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J R Small

Publications and source records attributed to J R Small.

24 records · Page 2Linked to original sources
PubMed1990

A fluorescence study of changes in noradrenergic sympathetic fibres in experimental peripheral nerve neuromas.

Experimental neuromas were produced in rats by sciatic nerve section and avulsion of the distal stumps. At intervals varying from 3 days to 8 weeks after nerve section, the developing neuromas were resected and processed for noradrenaline (NA) fluorescence microscopy by the sucrose-phosphate-glyoxylic acid (SPG) method. From serial longitudinal sections through the neuromas and the nerve proximally, counts of noradrenergic sympathetic axons were made, together with qualitative observations of axon sprouting and NA content. By 3 days after nerve section there was a massive sprouting of sympathetic axons, with increased NA content, particularly towards the distal tip of the neuroma. Axon counts remained high 1 week following section then fell to below normal levels at 2 weeks, returning towards normal 8 weeks after nerve section. These results are discussed in relation to the known pathophysiological interaction between sympathetic efferent and sensory afferent fibres, which develops in neuromas following nerve section.

Adrenergic Fibers↗
PubMed1989

The matrix method of metabolic control analysis: its validity for complex pathway structures.

The sensitivities of the variables of a metabolic system (such as fluxes and concentrations) to variations in enzyme concentration are expressed in metabolic control analysis as control coefficients. The matrix method is a system of writing matrix equations that generate expressions for the control coefficients in terms of the characteristics of the components (principally the enzymes). Previously, the matrix method has been considered in terms of simple pathway structures; here we justify its applicability to complex pathways, such as those with multiple branches. It is shown that this requires modification of the branch point relationship to take account of changes of flux along the limbs of the branch and of stoichiometric factors. The method of deriving the flux control coefficients with respect to different fluxes in the system is extended to cope with these circumstances.

Animals↗
PubMed1987

Metabolic control and its analysis. Extensions to the theory and matrix method.

The matrix algebra procedure for determining the flux control coefficients of enzymes in metabolic pathways has been extended to allow determination of the concentration control coefficients. Although it is shown that the procedure is essentially unchanged in most cases, the presence of moiety-conserved cycles in a pathway places additional limitations on the form of the equations that can be used in the matrix formulation for concentration control coefficients. In the case of branched pathways, a new coefficient has been defined, the branch distribution control coefficient, which can be obtained via the matrix procedure. Thus a single matrix equation permits calculation or algebraic evaluation of the control coefficients for flux, concentration and distribution of flux at branches, so that the complete response of a pathway to alteration of enzyme content, or to modulation by an effector, can be determined. The relationships have been determined between flux control coefficients in isolated sections of metabolic pathways and the coefficients for the same enzymes when part of a larger metabolic system. It is shown that the control analysis of the isolated system provides useful information towards determining the control properties of the extended system.

Enzymes↗
PubMed1987

The development of Schmidt-Lanterman incisures: an electron microscope study.

The development of Schmidt-Lanterman incisures was investigated in the rat sural nerve during an active phase of postnatal myelination (5-21 days post partum). Two distinct populations of incisures were recognised and the following nomenclature for their developmental stages is proposed. Primary incisures which appear ab initio in myelination and always extend across the whole radial thickness of the myelin sheath but initially around only part of its circumference. Consequently they appear in transverse section as sectoral incisures (occupying less than half the circumference) and in longitudinal section as asymmetric incisures (involving one side only of the myelin sheath). Secondary incisures appear later, in regions of a compact myelin sheath, initially traversing only part of its radial thickness but commonly occupying its whole circumference. Thus they usually appear in transverse section as circumferential incisures and in longitudinal section as symmetric incisures (involving both sides of the myelin sheath). Less commonly secondary incisures may form in a sector of the myelin sheath but still in regions of compact myelin and thus appear asymmetric in longitudinal section and sectoral in transverse section. Secondary incisures appear mainly adaxonally in the earlier stages examined and mainly abaxonally in the later stages. The maturation of primary and secondary incisures into the radially and circumferentially complete incisure characteristic of the mature myelinated nerve fibre is described. The above mechanisms of incisural formation are contrasted with mechanisms previously suggested to occur during normal development and remyelination and related to the plasticity and ultrastructure of the myelin sheath.

Animals↗
PubMed1986

Fat synthesis in adipose tissue. An examination of stoichiometric constraints.

The requirement for net balance of synthesis, degradation and transport for all intermediates in the pathways from glucose to fat imposes constraints on the balance of fluxes between different pathways. Linear programming has been used to examine the interactions between these constraints on metabolism in adipocytes and the requirement for efficiency in the conversion of glucose into fat. The circumstances under which excessive ATP synthesis would accompany this conversion have been investigated.

Adipose Tissue↗