Effects of acute and chronic ethanol administration on whole mouse brain synaptosomal calcium influx

Stimulation of cannabinoid receptor agonist 2-arachidonylglycerol by chronic ethanol and its modulation by specific neuromodulators in cerebellar granule neurons

In an earlier study, we reported that chronic ethanol (EtOH) stimulates the formation of anandamide in human SK-N-SH cells. In the present study, we investigated the effect of chronic EtOH on the formation of yet another cannabinoid receptor (CB1) agonist, 2-arachidonylglycerol (2-AG), in cerebellar granule neurons (CGNs). The formation of 2-[(3)H]AG without any stimulation was more pronounced in the older cultures than in younger cultures. Exposure of CGNs to EtOH led to a significant increase in the level of 2-[(3)H]AG (P<0.05). Incubation with the anandamidehydrolase inhibitor phenylmethylsulfonyl fluoride and EtOH did result in an additive increase in 2-[(3)H]AG, but did not with E-6-(bromomethylene)tetrahydro-3-(1-naphthelenyl)-2H-pyran-2-one. The formation of 2-[(3)H]AG was enhanced by ionomycin in both the control and EtOH-exposed CGNs, and the ionomycin-stimulated 2-[(3)H]AG synthesis was inhibited by the intracellular chelating agent 1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid. Further, glutamate increased the formation of 2-[(3)H]AG only in control CGNs. MK-801 inhibited the EtOH-induced 2-[(3)H]AG synthesis, suggesting the participation of intracellular Ca(2+) in EtOH-induced 2-[(3)H]AG synthesis. The dopamine receptor (D2) agonist did not modify the 2-AG synthesis in either the control or EtOH-exposed CGNs. However, the D2 receptor antagonist inhibited the EtOH-induced formation of 2-[(3)H]AG. The EtOH-induced 2-[(3)H]AG formation was inhibited by SR141716A and pertussis toxin, suggesting the CB1 receptor- and Gi/o-protein-mediated regulation of 2-AG. The observed increase in 2-AG level in CGNs is possibly a mechanism for neuronal adaptation to the continuous presence of EtOH. These findings indicate that some of the pharmacological actions of EtOH may involve alterations in the endocannabinoid signaling system.

Chronic ethanol increases the cannabinoid receptor agonist anandamide and its precursor N-arachidonoylphosphatidylethanolamine in SK-N-SH cells

In an earlier study, we demonstrated that chronic ethanol (EtOH) exposure down-regulated the cannabinoid receptors (CB1) in mouse brain synaptic plasma membrane. In the present study, we investigated the effect of chronic EtOH on the formation of anandamide (AnNH), an endogenous cannabimimetic compound, and its precursor N-arachidonoylphosphatidylethanolamine (N-ArPE) in SK-N-SH cells that were prelabeled with [3H]arachidonic acid. The results indicate that exposure of SK-N-SH cells to EtOH (100 mM) for 72 h significantly increased levels of [3H]AnNH and [3H]N-ArPE (p < 0.05) (1.43-fold for [3H]AnNH and 1.65-fold for [3H]N-ArPE). Exposure of SK-N-SH cells to EtOH (100 mM, 24 h) inhibited initially the formation of [3H]AnNH at 24 h, followed by a progressive increase, reaching a statistical significance level at 72 h (p < 0.05). [3H]N-ArPE increased gradually to a statistically significant level after 48 and 72 h (p < 0.05). Incubation with exogenous ethanolamine (7 mM) and EtOH (100 mM, 72 h) did not result in an additive increase in the formation of [3H]AnNH. The formation of [3H]AnNH and [3H]N-ArPE by EtOH was enhanced by the Ca2+ ionophore A23187 or by the depolarizing agent veratridine and the K+ channel blocker 4-aminopyridine. Further, the EtOH-induced formation of [3H]AnNH and [3H]N-ArPE was inhibited by exogenous AnNH, whereas only [3H]AnNH formation was inhibited by the CB1 receptor antagonist SR141716A and pertussis toxin, suggesting that the CB1 receptor and G(i/o) protein mediated the regulation of AnNH levels. The observed increase in the levels of these lipids in SK-N-SH cells may be a mechanism for neuronal adaptation and may serve as a compensatory mechanism to counteract the continuous presence of EtOH. The present observation taken together with our previous results indicate the involvement of the endocannabinoid system in mediating some of the pharmacological actions of EtOH and may constitute part of a common brain pathway mediating reinforcement of drugs of abuse including EtOH.

Ethanol exposure during the third trimester equivalent results in long-lasting decreased synaptic efficacy but not plasticity in the CA1 region of the rat hippocampus

Fetal alcohol syndrome is a major cause of mental retardation. We investigated possible long-lasting effects of alcohol on the hippocampus using a model for human third trimester brain development. Treatment of neonatal rats with an ethanol vapor atmosphere of 39.4+/-2.6 mg ethanol/liter of air for 3 h a day from postnatal day 4 through 9 produced daily blood ethanol levels of 351+/-14 mg/dL. Separation control animals were removed from their mothers in parallel with the ethanol vapor treatment, while suckle controls were left to develop normally. We prepared hippocampal slices from these animals between postnatal days 45 and 60 and recorded extracellular responses to Schaffer collateral stimulation. The maximum population spike in the CA1 pyramidal region and population excitatory postsynaptic potentials in the stratum radiatum did not differ significantly between groups. However, slices prepared from ethanol-treated rats as opposed to separation and suckle controls required larger stimulus currents to produce normal postsynaptic responses. In addition, the ratio of the population excitatory postsynaptic potential (pEPSP) slope to the presynaptic volley was significantly reduced in ethanol-treated rats. Ethanol vapor-treated rats and separation control rats did not exhibit any significant changes in long-term potentiation or paired-pulse potentiation compared with normal suckle controls. These results suggest that early postnatal ethanol treatment produces a long-lasting reduction in synaptic efficacy but not plasticity.

