Local cerebral glucose utilization in perfusion-fixed rat brains

Area of Science:

• Neuroscience
• Biochemistry

Background:

• Local cerebral glucose utilization (LCGU) is a key indicator of brain activity.
• The [14C]2-deoxyglucose (2-DG) technique is widely used to measure LCGU.
• Tissue fixation methods can potentially introduce artifacts in quantitative measurements.

Purpose of the Study:

• To investigate the impact of paraformaldehyde fixation on LCGU measurements in Wistar rats using the [14C]2-DG technique.
• To quantify the effect of tissue shrinkage on LCGU values derived from fixed versus unfixed brain tissue.

Main Methods:

• LCGU was measured in 75 cortical areas and nuclei of adult Wistar rats using the [14C]2-DG autoradiography technique.
• Radioactivity was measured in both fresh, unfixed brain tissue and tissue fixed by perfusion with paraformaldehyde.
• Tissue shrinkage was assessed in the fixed brains.

Main Results:

• No significant difference in total brain radioactivity content was observed between fixed and unfixed material.
• Fixed brain tissue exhibited a mean LCGU increase of approximately 25% compared to unfixed specimens.
• Tissue shrinkage of 7.2% in fixed brains led to a higher volume density of [14C]2-deoxyglucose-6-phosphate, resulting in increased autoradiograph grain density.
• Wash-out of blood-borne [14C]2-DG was negligible except in highly vascularized regions.

Conclusions:

• Paraformaldehyde fixation significantly increases apparent LCGU values by approximately 25% due to tissue shrinkage.
• This shrinkage artifact leads to an overestimation of LCGU in quantitative autoradiography.
• Researchers must consider and account for fixation-induced shrinkage when interpreting [14C]2-DG-based LCGU data.