Sampling extracellular aspartate, glutamate and gamma-aminobutyric acid instriate cortex of awake cat by in vivo microdialysis: surgical and methodological aspects

A method which permits repeated microdialysis in the cortical layers of are a 17 of the awake cat is described. Under visual control through a surgical microscope and using a stereotactic instrument, four probe guides are perm anently implanted in area 17 of one hemisphere of the anesthetized animal a nd two fixation bars an mounted on the skull to allow fixation of the cat i n a stereotactic frame. The implantation of four probe guides in the same h emisphere allows simultaneous sampling from different cortical regions serv ing different parts of the visual held. A removable transparent cover prote cts the probe guides. After recovery from surgery the awake cats are traine d to adapt to a fixation of 5 h in a stereotaxic apparatus. Once adapted to that situation, the cats are ready for microdialysis experiments without a nesthesia. The day of the experiment, the awake animal was fixed in the ste reotactic frame and the probes inserted into the guides. To test the validi ty of the method, the basal efflux and the depolarization efflux, triggered by the addition of 65 mM K+ to the artificial cerebrospinal fluid, of the amino acids aspartate, glutamate and gamma-aminobutyric acid are measured b y two HPLC-electrochemical detection methods. The exact localization of the probes and the reaction of the surrounding tissue is studied using immunoc ytochemistry for glutamate and glial fibrilary acidic protein. Our neuroche mical and morphological results suggest the feasibility of multiple and rep eated probe insertions for microdialysis experiments in the cerebral cortex of awake and behaving cat. This method provides a new tool to investigate the cortical plasticity. (C) 2000 Elsevier Science B.V. All rights reserved .