EVIDENCE THAT SYMPATHETIC PREGANGLIONIC NEURONS ARE ARRANGED IN TARGET-SPECIFIC COLUMNS IN THE THORACIC SPINAL-CORD OF THE RAT

It is recognised that selective activation of different target-specifi c sympathetic preganglionic neurones forms the basis of many autonomic responses. The anatomical basis for this could be the spatial arrange ment of these neurones in the spinal cord nuclei. The present study te sted this possibility in the rat by determining the location in single animals of three distinct groups of sympathetic preganglionic neurone s, one group projecting to the superior cervical ganglion, another to the stellate ganglion and one to the adrenal medulla. Sympathetic preg anglionic neurones to each of these targets were simultaneously labele d with fluorescent dyes, either Fluorogold, Fast Blue, or Diamidino Ye llow. The numbers and general morphology of the neurones were similar to previous descriptions, and they were distributed in four subnuclei, the nucleus intermediolateralis pars principalis, the nucleus interme diolateralis pars funiculus, the nucleus intercalatus spinalis, and th e nucleus intercalatus spinalis pars paraependymalis. It was shown tha t all three groups of neurones were represented in the more medial sym pathetic nuclei, but in the nuclei at the lateral border of the interm ediate grey matter each one of the three groups of neurones occupied a discrete location. Adrenal medullary sympathetic preganglionic neuron es occupied a lateral aspect, the superior cervical ganglion sympathet ic preganglionic neurones a medial aspect, and the stellate ganglion s ympathetic preganglionic neurones a space between. Some sympathetic pr eganglionic neurones were double labeled after dye injections into the superior cervical and stellate ganglion thus indicating that they pro jected to both ganglia. It is concluded that there are populations of sympathetic preganglionic neurones arranged in horizontal columns whic h only send axonal projections to the superior cervical, stellate gang lia, or adrenal medulla, respectively, and hence are target specified for each structure. This arrangement is likely to be of importance in understanding selective activation of autonomic effecters, a feature o f different types of behaviour. (C) 1994 Wiley-Liss, Inc.