Spinal Cord Projections of the Upper Intercostal Nerve In the Rabbit Studied by Wheat Germ Agglutinin Conjugated Horseradish Peroxidase

Abstract

Spinal cord projections of the upper intercostal nerve in the rabbit were studied using axonal transport of wheat germ agglutinin conjugated horseradish peroxidase (WGA-HRP) .
To label the spinal motoneurons, WGA-HRP was injected into three intercostal nerve branches: the external intercostal (EIC) nerve, and the medial (MIIC) and lateral (LIIC) branches of the internal intercostal nerve. The locations, the numbers and the soma size (average soma diameter) of 451 labeled motoneurons were analyzed in this study.
TMB reaction products were identified in the spinal cord from one and a half segments rostral to half a segment caudal to the entry segment. No reaction products were found on the contralateral side. Labeled motoneurons containing dense granular reaction products and their dendritic processes were located in the lateral portion of the ventral horn gray matter. Soma diameter ranged between 12μm and 45μm (average 23-25μm) . Motoneurons labeled after injections into the three intercostal nerves (T4 or T5) overlapped extensively on transverse sections of ventral horn spinal cord. The results indicate that the LIIC nerve, which is neuroanatomically named the lateral cutaneous branch of the internal intercostal nerve, contains motor fibers originating from ventral horn motoneurons.