The impact of poverty on educational outcomes for children

Over the past decade, the unfortunate reality is that the income gap has widened between Canadian families. Educational outcomes are one of the key areas influenced by family incomes. Children from low-income families often start school already behind their peers who come from more affluent families, as shown in measures of school readiness. The incidence, depth, duration and timing of poverty all influence a child’s educational attainment, along with community characteristics and social networks. However, both Canadian and international interventions have shown that the effects of poverty can be reduced using sustainable interventions. Paediatricians and family doctors have many opportunities to influence readiness for school and educational success in primary care settings.     

Muscle fiber types and function.

A major recent advance in the field of muscle fiber types has been the discovery that myogenic factors regulate fiber phenotypic properties. Myogenic influences occur in limb and trunk (somitic) muscle, but are particularly strong in jaw-closing muscles and extraocular muscles that express some unique myofibrillar proteins. In somitic muscles, a variant of fast fiber has been discovered, making four types of fibers: I, IIA, IIX, and IIB. These fibers express different isoforms of myofibrillar and other proteins. The speed and power of the four types of fibers are distinct and are controlled principally by their myosin heavy chains, which modulate the two regulatory steps in the crossbridge cycle, one controlling the rate of development of force, the other controlling the maximal velocity of shortening. Fast fibers have a higher threshold for Ca(2+)-activated force and a steeper force-pCa relation than do slow fibers. This difference is largely attributable to the cooperativity in the attachment of crossbridges and to the difference in Ca2+ binding capacity of their troponin C. Ca2+ initiates force development in muscle by increasing the rate of attachment of crossbridges. The phosphorylation of myosin light chain enhances this action. This effect of phosphorylation underlies the phenomenon of posttetanic potentiation of the isometric twitch in fast fibers.     

Contraceptive potential of a mifepristone-nomegestrol acetate sequential regimen in women

The effectiveness of a sequential regimen consisting of mifepristone, 10 mg/day for 15 days, followed by nomegestrol acetate (NOMA), 5 mg/day for the next 13 days, for inhibiting ovulation and maintaining regular bleeding cycles was assessed in 10 surgically sterilized volunteers who were followed for one pretreatment and three treated cycles. Hormonal determinations in blood and urine, ovarian ultrasonography, bleeding records in all cycles and an endometrial biopsy taken on day 22-25 of the third treatment cycle were used to monitor the effects of treatment. During treatment, 24 monophasic (no sustained progesterone rise above 12 nmol/l) and six biphasic cycles were recorded. Nine follicular ruptures were detected echographically in these 30 treated cycles, five of which occurred in monophasic cycles. All follicular ruptures occurred on days 1-7 of NOMA treatment. Echographic and endocrine features of ovulatory cycles were both present in only four treated cycles (13.3%). Development of a secretory endometrium was achieved in all cases, but it was always irregular. Regular withdrawal bleeding occurred in all subjects and no adverse reactions were recorded. The ovarian and endometrial effects of this regimen justify testing its contraceptive effectiveness in phase 2 clinical trials.      

A protein kinase A-dependent molecular switch in synapsins regulates neurite outgrowth

Cyclic AMP (cAMP) promotes neurite outgrowth in a variety of neuronal cell lines through the activation of protein kinase A (PKA). We show here, using both Xenopus laevis embryonic neuronal culture and intact X. laevis embryos, that the nerve growth-promoting action of cAMP/PKA is mediated in part by the phosphorylation of synapsins at a single amino acid residue. Expression of a mutated form of synapsin that prevents phosphorylation at this site, or introduction of phospho-specific antibodies directed against this site, decreased basal and dibutyryl cAMP-stimulated neurite outgrowth. Expression of a mutation mimicking constitutive phosphorylation at this site increased neurite outgrowth, both under basal conditions and in the presence of a PKA inhibitor. These results provide a potential molecular approach for stimulating neuron regeneration, after injury and in neurodegenerative diseases.     

