Journal of Applied Physiology, Vol 80, Issue 5 1490-1494, Copyright © 1996 by American Physiological Society

ARTICLES

On the mechanism of the mediolateral gradient of parasternal activation

A. De Troyer, A. Legrand, G. Gayan-Ramirez, M. Cappello and M. Decramer
Laboratory of Cardiorespiratory Physiology, Brussels School of Medicine, Erasme University Hospital, Belgium.

Recent studies have shown that in spontaneously breathing dogs the parasternal intercostals are activated according to a mediolateral gradient. To assess the mechanism of this regionalization of activity, we assessed the pattern of activation of these muscles after section of the dorsal roots and examined the topographic distribution of the muscle fiber types from the sternum to the chondrocostal junctions. The pattern of parasternal activity after dorsal rhizotomy was similar in all respects to that previously observed in intact animals. Thus activity in the medial parasternal bundles at the onset of inspiration frequently preceded activity in the middle bundles, and no activity was recorded from the lateral bundles. The amount of medial activity, when expressed as a percentage of the activity recorded during supramaximal tetanic stimulation of the internal intercostal nerve (maximal activity), was also consistently greater than the amount of middle activity (52.6 +/- 4.6 vs. 23.1 +/- 2.6% maximal activity; P < 0.001). Furthermore, the medial, middle, and lateral parasternal bundles had a higher proportion of slow-twitch oxidative fibers than of fast-twitch oxidative-glycolytic fibers; no topographic difference in fiber type distribution was observed. We conclude, therefore, that the mediolateral gradient of parasternal activity is probably due to the unequal distribution of central inputs throughout the pool of alpha-motoneurons.

This article has been cited by other articles:

				J. E. Butler and S. C. Gandevia The output from human inspiratory motoneurone pools J. Physiol., March 1, 2008; 586(5): 1257 - 1264. [Abstract] [Full Text] [PDF]

				A. L. Hudson, S. C. Gandevia, and J. E. Butler The effect of lung volume on the co-ordinated recruitment of scalene and sternomastoid muscles in humans J. Physiol., October 1, 2007; 584(1): 261 - 270. [Abstract] [Full Text] [PDF]

				S. Levine, T. Nguyen, M. Friscia, J. Zhu, W. Szeto, J. C. Kucharczuk, B. A. Tikunov, N. A. Rubinstein, L. R. Kaiser, and J. B. Shrager Parasternal intercostal muscle remodeling in severe chronic obstructive pulmonary disease J Appl Physiol, November 1, 2006; 101(5): 1297 - 1302. [Abstract] [Full Text] [PDF]

				S. C. Gandevia, A. L. Hudson, R. B. Gorman, J. E. Butler, and A. De Troyer Spatial distribution of inspiratory drive to the parasternal intercostal muscles in humans J. Physiol., May 15, 2006; 573(1): 263 - 275. [Abstract] [Full Text] [PDF]

				A. De Troyer, P. A. Kirkwood, and T. A. Wilson Respiratory Action of the Intercostal Muscles Physiol Rev, April 1, 2005; 85(2): 717 - 756. [Abstract] [Full Text] [PDF]

				W.-Z. Zhan, C. B. Mantilla, P. Zhan, A. Bitton, Y. S. Prakash, A. de Troyer, and G. C. Sieck Regional differences in serotonergic input to canine parasternal intercostal motoneurons J Appl Physiol, May 1, 2000; 88(5): 1581 - 1589. [Abstract] [Full Text] [PDF]