From A to B to serendipity: the story of a monoamine oxidase knockout.
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Aggression↗
Biomedical subjects
B Tabakoff
Publications and source records attributed to B Tabakoff.
Platelet adenylyl cyclase activity in alcoholics and subtypes of alcoholics. WHO/ISBRA Study Clinical Centers.
Adenylyl cyclase (AC) activity was measured in membrane preparations of platelets from control and alcoholic subjects. The sample consisted of 51 alcoholics who were categorized as type I or type II using the criteria of Gilligan et al. (Genet. Epidemiol. 4:395-414, 1987) and 54 normal controls. Alcoholic males exhibited significantly lower values than controls in basal and fluoride-stimulated platelet AC activity. When male alcoholics were segregated into type I and type II categories, the platelet AC activity did not differ between subtypes, and both subtypes had AC activity that was below control values. Western blot analysis of the quantity of Gs alpha and Gi alpha proteins in a subset of male controls and alcoholic subjects demonstrated no significant relationship between quantity of G proteins and AC activity. The results confirm lower platelet AC activity in male alcoholics, compared with controls. Given the lack of quantitative relations between Gs alpha and Gi alpha proteins and AC activity, the results support the contention that individual differences in platelet AC activity in the alcoholic subjects may reflect quantitative or qualitative differences in the AC catalytic units.
Adenylyl Cyclases↗
The WHO/ISBRA study on state and trait markers in alcoholism: progress report.
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Adolescent↗
Mechanism of ethanol inhibition of NMDA receptor function in primary cultures of cerebral cortical cells.
Ethanol is a potent inhibitor of the function of the N-methyl-D-aspartate (NMDA) subtype of glutamate receptor in various neuronal preparations. In primary cultures of cerebellar granule cells, ethanol was suggested to interact with the glycine co-agonist site of the receptor by a mechanism involving protein kinase C. In the present study, the interaction of ethanol with various sites on the NMDA receptor was examined in primary cultures of cerebral cortical cells from embryonic rats. NMDA receptor function was determined by measuring increases in intracellular Ca2+ with fura-2 fluorescence. Ethanol inhibited the function of the NMDA receptor in cerebral cortical cells, but in contrast to the results in cerebellar granule cells, phorbol ester treatment did not inhibit the NMDA response, and ethanol did not alter the effect of glycine on NMDA receptor function. Ethanol also did not affect inhibition of the NMDA response by Mg2+ or dizocilpine. The results support the hypothesis that the mechanism of ethanol inhibition of NMDA receptor function can vary in neurons from different brain regions.
Animals↗
mu-Opioid receptors inhibit dopamine-stimulated activity of type V adenylyl cyclase but enhance dopamine-stimulated activity of type VII adenylyl cyclase.
The introduction of D1A dopamine receptors and mu-opioid receptors into HEK 293 cells that were also transiently transfected with adenylyl cyclase cDNA imparted to dopamine and to mu-opioid receptor agonists the ability to modulate the activity of the expressed adenylyl cyclase. Dopamine added to cells expressing D1A receptors and type V adenylyl cyclase significantly stimulated type V enzyme activity. The concomitant addition of morphine produced a dose-dependent inhibition of dopamine-stimulated type V adenylyl cyclase activity. On the other hand, if the HEK 293 cells were transfected with cDNA for type VII adenylyl cyclase instead of the type V isoform, morphine stimulated this adenylyl cyclase activity beyond the stimulation produced by dopamine. Both the inhibitory and stimulatory effects of morphine were blocked by naloxone or pretreatment of the transfected HEK 293 cells with pertussis toxin. When expressed in the HEK 293 cells, the alpha subunit of transducin, which is considered to be the putative scavenger of the beta gamma subunits of G proteins, suppressed the stimulatory effect of morphine on type VII adenylyl cyclase. We also expressed the adenylyl cyclases in cells that were transfected with D1A receptor and G beta 1 and G gamma 2 cDNAs. Dopamine was more efficacious in stimulating type VII adenylyl cyclase activity in cells concomitantly transfected with the beta gamma subunit cDNAs than in cells not transfected with these G protein subunits. Transfection with beta gamma subunit cDNAs did not affect dopamine stimulation of type V adenylyl cyclase activity, and morphine-induced inhibition of type V adenylyl cyclase activity was still evident in cells cotransfected with the alpha subunit of transducin. These data support the contention that the effects on type VII adenylyl cyclase activity mediated through the G1/G(o) proteins may depend on the actions of the beta gamma subunits. The same is not the case for type V adenylyl cyclase. Our data demonstrate that both qualitative and quantitative responses to mu-opioid receptor stimulation depend on the isoform of adenylyl cyclase expressed in neurons or other cells of the body.
