Histochemical demonstration of neural carbonic anhydrase activity within the mandibular molar and incisor tooth pulps of the rat

Carbonic anhydrase (CA) activity was enzyme histochemically assessed in: (1) neuronal cell bodies in the rat trigeminal ganglion that were retrogradely labeled with FITC-WGA from the mandibular molar and incisor tooth pulps; (2) cell bodies retrogradely labeled with HRP-WGA from the mandibular molar tooth pulp; and (3) nerve fibers within the decalcified mandibular molar and incisor tooth pulps. The cell size spectrum of the FITC-WGA-labeled neurons was similar for both molar and incisor tooth pulps with about 90% being medium or large (≥ 300 μm² in cross-sectional area). About 30% of the FITC-WGA-labeled cell bodies exhibited CA activity for both tooth pulps. The HRP-WGA-labeled cells also showed CA activity. In the molar root pulp, finely myelinated nerve fibers exhibited CA activity. Histochemical reaction products were distributed in the axoplasm and the cytoplasmic pocket of Schwann cell inside the compact myelin. In the incisor pulp, CA-reactive unmyelinated axons coexisted with non-reactive axons within the same Schwann units. The Schwann cell cytoplasm directly surrounding reactive axons also exhibited histochemical stainability. In the light of known distribution of CA in the peripheral nervous system, the present data suggest that the rat molar and incisor tooth pulps receive substantial innervation of large myelinated primary afferent fibers. The finely myelinated and unmyelinated axons, that have been repeatedly shown to predominate the intrapulpal nerve fibers, are considered to represent intrapulpal, terminal and preterminal specialization of otherwise large myelinated nerve fibers.