COMBINED RETROGRADE TRACING AND IMMUNOHISTOCHEMISTRY OF TRIGEMINAL GANGLION NEURONS PROJECTING TO GINGIVA OR TOOTH PULPS IN THE LOWER JAW OF THE CICHLID TILAPIA-MARIAE

Rat trigeminal ganglion neurons projecting to the oral mucosa or to to oth 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 th e cichlid Tilapia mariae differ in a similar way. Retrograde tracing w ith fluorescent latex microspheres revealed labelled gingival and pulp al neurons in the caudal part of the trigeminal ganglion. The gingival neurons had a unimodal size distribution (peak 11 mu m; range 8-14 mu m) and the pulpal neurons exhibited a bimodal size distribution (peak s 12 and 25 mu m; range 10-40 mu m) Immunohistochemistry revealed a ca lcitonin gene-related peptide-like immunoreactivity in some 40% of the gingival neurons and a substance P-like immunoreactivity in 30%. Of t he small pulpal neurons about 60% exhibited a calcitonin gene-related peptide-like immunoreactivity and 15% showed a substance P-like immuno reactivity. Of the large pulpal neurons some 70% exhibited a calcitoni n gene-related peptide-like immunoreactivity. These neurons did not sh ow a substance P-like immunoreactivity. In some animals a few trigemin al ganglion neurons showed a neuropeptide Y- or a vasoactive intestina l polypeptide-like immunoreactivity. Perikarya with a tyrosine hydroxy lase- or a choline acetyl transferase-like immunoreactivity were not o bserved. We conclude that gingiva and tooth pulps in the lower jaw of T. murine are innervated by trigeminal ganglion neurons, the cell diam eters and neuropeptide contents of which differ in a pattern similar t o that in the rat. Hence, this seems to represent a conserved evolutio nary pattern.