Dear Hadeel,

what we typically use in our laboratory is to preserve the brain in a solution of paraformaldehyde at 4% for 24h at 4ºC. Some publications recommend a shorter period (4-6h), which should be enough to maintain the structure without altering too much molecular structures. Afterwards, you should dehydrate the sample in a solution at 30% sucrose, at 4ºC for 24h-48h. Then, completely dry the sample and keep it at -80ºC. This sample will be useful to be cut in a cryostat (optimal cutting temperature for brain: -20ºC).

Other option will be formalin-fixed and paraffin embedding.

Hope this helps!

Your question needs more elaboration. Variations in technique happens according to the need for specific methodology. In addition to Teresa GB's answer I just want to add 30% sucrose solution (for over night) for better sectioning results.

For cryocut sections of mice brain following article of us can be followed for histoenzymology and immunohistochemistry:

"Global Loss of Acetylcholinesterase Activity With Mitochondrial Complexes Inhibition and Inflammation in Brain of Hypercholesterolemic Mice"

Rajib Paul et al. Sci Rep. 2017

For paraffin embedding sections the protocol for histology is different.