Bilateral transport of neuronal tracer after unilateral administration: Investigation of potential peripheral mechanism

Previous studies have shown pain attenuation after the administration of botulinum neurotoxin type A into the whisker pad contralateral to the nerve injury. It further showed localization in the neurons of the bilateral trigeminal ganglia, indicating a possible connection between the trigeminal nerves. Thus, this study aimed to investigate the potential link between the right and left trigeminal ganglia, considering their anatomical proximity and the possible neural interactions between these structures. The fluorogold (FG) neuronal tracer was localized in the neurons of both the right and left trigeminal ganglia (TG) after unilateral injection into the whisker pad. In contrast, there was a substantial decrease in FG localization in the contralateral ganglion following colchicine (CCh) administration or after midline incision surgery. Moreover, FG injected directly into the trigeminal ganglion was exclusively localized on the ipsilateral side. Additionally, systemic administration of FG revealed its localization not only within the bilateral TG neurons but also in the bilateral dorsal root ganglia (DRG) neurons, mirroring the findings following whisker pad injection. These findings suggest that bilateral transport of fluorogold occurs at the peripheral level, possibly through its diffusion from the injection site to the contralateral whisker pad and/or nerve axonal crossover through the midline. Further studies are required to clarify the specific peripheral pathways and explore the bilateral nerve connections.