AJP - Regulatory, Integrative and Comparative Physiology, Vol 265, Issue 3 494-R503, Copyright © 1993 by American Physiological Society
Ventilatory CO2-induced optical activity changes of cat ventral medullary surface
X. W. Dong, D. Gozal, D. M. Rector and R. M. Harper
Department of Anatomy and Cell Biology, University of California Los Angeles School of Medicine.
We examined neuronal activation of the ventral medullary surface (VMS)
during hypercapnic challenges using optical recording procedures. With a
coherent imaging probe, we assessed reflected 700-nm light from 18 VMS
sites in 11 spontaneously breathing adult cats and from the suprasylvian
cortex in two cats. Video frames were acquired during a baseline period,
hypercapnic (3, 5, and 10% CO2 in O2) exposure, and recovery. Hypercapnic
exposure elicited overall reflectance changes in all VMS sites, but no
changes in the suprasylvian cortex. Light reflectance changes, suggesting
altered neuronal activity, were reproducible, occurred as early as 30 s
after CO2 exposure, and were dose dependent. The changes persisted
approximately 20-25 min beyond the stimulus, but respiratory responses
consistently recovered within 2-3 min. Although more rostral VMS sites
tended to be associated with decreased activity and caudal regions with
increased excitation, no uniform topographical organization was apparent
across animals. The variability in VMS optical reflectance patterns across
animals during CO2 stimulation may reflect the heterogeneous topographical
distribution of responsive neurons in the structure.
