Compositions for identifying lead compounds for pharmacological agents useful in the diagnosis or treatment of neurological disease or injury include mixtures comprising an isolated netrin and an isolated natural netrin receptor such as "Deleted in Colorectal Carcinoma" (DCC) and neogenin. The general methods involve incubating a mixture of an isolated mammalian netrin, an isolated natural mammalian netrin receptor, and a candidate pharmacological agent, and determining if the presence of the agent modulates the binding of the netrin to the receptor.