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T K Li

Publications and source records attributed to T K Li.

At least 127 records · Page 7Linked to original sources
PubMed1997

cDNA sequence and catalytic properties of a chick embryo alcohol dehydrogenase that oxidizes retinol and 3beta,5alpha-hydroxysteroids.

This study was undertaken to identify the cytosolic 40-kDa zinc-containing alcohol dehydrogenases that oxidize all-trans-retinol and steroid alcohols in fetal tissues. Degenerate oligonucleotide primers were used to amplify by polymerase chain reaction 500-base pair fragments of alcohol dehydrogenase cDNAs from chick embryo limb buds and heart. cDNA fragments that encode an unknown putative alcohol dehydrogenase as well as the class III alcohol dehydrogenase were identified. The new cDNA hybridized with two messages of approximately 2 and 3 kilobase pairs in the adult chicken liver but not in the adult heart, muscle, testis, or brain. The corresponding complete cDNA clones with a total length of 1390 base pairs were isolated from a chicken liver lambdagt11 cDNA library. The open reading frame encoded a 375-amino acid polypeptide that exhibited 67 and 68% sequence identity with chicken class I and III alcohol dehydrogenases, respectively, and had lower identity with mammalian class II (55-58%) and IV (62%) isozymes. Expression of the new cDNA in Escherichia coli yielded an active alcohol dehydrogenase (ADH-F) with subunit molecular mass of approximately 40 kDa. The specific activity of the recombinant enzyme, calculated from active site titration of NADH binding, was 3.4 min-1 for ethanol at pH 7.4 and 25 degrees C. ADH-F was stereospecific for the 3beta,5alpha- versus 3beta,5beta-hydroxysteroids. The Km value for ethanol at pH 7.4 was 17 mM compared with 56 microM for all-trans-retinol and 31 microM for epiandrosterone. Antiserum against ADH-F recognized corresponding protein in the chicken liver homogenate. We suggest that ADH-F represents a new class of alcohol dehydrogenase, class VII, based on its primary structure and catalytic properties.

Alcohol Dehydrogenase↗
PubMed1997

Research direction.

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Alcohol Dehydrogenase↗
PubMed1997

Comparison of rats selectively bred for high and low ethanol intake in a forced-swim-test model of depression: effects of desipramine.

This investigation examined if there is a relationship between selective breeding for high or low alcohol intake and immobility in a force-swim-test (i.e., "behavioral despair") model of depression. Time spent immobile in a water-filled cylinder was measured in the alcohol-preferring (P and nonpreferring (NP) lines of rats, and in the high-alcohol-drinking (HAD) and low-alcohol-drinking (LAD) lines. Each rat was tested for 2 10-min trials administered 24 h apart, and pretreatment with saline or desipramine (10.0 or 20.0 mg desipramine/kg b.wt. i.p.) also was evaluated. Drug was administered immediately after Trial 1 and again 1 h before Trial 2. When tested without pretreatment in Trial 1 or with saline pretreatment in Trial 2, NP rats spent significantly more time immobile than did P rats, but no comparable line differences were found when HAD and LAD rats were tested. Desipramine pretreatment reduced the time spent immobile in rats of the 2 alcohol-nonpreferring lines (i.e., the NP and LAD rats), but had no significant effect in rats of the 2 alcohol-preferring lines (the P and HAD rats). These findings do not support the hypothesis that there is a functional relationship between high alcohol drinking and susceptibility to "behavioral despair" as measured by the forced-swim test. The results with desipramine suggest that selection for high alcohol intake may be associated with insensitivity to desipramine.

Alcohol Drinking↗
PubMed1997

Regional densities of benzodiazepine sites in the CNS of alcohol-naive P and NP rats.

