Ideally, animals should be euthanized and tissues placed immediately into appropriate fixativeIf you cannot necropsy the animal immediately:
- At the very least, put it at 4C (DO NOT FREEZE)
- Preferably place entire animal in fixative (flat bottomed container)
- Open abdominal & thoracic viscera and snip skull
- fix (± gently inflating lungs and GI with fix)
- Single small incision in kidneys and liver if possible
Fixation methods
- Perfusion fixation followed by immersion fixation
- Immersion fixation (do not re-use fixative)
- Ideal fixative-tissue ratio 10:1—thus the mouse in a 50 mL conical is not ideal (use a flat bottomed container)
- Tissues should be no thicker than 5 mm for optimal fixation
- Bones should be cracked to allow for fixation of marrow
- Infusion of nasal cavities for optimum fixation of nasal structures
- Inflate lungs and intestinal tract with fixative
- If eyes are primary interest, need to identify appropriate fixative for your interests
- If testes are primary interest, consider Bouin’s
Fixative options10% Neutral Buffered Formalin
Zinc Formalin
4% Paraformaldehyde
Bouin's Solution
Frozen tissues (Frozens)