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T E Johnson

Publications and source records attributed to T E Johnson.

At least 91 records · Page 5Linked to original sources
PubMed1996

Quantitative trait locus analyses of sleep-times induced by sedative-hypnotics in LSXSS recombinant inbred strains of mice.

The long-sleep (LS) and short-sleep (SS) selected lines of mice show highly significant differences in sleep-time for many sedative-hypnotic drugs, and the quantitative genetic nature of these differences has been well-established. Using an interval-mapping approach, quantitative trait locus (QTL) analyses of LSXSS recombinant inbred (RI) strains have been applied to sleep-time responses for various classes of sedative-hypnotic drugs: alcohols (ethanol, n-propanol, and n-butanol), the atypical anesthetic chloral hydrate, barbiturates (pentobarbital and secobarbital), and benzodiazepines (chlordiazepoxide and flurazepam). Several provisional QTLs were mapped to similar locations within and between drug classes, suggesting that some common loci are involved in sleep-times elicited by these drugs. Consistent with correlations of strain mean sleep-times between drugs tested in the LSXSS recombinant inbred strains, the number of provisional QTLs mapping to the locations of highest significance for ethanol decreases when the lipid solubility of a particular drug becomes less similar to that of ethanol. Provisional QTLs mapped for the benzodiazepines, however, revealed considerable overlap with those mapped for ethanol, although these drugs represented the most lipid-soluble category of sedative-hypnotics tested. Provisional QTLs for pentobarbital and secobarbital differed from most of those mapped for the alcohols, which supports the hypothesis that alcohols and barbiturates exert their effects mainly through different biological mechanisms in the LS and SS lines. Blood ethanol concentrations at regaining the righting reflex also mapped to several provisional QTLs corresponding to ethanol-induced sleep-times that support the contention that sleep-time is a reasonable index of the observed differences in central nervous system sensitivities to ethanol between LS and SS mice.

1-Butanol↗
PubMed1995

Total RNA, rRNA and poly(A)+RNA abundances during aging in Caenorhabditis elegans.

This is the second in a series of studies in which we characterize gene expression at the level of RNA during aging in the nematode Caenorhabditis elegans. Here, we quantitatively analyzed total RNA, poly(A)+ RNA, and ribosomal RNA as a function of chronological age in two different strains (TJ1060 and TJ1061) having wild-type life spans and in a long-lived age-1 mutant strain (TJ1062). In addition, we compared the age-dependent abundance patterns of these RNAs in two different culture environments. Total RNA yield did not show a consistent pattern of age-related changes. However, total RNA yield was significantly higher in all three strains when grown on agar than when grown in liquid. In addition, total RNA yield was significantly lower from strain TJ1061 than from strain TJ1060 and TJ1062. Relative to total RNA, rRNA did not exhibit any consistent differences with age, strain or environment. Poly(A)+ RNA decreased by 23-43% in old animals from the long-lived strain and one of the wild-type strains, but was not changed in the second wild-type strain. In addition, control experiments to determine the amount of RNA contributed by E. coli bacteria (present in the nematode culture medium as a food source) suggest that the age-1 mutant strain has a lower bacterial infection rate, which may contribute to the increased life span of this strain.

Aging↗
PubMed1995

Thermotolerance and extended life-span conferred by single-gene mutations and induced by thermal stress.

We have discovered that three longevity mutants of the nematode Caenorhabditis elegans also exhibit increased intrinsic thermotolerance (Itt) as young adults. Mutation of the age-1 gene causes not only 65% longer life expectancy but also Itt. The Itt phenotype cosegregates with age-1. Long-lived spe-26 and daf-2 mutants also exhibit Itt. We investigated the relationship between increased thermotolerance and increased life-span by developing conditions for environmental induction of thermotolerance. Such pretreatments at sublethal temperatures induce significant increases in thermotolerance and small but statistically highly significant increases in life expectancy, consistent with a causal connection between these two traits. Thus, when an animal's resistance to stress is increased, by either genetic or environmental manipulation, we also observe an increase in life expectancy. These results suggest that ability to respond to stress limits the life expectancy of C. elegans and might do so in other metazoa as well.

Aging↗
PubMed1995

Increased frequency of deletions in the mitochondrial genome with age of Caenorhabditis elegans.

We have developed a long-extension-PCR strategy which amplifies approximately half of the mitochondrial genome (6.3 kb) of Caenorhabditis elegans using an individual worm as target. We analyzed three strains over their life span to assess the number of detectable deletions in the mitochondrial genome. Two of these strains are wild-type for life span while the third is mutant in the age-1 gene, approximately doubling its maximum life span. At the mean life span in wild-type strains, there was a significant difference between the frequency of deletions detected in the mitochondrial genome compared with the mean number of deletions in young animals. In addition, deletions in the mitochondrial genome occur at a significantly lower rate in age-1 mutants as compared with wild type. We cloned and identified the breakpoints of two deletions and found that one of the deletions had a direct repeat of 8 bp at the breakpoint. This is the largest single study (over 900 individual animals) characterizing the frequency of deletions in the mitochondrial genome as a function of age yet carried out.

