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L D Smith

Publications and source records attributed to L D Smith.

At least 73 records · Page 4Linked to original sources
PubMed1988

Discrimination of temporal relations by pigeons.

In four experiments, pigeons were tested on a duration comparison task involving the successive presentation of two visual stimuli that varied in duration from trial to trial. Following presentation of the durations, two choice keys were lit, and reinforcement for choices was based on the temporal relation between duration of the pair. In Experiment 1, the range of durations was varied over conditions. Responding changed as an orderly function of the ratio of the two durations. There was a decrease in discrimination accuracy as average duration increased over condition but no difference in accuracy between shorter and longer problems within a duration range. There was no systematic response bias over conditions for all problems within a range, but there was a bias to report the second duration longer than the first for "long" problems within a range. In Experiment 2, the pigeons were transferred from a task involving spatially differentiated choices to one involving hue-differentiated choices. Performance was similar to that of the spatial procedure of Experiment 1. Additional analyses revealed that although information provided by a single duration of the pair was sometimes predictive of the temporal relation between pair members, responding was also based on the relation and comparison of both durations. In Experiment 3, the pigeons were exposed to a single duration range that included many durations from the four ranges of Experiment 1. Discrimination accuracy was comparable in the fourth and longest category. Manipulation of absolute reinforcement rate in Experiment 4 resulted in no chang in discrimination accuracy, suggesting that the decline in accuracy over conditions of Experiment 1 could not be attributed to decreases in reinforcement rate that accompanied lengthier durations. The results are discussed in terms of theories of animal timing, with Staddon's (1983, 1984) temporal perspective model providing the most systematic account of all aspects of performance.

Animals↗
PubMed1988

Motor neuron disease in the Rocky Mountain region.

We saw 166 patients with motor neuron disease over a ten-year period, 116 with amyotrophic lateral sclerosis-111 sporadic and 5 familial-and 50 with progressive muscular atrophy. The age at onset varied widely, with the youngest mean onset occurring in the familial group. The most common presenting symptoms were leg or arm weakness and difficulty speaking or swallowing; fewer patients reported cramping, fasciculation, or fatigue. Mean survival time was less in familial cases, women, older patients, and in those with difficulty speaking and swallowing. A total of 50% of all patients were alive after four years; 13% were alive after ten years. Previous reports on the natural history of motor neuron disease may be overly pessimistic in suggesting that survival time rarely exceeds two years.

Adolescent↗
PubMed1987

Native blot and immunotransfer of human prostatic acid phosphatase isozymes.

Agarose gel isoelectrofocusing is used to separate the isozymes of human prostatic acid phosphatase with retention of enzyme activity. The native blotting of the isozymes onto a nitrocellulose membrane increases the sensitivity of the enzyme stain and is suitable for analysis of isozymes in prostate tissue, which contains little nonprostatic acid phosphatase. The specificity of the transfer is increased by treating the membrane with antibody to human prostatic acid phosphatase prior to the transfer. The specificity of the antibody is conferred to the membrane resulting in a transfer specific for prostatic acid phosphatase. The immunotransfer procedure is applicable to serum which contains appreciable amounts of nonprostatic acid phosphatase.

Acid Phosphatase↗
PubMed1987

Do calcium and calmodulin trigger maturation in amphibian oocytes?

