Biocytin can be used as microinjectable anterograde and transneuronal tracers that is fixable with aldehyde-based fixatives. Additionally the primary amine on the lysine can be reversibly coupled to aldehydes and ketones to form a Schiff base - which can be reduced to a generate stable amine derivative by sodium borohydride (NaBH₄) or sodium cyanoborohydride (NaCNH₃). Carboxylic acids of proteins and other water-soluble biopolymers can be coupled to this molecule in aqueous solution using water-soluble carbodiimides such as EDAC (E2247).