Molecular pathogenesis of alcohol withdrawal seizures: the modified lipid-protein interaction mechanism

The phrase alcohol withdrawal seizures (AWS) refers to seizures that result from the withdrawal of alcohol after a period of chronic alcohol administration. A mechanism of AWS is postulated, namely the modified lipid-protein interaction (MLPI) mechanism. This hypothesis is based upon an evaluation of the mechanisms of membrane fluidity, calcium channels, gamma-aminobutyric acid (GABA) and glutamate in the molecular pathogenesis of AWS. The mechanism hypothesizes that acute ethanol treatment alters the neuronal membrane lipids which then perturbs protein events, such as affecting the GABAA receptors, NMDA receptors and voltage-dependent Ca2+ channels synergistically or in combination. Subsequent adaptations in these systems occur after prolonged administration of ethanol. A sudden withdrawal of ethanol then leads to hyperexcitability which results in AWS.

Sleep induction by microinjection of pentobarbital into the medial preoptic area in rats

In a previous study we have shown that microinjection of the benzodiazepine hypnotic triazolam into the medial preoptic area increases sleep in rats. In order to determine whether this effect is specific to benzodiazepines, or whether it occurs with hypnotic medications from other pharmacologic classes, we have microinjected pentobarbital (1 and 100 micrograms) and vehicle in random sequence into rats and performed two hour sleep studies in the daytime with the lights on. Both doses significantly decreased sleep latency and increased nonREM and total sleep. The amount of REM sleep, REM latency, and intermittent waking time were not significantly altered. These data are consistent with the hypothesis that the medial preoptic area may be involved in sleep induction by both benzodiazepine and barbiturate hypnotic medications.

The effect of ethanol and calcium channel antagonists on rabbit EEG

The influence of nifedipine, verapamil, and cinnarizine on the effect of ethanol on EEG of rabbits (frontal cortex, hippocampus, MRF) was tested. Nifedipine (1.75 mg/kg, IP) and cinnarizine (7.5 mg/kg, IP) were given 30 min before ethanol administration. Verapamil (0.2 mg/kg, IV) was given 15 min before ethanol injection in a dose of 0.8 g/kg IV. Ethanol caused the increase of the frequencies 0.5-4 cps in the recording, as well as a marked decrease of the fastest frequencies. Verapamil prevented ethanol's effect on EEG recording. Cinnarizine antagonized this action to a smaller extent and the influence of nifedipine is transitory and less pronounced.

Calcium channel blockers improve hypoxia/hypoglycemia-induced impairment of rat hippocampal 2-deoxyglucose uptake in vitro after ethanol withdrawal

The aim of the present study was to determine whether calcium channel antagonists attenuated hypoxia/hypoglycemia- or glutamate-induced reduction in 2-deoxyglucose (2-DG) uptake of hippocampal slices obtained from ethanol withdrawal rats. Ethanol withdrawal significantly potentiated the hypoxia/hypoglycemia- and glutamate-induced reductions in 2-DG uptake of hippocampal slices. Both nifedipine and flunarizine exhibited attenuating effects on ethanol withdrawal-induced potentiation of impairment of 2-DG uptake caused by hypoxia/hypoglycemia or glutamate. Hypoxia/hypoglycemia-induced deficit of 2-DG uptake was prevented by ethanol, but chronic consumption of ethanol resulted in the development of tolerance to neuroprotective effect. These findings suggest that the increased sensitivity of neurons to ischemic damage by ischemia may involve in the increased activity of calcium channels in the hippocampus.

Effects of flunarizine and diltiazem on physical dependence on barbital in rats

The effects of flunarizine and diltiazem both on development of physical dependence on barbital and on barbital withdrawal signs in rats were examined using the drug-admixed food (DAF) method. Rats were chronically treated with barbital or barbital in combination with flunarizine (fixed at 1.5 mg/g of food) or diltiazem (fixed at 0.75 mg/g of food)-admixed food on the schedule of gradually increasing doses of barbital. Motor incoordination during the treatment was potentiated by coadministration of flunarizine, but not by coadministration of diltiazem. After the termination of drug treatment, the body weight loss and withdrawal scores were significantly suppressed in the group coadministered flunarizine, but not in that coadministered diltiazem. There were no significant differences in plasma barbital levels after the withdrawal between groups. In the substitution test, flunarizine (20 and 40 mg/kg, IP) significantly suppressed the body weight loss and withdrawal scores after the withdrawal, but diltiazem (20 mg/kg, IP) did not. These results indicated that flunarizine suppressed both the development of physical dependence on barbital and barbital withdrawal signs, mainly according to the suppression of convulsions, but not diltiazem, which is known to poorly penetrate into the brain. Therefore, the present findings suggest that central calcium channels may be involved in both the development of physical dependence on barbital and the appearance of barbital withdrawal signs.

Increased intracellular calcium level in peripheral blood mononuclear cells of alcoholic patients under withdrawal

Cytosolic free Ca2+ functions as a main regulator of numerous cellular processes, including those implicated in synthesis, release and responsiveness of hormones and neurotransmitters are discussed. To examine whether a change in the intracellular free calcium ion concentration [Ca2+]i occurs associated with delirium tremens and related states we compared [Ca2+]i in peripheral blood mononuclear cells (PBMC) of alcoholic patients under withdrawal with that of non-alcoholic patients and of healthy controls. [Ca2+]i in PBMC of alcoholic patients was significantly higher (P < 0.001) compared to both control groups, suggesting that changes in [Ca2+]i may be relevant to increased excitability of the central nervous system. Increased [Ca2+]i in PBMC might be diagnostically valuable as a biological marker of alcohol dependency.

