Which fixative is recommended for frozen sections of brain tissue to diagnose rabies and can be used to fix tissue for demonstration of cell surface antigens, while over hardening tissue but preserving glycogen and some enzymes?

• A. Acetone
• B. Formalin ammonium bromide
• C. 10% Formalin
• D. 95% Ethanol

Answer: (A)

When fixing tissue for frozen sections used to diagnose rabies and to demonstrate cell surface antigens, you want a fixative that preserves antigenicity without creating a strong cross‑link that hides epitopes. Acetone fits this need by fixing rapidly through protein precipitation at low temperature, which keeps cell surface antigens accessible to antibodies used in immunostaining. It also tends to preserve glycogen and some enzyme activities, and it doesn’t over‑harden tissue the way formalin‑based fixatives do. Formalin or formalin-containing fixes cross‑link proteins, which can mask antigens and hamper immunostaining on frozen sections, making rabies antigen detection more difficult. Ethanol can dehydrate and shrink tissue and may not preserve antigens as reliably for this specific use, whereas acetone provides a good balance for antigen preservation and tissue integrity in frozen brain sections.