Comparison of the brain penetration injury associated with microdialysis and voltammetry

Emerging evidence suggests that differences between microdialysis- and voltammetry-based estimates of extracellular dopamine in the brain might originate in the different penetration injury associated with each technique. To address this issue in a direct fashion, microdialysis probes and voltammetric microelectrodes were implanted in the rat striatum for 1, 4, or 24 h. Tissues were perfused with a suspension of fluorescently labeled nanobeads to assess blood vessels near the implant. Tissue sections (30 microm) were labeled with antibodies for PECAM, an endothelial cell marker, or GFAP, a glial marker. In non-implanted control tissue, blood vessels were reliably double-labeled with nanobeads and antiPECAM. Tissue near microdialysis probe tracks exhibited ischemia in the form of PECAM immunoreactive blood vessels devoid of nanobeads. Ischemia was most apparent after the 4-h implants. Probe tracks were surrounded by endothelial cell debris, which appeared as a diffuse halo of PECAM immunoreactivity. The halo intensity decreased with implant duration, indicative of an active wound-healing process. Consistent with this, after 24-h implants, the probe tracks were surrounded by hyperplasic and hypertrophic glia and glial processes were extending towards, and engulfing, the track. Carbon fiber microelectrodes produced a diffuse disruption of nanobead labeling but no focal disruption of blood vessels, no PECAM immunoreactive halo, and no glial activation. These findings illuminate the differences between the extent and nature of the penetration injuries associated with microdialysis and voltammetry.