Effects of Ca2+ channel blockers on physical dependence on diazepam in mice

The effects of Ca2+ channel blockers on the development of physical dependence on diazepam were examined in mice. Co-administration of flunarizine (T-type Ca2+ channel sensitive blocker), but not of either nifedipine or diltiazem (L-type Ca2+ channel sensitive blockers), with diazepam significantly suppressed the hypersensitivity to FG 7142 following chronic treatment with diazepam. The hypersensitivity to FG 7142 may reflect benzodiazepine withdrawal convulsions. These results suggest that flunarizine, but not nifedipine or diltiazem, may suppress the development of physical dependence on diazepam, and that T-type Ca2+ channels in the brain, rather than L-type Ca2+ channels, may be involved in the development of physical dependence on diazepam.

Isradipine and other calcium channel antagonists attenuate ethanol consumption in ethanol-preferring rats

The present work is concerned with studying of the ability of different calcium channel antagonists to modify voluntary ethanol ingestion by rats selectively bred for high ethanol preference. The compounds were given s.c. thrice daily for 5 days at doses that did not produce locomotor impairment. While nifedipine, darodipine, and verapamil (each at the dose of 20 mg/kg thrice daily) produced a modest reduction in ethanol intake, isradipine (at the dose of 1 mg/kg three times a day) reduced ethanol intake by over 70%. For all compounds, the reduction in ethanol intake was compensated by a proportional increase in water consumption and the inhibitory effect persisted throughout the 5 days of treatment. The data indicate that calcium channel antagonists exhibit quite different potency in reducing ethanol preference, however this action is a general property of this class of compounds.

The effects of chronic treatment with the dihydropyridine, Bay K 8644, on hyperexcitability due to ethanol withdrawal, in vivo and in vitro

1. The effects of chronic treatment with the dihydropyridine, Bay K 8644, were studied on the ethanol withdrawal syndrome, in vivo and in vitro. 2. Addition of racemic Bay K 8644 to the drinking mixture, throughout the chronic ethanol treatment, decreased the behavioural excitability seen during ethanol withdrawal in vivo. 3. All the signs of hyperexcitability in field potentials in the isolated hippocampal slice, caused by ethanol withdrawal, were decreased by the chronic administration of Bay K 8644. 4. These effects resembled those previously reported for chronic administration of calcium channel antagonists; racemic Bay K 8644 has both calcium channel activating and antagonist properties. 5. Measurement of brain levels of Bay K 8644 at the end of the chronic treatment showed that the compound reached micromolar concentrations during the treatment, but none could be detected in the tissues at the time of the above measurements. 6. It is possible that the results might be explained by predominance of the calcium channel antagonist properties of this compound, owing to the high central concentrations achieved during the treatment. Tolerance to the calcium channel activating properties of Bay K 8644 may also have occurred during the chronic treatment.

Recent Advances in Pharmacological Research on Alcohol

Alcohol dependence is a major public health problem. Studies have shown that a person dependent on alcohol often coabuses other substances, such as cocaine. Cocaine is a powerful stimulant whereas ethanol is generally considered to be a depressant, with some stimulating properties. The subjective effects of these two substances in a dependent individual may often appear to be more similar than they are different. Animals also self-administer both substances. Basically, although both substances have anesthetic properties and both act to functionally increase catecholaminergic function, especially that of dopamine, there are some differences in their actions. Both alcohol and cocaine have various effects on several neurotransmitters and systems, which ultimately interact to produce the feeling of well-being avidly sought by many individuals today. This drive often eventually produces a dependence which has associated social and medical consequences. It seems likely that the neurochemical changes that ensue following abuse of these substances underlie the phenomena of dependence, tolerance, and subsequent withdrawal. The apparent similarities and differences between these two substances will be reviewed in this chapter.

Nitrendipine, given during drinking, decreases the electrophysiological changes in the isolated hippocampal slice, seen during ethanol withdrawal

1. Extracellular recordings were made from mouse isolated hippocampal slices prepared after chronic treatment in vivo with either ethanol or ethanol plus the dihydropyridine calcium channel antagonist, nitrendipine. 2. The withdrawal of ethanol caused a variety of changes in the field potentials, as previously reported, including decreases in the thresholds for eliciting single and multiple population spikes, increases in paired pulse potentiation and shifts to the left of the input/output curves. 3. The addition of nitrendipine to the drinking mixture in the chronic ethanol treatment significantly decreased all the changes in the field potentials that were seen after ethanol withdrawal. 4. Addition of nitrendipine to the perfusion medium also decreased the signs of hyperexcitability seen in the hippocampal slices during ethanol withdrawal. 5. The results provide further evidence that neuronal calcium channels may be involved in ethanol dependence and that the adaptive changes caused by chronic ethanol treatment can be modulated by alterations at dihydropyridine-sensitive sites.

Focal application of alcohols elevates extracellular dopamine in rat brain: a microdialysis study

Dopaminergic systems are thought to play a major role in the stimulant and reinforcing properties of drugs of abuse, including ethanol. The present study describes the effects of local perfusion with ethanol (and other alcohols) on extracellular dopamine in the striatum and nucleus accumbens. Following the establishment of basal dopamine levels (2-3 h), various concentrations of ethanol in artificial CSF (0.01-10% v/v) were slowly perfused through a microdialysis probe. Each dose of ethanol was found to increase dopamine concentrations in both the striatum and nucleus accumbens. This increase was dose-related in the striatum. The exclusion of calcium and inclusion of 12.5 mM magnesium in the perfusion medium prevented, or greatly attenuated the ethanol-induced dopamine (DA) release. Thus, the release of DA by ethanol is exocytotic in nature and involves calcium-dependent processes. The other alcohols tested, namely methanol and butanol, demonstrated a structure-activity relationship together with ethanol, in their ability to increase extracellular DA. The relative potency was butanol greater than ethanol greater than methanol. The diffusion of ethanol into the brain tissue was investigated following perfusion through the probe. Relatively low concentrations of ethanol were found in striatal tissue during perfusion and they declined rapidly with time, following the removal of ethanol from the perfusate. The concentrations of ethanol achieved in brain tissue following focal application through the microdialysis probe were relevant to human intoxication.

