The morphology of spinocervical tract neurones in the cat.

Abstract

The morphology of physiologically identified spinocervical tract (SCT) neurons was studied using the intracellular injection of Procion dyes in anesthetized and decerebrate cats. Extracellular recordings were made from SCT neurons at depths between 1000-2825 .mu.m from the cord surface but neurons were only stained at depths between 1100-2400 .mu.m. The dendritic trees of stained SCT neurons were reconstructed in the transverse plane of the spinal cord. All SCT neurons had well developed dorsal dendrites, despite this it was not possible to consider the 22 SCT cells in the sample as constituting a morphologically homogeneous population. There was no correlation between the form of the dendritic trees and the depth of SCT neurons in the dorsal horn as determined both from measurements from the dorsal grey-white border and the position of cells with respect to the border between Rexed''s laminae II and III. Six types of SCT neurons were identified on the basis of the form of their dendritic trees as viewed in the transverse plane: radially symmetrical, semicircular, large elliptical, bilobed, triangular and small elliptical. Each of these types found only in a certain region across the dorsal horn, although any 1 region could contain more than 1 type. Spinocervical tract neurons with small elliptical dendritic trees always had receptive fields encompassing part of the hip or thigh and were unique in being located in the lateral portions of the horn. There was no correlation between the morphology of SCT neurons and their excitatory cutaneous inputs, receptive field size, axonal conduction velocity or depth in the dorsal horn.