The regional densities of benzodiazepine (BDZ) recognition sites coupled to GABAA receptors were studied in ethanol-naive alcohol-preferring (P) and -nonpreferring (NP) lines of rats by using quantitative autoradiography to measure the amount of 2 nM [3H]flunitrazepam (FNZ) binding in the absence and presence of 100 microM GABA. Lower values (p < 0.025) for [3H]FNZ binding (in the absence of GABA) were observed in the prefrontal cortex, layer 4 of the parietal cortex, and the nucleus accumbens shell of the P relative to the NP line. GABA significantly (p < 0.025) stimulated [3H]FNZ binding in all 50 central nervous system regions examined in both the P and the NP rats. The largest percent increases (190-220%) were observed in the prefrontal, cingulate, frontal, and parietal cortices; shell and core nucleus accumbens; caudate putamen; dorsal lateral, intermediate lateral, ventral lateral, and medial septal nuclei; and lateral hypothalamus. In several layers of the frontal and parietal cortices, a 25-30% greater net or percent increase (p < 0.025) in GABA-enhanced [3H]FNZ binding was observed in the P rats compared with the NP rats. In contrast, lower net or percent increases (p < 0.025) in GABA-enhanced [3H]FNZ binding were found in the entorhinal cortex, the mediodorsal thalamus, and the dorsal CA3 area and middle dentate gyrus of the posterior hippocampus of the P line relative to the NP line. The present findings suggest that there are innate regional differences between P and NP rats in the densities and/or affinities of BDZ recognition sites and in the coupling between the GABAA and BDZ binding sites.

Alcohol Drinking↗
PubMed1997

Alcohol intake of P rats is regulated by muscarinic receptors in the pedunculopontine nucleus and VTA.

Experiments were conducted to determine whether muscarinic receptors within the pedunculopontine nucleus (PPN) and ventral tegmental area (VTA) are involved in regulating ethanol drinking behavior in the alcohol-preferring P line of rats. Female P rats were given limited access (2 h/day) to 10% (v/v) ethanol and 0.0125% (g/100 ml) saccharin solutions. Food was available ad libitum. Cholinergic agents were microinjected unilaterally into the PPN or VTA immediately prior to ethanol access. Intra-PPN carbachol (1-4 microg/0.5 microl), which can inhibit cholinergic neuronal activity within the PPN, decreased ethanol (70% decrease at the highest dose; p < 0.05) and saccharin (90% decrease at the highest dose; p < 0.05) intake in a dose-dependent manner within the first 30 min. Intra-PPN scopolamine (5-15 microg/0.5 microl), which can stimulate cholinergic neuronal activity within the PPN, decreased ethanol intake in a dose-dependent manner within the first 30 min (65% decrease at the highest dose; p < 0.05) without reducing saccharin intake. Intra-VTA methylscopolamine (1-10 microg/0.5 microl), a muscarinic antagonist, significantly (p < 0.05) reduced ethanol (60% decrease at the highest dose) and saccharin (50% decrease at the highest dose) intakes during the 2-h access period. Intra-VTA carbachol, a cholinergic agonist (1 and 2 microg/0.5 microl) decreased ethanol consumption in a dose-dependent manner within the first 60 min (50% decrease at the highest dose) without reducing saccharin intake. Overall, these results support an involvement of the cholinergic PPN-VTA system in regulating alcohol drinking and general consummatory behaviors of the P line of rats.

Alcohol Drinking↗
PubMed1997

Incompatibility of Escherichia coli rho mutants with plasmids is mediated by plasmid-specific transcription.

The Escherichia coli rho-15 mutant (deficient in transcription termination) is known to be incompatible with pBR322 and other plasmids (J. S. Fassler, G. F. Arnold, and I. Tessman, Mol. Gen. Genet. 204:424-429, 1986). We show that failure of pBR322 to transform rho-15 is mediated by transcription from the tet promoter and readthrough from the tet gene into the rom region. Using an isopropyl-beta-D-thiogalactopyranoside-inducible promoter to replace the tet promoter, we have demonstrated that plasmid-specific transcription inhibits growth of the rho-15 host, possibly due to the expression of the Rom protein. The involvement of Rom protein in pBR322-rho-15 incompatibility is further indicated by the following two experiments. (i) Functional inactivation of the rom gene in pBR322 enabled plasmids to transform E. coli rho-15. (ii) Specific overexpression of the rom gene abolished plasmid transformation into E. coli rho-15. An rpoB8(Ts) mutant RNA polymerase which compensated for the termination defect in E. coli rho-15 also restored plasmid-host compatibility, suggesting that Rom-mediated plasmid-host incompatibility is linked to a defect in transcription termination.

