Neutrophil responses are substantially prolonged and robust following early postnatal chorda tympani or lingual nerve transection

While the mature gustatory and trigeminal systems are capable of regeneration following surgical nerve transection, transections occurring early in life result in permanent effects on innervated tissues. Converging evidence suggests that facilitators of the innate immune response, such as neutrophils, may contribute to these developmental differences in injury recovery. In the current study, Sprague-Dawley rats underwent transection of the trigeminal lingual nerve (LX) or gustatory chorda tympani nerve (CTX) at either 10, 25, or 65 days of age. Tongues were extracted 12, 24, or 48 h post-surgery, and MPO+ leukocyte (neutrophil) densities in the taste buds and surrounding muscle and epithelium were assessed. The neutrophil response to LX or CTX performed at 25 or 65 days of age was minimal to non-existent at all time points examined. In contrast, we observed a robust neutrophil response on both the ipsilateral and contralateral sides of the tongue starting 12 h after LX or CTX performed at 10 days of age, continuing through 24 h post-surgery, before returning to baseline quantities at 48 h. These results add to growing evidence that differences in the innate immune response may contribute to developmental differences in gustatory and trigeminal system injury recovery.