Aging↗
PubMed1995

Identification of urinary and biliary conjugated metabolites of the neuromuscular blocker 51W89 by liquid chromatography/mass spectrometry.

Cisatracurium, (1R, 1'R, 2R, 2'R)-2,2-[1,5-pentanediylbis-[oxy(3-oxo- 3,1-propanediyl]]bis[1-[(3,4-dimethoxyphenyl)-methyl]-1,2,3,4- tetrahydro-6,7-dimethoxy-2-methylisoquinolinium] dibenzenesulphonate (51W89), is an intermediate-acting neuromuscular blocking agent. 51W89 is one of ten isomers contained in Tracrium (atracurium besylate) and represents approximately 15 percent of the atracurium mixture. Clinical studies have indicated that 51W89 is more potent and is significantly weaker as a histamine releaser than atracurium. In vitro studies in human plasma have shown that, like atracurium, 51W89 spontaneously degrades at physiological pH by Hoffmann elimination to form laudanosine and the quaternary monoacrylate. Subsequent ester hydrolysis of the monoacrylate generates the monoquaternary alcohol. In rat plasma, 51W89 is also metabolized by non-specific carboxylesterases to the monoquaternary alcohol and the monoquaternary acid, the former being rapidly hydrolysed further to the more stable acid. It has been reported that laudanosine can be further metabolized via N-dimethylation to yield tetrahydropapaverine. The rate-limiting step in the degradation of 51W89 in human plasma is Hofmann elimination, whilst in rat plasma, the action of non-specific carboxylesterases is rate limiting. As part of the development of 51W89, the disposition of 14C-51W89 following a single intravenous bolus dose was studied in various animal species and humans. In the present work, we describe the identification of 51W89 metabolites in urine and bile from these studies by high performance liquid chromatography/mass spectrometry using pneumatically-assisted electrospray ionization coupled to an on-line radioactivity monitor.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1995

Ethanol-induced anesthesia in inbred strains of long-sleep and short-sleep mice: a genetic analysis of repeated measures using censored data.

We present a repeated-measures, genetic analysis of ethanol-induced anesthesia (sleep time) in mice from the inbred long-sleep (ILS) and short-sleep (ISS) strains of mice and their derived F1 and F2 generations. Mice (total N > 1300) were administered a 4.1 g/kg intraperitoneal dose of ethanol at two times, 7 to 10 days apart. A method suggested by Cohen was used to analyze the resulting data, which contained a known number of unmeasured observations. A genetic model that included both additive and epistatic parameters fitted the adjusted data well. A novel procedure for estimating heritability, based on a comparison of repeatability coefficients from the isogenic and genetically segregating populations, was also employed. Results of this analysis suggested that the heritability for individual measurements of sleep time is about .30, whereas the heritability of average scores is about .40. Results of this analysis also confirm that the ILS and ISS strains differ for genes at seven or more loci that influence sleep time. Since the ILS and ISS were derived by inbreeding the LS and SS lines, these results further suggest that almost all of the genetic variation present in the selected lines have been maintained in the ILS and ISS strains.

Animals↗
PubMed1995

Identification genes that are differentially expressed during aging in Caenorhabditis elegans.

We isolated cDNA clones of transcripts that undergo change in abundance over the adult life span of the nematode Caenorhabditis elegans. Replicas of a C. elegans cDNA library were probed with cDNA synthesized from poly(A) + RNA isolated from young or old nematodes. We identified clones corresponding to nine distinct transcripts that decreased in abundance with age, two distinct transcripts that increased slightly in abundance with age, and one transcript that peaked in abundance during the early to middle part of the adult life span. Six of the twelve transcripts were quantitated as a function of age by means of a dot blot assay using total RNA isolated at several ages from two strains that have wild-type life spans. All six mRNAs showed similar age-dependent abundance patterns in these two strains. Mutation of the age-1 gene, which lengthens life span, did not appear to alter these patterns. Nucleotide sequence analysis of clone inserts revealed that three of the mRNAs that decreased in abundance with age corresponded to previously identified C. elegans vitellogenin genes. One transcript that showed a small increase in abundance with age appears to encode translation factor EF1-alpha. The other five clones represent novel nematode genes.

Aging↗
PubMed1995

Movement as an index of vitality: comparing wild type and the age-1 mutant of Caenorhabditis elegans.