In contrast to earlier reports (J. L. Maller and E. G. Krebs, 1980, Curr. Top. Cell. Regul. 16, 271-311; M. Moreau, J. P. Vilian, and P. Guerrier, 1980, Dev. Biol. 78, 201-214; W. J. Wasserman and L. D. Smith, 1981, J. Cell Biol. 89, 389-394; D. Huchon, R. Ozon, E. H. Fischer, and J. G. Demaille, 1981, Mol. Cell. Endocrinol. 22, 211-222) calmodulin preparations isolated from Xenopus laevis ovaries or obtained commercially rarely induced maturation upon microinjection into individual oocytes. Calmodulin injections did result in significant cases of maturation when oocytes were first pretreated (primed) with calcium-free (EGTA) OR-2 and then injected in regular OR-2 medium. However, under these conditions the injected buffer solution alone was sometimes found to induce maturation. Under more optimal priming conditions, cases were found where as high as 100% of the oocytes matured simply by returning them to regular OR-2 medium. To determine which divalent cations could be involved in the priming effects of EGTA pretreatment we repeated the earlier ionophore work of W. J. Wasserman and Y. Masui (1975, J. Exp. Zool. 193, 369-375), looking not just at calcium and magnesium but other divalent cations as well. Several divalent cations (10 mM) were found to induce germinal vesicle breakdown with the following tentative order of efficacy, Co2+ greater than or equal to Zn2+ greater than or equal to Mn2+ greater than Ca2+ greater than Mg2+ greater than Ba2+, regardless of whether or not ionophore A23187 was present. These results, along with other reports in the literature, are discussed with respect to the theory that a rise in free calcium and calmodulin is involved in triggering oocyte maturation; we conclude that neither is involved.

Animals↗
PubMed1987

Induction of maturation in small Xenopus laevis oocytes.

The competence of Xenopus laevis oocytes in various stages of growth to respond to progesterone treatment was investigated. Full-grown (stage 6) oocytes undergo nuclear membrane dissolution and resume meiosis in response to progesterone exposure, while smaller oocytes (stages 3-5; less than 1100 micron in diameter) do not. The defect which prevents 750- to 1050-micron oocytes from responding to progesterone can be overcome by microinjecting cytoplasm withdrawn from a stage 6 oocyte. Germinal vesicle breakdown in these small oocytes occurs on a timetable similar to that of stage 6 oocytes exposed to progesterone and is accompanied by a twofold increase in protein synthesis as well as the activation of MPF. The results argue that a cytoplasmic factor(s) which probably first appears at late stage 5 is required for progesterone responsiveness. The identity and role of the factor(s) in the development of maturation competence and the regulation of maternal mRNA translation are discussed.

Animals↗
PubMed1987

Accumulation of free amino acids in growing Xenopus laevis oocytes.

The sizes of amino acid pools in growing Xenopus laevis oocytes have been measured. The total free amino acid content per oocyte increases nearly 25-fold during oocyte growth. Together, glutamic acid and aspartic acid account for approximately 59-75% of the total amino acid pool in Xenopus oocytes. On the other hand, methionine and cysteine are the least abundant of the amino acids detected, each accounting for less than 0.7% of the total pool in developing oocytes. It is argued that the acid-extractable amino acid pool represents the precursor pool used in protein synthesis.

Amino Acids↗
PubMed1987

Adenylosuccinate lyase as an indicator of breast and prostate malignancies: a preliminary report.

The high activity of adenylosuccinate (SAMP) lyase found in rat breast tumor, and its relative absence from normal rat breast tissue, suggests that it may serve as an indicator for human breast malignancy. Its activity has been measured in human breast tumors, both malignant and benign. The two were clearly separated with no overlap in activity between the malignant and benign tissues. Human prostate tissues were also examined for SAMP lyase. A cut-off level of 5 U/mL gave a false-positive rate of 11% with no false negatives. These results indicate that further work is warranted to determine the effectiveness of SAMP lyase as an indicator of breast and prostatic cancers.

Adenylosuccinate Lyase↗
PubMed1987

Transposon Tn5 mutagenesis of Brucella abortus.

We demonstrate that transposon-mediated mutagenesis can be used to construct mutations in the pathogen Brucella abortus. We have used both a plasmid and a bacteriophage to introduce either Tn5 or Tn5 lac into the Brucella chromosome. B. abortus is naturally sensitive to kanamycin. We have selected 22 independent kanamycin-resistant colonies in strain US-19 and 19 colonies in strain 2308. We have demonstrated by Southern hybridization that Tn5 was inserted into the chromosome.

Brucella abortus↗
PubMed1987

Does contingent reinforcement strengthen operant behavior?

