Abstract
Histochemical distribution of sugar chains in the substantia gelatinosa of the dorsal horn in the rat spinal cord, where there are mainly small-diameter sensory neurons, was studied with labeled lectins used as a probe. Cryostat sections were prepared from the pre-fixed thoracic spinal cord. For light microscopy, the sections were stained with the biotinylated lectins followed by avidin-Cy3, and observed under a confocal laser scanning microscope. For electron microscopy, the sections were treated with horseradish peroxidase (HRP)-labeled lectins. Among more than 20 different kinds of lectins tested, GS I-B4, Griffonia simplicifolia I-B4, was shown light-microscopically to selectively bind to sites in nerve fibers of the substantia gelatinosa, and also to those on the surface of unmyelinated nerve fibers and Schwann cells in the dorsal root. Electron microscopy revealed that GS I-B4 bound to the axolemma of the unmyelinated nerve fibers and microglial cell membranes in the substantia gelatinosa, and also to the axolemma of the unmyelinated nerve fiber and to the surface layer of the myelinated nerve fiber in the dorsal root, i.e., to the Schwann cell membrane. On the other hand, GS I-B4 binding was negative in the oligodendroglia except for the trans side of the Golgi complex.
The present results indicate that the carbohydrate structure containing Gal α1-3Gal sequence and related sugar structures, which has a strong affinity for GS I-B4, is distributed in the axolemma of the unmyelinated nerve fibers, in the microglial cell membranes in the substantia gelatinosa, and in the Schwann cell membranes in the dorsal root. A marked difference between the oligodendroglial cell membrane and the Schwann cell membrane was found in terms of the distribution of Gal α1-3Gal-type sugar structures. Differences in these myelin-forming cells may have some relevance to their functions as well as to demyelinating disease processes selectively confined to the central or the peripheral nervous system.
