Lesions in the cerebellar fastigial nucleus have a small effect on the hyperpnea needed to meet the gas exchange requirements of submaximal exercise

1 Department of Physiology, Medical College of Wisconsin, 2 Department of Physical Therapy, Marquette University, and 3 Zablocki Veterans Affairs Medical Center, Milwaukee, Wisconsin Submitted 18 March 2006 ; accepted in final form 26 May 2006 The purpose of this study was to test the hypothesis that an intact cerebellar fastigial nucleus (CFN) is necessary for the hyperpnea to meet the gas exchange needs of submaximal exercise. Bilateral stainless steel microtubules were implanted in the cerebellum inside ( n = 12) or outside ( n = 2) the CFN for injection (0.5 to 10 µl) of the neurotoxin ibotenic acid. All goats had difficulty maintaining normal posture and walking for up to 1 mo after the implantation of the microtubules and again for hours or days after the neurotoxin was injected. Postmortem histology indicated there were 55% fewer living neurons ( P < 0.001, n = 9, 3,720 ± 553 vs. 1,670 ± 192) in the CFN of the experimental goats compared with a control group of goats. As is typical for goats before implantation of the microtubules, the decrease in arterial P CO 2 from rest during mild and moderate treadmill exercise was 2.0 ± 0.39 and 3.5 ± 0.45 Torr, respectively. Implantation of the microtubules did not significantly change this exercise hyperventilation. However, neurotoxic lesioning with 10 µl ibotenic acid significantly ( P < 0.05) attenuated the decrease in arterial P CO 2 by 1.3 and 2.8 Torr at the first and second workload, respectively. The modest attenuation of the exercise hypocapnia at both workloads in CFN-lesioned goats suggests that the CFN is part of the control system that enables the ventilatory response to meet the gas exchange requirements of submaximal exercise. neural control of breathing Address for reprint requests and other correspondence: H. V. Forster, Dept. of Physiology, The Medical College of Wisconsin, 8701 Watertown Plank Rd., Milwaukee, WI 53226 (e-mail: bforster{at}mcw.edu )