PubMed Health⌕ Search

Biomedical subjects

N Stephens

Publications and source records attributed to N Stephens.

36 records · Page 2Linked to original sources
PubMed1987

Reformation of the pattern of neuromuscular connections in the regenerated axolotl hindlimb.

Retrograde neuronal tracing with horseradish peroxidase (HRP) was used to determine the position in the spinal cord of motor neurone pools innervating muscles in the regenerated axolotl hindlimb. This method allows a detailed analysis of the accuracy of reformation of neuromuscular connections. The results show that regenerated distal limb muscles are reinnervated by motor neurones in the same region of the cord as those that innervate normal control distal limb muscles but that proximal muscles are innervated by a mixture of motor neurones in a normal position and motor neurones in a region of the spinal cord that normally supplies innervation to distal limb muscles. This difference between the reinnervation of proximal and distal limb muscles suggests that axons destined for proximal muscles may not enter distal limb territory during reinnervation of the regenerated limb.

Ambystoma↗
PubMed1986

Marketing to older American consumers.

Older adults are examined as a potential market for American businesses. Data indicate that in terms of size and income, senior citizens comprise a substantial buying group. Their buying styles, product and service needs, and shopping behavior are shown to vary from those of younger adults and, in fact, vary substantially within the older adult population. Differences are speculated to be the result not only of age influence, but also of cohort and period influences. Strategies for successful marketing are suggested. These strategies relate directly to the identified characteristics of older adults.

Advertising↗
PubMed1985

A horseradish peroxidase study of motorneuron pools of the forelimb and hindlimb musculature of the axolotl.

Motorneuron pools innervating axolotl limb muscles have been investigated by using the retrograde neuronal tracer horseradish peroxidase. Four muscles in the forelimb (biceps, anconeus, flexor digitorum and extensor digitorum) and four functionally equivalent muscles in the hindlimb (puboischiotibialis, iliotibialis, flexor digitorum and extensor digitorum) were studied. Motorneuron pools were characterized by using four criteria: position in the rostrocaudal axis; position of the median in the rostrocaudal axis; number of labelled cells; position of cells in the transverse plane of the spinal cord. Each pool was uniquely defined by the four characteristics, although overlap was found between pools. Two types of motorneuron were found in each pool, distinguished on the basis of size, shape and position in the spinal cord. The first type constituted the majority of cells in a pool, and occupied different positions in the transverse plane for each muscle. The second type was less common and always occupied a characteristic medial ventral position. These data will allow an assay of correct or incorrect innervation in experiments on the regeneration of specific neuromuscular connections in these animals.

Ambystoma↗
PubMed1985

Motorneuron pools innervating muscles in vitamin A-induced proximal-distal duplicate limbs in the axolotl.

Serially duplicated limbs containing two sets of proximal muscles were created in axolotls by vitamin A treatment. The innervation of three replicated proximal muscles was studied by using retrograde transport of horseradish peroxidase. These were the forelimb muscles biceps (seven cases) and anconeus (five cases) and the hindlimb muscle puboischiotibialis (five cases). In two cases (both of anconeus) innervation was from a correct motorneuron pool. In the other 15 cases the innervation was from an incorrect, distal limb muscle, motorneuron pool. These results are interpreted as evidence against long range signals between nerve and muscle controlling specific nerve regeneration. However, the data are compatible with models of axonal guidance that use local pathway cues.

Ambystoma↗
PubMed1983

Quantitative analysis of ether-linked lipids as alkyl- and alk-1-enyl-glycerol benzoates by high-performance liquid chromatography.

