Rat central ORL-1 receptor uncouples from adenylyl cyclase during membrane preparation

Nociceptin/orphanin FQ is the endogenous agonist of the orphan receptor ORL-1. In this study, we sought to examine any possible regional differences of nociceptin binding using [ 125 I]Tyr 14 -nociceptin, and of agonist induced inhibition of cAMP formation in membranes prepared from cerebrocortex, cerebellum and brainstem. The binding of [ 125 I]Tyr 14 -nociceptin was concentration-dependent and saturable, with B max and p K d (pM) values of 179.7±15.3 fmol/mg protein and 10.26±0.09 (60.0), 12.4±1.8 fmol/mg protein and 10.44±0.07 (37.0), 52.3±0.8 fmol/mg protein and 10.16±0.08 (74.0) in cerebrocortical, cerebella and brainstem membranes, respectively. In all preparations, nociceptin up to 1 μ M failed to inhibit basal and forskolin stimulated cAMP formation. In all tissues forskolin stimulated and nabilone (acting at the central cannabinoid receptor) inhibited cAMP formation. Collectively these data report regional differences in ORL-1 receptor expression and that these receptors uncouple during membrane preparation.