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J Appl Physiol (December 12, 2003). doi:10.1152/japplphysiol.00992.2003
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Submitted on September 12, 2003
Accepted on December 11, 2003

The Effects on Breathing in Awake and Sleeping Goats of Focal Acidosis in the Medullary Raphe

Matthew R Hodges1*, Leeanne Klum1, Tracy Leekley1, Daniel T Brozoski1, Jeffrey Bastasic1, Suzanne Davis1, Julie M Wenninger1, Thom R Feroah2, Lawrence G Pan3, and Hubert V Forster4

1 Department of Physiology, Medical College of Wisconsin, Milwaukee, Wisconsin, USA
2 Department of Pediatrics, Medical College of Wisconsin, Milwaukee, Wisconsin, USA
3 Department of Physical Therapy, Marquette University, Milwaukee, Wisconsin, USA
4 Department of Physiology, Medical College of Wisconsin, Milwaukee, Wisconsin, USA; Zablocki V.A. Medical Center, Milwaukee, Wisconsin, USA

* To whom correspondence should be addressed. E-mail: hodgesmr{at}mcw.edu.

Our aim was to determine the effects of focal acidification in the raphe obscurus (RO) and raphe pallidus (RP) on ventilation and other physiologic variables in both the awake and sleep states in adult goats. Through chronically implanted microtubules: 1) a focal acidosis was created by microdialysis (MD) of mock cerebral spinal fluid (mCSF) equilibrated with various levels of CO2, and 2) medullary extracellular fluid (ECF) pH was measured using a custom-made pH electrode. Focal acidosis (FA) in the RO or RP by dialyzing either 25% or 80% CO2 (mCSF pH~6.8 or 6.3) increased (P<0.05) inspiratory flow (VI) 8% and 12% respectively, while awake during the day but not at night while awake or in NREM sleep. While awake during the day there were also increases in heart rate and blood pressure (p<0.05), but no significant change in metabolic rate or PaCO2. Dialysis with mock CSF equilibrated with 25% or 80% CO2 reduced ECF pH by the same amount (25%) or three times more (80%) than when inspired CO2 was increased to 7%. During CO2 inhalation, the reduction in ECF pH was only 50% of the reduction in arterial pH. Finally, dialysis in vivo only decreased EFC pH by 19.1% of the change during dialysis in an in vitro system. We conclude that: 1) the physiologic responses to FA in the RO and RP are consistent with the existence of chemoreceptors in these nuclei, and 2) local pH buffering mechanisms act to minimize changes in brain pH during systemic induced acidosis and microdialysis induced focal acidosis, and that these mechanisms could be as or more important to pH regulation than the small changes in VI during a focal acidosis.




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