Induction of Immediate Early Response Genes by Hypoxia

Abstract

One of the distinguishing characteristics of living organisms is their ability to compensate for stresses in the environment, such as hypoxia, which disturb homeostasis. Homeostasis is preserved mainly by control systems, which maintain levels of crucial chemicals in the body such as oxygen within acceptable limits. These control systems operate largely through negative feedback of signals from sensory receptors like the peripheral chemoreceptors (Longobardo & Cherniack, 1986). Over the years much has been learned about the operation of biological control systems using the same techniques employed to analyze man-made control systems. Both types of systems can be considered to consist of a controller (the brain and the chemoreceptors in the case of O₂ control), and the plant (the O₂ stored in the blood and in the lungs), which the controller manipulates by producing changes in ventilation and blood flow. The response characteristics of each of these components is studied in isolation and while connected; and these relationships are expressed quantitatively so that the overall function of the system is described by a set of mathematical equations. This kind of analysis assumes that the properties of the components, both static and dynamic are fixed. Although important gaps in our knowledge remain, this approach has been quite successful in predicting ventilatory changes during acute hypoxia (Yang & Khoo, 1994). However, the changes in system responses that occur as the time of hypoxic exposure lengthens suggest that the properties of the control system itself are not fixed and even may be subject to some higher order regulation.