Local cerebral glucose utilization in perfusion-fixed rat brains

Local cerebral glucose utilization (LCGU) was measured in 75 cortical areas and nuclei of adult, 3–4-month-old Wistar rats, using the [ 14C]2-deoxyglucose (2-DG) technique. Measurement of total brain radioactivity content was not significantly different in unfixed material compared to fixed brain tissue. Values of LCGU derived from fresh, unfixed material were compared with valucs obtained from rats fixed by perfusion 45 min after the [ 14C]2-DG bolus injection with phosphate-buffered 3.3% paraformaldehyde at room temperature. In the fixed material, the mean LCGU of all brain regions was significantly increased by about 25% compared with the unfixed specimen due to tissue shrinkage of 7.2% in the fixed brains. Shrinkage leading to a higher volume density of [ 14C]2-deoxyglucose-6-phosphate in brain tissue results in a higher grain density in the respective autoradiographs. The wash-out of blood-borne [ 14C]2-DG is negligible except for blood-rich structures like the pineal gland and the choroid plexus.