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CO₂/H⁺ chemoreceptors in the cerebellar fastigial nucleus do not uniformly affect breathing of awake goats

¹Department of Physiology, Medical College of Wisconsin, ²Department of Physical Therapy, Marquette University, and ³Zablocki Veterans Affairs Medical Center, Milwaukee, Wisconsin

Submitted 8 August 2005 ; accepted in final form 20 February 2006

Our objective in this study was to test the hypothesis that focal acidosis (FA) in the cerebellar fastigial nucleus (CFN) of awake goats arising from global brain acidosis induced by increasing inspired CO₂ will increase breathing. FA was created by reverse microdialysis of mock cerebral spinal fluid, equilibrated with 6.4, 25, 50, or 80% CO₂ through chronically implanted microtubules (cannula). Dialysis with 6.4% CO₂ had no significant effects on any physiological parameters. However, microdialysis at higher levels of CO₂ increased pulmonary ventilation (I) in one group of studies and decreased I in a second group and the difference between the groups was significant (t = 9.16, P < 0.001). In one group of studies (n = 8), FA with 50 and 80% CO₂ significantly increased (P < 0.05) I by 16 and 12%, respectively, and significantly increased (P < 0.05) heart rate by 13 and 9%, respectively. In contrast, in another group of studies (n = 6), FA with 25 and 50% CO₂ significantly decreased (P < 0.05) I by 7 and 10%, respectively. In this group oxygen consumption was decreased during dialysis with 80% CO₂. On the basis of histology, we estimate that the increased and decreased responses were associated with FA primarily in the rCFN and cCFN, respectively. We conclude that there are CO₂/H⁺-sensitive neurons in the CFN that do not uniformly affect breathing. In addition, the significant changes in heart rate and oxygen consumption during FA indicate that the CFN can also influence non-respiratory-related control systems.

microdialysis; focal acidosis

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