STRUCTURAL TYPES OF MARGINAL (LAMINA-I) NEURONS PROJECTING TO THE DORSAL RETICULAR NUCLEUS OF THE MEDULLA-OBLONGATA

The morphological features of lamina I neurons labelled from the medullary dorsal reticular nucleus with free or wheat germ agglutinin conjugated horseradish peroxidase and cholera toxin subunit B, were studied in the three standard anatomical planes in the rat. Orientation and way of branching of the dendritic arbors were further analysed by the method of Sholl in cells labelled with cholera toxin subunit B. Most marginal cells belong to the multipolar type (70%) of our Golgibased classification, and a minority to the pyramidal (15%) and flattened (15%) types. Following unilateral lesions severing the greatest part of the cuneate fasciculus, a considerable decrease of the numbers of labeled cells of the three types was observed caudal and ipsilaterally to the lesion. Contralateral labelling of multipolar and pyramidal cells was less decreased, and that of flattened cells was apparently unchanged. While multipolar cells, which make up the bulk of marginal spinobulbar neurons, appear to have no other supraspinal target, pyramidal and flattened cells have been labelled from the mesencephalon and the thalamus, respectively. It is suggested that the three structural cell types subserve different aspects of the spinofugal nociceptive output. © 1990.