Influence of early chronic phenobarbital treatment on cerebral arteriovenous differences of glucose and ketone bodies in the developing rat

The influence of an early chronic phenobarbital treatment on cerebral arteriovenous differences of glucose, lactate, pyruvate, beta-hydroxybutyrate and acetoacetate was studied in suckling rats. The animals were treated from day 2 to 21 after birth by a daily injection of 50 mg/kg phenobarbital or by saline and were studied at 10, 14 and 21 days. Phenobarbital treatment induced a decrease in cerebral arteriovenous difference of glucose at P14 and no change at P10 and P21. The barbiturate did not have any influence on cerebral arteriovenous difference of lactate and pyruvate at the three stages studied. Cerebral uptake of beta-hydroxybutyrate was unchanged at P10 and increased by two-fold at P14 and by threefold at P21 by phenobarbital. Cerebral arteriovenous difference of acetoacetate was low and did not change with the pharmacological treatment. At P14 and P21, the calculated amount of oxygen used by the brain for the oxidation of ketone bodies was twice as high in barbiturate- as in saline-treated rats and reached values of 47 and 16% respectively in phenobarbital-exposed animals. In addition, the barbiturate seemed to affect the carrier process of beta-hydroxybutyrate from blood to brain. The results of the present study are in good agreement with previous data from our laboratory showing that an early chronic phenobarbital treatment is able to induce a shift in the cerebral energy metabolism balance in favor of ketone bodies.

The role of neuronal calcium channels in dependence on ethanol and other sedatives/hypnotics

This review discusses the importance of neuronal calcium currents in dependence on ethanol, barbiturates, benzodiazepines and opiates. The main sections describe the actions of ethanol on control of intracellular calcium and on calcium and calcium-dependent conductance mechanisms. In particular, the effects of both acute and chronic ethanol treatment on dihydropyridine-sensitive, voltage-dependent, calcium channels are described. The later sections cover the effects of barbiturates, benzodiazepines and opiates on these systems. The conclusions suggest that dihydropyridine calcium channel antagonists may offer a new therapeutic approach to the treatment of ethanol and opiate dependence.

Decreased alcohol consumption by verapamil in alcohol preferring rats

1. Calcium channel blockers have been proposed, in addition to inhibiting the influx of Ca++ into the cells, to possess a wide variety of pharmacological effects, including interference with certain neurotransmitters involved in mood, mental disorders and alcohol craving. Further, it has been documented that certain neurotransmitters are involved in alcohol craving both in animals and humans. 2. To investigate the effects of Ca(++)-channel antagonist on alcohol preference, verapamil in three doses (5, 10 and 15 mg/kg) was injected (S.C.) twice daily over a period of one day in alcohol-preferring (P) and alcohol non-preferring (NP) rats at 9:00 a.m. and 4:00 p.m. 3. Water, alcohol and food intake were monitored. 4. Our results show that verapamil in doses of 10 and 15 mg/kg significantly (p less than 0.02 and 0.01, respectively) reduced the intake of ethanol and increased the intake of water by P rats. However, injection of an equal volume of saline did not change the pattern of alcohol intake. 5. These results suggest that a (++(+)-channel blocker such as verapamil, could, at least partially, attenuate alcohol preference in alcohol preferring rats. It is possible that verapamil exerts an inhibitory effect on alcohol preference by interfering with Ca++ channels, blocking serotonin uptake or through another mechanism(s).

Central neurochemical effects of dihydropyridine calcium antagonists

Recent advances in central dihydropyridine (DHP)-binding sites are reviewed. DHP-binding sites are pre-synaptically and post-synaptically localized in the brain. The functional role of post-synaptic sites is still unknown, whereas pre-synaptic sites seem to contribute to the control of calcium uptake and of neurotransmitter release. DHP-binding sites may be modualated in physiological (age, sex) and pathological events (hypertension, ischaemia, neurological diseases) or after drug treatments (alcohol, morphine, etc.). The reviewed data suggest new therapeutic implications of DHP calcium channel antagonists in the treatment of other diseases and of drug withdrawal syndrome.

Development of tolerance in brain mitochondria for calcium uptake following chronic ethanol ingestion

Brain mitochondria isolated from rats following 10 weeks of chronic exposure to ethanol were not deficient in respiratory function or in rates of calcium uptake under control conditions. Ethanol (80 mM) in the incubation medium caused significant depression in the respiratory and ATP-dependent rates of calcium uptake in control mitochondria, but did not affect mitochondria from ethanol-tolerant rats. Chronic exposure to ethanol causes mitochondria to take calcium up at a normal rate when challenged acutely by ethanol.

