Biocytin is a classical neuroanatomical tracer commonly used to map brain connectivity. Biocytin is a conjugate of D-biotin and L-lysine, where the carboxylate of D-biotin is coupled with the ?-amine of L-lysine via a secondary amide bond.

L-Citrulline is an amino acid derived from ornithine in the catabolism of proline or glutamine and glutamate or from l-arginine via arginine-citrulline pathway.

Phosphorylcholine is a small haptenic molecule is found in a wide variety of organisms. Human hepatic tumors undergo an elevation in the concentration of phosphorylcholine as the principal metabolic change is observed .