Microglial Activation After Acute Spinal Cord Electrode Implant

Spinal cord stimulation has become a widely used and efficient alternative for the management of neurological disorders such as refractory chronic pain. The implanted devices likely induce activation of microglia, the cells responsible for the initiation of inflammatory response in the central nervous system. However, so far there are no available data on the microglial response following spinal cord epidural implants. This study intended to characterize the acute microglial response after spinal cord electrode implantation. To evaluate the acute response, a custom-made flat bipolar platinum electrode was implanted in the epidural space under the thoracic vertebra 4 (T4) in Wistar rats. Two days after implantation, morphological changes of microglia were evaluated by immunohistochemistry staining for ionized calcium-binding adaptor protein-1 (IBA-1) in spinal cord sections. Substantial loss of microglia ramification was found throughout the spinal cord at the implant site (T4). In contrast, microglia was not activated in areas distant from the implant such as cervical vertebra 4 (C4) and thoracic vertebra 11 (T11). This result interestingly demonstrates that semi-invasive implants in the spinal cord are able to induce the activation of microglial cells at the implant region. This work is the first step towards understanding the impact of epidural implants in spinal cord tissue.