LOCALIZATION OF UNMYELINATED AXONS IN RAT SKIN AND MUCOCUTANEOUS TISSUE UTILIZING THE ISOLECTIN GS-I-B-4

The alpha-D-galactose specific isolectin I-B-4 from Griffonia simplici folia (GS-I-B-4) labels CNS microglia and certain peripheral neurons, including a subpopulation of small dark, type B dorsal root ganglion c ells, some post-ganglionic sympathetic axons, and nearly all periphera l gustatory axons. The innervation patterns of GS-I-B-4 reactive senso ry ganglion cells are unknown for many peripheral target tissues, incl uding their probable primary target, the skin. The present study descr ibes the distribution of GS-I-B-4 reactive axons in hairy and glabrous hindpaw skin and in the glans penis of rats, using both single and do uble-labelling histochemical techniques. Neuronal processes were ident ified using (1) histochemistry with horseradish peroxidase conjugated GS-I-B-4 or (2) immunohistochemistry against PGP 9.5 to identify all a xons, and biotinylated lectin histochemistry with avidin-FITC to ident ify the subpopulation of GS-I-B-4 reactive axons. GS-I-B-4 strongly la belled unmyelinated cutaneous sensory afferents, as well as some sympa thetic efferents and visceral afferents. Lectin reactive axons were se en to innervate the upper hair shaft epidermis in hairy skin, and were abundant in the shallow dermis in hairy and glabrous skin and glans p enis. Lectin reactive axons were also abundant in the lamina propria a nd distal urethral epithelium of the penis. These results provide new evidence for the cutaneous sensory role of GS-I-BI reactive primary af ferents, as well as evidence to support the contention that the lectin is a specific marker for a subpopulation of unmyelinated axons and no t simply a marker for the myelination state of an axon.