DIFFERENT LOCALIZATIONS OF GROWTH-ASSOCIATED PROTEIN (GAP-43) IN MECHANORECEPTORS AND FREE NERVE-ENDINGS OF ADULT-RAT PERIODONTAL-LIGAMENT,DENTAL-PULP AND SKIN

Distributions of growth-associated protein-43 (GAP-43) in the periodon tal ligament and dental pulp of adult rats were studied by light and e lectron microscopy. The mature periodontal ligament and dental pulp co ntained numerous GAP-43-positive neural elements, comprising periodont al Ruffini endings and thin nerve fibers, but expression patterns diff ered among the kinds of nerves, In the periodontal ligament of rat mol ars, immunoelectron microscopy revealed that GAP-43 like immunoreactiv ity in the Ruffini ending, an essential mechanoreceptor, was confined to the Schwann sheaths around the axon terminals and was not in the ax on terminals themselves, unlike free endings that revealed axonal GAP- 43, However, the lamellar Schwann cells associated with the cutaneous receptors did not exhibit any GAP-43 like immunoreactivity though they were intensely reactive for low affinity nerve growth factor receptor (p75-NGFR), a marker for lamellar Schwann cells in mechanoreceptors, The characteristically uniform expression of GAP-43 in the Schwann lam ellae that surround the Ruffini mechanoreceptors of rat molar ligament suggests that Schwann cells are involved in the GAP-43 mediated plast icity of these receptors. On the other hand, the pulpal nerves were fi lled with the reaction products in their axonal spaces, suggesting the potential for neuronal plasticity during normal function and after to oth injury.