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Biomedical subjects

M E Burrows

Publications and source records attributed to M E Burrows.

7 recordsLinked to original sources
PubMed2006

Biometrical genetic analysis of luteovirus transmission in the aphid Schizaphis graminum.

The aphid Schizaphis graminum is an important vector of the viruses that cause barley yellow dwarf disease. We studied the genetic architecture of virus transmission by crossing a vector and a non-vector genotype of S. graminum. F1 and F2 hybrids were generated, and a modified line-cross biometrical analysis was performed on transmission phenotype of two of the viruses that cause barley yellow dwarf: Cereal yellow dwarf virus (CYDV)-RPV and Barley yellow dwarf virus (BYDV)-SGV. Our aims were to (1) determine to what extent differences in transmission ability between vectors and non-vectors is due to net additive or non-additive gene action, (2) estimate the number of loci that determine transmission ability and (3) examine the nature of genetic correlations between transmission of CYDV-RPV and BYDV-SGV. Only additive effects contributed significantly to divergence in transmission of both CYDV-RPV and BYDV-SGV. For each luteovirus, Castle-Wright's estimator for the number of effective factors segregating for transmission phenotype was less than one. Transmission of CYDV-RPV and BYDV-SGV was significantly correlated in the F2 generation, suggesting that there is a partial genetic overlap for transmission of these luteoviruses. Yet, 63% of the F2 genotypes transmitted CYDV-RPV and BYDV-SGV at significantly different rates. Our data suggest that in S. graminum, the transmission efficiency of both CYDV-RPV and BYDV-SGV is regulated by a major gene or set of tightly linked genes, and the transmission efficiency of each virus is influenced by a unique set of minor genes.

Animals↗
PubMed1983

Avian renal portal valve: a reexamination of its innervation.

The renal portal circulation of the avian kidney contains a unique smooth muscle valve that can direct blood flow from the posterior extremities to the central circulation or through the kidney. The neural control of the valve and adjacent venous tissue from Rhode Island Red roosters was characterized by measuring the isometric force developed following transmural nerve stimulation (TNS). During TNS, the valve relaxed while the iliac vein contracted. In the valve, a poststimulus contraction followed the relaxation. Propranolol and guanethidine abolished the TNS-induced relaxation of the valve, leaving a contraction that was increased by physostigmine and partially blocked by atropine or prazosin. In contrast, the TNS-induced contraction of the vein was blocked by guanethidine or prazosin. Measurement of choline acetyltransferase activity and norepinephrine content confirms that the valve is densely innervated with both cholinergic and adrenergic nerves. Thus the vein shows a predominantly adrenergic contractile response typical of most vascular smooth muscle, but the valve demonstrates a dual control, i.e., adrenergic nerves producing relaxation and cholinergic nerves causing contraction. Knowledge of the nature of neuronal control of the valve should aid in the design of experiments to determine its functional role.

Animals↗
PubMed1983

Arteriolar responses to elevation of venous and arterial pressures in cat mesentery.

These studies were undertaken to determine the importance of metabolic (flow-dependent) and myogenic (pressure-dependent) factors in the response of arterioles to changes in intravascular pressure. The response of 26 arterioles in the isolated cat mesentery to increased venous and arterial pressure was studied by measuring changes of arteriolar diameter, red blood cell velocity, and intravascular pressure. Circumferential wall tension and volume flow in the arterioles were calculated. The fraction of the arteriolar responses to intravascular pressure elevation that could be attributed only to a myogenic response in which wall tension is regulated varied from 20 to 56%, depending on the method of pressure elevation. The largest fraction of the response attributable to a myogenic mechanism (ignoring the contributions of flow) varied from 50 to 93%. The fraction of the responses attributable only to flow dependency varied from 0 to 23%, whereas the largest fraction attributable to this mechanism varied from 18 to 73%, depending on the method of pressure elevation. It is concluded that, in cat mesentery, both metabolic and myogenic mechanisms appear to contribute to local regulation of flow with elevation of intravascular pressure, but other factors cannot be excluded.

Animals↗
PubMed1981

Diameter, wall tension, and flow in mesenteric arterioles during autoregulation.

The effect of arterial pressure on vessel diameter, blood velocity, and intravascular pressure was examined in cat mesenteric arterioles in the arterial pressure range of 120--40 mmHg. Circumferential wall tension and volume flow in individual vessels were calculated. Twenty-nine arterioles with an average diameter of 25.1 micrometers were studied. Twenty-six reactive vessels dilated by an average of 6.5 micrometers with arterial pressure reduction, whereas three nonreactive arterioles narrowed by an average of 5.9 micrometers. When pressure was reduced, circumferential wall tension in reactive arterioles tended to be maintained, whereas in nonreactive vessels tension decreased more than pressure. Data from 25 of 26 reactive arterioles were consistent with the hypothesis that regulation of wall tension accounts for the autoregulatory response; however, in 18 of these vessels a flow-dependent mechanism could also account for the response. Thus the hypothesis that wall tension is a controlled variable responsible for autoregulation is supported, but an important role for flow regulation in local control is also supported.

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