The organization of the substantia gelatinosa rolandi in the cat lumbosacral spinal cord

Summary The organization of the substantia gelatinosa and adjacent lamina III in cat lumbo-sacral spinal cord has been studied by light and electron microscopical techniques in normal cord and following dorsal root section.The substantia gelatinosa (lamina II of Rexed) is characterized by bundles of small, non-myelinated axons, principally oriented longitudinally. The substantia gelatinosa cells are small, spindle shaped, with a cytoplasm generally devoid of Nissl substance. There are extensive axo-dendritic and axo-axonal contacts within the substantia gelatinosa and less frequent axo-somatic contacts.Larger marginal cells oriented horizontally on the surface of the substantia gelatinosa and containing Nissl substance are also seen.Lamina III is somewhat similar to the substantia gelatinosa, but lacks the complex bundles of non-myelinated axons.Following dorsal root section, heavy degeneration is seen by light and electron microscopy in lamina III, but is rarely seen in the substantia gelatinosa. It is concluded that the substantia gelatinosa and lamina III are distinct anatomically and therefore may differ functionally.The possible physiological role of the substantia gelatinosa is discussed.This work was supported by a Special Fellowship 2F11 NB 1140 02 NSRB from the National Institute of Neurological Diseases and Blindness, United States Public Health Service.The author is indebted to Dr. E. G.Gray for his excellent advice. I thank Dr. R. W. Guillery, Dr. L. E. Westeum and Dr. B. G. Cragg for their assistance, and Prof. J. Z. Young, F. R. S. for his kind suggestions. I also wish to thank Mr. S. Waterman for the photography.