Immunohistochemical Analysis of Maxillary Nerve Distribution in Rats
Previous studies of nerve distribution in the orofacial complex have focused primarily on the anatomic courses of nerve fibers and have rarely addressed the density of nerve distribution. The nerve distribution in the mandible was described in only one report which showed an increase in nerve distribution density moving from the alveolar crest toward the inferior alveolar nerve. However, no previous reports have focused on the nerve distribution density in the maxilla. In this study involving 6 Wistar rats, tissue samples from the maxillary molar region were obtained and sectioned for staining and analysis. All nerves including nociceptive nerves in 5 regions of the maxilla samples, ranging from the alveolar crest to the superior alveolar nerve, were immunohistochemically stained with antibodies to protein gene product (PGP) and calcitonin gene-related peptide (CGRP) to identify and measure the vertical and horizontal nerve distribution densities in the 5 regions under an optical microscope. We also determined the ratio of nociceptive (CGRP-positive) nerves to all (PGP-positive) nerves. The densities of both PGP- and CGRP-positive nerves increased vertically from the alveolar crest to the superior alveolar nerve and horizontally from the periosteal side to the periodontal ligament side within the maxilla. The ratio of CGRP- to PGP-positive nerves was on average greater than 80%. These findings were consistent with those of the previous report on mandibular nerve distribution. However, our results suggest that the overall nerve distribution density in the maxilla is approximately one-third of that in the mandible. The results of this study, which report the nerve distribution density in the posterior maxilla, may support future research on pain and local anesthesia.Objective
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Cross-sectional Specimen of Rat Maxillary Molar Alveolar Bone
The enclosed region is the alveolar bone which was divided vertically into 5 sections (A, B, C, D, and E) spanning from the alveolar crest to near the superior alveolar nerve. Region C was subdivided horizontally into equal thirds (CL, CC, and CP) spanning the periosteal side to periodontal ligament side. Nerve distribution density was measured in each region (No. of nerve fibers/mm2).
Immunohistochemical Staining With Antibodies
The black arrows indicate nerves. The left image shows a specimen stained with protein gene product (PGP) antibody, while the right image shows a specimen stained with calcitonin gene-related peptide (CGRP) antibody. The area of bone in each region was measured, and the number of nerves per area was measured using ZEN blue image analysis software.
Vertical Nerve Distribution Density Analysis
The left panel presents a photograph of the tissue specimen with black lines and letters indicating the 5 vertical regions. The right panel shows bar graphs of mean distribution density values. There were significant differences in the distribution density of PGP-positive (all) and CGRP-positive (nociceptive) nerves (P = 9.012−7 and P = .0002, respectively). The nerve distribution density increased significantly toward the superior alveolar nerve from the alveolar crest. PGP, protein-gene product; CGRP, calcitonin gene-related peptide.
Horizontal Nerve Distribution Density Analysis
The bottom panel shows a photograph of the tissue specimen with the 3 horizontal subregions represented by black line and letters. The top panel shows bar graphs corresponding to each region. There were significant differences in the mean distribution density of PGP-positive (all) and CGRP-positive (nociceptive) nerves (P = .0025 and P = .0021, respectively). The nerve distribution density increased significantly toward the periodontal ligament side. PGP, protein-gene product; CGRP, calcitonin gene-related peptide; CL, periodontal ligament third; CC, center third; CP, periosteal third.
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