SR101 can be tricky, but I think its worth a shot, though admittedly I only have mammalian experience. Perhaps support it with fluo-4/colocalization during in vivo imaging or just do some good old fashioned IHC looking at SR101/GFAP colocalization after your experiment.

What is fluo-4?

Fluo-4 is a good Ca++ imaging dye from experience. Its also possible to distinguish between astrocytes and neurons just using the dye itself. Most astrocytes seem to preferentially take it up - so they'll look a bit brighter and you can see from the smaller size and morphology etc. But certainly for reliability confirm using post imaging staining with s100 or gfap.