Methodology for the quantitative and qualitative analyses of alkyl- and alk-l-enyl-glycerols derived by Vitride reduction of ether-linked glycerolipids in the presence of an internal standard was developed. The procedure involved preparation of benzoate derivatives that were subsequently analyzed by high-performance liquid chromatography with detection at 228 nm. Separation of the glycerol ether dibenzoates on a C18 reverse-phase column allowed for the simultaneous quantitation and the determination of chain length of both alkyl- and alk-l-enyl-glycerols in a single chromatographic run of less than 15 min. The method was accurate (less than 10% error), reproducible, and sensitive (less than 1 microgram per component). Application of the method to the analysis of phospholipids from L-M cells grown in the presence and absence of elaidic acid demonstrated that the cells incorporated a portion of the trans acid supplement (presumably via the fatty alcohol) into the side chains of both alkyl- and alk-l-enyl-glycerol-containing phosphatides.

Animals↗
PubMed1983

Airway smooth muscle mechanics: reduced activation and relaxation.

Reduced activation of skeletal muscle fibers at below-optimal lengths has been reported before. We studied tracheal smooth muscle (TSM) as a model of airway smooth muscle to see whether such a phenomenon existed in smooth muscle also; we found that active length-tension curves at normal and raised Ca2+ concentrations were significantly different. This indicated reduced activation of the TSM at below-optimal lengths. This reduction was in addition to that arising from the length-tension effect. We also studied the mechanics of relaxation in TSM and noted that in afterloaded isotonic tension records the time course of TSM relaxation appeared to closely follow that of the isometric contraction at all loads. In this it differed markedly from relaxation in skeletal muscle where the time courses of relaxation at different loads differed from each other and from that of the isometric muscle.

Animals↗
PubMed1982

The modification of lipid composition in L-M cultured cells supplemented with elaidate. Increased formation of fatty alcohols.

Supplementation of culture medium with elaidic acid (40 micrograms/ml) resulted in the incorporation of this acid into 50% of the acyl groups of phospholipids in L-M cells; elaidate was esterified at both the sn-1 and the sn-2 positions of phosphatidylcholine and phosphatidylethanolamine. In addition, elaidate supplementation of L-M cells induces the accumulation of free fatty alcohols, alkyldiacylglycerols and wax esters/cholesterol esters. The concentration of intracellular free fatty alcohols increased as a function of the concentration of elaidic acid in the growth medium and the duration of exposure. However, the concentration of alcohol-containing lipids, total alkyl and alk-1-enyl lipids, was only slightly decreased. This decrease was much less than the increase in the level of free fatty alcohols. Therefore, we conclude that when elaidic acid is supplemented to L-M cells in culture, a net increase in the production of free fatty alcohols occurs.

Animals↗
PubMed1980

Activities of enzymes involved in the metabolism of ether-linked lipids in normal and neoplastic tissues of rat.

We have compared the activities of three enzymes (acyl-CoA reductase, fatty alcohol:NAD+ oxidoreductase, and alkyl synthase) involved in the metabolism of ether lipids in rat liver and two tumors that contained various levels of ether lipids. The activity of fatty alcohol:NAD+ oxidoreductasee was high and the activities of acyl-CoA reductase and alkyldihydroxyacetone-P synthase were low in liver, which has low amounts of ether glycerolipids. On the other hand in Fischer R-3259 sarcoma, where high concentrations of ether-linked lipids were present, the reverse pattern was observed. In Morris hepatomas 5123C, with an intermediate value of ether lipids, the activities of all three enzymes ranged between that found in liver and Fischer sarcomas.

Acetone↗
PubMed1979

Sex-role identity, parental identification, and self-concept of adolescent daughters from mother-absent, father-absent, and intact families.

The effects of divorce and resulting paternal or maternal absence on the sex-role identity, parental identification, and self-concept of 39 adolescent daughters were investigated. Differences among the mean sex-role identity scores and self-concept scores of the daughters of mother-absent (MA), father-absent (FA), and intact (IF) families were not found. Parental identification with the mother and the father in the IF group was greater than identification with the mother in the FA group. Fathers in the MA and IF groups did not differ on the sex-role identity measure; FA and IF mothers also did not differ on this measure. The sex-role identity scores of the daughters were not related to the sex-role identity scores of either their mothers or fathers. The results revealed no negative consequences of the father receiving custody of an adolescent daughter and, therefore, suggest that fathers of adolescent daughters should be given greater consideration in custody cases.