Adenylate Cyclase Toxin↗
Gangliosides reduce the development of ethanol dependence without affecting ethanol tolerance.
Mice given an ethanol-containing liquid diet, as their sole source of nutrients and fluid, rapidly developed functional tolerance to and physical dependence on ethanol. The presence of physical dependence was demonstrated by measured signs of central nervous system hyperexcitability upon withdrawal of ethanol. The withdrawal hyperexcitability, which included tremors, handling-induced seizures and spontaneous clonic/tonic seizures, was more pronounced when mice consumed the ethanol-containing diet for 7 days, compared with 5 days. Daily treatment of the animals with either a ganglioside mixture (extracted bovine brain gangliosides, 250 or 500 mg/kg i.p.) or ganglioside GM1 (100 mg/kg i.p.) for the terminal two-thirds of the ethanol administration period resulted in a significant reduction in the ethanol withdrawal signs. On the other hand, tolerance to the hypnotic action of ethanol, tested 30 hr after withdrawal of ethanol, was unaffected by ganglioside treatment. Ganglioside GM1 given i.c.v. at a daily dose of 10 micrograms during the ethanol ingestion period was as effective as 100 mg/kg GM1 given i.p. in reducing signs of ethanol withdrawal. The daily administration of gangliosides during the feeding of the ethanol diet did not alter the animals' ethanol consumption, intoxication or blood ethanol levels at the time of ethanol withdrawal. A single dose of GM1 given either i.p. or i.c.v. 16 hr before withdrawal produced no effect on the measured ethanol withdrawal signs. Our prior work and the work of others has demonstrated a relationship between up-regulation of N-methyl-D-aspartate receptor numbers in brain and the manifestation of ethanol withdrawal signs. Daily administration of GM1, during the last 5 days of a 7-day period of ethanol ingestion, prevented the up-regulation of N-methyl-D-aspartate receptors in the hippocampus and reduced the ethanol withdrawal signs. Our data demonstrate that the daily administration of gangliosides during the period of ethanol consumption may prevent the development of ethanol physical dependence, while leaving ethanol tolerance intact.
Animals↗
Monoamine oxidases and alcoholism. I. Studies in unrelated alcoholics and normal controls.
Low platelet MAO activity has been associated with alcoholism. In order to evaluate the role of MAO genes in susceptibility to alcoholism, we have taken a biochemical and molecular genetic approach. The sample consisted of 133 alcoholic probands who were classified by subtypes of alcoholism and 92 normal controls. For those subjects typed for platelet MAO activity, alcoholics (N = 74) were found not to differ from the non-alcoholics controls (N = 34). Neither was there a significant difference between type I and type II alcoholics or between either subtype and normal controls. However, we do find significant differences between male and female alcoholics, but not between male and female controls. The allele frequency distribution for the MAO-A and MAO-B dinucleotide repeats is different between the alcoholic sample (N = 133) and the normal control sample (N = 92). In a two-way analysis of variance of MAO-B activity as a function of the allelic variation of each marker locus and diagnosis, there is no evidence for mean differences in activity levels for the different alleles. Our findings do not rule out a role for the MAO-B gene in controlling the enzyme activity because the dinucleotide repeats are located in introns.
Adult↗
Platelet monoamine oxidase activity levels in subgroups of alcoholics: diagnostic, temporal, and clinical correlates.
Platelet monoamine oxidase (MAO) activity levels were measured in 47 male inpatient alcoholics to determine whether this biological marker might be useful in differentiating subtypes of alcoholics. Of the subgrouping methods tested, only type 2 alcoholics defined by the criteria of Gilligan et al had significantly lower platelet MAO activity than type 1 alcoholics at intake, but this finding was not stable over time in a subset of subjects. Neither separating male veteran alcoholics into either of two other variations of the type 1/type 2 subtypes, nor classifying the sample into primary alcoholics versus primary ASPD with secondary alcoholism categories, yielded significant differences between subgroups. Generally, enzyme activity levels (Vmax) were higher about 10 days after stopping drinking compared to platelet MAO values determined in thrombocytes obtained after approximately 4 weeks abstinence; these levels remained relatively stable 3 months later in a cohort of subjects. Tobacco smoking was significantly negatively correlated to platelet MAO activity levels.
