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Biomedical subjects

D Wise

Publications and source records attributed to D Wise.

At least 19 recordsLinked to original sources
PubMed2000

Influence of glial growth factor and Schwann cells in a bioresorbable guidance channel on peripheral nerve regeneration.

Using an established rat peripheral nerve regeneration model, we investigated the role of glial growth factor (GGF) in nerve regeneration in combination with a novel bioresorbable poly(lactic-co-glycolic) acid (PLGA) guide in vivo. Schwann cells, established from a 1-cm segment of excised rat sciatic nerve, were isolated and seeded onto nerve guides with or without GGF (n = 24/group). Living nerve guides were re-established in these animals, and nerve regeneration was assessed over a period of 12 weeks. Histological studies revealed a reduction in the total axon count and the number of myelinated axons in the presence of exogenously added Schwann cells compared to saline controls. In contrast, the addition of GGF alone enhanced the total number of axons and significantly increased the number of blood vessels. Although combining GGF with Schwann cells negated the enhanced numbers of axons and blood vessels seen with GGF alone, this combination resulted in the highest myelination index and the fastest conduction velocities recorded. The PLGA guide material did not trigger any histologically detectable host response and was permissive for nerve regeneration in this animal model. The results from this study demonstrate the potential utility of this guide in vivo and establish a promotional role for GGF in nerve regeneration.

Animals↗
PubMed2000

The pattern of sex chromosome kinetochore phosphorylation during nonrandom segregation in a flea beetle.

In the flea beetle species, Alagoasa bicolor, males have two sex chromosomes, X and Y, each of which is larger than the rest of the genome combined. These large sex chromosomes do not pair at meiosis I, and are therefore not joined at metaphase I. Nevertheless, they always segregate from each other at anaphase I. As prometaphase I progresses, the unpaired X and Y undergo reorientation from a parallel to a linear configuration. Using 3F3/2, an antibody that detects the level of phosphorylation of a kinetochore protein or proteins, we have determined that this reorientation is not accompanied by a change in the level of phosphorylation of the kinetochores of either X or Y. This implies that: i) either the reorientation does not involve the loss or gain of kinetochore microtubules, or ii) if such loss or gain occurs, it does not effect a change in the tension placed on the nonrandomly segregating kinetochores, or iii) the sex chromosomes, as in some other species, have lost the ability to sense kinetochore tension changes. Evolution of nonrandom segregation may necessitate the inability of the participating chromosomes to affect the metaphase checkpoint.

Animals↗
PubMed2000

Behavior of sex chromosomes, autosomes, and the spindle during nonrandom segregation in a flea beetle.

We have analyzed autosome, sex chromosome, and spindle behavior in spermatocytes of the flea beetle, Alagoasa bicolor. In this species, males have very large X and Y chromosomes, which, although they are never physically connected, always segregate to opposite spindle poles at anaphase I, thus preserving the sex ratio in the next generation. We find that the sex chromosomes are partitioned to a peripheral spindle domain early in prometaphase I and that their segregation can be accounted for mainly by their reorientation from the parallel to the linear configuration, and little by chromosome-to-pole movement. Further, the behavior of the autosomes and that of the sex chromosomes seem to have little to do with each other. Spindle elongation is minimal; barely segregating the large sex chromosomes into the daughter cells at telophase I.

Animals↗
PubMed1999

Social Security, retirement incentives, and retirement behavior: an international perspective.

Escalating rates of early retirement are imposing fiscal pressure on retirement systems around the world. In some developed countries, the labor-force participation rates of men ages 60-64 have fallen by 75 percent over the last three decades. One explanation for this striking decline is social security program provisions which create disincentives to continued labor-force participation by older workers. There are substantial differences among developed nations in the labor-force participation of older workers. While two-thirds of 60-year-old American males are working, only one-quarter of men that age are working in Belgium. Over the entire 55-65 age range, 63 percent of American males are working, compared with only 40 percent of French males and 33 percent of Belgians males. There is strong evidence that the early retirement provisions of social security systems in developed countries determine the modal age of retirement. There is a strong relationship between early retirement ages and labor-force withdrawal rates; for example, in France, 60 percent of those working at the early entitlement age of 60 leave the labor force at that age. The core of this analysis is the construction of "implicit tax/subsidy rates" on additional work at older ages through each nation's social security system. These rates measure the change in a worker's retirement wealth entitlement from delaying retirement for one year, relative to the amount that would have been earned over that year. The U.S. Social Security system has an actuarial adjustment for delayed benefits claiming and other features that avoid financial incentives to leave the labor force at age 62 for a married worker, there is a slight disincentive to work for single workers and high wage earners. However, at ages 65 and older there is a stronger incentive to leave the labor force, with implicit tax rates on work of 19 percent for married workers and 33 percent for single workers. By comparison, other nations do not have actuarially fair adjustments, and as a result impose substantial taxes on additional work at older ages. In several countries, implicit tax rates on work at older ages approach or exceed 100 percent. This is because by delaying retirement, workers forgo benefits which often replace close to their full wage, in addition to having to pay the high payroll taxes required to finance generous social security benefits. There is a striking correlation across nations between high implicit tax rates on additional work and low labor-force participation rates among older workers. This suggests that social security program incentives are an important determinant of retirement. These findings have important policy implications for reforming social security programs in the United States and abroad. Policymakers must consider how program reforms will affect incentives for continued work at older ages.

