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Department of Physiology, Dartmouth Medical School, Lebanon, New Hampshire 03756-0001
Received 6 January 1997; accepted in final form 18 May 1997.
Li, Aihua, and Eugene E. Nattie. Focal central
chemoreceptor sensitivity in the RTN studied with a
CO2 diffusion pipette in vivo.
J. Appl. Physiol. 83(2): 420-428, 1997.
We describe and use a CO2
diffusion pipette to produce a quickly reversible focal acidosis in the
retrotrapezoid nucleus region of the rat brain stem. No tissue
injection is made. Instead, artificial cerebrospinal fluid (aCSF)
equilibrated with CO2 circulates
within the micropipette, providing a source for continued
CO2 diffusion into the tissue from
the pipette tip. Tissue pH electrodes show the acidosis is limited to
500 µm from the tip. In controls (aCSF equilibrated with air), 1-min
pipette perfusions increased tissue pH slightly and decreased phrenic
nerve amplitude. In moderate- and
high-CO2 groups (aCSF equilibrated
with 50 or 100% CO2), 1-min
perfusions significantly decreased tissue pH and increased phrenic
nerve amplitude in a dose-dependent manner. The responses developed and
reversed within minutes. Compared with our prior use of medullary acetazolamide injections to produce a focal acidosis, in this approach
the acidosis 1) arises and reverses
quickly and 2) its intensity can be
varied. This allows study of sensitivity and mechanism. We conclude
from this initial experiment that retrotrapezoid nucleus region
chemoreceptors operate within the normal physiological range of
CO2-induced tissue pH changes.
ventral medulla; control of breathing; carbon dioxide sensitivity; retrotrapezoid nucleus
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