Influence of ethanol on calcium, inositol phospholipids and intracellular signalling mechanisms

Studies have implicated Ca++ in the actions of ethanol at many biochemical levels. Calcium as a major intracellular messenger in the central nervous system is involved in many processes, including protein phosphorylation enzyme activation and secretion of hormones and neurotransmitters. The control of intracellular calcium, therefore, represents a major step by which neuronal cells regulate their activities. The present review focuses on three primary areas which influence intracellular calcium levels; voltage-dependent Ca++ channels, receptor-mediated inositol phospholipid hydrolysis, and Ca++/Mg++-ATPase, the high affinity membrane Ca++ pump. Current research suggests that a subtype of the voltage-dependent Ca++ channel, the dihydropyridine-sensitive Ca++ channel, is uniquely sensitive to acute and chronic ethanol treatment. Acute exposure inhibits, while chronic ethanol exposure increases 45Ca++-influx and [3H]dihydropyridine receptor binding sites. In addition, acute and chronic exposure to ethanol inhibits, then increases Ca++/Mg++-ATPase activity in neuronal membranes. Changes in Ca++ channel and Ca++/Mg++-ATPase activity following chronic ethanol may occur as an adaptation process to increase Ca++ availability for intracellular processes. Since receptor-dependent inositol phospholipid hydrolysis is enhanced after chronic ethanol treatment, subsequent activation of protein kinase-C may also be involved in the adaptation process and may indicate increased coupling for receptor-dependent changes in Ca++/Mg++-ATPase activity. The increased sensitivity of three Ca++-dependent processes suggest that adaptation to chronic ethanol exposure may involve coupling of one or more of these processes to receptor-mediated events.

Chronic alcohol intake modifies phorbol ester binding in selected rat brain areas

3H-Phorbol 12,13 dibutyrate binding to rat brain was modified by chronic ethanol treatment. Among the areas examined hippocampus and cortex showed a decrease in Bmax values of 32 and 24% respectively. No significant effect was observed in hypothalamus and cerebellum. In vitro ethanol did not modify the binding in all the areas except at molar concentrations. In hippocampus and cortex the direct measurement of protein kinase C activity indicated that the decrease in phorbol ester binding was accompanied with a concomitant decrease in kinase activity. The results indicate that chronic ethanol treatment leads to an inhibition of brain protein kinase C function.

Different effect of diltiazem and nifedipine on some central actions of ethanol in the rat

The effect of two Ca2+ channel inhibitors (CCIs) on ethanol-induced hypothermia and hypnosis, on tolerance formation to both effects, and on audiogenic convulsions during ethanol withdrawal was studied in rats. Nifedipine, 2 and 5 mg/kg IP, significantly augmented the hypnotic action of ethanol without affecting hypothermia. Diltiazem failed to influence either effect of the toxin. Rectal temperature did not change in ethanol-naive rats after acute injection of diltiazem or nifedipine. Both drugs dose-dependently suppressed the development of tolerance to the hypothermic effect of ethanol without affecting the tolerance to the hypnotic action. Only nifedipine markedly suppressed the audiogenic seizure response in ethanol withdrawn animals. These data suggest that Ca2+ channels play a role in both acute and chronic effects of ethanol while pointing to certain differences in behavioral effects of various CCIs.

Spontaneous calcium release induced by ethanol in the isolated rat brain microsomes

Ethanol-induced neurotransmitter release in unstimulated synaptosomes was found to be independent of extrasynaptosomal Ca2+ concentration, indicating a redistribution of intracellular Ca2+. The effects of alcohol on microsomal Ca2+ uptake and release were studied. In vitro addition of 100 mM ethanol had no effect on ATP-dependent Ca2+ accumulation in the microsomes. However, the same amount of ethanol released 25% of total accumulated Ca2+ from the microsomes. Ethanol induced Ca2+ release in a concentration-dependent manner over the range 30 mM-500 mM. The amount of Ca2+ release increased with higher alcohols. The effect of alcohol was temperature-dependent and inhibited at 0 degrees C. These results indicate that the known stimulatory effects of ethanol on resting release of neurotransmitters may be due to the microsomal release of Ca2+.

Biochemical and behavioral evidence for an interaction between ethanol and calcium channel antagonists

In the present series of experiments we have studied the effects of the dihydropyridine calcium channel antagonist nifedipine on ethanol-induced changes in behavior and dopamine (DA) release and metabolism. The locomotor-stimulatory effect of low doses of ethanol (2.5 g/kg) was antagonized by nifedipine, whereas ethanol-induced sedation observed after higher doses (4.5 g/kg) was potentiated. Biochemical studies indicated that ethanol enhanced the metabolism and release of DA in the striatum and the DA-rich limbic regions measured by post mortem analyses of DA-metabolites by HPLC with electrochemical detection and by in vivo voltammetry in anaesthetized rats, respectively. Pretreatment with nifedipine antagonized the stimulatory effects of ethanol on the DA-system. Nifedipine reduced the preference for ethanol, estimated by the relative intake of ethanol (6% v/v) and water in a free-choice situation, suggesting an influence of nifedipine not only on the stimulatory but also on the positive reinforcing effects of ethanol. The present results suggest that the locomotor-stimulatory and positive reinforcing effects of ethanol as well as its enhancing effect on dopaminergic activity may involve an enhancement of calcium mediated mechanisms.

Acute ethanol and acetaldehyde administration produce similar effects on L-type calcium channels in rat brain

The present study investigates the effect of acute ethanol and acetaldehyde administration on neuronal L-type calcium channels by measuring the binding of 3H-nitrendipine (3H-NTP). Acute ethanol (3 g/kg orally) transiently increases (+40% at 40 min) 3H-NTP binding. Acetaldehyde has a similar effect, but the onset of action is shorter; in fact the binding increase peaks 15 min following administration and is completely reversible within 2 hours. Disulfiram pretreatment does not modify the effect produced by acute ethanol on 3H-NTP binding. The results indicate that acetaldehyde may participate in mediating the action of ethanol on voltage sensitive L-type calcium channels with consequent alterations of neuronal excitability.

Ethanol increases synaptosomal free calcium concentration

The effect of ethanol on synaptosomal free calcium concentration [( Ca2+]i) and 45Ca2+ uptake was studied in vitro. Synaptosomes were prepared from forebrains of adult rats and incubated in the presence of ethanol 50-500 mM. [Ca2+]i determined by means of the Ca2+-sensitive dye, fura-2, was increased by ethanol in polarized and depolarized synaptosomes, whereas 45Ca2+ uptake was decreased. The results suggest that ethanol may influence neuronal calcium homeostasis by increasing rather than decreasing [Ca2+]i.

