The present invention provides for assay systems that may be used to detect and/or measure neurotrophin activity or to identify agents that exhibit neurotrophin-like activity. It is based, at least in part, on the discovery that the trkB proto-oncogene encodes a tyrosine kinase receptor that may serve as a functional binding protein for BDNF and NT-3. The present invention also provides for diagnostic and therapeutic methods based on the interaction between BDNF and/or NT-3 and trkB, and for a number of orphan receptor molecules.
