Serotonin-immunoreactive axons in the cell column of sympathetic preganglionic neurons in the spinal cord of the filefish Stephanolepis cirrhifer

Serotonin-immunoreactive axonal components were observed in the central aut onomic nucleus (CAN), a cell column of sympathetic preganglionic neurons in the rostral spinal card of the filefish Stephanolepis cirrhifer. Serotonin -positive axonal varicosities were seen around neuronal perikarya through t he whole rostrocaudal extent of the CAN, although their distribution patter n in the rostral CAN was different from that in the caudal CAN. Electron mi croscopically, serotonin-positive axonal varicosities were found to make ax odendritic and axosomatic synapses on CAN neurons. Many serotonin-positive neuronal cell bodies were seen in the raphe nuclei in the lower brainstem, whereas only a few were found in the spinal cord. Thus most of serotoninerg ic axons within the CAN were considered to originate from the raphe nuclei in the lower brainstem. (C) 2000 Elsevier Science Ireland Ltd. All rights r eserved.