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Department of Physiology, University of Kentucky, Lexington, Kentucky 40536
Received 11 October 1996; accepted in final form 3 February 1997.
Xu, Fadi, and Donald T. Frazier. Involvement of the
fastigial nuclei in vagally mediated respiratory responses.
J. Appl. Physiol. 82(6):
1853-1861, 1997.
Previous studies have demonstrated that the
cerebellum, especially the fastigial nucleus (FN), is capable of
modulating respiratory responses to chemical and mechanical stimuli.
Because there is evidence to show projections from vagal afferents to
the FN, the goal of this study was to determine the role of the FN in
the respiratory reflexes elicited by activation of vagal afferents.
Experiments were performed in anesthetized (chloralose), paralyzed, and
artificially ventilated cats with an occipital exposure of the
cerebellum. Administration of capsaicin (Cap; 5-10 µg/kg) via
the right external jugular vein at the end of inspiration and
application of lung inflation (LI; 10 cmH2O) during inspiration were
carried out to stimulate nonmyelinated and myelinated vagal afferents,
respectively. The phrenic neurogram was recorded as an
index of the respiratory motor output. Control cardiorespiratory
variables [expiratory duration
(TE), arterial blood
pressure] and their immediate responses to stimuli were compared
before and after bilateral lesions of the FN. The results showed the
following. 1) Cap
injection and LI resulted in a dramatic increase in
TE (apnea).
2) FN lesions did not significantly
alter the control TE; however,
the apneic duration induced by Cap injection was prolonged.
3) Neither FN lesions nor
cerebellectomy affected the apneic duration that resulted from
application of LI. 4) Cold blockade
of the vagi (6-8°C) eliminated the respiratory responses elicited by LI but not Cap injection; vagotomy abolished the responses to both stimuli. 5) FN lesions did
not change the control ABP or its responses to either LI or Cap
injection. It is concluded that the FN is involved in vagally mediated
respiratory reflexes elicited by activation of nonmyelinated (C-fiber)
vagal afferents.
cats; respiratory control; cerebellum; lung inflation; capsaicin; apnea; differential vagal block; vagotomy
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