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Postnatal developmental changes in CO₂ sensitivity in rats

Department of Physiology, Medical College of Wisconsin and Zablocki Veterans Affairs Medical Center, Milwaukee, Wisconsin

Submitted 29 March 2006 ; accepted in final form 15 June 2006

Ventilatory sensitivity to CO₂ in awake adult Brown Norway (BN) rats is 50–75% lower than in adult Sprague-Dawley (SD) and salt-sensitive Dahl S (SS) rats. The purpose of the present study was to test the hypothesis that this difference would be apparent during the development of CO₂ sensitivity. Four litters of each strain were divided into four groups such that rats were exposed to 7% inspired CO₂ for 5 min in a plethysmograph every third day from postnatal day (P) 0 to P21 and again on P29 and P30. From P0 to P14, CO₂ exposure increased pulmonary ventilation (E) by 25–50% 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 P19–21 when E during hypercapnia was 175–225% 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 CO₂ in the SS and SD strains was near the adult response, 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 physiological 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.

neural control of breathing; consomics; hypercapnia

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