Bacterial Proteins↗
PubMed1997

The neurobiology of alcoholism in genetically selected rat models.

Rats selectively bred for their tendency to drink large or small quantities of alcohol are a useful model for investigators examining the possible neurobiological processes underlying alcoholism. Studies with the alcohol-preferring (P) and alcohol-nonpreferring (NP) and the high-alcohol-drinking (HAD) and low-alcohol-drinking (LAD) pairs of rat lines developed at Indiana University have illustrated differences in several behavioral and neurobiological characteristics associated with alcohol consumption. Specifically, compared with alcohol-avoiding rats, rats with an affinity for alcohol have a greater sensitivity to the stimulatory effects of low to moderate doses and a reduced sensitivity to the negative effects of high doses. Rats that voluntarily drink large quantities of alcohol also acquire tolerance to alcohol's aversive effects. In addition, these rats differ from their alcohol-avoiding counterparts in the levels of several chemical mediators (i.e., neurotransmitters) found in the brain, including serotonin, dopamine, gamma-aminobutyric acid (GABA), and the endogenous opioids.

Alcohol Drinking↗
PubMed1997

Behavioral similarities and differences among alcohol-preferring and -nonpreferring rats: confirmation by factor analysis and extension to additional groups.

Thirteen behavioral variables from six tasks were measured in alcohol-preferring (AA, FH, and P) and -nonpreferring (ANA, FRL, and NP) rat lines/strains and subjected to Factor Analysis. Four Independent factors accounted for > 90% of the variance. Defecation in the open field and ultrasonic vocalizations after an air puff were negatively correlated with alcohol intake and preference, whereas the increase in daily fluid intake in the presence of saccharin was positively correlated. Other factors could be labeled Activity, Emotionality, and immobility Factors, and each was independent of the Alcohol Factor. When an additional alcohol-preferring rat line (HAD) and two additional nonpreferring groups (LAD and ACI) were tested, they were found to differ on most behaviors that were associated with alcohol intake and preference in the Factor Analysis; vocalizations and saccharin-induced increase in fluid intake, but not defection. A new Factor Analysis was then performed incorporating these three new groups and including five new behavioral measures. The following measures had high loadings on the Alcohol Factor: alcohol intake under choice conditions; alcohol preference; forced alcohol intake; alcohol acceptance (forced alcohol intake/basal water intake x 100); ultrasonic vocalization; saccharin intake; saccharin-induced increase in daily fluid intake; defecation in the open field test; and immobility in a modified forced swim test. These findings indicate that there are indeed certain behavioral characteristics that are common among alcohol-preferring rat lines/strains, but there are also substantial group differences on other behavioral measures. For those behavioral measures reflecting emotionality (defecation and ultrasonic vocalization) that loaded highly on the Alcohol Factor, the alcohol-preferring rats had lower scores.

Alcohol Drinking↗
PubMed1997

6-OHDA-lesions of the nucleus accumbens disrupt the acquisition but not the maintenance of ethanol consumption in the alcohol-preferring P line of rats.

The aim of the present study was to determine whether reduction of dopamine (DA) innervation to the nucleus accumbens (ACB) alters the maintenance and/or acquisition of ethanol drinking in female alcohol-preferring P rats. Compared with sham-lesioned animals, bilateral microinjections of 6-OHDA (12 micrograms/2.4 microliters/site) into the ACB did not alter the consumption of 10% ethanol in rats that had prior experience of ethanol drinking, with both sham- and 6-OHDA-lesioned groups recovering to presurgical consumption levels at similar rates. On the other hand, the identical lesion procedure disrupted the acquisition of ethanol intake in rats with no ethanol-drinking experience prior to the lesions. A sham-lesioned group attained an ethanol intake of approximately 7 g/kg/day in 1 week, which was maintained over the following 2-week period, while the ethanol intake of the 6-OHDA-lesioned group was approximately 60% lower after 1 week and 30% lower at the end of 3 weeks. DA content of the ACB was 60% lower in both groups of the 6-OHDA-treated rats compared with the controls. The results suggest that different neural mechanisms may underlie the acquisition and maintenance of ethanol drinking behavior; the ACB DA system appears to play an important role in the acquisition of ethanol drinking.

