Injury induced changes in TRPV1 expression in the trigeminal ganglion

Objectives: Lingual nerve injury leads to retrograde changes in the associated cell bodies in the trigeminal ganglion. In this study we have quantified changes in expression of vanilloid receptor 1 (TRPV1), a transducer of noxious stimuli. Methods: In nine anaesthetised adult ferrets the left lingual nerve was sectioned and recovery was permitted for 3 days, 3 weeks or 3 months (3 ferrets per group). Three days before the end of the recovery period a retrograde tracer, fluorogold, was applied to the nerve to allow identification of cell bodies in the trigeminal ganglion with axons in the injured nerve. After perfusion fixation, under general anaesthesia (sodium pentobarbitone 42mg/kg i.p., maintenance 3mg/kg i.v.), the left trigeminal ganglion was harvested and frozen sections (14µm) processed using indirect immunofluorescence for TRPV1. The proportion of fluorogold positive cells that expressed TRPV1 was determined and compared with expression in non-fluorogold containing cells in another part of the ganglion. Comparisons were also made with results from control animals that only received the tracer injection. Results: In control ganglia 13.1±1.0(SD)% of the cells expressed TRPV1. Fewer cells expressed TRPV1 3 days after injury, although this difference was not significant (8.3±3.1%, p>0.05, ANOVA with Tukey-Kramer post hoc test). Compared to controls, significantly more cells expressed TRPV1 at 3 weeks (18.9±1.8%, p<0.05) but by 3 months the proportion was not significantly different (11.8±1.5%, p>0.05). TRPV1 expression in fluorogold negative cells in the ganglion was not affected by the injury. Conclusion: These results suggest that after lingual nerve injury TRPV1 expression in the associated trigeminal ganglion cells initially declines but is significantly increased by 3 weeks. These changes in expression may be involved in the excitability changes seen in ganglion cells after injury. Supported by the MRC (UK) and GlaxoSmithKline.