Multiple Implants Do Not Aggravate the Tissue Reaction in Rat Brain

Abstract

Chronically implanted microelectrodes are an invaluable tool for neuroscientific research, allowing long term recordings in awake and behaving animals. It is known that all such electrodes will evoke a tissue reaction affected by its’ size, shape, surface structure, fixation mode and implantation method. However, the possible correlation between tissue reactions and the number of implanted electrodes is not clear. We implanted multiple wire bundles into the brain of rats and studied the correlation between the astrocytic and microglial reaction and the positioning of the electrode in relation to surrounding electrodes. We found that an electrode implanted in the middle of a row of implants is surrounded by a significantly smaller astrocytic scar than single ones. This possible interaction was only seen between implants within the same hemisphere, no interaction with the contralateral hemisphere was found. More importantly, we found no aggravation of tissue reactions as a result of a larger number of implants. These results highlight the possibility of implanting multiple electrodes without aggravating the glial scar surrounding each implant.

The density difference between tissue and neural probes is a key factor for glial scarring

“…The general tissue reactions to the high-density (HD) probes were qualitatively fully comparable to the tissue reactions observed in our previous studies, as well as to those reported by other laboratories1416192021. In brief, we found a dense astrocytic scar of about 10–20 μm encapsulating the probes diminishing further away from the wound, and a relatively sparse distribution of microglia confined to the immediate vicinity of the probes (Fig.…”

“…In fact, several areas surrounding the LD probes (but none surrounding the HD probes) did not have any reactive astrocytes (Fig. 2j), which was never observed in our previous experiments161920. Hence, given that the probes used here are very similar apart from with respect to density, we propose that the mechanical forces between probes and neural tissues that arise because of differences in inertial forces every time the animal accelerates or because of difference in gravitational pull on the implants trigger astrocyte reactivity and the development of a glial scar.…”

“…The probes used in this study were larger than the electrodes that are used in current experiments, such as the Michigan probe (with typical shank dimensions of 15 × 60 μm30) or the Utah probe (with a typical shank diameter of less than 90 μm31) and the probes used in biocompatibility studies from our laboratory (where diameters of approximately 200 μm is the largest used hitherto161920). Despite this, the astrocytic reactions elicited by LD probes are some of the lowest we have seen in long-term studies of neural probes.…”

“…Area under curve was calculated for 0–50 μm and 50–100 μm for the mean profile of each image. For ED1 staining, the quantification method used in our previous studies was used161920. This was because the ED1 staining was too sparse to allow the use of the same quantification method applied to the GFAP staining, and was too diffuse to allow counting cells.…”

FEF inactivation with improved optogenetic methods

“…3F). Along with reducing penetration damage proportional to diameter, two separate penetrations cause less damage than a single penetration with coupled devices, particularly with 1-mm separation (50,51) and our illuminator's increased mechanical compliance vs. glass (52). We illustrate light spread of at least 1 mm laterally along the illuminator tip with multicontact electrode recordings from representative neurons (Fig.…”