Effects of early chronic phenobarbital treatment on the maturation of energy metabolism in the developing rat brain. I. Incorporation of glucose carbon into amino acids

The influence of phenobarbital (PhB) on the utilization of glucose by the cerebral cortex and the cerebellum was studied in rats during postnatal development. The animals were treated from day 2 to day 35 after birth by a daily injection of 50 mg/kg PhB or by saline. The rats were studied at 5 postnatal stages: 7, 10, 14, 21 and 35 days. PhB treatment induced a 10% decrease in body and brain weight over the whole period studied and a transient significant decrease in circulating thyroxin levels at 14 days after birth. Amino acid levels in the cerebral cortex and particularly in the cerebellum were not greatly affected by the pharmacological treatment. The conversion of [2-14C]glucose into amino acids was significantly decreased in both cerebral structures between day 7 and day 14 after birth. The distribution of radioactivity between amino acids was not affected in the cerebral cortex but was significantly changed by PhB treatment in the cerebellum. Specific radioactivity values of amino acids were lower in PhB- than in saline-treated animals in both studied structures. The results of the present study show that glucose utilization is reduced in the brain of PhB-treated animals as compared to the controls and that the cerebellum seems to be more affected than the cerebral cortex.

Calcium uptake in brain synaptosomes from rats exposed to daily toluene for up to 80 weeks

Rats were exposed to toluene, 500 p.p.m., for 12 hrs/day for up to 80 weeks. The brains were removed and the synaptosomes were prepared. Potassium-stimulated and unstimulated synaptosomes were incubated with 45Ca2+ for 1/2, 2, 4, 8, and 16 min. Toluene exposure for 4 and 12 weeks caused a significant, approximately 20%, increase in 45Ca2+ uptake into unstimulated synaptosomes. The effect was of moderate quantity and transient, since it was not significant after 30 and 80 weeks of exposure. It seems doubtful whether the demonstrated change in calcium uptake should have any relevance in connection with the "organic solvent neurotoxicity syndrome".

Effects of 1,1,1-trichloroethane on synaptosomal calcium accumulation in mouse brain

Addition of 1,1,1-trichloroethane (TCE), in vitro to synaptosomes isolated from the mouse cerebellum and cerebral cortex inhibited the slow phase of K+-stimulated 45Ca2+ influx and the net 45Ca2+ influx (delta k). In the brain stem, however, TCE increased the fast and slow phases of calcium uptake under depolarizing conditions and also delta k. The non-depolarized calcium influx was not altered by TCE added in vitro. Two hours after injection of TCE (2.4 g/kg) the calcium accumulation in the presence of high K+ was lowered in the cerebellar synaptosomes, while it was increased in brain stem synaptosomes. TCE administered in vivo did not alter the calcium influx into cerebrocortical synaptosomes nor did it affect the non-depolarization-induced 45Ca2+ influx. Thus, these data indicate that TCE may influence voltage-dependent calcium channels in mouse brain synaptosomes.

Acute ethanol effect on calcium antagonist binding in rat brain

We investigated the effect of acute ethanol administration on voltage-sensitive calcium channels (VSCC) by measuring [3H]nitrendipine ([3H]NTP) binding to crude synaptosomal membrane preparations from different rat brain areas, i.e. cerebral cortex, hippocampus and striatum. Ethanol enhances the number of binding sites shortly after the administration (40 min), then Bmax returns towards control values while the binding affinity increases. Kd decreased peaks 8 h after the oral administration and returns within the range of control values at 36 h. The in vitro addition of ethanol has no effect on [3H]NTP binding at various concentrations up to 600 mM. These results suggest that acute ethanol treatment modifies VSCC supporting the concept that the short-term neurochemical alterations induced by in vivo ethanol administration involve calcium channels.

Influence of mouse genotype on responses of central biogenic amines to alcohol intoxication and aging

Dopamine and serotonin responses to various periods of alcohol treatment have been followed in striatum and hippocampus of two inbred strains of mice and related to the effect of aging. A striking strain dependency was noted for chronic alcohol effects and also for senescence. For both neurotransmitters studied the C57Bl strain loses tolerance to prolonged alcohol injury earlier than the Balb/c strain. This loss of tolerance accompanying aging may be indicative of more widespread changes in CNS adaptability in this strain. The unequal capacity to adapt also appears to depend on the nervous structure and the neurotransmitter considered. Alcohol and aging induced changes are not identical. In a given mouse strain, significant effects of either drug or aging induced disturbances are noted. A similar molecular process could operate in both aging and alcohol abuse, but the neurochemical effect might depend on the nervous structure or neurotransmitter involved. Such a phenomenon may be the basis of differences in behavioral changes observed in alcoholics.

Altered calcium signal transduction after chronic ethanol consumption

Calcium and calcium-calmodulin dependent phosphorylation of several protein bands was found altered in synaptosomal membranes prepared from ethanol treated rats. The ethanol induced effect on Ca++ and Ca++-calmodulin phosphorylation presented regional differences. In particular 32P incorporation was lower in the striatum and cerebellum, higher in the hippocampus and unmodified in the cortex. Part of the phosphorylated bands had an apparent molecular weight similar to that of the phosphoproteins involved in neurotransmission. These results extend previous observations indicating that calcium movement control is modified during chronic ethanol consumption and suggest that ethanol may interfere at various steps in the calcium-promoted events.

