For anyone who is interested, I recently piloted using noxious heat stimulation (55C for 30 s) in a FosGFP animal (Barth 2004). https://www.jax.org/strain/014135
Looks pretty good. Fos IHC is superior no doubt, but that has been reported. For electrophysiology, this is useful. I perfused 2 hours after stimulation.