Dasiel O. Borroto-Escuela, Ismel Brito, Michael Di Palma, Antonio Jiménez-Beristain, Manuel Narváez, Fidel Corrales, Mariana Pita-Rodríguez, Stefano Sartini, Patrizia Ambrogini, Davide Lattanzi, Riccardo Cuppini, Luigi F. Agnati and Kjell Fuxe

The early work on neuropeptide-monoamine receptor-receptor interactions in the Central Nervous System gave the first indications of the existence of G protein-coupled receptors (GPCRs) heteroreceptor complexes and the GPCR field began to expand from monomers into heteromers and higher order heteromers, including also GPCR-ion channel, Receptor Tyrosine Kinases (RTK)-GPCR and Receptor activity-modifying proteins-GPCR heteroreceptor complexes. The existence of heteroreceptor complexes with allosteric receptor-receptor interactions increases the diversity of receptor function including recognition, trafficking and signalling. We have proposed the molecular phenomenon of receptor-receptor interactions as a good way to understand of how brain function can increase through molecular integration of signals. An alteration in specific receptor-receptor interactions or their balance/equilibrium (with the corresponding monomers-homomers) are indeed considered to have a role in the pathogenic mechanisms that lead to various diseases, including drug addiction, depression, Parkinson's disease and schizophrenia. Therefore, targeting protomer-protomer interactions in heteroreceptor complexes or the balance with their corresponding homoreceptor complexes in discrete brain regions may become an important field for developing novel drugs, including heterobivalent drugs and optimal types of combined treatments. Increasing our understanding of molecular integration of signals via allosteric receptor-receptor interactions in the heteroreceptor complexes will have a major impact on the molecular medicine, leading to novel strategies for drug discovery and treatment of diseases.