Adrenergic Agents↗
PubMed1997

Polymorphism of ADH and ALDH genes among four ethnic groups in China and effects upon the risk for alcoholism.

The alcohol dehydrogenases (ADHs) and aldehyde dehydrogenases (ALDHs) that metabolize ethanol are polymorphic. Different alleles encode subunits of the enzymes that differ in their rate of metabolizing ethanol. These polymorphisms are distributed differently among populations and have been shown to influence the risk for alcoholism in some Asian populations. We have examined the allele frequencies at the ADH2, ADH3, and ALDH2 loci in four populations from China (Han, Mongolian, Korean, and Elunchun) and in alcoholics within each population. The four populations differ in allele frequencies, with the Elunchun having a much lower frequency of ADH2*2 alleles, and the Mongolian and Elunchun having a much lower frequency of ALDH2*2 alleles. Within each population, alleles at one or more of these three loci are protective against alcoholism, although the populations differ in which loci play significant roles. The protective allele at each locus (ALDH2*2, ADH2*2, and ADH3*1) encodes a subunit that either metabolizes ethanol to acetaldehyde more rapidly or slows the conversion of acetaldehyde to acetate. Taken as a whole, data demonstrate that genetic differences in the enzymes that metabolize alcohol can substantially affect the risk for alcoholism.

Adolescent↗
PubMed1996

Effects of the benzodiazepine inverse agonist RO19-4603 alone and in combination with the benzodiazepine receptor antagonists flumazenil, ZK 93426 and CGS 8216, on ethanol intake in alcohol-preferring (P) rats.

The present study investigated dose dependence and time course effects of the benzodiazepine (BDZ) partial inverse agonist, RO19-4603 (0.005-0.30 mg/kg) alone, and in combination with the BDZ receptor antagonists flumazenil, ZK 93426, and CGS 8216 (20 mg/kg) in selectively bred alcohol-preferring (P) rats provided a two-bottle choice test between ethanol (EtOH) (10% v/v), and a palatable saccharin (0.0125% g/v) solution. A single dose of RO19-4603 as low as 0.009 mg/kg selectively reduced EtOH drinking during the initial 15 min of a 4 h access to 19-0% of control levels on day 1. The 0.08, 0.15 and 0.30 mg/kg doses of RO19-4603 significantly reduced total EtOH intake in the 4 h access period to 57-45% of controls on day 1. On day 2, no RO19-4603 injections were given; however, six of the seven doses of RO19-4603 (0.009, 0.02, 0.04, 0.08, 0.15, and 0.30 mg/kg) continued to reduce EtOH intake to 42-3% of control levels at the initial 15 min interval, while the 0.005, 0.009, 0.08, and 0.30 mg/kg doses reduced total 4 h EtOH intake to 60-42% of controls. Saccharin intake was either not altered by RO19-4603 or showed increases during the initial 15 min intervals and the total 4 h sessions on days 1 and 2. Food intake was also unaffected by RO19-4603. The CGS 8216, but neither flumazenil nor ZK 93426, reliably reversed the RO19-4603-induced suppression of EtOH intake on days 1 and 2. That certain BDZ inverse agonists can attenuate motivated behavior for EtOH reinforcement over a prolonged time course may provide a possible therapeutic approach to reducing EtOH consumption associated with alcoholism.

Alcohol Drinking↗
PubMed1996

Genetic differences in tolerance and sensitization to the sedative/hypnotic effects of alcohol.