Central Ca++-channel blockade reverses ethanol-induced poikilothermia in the rat

Two series of experiments were performed to determine the possible involvement of Ca++ channels in the thermolytic action of ethanol administered at a room temperature of 22 degrees C. In one group of 11 adult female Sprague-Dawley rats, stainless steel guide cannulae were implanted stereotaxically above the lateral cerebral ventricle. Prior to an experiment, a thermistor probe was inserted into the colon so that core temperature could be monitored continuously for up to six hours or until the temperature had returned to a previous baseline level. When the animal's body temperature had stabilized, a dose of 4.0 g/kg in a v/v solution of 20% ethanol was given by intragastric gavage. After the body temperature had declined by about 2.0 degrees C, ordinarily 30 min after ethanol administration, either control CSF or the vehicle plus one of four doses of verapamil (8.3, 25, 50 and 100 micrograms) was infused intracerebroventricularly (ICV) in a volume of 10 microliter. In a second group of 7 unoperated rats, either 4.0 g/kg ethanol or a physiological saline control solution was administered isovolumetrically by intragastric gavage; then, 30 min later, either 3.0 or 10.0 mg/kg verapamil was injected intraperitoneally. At an ambient temperature of 22 degrees C, ethanol gavage produced a significant decline in colonic temperature which was unaffected by physiological saline given by the same route. Although the CSF control vehicle was without effect, verapamil administered ICV attenuated the thermolytic action of ethanol in all doses tested; however, the lowest dose exerted its antagonist effect but with a longer latency. Conversely, when verapamil was given systemically, the hypothermic action of ethanol was significantly potentiated in a dose-dependent manner.(ABSTRACT TRUNCATED AT 250 WORDS)

Genotypic differences in age and chronic alcohol exposure effects on somatostatin levels in hippocampus and striatum in mice

Somatostatin contents of striatum, hippocampus, and pons medulla have been followed in two inbred strains of mice (C57B1/6J and Balb/cJ) with aging and long term alcohol exposure (over a 25 month period of intoxication). Marked strain dependent differences in basic levels of somatostatin and genotypic variations in reactivity of this neuropeptide to aging processes and chronic alcohol exposure were demonstrated. The Balb/c strain exhibits a significant age dependent decrease in striatal and hippocampal somatostatin levels whereas the C57B1 mice remain unchanged until the 27 month. Moreover, only the Balb/c strain reacts to chronic alcohol exposure, showing a significant increase in somatostatin levels in those structures affected by the aging process. Such genotypic differences may be involved in man in specific pathologies in aged individuals and in alcohol induced behavioral alterations in alcoholics.

Ethanol blocks tetanic and calcium-induced long-term potentiation in the hippocampal slice

Long-term potentiation (LTP) of the CA1 population spike in the hippocampal slice was produced by a tetanic stimulus in the stratum radiatum or by doubling the calcium concentration in the medium to 4 mM for 10 min. Ethanol (0.1 M) antagonized both tetanic- and ethanol-induced LTP. Since the hippocampus is known to be involved with memory, and ethanol interferes with memory and the production of LTP, the results are consistent with the notion that LTP may be related to memory processes.

Differential effects of ethanol on two synaptic membrane Ca2+ transport systems

The Na+-Ca2+ exchange activity in synaptic plasma membranes is inhibited by very low concentrations of ethanol (less than 25 mM). The high affinity Mg2+- and ATP-dependent Ca2+ transport in highly purified synaptic membranes is much less sensitive to inhibition by ethanol, with no statistically significant inhibition observed until an ethanol concentration of nearly 800 mM was used. Manipulations of the lipid environment designed to increase membrane fluidity enhanced the activity of the Na+-Ca2+ exchange system but inhibited the ATP-dependent Ca2+ pump. The differential responses of the two synaptic plasma membrane Ca2+ transporting systems to such modifications of membrane structure suggest that these two ion transport processes differ in the extent to which their activity is dependent on the lipid microenvironment in which they reside. Thus, the effects of ethanol on the Na+-Ca2+ antiporter may represent a fairly selective inhibitory process.

Effect of ethanol on [3H]nitrendipine binding to calcium channels in brain membranes

We examined the effect of ethanol on [3H]nitrendipine binding to rat brain membranes, to investigate the possibility that voltage-dependent calcium channels are involved in synaptic actions of ethanol. Ethanol inhibited specific [3H]nitrendipine binding with Ki = 460 mM, by decreasing binding affinity without altering the maximal number of sites labeled. At a lower concentration (100 mM), ethanol had no effect on inhibition of binding by verapamil or diltiazem. The high concentrations of ethanol required to produce alterations in [3H]nitrendipine binding suggest that ethanol and classical calcium channel antagonists influence calcium-mediated synaptic processes by separate mechanisms.

Alcohol and local anesthetic effects on Na+-dependent Ca2+ fluxes in brain synaptic membrane vesicles

Resealed synaptic plasma membrane vesicles exhibit Na+-dependent Ca2+ transport activity which may participate in regulation of free Ca2+ concentrations in nerve endings. Sodium chloride-loaded vesicles took up Ca2+ from the external medium (150 mM KCl-25 mM Tris/HCl) in the presence of an outward-directed Na+ gradient, a Ca2+ concentration of 38.6 microM producing half-maximal uptake at 23 degrees. Methanol (5-200 mM) and low concentrations of ethanol (5-25 mM) enhanced the Na+-dependent Ca2+ influx measured at 23 degrees. Higher ethanol concentrations (100-600 mM), as well as 1-propanol and 1-butanol (10-200 mM), produced only inhibition of Ca2+ fluxes. Dixon plot analysis of the inhibitory phase revealed that ethanol inhibited Ca2+ uptake in an apparently competitive manner with respect to Ca2+ concentration, and the Ki obtained from these experiments was 1.01 M ethanol. The inhibition of Ca2+ fluxes by butanol was non-competitive, and the Ki was 68.6 mM. The local anesthetics dibucaine and tetracaine also inhibited Ca2+ fluxes with IC50 values of 1.8 mM for tetracaine and 0.46 mM for dibucaine. The possible physiologic consequences of this inhibition of Na+-Ca2+ countertransport is synaptic membranes by the alcohols and local anesthetics are discussed with regard to neuronal transmission and membrane conductance.

