Thionin for Nissl Staining

From Jackson Bittencourt's protocol (Salk Inst., 1989)

A. Stock Solution

1. 1 M Acetic Acid (Add 60 ml glacial acetic acid (GAA) to 940 ml DI)
2. 1 N Sodium Hydroxide (40g NaOH/L)

B. Mixing the Stain

1. Add 36 ml 1 N NaOH to 200 ml acetic acid stock solution. Add DI to make a final volume of 1000 ml
2. Heat mixture to about 60º C. Add 2.5 g Thionin (for 0.25%) slowly while stirring
3. Bring Thionin solution to boil for 45 min
4. Let cool and store in a brown, well stoppered bottle at RT
5. Filter stain before use.

States that Thionin should be good for 4 months (but also says to store at 37º C...)