Serial microPET measures of the metabolic reaction to a microdialysis probe implant

Despite the widespread use of chronic brain implants in experimental and clinical settings, the effects of these long-term procedures on brain metabolism and receptor expression remain largely unknown. Under the hypothesis that intracerebral microdialysis transiently alters tissue metabolism, we performed a series of ¹⁸FDG microPET scans prior to and following surgical implantation of microdialysis cannulae. Parallel microPET measures using the competitive dopamine (DA) D₂ receptor antagonist, ¹¹C-raclopride, provided an assay of DA stability in these same animals. ¹⁸FDG scans were performed prior to microdialysis cannulation and again at 2, 12, 24, 48, 120, 168, 360 and 500 h (0.2, 0.5, 1, 2, 5, 7, 15 and 25 days). Separate animals received a sham surgery and the control group had no surgical intervention. For the first 24 h (scans at 2, 12 and 24 h post-surgery) uptake was reduced in both hemispheres. However, by 48 h, contralateral uptake had returned to pre-surgical levels. The striking finding was that from 48 to 500 h, the microdialysis cannulation produced widespread ipsilateral reductions in ¹⁸FDG uptake that encompassed the entire hemisphere. Despite the extent and persistence of these reductions, ¹¹C-raclopride binding and ECF DA concentrations remained stable.