Hypercapnia and medullary neurons in the isolated brain stem-spinal cord of the rat.
We have extracellularly recorded single neuron activity in the ventral medulla of the isolated brain stem-spinal cord preparation of the neonatal rat (37 preparations) in order to test their sensitivity to changes in CO2/H+. Search for neuronal activity was performed when the preparation was superfused with control mock CSF (equilibrated with 2% CO2, 90% O2 in N2; pH = 7.8 at 27 degrees C). Neurons, found down to about 500 microns from the surface, could be classified as R neurons when they showed rhythmic discharge in phase with phrenic activity, recorded from C4 ventral roots; or as Non-R neurons when they did not exhibit such phasic discharge. Among the 89 Non-R neurons, 20 responded to rapidly replacing the control CSF by hypercapnic CSF (8% CO2, 90% O2 in N2; pH = 7.2) with increased, 44 with reduced activity, while 25 did not respond to hypercapnia. Five Non-R neurons became phasic with respiration during hypercapnia. Of the 14 R neurons, 10 fired predominantly in expiration (R-E), 4 in inspiration (R-I). Only one R-E and two R-I neurons were excited by hypercapnia, the remaining were either inhibited or did not respond. Excited Non-R and R neurons were mainly encountered in rostral parts of those areas in the ventral medulla that have been reported as chemosensitive.
Okada
Y
Y
Institut für Physiologie, Ruhr-Universität Bochum, Germany.
Mückenhoff
K
K
Scheid
P
P
D000818:Animals; D001933:Brain Stem / Q000473:pathology / Q000503:physiopathology*; D004594:Electrophysiology; D006935:Hypercapnia / Q000473:pathology / Q000503:physiopathology*; D066298:In Vitro Techniques; D008526:Medulla Oblongata / Q000473:pathology / Q000503:physiopathology*; D009474:Neurons / Q000502:physiology*; D051381:Rats; D012137:Respiratory System / Q000503:physiopathology; D013116:Spinal Cord / Q000473:pathology / Q000503:physiopathology*