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.