Multielectrodes have been used with great success to simultaneously record the activity of neuronal populations in awake,\nbehaving animals. In particular, there is great promise in the use of this technique to allow the control of neuroprosthetic\ndevices by human patients. However, it is crucial to fully characterize the tissue response to the chronic implants in animal\nmodels ahead of the initiation of human clinical trials. Here we evaluated the effects of unilateral multielectrode implants on\nthe motor cortex of rats weekly recorded for 1ââ?¬â??6 months using several histological methods to assess metabolic markers,\ninflammatory response, immediate-early gene (IEG) expression, cytoskeletal integrity and apoptotic profiles. We also\ninvestigated the correlations between each of these features and firing rates, to estimate the impact of post-implant time\non neuronal recordings. Overall, limited neuronal loss and glial activation were observed on the implanted sites. Reactivity\nto enzymatic metabolic markers and IEG expression were not significantly different between implanted and non-implanted\nhemispheres. Multielectrode recordings remained viable for up to 6 months after implantation, and firing rates correlated\nwell to the histochemical and immunohistochemical markers. Altogether, our results indicate that chronic tungsten\nmultielectrode implants do not substantially alter the histological and functional integrity of target sites in the cerebral\ncortex.
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