Ultrastructure at carbon fiber microelectrode implantation sites after acute voltammetric measurements in the striatum of anesthetized rats.

This work seeks to establish the feasibility of characterizing the ultrastructure of brain tissue disruption associated with the implantation of carbon fiber voltammetric microelectrodes. In vivo recording was performed by fast scan cyclic voltammetry in conjunction with carbon fiber microelectrodes (3.5 microm radius) in the striatum of rats anesthetized with chloral hydrate. After 4 h of in vivo recording, the microelectrodes were removed from the brain and the animals underwent intracardial perfusion. Brain tissue was collected and sectioned in the horizontal plane perpendicular to the axis of the microelectrodes. With microelectrodes of a conventional single barreled design, the tissue tracks were often too small to be followed by light microscopy to the point of deepest penetration, which would correspond to the implantation site of the carbon fiber itself. The enlarged tissue tracks formed by the implantation of double barreled electrodes, however, could be followed to their termination by light microscopy. Anatomical mapping was used to identify the fields laying 100 microm deeper than the deepest trace of such tracks. Electron microscopy of these fields revealed a spot of tissue damage presumed to be associated with the implantation site of the carbon fiber microelectrode. The spot of maximal tissue damage had a radius of 2.5 microm and was surrounded by an annular region with a width of 4 microm that contained a mix of healthy and damaged elements. Beyond this annular region, i.e. beyond 6.5 microm from the center of the spot of maximal damage, signs of microelectrode-associated damage were rare and consisted primarily of neurons with darkened cytoplasm.