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J M Littleton

Publications and source records attributed to J M Littleton.

At least 37 records · Page 2Linked to original sources
PubMed1995

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.

Alcohol Withdrawal Delirium↗
PubMed1994

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.

Alcoholism↗
PubMed1994

The possible role of voltage-operated calcium channels in the enhancement of excitatory amino acid toxicity following chronic ethanol exposure in vitro.

It is well established that ethanol withdrawal is associated with hyperexcitability of central neurons, and that the increased responsiveness demonstrated to excitatory amino acids (EAAs) may contribute to the physical signs of ethanol withdrawal and to neurodegeneration. Although the mechanisms of neuronal hyperexcitation are not fully understood, there is considerable evidence to suggest an increase in both NMDA receptors and voltage operated calcium channels (VOCCs) may play an important role. Cultures of bovine adrenal chromaffin cells (BACCs) and fetal rat neocortical neurons chronically treated with ethanol showed enhanced toxicity when challenged with various EAAs. Quantitative assessment of cell survival was determined by catecholamine release (CA), and fluorescein diacetate (FDA) staining in BACCs, and lactate dehydrogenase (LDH) release in cortical neurons. The dihydropyridine (DHP) calcium channel blocker, nicardipine, was found to significantly attenuate EAA-induced cytotoxicity in ethanol withdrawn cell cultures with all indices measured. These results suggest that increased Ca2+ influx through VOCCs and NMDA receptors may each contribute to ethanol-mediated neurodegeneration.

Animals↗
PubMed1991

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.

8-Hydroxy-2-(di-n-propylamino)tetralin↗
PubMed1991

Characteristics of catecholamine release from adrenal chromaffin cells cultured in medium containing ethanol--I. Spontaneous and K(+)-induced release.

Bovine adrenal chromaffin cells were dissociated and grown in primary culture for 9 days. Three days after plating, half the cultures were grown in a medium containing 200 mM ethanol and the other half in a control medium, for a further 6 days. The catecholamine content of the ethanol-treated cells was increased after 6 days of ethanol treatment, compared to control cells and there was a slight reduction in protein and DNA content. An enhanced spontaneous release of catecholamines was seen, which was Ca(2+)-dependent and was inhibited by cadmium but not by the organic dihydropyridine Ca2+ antagonist nitrendipine. The fraction of catecholamines released by K+ was also enhanced in ethanol-treated preparations, particularly at high K+ or Ca2+ concentrations. Release induced by K+ was sensitive to inhibition by both cadmium and organic dihydropyridine Ca2+ antagonists. The results show many similarities with changes observed in catecholaminergic transmission in rat brain during the development of ethanol physical dependence.

Adrenal Glands↗
PubMed1991

Characteristics of catecholamine release from adrenal chromaffin cells cultured in medium containing ethanol--II. Carbachol and veratrine-induced release.

Dissociated bovine adrenal chromaffin cells were grown in culture either in control medium or in medium containing ethanol (200 mM) and the release of catecholamines induced by veratrine and carbachol was then studied. Cells grown in ethanol showed greater spontaneous release of catecholamines, but both carbachol and veratrine evoked release of a smaller maximum fraction of stored catecholamines than that from control cells. Spontaneous catecholamine release as well as that induced by veratrine were sensitive to inhibition by tetrodotoxin. Catecholamine release induced by veratrine could be prevented almost completely by the Ca2+ channel blocker cadmium, but not to any great extent by the organic dihydropyridine Ca2+ antagonist nitrendipine. Carbachol-induced catecholamine release was similarly resistant to inhibition by nitrendipine, but was inhibited by cadmium. The results suggest that cell cultures grown in ethanol-containing medium show many alterations in the characteristics of catecholamine release. Alterations in receptor- and voltage-operated ion channels in the membrane of ethanol-treated cells may underlie these changes.

Adrenal Glands↗
PubMed1990

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.

3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethy↗
PubMed1990

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.

3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethy↗
PubMed1990

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.

Alcoholism↗
PubMed1990

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.

3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethy↗
PubMed1989

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.

3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethy↗
PubMed1989

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.

3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethy↗
PubMed1987

Altered characteristics of catecholamine release from rat cortical slices and bovine adrenal chromaffin cells in culture after chronic exposure to ethanol and the effect of the dihydropyridine drugs on these systems.

The depolarisation-induced release of dopamine from control rat striatal slices is inhibited by ethanol in vitro. The same parameter is enhanced in preparations from ethanol-treated rats. Under conditions of superfusion with normal physiological solutions we were unable to see similar results in noradrenaline (NA) release from cortical slices. Since we believed altered intracellular Ca2+ metabolism might underlie changes induced by ethanol in dopamine neurones, we superfused cortical slices with low K+ solutions which raise intracellular Ca2+. Under these conditions, ethanol in vitro inhibited depolarisation-induced NA release in control preparations. In preparations from ethanol tolerant animals, ethanol enhanced depolarisation-induced release. In cultures of adrenal chromaffin cells, similar alterations in coupling between Ca2+ and catecholamine release can be seen. Some of these changes may be a consequence of increased functional activity of dihydropyridine-sensitive Ca2+ channels.

3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethy↗
PubMed1987

The potentiation of platelet aggregation by mechanical stimuli is inhibited by ethanol in vitro.

Previous work on inhibition by ethanol of human platelet aggregation suggested that this was a consequence of inhibition of the activation of platelet membrane phospholipase A2 (PLA2) which precedes aggregation. In these experiments, the effect of ethanol in vitro on human gel-filtered platelets activated with A23187 or with collagen was studied at different levels of mechanical stimulus (stirring rate) in the platelet aggregometer. The dose response curve obtained by varying the concentration of aggregating agent at constant stirring rate was shifted to the right in the parallel fashion by ethanol. A23187-induced aggregation was inhibited to a greater extent than that due to collagen. When a stirring rate: response curve for platelet aggregation was obtained at a constant concentration of either chemical aggregating agent ethanol shifted the curve to the right in a non-parallel fashion, its effect being greater at greater levels of mechanical stimulus. The effects of acetylsalicylic acid, known to act at a step subsequent to PLA2 activation, were completely unlike those of ethanol. The results are consistent with an inhibitory effect of ethanol on activation of phospholipase A2 by mechanical stimuli which deform platelet membranes.

Aspirin↗