Neuropeptide Expression and T-Lymphocyte Recruitment in Facial Nucleus After Facial Nerve Axotomy

Axonal injury in the peripheral nervous system can have a strong impact on the neurons and the surrounding non-neuronals cells. The aim of this study was to evaluate the immunohistochemistry signals of the vasoactive intestinal peptide (VIP), substance P (SP), and CD3(+) T cells and the messenger RNA levels of neuropeptides in the facial nucleus (FN) at 7, 14, and 21 days after peripheral facial nerve axotomy. Moreover, the authors assayed the peripheral blood levels of interleukin (IL-1 beta), tumor necrosis factor-alpha, and IL-6 serum levels at 24 and 48 hours after the surgical procedures. Immunohistochemistry analysis revealed that VIP and SP expression is strongly induced in FN after peripheral facial nerve axotomy at 7 days, the CD3(+) pan-T cells peak at 14 days. Polymerase chain reaction analysis for VIP and SP messenger RNA levels confirms the immunohistochemical data, but VIP level remains significantly high for 14 days. The serum level of IL-6 48 hours after axotomy was significantly higher than after 24 hours; there were no significant changes for IL-1 beta and tumor necrosis factor-alpha serum levels between 24 and 48 hours. Our data reveal that FN neurons are under neuropeptidergic influence and show that modulation/modification of VIP and SP expression in FN injury models facilitates the crossing of the blood-brain barrier. On the contrary, our results emphasize the role of the T cells in preventing initial neurodegeneration or neuronal death. The high serum levels of IL-6 at 1 to 2 days suggest that this cytokine could play a central role in the initiation of immunosurveillance and provide advance information on the recruitment of CD3(+) T lymphocytes in the FN.