Abstract: As described herein, signaling events occurring in neurons or at neuronal synapses have been identified that involve Cdk5 and various other molecules which bind to, are activated by, and/or activate Cdk5. Of particular relevance are interactions that stimulate calpain cleavage of p35 into p25, which binds Cdk5 in pathologic states. Assays to identify modulators of these interactions are provided.

Abstract: The present invention relates to a monoclonal antibody or fragment thereof, which binds specifically to the cyclin-dependent kinase 5 (Cdk5) activating protein, p25 and not to p35, a hybridoma cell line producing the monoclonal antibody, and methods for the detection and/or isolation of p25, p25 fragments or homologs thereof from biological material. The invention further relates to the use of the monoclonal antibody or fragment thereof for detection and treatment of neuronal disorders and cancers.