In Experiment 1, pigeons were trained to peck keys with equal food-reinforcement schedules in components that ended with either noncontingent or contingent transitions to a third component with a five-fold richer schedule. Response rates were higher in the initial component with contingent transitions, but resistance to prefeeding or extinction was not consistently greater. Experiment 2 also included noncontingent or contingent transitions to a signaled period of nonreinforcement. There was no effect of the contingency on transitions to nonreinforcement, but the difference in response rates maintained by contingent versus noncontingent transitions to the richer schedule was replicated. In addition, response rates were higher in components that preceded nonreinforcement than in components that preceded the richer schedule. However, resistance to extinction was greater for noncontingent transitions to the richer schedule than to nonreinforcement, implicating stimulus-reinforcer relations in the determination of resistance to change. Resistance to change was also somewhat greater for noncontingent than for contingent transitions to the richer schedule. The latter result, together with the results of Experiment 1 and related research, suggests that response-contingent reinforcement does not increase resistance to change.

Journal Article↗
PubMed1986

Synthetic oligonucleotide tails inhibit in vitro and in vivo translation of SP6 transcripts of maize zein cDNA clones.

A maize zein cDNA clone was used to synthesize mRNA with the SP6 in vitro transcription system. Although we obtained full-length transcripts of the cDNA sequence, these were inefficient templates for protein synthesis. Removal of the 5' oligo(G) sequence that was synthesized during the cDNA cloning procedure allowed efficient translation of the mRNAs in a wheat germ cell-free protein synthesis system or in Xenopus laevis oocytes. The alteration in translational efficiency did not result from an interaction of the 5' oligo(G) homopolymer tail with the 3' oligo(C) sequence, as transcripts with or without the oligo(C) tail were translated similarly in both protein synthesis systems. Ribosome interaction with the mRNA may be affected due either to the secondary structure of the oligo(G) sequence itself, or an unusual secondary structure between the oligo(G) sequence and another region in the mRNA. Synthetic oligonucleotides at the 5' end of cloned cDNA sequences may generally be inhibitory for translation of mRNAs transcribed in vitro.

Animals↗
PubMed1986

Calmodulin synthesis and accumulation during oogenesis and maturation of Xenopus laevis oocytes.

The calmodulin levels in stage 6 Xenopus oocytes averaged 89 +/- 24 (SD) ng/oocyte and had largely accumulated by stage 3 of oogenesis. From stage 3 to early stage 6, calmodulin levels did not increase further. However, in large stage 6 oocytes (greater than 1.25 mm diam) calmodulin levels again rose to a level as high as 121 ng/oocyte. Calmodulin levels did not change during the maturation of stage 6 oocytes and the results of measurements on animal and vegetal oocyte halves from control and mature oocytes showed no evidence of a redistribution of calmodulin during maturation. Measurements of calmodulin synthesis in stages 1 and 2 oocytes, stage 4 oocytes, and stage 6 oocytes indicated that calmodulin was being synthesized continuously during oogenesis and that the rate of synthesis increased during oogenesis. In stage 1 and 2 oocytes (combined), the synthesis rate was 3.5 pg/hr/oocyte; in stage 4 oocytes it was 48 pg/hr/oocyte, and in large stage 6 oocytes the rate had increased to 160 pg/hr/oocyte. These changes in the rates of synthesis were discussed as they relate to the pattern of calmodulin accumulation during oogenesis.

Animals↗
PubMed1986

Idiopathic periodic hypothermia and bizarre behaviour in the presence of occult syringomyelia.

Overt psychological, neurological and haematological abnormalities were present in a 35 year old Jamaican female diagnosed as having idiopathic periodic hypothermia. Although symptoms and signs were ameliorated by warming, no long term satisfactory therapeutic measure was identified. Despite extensive clinical and subsequently histological investigation no cause for the hypothermia was found although she had clinically unsuspected cervical syringomyelia.

Adult↗
PubMed1986

Comparison of lung sounds and gas trapping in the study of airway mechanics.

We have previously shown that gas is trapped in isolated animal lungs and have proposed that this gas-trapping process is related to meniscus formation in the small airways of the lung. The purpose of this investigation was to compare how the lung sound-generation process and the gas-trapping process are related to airway mechanics and each other. Rats were anesthetized, the heart and lungs were removed en bloc and placed in a liquid-filled plethysmograph. Lung sounds were recorded by using a microphone acoustically coupled to the tracheal cannula. The results show that discontinuous lung sounds in the form of crackles occur during lung inflation at the same time gas trapping takes place.