Alcohol effects on synaptic membrane calcium ion fluxes

The effects of ethanol on Na+-dependent CA2+ fluxes have been examined in resealed synaptic membrane vesicles assayed at 3 different temperatures. Sodium chloride-loaded vesicles were preincubated with various concentrations of ethanol for 120 sec prior to being diluted into a 45CaCl2-containing medium in the presence or absence of an outward-directed Na+ gradient. The effect of ethanol on Na+-dependent Ca2+ transport measured at 23 degrees C was biphasic. However, when the assay was conducted either at 16 degrees C or at 35 degrees C, all ethanol concentrations tested (10-300 mM) produced only inhibition of Ca2+ influx. The role of membrane fluidization in the ethanol-induced inhibition was explored by determining the effects of incorporating various fatty acids into the membranes. Membrane fluidizing agents such as cis-vaccenic acid stimulated Ca2+ influx whereas trans-vaccenic and saturated fatty acids had little effect. The fluidizing effect of incorporating cis-vaccenic acid into the membranes was confirmed with electron paramagnetic resonance (EPR) spectroscopy. The data obtained from these studies suggest that the inhibition of Ca2+ fluxes produced by alcohol and local anesthetics is not the result of a general increase in bulk phase synaptic membrane fluidity.

Ethanol effects on synaptic glutamate receptor function and on membrane lipid organization

The enhancement of L-glutamic acid binding activity of brain synaptic membranes by low concentrations of ethanol (less than 50 mM) and the decrease in binding at high concentrations (greater than 100 mM) was not due to a direct action by ethanol on the glutamate binding protein. Biphasic effects of ethanol on membrane protein complexes such as the glutamate binding sites might be the result of biphasic changes in membrane lipid organization. Low ethanol concentrations (0.1-4.0 mM) were shown to decrease fatty acid chain motion detected by the EPR probe 5-doxyl stearic acid, whereas high concentrations (greater than 400 mM) increased lipid motion in egg phosphatidylcholine liposomes. The function of the L-glutamate receptor-ion channel complex in the presence of ethanol was also determined by measuring the changes in thiocyanate (SCN-) influx brought about by L-glutamate or ethanol. A low concentration of ethanol (9.4 mM) diminished the L-glutamate-induced depolarization of synaptic membranes, while a high concentration (93.7 mM) increased the passive SCN-influx and produced a transient overshoot in glutamate-stimulated SCN-flux.

Electrophysiologic effects of acute ethanol exposure. II. Alterations in the calcium component of action potentials from sensory neurons in dissociated culture

Dissociated dorsal root ganglion neurons were exposed to 0.05-0.50 g% ethanol. The recording medium was altered in order to produce an action potential with an increased duration which was Ca2+-dependent. Ethanol was observed to decrease the duration of sensory neuron action potentials indicating a decreased inward Ca2+ current. The ethanol induced decrease in duration was reversible and dose-dependent. No alterations in resting membrane potential, spike amplitude, or maximum rate of rise were observed during ethanol exposure. An increased threshold was also observed with application of ethanol. These findings are discussed in regard to the possible effects of ethanol on Ca2+ movement at the presynaptic terminal.

Ethanol alters synaptic activity in cultured spinal cord neurons

The acute effects of ethyl alcohol on mammalian central neurons were investigated using electrophysiological techniques and an in vitro model system, cultured fetal mouse spinal cord neurons. Intracellular recordings were made from the cultured neurons to evaluate the effect of alcohol (10-100 mM) on membrane potential, membrane permeability, amplitude of the action potential, sensitivity of the neurons to putative neurotransmitters and the process of synaptic transmission. Alcohol was applied by superfusion; putative amino acid neurotransmitters were applied by micropressure ejection. The most dramatic effect of alcohol on the spinal cord neurons was a reduction in the spontaneous activity (excitatory and inhibitory synaptic potentials and action potentials) and the glutamate evoked synaptic activity. Alcohol doses as low as 20-30 mM, concentrations which reflect blood levels during intoxication, were effective. Membrane potential, membrane permeability, and amplitude of the action potential were relatively resistant to these low doses of alcohol; at the higher alcohol doses, no effect or only modest alterations of these characteristics were observed. The responses of the neurons to the putative excitatory neuro-transmitter glutamate, and inhibitory transmitters GABA and glycine were also relatively resistant to alcohol exposure. These data indicate that acute exposure to alcohol has a predominantly inhibitory action on the activity of the cultured mammalian CNS neurons, and that this inhibition is most likely due to an alteration in the process of synaptic transmission.

An ion exchange chromatographic method for the determination of synaptosomal calcium uptake

A simple, rapid method for determining depolarization-induced 45Ca influx into synaptosomes is described. Synaptosomes which had been depolarized in the presence of 45Ca were applied to a small column of Chelex-100 resin to separate free Ca2+ from that taken up by the tissue. Approximately 70% of the synaptosomal protein applied to the column was recovered in the initial eluate. The magnitude of 45Ca uptake was dependent on the amount of Ca2+ in the incubation medium and on the KCI concentration. Calcium influx reached a plateau after 90 sec of incubation at 24 degrees C. The Na+ channel activator veratridine also produced a substantial influx of 45Ca, and this effect was blocked by tetrodotoxin. Thus, this ion exchange procedure makes it possible to measure depolarization-induced Ca2+ influx in synaptosomes without subjecting them to high vacuum or centrifugation pressures or to EGTA-containing solutions.