Objective: Neural interfacing technologies could significantly improve quality of life for people living with the loss of a limb. Both motor commands and sensory feedback must be considered; these complementary systems are segregated from one another in the spinal nerve.
Approach: The dorsal root ganglion-ventral root (DRG-VR) complex was targeted chronically with floating microelectrode arrays designed to record from motor neuron axons in the VR or stimulate sensory neurons in the DRG. Hematoxylin and eosin and Nissl/Luxol fast blue staining were performed. Characterization of the tissue response in regions of interest and pixel-based image analyses were used to quantify MAC387 (monocytes/macrophages), NF200 (axons), S100 (Schwann cells), vimentin (fibroblasts, endothelial cells, astrocytes), and GLUT1 (glucose transport proteins) reactivity. Implanted roots were compared to non-implanted roots and differences between the VR and DRG examined.
Main results: The tissue response associated with chronic array implantation in this peripheral location is similar to that observed in central nervous system locations. Markers of inflammation were increased in implanted roots relative to control roots with MAC387 positive cells distributed throughout the region corresponding to the device footprint. Significant decreases in neuronal density and myelination were observed in both the VR, which contains only neuronal axons, and the DRG, which contains both neuronal axons and cell bodies. Notably, decreases in NF200 in the VR were observed only at implant times less than ten weeks. Observations related to the blood-nerve barrier and tissue integrity suggest that tissue remodeling occurs, particularly in the VR.
Significance: This study was designed to assess the viability of the DRG-VR complex as a site for neural interfacing applications and suggests that continued efforts to mitigate the tissue response will be critical to achieve the overall goal of a long-term, reliable neural interface.