We have asked whether the mutant form of the age-1 gene, which lengthens the life span of the nematode Caenorhabditis elegans up to 70%, also affects the ability to move during this extended period of life. Both age-1 mutants and wild-type controls display a linear loss of movement as the nematodes age. age-1 mutant strains moved faster early in life when compared with non-Age strains and continued low rates of movement at older ages than did non-Age strains. Movement rates were not, in general, a good predictor of movement rates at any later age or of life span. Cumulative lifetime movements of individuals were highly correlated with, and thus a good predictor of, individual life span. These findings are similar to earlier studies of movement in long-lived recombinant-inbred strains of C. elegans and imply that the physiological process altered by the age-1 mutation results in increased health during later life as monitored by increased ability to move.

Aging↗
PubMed1995

Use of repeated measures in an analysis of ethanol-induced loss of righting reflex in inbred long-sleep and short-sleep mice.

We present a repeated-measures analysis of ethanol-induced loss of righting reflex (LRR) in Inbred Long-Sleep (ILS) and Inbred Short-Sleep (ISS) strains of mice and their F1 and F2 cross progeny. Mice were administered a 4.1 g/kg intraperitoneal dose of ethanol at two times, 7-10 days apart. Repeatability is nonsignificant in ILS, ISS, and F1 mice, but is highly significant (0.47, p < 0.01) in the F2 mice. Mean LRR does not differ between trials 1 and 2, with the exception of the ISS strain in which the interaction of sex with LRR sensitization is significant. This two-trial method leads to increased accuracy of genotype assessment for pharmacological or behavioral traits where trial 1 does not influence the outcome of trial 2. The repeated-measures design facilitates novel analyses of the duration of LRR, and results suggest that most environmental variance for LRR is due to nonreplicable influences.

Alcoholic Intoxication↗
PubMed1994

Chromosome aberrations: persistence of alkylation damage and modulation by O6-alkylguanine-DNA alkyltransferase.

Alkylating agents produce a spectrum of DNA lesions alkylated at different sites on the molecule. These lesions differ in their propensities to cause effects such as cytotoxicity, mutations and sister-chromatid exchanges. We have used our observations that some methylating agents produce increasing levels of chromosome aberrations (abs) through successive cell cycles in Chinese hamster ovary cells, but not in normal human cells, to begin a study of which alkylated products are most likely to lead to chromosome abs, and in particular which adducts persist in DNA and cause abs after the first cell cycle. We previously observed increasing yields of abs with successive cell cycles in CHO-WBL cells treated with dimethyl nitrosamine (DMN), e.g., at 10 mM DMN, 8.8% cells with abs at first metaphase (M1) and 26.0% at third metaphase (M3) after treatment. Here we tested 4 methylating agents and their ethyl analogs in CHO cells, normal human fibroblasts (L136), and human lymphocytes. We sampled cells at several times after treating for 3 h (CHO and lymphocytes) or 4.5 h (L136). S9 metabolic activation was used for DMN and diethyl nitrosamine. BrdUrd labeling was used to identify cells in M1, M2 and M3. The methylating agents were more potent aberration (ab) inducers than ethylating agents, on a molar basis. In CHO cells, yields of abs were maintained or increased through up to 3 cell cycles after treatment with DMN, methyl methanesulfonate, methyl nitrosourea and 1-methyl-3-nitro-1-nitrosoguanidine (MNNG). With ethylating agents the ab yields in CHO cells were similar or lower in second and third cycles. In contrast, there was no evidence for persistence of lesions leading to abs in either human cell type; ab yields were markedly decreased with subsequent cell cycles for all agents. Normal human cells are proficient in repair of alkylation at the O6 site of guanine by O6-alkylguanine-DNA alkyltransferase (AGT), whereas CHO cells lack AGT activity. To explore the role of repair by AGT on the lesions involved in production of abs, we studied L136 cells, with and without O6-benzylguanine (BZG), a specific inhibitor of AGT. With MNNG, inhibition of AGT resulted in higher ab yield and production of abs through later cell cycles, so that human fibroblasts now behaved similarly to CHO cells. Preliminary data from the reciprocal experiment in CHO cells engineered to express high levels of AGT revealed a greatly decreased ab response to MNNG. In addition, the low ab yields observed were similar through later cycles or increased only slightly.(ABSTRACT TRUNCATED AT 400 WORDS)

Alkylating Agents↗
PubMed1994

Detection of deletions in the mitochondrial genome of Caenorhabditis elegans.

We have examined an aging population of Caenorhabditis elegans via a PCR assay to determine if deletions in the mitochondrial genome occur in the nematode. We detected eight such deletions, identified the breakpoints of four of these, and discovered direct repeats of 4-8 base pairs at the site of all four deletions. Six of the eight repeats involved in the deletions are located in or immediately adjacent to tRNAs. Without a biochemical bias, the probability of direct repeats being present at all four breakpoints was 4 x 10(-6).

