Identification of opioid receptor-like (ORL1) peptide-stimulated [35S]GTP gamma S binding in rat brain.

Recent reports have identified an endogenous peptide ligand for the opioid receptor-like (ORL1) receptor. In the present study, ORL1 peptide-stimulated [35>]GTP gamma S binding was assessed in rat cortical membranes and brain sections to localize ORL1 receptor-activated G-proteins. In membrane assays, with 20 microM GDP, ORL1 peptide stimulated [35S]GTP gamma S binding by approximately two-fold with an ED50 value of 20 nM. ORL1 peptide-stimulated [35S]GTP gamma S binding was unaffected by opioid or other G-protein-coupled receptor antagonists. In brain sections, ORL1 peptide-stimulated [35S]GTP gamma S binding was identified in regions including cortex, amygdala, hypothalamus, thalamus and brain stem. The anatomical distribution of ORL1 peptide-stimulated [35S]GTP gamma S binding suggests its involvement in cognition, emotion and homeostasis.