Hypercapnic and hypoxic responses require intact neural transmission from the pre-Bötzinger complex

The central respiratory network that includes the pre-Bötzinger complex (pre-BötC), a region believed to contain rhythmogenic neurons, is capable of responding to fluctuations in CO2 and pH. However, the role of inputs from this site in mediating ventilatory responses to hypercapnia and/or hypoxia in nonsedated animals is not well established. Therefore, in the present study we tested the hypothesis that altered transmission from the pre-BötC to its target sites would decrease chemosensory responsiveness to acute hypercapnia and modulate the ventilatory response to hypoxia. Colchicine was used to block axonal transport. At 48 h after bilateral microinjections of colchicine into the pre-BötC (100 microg/uL, 100 nL/site), but not saline, the baseline frequency of breathing decreased; however, rhythmicity was not altered. In addition, there was a significant fall in the ventilatory response to hypercapnia (5 and 12% CO2) and hypoxia (8% O2). These findings indicate that, inputs from pre-BötC neurons are of critical importance in providing the normal ventilatory response to both hypercapnia and hypoxia.