may therefore inhibit platelet aggregation by reducing the effect of mechanical and chemical stimuli on the activation of phospholipase A2. In contrast ethanol has rather little effect on the receptor-mediated breakdown of phosphatidylinositol which is apparently sufficient to trigger the release of platelet contents.

Effect of ethanol in vitro and in vivo on Ca2+-activated metabolism of membrane phospholipids in rat synaptosomal and brain slice preparations

Phospholipase C (PLC) activity was measured by the incorporation of [3H]-inositol into lipids and by the breakdown of [3H]-inositol-labelled phosphatidylinositols (PI) and polyphosphatidylinositols (PPI) to [3H]-inositol phosphates; phospholipase A2 (PLA2) activity by the breakdown of [3H]oleic acid-labelled phosphatidylcholine [( 3H]PC) to [3H]oleic acid and the enzymes of phospholipid base exchange (PLBE) by the incorporation of [14C]serine into membrane lipids. The activities of these enzymes in rat brain preparations were all increased by procedures which increase intracellular Ca2+, and were all inhibited to a varying extent by the presence of ethanol, 50 mM, in vitro. In contrast, the activities of PLA2 and PLBE enzymes were markedly increased in preparations from animals which had received ethanol chronically in vivo. Similarly, although the basal activity of PLC was only slightly increased in such preparations, depolarization induced the breakdown of a significantly greater fraction of radiolabelled PI than that which was obtained in control preparations. The results suggest compensatory alterations in the activity of Ca2+-activated enzymes of phospholipid metabolism in brain tissue during the continued presence of ethanol in vivo.

Alterations in Ca2+-dependent and Ca2+-independent release of catecholamines in preparations of rat brain produced by ethanol treatment in vivo

Compared to preparations from control animals, superfused striatal slice preparations from brains of rats treated chronically with ethanol released a significantly greater fraction of stored [3H] dopamine on depolarisation in 40 mM K+. Similarly, the electrically-evoked release of [3H]-norepinephrine from cortical slices and of [3H]-dopamine from striatal slices is also increased, although with this mechanism of depolarisation the change is significant only in the case of [3H] norepinephrine release. In contrast to this tendency to enhancement of Ca2+-dependent depolarisation-induced release, a reduced fraction of stored [3H]-catecholamines was released from these preparations by the indirect sympathomimetics tyramine and (+)-amphetamine. The catecholamine release induced by these indirect sympathomimetics is largely independent of external Ca2+ and the results are interpreted as suggesting that chronic alcohol treatment changes the distribution of catecholamine neurotransmitters between storage pools in the nerve terminal which do or do not require Ca2+ entry for release.

Interactions between ethanol and dietary fat in determining human platelet function

Platelet aggregation to collagen and ADP in vitro was assessed in the plasma of healthy human volunteers both before and after drinking 700 ml of white wine. This had no effect on platelet aggregation when compared with samples from the same individuals taken on a separate occasion without alcohol consumption. However, when alcohol was taken with a meal high in saturated fat, a significant inhibitory effect on platelet aggregation was observed when compared to the effect of the meal alone. There was no such interaction when the meal associated with alcohol ingestion contained mainly unsaturated fats. The fatty acid composition of plasma and platelet membranes from these volunteers showed a significantly increased proportion of saturated fats after the saturated fat meal. The concomitant ingestion of ethanol did not prevent this change. The concentration of alcohol in plasma achieved (c. 25 mM) may directly inhibit platelet aggregation when the platelet membrane content of saturated fats is high.

The human blood platelet as a model for studying interactions of ethanol with membrane lipids

The effect of ethanol on human blood platelet aggregation is generally inhibitory, but aggregation caused by arachidonic acid is either unaffected or potentiated by ethanol. Of the other aggregatory agents tested, the calcium ionophore A23187, collagen, and thrombin were most inhibited by ethanol. These results suggest that in the case of collagen and ionophore A23187 ethanol may act to inhibit aggregation at some point between the rise in cytosolic calcium and the cleavage of membrane phospholipids associated with the platelet release reaction. A similar spectrum of inhibition was produced by the incorporation of unsaturated fats into the platelet or by reduction of divalent cations by addition of EDTA to the external medium. Platelets in which unsaturated fats were incorporated were less susceptible to inhibition by ethanol than those into which saturated fats had been incorporated.