Initial sensitivity to alcohol and the development of alcohol tolerance were examined in rats of the selectively bred alcohol-preferring (P) and -nonpreferring (NP) lines. All rats received two alcohol injections (3.0 g/kg b.wt., IP) separated by either 1 or 2 days. P rats were less sensitive to the behaviorally impairing effects of alcohol than were NP rats, as evidenced by a longer latency to lose righting reflex (RR) and a shorter time to recover RR following an initial alcohol injection. When 1 day separated the two alcohol injections, P rats recovered the RR more rapidly following a second injection compared to the first, indicating that the P rats developed tolerance to the sedative/hypnotic effects of alcohol. In contrast, the NP rats recovered the RR more slowly following the second injection compared to the first, indicating that the NP rats developed sensitization to alcohol. Tolerance in the P line and sensitization in the NP line disappeared when 2 days separated the two alcohol injections. Line differences in initial sensitivity and tolerance/sensitization to the behaviorally impairing effects of alcohol may contribute to the differences in alcohol consumption observed in the P and NP lines.

Alcohol Drinking↗
PubMed1996

Place conditioning with alcohol in alcohol-preferring and -nonpreferring rats.

A place-conditioning procedure was used to examine the effect of selective breeding for ethanol preference on sensitivity to the rewarding and/or aversive effects of ethanol. On 4 alternate days, groups of seven to eight alcohol-preferring (P) and alcohol-nonpreferring (NP) rats received IP injections of 0.0 (saline controls), 0.5, 1.0, or 1.5 g ethanol/kg body wt. immediately before 15-min confinement in a novel environment. On the 4 intervening days the same rats received saline injections before 15 min confinement in a different environment. On day 9, a 15-min choice test was given with no injections, in which the rats could move freely between the ethanol and the saline-paired environments. Dose-dependent avoidance of the ethanol-paired environment was observed in both lines of rats (1.0 and 1.5 g/kg), but the magnitude of the avoidance was less in the P relative to the NP rats, indicating that ethanol was less aversive for the P rats. No evidence for a place preference was observed in either line with any of the ethanol doses. An innate reduced sensitivity to the aversive effects of ethanol in rats of the P line and/or an enhanced sensitivity to the aversive effects of ethanol in rats of the NP line may contribute to the different levels of oral ethanol self-administration observed in these selectively bred rat lines.

Animals↗
PubMed1996

Characterization of a new hereditary thrombopathy in a closed colony of Wistar rats.

A new hereditary thrombopathy has been identified in a closed colony of Wistar rats. A simple and reproducible cuticle bleeding time test was developed as a rapid screening procedure for the bleeding diathesis. Affected animals exhibit markedly prolonged bleeding times and complete absence of platelet aggregation either with adenosine diphosphate (ADP) or with thrombin. Inheritance data suggest an autosomal dominant inheritance pattern with variable penetrance. Coagulation tests, platelet counts, plasma von Willebrand factor (vWF) activity, and clot retraction are within normal limits in thrombopathic animals. GPIb-dependent botrocetin-induced platelet agglutination was present in washed thrombopathic rat platelets. No discernible abnormality of intraplatelet organelles or granules was seen by transmission electron microscopy of thrombopathic platelets. A qualitative morphologic assessment of intraplatelet fibrinogen in thrombopathic rat platelets showed no discernible difference as compared with control rat platelets. Thrombopathic rat platelets exhibit decreased glycoprotein IIb/IIIa (GPIIb/IIIa) antigen by flow cytometric analysis and markedly decreased iodine 125-labeled fibrinogen binding to platelet GPIIb/IIIa after ADP activation. This rat colony demonstrates a unique thrombopathy, distinct from previously described animal thrombopathies, with some characteristics of variant Glanzmann's thrombasthenia. This animal model may provide further insight into the regulatory mechanisms and pathophysiology of platelet GPIIb/IIIa.

Animals↗
PubMed1996

Benzodiazepine receptor ligands with different intrinsic efficacies alter ethanol intake in alcohol-nonpreferring (NP) rats.

