Immune regulation of neuronal injury and repair by observing T cell activation

Background and Hypothesis: It is unknown how the immune system maintains the majority of facial motoneuron (FMN) survival after axotomy. IL-10 cytokine is necessary for FMN survival and CD4+ T cells are activated and play a critical role in survival, but do not produce IL-10. It was proposed that the source of IL-10 resides in the CNS; however, it is possible that antigen presenting cells (APC) produce IL-10 which activate CD4+ T cells to a neuroprotective phenotype. The regulation of IL-10 receptors (IL-10R) in immunodeficient compared to wild-type (WT) mice in the facial nucleus was studied in this experiment, as well as the possibility of the PNS producing IL-10. Experimental Design or Project Methods: To study APC’s role in motoneuron survival, we transferred WT whole splenocytes into global IL-10 knock out (KO) mice prior to axotomy. To study IL-10R gene expression, immunodeficient RAG-2 KO mice received WT or IL-10R-/- CD4+ T cells prior to axotomy. Results: qPCR revealed that WT mice upregulate IL-10R after axotomy, whereas RAG-2 KO mice had decreased expression comparatively. RAG-2 mice who received WT CD4+ T cells transfer restored IL-10R comparable to WT values.IL-10R was rescued in RAG-2 mice after the adoptive transfer of WT CD4+T cells. When IL-10R-/- CD4+ cells were transferred into RAG-2 mice, IL-10R values were restored; however, these T cells were unable to rescue FMN survival. Conclusion and Potential Impact: If WT whole splenocytes transferred into global IL-10 KO mice rescue FMN survival, it implies that APC play a role in producing IL-10. If they cannot mediate rescue, then peripheral IL-10 is unlikely sufficient for FMN survival. CD4+ T cells regulate central IL-10R response and must respond to IL-10 to mediate FMN survival. The transfer of whole splenocytes provides APCs capable of producing IL-10 and CD4+ T cells capable of responding to IL-10.

Pulmonary C-fiber receptor activation abolishes uncoupled facial nerve activity from phrenic bursting during positive end-expired pressure in the rat

Phasic respiratory bursting in the facial nerve (FN) can be uncoupled from phrenic bursting by application of 9 cmH2O positive end-expired pressure (PEEP). This response reflects excitation of expiratory-inspiratory (EI) and preinspiratory (Pre-I) facial neurons during the Pre-I period and inhibition of EI neurons during inspiration (I). Because activation of pulmonary C-fiber (PCF) receptors can inhibit the discharge of EI and Pre-I neurons, we hypothesized that PCF receptor activation via capsaicin would attenuate or abolish uncoupled FN bursting with an increase from 3 cmH2O (baseline) to 9 cmH2O PEEP. Neurograms were recorded in the FN and phrenic nerve in anesthetized, ventilated, vagally intact adult Wistar rats. Increasing PEEP to 9 cmH2O resulted in a persistent rhythmic discharge in the FN during phrenic quiescence (i.e., uncoupled bursting). Combination of PEEP with intrajugular capsaicin injection severely attenuated or eliminated uncoupled bursting in the FN ( P < 0.05). Additional experiments examined the pattern of facial motoneuron (vs. neurogram) bursting during PEEP application and capsaicin treatment. These single-fiber recordings confirmed that Pre-I and EI (but not I) neurons continued to burst during PEEP-induced phrenic apnea. Capsaicin treatment during PEEP substantially inhibited Pre-I and EI neuron discharge. Finally, analyses of FN and motoneuron bursting across the respiratory cycle indicated that the inhibitory effects of capsaicin were more pronounced during the Pre-I period. We conclude that activation of PCF receptors can inhibit FN bursting during PEEP-induced phrenic apnea by inhibiting EI and I facial motoneuron discharge.