Genetic determinants on rat chromosome 6 modulate variation in the hypercapnic ventilatory response using consomic strains
To understand the genetic basis of pathways involved in the control of breathing, a large scale, high-throughput study using chromosomal substitution strains of rats is underway. Eight new consomic rat stains (SS-2BN, SS-4BN, SS-6BN, SS-7BN, SS-8BN, SS-11BN, SS-12BN, SS-14BN, SS-YBN), containing one homozygous BN/NHsdMcwi (BN) chromosome on a background of SS/JrHsdMcwi (SS), were created by PhysGen ( http://pga.mcw.edu ) Program for Genomic Applications. Male and female rats were studied using standard plethysmography under control conditions and during acute hypoxia (inspired oxygen fraction = 0.12) and hypercapnia (inspired CO2 fraction = 0.07). The rats were also studied during treadmill exercise. Both male and female BN rats had a significantly lower ventilatory response during 7% CO2 compared with SS rats of the same gender. SS-6BN female rats had a significantly reduced ventilatory response, similar to BN rats due primarily to a reduced tidal volume. Male SS-6BN rats had a significantly reduced tidal volume response to hypercapnia but a slightly increased frequency response during hypercapnia. Gene(s) on the Y chromosome may play a role in this increased frequency response in the male rats because the SS-YBN hypercapnic ventilatory response involves a significantly increased frequency response. Several chromosomal substitutions slightly altered the ventilatory responses to hypoxia and exercise. However, genes on chromosomes 6 and Y of those studied are of primary importance in aspects of ventilatory control currently studied.