Actuarial Analysis↗
PubMed1997

A positron emission tomographic study of impaired word recognition and phonological processing in dyslexic men.

BACKGROUND: Developmental dyslexia is characterized by impaired word recognition, which is thought to result from deficits in phonological processing. Improvements during the course of development are thought to disproportionately involve orthographic components of reading; phonological deficits persist into adulthood. OBJECTIVE: To localize the neural correlates of impaired word recognition and phonological processing in men with developmental dyslexia. METHODS: Regional cerebral blood flow was measured with oxygen 15 positron emission tomography in 17 men with dyslexia and in 14 matched controls during the performance of phonological and orthographic tasks--pronunciation (reading aloud) and lexical decision making--designed to activate posterior and anterior perisylvian cortices, respectively. RESULTS: Altered patterns of activation (reduced activation, unusual deactivation) were seen in dyslexic men in mid- to posterior temporal cortex bilaterally and in inferior parietal cortex, predominantly on the left, during both pronunciation and decision making. In contrast, dyslexic men demonstrated essentially normal activation of left inferior frontal cortex during both phonological and orthographic decision making. CONCLUSION: These, along with prior findings, are compatible with a hypothesis of bilateral involvement of posterior temporal and parietal cortices in dyslexia.

Adolescent↗
PubMed1996

Mitotic arrest in Ptk(2) cells induced by microinjection of a rabbit antiserum and affinity-purified antibodies against a 66-kDa PtK(2) cell polypeptide.

Cell division was arrested by injection of a preimmune rabbit serum, B-61, into PtK(2) cells during interphase and prometaphase. Identical results were obtained by injection of whole B-61 antiserum and of antibodies affinity-purified from the serum against a 66-kDa PtK(2) cell polypeptide. When injected into interphase cells, the antibodies arrested further development and cell division. When injected into prometaphase and metaphase cells, spindles shortened and poles moved together at a rate of 0.2-0.4 mu m/min, approximately half the rate of anaphase A chromosome movements in normally dividing PtK(2) cells. Chromosomes decondensed and cells did not reenter division. Both whole antisera and affinity-purified antibodies stained antigens diffusely localized throughout the cytoplasm in dividing and interphase cells. These results suggest that the 66-kDa antigen is a nonspindle protein that may regulate mitotic progression in PtK(2) cells.

Animals↗
PubMed1996

Evaluation of triple-quantum-filtered 23Na NMR in monitoring of Intracellular Na content in the perfused rat heart: comparison of intra- and extracellular transverse relaxation and spectral amplitudes.

Multiple-quantum filtered (MQF) NMR offers the possibility of monitoring intracellular (IC) Na content in the absence of shift reagents (SR), provided that (i) the contribution from IC Na to the MQF spectrum is substantial and responds to a change in IC Na content, and (ii) the amplitude of the extracellular (EC) MQF component remains constant during a change in IC Na content. The validity and basis for these conditions were examined in isolated perfused rat hearts using SR-aided and SR-free triple-quantum filtered (TQF) 23NaNMR. Despite a myocardial Na content that was only approximately 1/70 that of EC Na. IC Na contributed to over 25% of the total TQF spectrum acquired in the absence of SR. Transverse relaxation times (T2) were approximately twice as long for EC compared to IC Na, despite SR-induced relaxation of T2 for the former pool. However, the efficiency of generation of the TQF signal was similar for IC and EC Na, indicating that a much greater percentage of IC relative to EC Na exhibits TQ coherence. During constant perfusion with ouabain (0.2 mM for 25 min) or with a hypoxic and aglycemic solution (50 min), the amplitude of the IC TQF spectrum increased by approximately 330% and -280%, respectively. In contrast, the amplitude of the EC TQF spectra remained essentially constant for both interventions. The amplitude for IC Na increased approximately 250% relative to baseline during no-flow ischemia (60 min), whereas the amplitude of the EC TQF spectra decreased by approximately 33% before stabilizing. In SR-free experiments, the TQF spectral amplitude increased approximately 2-fold during the constant perfusion interventions, but did not change significantly during no-flow ischemia. These data suggest that the change in the TQF spectral amplitude during constant perfusion interventions is from IC Na, and that TQF techniques in the absence of SR may be useful in monitoring IC Na during these interventions. The fall in the amplitude of the EC TQF spectral amplitude during no-flow ischemia complicates the use of TQF techniques without SR during this intervention.

Animals↗