Ethanol-induced conformational changes in rat brain microsomal membranes

Time-course of extracellular nicotine and cotinine levels in rat brain following administration of nicotine: effects of route and ethanol coadministration

RATIONALE

Nicotine and ethanol are commonly coabused drugs, and nicotine-laced ethanol products are growing in popularity. However, little is known about time-course changes in extracellular nicotine and cotinine levels in rat models of ethanol and nicotine coabuse.

OBJECTIVES

The objective of the present study was to determine the time-course changes in brain levels of nicotine and cotinine following subcutaneous (SC) and intragastric (IG) nicotine administration in alcohol-preferring (P) and Wistar rats.

METHODS

In vivo microdialysis was used to collect dialysate samples from the nucleus accumbens shell (NACsh) for nicotine and cotinine determinations, following SC administration of (-)-nicotine (0.18, 0.35, and 0.70 mg/kg) in female P and Wistar rats or IG administration of (-)-nicotine (0.35 and 0.70 mg/kg) in 15 % (v/v) ethanol or water in female P rats.

RESULTS

SC nicotine produced nicotine and cotinine dialysate levels as high as 51 and 14 ng/ml, respectively. IG administration of 15 % EtOH + 0.70 mg/kg nicotine in P rats resulted in maximal nicotine and cotinine dialysate levels of 19 and 14 ng/ml, respectively, whereas administration of 0.70 mg/kg nicotine in water resulted in maximal nicotine and cotinine levels of 21 and 25 ng/ml, respectively. Nicotine and cotinine levels were detectable within the first 15 and 45 min, respectively, after IG administration.

CONCLUSIONS

Overall, the results of this study suggest that nicotine is rapidly adsorbed and produces relevant extracellular brain concentrations of nicotine and its pharmacologically active metabolite, cotinine. The persisting high brain concentrations of cotinine may contribute to nicotine addiction.

Cholesterol exchange and lateral cholesterol pools in synaptosomal membranes of pair-fed control and chronic ethanol-treated mice

Most studies on effects of ethanol on membrane cholesterol have reported on changes in the total or bulk amount of cholesterol. Membrane cholesterol, however, can be described in terms of its kinetics and domains. The kinetics and size of lateral cholesterol exchangeable and nonexchangeable pools were examined in synaptosomes of pair-fed controls and chronic ethanol-treated mice. Effects of sphingomyelin, an exofacial leaflet phospholipid, that has been shown to affect cholesterol pools, were also examined. Radiolabeled small unilamellar vesicles were used to exchange cholesterol with synaptosomes. The total amounts of membrane cholesterol, phospholipid phosphorus, and the ratio of cholesterol to phospholipid did not differ between the pair-fed control and ethanol groups. In control mice, the rate constant (hr-1) and the t1/2 (hr) of cholesterol exchange were 0.065 +/- 0.001 and 10.7 +/- 0.25 (hr), respectively. The rate constant was significantly slower (0.053 +/- 0.001, p < 0.05) and the t1/2 significantly longer (13.33 +/- 0.58, p < 0.05) in synaptosomes of the ethanol group compared with the control group. The size of the exchangeable pool of cholesterol did not differ significantly between the two groups. Sphingomyelinase-induced hydrolysis of sphingomyelin significantly slowed cholesterol exchange with the largest effect in synaptosomes of the control group as compared with the ethanol group (p < 0.05). Hydrolysis of sphingomyelin had significantly (p < 0.05) less of an effect on cholesterol exchange in synaptosomes of the ethanol group. Membrane cholesterol can be described in terms of total content, transbilayer distribution, kinetics, and size of lateral pools.(ABSTRACT TRUNCATED AT 250 WORDS)

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+.

Acute alcohol decreases gangliosides in mouse brain

We have reported that single doses of alcohol diminish total sialic acid in rat brain. Recent results indicate that this effect seems to be largely accounted for by alcohol-induced reduction in gangliosides. In these experiments, five replicate groups of mice were injected IP with a single dose of 20% alcohol and saline as control. At 1 hour postinjection, alcohol decreased total brain gangliosides (p less than 0.03) at 1 and 2 g/kg, but not at 3, 4, and 6 g/kg. Free whole-brain sialic acid was increased by 2 g/kg alcohol, which is consistent with the observed decrement in gangliosides at this dose. However, activity of sialidase on the endogenous substrates was not greatly affected by 2 g/kg of alcohol, indicating that ganglioside decrement is probably not attributable to activation of the catabolic enzyme. These results confirm and extend our earlier reports that incriminated gangliosides in the acute action of alcohol. The data also raise the possibility that the effect is due to the "excitatory," rather than the depressive actions of alcohol. Moreover, the action may involve an increased hydrolysis of membrane gangliosides by sialidase.