Benzodiazepine (BDZ) receptor ligands with varying intrinsic efficacies [RO19-4603, 0.02-0.15 mg/kg; FG 7142 1-16 mg/kg; DMCM, 1-8 mg/kg; RO16-6028 (bretazenil), 8-32 mg/kg] in modulating GABAergic activity were examined for the ability to alter palatability-induced ethanol (EtOH) intake in the alcohol-nonpreferring (NP) line of rats. NP rats on a 22-hour fluid-deprivation schedule were given 2-hour daily access to a 10% (v/v) EtOH/3% (g/v) polycose solution and water. Average EtOH intake was 2.1 +/- 0.2 g/kg/2 hours, and water intake was 17.1 +/- 0.9 ml/2 hours. During the initial 15 minutes of the 2-hour session, RO19-4603, the imidazothienodiazepine partial inverse agonist reduced EtOH intake to 19% of control values at 0.04 mg/kg and completely suppressed drinking of the EtOH solution at 0.15 mg/kg. Twenty-four-hour postdrug administration, the 0.08-mg/kg dose of RO19-4603 completely suppressed drinking of the EtOH solution at the 60-minute interval, and the 0.15-mg/kg dose reduced intake to 20% of control levels at the 15-minute interval. FG 7142, the partial beta-carboline inverse agonist reduced EtOH drinking at the 60-minute interval with the 1-mg/kg dose, and the 16-mg/kg dose reduced water intake at the 15-minute interval. DMCM, the full beta-carboline inverse agonist, significantly reduced water intake at 15 minutes (4 and 8 mg/kg), and the same doses caused a substantial increase in EtOH drinking at the 120-minute interval. The anxiolytic agent bretazenil (16 and 32 mg/kg) increased EtOH consumption during the initial 15 minutes to 270% to 425% of control levels, and water intake increased by the end of the 2-hour session to as much as 210% of control following administration of the 32-mg/kg dose. These findings support existing evidence suggesting that BDZ receptor ligands may modify neuronal processes that mediate some reinforcing and/or aversive properties of alcohol. They further demonstrate a potential importance of the GABAA-BDZ receptor complex in mediating palatability- (environmentally) induced EtOH drinking even in rats selectively bred for low alcohol preference.

Analysis of Variance↗
PubMed1996

Cholera toxin B subunit binding to an antigen-presenting cell directly co-stimulates cytokine production from a T cell clone.

Cholera toxin (CT) is a powerful immunomodulator with strong adjuvant activity. Much of this activity is retained by the binding component alone, cholera toxin B subunit (CTB). Little is known about the mechanism of the immunomodulatory activity of CTB. In this study, both CT and CTB were found to dramatically enhance IL-4 production from a T cell clone stimulated with antigen and the B cell hybridoma LB as antigen-presenting cell (APC). Enhancement of cytokine production was seen following pretreatment of the APC with CT or CTB, while pretreatment of the T cells had no effect. Furthermore, stimulatory activity on the APC was stable to fixation with paraformaldehyde, demonstrating that the activity was mediated by a surface molecule on the APC. CT-pretreated APC also enhanced IL-4 production from anti-CD3 mAb-stimulated T cells, indicating that CT was providing a co-stimulatory signal. CT treatment of LB cells did not alter the expression of class II MHC molecules, CTLA-4 counter-receptors, LFA-1 or ICAM-1. When mAb were raised against the CT-pretreated APC, the only antibodies that were found to inhibit IL-4 production were those specific for CTB itself. The antibodies blocked even when the CT or CTB were already bound to the APC, arguing that co-stimulation was provided by a direct interaction with CTB. Blocking experiments suggested that APC-associated CTB molecules are interacting with non-GM1 receptors on the T cells. This novel finding of CTB-mediated T-B interaction provides one of the first potential mechanisms for the adjuvant activity of CTB.

Animals↗
PubMed1996

Genetic analysis of the resting electroencephalographic power spectrum in human twins.

Most twin studies have provided evidence for genetic effects on the electroencephalogram (EEG). In two twin studies, monozygotic (MZ) cotwin covariance for EEG power was greater than expected for additive gene actions, as compared with dizygotic (DZ) cotwin covariance. These findings were attributed to complex gene interactions, termed emergenesis. In the present study of 53 MZ and 38 DZ twin pairs departures from the additive genetic model were tested on resting EEG power. Total spectral power and the quotient of (beta band power)/(total power) both fit gene interaction models significantly better than did additive genetic models. These findings support the previous findings of MZ covariance for EEG power as much greater than DZ covariance; these findings can be explained entirely by the additive effects of genes. This pattern of twin covariances could be due to gene interactions but also to greater MZ than DZ environmental covariance.

Adult↗