Fig. 3. Deletion of DR but not MR serotonin neurons prevents hypercapnic arousal.

Correlations of DR^Sert and MR^Sert neuronal loss to the CO₂ arousal (a–b), and effects on the respiration (c–d). Panels a and b are the regression graphs showing the correlation of the loss of DR^Sert and MR^Sert neurons, respectively, to the latency of arousal to CO₂ across all three treatment groups, WT, DR/DTA, and MR/DTA. Note the close correlation of the loss of DR^Sert neurons with mean latency to arousal, even in experiments where the deletion was aimed at the MR (P < 0.001, Pearson’s correlation coefficient), and the lack of correlation of loss of MR^Sert neurons with latency to CO₂ arousal (P = 0.82). The tidal volume (c) and the respiratory rate (d) both before and after exposure (mean ± SEM) to CO₂ did not differ among the treatment groups, indicating that the DR^Sert neurons appear to have little role in modulating the ventilatory response to CO₂. Data in c and d are presented as mean values ± SEM.