There is too little information here to provide a meaningful answer.  What I would look for is, do the cells look healthy? Cell bodies should be glassy and "full" looking and not dark and non reflective.  Dendrites should look smooth (depending on magnification) and should not have varicosities (like pearls on a string).  If you are at plating at high density and cells look good, don't forget these cultures are extremely active, meaning that depolarization or activation may not have a huge effect compared to basal.  I can't tell you how often this affects studies in primary cultures.  Try instead inhibiting using something like TTX and look for a difference.  But if you just can't see anything, perhaps you aren't properly loading calcium dyes, or your gcamp proteins aren't being well expressed.

Be sure calcium dye loaded properly, also try to apply high potassium onto cells through puffing (perfusion is too slow for this purpose)

Thank you for your helpful comments.

I replaced regular ACSF with Tris ACSF (replacing NaCl with Tris ) while slicing the tissue and this has greatly helped with cell viability. I think the cells were under a lot of stress during slicing/dissociation and replacing high sodium may have helped. I will perform replicates to see if I continue to get healthy cultures. As of now, it looks like it worked :)

I found the attached poster very helpful in this regard.