title: Dental pulp and gingivomucosa in rats are innervated by two morphologically and neurochemically different populations of nociceptors.
abstract: OBJECTIVE
  Difference in phenotypes of sensory neurons innervating dental pulp or gingivomucosa may be responsible for intense pain sensations in pulpitis in contrast to relatively painless chronic periodontitis. Therefore, we classified these neurons according to their size and two neurochemical characteristics of nociceptors, their TrkA expression and isolectin IB4 binding.
  
  
  METHODS
  In rats (n=6) fluorescent tracers Fluorogold and TrueBlue were simultaneously applied into the standard-sized tooth cavity and nearby gingival sulcus, respectively. After the fluorescence on paraffin trigeminal ganglia (TG) sections was identified and photographed, immunohistochemistry for TrkA expression and IB4 binding was performed on the same sections.
  
  
  RESULTS
  The average sizes of TG neurons projecting to the gingivomucosa and dental pulp were 894±441μm(2) and 1012±381μm(2), respectively. The proportions of small-sized gingival and pulpal neurons were 14% and 5%, respectively (p<0.05). The proportions of TrkA-positive neurons among all gingival or pulpal neurons were 76% and 86%, respectively (p<0.05). Among all gingival or pulpal neurons the proportions of IB4-positive neurons were 46% and 3% (p<0.001), respectively, and the majority of them were small-medium sized.
  
  
  CONCLUSIONS
  Dental pulp and gingivomucosa are richly innervated by nociceptive TrkA-expressing neurons. However, while great majority of pulpal neurons are larger NGF-dependent A-fibre nociceptors without affinity to bind IB4, almost half of the gingival neurons are smaller IB4 binding C-fibre nociceptors. The difference in phenotype of sensory neurons might partially explain the different sensitivity of both tissues during normal and pathological conditions.
authors: Institute of Pathophysiology, Faculty of Medicine, University of Ljubljana, Zaloška 2, 1000 Ljubljana, Slovenia.
authors: Uroš
authors: U
authors: Kovačič
authors: Blaž
authors: B
authors: Tesovnik
authors: Nikola
authors: N
authors: Molnar
authors: Andrej
authors: A
authors: Cör
authors: Uroš
authors: U
authors: Skalerič
authors: Rok
authors: R
authors: Gašperšič
mesh_terms: D000818:Animals; D003782:Dental Pulp / Q000294:innervation* / Q000378:metabolism; D005260:Female; D005881:Gingiva / Q000294:innervation* / Q000378:metabolism; D007150:Immunohistochemistry; D009061:Mouth Mucosa / Q000294:innervation*; D009619:Nociceptors / Q000378:metabolism*; D037121:Plant Lectins / Q000276:immunology; D051381:Rats; D017208:Rats, Wistar; D020917:Receptor, trkA / Q000378:metabolism*; D012668:Trigeminal Ganglion / Q000166:cytology* / Q000378:metabolism
chemical_list: C045475:Griffonia simplicifolia lectins; D037121:Plant Lectins; D020917:Receptor, trkA