Abstract
Rat trigeminal ganglion neurons projecting to the oral mucosa or to tooth pulps have different cell diameters and contain different chemical markers. In the present paper we examine whether trigeminal ganglion neurons sending axons to gingiva or tooth pulps in the lower jaw of the cichlid Tilapia mariae differ in a similar way. Retrograde tracing with fluorescent latex microspheres revealed labelled gingival and pulpal neurons in the caudal part of the trigeminal ganglion. The gingival neurons had a unimodal size distribution (peak 11 microns; range 8-14 microns) and the pulpal neurons exhibited a bimodal size distribution (peaks 12 and 25 microns; range 10-40 microns). Immunohistochemistry revealed a calcitonin gene-related peptide-like immunoreactivity in some 40% of the gingival neurons and a substance P-like immunoreactivity in 30%. Of the small pulpal neurons about 60% exhibited a calcitonin gene-related peptide-like immunoreactivity and 15% showed a substance P-like immunoreactivity. Of the large pulpal neurons some 70% exhibited a calcitonin gene-related peptide-like immunoreactivity. These neurons did not show a substance P-like immunoreactivity. In some animals a few trigeminal ganglion neurons showed a neuropeptide Y- or a vasoactive intestinal polypeptide-like immunoreactivity. Perikarya with a tyrosine hydroxylase- or a choline acetyl transferase-like immunoreactivity were not observed. We conclude that gingiva and tooth pulps in the lower jaw of T. mariae are innervated by trigeminal ganglion neurons, the cell diameters and neuropeptide contents of which differ in a pattern similar to that in the rat. Hence, this seems to represent a conserved evolutionary pattern.
Published Version
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