I am injecting 1.0uL of viral vector into the locus coeruleus and looking for axon projections in the BLA and IL. When I do immuno for the control virus (2.1x10^12 concentration) it all looks great and I can see plenty of somas in the LC with projections in the IL and BLA. However, when I do a halo virus (5.4x10^12 concentration) with the same methods I can't see the projections. HELP.