Experimental study following inactive implantation of an auditory brain stem implant in nonhuman primates

We report changes in the cochlear nuclei (CNs) after 3 months of bilateral auditory deafferentation and simultaneous unilateral implantation of a dummy auditory brain stem implant (ABI) in 6 nonhuman primates (Macaca fascicularis). These specimens were compared to CNs of 9 controls and 7 bilaterally deafferented animals without implantation. The ABI array consists of 3 platinum electrodes mounted on a silicone pad with the back side covered with Dacron. No migration of the ABI was observed. All deafferented animals showed astrocytic reorganization in the CNs. Histologic changes consisted of superficial reactions around the implant, with formation of fibrillar bundles of fusiform cells, and the presence of giant cells close to the Dacron. Other findings were related to surgical trauma. The dummy ABI did not itself provoke serious adverse reactions in the CNs. Our observations support the possibility of ABI reimplantation surgery.