Adolescent↗
The characterization of a novel human adenylyl cyclase which is present in brain and other tissues.
We characterized a human cDNA clone which encodes a novel adenylyl cyclase. Data from Southern and Northern blot analysis, and analysis of sequence similarity with a recently cloned mouse adenylyl cyclase (10), indicated that the human adenylyl cyclase was a species variant of type VII adenylyl cyclase. The sequence of the novel human adenylyl cyclase indicated it was a member of the type II adenylyl cyclase family, and we compared the regulatory characteristics of the novel human enzyme with those of type II adenylyl cyclase. The human type VII and rat type II adenylyl cyclases, expressed in human embryonic kidney 293 cells, were activated by prostaglandin E1 (PGE1), but only type VII was activated by isoproterenol. The stimulation of type VII adenylyl cyclase by PGE1 and isoproterenol was attenuated by pretreatment of the cells with staurosporine. Phorbol 12,13-dibutyrate synergistically enhanced the stimulation of both type VII and type II enzyme activity by PGE1 and by the constitutively active Gs mutant Gs (Q227L). The human type VII adenylyl cyclase activity was unresponsive to capacitatively induced changes in intracellular Ca2+. The functional characteristics of human type VII adenylyl cyclase resemble those of the rat type II enzyme, but the enzymes may respond differently to in vivo phosphorylation conditions. While the mRNA for adenylyl cyclase type II was found in several brain areas, the message for type VII adenylyl cyclase was localized primarily to the cerebellar granule cell layer.
Adenylyl Cyclases↗
Localization of the gene for a novel human adenylyl cyclase (ADCY7) to chromosome 16.
A novel form of human adenylyl cyclase (ADCY7) has been discovered in the human erythroleukemia cell line (HEL). This cell line has been widely used as a model for studies of the characteristics of human platelets. Data from HEL cells suggests that ADCY7 may be the major AC form in human platelets. In the current study polymerase chain reaction (PCR) techniques coupled with use of human/rodent somatic hybrid panels and a yeast artificial chromosome (YAC) library were used to determine the chromosomal localization of the gene (adcy7) for ADCY7 enzyme. A 251-bp product from the 3' untranslated region of human adcy7 was amplified for PCR mapping and the results localize the adcy7 gene to region 16q12-16q13 of the human genome. The AC enzyme family is characterized by the presence of 12 membrane-spanning domains in its sequences, and this chromosomal region is known to contain other genes coding for proteins characterized by 12 membrane-spanning domains.
Adenylyl Cyclases↗
Selective effects of ethanol on the generation of cAMP by particular members of the adenylyl cyclase family.
A selective action of ethanol on major signal transduction proteins, such as adenylyl cyclase, has been considered to be important for certain actions of ethanol, and alcoholics have been demonstrated to differ from controls in measures of platelet adenylyl cyclase activity. Recent advances in identification and characterization of isoforms of adenylyl cyclase have demonstrated that there exists at least eight different forms of this enzyme. To examine whether the effect of ethanol on generation of cAMP is modified by the presence of particular isoforms of adenylyl cyclase within a cell, we transiently expressed each of six adenylyl cyclases in human embryonic kidney (HEK293) cells and measured cAMP accumulation in whole cells in the presence and absence of ethanol. The treatment of cells expressing the various adenylyl cyclases with ethanol alone did not enhance cAMP generation. In the presence of prostaglandin E1, cAMP generation by type I and type III adenylyl cyclases was insensitive to ethanol. cAMP accumulation generated by the other adenylyl cyclases was, however, increased by incubation of cells with ethanol in the presence of stimulatory agonists (e.g., prostaglandin E1). Stimulation by ethanol of cAMP generation by type VII adenylyl cyclase was 2- to 3-fold greater than that seen with the other tested adenylyl cyclases. The noted stimulation of cAMP generation by ethanol was dose-dependent and required concurrent activation of adenylyl cyclase through the stimulatory G protein. The effects of ethanol were reversible and mimicked by butanol but not by chloroform.
Adenylyl Cyclases↗
Ethanol's action on the GABAA receptor: is there a requirement for parsimony?
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Alcoholism↗
Quantitative changes in G proteins do not mediate ethanol-induced downregulation of adenylyl cyclase in mouse cerebral cortex.
