TISSUE AND MICRODIALYSATE CHANGES AFTER REPEATED AND PERMANENT PROBE IMPLANTATION IN THE STRIATUM OF FREELY MOVING RATS

Neurochemical and morphological effects of repeated microdialysis or p ermanent microdialysis probe implantations in striatum were studied. T he extracellular levels of dopamine did not change between a first and a second probe insertion separated by 2 weeks or at a third dialysis session 2 days later. The 3,4-dihydroxyphenylacetic acid and homovanil lic acid levels were similar at the first and second microdialysis ses sion, but decreased at the third. Probes implanted permanently for 2 w eeks clogged, and the recovery varied markedly after insertion of new probes. Tyrosine hydroxylase-stained dopamine fibers appeared unaffect ed after all dialysis sessions, although some swollen fibers were obse rved surrounding the probes. No change in the glial fibrillary acidic protein staining was seen immediately after the first dialysis session , although 2 weeks later gliosis was observed. After the second and th ird dialysis a diffuse gliosis was observed, while a glial barrier was seen surrounding the permanently implanted probes. Immediately after the first dialysis session enlarged laminin-stained blood vessels were seen, whereas repeated probe implantation also increased the blood ve ssel density. Thus, chronic in vivo microdialysis with permanently imp lanted probes is limited by severe technical problems and marked tissu e changes. On the other hand, repeated probe insertion in the same bra in site appears to be acceptable for performing chronic microdialysis studies in the same subject, provided neurochemical and morphological changes are taken into consideration.