An ultrastructural study of the binding of an alpha-D-galactose specific lectin from Griffonia simplicifolia to trigeminal ganglion neurons and the trigeminal nucleus caudalis in the rat.

The pattern of binding by the isolectin I-B4 from Griffonia simplicifolia to trigeminal ganglion neurons and the trigeminal nucleus caudalis has been investigated at the ultrastructural level in the rat. This lectin bound to small ganglion neurons with two different binding patterns. The majority of the ganglion cells labelled had reaction product throughout their cytoplasm and this was associated with the Golgi apparatus and endoplasmic reticulum. In a second group of small ganglion neurons the binding was only found on the surface plasma membrane of the cells. In the trigeminal tract the cytoplasm of many unmyelinated axons and a few small myelinated axons was found to bind this lectin. A very thin band of staining was also found on the inner and outer edges of the myelin sheaths of other myelinated axons. Staining of synapses was found throughout laminae I and II with the highest frequency in the inner part of laminae II. These synapses made both simple and complex connections with one or more dendrites, contained clear round vesicles and had asymmetric synaptic densities. Some of the glomerular synapses stained were observed to receive presynaptic synapses containing small clear flattened vesicles. Synapses containing both clear round and large dense core vesicles were unstained. Some staining was also found in dendrites. In weakly fixed tissue, staining was also found around some glial cells and on the luminal membranes of capillary endothelial cells. This lectin is a valuable tool for studies of the "non-peptide" group of C-fibre primary afferents.