Animals↗
PubMed1985

A comparison of succinyladenylate lyase activity and serum sialic acid as markers of malignancy.

A comparison was made of succinyladenylate lyase (SAMP lyase), total serum sialic (TSA), and lipid soluble serum sialic acid (LSA) as early markers of malignancy in three experimentally induced rat tumor models. Elevation of SAMP lyase in 3'-methyl-dimethylaminoazobenzene-induced hepatic tumors at 2 weeks corresponded with microscopic detection of preneoplastic lesions with elevation of LSA occurring 2 weeks later. Elevation of breast SAMP lyase concurred with macroscopic presence of dimethylbenzanthracene involved breast tumors with elevation of LSA occurring 12 weeks later. Neither colon SAMP lyase nor LSA increased in rats bearing colon tumors induced by dimethylhydrazine. The determination of TSA was not a reliable indicator of tumor presence for the three types of tumors investigated. Both SAMP lyase and LSA are very good early indicators of hepatic tumor with SAMP lyase an earlier indicator of breast tumor than LSA.

9,10-Dimethyl-1,2-benzanthracene↗
PubMed1985

Cyclic AMP levels during the maturation of Xenopus oocytes.

While several studies have suggested that the induction of oocyte maturation results from a transient decrease in cAMP levels, attempts to demonstrate such a change have led to inconsistent results with respect to whether or not a decrease occurs as well as timing of the decrease. In this report the results of experiments designed to demonstrate small changes in cAMP content in Xenopus laevis oocytes are presented and a statistically significant 20% decrease in cAMP content from between 2 and 50 min postprogesterone addition is found. The cAMP content subsequently rises to 12% higher than control levels and then becomes indistinguishable from control values for the remainder of the maturation period.

Animals↗
PubMed1985

Quantitative changes in protein synthesis during oogenesis in Xenopus laevis.

Protein synthesis rates in Xenopus laevis oocytes from stage 1 through stage 6 were measured. In addition, the translational efficiencies, total RNA contents, and percentages of ribosomes in polysomes in growing oocytes at several stages were determined. Stage 1 oocytes synthesize protein at a mean rate of 0.18 ng hr-1 while stage 6 oocytes make protein at a rate of 22.8 ng hr-1. Polysomes from growing and full-grown oocytes sedimented in a sucrose gradient with a peak value of 300 S, corresponding to a weight-average packing density of 10 ribosomes per mRNA. Ribosome transit times of endogenous mRNAs were essentially unchanged at all stages examined. While the oocyte's total ribosomal RNA content was observed to increase about 115-fold during oogenesis, the percentage of ribosomes in polysomes remained constant at approximately 2%. Taken together, the data suggest that the 127-fold increase in protein synthesis which occurs during Xenopus oogenesis involves the progressive recruitment onto polysomes of mRNA from the maternal stockpile.

Animals↗
PubMed1985

Growing Xenopus oocytes have spare translational capacity.

Previous studies have shown that exogenous mRNAs injected into full-grown (stage 6) Xenopus oocytes are translated only at the expense of endogenous messages; translational capacity is limited. In this report, we demonstrate that injection of globin mRNA into small, stage 4 oocytes results in an increase in total protein synthesis without a concomitant decrease in the translation of endogenous mRNAs. The absence of competition with endogenous messages in stage 4 oocytes, injected with globin mRNA, compared with stage 6 oocytes, was not due to differential turnover of the injected mRNA. Hybridization of RNA from mRNA-injected oocytes at both stages revealed that similar amounts of globin mRNA were present. These results are interpreted to mean that protein synthesis in growing oocytes is limited by the availability of mRNA and not components of the translational machinery. This conclusion, however, does not apply to all mRNA classes. The capacity of stage 4 oocytes to translate a mRNA (zein) on membrane-bound polysomes is as restricted as reported previously for stage 6 oocytes. This result suggests that putative membrane binding sites or rough endoplasmic reticulum content are limited in oocytes at both stages. The possible role of association of injected mRNA with endogenous proteins that prevent translation is discussed.

Animals↗