Physiological and Genomic Consequences of Intermittent Hypoxia: Selected Contribution: Altered vascular reactivity in arterioles of chronic intermittent hypoxic rats

Recurrentepisodic hypoxia (EH) is a feature of sleep apnea that may beresponsible for some chronic cardiovascular sequelae such as systemichypertension. Chronic EH (8 h/day for 35 days) causes elevation ofdiurnal resting (unstimulated) mean arterial blood pressure (MAP) inthe rat. We used in vivo video microscopy to examine arteriolarreactivity in the cremaster muscle of male Sprague-Dawley ratssubjected to 35 days of EH. Cremaster muscles of EH (n = 6) and control (n = 6) rats were exposed to varying doses of norepinephrine (NE) (10¹⁰ to 10⁵M), ACh (10⁹ to 10⁵ M), and endothelin-1(10¹² to 10⁸ M). In a separate experiment,EH (n = 5) and control (n = 6) ratswere given one dose of a nitric oxide synthase (NOS) inhibitor N^G-nitro-L-arginine methylester (L-NAME; 10⁵ M). We also examinedendothelial NOS mRNA from the kidneys of EH-stimulated and control(unstimulated) rats. Telemetry-monitored EH rats showed a 16-mmHgincrease in MAP over 35 days, whereas control rats showed no change.The response to NE and endothelin-1 were similar for EH and controlrats. ACh vasodilatation of arterioles in EH rats was significantlyattenuated compared with that of controls. The degree ofvasoconstriction in response to blockade of the nitric oxide system byL-NAME was significantly less (83% of baseline diameterwith L-NAME) for arterioles of EH rats compared with thatfor controls (61% of baseline diameter), implying lower basal restingnitric oxide release in the EH rats. Whole kidney mRNA endothelial NOSlevels were not different between groups. These data support thehypothesis that chronic elevation of blood pressure associated with EHinvolves increased peripheral resistance from decreased basal releaseor production of nitric oxide after 35 days of EH.

     

Field of genes: the politics of science and identity in the Estonian Genome Project

This case study of the Estonian Genome Project (EGP) analyses the Estonian policy decision to construct a national human gene bank. Drawing upon qualitative data from newspaper articles and public policy documents, it focuses on how proponents use discourse to link the EGP to the broader political goal of securing Estonia's position within the Western/European scientific and cultural space. This dominant narrative is then situated within the analytical notion of the "brand state", which raises potentially negative political consequences for this type of market-driven genomic research. Considered against the increasing number of countries engaging in gene bank and/or gene database projects, this analysis of Estonia elucidates issues that cross national boundaries, while also illuminating factors specific to this small, post-Soviet state as it enters the global biocybernetic economy.     

Analysis of genomic sequences by Chaos Game Representation

MOTIVATION: Chaos Game Representation (CGR) is an iterative mapping technique that processes sequences of units, such as nucleotides in a DNA sequence or amino acids in a protein, in order to find the coordinates for their position in a continuous space. This distribution of positions has two properties: it is unique, and the source sequence can be recovered from the coordinates such that distance between positions measures similarity between the corresponding sequences. The possibility of using the latter property to identify succession schemes have been entirely overlooked in previous studies which raises the possibility that CGR may be upgraded from a mere representation technique to a sequence modeling tool. RESULTS: The distribution of positions in the CGR plane were shown to be a generalization of Markov chain probability tables that accommodates non-integer orders. Therefore, Markov models are particular cases of CGR models rather than the reverse, as currently accepted. In addition, the CGR generalization has both practical (computational efficiency) and fundamental (scale independence) advantages. These results are illustrated by using Escherichia coli K-12 as a test data-set, in particular, the genes thrA, thrB and thrC of the threonine operon.     

Intermittent hypoxia: cell to system

This symposium was organized to present research dealing with the effects of intermittent hypoxia on cardiorespiratory systems and cellular mechanisms. The pattern of neural impulse activity has been shown to be critical in the induction of genes in neuronal cells and involves distinct signaling pathways. Mechanisms associated with different patterns of intermittent hypoxia might share similar mechanisms. Chronic intermittent hypoxia selectively augments carotid body sensitivity to hypoxia and causes long-lasting activation of sensory discharge. Intermittent hypoxia also activates hypoxia-inducible factor-1. Reactive oxygen species are critical in altering carotid body function and hypoxia-inducible factor-1 activation caused by intermittent hypoxia. Blockade of serotonin function in the spinal cord prevents long-term facilitation in respiratory motor output elicited by episodic hypoxia and requires de novo protein synthesis. Chronic intermittent hypoxia leads to sustained elevation in arterial blood pressure and is associated with upregulation of catecholaminergic and renin-angiotensin systems and downregulation of nitric oxide synthases.     

Equivalence relationships between stage-structured population models

Matrix population models are widely applied in conservation ecology to help predict future population trends and guide conservation effort. Researchers must decide upon an appropriate level of model complexity, yet there is little theoretical work to guide such decisions. In this paper we present an analysis of a stage-structured model, and prove that the model's structure can be simplified and parameterised in such a way that the long-term growth rate, the stable-stage distribution and the generation time are all invariant to the simplification. We further show that for certain structures of model the simplified models require less effort in data collection. We also discuss features of the models which are not invariant to the simplification and the implications of our results for the selection of an appropriate model. We illustrate the ideas using a population model for short-tailed shearwaters (Puffinus tenuirostris). In this example, model simplification can increase parameter elasticity, indicating that an intermediate level of complexity is likely to be preferred.