Adolescent↗
PubMed1977

Evidence for participation of cytochrome b5 in microsomal delta-6 desaturation of fatty acids.

The delta-6 desaturation of linoleic acid to gamma-linolenic acid and oleic acid to 6,9-octadecadienoic acid by rat liver microsomes was investigated. Using a specific antibody prepared against purified rat liver cytochrome b5, we demonstrated that cytochrome b5 participated in delta-6 desaturation of both fatty acids. The reaction products were identified as their methyl ester derivatives by argentation thin-layer chromatography, gas-liquid chromatography, and reductive ozonolysis followed by gas-liquid chromatography.

Animals↗
PubMed1971

On the analysis of long-chain alkane diols and glycerol ehters in biochemical studies.

The chromatographic behavior of 1,2-, 1,3-, 1,4-, and 1,12-long-chain alkane diols and 1-O-alkylglycerols and their derivatives has been compared. Thin-layer chromatography on Silica Gel G gives poor separations of the 1,2-, 1,3-, and 1,4-alkane diols, O-alkylglycerols, and some of their isopropylidene derivatives. However, gas-liquid chromatography on 10% EGSS-X (coated on 100-120 mesh Gas-Chrom P) resolves the isopropylidenes of the alkane diols and O-alkylglycerols. We also document the formation of 1,3-alkane diols (after LiAlH(4) reduction) from 1-(14)C-labeled fatty acids incubated with mitochondrial fractions from heart and liver of rats. The labeled 1,3-alkane diol was identified by gas-liquid chromatography of its isopropylidene derivative and by its behavior after periodate oxidation. These results serve to caution investigators in the glycerol ether field against incorrect interpretation of data obtained on the incorporation of labeled fatty acids into alkyl ether bonds of glycerolipids. The methodology described points out a technique for distinguishing several types of alkane diols from O-alkylglycerols.

Aluminum↗
PubMedDate not supplied

Neurotransmission in human resistance arteries: contribution of alpha 1- and alpha 2-adrenoceptors but not P 2-purinoceptors.

The contribution of postjunctional alpha 1- and alpha 2-adrenoceptors and P2-purinoceptors to the neuroeffector response was examined in isolated segments of human subcutaneous resistance arteries. Electrical field stimulation (EFS, 20 V, 0.2 ms, 1-25 Hz) elicited a maximum contractile response which was 38.2 +/- 1.6% of that elicited by exogenously applied (5 microM) noradrenaline (n = 56). Tetrodotoxin (1 microM), used to inhibit neurotransmission, reduced the electrically evoked response to 24.7 +/- 4.4% (n = 10) of the control response. The alpha 1-adrenoceptor antagonist prazosin (1 microM) reduced the maximum EFS contractile response to 64.8 +/- 5.5% of the control response (n = 17). Application of the alpha 2-adrenoceptor antagonist yohimbine (0.1 microM) reduced the maximum EFS response to 68.2 +/- 8.2% of the control response (n = 9). In the presence of prazosin plus yohimbine at the above-mentioned concentrations the maximum response to EFS was reduced to 47.6 +/- 6.7% (n = 11). Responses following alpha-blockade were not statistically different from those in the presence of tetrodotoxin, but the mean responses indicate that a non-adrenergic component to the EFS response cannot be discounted. Desensitisation of P 2-purinoceptors with alpha, beta-methylene ATP had no effect on responses to EFS; therefore under the conditions studied these receptors do not appear to be involved in neurotransmission. These results confirm the presence of postjunctional alpha 1- and alpha 2-adrenoceptors in human resistance arteries and for the first time demonstrate that the postjunctional alpha 2-adrenoceptor is important in modulating vascular responses elicited by intramural sympathetic nerve fibres.

Adrenergic alpha-Antagonists↗
PubMedDate not supplied

Time to work together.

Explore the source record for details and available documents.

Hospital Departments↗