Reliability of the acetabular teardrop as a landmark

Summary This study investigated the effect of tilt and observer reliability on radiographic measurements of the position of a prosthetic acetabular cup in seven dry bone pelves using the teardrop as a landmark. Coronal or sagittal tilt of more than five degrees was easily recognisable and there was effectively no observer variation in the measurements up to this limit. In addition, 90 out of 100 randomly selected antero-posterior pelvic radiographs from an outpatient department were not significantly rotated and 93 demonstrated a clearly defined teardrop. Measurements about the teardrop on routine radiographs are therefore sufficiently accurate to allow assessment of prosthetic position.

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La valeur du sourcil cotyloidien comme repère d'analyse radiologique

Résumé Cette étude, conduite sur 7 bassins secs, apprécie l'effet de l'inclinaison du bassin sur la qualité de l'analyse radiographique de la position d'une cupule prothétique de hanche en utilisant le sourcil cotyloïdien comme repère. Une inclinaison du bassin dans les plans coronal et sagittal est aisément détectable et il n'existe pas de variation d'analyse entre les différents observateurs en dessous de 5° d'inclinaison. De plus, sur 100 radiographies antéro-postérieures de bassin choisies au hasard dans les dossiers de consultation, 90 avaient été réalisées sans incidence particulièrement adaptée et l'on pouvait repérer facilement le sourcil sur 93% d'entre elles. Les mesures faites sur des radios de routine sont donc suffisamment précises pour permettre l'évaluation de la position d'une prothèse à partir du sourcil cotyloïdien.

     

Analysis of myocilin mutations in 1703 glaucoma patients from five different populations

A glaucoma locus, GLC1A, was identified previously on chromosome 1q. A gene within this locus (encoding the protein myocilin) subsequently was shown to harbor mutations in 2-4% of primary open angle glaucoma patients. A total of 1703 patients was screened from five different populations representing three racial groups. There were 1284 patients from primarily Caucasian populations in Iowa (727), Australia (390) and Canada (167). A group of 312 African American patients was from New York City and 107 Asian patients from Japan. Overall, 61 different myocilin sequence variations were identified. Of the 61 variations, 21 were judged to be probable disease-causing mutations. The number of probands found to harbor such mutations in each population was: Iowa 31/727 (4.3%), African Americans from New York City 8/312 (2.6%), Japan 3/107 (2.8%), Canada 5/167 (3.0%), Australia 11/390 (2.8%) and overall 58/1703 (3. 4%). Overall, 16 (76%) of 21 mutations were found in only one population. The most common mutation observed, Gln368Stop, was found in 27/1703 (1.6%) glaucoma probands and was found at least once in all groups except the Japanese. Studies of genetic markers flanking the myocilin gene suggest that most cases of the Gln368Stop mutations are descended from a common founder. Although the specific mutations found in each of the five populations were different, the overall frequency of myocilin mutations was similar ( approximately 2-4%) in all populations, suggesting that the increased rate of glaucoma in African Americans is not due to a higher prevalence of myocilin mutations.     

Force: velocity pproperties of kitten muscles

1. The characteristics of isometric contractions and force:velocity properties of the extensor digitorum longus (EDL) and soleus (SOL) muscles of neonatal kittens were determined in situ.

2. The mean contraction time is 51 msec for EDL and 70 msec for SOL and the half-relaxation time is 51 msec for EDL and 109 msec for SOL.

3. The average maximum isometric tetanic tension per unit cross-sectional area of muscle is 1·27 kg/cm² for EDL and 1·17 kg/cm² for SOL.

4. The average twitch:tetanus ratio is 0·28 for EDL and 0·119 for SOL; the low value for SOL was found for both indirect and direct stimulation.

5. The average maximum speed of shortening of a sarcomere is 22·8 μ/sec for EDL and 12·7 μ/sec for SOL.

6. These properties of neonatal muscles are compared with those of adult cat muscles and discussed in connexion with differentiation of mammalian muscles into fast and slow types.