(a) Unilateral microinjection of 0.1 μl ACSF (pH 6.5) into the VLM increased raw PND (middle) and iPND (bottom), but not blood pressure (BP, top). Pre-treatment of amiloride (10 mM, 0.1 μl) blocked the effect. Microinjection of ACSF (pH 7.4) served as the control. (b) The records were recorded from the same animal. Pre-treatment of PcTx1 (100 nM, 0.1 μl) blocked the stimulating effect of ACSF (pH 6.5) on PND (middle) and iPND (bottom), but not BP (top). (c) Unilateral microinjection of 0.1 μl ACSF (pH 6.5) into the control point had no effect on raw PND, iPND and BP. (d) The detailed information from (a). (e) Histological staining with neutral red: the sky blue spot was the injection site in the VLM, and the injection plot was confirmed by compared with Bregma −12.3 mm coronal diagram in Paxinos & Watson stereotaxic atlas of rat brain. In the diagram, arrowheads represent the injection points and hollow dots signify control points. (f) The inhibitory effects of amiloride or PcTx1 on acidification-induced iPND (***p < 0.001 relative to control; ###p < 0.001 relative to pH 6.5, n = 6). (g) Acidification did not alter RR (p > 0.05; n = 6). (h) Ti was increased by acidification and the effect was inhibited by amiloride and PcTx1 (***p < 0.001 relative to pH 7.4, ###p < 0.001 relative to pH 6.5, n = 6). (i) The respiratory drive (iPND/Ti) was increased by microinjection of pH 6.5 in the VLM and blocked by amiloride and PcTx1 (**p < 0.01 relative to pH 7.4, ##p < 0.01 relative to pH 6.5, n = 6).