The present invention relates to the use of p11 as a drug target as well as a tool for the diagnosis, treatment and development of p11/5-HT receptor related disorders. The invention further relates to p11 knock-out animals as well as p11 transgenic animals and their use as models for the development of novel psychotherapeutic agents, and to methods of diagnosis, prophylaxis and treatment of p11/5-HT receptor related disorders.