Aging↗
PubMed1994

Mortality rates in a genetically heterogeneous population of Caenorhabditis elegans.

Age-specific mortality rates in isogenic populations of the nematode Caenorhabditis elegans increase exponentially throughout life. In genetically heterogeneous populations, age-specific mortality increases exponentially until about 17 days and then remains constant until the last death occurs at about 60 days. This period of constant age-specific mortality results from genetic heterogeneity. Subpopulations differ in mean life-span, but they all exhibit near exponential, albeit different, rates of increase in age-specific mortality. Thus, much of the observed heterogeneity in mortality rates later in life could result from genetic heterogeneity and not from an inherent effect of aging.

Aging↗
PubMed1994

Aging. Stopping the clock.

Two genes that control dauer formation in the soil nematode Caenorhabditis elegans have direct effects on senescence.

Aging↗
PubMed1994

Initial characterization of STS markers in the LSXSS series of recombinant inbred strains.

We are mapping quantitative trait loci (QTLs) that influence ethanol-induced anesthesia (sleep time) in the Long-sleep (LS) and Short-sleep (SS) selected lines of mice. Fifty microsatellite-STS markers were initially screened for simple-sequence length polymorphisms between the LS and SS lines. Nineteen markers were polymorphic. Eleven markers unequivocally differentiated the LS and SS lines and were used to establish strain distribution patterns for the LSXSS series of recombinant inbred strains. Five markers each accounted for at least 5% of sleep-time genetic variance among the RI strains. Linkage of provisional QTLs detected among RIs will be confirmed or disproved in a large F2 population. This ongoing QTL-mapping project eventually will result in a strain distribution pattern for the LSXSS RI series with an average marker spacing of 5 centimorgans.

Anesthesia, General↗
PubMed1994

Production of age-synchronous mass cultures of Caenorhabditis elegans.

Methods are described for culturing large populations of age-synchronous Caenorhabditis elegans throughout the adult life span. Contamination of adult populations by progeny was prevented by constructing double-mutant strains that produce progeny at a frequency of less than .005 per adult at the nonpermissive temperature (25.5 degrees C). Of four double-mutant strains that we have characterized, three have wild-type life spans at 25.5 degrees. The other strain contains a mutant allele, age-1(hx542), that results in an increase in life span of 60% over wild type. All four strains produced sufficient numbers of progeny at the permissive temperature (20 degrees C) to generate populations containing 1-5 x 10(6) nematodes within two weeks. Age-synchronous young adult populations were produced using these strains and have been maintained as adults both in liquid culture and on agar medium. Procedures that reduce E. coli contamination by 30-fold in harvested samples of adults are also described.

Aging↗
PubMed1994

Thermotolerance of a long-lived mutant of Caenorhabditis elegans.

Age-synchronous cohorts of Caenorhabditis elegans were grown at 20 degrees C, then stressed at 30 degrees C or 35 degrees C. Intrinsic thermotolerance of wild type and age-1 mutant strains was assessed by measuring either progeny production or survival. In addition to increased life span (Age), mutation of age-1 results in a highly significant increased intrinsic thermotolerance (Itt) as measured by survival at 35 degrees C. Mean survival of Age strains is approximately 45% longer than that of non-Age strains for both sterile and nonsterile worms. Thermotolerance declines across the life span of both Age and non-Age strains, but Itt was observed at almost all ages. Unstressed age-1 animals showed a consistent and significant fertility deficit. Short thermal stresses can cause a dramatic reduction in progeny production for both Age and non-Age genotypes. Mutants of age-1 showed a small but consistent increased thermotolerance as measured by fertility. We propose that the enhanced ability of Age strains to cope with environmental stress may be mechanistically related to their lower age-specific mortality rates.

Aging↗
PubMed1994

Mapping quantitative trait loci for ethanol-induced anesthesia in LSxSS recombinant inbred and F2 mice: methodology and results.

QTL (quantitative trait locus) mapping is an exciting new technique currently being applied to many quantitative traits. We review the animal models and molecular genetic techniques of QTL mapping with particular reference to ethanol-induced anesthesia (sleep time). Sleep time is an easily obtained measure of initial sensitivity to ethanol. We are using three-stage strategy to map QTLs causing the difference in sleep time between selected strains of mice. This project has been expedited by the use of polymorphic genetic markers (simple sequence repeats) which are amplifiable by the polymerase chain reaction. Over 115 strain distribution patterns have been characterized in the 27 LSxSS recombinant inbred strains. Provisional QTLs have been identified in the RI strains and will be confirmed or rejected in an F2 population of 1063 mice. A new statistical technique, interval mapping, allows the use of all polymorphic markers simultaneously to locate QTLs.

Anesthesia↗