Fig. 3 shows the effects of PPADS or saline microinjected into the rostral MR on, V˙E (panel A), fR (panel B), and V  T (panel C) during 30 min of 7% hypercapnic exposure. Typical hypercapnia-induced

hyperpnea was observed after saline microinjection (n   = 5), whereas PPADS treatment (n   = 7) attenuated that response at 5 (p   = 0.011), 10 (p   = 0.02), 20 (p   = 0.023) and 30 min (p   = 0.016) of hypercapnic exposure. The decrease in both V  T ( Fig. 3C) and fR ( Fig. 3B) were not significant (p   > 0.05) after PPADS, but in conjunction they accounted for attenuated V˙E ( Fig. 3A). Microinjection of PPADS elicited a 34% and 32% attenuation of the ventilatory response to hypercapnia at 5 and 30 min (1857 ± 174 vs. 1412 ± 103 mL kg−1 min−1 at 5 min and 1882 ± 148 vs. 1468 ± 86 mL kg−1 min−1 at 30 min). 20 min after hypercapnia exposure, we did not observe a Ku0059436 significant

difference in the respiratory variables between the groups (p > 0.05). In addition, during hypercapnia exposure, no difference in body temperature was observed in rostral MR PPADS-treated animals compared with those in the vehicle group (36.7 ± 0.05 vs. 36.5 ± 0.4 (p > 0.05), respectively). Microinjection of PPADS into the caudal MR had no effect on the respiratory responses to hypercapnia (p   > 0.05). Fig. 4 shows the effect of PPADS microinjected into the caudal MR on V˙E (panel A), fR (panel B), and VT (panel C) during 7% hypercapnic exposure. Typical hypercapnia-induced increase in

the respiratory Cyclopamine in vivo variables was observed after saline microinjection (n = 5), but no change in these responses (p > 0.05) was aminophylline observed in the group of animals treated with PPADS (n = 5) into the caudal MR ( Fig. 4). As in the rostral PPADS injected group, there was no difference in body temperature between PPADS injected in the caudal MR group and the vehicle group (36.6 ± 0.04 vs. 36.5 ± 0.03 (p > 0.05), respectively). The present study provides evidence that P2X purinoceptors within the rostral, but not caudal MR, exert an excitatory modulation of the ventilatory response to hypercapnia in conscious rats. This is suggested since microinjection of PPADS, a broad spectrum P2X receptor antagonist, in the rostral MR, attenuated hyperpnea during 7% CO2 exposure. The rostral aspect of MR includes the RMg whereas the caudal MR refers to the ROb nucleus. We chose to study these areas separately because it has been previously suggested that there is a heterogeneity in MR function with regard to respiratory control, when these rostral and caudal regions are compared (da Silva et al., 2011, Dias et al., 2008 and Li et al., 2006). Chemical 5-HT neuronal lesion in the RMg (rostral MR) attenuated the hypercapnic ventilatory response by 31%, whereas the same chemical lesion in the ROb (caudal MR) reduced the hypercapnic ventilatory response by 12% (da Silva et al., 2011).