SPINAL AND VAGAL PROJECTIONS TO THE SYMPATHETIC TRUNK OF THE WRASSE, HALICHOERES POECILOPTERUS

The sympathetic preganglionic neurons of the teleost, Halichoeres poec ilopterus, were identified by retrograde axonal tracing. After horsera dish peroxidase was applied to the sympathetic trunk, labeled neurons were found at the caudalmost level of the medulla, in the spinal cord near the fourth spinal nerve root (rostral spinal group), and in the s pinal cord from rostral to the sixth spinal nerve root to caudal to th e tenth spinal nerve root (caudal spinal group). The rostral spinal gr oup has three cell columns segregated mediolaterally from the central gray zone to the lateral funiculus. Labeled neurons were found predomi nantly on the side ipsilateral to the application. In the caudal spina l group, labeled neurons were found bilaterally in the central gray zo ne. This condition is different from that previously reported in I-he puffer fish and filefish. The labeling in the medulla suggests that th e preganglionic neurons in the brainstem may send fibers to the sympat hetic trunk of this fish, although their peripheral targets are unknow n. (C) 1997 Elsevier Science B.V.