The neurons in the gelatinosal complex (laminae II and III) of the monkey (<i>Macaca mulatta</i>): A golgi study

Abstract

Abstract The nerve cells of the gelatinosal complex (laminae II and III) were examined in various planes of section in Golgi and Nissl preparations of the lumbosacral spinal cord of the adult monkey. An attempt was made to characterize the neurons based on morphological variations and establish criteria for consolidation or separation of laminae II and III. In Nissl preparations the laminae essentially conform to Rexed's ('52) description for the cat. In Golgi preparations impregnated neurons of the gelatinosal complex show a spectrum of morphological variation. These variations, however, are not restricted by Rexed's border between laminae II and III. In either lamina the cells vary in size from small (12 µm × 8 µm) to medium (30 µm × 25 µm) and in shape from fusiform to polygonal. Polygonal neurons are prevalent in the dorsal part of lamina II (Rexed's outer zone) and some have craggy contours. Axons of the cells of the gelatinosal complex vary in diameter, but most measure around 1.0 µm with some up to 2.0 µm. Their course is often a meandering one which cannot be followed. Those from cells in the outer zone of lamina II are different. They issue collaterals to lamina I then immediately enter the overlying white matter. Golgi type II (short axoned) cells were not definitively demonstrated. Nonetheless, the neurons of the gelationosal complex display stalked dendritic appendages and axon‐like processes which are similar to those described on Golgi type II interneurons elsewhere in the central nervous system. For this reason, in spite of the long axons and relatively large dimensions of the neurons of the gelationosal complex, their circuitry is suspected to be similar to that of local circuit interneurons. The dendritic arbor of the cells of the gelatinosal complex, as viewed in horizontal sections, generally extends longitudinally with little mediolateral spread. In sagittal sections a stratified pattern of dendritic arborization divides the gelatinosal complex into three regions: (1) an outer region which corresponds to Rexed's ('52) outer zone of lamina II, (2) a middle region composed of the remainder of lamina II and the dorsal portion of lamina III, and (3) an inner region or ventral part of lamina III. A large portion of the dendritic arbors of cells in the outer region spread ventrally at oblique angles while those from the inner region spread dorsally. Dendrites arising from cells in the middle region, on the other hand, extend almost exclusively in the longitudinal plane, are often of considerable lengths, and give rise to unique recurrent branches. The dendritic arborization is discussed in relation to the primary afferents to the gelatinosal complex.