AN ANALYSIS OF THE SYMPATHETIC PREGANGLIONIC NEURONS PROJECTING FROM THE UPPER THORACIC SPINAL ROOTS OF THE CAT

The distribution of sympathetic preganglionic neurons projecting via the right stellate ganglion were studied quantitatively in adult cats. Retrograde transport of horseradish peroxidase (HRP) injected into the ganglion or applied to transected axons of the cervical sympathetic trunk (CST) resulted in labeling of neurons in the ipsilateral spinal cord over T1-T9 [thoracic segments 1-9] and T1-T7, respectively. Their distribution and morphology in the subnuclei of the intermediate zone were determined. Neurons within the principal part of the intermediolateral column (ILp) comprised the majority of labeled cells at all levels, irrespective of the site of HRP application; more medially located neurons projected differentially. A combination of the application procedures labeled an apparent sum of the individual projections. Few ILp cells remained unlabeled in the most rostral segments. From reconstructions of different segmental levels most of the cells in the ILp were in a column .apprx. 200 .mu.m in diameter composed of a series of cell aggregations of 20-150 neurons at intervals of .apprx. 300 .mu.m. Less frequently, mediolaterally aligned cells extended toward the central canal, near which small cell clusters were detected. After selective HRP application to individual rami of T1-T3, labeled cells were restricted to 1 segment''s length, i.e., neurons located more caudally must projected extraspinally to the stellate ganglion. The maximum cell numbers labeled by each procedure were considered. Preganglionic collaterals (probably unmyelinated) diverging from the pathway to the preferred target of their parent neuron were not labeled by this technique.