Effects of chronic alcohol consumption in weanling rats on brain gangliosides

Chronic ingestion of ethyl alcohol in pre-weanling rats can decrease whole-brain levels of sialic acid (SA), an acidic sugar that serves as terminal groups on glycolipids (gangliosides) and glycoproteins. Because SA occurs in both classes of membrane-bound chemicals, the alcohol effect could be on either or both parent compounds. We examined the effects of alcohol on gangliosides by measuring levels of six specific ganglioside species in post-weanling rats that were fed liquid alcohol diet for 35 days. We found no major effect on any of the ganglioside species in the alcohol-fed rats compared with their pair-fed littermates. These data suggest that alcohol may have acute effects on membrane gangliosides, but during chronic exposure in more mature animals, the membrane may adapt and maintain near-normal ganglioside composition. Thus, gangliosides may reflect mechanisms of membrane tolerance; they could also be involved in mediating metabolic dependencies in neuronal membranes, a possibility that needs testing.

Biochemical basis of alcoholism: statements and hypotheses of present research

Experimental results and theoretical considerations on the biology of alcoholism are devoted to the following topics: genetically determined differences in metabolic tolerance; participation of the alternative alcohol metabolizing systems in chronic alcohol intake; genetically determined differences in functional tolerance of the CNS to the hypnotic effect of alcohol; cross tolerance between alcohol and centrally active drugs; dissociation of tolerance and cross tolerance from physical dependence; permanent effect of uncontrolled drinking behavior induced by alkaloid metabolites in the CNS; genetically determined alterations in the function of opiate receptors; and genetic predisposition to addiction due to innate endorphin deficiency. For the purpose of introducing the most important research teams and their main work, statements from selected publications of individual groups have been classified as to subject matter and summarized. Although the number for summary-quotations had to be restricted, the criterion for selection was the relevance to the etiology of alcoholism rather than consequences of alcohol drinking.

Effects of ATP on calcium binding to synaptic plasma membrane

The release of labeled norepinephrine from preloaded synaptosomes requires the presence of potassium and calcium. ATP-dependent binding of calcium to synaptic plasma membranes (SPM) may provide a means of maintaining the cation in a readily available pool for the triggering of transmitter release. A high Ca-binding capacity was demonstrated in SPM. The Km for calcium is 5.5 X 10(-5) M. The dependence of the system on the gamma phosphate of ATP was demonstrated by an increase in Ca-binding with increasing ATP concentration and by competitive inhibition of binding by ADP and AMP. Magnesium is also required for ATP-dependent Ca-binding. The optimum pH for the Ca binding was 7.0. Pretreatment of SPM with phospholipase A2 lowered the binding capacity. Sulfhydryl groups are also critical for ATP-dependent Ca binding to occur. A model for ATP-dependent Ca-binding was proposed.

Effects of ethanol on Arrhenius parameters and activity of mouse striatal adenylate cyclase

Arrhenius plots of basal and dopamine (DA)-stimulated adenylate cyclase activities exhibited discontinuities at 20 degrees, while the plot of fluoride-stimulated adenylate cyclase activity was linear over the studied temperature range. None of the Arrhenius parameters were altered by in vitro addition of ethanol (75 or 750 mM) to enzyme assay mixtures, and Arrhenius parameters were found to be unchanged when enzyme obtained from animals rendered tolerant to, and physically dependent on, ethanol was assayed. The differences between the response to ethanol of adenylate cyclase and the response of other membrane-bound enzymes [e.g. (Na+-K+)ATPase], as measured by Arrhenius plots, may indicate different sites of action of ethanol. When the specific activity of adenylate cyclase was examined, ethanol was found to stimulate activity at all temperatures tested. The dose-response curve for ethanol activation of basal adenylate cyclase activity was shifted to the right for enzyme obtained from mice chronically treated with ethanol. Analysis of the data indicated that activation of adenylate cyclase by ethanol (as well as by DA) was an entropy-driven process. Since ethanol treatment did not affect the Arrhenius parameters, which appear to be associated with membrane lipids, it is suggested that enzyme activation by ethanol results from direct effects on the enzyme or regulatory protein. Resistance to this effect occurs through changes in protein conformation following chronic ethanol treatment.

