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Effects on breathing of focal acidosis at multiple medullary raphe sites in awake goats. J Appl Physiol (1985) 2004 Dec;97(6):2303-9 PMID: 15322068

Abstract

To gain insight into why there are chemoreceptors at widespread sites in the brain, mircrotubules were chronically implanted at two or three sites in the medullary raphe nuclei of adult goats (n = 7). After >2 wk, microdialysis (MD) probes were inserted into the microtubules to create focal acidosis (FA) in the awake state using mock cerebral spinal fluid (mCSF) equilibrated with 6.4% (pH = 7.3), 50% (pH = 6.5), or 80% CO(2) (pH = 6.3), where MD with 50 and 80% CO(2) reduces tissue pH by 0.1 and 0.18 pH unit, respectively. There were no changes in all measured variables with MD with 6.4% at single or multiple raphe sites (P > 0.05). During FA at single raphe sites, only 80% CO(2) elicited physiological changes as inspiratory flow was 16.9% above (P < 0.05) control. However, FA with 50 and 80% CO(2) at multiple sites increased (P < 0.05) inspiratory flow by 18.4 and 30.1%, respectively, where 80% CO(2) also increased (P < 0.05) tidal volume, heart rate, CO(2) production, and O(2) consumption. FA with 80% CO(2) at multiple raphe sites also led to hyperventilation (-2 mmHg), indicating that FA had effects on breathing independent of an increased metabolic rate. We believe these findings suggest that the large ventilatory response to a global respiratory brain acidosis reflects the cumulative effect of stimulation at widespread chemoreceptor sites rather than a large stimulation at a single site. Additionally, focal acidification of raphe chemoreceptors appears to activate an established thermogenic response needed to offset the increased heat loss associated with the CO(2) hyperpnea.

Author List

Hodges MR, Martino P, Davis S, Opansky C, Pan LG, Forster HV

Author

Matthew R. Hodges PhD Associate Professor in the Physiology department at Medical College of Wisconsin

MESH terms used to index this publication - Major topics in bold

Acidosis, Respiratory
Animals
Carbon Dioxide
Chemoreceptors
Female
Goats
Male
Medulla Oblongata
Microdialysis
Raphe Nuclei
Respiration
Respiratory Mechanics
Rest
Wakefulness



View this publication's entry at the Pubmed website PMID: 15322068
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