Fixation and Processing of Central Nervous System Tissue

The dense, lipid-rich neuropil of central nervous system (CNS) specimens necessitates special consideration when harvesting tissue for diagnostic procedures and neuroanatomical analyses. Optimal tissue integrity is obtained by intravascular perfusion fixation, which is readily possible chiefly for animal studies. Immersion fixation may be used for diagnostic specimens from any species. In general, CNS tissues for standard morphological investigations are embedded in paraffin. Cryomicrotomy (frozen sectioning) may be employed for studies where delicate molecules (e.g., epitopes suitable for immunohistochemical detection) will be destroyed by harsh (or any) fixation. Resins (‘plastic’) may be utilized as the embedding medium to obtain high-resolution morphology by light microscopy, particularly for neurons and peripheral nerves, and to facilitate electron microscopy.