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1 Department of Physiology, Medical College of Wisconsin, Milwaukee, Wisconsin, USA
2 Department of Physical Therapy, Marquette University, Milwaukee, Wisconsin, USA
3 Department of Physiology, Medical College of Wisconsin, Milwaukee, Wisconsin, USA; Zablocki VA Medical Center, Milwaukee, Wisconsin, USA
* To whom correspondence should be addressed. E-mail: matthew.hodges{at}yale.edu.
Our aim was to determine the effects of carotid body denervation (CBD) on the ventilatory responses to focal acidosis and ibotenic acid (IA) injections into the medullary raphe-area of awake, adult goats. Multiple microtubules were chronically implanted into the midline raphe-area nuclei either before or after CBD. For up to 15 days after bilateral CBD, PaCO2 (13.3 ± 1.9 torr) was increased (P < 0.001), and CO2 sensitivity (-53.0 ± 6.4%) was decreased (P < 0.001). Thereafter, resting PaCO2 and CO2 sensitivity returned (P < 0.01) toward control but PaCO2 remained elevated (4.8 ± 1.9 mmHg) and CO2 sensitivity reduced (-24.7 ± 6.0%) 
40 days after CBD. Focal acidosis (FA) at multiple medullary raphe-area sites 23-44 days post-CBD with 50% or 80% CO2 increased inspiratory flow (VI), tidal volume (VT), metabolic rate (VO2) and heart rate (HR)(P<0.05). The effects of FA with 50% CO2 after CBD did not differ from intact goats. However, CBD attenuated (P<0.05) the increase in VI, VT and HR with 80% CO2, but had no effect on the increase in VO2. Rostral but not caudal raphe-area IA injections increased VI, BP and HR (P<0.05), and these responses were accentuated (P<0.001) after CBD. CO2 sensitivity was attenuated (-20%, P< 0.05) <7 days after IA injection, but thereafter returned to pre-lesion values in CBD goats. We conclude: 1) the attenuated response to FA after CBD provides further evidence that the carotid bodies provide a tonic facilitory input into respiratory control centers, 2) the plasticity after CBD is not due to increased raphe chemoreceptor sensitivity, and 3) the "error sensing" function of the carotid body blunts the effect of strong stimulation of the raphe.
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