Submitted on September 13, 2008
Revised on January 12, 2009
Accepted on January 12, 2009
Characterization of the Chemosensitive Response of Individual Solitary Complex (SC) Neurons from Adult Rats
Nicole L. Nichols1, Daniel K. Mulkey2, Katherine A. Wilkinson3, Frank L. Powell3, Jay B. Dean4, and Robert W. Putnam1*
1 Wright State University Boonshoft School of Medicine
2 University of Connecticut
3 University of California, San Diego
4 University of South Florida
* To whom correspondence should be addressed. E-mail: robert.putnam{at}wright.edu.
We studied the CO2/H+-chemosensitive responses of individual solitary complex (SC) neurons from adult rats, by simultaneously measuring the intracellular pH (pHi) and electrical responses to hypercapnic acidosis (HA). SC neurons were recorded using the blind whole cell patch clamp technique and loading the soma with the pH-sensitive dye pyranine through the patch pipette. We found that SC neurons from adult rats have a lower steady state pHi than SC neurons from neonatal rats. In the presence of chemical and electrical synaptic blockade, adult SC neurons have firing rate responses to HA (percentage of neurons activated or inhibited and the magnitude of response as determined by the chemosensitivity index) that are similar to SC neurons from neonatal rats. They also have a typical response to isohydric hypercapnia including decreased 
pHi, followed by pHi recovery, and increased firing rate. Thus, the chemosensitive response of SC neurons from adults is similar to the chemosensitive response of SC neurons from neonatal rats. Since our findings for adults are similar to previously reported values for neurons from neonatal rats, we conclude that intrinsic chemosensitivity is established early in development for SC neurons and is maintained throughout adulthood.
