Implantation of Optoelectronic Devices in the Rodent Spinal Cord

We introduce an innovative and easy to perform methodology for the implantation and securement of neural probes in the rodent spinal cord. The implantation protocol is for neural probes that require direct contact with the spinal cord and can be tailored for probes that do not require direct contact. Recent advances in flexible bioelectronics have greatly improved implantable neuromodulatory devices.

While these devices have been extensively used in brain studies, there are limited reports on their application in the delicate and mobile tissue of the spinal cord. In addition, the cervical spine is particularly deep relative to the rest of the spine, further complicating the secureness of a probe. The protocols outlined in this paper enable researchers without experience in surgery to explore the intricate circuitry of the spinal cord.

Specifically, the implementation of fully implantable optoelectronic devices can unlock questions related to the spinal cord circuitry and function. To begin, secure the shaved, anesthetized rat on a stereotaxic frame. Using sterile forceps, palpate the base of the skull, feel for a prominent spinous process extending rostral caudally near the base of the skull, identified as C2.Proceed with palpation caudal to C2 to find a notably sharp and pointed spinous process identifiable as T2.Create an incision in the skin using a scalpel, starting from C2 and extending caudally for about 1.5 centimeters.

Carefully cut through the subcutaneous adipose layer to expose the intact underlying dorsal musculature. Then perform blunt dissection on the dorsal muscles by pulling them apart from the midline with two Adson forceps. Using rongeur and sterile forceps, lift a flap of skin immediately caudal to the incised area.

Then with the help of rongeurs, create a small subcutaneous pocket for the optoelectronic device. Place a retractor to expose the vertebral column. Using rongeurs, remove any remaining muscles or tissues covering the vertebrae, and begin to identify the spinal cord segments.

Immediately caudal to the ball-shaped muscle is C4, followed by C5 and C6.Once complete, rinse the surgical area with sterile saline and dry with sterile gauze. To place a probe under the lamina, perform a lateral laminectomy at C5 and C6, creating a lateralized opening in the lamina. To place a probe over the lamina, perform a medial laminectomy of C5 merely exposing a medial pathway.

Following the laminectomy, rinse the region with sterile saline and dry with sterile gauze to remove any bone debris. Hold the sterile optoelectronic device with plastic tips sterile forceps, and drive it inside the subcutaneous opening. Suture or glue the device to the neighboring muscle layer.

Place the retractor around the spinal cord and open a suitable window to place the probe on the spinal cord. Next, carefully insert the probe using plastic tip forceps under the C5 and C6 laminae by sliding it through the lateralized channels. To place the probe over the spinal cord, adjust the probe using plastic tip forceps to align and place the probe tip on top of the medial window created at C5.Dry the intended cementing area completely before applying one to two drops of dental cement at the tip of the probe.

Finally, confirmed that the applied cement is secure. Motor function analysis indicated similar forelimb function scores in device implants and sham groups by day 7. Similarly, there were no statistically significant differences between groups for hindlimb scores across all time points.