Cloning, characterization and distribution of receptor activity central nervous system modifying proteins in the rat

Calcitonin gene-related peptide (CGRP), adrenomedullin (ADM), amylin and ca lcitonin (CT) are structurally and functionally related neuropeptides. It h as recently been shown that the molecular pharmacology of CGRP and ADM is d etermined by coexpression of one of three receptor activity-modifying prote ins (RAMPs) with calcitonin receptor-like receptor (CRLR). Furthermore, RAM P proteins have also been shown to govern the pharmacology of the calcitoni n receptor, which in association with RAMP1 or RAMP3, binds amylin with hig h affinity. In this study, we have cloned the rat RAMP family and character ized the pharmacology of rat CGRP and ADM receptors. Rat RAMP1, RAMP2 and R AMP3 shared 72%, 69% and 85% homology with their respective human homologue s. As expected CRLR-RAMP1 coexpression conferred sensitivity to CGRP, whils t association of RAMP2 or RAMP3 with CRLR conferred high affinity ADM bindi ng. Using specific oligonucleotides we have determined the expression of RA MP1, RAMP2 and RAMP3 mRNAs in the rat central nervous system by in situ hyb ridization. The localization of RAMP mRNAs was heterogeneous. RAMP1 mRNA wa s predominantly expressed in cortex, caudate putamen and olfactory tubercle s; RAMP2 mRNA was most abundant in hypothalamus; and RAMP3 was restrictivel y expressed in thalamic nuclei. Interestingly, in specific brain areas only a single RAMP mRNA was often detected, suggesting mutual exclusivity in ex pression. These data allow predictions to be made of where each RAMP protei n may heterodimerize with its partner G-protein-coupled receptor(s) at the cellular level and consequently advance current understanding of cellular s ites of action of CGRP, ADM, amylin and CT. Furthermore, these localization data suggest that the RAMP family may associate and modify the behaviour o f other, as yet unidentified neurotransmitter receptors.