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1 Physiology, Medical College of WI, Milwaukee, Wisconsin, United States
2 Physiology, Medical College of WI, 53226, Wisconsin, United States
3 Physiology, Medical College of Wisconsin, Milwaukee, Wisconsin, United States
4 Department of Physiology, Medical College of Wisconsin, 8701 Watertown Plank Road, Milwaukee, Wisconsin, 53226-4801, United States; Zablocki V.A. Medical Center, Milwaukee, Wisconsin, United States
* To whom correspondence should be addressed. E-mail: bforster{at}mcw.edu.
Ventilatory sensitivity to CO2 in awake adult Brown Norway (BN) rats is 50 to 75% lower than in adult Sprague Dawley (SD) and Dahl S (SS) rats (10, 14, 18, 20, 41). The purpose of the present study was to test the hypothesis that this difference would be apparent during the development of CO2sensitivity. Four litters of each strain were divided into four groups such that rats were exposed to 7% inspired CO2 for 5 minutes in a plethysmograph every third day from P0 to P21 and again on P29 and P30. From P0 to P14, CO2 exposure increased pulmonary ventilation (VE) by 25 to 50% in the BN and SD strains and between 25 to over 200% in the SS strain. In all strains beginning around P15, the response to CO2 increased progressively reaching a peak at P19-P21 when VE during hypercapnia was 175 to 225% above eucapnia. There were minimal changes in CO2 sensitivity between P21 and P30, and at both ages there were minimal between strain differences. At P30, the response to CO2in the SS and SD strains was near the published adult response (14,17,19), but the response in the BN rats was 100% greater at P30 than in adults. We conclude that: 1) CO2 sensing mechanisms, and/or mechanisms downstream from the chemoreceptors, change dramatically at the age in rats when other physiologic systems are also maturing (~P15), and 2) there is a high degree of age-dependent plasticity in CO2 sensitivity in rats, which differs between strains.
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