Binding of Griffonia simplicifolia I-B-4 lectin in the substantia gelatinosa of the rat spinal cord

Histochemical distribution of sugar chains in the substantia gelatinosa of the dorsal horn in the rat spinal cord, where there are mainly small-diamet er sensory neurons, was studied with labeled lectins used as a probe. Cryos tat sections were prepared from the pre-fixed thoracic spinal cord. For lig ht microscopy, the sections were stained with the biotinylated lectins foll owed by avidin-Cy3, and observed under a confocal laser scanning microscope . For electron microscopy, the sections were treated with horseradish perox idase (HRP)-labeled lectins. Among more than 20 different kinds of lectins tested, GS I-B-4. Griffonia simplicifolia I-B-4, was shown light-microscopi cally to: selectively bind to sites in nerve fibers of the substantia gelat inosa, and also to those on the surface of unmyelinated nerve fibers and Sc hwann cells in the dorsal root. Electron microscopy revealed that GS I-B-4 bound to the axolemma of the unmyelinated nerve fibers and microglial cell membranes in tl le substantia gelatinosa, and also to the axolemma of the u nmyelinated nerve fiber and to the surface layer of the myelinated nerve fi ber in the dorsal root, i.e., to the Schwann cell membrane. On the other ha nd, GS I-B-4 binding was negative in the oligodendroglia except for the tra ns side of the Golgi complex. The present results indicate that the carbohydrate structure containing Gal alpha 1-3Gal sequence and related sugar structures, which has a strong aff inity for GS I-B-4, is distributed in the axolemma of the unmyelinated nerv e fibers, in the microglial cell membranes in the substantia gelatinosa, an d in the Schwann cell membranes in the dorsal root. A marked difference bet ween the oligodendroglial cell membrane and the Schwann cell membrane was f ound in terms of the distribution of Gal alpha 1-3Gal-type sugar structures . Differences in these myelin-forming cells may have some relevance to thei r functions as well as to demyelinating disease processes selectively confi ned to the central or the peripheral nervous system.