Histopathologic and physiologic effects of chronic implantation of microelectrodes in sacral spinal cord of the cat.

Active microelectrodes were implanted for a period of 2 weeks to 3 months into the sacral spinal cord of 10 male cats in order to test the feasibility and the safety of discrete stimulation of the parasympathetic preganglionic nucleus for future clinical applications of microelectrode technology in micturition control. An array of four 50 microns-diameter iridium microelectrodes was inserted beneath the dura in each cat. At weekly intervals, bladder pressure was measured as hydrostatic pressure on an intraluminal catheter. At the end of the period, histopathology was evaluated with serial transverse epoxy sections. Observations included diffuse and focal axonal degeneration in white matter and possible neuronal loss around the electrode in the gray matter, meningeal ensheathment of the shafts, and occasional aseptic inflammation of tissue and apparent movement of the electrodes after implantation. Increased bladder pressure responses to individually pulsed electrodes located within the sacral parasympathetic nucleus were not consistent, and, surprisingly, at least 2 different sites were also effective. As long as 3 months after implantation, in 2 out of 5 animals, pulsing of electrodes consistently produced micturition. We conclude that while microelectrode implants are feasible, further modifications in electrode design are needed to eliminate movement and inflammation.