Our prior work, and the work of others, demonstrated that chronic administration of ethanol to cells in culture or to mice resulted in decreased responsiveness of adenylyl cyclase (EC4.6.1.1) to a number of stimulatory agents. In this study, we substantiated the ethanol-induced changes in cerebral cortical adenylyl cyclase activity in alcohol-tolerant and alcohol-dependent mice, and we examined whether chronic ethanol treatment of mice altered the quantity of heterotrimeric guanine nucleotide-binding regulatory proteins (G proteins) in cerebral cortex and other mouse brain areas. Amounts of various G protein subunits--including the alpha subunits of GS (GS alpha), Gi alpha 1-3, G(o) alpha, and beta subunits--were examined by Western blot analysis. There was no change in quantity of these G protein subunits in cerebral cortex, hippocampus, or cerebellum of ethanol-fed mice, compared with controls. In striatum of ethanol-fed mice, small increases in Gi alpha 1 and G(o) alpha were observed, but these changes could not explain the ethanol-induced desensitization of adenylyl cyclase in brain areas such as the cerebral cortex. Forskolin activation of cerebral cortical adenylyl cyclase activity showed two components of activation, with high and low "affinity" for forskolin. Ethanol treatment caused a decrease in the efficacy of forskolin for both components, whereas the EC50 of forskolin for each component did not change. Adenylyl cyclase activity measured in the presence of manganese was also diminished in cortical membranes of ethanol-treated mice.(ABSTRACT TRUNCATED AT 250 WORDS)
Adenylyl Cyclases↗
Attenuation of glutamate-induced neurotoxicity in chronically ethanol-exposed cerebellar granule cells by NMDA receptor antagonists and ganglioside GM1.
Ethanol, acutely, is a potent inhibitor of the function of the N-methyl-D-aspartate (NMDA) subtype of glutamate receptor. After chronic exposure of animals to ethanol, however, the NMDA receptor in brain is upregulated. This upregulation is associated with the occurrence of ethanol withdrawal seizures. When cultured cerebellar granule neurons are exposed chronically to ethanol, the resulting upregulation of NMDA receptor function renders the cells more susceptible to glutamate-induced neurotoxicity. The present studies show that chronic ethanol exposure produces an increase in NMDA receptor number in the cells, measured by ligand binding to intact cells. Glutamate-induced excitotoxicity, both in control and ethanol-exposed cells, is blocked by the same NMDA receptor antagonists previously shown to block ethanol withdrawal seizures in animals. In addition, glutamate neurotoxicity is blocked by acute (2-hr) pretreatment of cells with ganglioside GM1 or by chronic (3 days) treatment with the ganglioside. Acute ganglioside treatment does not interfere with the initial rise in intracellular calcium caused by glutamate, whereas this response is downregulated after chronic ganglioside treatment. These results suggest that therapeutic agents can be developed to block both ethanol withdrawal signs and the neuronal damage that accompanies ethanol withdrawal. Furthermore, chronic ganglioside treatment during ethanol exposure has the potential to prevent changes in the NMDA receptor that lead to withdrawal seizures and enhanced susceptibility to excitotoxicity.
Alcohol Withdrawal Delirium↗
Platelet MAO activity in type I and type II alcoholism.
Lowered activity of the enzyme MAOB in the platelets and other tissues of alcoholics than of nonalcoholics is the most replicated biological finding in genetic research in alcoholism. Data presented here and elsewhere also indicate that the relationship between MAOB activity and alcoholism extends to the clinical subtypes referred to as Type I and Type II alcoholism. A detailed examination of the relationship between in vitro platelet MAOB activity levels, alcoholic subtype, and general mental health status among the relatives of the probands suggests that low MAOB activity is a marker of increased risk overall and that the families of Type II alcoholics have a higher genetic risk loading than do the families of Type I alcoholics. This increased genetic loading is probably due to the classification of Type II alcoholics on the basis of features related to severity of illness and additional psychiatric features such as personality disorders. Although the families of alcoholics tend to have higher levels of psychiatric illness compared to the general population, the overall risk is compounded in the families of Type II alcoholics, and these differences in underlying risk are reflected in the observed differences in MAOB activities. Thus, MAOB is not a biological/genetic marker of alcoholism sensu stricto but is rather a biological/genetic marker of an underlying pathophysiologic process leading to alcoholism and other psychiatric illness. The task now before us is to understand this process and how the activity of MAOB is involved.
Alcoholism↗
The role of the NMDA receptor in ethanol withdrawal.
