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Department of Physiology, University of Kentucky, Lexington, Kentucky 40536
The rostral fastigial nucleus
(FNr) of the cerebellum facilitates the respiratory response to
hypercapnia. We hypothesized that some FNr sites are chemosensitive to
focal tissue acidosis and contribute, at least partially, to
respiratory modulation. Minute ventilation
(
E) was recorded in 21 anesthetized and
spontaneously breathing rats. Acetazolamide (AZ; 50 µM) was
microinjected unilaterally into the FNr while an isocapnic condition
was maintained throughout the experiment. AZ (1 or 20 nl) injection
into the FNr significantly elevated
E (46.0 ± 6.7%; P < 0.05), primarily via an increase in tidal
volume (31.7 ± 3.8%; P < 0.05), with little
effect on arterial blood pressure. This augmented ventilatory response
was initiated at 6.3 ± 0.8 min and reached the peak at 19.7 ± 4.1 min after AZ administration. The same dose of AZ delivered into the interposed and lateral cerebellar nuclei, or vehicle injection into
the FNr, failed to elicit detectable cardiorespiratory responses. To
determine whether the ventilatory response to AZ injection into the FNr
resulted from an increase in respiratory central drive, the minute
phrenic nerve activity (MPN) was recorded in seven paralyzed and
ventilated rats. Similar to
E, MPN was increased by
38.9 ± 8.9% (P < 0.05) after AZ
administration. Our results suggest that elevation of
CO2/H+ within the FNr facilitates respiratory
output, supporting the presence of ventilatory chemoreception in rat FNr.
ventilatory chemoreception; interposed nucleus; cerebellar lateral nucleus
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