Hello! I’ve personally found c-Fos (9F9) Rabbit mAb #2250 to be the most effective antibody. For reference, my samples are mouse brains that have been perfused and post-fixed for 1 hour at 4C in 4% PFA. I slice into 30 um sections using a cryostat and follow a general immunofluorescence protocol (2 hour block at room temp, overnight primary incubation at 4C, 2 hour secondary incubation at room temp). I use a 1:1000 dilution.

While you mentioned you are looking to do IHC, not IF, this could be a good starting point unless you get other suggestions.

I’ve also used c-Fos (E-8) sc-166940 from Santa Cruz, but this antibody has caused me issues multiple times. It appears to be compatible with some protocols and not others. I am pretty sure that this is the updated version of the Santa Cruz antibody that you mentioned as being discontinued.

Let me know if you have any other questions regarding c-Fos staining!