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81.
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83.
J S Taylor 《Development (Cambridge, England)》1990,108(1):147-158
The growth of optic axons towards experimentally rotated tecta has been studied. In stage 24/25 embryos, a piece of the dorsal neural tube, containing the dorsal midbrain rudiment, was rotated through 180 degrees. At later stages of development, the pathways of growing optic axons were investigated by labelling with either horseradish peroxidase or fluorescent dye. It is shown that retinal ganglion cell axons followed well-defined pathways, in spite of the abnormal structure of the brain, and were able to locate displaced tecta. This directed outgrowth of retinal axons in the optic tracts appears to be related either to the tectum or to some other component included in the graft operations. In tadpoles in which the midbrain rudiment was removed, optic axons still followed the normal course of the optic tract. This observation argues against long-range target attraction as being essential in guiding growing retinal axons towards the tectum. An alternative axon guidance mechanism, selective fasciculation, is discussed as a possible alternative to explain the directed axon outgrowth which occurs in both the normal and in these experimentally manipulated tadpoles. 相似文献
84.
R Taylor L Lovelock W M Tunbridge K G Alberti R G Brackenridge P Stephenson E Young 《BMJ (Clinical research ed.)》1990,301(6763):1243-1247
OBJECTIVE--To determine whether non-mydriatic Polaroid retinal photography was comparable to ophthalmoscopy with mydriasis in routine clinic screening for early, treatable diabetic retinopathy. DESIGN--Prospective study of ophthalmoscopic findings according to retinal camera screening and ophthalmoscopy and outcome of referral to ophthalmologist. SETTING--Outpatient diabetic clinics of three teaching hospitals and three district general hospitals. PATIENTS--2159 Adults selected randomly from the diabetic clinics, excluding only those registered as blind or those in wheelchairs and unable to enter the screening vehicle. MAIN OUTCOME MEASURES--Numbers of patients and eyes correctly identified by each technique as requiring referral with potentially treatable retinopathy (new vessel formation and maculopathy) and congruence in numbers of microaneurysms, haemorrhages, and exudates reported. RESULTS--Camera screening missed two cases of new vessel formation and did not identify a further 12 but indicated a need for referral. Ophthalmoscopy missed five cases of new vessel formation and indicated a need for referral in another four for other reasons. Maculopathy was reported in 147 eyes with camera screening alone and 95 eyes by ophthalmoscopy only (chi 2 = 11.2; p less than 0.001), in 66 and 29 of which respectively maculopathy was subsequently confirmed. Overall, 38 eyes received laser treatment for maculopathy after detection by camera screening compared with 17 after ophthalmoscopic detection (chi 2 = 8.0; p less than 0.01). Camera screening underestimated numbers of microaneurysms (chi 2 = 12.9; p less than 0.001) and haemorrhages (chi 2 = 7.4; p less than 0.01) and ophthalmoscopy underestimated hard exudates (chi 2 = 48.2; p less than 0.001). CONCLUSIONS--Non-mydriatic Polaroid retinal photography is at least as good as ophthalmoscopy with mydriasis in routine diabetic clinics in identifying new vessel formation and absence of retinopathy and is significantly better in detecting exudative maculopathy. 相似文献
85.
Phosphoinositide metabolism and the calcium response to concanavalin A in S49 T-lymphoma cells. A comparison with thymocytes. 下载免费PDF全文
Comparisons were made between transformed S49 T-lymphoma cells and normal murine thymocytes in their polyphosphoinositides, inositol polyphosphates and cytosolic free calcium concentrations ([Ca2+]i), and the effects of the T-cell mitogen concanavalin A (Con A) on these properties. 1. The ratios of the polyphosphoinositides to phosphatidylinositol in both exponential-phase S49 cells and mitogen-stimulated thymocytes (G1 phase) were greater than in quiescent (G0-phase) thymocytes. 2. In response to Con A, the amount of phosphatidylinositol 4,5-bisphosphate (PtdInsP2) in S49 cells decreased slightly (17% in 30 min), and this was sufficient to account for the small amounts of inositol phosphates that accumulated. In contrast, it has been shown previously that Con A stimulates a rapid resynthesis of PtdInsP2 in thymocytes and the amounts of inositol phosphates released rapidly exceed the steady-state amount of the PtdInsP2 precursor [Taylor, Metcalfe, Hesketh, Smith & Moore (1984) Nature (London) 312, 462-465]. 3. The [Ca2+]i did not differ significantly in S49 cells and thymocytes before the addition of Con A, and the increases in [Ca2+]i in response to Con A were similar in both types of cell. 4. The [Ca2+]i increase in response to Con A was inhibited by similar concentrations of intracellular cyclic AMP (2-10 microM) in S49 cells and thymocytes, suggesting that similar regulatory mechanisms act on this response in both types of cell. The data demonstrate that the basal [Ca2+]i and phosphoinositide metabolism is similar in both the normal cells and their transformed counterparts. In addition, they suggest that the activated Con A receptors generate very similar signals in the two cell types, and that any perturbations of primary signal transduction to the secondary phosphoinositide and [Ca2+]i responses in the S49 phenotype are quantitative rather than qualitative. 相似文献
86.
