Cytoarchitectonic organization of lumbar preganglionic sympathetic neurons in the cat

The location and dendritic projection of lumbar preganglionic sympathetic neurons (PSN) has been investigated in the cat. Horseradish peroxidase was either injected into lumbar paravertebral ganglia or directly applied to a lumbar ramus communicans albus. PSN were regularly found in the lateral funiculus and in the intermediate area of the ipsilateral spinal cord. They were concentrated in different nuclei: nuclei intermediolateralis pars principalis (IMLp) and pars funicularis (IMLf), nucleus intercalatus (IC) and medially near the central channel. Inconsistently, some PSN were observed in the ventral horn. Dendrites extending over a few soma were found in nearly all PSN, thus allowing description of the main dendritic projections of the preganglionic nuclei. Sometimes axons of IMLp and IC neurons could be traced into the ventral roots. In the IMLp the PSN were arranged in round clusters (up to 30 cells), which regularly followed each other in rostrocaudal direction. These clusters increased their mediolateral diameter from L1 to L4. Many cells distributed their dendrites longitudinally within the IMLp, but dendritic projections into the dorsal horn, the intermediate area and into the lateral funiculus were also frequently observed. The IMLf consisted of a few PSN only. These neurons were located in the tissue spaces between axon bundles and mediolaterally arranged, pointing towards the IMLp. The PSN of the IC were mediolaterally oriented and arranged in transverse bands extending from the lateral horn to the dorsal aspects of the central channel. All cells had mediolaterally oriented dendrites which sometimes crossed the spinal cord midline in case of the medially located neurons. The dendrites of the laterally located cells projected very often into the dorsal horn. In the medial region the PSN covered a narrow area extending from the dorsal aspects of the central channel in a ventrolateral direction up to the level of the ventral commissure. The neurons were localized in clusters and mediolaterally or longitudinally oriented. Dense clusters consisting of round cells were prevalent in the ventrolateral position. The dendrites had a rostrocaudal and mediolateral orientation and, in case of the dorsomedially located cells, sometimes crossed the spinal cord midline. The main dendritic projection areas of the different preganglionic nuclei have been compared with the location of the terminal fields of descending supraspinal and propriospinal systems and of primary afferents. It has been considered that this structural arrangement would allow for intricate interaction of the various systems with subpopulations of PSN. Thus each preganglionic nucleus might integrate specific neuronal information.