A computational model clarifies the roles of positive and negative feedback loops in the Drosophila circadian clock

2010 ◽  
Vol 374 (27) ◽  
pp. 2743-2749 ◽  
Author(s):  
Junwei Wang ◽  
Tianshou Zhou
Keyword(s):  
Circadian Clock ◽  
Computational Model ◽  
Negative Feedback ◽  
Feedback Loops ◽  
Negative Feedback Loops ◽  
Positive And Negative Feedback

The principle of homeostasis in the hypothalamus-pituitary-adrenal system: new insight from positive feedback

2007 ◽  
Vol 293 (1) ◽  
pp. R83-R98 ◽  
Author(s):  
A. Peters ◽  
M. Conrad ◽  
C. Hubold ◽  
U. Schweiger ◽  
B. Fischer ◽  
...  
Keyword(s):  
Negative Feedback ◽  
Positive Feedback ◽  
Glucocorticoid Receptors ◽  
Current Knowledge ◽  
Biological Systems ◽  
Feedback Loops ◽  
Endocrine Disorders ◽  
Negative Feedback Loops ◽  
Adrenal System ◽  
Positive And Negative Feedback

Feedback control, both negative and positive, is a fundamental feature of biological systems. Some of these systems strive to achieve a state of equilibrium or “homeostasis”. The major endocrine systems are regulated by negative feedback, a process believed to maintain hormonal levels within a relatively narrow range. Positive feedback is often thought to have a destabilizing effect. Here, we present a “principle of homeostasis,” which makes use of both positive and negative feedback loops. To test the hypothesis that this homeostatic concept is valid for the regulation of cortisol, we assessed experimental data in humans with different conditions (gender, obesity, endocrine disorders, medication) and analyzed these data by a novel computational approach. We showed that all obtained data sets were in agreement with the presented concept of homeostasis in the hypothalamus-pituitary-adrenal axis. According to this concept, a homeostatic system can stabilize itself with the help of a positive feedback loop. The brain mineralocorticoid and glucocorticoid receptors—with their known characteristics—fulfill the key functions in the homeostatic concept: binding cortisol with high and low affinities, acting in opposing manners, and mediating feedback effects on cortisol. This study supports the interaction between positive and negative feedback loops in the hypothalamus-pituitary-adrenal system and in this way sheds new light on the function of dual receptor regulation. Current knowledge suggests that this principle of homeostasis could also apply to other biological systems.

scholarly journals Robust, Tunable Biological Oscillations from Interlinked Positive and Negative Feedback Loops

Science ◽  
2008 ◽  
Vol 321 (5885) ◽  
pp. 126-129 ◽  
Author(s):  
T. Y.-C. Tsai ◽  
Y. S. Choi ◽  
W. Ma ◽  
J. R. Pomerening ◽  
C. Tang ◽  
...  
Keyword(s):  
Negative Feedback ◽  
Feedback Loops ◽  
Negative Feedback Loops ◽  
Positive And Negative Feedback
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