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J Appl Physiol 66: 687-694, 1989;
8750-7587/89 $5.00
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Journal of Applied Physiology, Vol 66, Issue 2 687-694, Copyright © 1989 by American Physiological Society

ARTICLES

Internal intercostal nerve discharges in the cat: influence of chemical stimuli

R. F. Fregosi and D. Bartlett Jr
Department of Physiology, Dartmouth Medical School, Hanover, New Hampshire 03756.

We studied the influence of central and peripheral chemoreceptor stimulation on the activities of the phrenic and internal intercostal (iic) nerves in decerebrate, vagotomized, and paralyzed cats with bilateral pneumothoraces. Whole iic nerves of the rostral thorax (T2-T5) usually discharged during neural inspiration, whereas those of the caudal thorax (T7-T11) were primarily active during neural expiration. Filaments of rostral iic nerves that terminated in iic muscles generally discharged during expiration, suggesting that inspiratory activity recorded in whole iic nerves may have innervated other structures, possibly parasternal muscles. All nerves were phasically active at hyperoxic normocapnia and increased their activities systematically with hypercapnia. Isocapnic hypoxia or intra-arterial NaCN injection consistently increased phrenic and inspiratory iic nerve activities. In contrast, expiratory iic nerve discharges were either decreased (10 cats) or increased (7 cats) by hypoxia. Furthermore, expiratory responses to NaCN were highly variable and could not be predicted from the corresponding response to hypoxia. The results show that central and peripheral chemoreceptor stimulation can affect inspiratory and expiratory motoneuron activities differentially. The variable effects of hypoxia on expiratory iic nerve activity may reflect a relatively weak influence of carotid body afferents on expiratory bulbospinal neurons. However, the possibility that the magnitude of expiratory motoneuron activity is influenced by the intensity of the preceding centrally generated inspiratory discharge is also discussed.


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F. Lu, C. Qin, R. D. Foreman, and J. P. Farber
Chemical activation of C1-C2 spinal neurons modulates intercostal and phrenic nerve activity in rats
Am J Physiol Regulatory Integrative Comp Physiol, June 1, 2004; 286(6): R1069 - R1076.
[Abstract] [Full Text] [PDF]


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