The hypercapnic ventilatory response displays time-of-day variability that is unaffected by acute light exposure in the early dark phase

The respiratory chemoreflex allows animals to dynamically respond to changes in blood gas levels. An example is the hypercapnic ventilatory response (HCVR), which measures an animal’s ventilatory response to increased CO 2 levels. The HCVR exhibits a circadian rhythm and is altered by chronic light exposure. Previous research demonstrates that eucapnic breathing is altered by an acute, 30-minute light pulse, but it is unknown if the HCVR is similarly affected. To assess if HCVR is modulated by acute light, mice (n=8) were habituated to a 12L:12D light cycle, and the chemoreflex response to 5% CO 2 challenge was measured with whole-body plethysmography. After acclimation to the plethysmograph chamber, and two hours into the animal’s habitual dark phase (ZT 14), HCVR was measured. Immediately afterwards, mice were exposed to broad-spectrum, white light (~450 lux) for 30 minutes. A second HCVR was assessed 90 minutes after light offset (ZT 16). The same protocol was administered to control animals (n = 6) receiving no light pulse. Consistent with previous data, we found that the HCVR is higher in mice at ZT 16 compared to ZT 14. Interestingly, 30 minutes of light in the early dark phase had no effect on the HCVR at ZT 16. This data supports the observation that the HCVR has a circadian rhythm but expands our understanding of how light affects breathing. These findings demonstrate that while light in the early dark phase can influence eucapnic breathing, it does not equally impact the chemoreflex. This may suggest that separate mechanisms are involved in how light affects eucapnic breathing and the respiratory chemoreflex. This research was supported by Marquette University. This abstract was presented at the American Physiology Summit 2025 and is only available in HTML format. There is no downloadable file or PDF version. The Physiology editorial board was not involved in the peer review process.