IDENTIFICATION AND NEUROPEPTIDE CONTENT OF TRIGEMINAL NEURONS INNERVATING THE RAT NASAL EPITHELIUM

Trigeminal ganglia provides sensory innervation to the rat nasal cavit y. The purpose of this study was to identify the location and characte rize the neuropeptide content of trigeminal neurons that project speci fically to the rat nasal epithelium. The right nasal cavity was instil led with 4 mu l of rhodamine-labelled latex microspheres. Seven, 10 or 14 days after tracer instillation, both trigeminal ganglia were remov ed and prepared for substance P and calcitonin gene-related peptide im munocytochemistry. Neurons labelled with microspheres were located in the trigeminal ganglia at the division of the ophthalmic and maxillary nerves and were only found on the side ipsilateral to the instillatio n. The percentage of labelled cell body profiles in the right trigemin al ganglia averaged 1.61 +/- .04% at seven days, 1.54 +/- .01% at 10 d ays, and 1.65 +/- .02% at 14 days after instillation. These values wer e not statistically different, but the fluorescence intensity in label led neurons was increased after 14 days. The right trigeminal ganglia contained a mean of 166 +/- 13.81 labelled cell body profiles represen ting 1.60 +/- .09% of the total. Of the labelled profiles, 81.6 +/- 3. 27% were immunoreactive for substance P and 35.2 +/- 4.00% for calcito nin gene-related peptide. Sections of nasal mucosa showed that the mic rospheres were localized only in the epithelial layer and did not ente r the lamina propria indicating that the microsphere transport was con fined to nerve fibres present in the epithelial layer. These studies h ave identified specific neurons in the trigeminal ganglia that project to the nasal epithelium. Most of the neurons retrogradely labelled fr om the nasal cavity contained substance P but some contained calcitoni n gene-related peptide, suggesting that the nasal epithelium is predom inantly targeted by substance P-containing neurons. (C) 1997 IBRO. Pub lished by Elsevier Science Ltd.