Abstract
Motor innervation of cat diaphragm was studied by retrograde tracer methods using HRP and fluorescent substances of primuline (Pr) and propidium iodide (Pi). In HRP study 20% HRP was injected into the left hemidiaphragm of kittens. After 48hr animals were perfused with glutaraldehyde and paraformaldehyde. Spinal cord from C1 to Th13 were resected, cut into 40μm serial frozen sections, and provided for TMB reaction. Under the darkfield microscope a cluster of HRP positive neurons was observed in the ventromedial portion of the left anterior horn of the lower cervical (C5 to C6) and lower thoracic (Th9 to Th12) spinal cord, ipsilaterally to the injected side. For the survey of the interrelation of motor innervation between the diaphragm and intercostal muscles, fluorescent dual labeling method was applied. 10% Pr was injected into the left hemidiaphragm, while 3% Pi was injected into the left 8th to 13th intercostal muscles in kittens simultaniously. After 36hr animals were perfused with 10% formalin. Resected spinal cords were cut into 25μm serial frozen sections and observed under the fluorescence microscope. At 360nm excitation wavelength a small cluster of neurons was illuminated in the specific yellow fluorescence for Pr, while at 550nm another cluster of neurons was visualized in the specific orange fluorescence for Pi. These two clusters formed a cell group in the ventromedial portion of the anterior horn from 9th to 12th thoracic cords.
Based on these experiments, motor innervation of cat diaphragm can be ascribed not only to the lower cervical but also to the lower thoracic motoneurons, probably via intercostal nerves. The present results might reappraise and consequently support the old hypothesis of “extra-phrenic motor innervation of diaphragm”.
