• M Iizuka, H Onimaru, and M Izumizaki.
• Center for Medical Sciences, Ibaraki Prefectural University of Health Sciences, 4669-2 Ami, Ibaraki 300-0394, Japan; Department of Physiology, Showa University School of Medicine, 1-5-8 Hatanodai, Shinagawa-ku, Tokyo 142-8555, Japan. Electronic address: iizukam@med.showa-u.ac.jp.
• Neuroscience. 2016 Feb 19; 315: 217-27.

AbstractThe inspiratory motor outputs are larger in the intercostal muscles positioned at more rostral segments. To obtain further insights into the involvement of the spinal interneurons in the generation of this rostrocaudal gradient, the respiratory-related neuronal activities were optically recorded from various thoracic segments in brainstem-spinal cord preparations from 0- to 2-day-old rats. The preparation was stained with a voltage-sensitive dye, and the optical signals from about 2.5s before to about 7.7s after the peak of the C4 inspiratory discharge were obtained. Respiratory-related depolarizing signals were detectable from the ventral surface of all thoracic segments. Since the local blockage of the synaptic transmission in the thoracic spinal cord induced by the low-Ca(2+) superfusate blocked all respiratory signals, it is likely that these signals came from spinal neurons. Under the-low Ca(2+) superfusate, ventral root stimulation, inducing antidromic activation of motoneurons, evoked depolarizing optical signals in a restricted middle area between the lateral edge and midline of the spinal cord. These areas were referred to as 'motoneuron areas'. The respiratory signals were observed not only in the motoneuron areas but also in areas medial to the motoneuron areas, where interneurons should exist; these were referred to as 'interneuron areas'. The upper thoracic segments showed significantly larger inspiratory-related signals than the lower thoracic segments in both the motoneuron and interneuron areas. These results suggest that the inspiratory interneurons in the thoracic spinal cord play a role in the generation of the rostrocaudal gradient in the inspiratory intercostal muscle activity. Copyright © 2015 IBRO. Published by Elsevier Ltd. All rights reserved.

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