Morphology of sympathetic preganglionic neurons innervating the superior cervical ganglion in the chicken: an immunohistochemical study using retrograde labeling of cholera toxin subunit B.

Preganglionic sympathetic neurons (SPNs) in the chicken were demonstrated immunohistochemically using cholera toxin subunit B (CTb) as a retrograde tracer. After injection of CTb-solution into the superior cervical ganglion, labeled SPNs were mainly found in the ipsilateral sympathetic preganglionic column of Terni (the column of Terni), with only a few in the intermediate zone. They were observed from the caudal half of the 15th cervical segment to the rostral tip of the 3rd thoracic segment. Cell somata of SPNs were loosely packed within the column of Terni, where they had an elliptic shape with the long axis oriented rostrocaudally. In the horizontal plane three kinds of dendrites could be discriminated on the basis of their orientation. Longitudinally oriented dendrites emanated from the rostral and the caudal poles of the SPNs. Medially oriented dendrites were observed to cross the midline and enter the contralateral column of Terni, where they further branched to form a loose dendritic plexus; some extended beyond the lateral limit of the contralateral column of Terni to reach the intermediate zone. Laterally oriented dendrites formed periodically arranged dendritic bundles projecting into the intermediate zone. The present findings provide a detailed account of the dendritic organization of SPNs in the chicken, and suggest that avian SPNs share certain structural features in common with mammalian SPNs.