The function of the N-methyl-D-aspartate (NMDA) subtype of glutamate receptor is very sensitive to acute inhibition by ethanol. Because of the role of this receptor in processes such as synaptic plasticity and neuronal development, it may contribute to the acute cognitive deficits caused by ethanol, or to the deleterious effects of ethanol during gestation. Excessive stimulation of the NMDA receptor is believed to be involved in the generation of epileptiform seizure activity as well as in excitotoxic cell death. Our studies have demonstrated that there is an adaptive "up-regulation" of NMDA receptor function in brains of chronically ethanol-treated animals and in cultured cells that have been exposed chronically to ethanol. This up-regulation appears to contribute to ethanol withdrawal seizure activity, since withdrawal seizures can be attenuated by specific NMDA receptor antagonists, and the time course of the change in receptor number parallels the time course of withdrawal seizures. In addition, cells exposed chronically to ethanol are significantly more susceptible to glutamate-induced cell death, which is mediated by the NMDA receptor, indicating a key role of the NMDA receptor in the well-characterized neuronal damage that is observed after chronic ethanol exposure and withdrawal in animals and humans. Understanding the basis for withdrawal seizures and withdrawal-induced neurotoxicity provides for the development of specific and selective therapeutic agents to ameliorate these consequences of chronic ethanol exposure and withdrawal.
Animals↗
The NMDA receptor antagonist dizocilpine differentially affects environment-dependent and environment-independent ethanol tolerance.
Antagonists of the N-methyl-D-aspartate subtype of glutamate receptor have been reported to block the development of tolerance to various effects of ethanol and opiates, using paradigms in which tolerance is believed to be governed by learning. There is considerable evidence to implicate the N-methyl-D-aspartate receptor in learning processes, and therefore the ability of the antagonists to block tolerance has been attributed to their effects on learning. To evaluate this hypothesis, we compared, in C57BL/6 mice, the effect of the uncompetitive N-methyl-D-aspartate receptor antagonist, dizocilpine, on environment-dependent (associative) tolerance to ethanol, which is governed by learning, and on environment-independent (nonassociative) ethanol tolerance, in which learning plays a minimal role. Environment-dependent tolerance was induced by repeated ethanol injections, and dizocilpine blocked the development of this type of tolerance to the hypothermic and incoordinating effects of ethanol. In contrast, when environment-independent ethanol tolerance was induced by feeding the mice an ethanol-containing liquid diet, dizocilpine treatment had no effect on the development of tolerance to the hypothermic, incoordinating or hypnotic effects of ethanol. The results support the hypothesis that the effect of N-methyl-D-aspartate receptor antagonists on ethanol tolerance reflects the more general role of this receptor in processes involving learning and memory.
Animals↗
Protein kinase C activation attenuates N-methyl-D-aspartate-induced increases in intracellular calcium in cerebellar granule cells.
Activation of the N-methyl-D-aspartate (NMDA) subtype of glutamate receptor increases levels of intracellular calcium and can lead to stimulation of protein kinase C activity. Several reports have demonstrated that stimulation of protein kinase C can, in turn, increase electrophysiological responses to NMDA in certain cells or in oocytes expressing certain NMDA receptor subunits. In the present study, the effects of protein kinase C activation on NMDA receptor-mediated increases in intracellular Ca2+ level were investigated in primary cultures of rat cerebellar granule cells using fura-2 fluorescence spectroscopy. Pretreatment of the cells with the protein kinase C activator phorbol 12-myristate 13-acetate (PMA), but not the inactive analogue 4 alpha-phorbol 12-myristate 13-acetate, inhibited NMDA-induced increases in intracellular Ca2+ levels. Coincubation of cells with PMA and the kinase inhibitor staurosporine or calphostin C blocked the PMA effect. The potency of NMDA was reduced twofold, and the potency of the NMDA receptor co-agonist, glycine, to enhance the response to NMDA was decreased fourfold by pretreatment of cells with PMA. The effect on glycine was mimicked by pretreatment with okadaic acid, a protein phosphatase inhibitor. PMA treatment did not significantly alter Mg2+ inhibition of the NMDA response but decreased the potency of the competitive antagonist CGS-19755. These data suggest that, in cerebellar granule cells, the function of the NMDA receptor may be subject to feed-back inhibition by protein kinase C stimulation. Under physiological conditions, this inhibition may result from a decreased effectiveness of the endogenous co-agonists, glutamate and glycine.
Alkaloids↗