Neurotoxicity of industrial chemicals and contaminants: aspects of biochemical mechanisms and effects

Nervous system toxicity by industrial chemicals and contaminants cannot be explained by a single mechanism because of the complex functional capacity of the brain and spinal cord. The nervous system is dependent on the adequate supply of oxygen, and therefore, its lack in the ambient air causes rapid dysfunction. Similar effects to hypoxia are caused by agents which reduce oxygen availability at the cellular level by histotoxic mechanisms, e.g., through the inhibition of mitochondrial respiration. Hypoxic effects are rapidly produced, and in cases where a significant number of cells are fatally damaged permanent disability may remain. Acutely harmful effects are also brought about by organic solvents. The typical mode of exposure is that of vapour inhalation. The lipid-soluble molecules pass the blood-brain barrier rapidly and depress the nerve cell membrane functions. This hinders the formation of action potentials. Neuronal cells acquire tolerance towards the membrane-depressant effects in repeated or prolonged exposure so that similar doses do not produce equivalent effects. The development of the tolerance can be regarded as one of the long-term effects of lipophilic chemicals. They may also produce metabolic adaptation so that their biotransformation is enhanced. This may increase the risk of producing more toxic intermediates. The toxic effects thus created can be cumulative since neurons do not multiply by cell division in the postnatal life. The neurotoxicity of metals is more clearly associated with the accumulation of the dose. Adult brain possesses a blood-brain barrier to many water-soluble compounds such that a threshold concentration must be overcome before appreciable toxic effects are seen. Children are in this respect more vulnerable because of their immature barrier function.

Receptor and membrane function in the alcohol tolerant/dependent animal

Neurochemical changes which are associated with the development or expression of tolerance to or physical dependence on ethanol may be expected to display a time course of appearance and disappearance which correlates positively with the time course for tolerance or dependence. Previous studies of striatal dopaminergic receptor function indicated that ethanol-withdrawn mice displayed decreased physiological and biochemical responses to dopamine (DA) agonists, which could be best explained by postulating an inefficient coupling between DA receptors and various receptor-mediated processes, possibly as a result of ethanol-induced changes in neuronal membrane properties. The membrane-bound enzyme, (Na+-K+)ATPase, obtained from ethanol-withdrawn animals, displays an altered transition temperature and resistance to the effects of ethanol on enzyme activity. These changes also suggest compensatory alterations in neuronal membrane properties. All of these alterations show a time course of disappearance which corresponds to that for the disappearance of tolerance to the hypothermic and sedative effects of ethanol. Ethanol-withdrawn mice also display increased numbers of hippocampal muscarinic cholinergic receptors; however, the time course for the increase in receptor number appears to correlate with that of withdrawal symptomatology. Thus, compensatory changes in neuronal membrane properties in response to ethanol may be expressed via diverse functional changes.

Neurochemical and behavioural effects of extended exposure to isopropanol vapour with simultaneous ethanol intake

Exposure of male Wistar rats to 12.3 mumol/l (300 ppm) isopropanol vapour for 5-21 weeks, 5 days a week for 6 h daily with a simultaneous ethanol administration in drinking water (5% v/v) caused a significant increase in isopropanol removal as assessed by blood isopropanol and acetone determinations. Ethanol treatment caused a marked synergistic effect during early exposure. Neurochemical studies revealed decreased superoxide dismutase and azoreductase activities at the end of the exposure whereas increased protein degradation was found in glial cells isolated from ethanol-fed rats throughout the experiment. Analyses of spinal cord axon lipid composition showed increases in cholesterol content in relation to lipid phosphorus in animals exposed to isopropanol or to the isopropanol and ethanol combination. Behavioural tests indicated minor effects on emotional reactivity from the 10th week onwards with isopropanol exposure whereas caffeine-stimulated activity was augmented only in rats ingesting ethanol. Co-exposure to isopropanol vapour abolished the increased excitability. The data indicate that marked metabolic and functional adaptation towards the small-molecular-weight alcohols takes place at moderate dose levels.

Histochemical and atomic absorption demonstration of trace metal mobilization in the central nervous system and liver of the rat

Histochemical and atomic absorption spectrophotometric analysis of trace metal mobilization caused by the action of ethanol in the central nervous system (CNS) and liver of the rat is described. Histochemically it has been shown that in all neurons examined (motoneurons, pyramidal and Purkinje cells) the trace metals (mainly Zn2+ and Cu2+) are mobilized. Most of the stained materials disappear from the perikaryon of the Purkinje cells, while in both the motoneurons and the pyramidal cells the trace metals are displaced from the perikaryon into the axon and axon hillock. At the same time, some of the glia cells display a high metal content. Quantitative determination of the Zn2+ and Cu2+ by means of atomic absorption spectrophotometry reveals that after 2 hours ethanol treatment both the Zn2+ and the Cu2+ levels are decreased in the archicerebellar cortex, while after 4 hours the Zn2+ levels are increased in the cerebrum and the spinal cord. The present observations on the histochemical localization and the contents of zinc and copper in different parts of the CNS and liver reveal the important role of the effect of ethanol on the trace metal mobilization.