Thin microelectrodes reduce GFAP expression in the implant site in rodent somatosensory cortex

The objective of this study was to test the hypothesis that neural implants with reduced cross-sectional areas will have less glial scarring associated with implantation injury in long-term experiments. In this study, we implanted nine adult rats with two different implants of 12 microm (n = 6), and 25 microm (n = 6) diameters (cross-sectional areas of 68 microm(2), 232 microm(2) respectively) and the expression of glial fibrilliary acidic protein (GFAP) was assessed after 2 weeks and 4 weeks of implantation. In order to facilitate implantation, the 12 microm diameter implants were coated with poly-glycolic acid (PGA), a biodegradable polymer that degraded within minutes of implantation. In n = 3 animals, 25 microm diameter implants also coated with PGA were implanted and assessed for GFAP expression at the end of 4 weeks of implantation. Statistical analysis of the GFAP expression around the different implants demonstrated that after 2 weeks of implantation there is no statistically significant difference in GFAP expression between the 12 microm and the 25 microm diameter implants. However, after 4 weeks of implantation the implant site of 12 microm diameter implants exhibited a statistically significant reduction in GFAP expression when compared to the implant sites of the 25 microm diameter implants (both with and without the PGA coating). We conclude that in neural implants that are tethered to the skull, implant cross-sectional areas of 68 microm(2) and smaller could lead to a reduced glial scarring under chronic conditions. Future studies with longer implant durations can confirm if this observation remains consistent beyond 4 weeks.