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

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Abstract
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 (V̇i) in one group of studies and decreased V̇i 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) V̇i 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) V̇i 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.