Biomedical subjects

F M Butler

Publications and source records attributed to F M Butler.

5 recordsLinked to original sources

PubMed2001

Teaching mathematics to students with mild-to-moderate mental retardation: a review of the literature.

A systematic search of the literature from 1989 through 1998 was conducted to identify and analyze mathematics interventions for students with mild-to-moderate mental retardation. We found that the focus of instruction has shifted from basic skills instruction to computation and problem-solving instruction. Techniques such as constant-time delay, peer tutoring, time trials, and direct instruction proved beneficial in improving mathematics skills. Further, students with mental retardation learned to employ cognitive strategies successfully when these techniques were included. Although this information is promising, we recommend that further studies be conducted in secondary schools and in inclusive settings.

Adolescent↗

PubMed1994

Exercise studies with elderly volunteers.

The practicalities of conducting exercise studies with elderly and very elderly people have not been well described. In order to help others plan and perform such studies we describe our experience of recruiting volunteers, applying selection criteria, measuring strength, power, cardiorespiratory responses, and potentially related functional abilities. Exclusion criteria are offered, for safety and to characterize subjects as free of disease which might alter their exercise performance. International agreement on these, or similar, criteria would be valuable. The budget must be adequate for prolonged recruitment before a study and for the liberal use of taxis during it. With healthy subjects in their seventies, the coefficients of variation (CV) for repeated measurements of strength and power were: handgrip 3%, isometric knee extension 6%, isometric elbow flexion 6%, and lower limb extensor power 9%. CV for isometric knee extension by healthy subjects in their eighties was 4%. Treadmill ergometry is more time-consuming than with younger subjects. During progressive treadmill tests, the heart rate interpolated to oxygen consumptions of 10 and 15 ml.kg-1.min-1 had CV = 4% and 7%, respectively.

Aged↗

PubMed1987

Magnesium ion effects on microtubule nucleation in vitro.

Much interest has currently been attached to the length distribution of microtubules polymerized in vitro and the related question of their possible 'dynamic instability'. Fundamental to this question is the mechanism of microtubule nucleation, which controls the rates of assembly and disassembly of microtubule protein in vitro. These kinetics are affected by a number of factors, including both the guanine nucleotides, GTP and GDP, and magnesium ion. Mg2+ exerts complex effects, as indicated by the existence of an optimal Mg2+ concentration for the maximum assembly rate of microtubule protein, and we investigate these effects in this report. At [Mg2+] greater than 0.5 mM, the characteristic lag-phase is substantially increased and the rate of assembly is greatly reduced without affecting the critical concentration significantly. We show that increasing [Mg2+] has two effects on the assembly process: nucleation is less efficient and the intrinsic rate constant for the elongation reaction is reduced. Lowering [Mg2+] (less than 0.5 mM) also inhibits nucleation. These effects of varying [Mg2+] can be explained predominantly in terms of enhanced stability of the microtubule-associated protein-containing oligomeric species present in the microtubule protein preparation. [Mg2+] is thus found to be a further important factor in microtubule nucleation, and hence, in determining length distributions in assembling microtubules.

Animals↗

PubMed1986

Control of nucleation in microtubule self-assembly.

The inhibition of the rate and amplitude of assembly of microtubule protein at low GTP concentration is shown by measurement of microtubule length distributions to be due to the suppression of microtubule nucleation. This inhibitory effect is enhanced by GDP added before assembly, but can be overcome by a number of molecules such as pyrophosphate or ADP. The selective inhibition of nucleation by GDP in vitro, which occurs in addition to inhibition of elongation, could provide a mechanism for the control of spontaneous microtubule nucleation in vivo.

Animals↗

PubMed1985

The assembly of microtubule protein in vitro. The kinetic role in microtubule elongation of oligomeric fragments containing microtubule-associated proteins.

The kinetics of assembly were studied for bovine and pig microtubule protein in vitro over a range of conditions of pH, temperature, nucleotide and protein concentration. The kinetics are in general biphasic with two major processes of similar amplitude but separated in rate by one order of magnitude. Rates and amplitudes are complex functions of solution conditions. The rates of the fast phase and the slow phase attain limiting values as a function of increasing protein concentration, and are more stringently limited at pH 6.5 than pH 6.95. Such behaviour indicates that mechanisms other than the condensation polymerization of tubulin dimer become rate-limiting at higher protein concentration. The constancy of the wavelength-dependence of light-scattering and ultrastructural criteria indicate that microtubules of normal morphology are formed in both phases of the assembly process. Electrophoretic analysis of assembling microtubule protein shows that MAP- (microtubule-associated-protein-)rich microtubules are formed during the fast phase. The rate of dissociation of oligomeric species on dilution of microtubule protein closely parallels the fast-phase rate in magnitude and temperature-dependence. We propose that the rate of this process constitutes an upper limit to the rate of the fast phase of assembly. The kinetics of redistribution of MAPs from MAP-rich microtubules may be a factor limiting the slow-phase rate. A working model is derived for the self-assembly of microtubule protein incorporating the dissociation and redistribution mechanisms that impose upper limits to the rates of assembly attainable by bimolecular addition reactions. Key roles are assigned to MAP-containing fragments in both phases of microtubule elongation. Variations in kinetic behaviour with solution conditions are inferred to derive from the nature and properties of fragments formed from oligomeric species after the rapid temperature jump. The model accounts for the limiting rate behaviour and indicates experimental criteria to be applied in evaluating the relative contributions of alternative pathways.

Animals↗