Synthesis of a trans-syn thymine dimer building block. Solid phase synthesis of CGTAT[t,s]TATGC. 总被引:5,自引:3,他引:2 下载免费PDF全文
The synthesis of a building block for the sequence specific introduction of the trans-syn thymine dimer into oligonucleotides via solid phase DNA synthesis technology is described. CGTAT[t,s]TATGC was synthesized in 48% overall yield by a partially automated procedure. The stepwise coupling yield for addition of the trans-syn thymine dimer building block was 58%. The dimer containing oligonucleotide was characterized by 500 MHz 1H COSY and NOESY spectroscopy and 202.5 MHz 31P NMR. The 1H chemical shifts for the trans-syn thymine dimer unit of the decamer were found to be quite similar to those found for the trans-syn thymine dimer of TpT. Upon photolysis at 254 nm, CGTAT[t,s]TATGC was converted to a major product which coeluted with authentic CGTATTATGC and a minor product which coeluted with authentic CGTAT[c,s]TATGC, further supporting the presence of an intact trans-syn thymine dimer unit. 相似文献
87.
Breakage of the T cell receptor α chain locus in non malignant clones from patients with ataxia telangiectasia 总被引:3,自引:0,他引:3
A. Heppell S. V. Butterworth R. J. Hollis A. A. Kennaugh D. W. Beatty A. M. R. Taylor 《Human genetics》1988,79(4):360-364
Summary Patients with ataxia telangiectasia (A-T) develop specific chromosome translocations, which may confer a proliferative advantage, resulting in the appearance of large clones in the peripheral blood lymphocytes. These lymphocytes are not malignant. Using in situ hybridisation techniques we have investigated a consistent 14q11 translocation break-point observed in a t(X;14)(q28;q11) translocation clone from each of two different patients and a t(14;14)(q11;q32) clone from a third patient. In all cases the chromosome translocation involved breakage within the chain locus of the T cell receptor (TCR), between the variable and constant regions, at 14q11. Chromosome rearrangement involving breakage within TCR can therefore precede the development of malignancy. Further chromosomal rearrangement may be required in these patients, for progression to the leukaemic state. 相似文献
88.
Synthesis and biological evaluation of pNPY fragments 总被引:3,自引:0,他引:3
W Danho J Triscari G Vincent T Nakajima J Taylor E T Kaiser 《International journal of peptide and protein research》1988,32(6):496-505
Peptide fragments of pNPY corresponding to the C-terminal segments (13-36) and (25-36), the N-terminal segments (1-12) and (1-24), the segments (6-14) and (7-20), which contain a putative beta-turn, and the internal segments (13-24) and (20-30) were synthesized using solid phase methodology. These fragments were assayed for NPY receptor binding activity in the rat hypothalamus membrane preparation, enhancement of food intake in the rat following ivt administration and inhibition of electrically stimulated muscle contraction in the rat vas deferens. Only the C-terminal fragment (13-36) retained some of the activities of pNPY, appearing to act as a weak agonist, having an additive effect with pNPY on the inhibition of muscle contraction and prolonging the duration of action of pNPY in the feeding assay. It also had considerable alpha-helical character, as did pNPY. None of the other peptide fragments had any agonist or antagonist activity. These results suggest that the expression of full biological NPY activity requires both the C- and the N-terminal segments as well as a putative amphiphilic alpha-helical segment (14-31). 相似文献
89.
Geraldine E. Oliva George W. Rutherford Moses Grossman Janet Shalwitz Abigail English Frances Taylor David Werdegar 《The Western journal of medicine》1988,148(5):586-589
Although adolescents account for only 0.4% of reported cases of the acquired immunodeficiency syndrome (AIDS) in the United States, they are sexually active and, therefore, at risk of acquiring human immunodeficiency virus (HIV) infection. To address issues of HIV control in adolescents, we developed guidelines that emphasize education and medical care and deemphasize antibody testing. For adolescents known to be infected with HIV, we recommend no restrictions on access to educational or treatment programs except when their health providers recommend such restrictions to protect them from exposure to opportunistic infections. For adolescents of unknown antibody status with a possible previous exposure to HIV, we recommend that as long as the incidence of HIV infection and clinical AIDS remains low, there should be no restrictions on residential placements and no routine antibody testing. 相似文献
90.