Picrotoxin inhibits the effect of ethanol on the spontaneous efflux of [3H]-dopamine from superfused slices of rat corpus striatum

The presence of ethanol, 100 microM, in the superfusate enhanced the spontaneous release of previously uptaken [3H]-dopamine from slices of rat corpus striatum, but produced a small inhibition of K+-stimulated release. The concomitant presence of picrotoxin, 10 microM, in the superfusate prevented the enhancement of spontaneous release of [3H]-dopamine by ethanol with equivocal effects on K+-stimulated release. When present in the superfusate alone picrotoxin had no effect on [3H]-dopamine release.

Lack of stereoselectivity in ability of nicotine to release dopamine from rat synaptosomal preparations

Both the naturally occurring (-)-isomer and the synthetic (+)-isomer of nicotine caused release of 3H from a crude synaptosomal fraction of rat brain preincubated with [3H]dopamine. The isomers were equipotent in producing this response, which was concentration-dependent, a significant effect on the fractional release of dopamine being observed at 10(-4) M nicotine. The effect did not appear to be the result of synaptosomal damage, as levels of the intrasynaptosomal marker lactate dehydrogenase did not increase in the supernatant. Nicotine-induced release was inhibited by removal of external Ca2+ and by the presence in vitro of pempidine (230 microM). Neither hexamethonium (500 microM) in vitro nor the chronic administration of (-)-nicotine in vivo had any effect on the nicotine-induced release of [3H]dopamine. It is concluded that nicotine exerts this effect via a presynaptic nicotinic receptor of the "ganglionic" type, but that this receptor differs from that in the periphery by showing a relative lack of stereospecificity. There is no evidence of a functional "down regulation" in this receptor on chronic exposure to nicotine in vivo.

Interactions of ethanol with ionophore A23187 in human platelets and erythrocytes and in rat brain slices

The aggregation of gel-filtered human platelets induced by A23187 is very sensitive to inhibition by ethanol. Similarly when platelets preloaded with [3H]5-hydroxytryptamine ([3H]5HT) are studied in a superfusion system under conditions where aggregation is likely (high platelet density, presence of Ca2+) the rate of release of [3H]5HT induced by A23187 is reduced by the presence of ethanol. However when platelet aggregation is less likely (low platelet density, absence of Ca2+) ethanol does not reduce the rate of [3H]5HT efflux induced by A23187 in superfused platelets. In addition, in contrast to the effects of ethanol on platelet aggregation, the transformation of human red cells to echinocytes induced by A23187 is accelerated by the presence of ethanol. Similarly the increased efflux of 3H from superfused rat striatal slices preloaded with [3H]dopamine which is produced by A23187 is potentiated by ethanol. It is concluded that the inhibitory effect of ethanol on the action of A23187 may be confined to platelet aggregation. This may be because the mechanisms of action of either A23187 or ethanol on platelet aggregation differ from those on other cell functions.

Possible association of alcohol tolerance with increased synaptic Ca2+ sensitivity

The inhibitory effect of ethanol on neurotransmitter release has been suggested to be due to either reduced Ca2+ entry or increased removal of free intracellular Ca2+ from the synapse. The use of the Ca2+ ionophore, A23187, to allow direct access of external Ca2+ to the presynaptic interior should help to determine which of these two factors is the more important, as ethanol should inhibit A23187-induced release of transmitter only if increased Ca2+ removal from the synapse is important. Here we show in rat striatal slices that, although 3H-dopamine release evoked by depolarization with 40 mM K+ is inhibited by 50 mM ethanol, the release evoked by A23187 is enhanced by the presence of ethanol in vitro. The results suggest that ethanol reduces depolarization-induced transmitter release by reducing Ca2+ entry to the presynaptic terminal. However, for brain slices taken from rats made tolerant to ethanol, 3H-dopamine release in the absence of ethanol showed altered characteristics; both K+ depolarization and A23187 released a significantly greater fraction of 3H-dopamine from these slices than from controls. Thus tolerance to the inhibitory effect of ethanol on release may develop by a mechanism involving increased sensitivity of the terminal to Ca2+ entry.