Abstract
Recent data suggest that the caudal medullary raphe (MR) does not contribute to chemoreception directly but modulates breathing by interaction with the RTN (Li et al., J Physiol 2006). To investigate this hypothesis, we dialyzed artificial cerebrospinal fluid equilibrated with 25% CO2 into RTN and ROb simultaneously in male rats in a whole body plethysmograph at a temperature within the rat thermoneutral zone (30°C). We compared data from animals with both probes correctly placed to data from rats with both probes misplaced. Simultaneous acidification of RTN and ROb increased VE up to 23%, compared with the baseline and up to 28% compared to the control group, since focal acidification in the control group decreased VE. The responses were similar in wakefulness and sleep. For single site dialysis experiments, both probes received 25% CO2 dialysis, but just one of the probes was correctly placed. The 25% CO2 dialysis into RTN caused a small increase in VE (∼8%; n=05), and this effect was due to an increased f. The focal acidification of the ROb had no effect on VE (N=04). Although there was no response to CO2 dialysis in the ROb, the simultaneous dialysis into the RTN and ROb potentiated the effect of the focal acidification of RTN alone. These results indicate a modulatory role of caudal MR with respect to central chemoreception at the RTN. (Supported by FAPESP and R37 HL 28066)
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