Stimulation and Sensitization of Adult Mouse Dorsal Root Ganglion Neurons in Vitro

Dorsal root ganglion (DRG) neurons are primary sensory neurons that relay information from skin and muscle to the spinal cord. Under physiological conditions, nociceptors are quiescent and have relatively high thresholds for activation. However, tissue injury and inflammation can lead to DRG hyper-excitability, which mediates chronic pain. Several in vitro DRG models are currently used to study development of DRG hyperexcitability. However, they are low throughput and use embryonic neurons and cell lines that do not reflect the adult DRG physiology. Therefore, we believe that new strategies are needed to improve our understanding of the underlying cellular mechanisms associated with DRG sensitization and resulting hyperexcitability. This study takes a unique approach to overcome some of these limitations by evaluating functional activity of adult mouse DRG neurons using micro-electrode arrays (MEAs). Adult DRG neurons were extracted from naïve mice and their spontaneous activity was monitored for 3 weeks. We observed the spontaneous functional activity of these neurons peaked at day 11, and remained silent afterwards. Thereafter, we showed that adult DRG neurons were responsive to acute exposure of capsaicin and temperature increase. We also demonstrate that interleukin-6 and nerve growth factor can induce sensitization in the adult DRGs, an observation consistent with what is observed in vivo. Thus, adult DRG neurons cultured on MEAs for 3 weeks may serve as an in vitro model for evaluating the molecular and cellular mechanism of neuropathic pain, as well as a screening platform for the discovery of novel analgesics.