Sudan Black
We have used Sudan Black injections as a stain to verify cannula placements:
0.3g Sudan Black B in 100 ml 70% Ethanol (then filter), inject 0.4 ul for site specific injections.
The rational for the use of Sudan Black is that it is lipophilic and will stain neuronal membranes well, and stays in the tissue even after perfusion.
It can also be used to suppress tissue autofluoresence, but I do not think we found it very helpful in our hands.
http://journals.sagepub.com/doi/full/10.1177/002215549904700211#F1
References:
K. Burdon, J. Stokes, and C. Kimbrough. “Studies of the common aerobic spore-forming bacilli.” Journal of Bacteriology 43(6):717-724, 1941
(Burdon has another technique paper: K. Burdon. “Fatty material in bacteria and fungi revealed by staining dried, fixed slide preparations.” Journal of Bacteriology 52(6):665-678, 1946.)