Dual coupling of opioid receptor-like (ORL1) receptors to adenylyl cyclasein the different layers of the rat main olfactory bulb

The coupling of opioid receptor-like (ORL1) receptors to adenylyl cyclase h as been investigated in specific layers of the rat main olfactory bulb. Mem branes prepared from the olfactory nerve-glomerular layer (ON-G layer), ext ernal plexiform layer (EP layer) and granule cell layer (GR layer) displaye d specific: binding: sites for [H-3]-nociceptin/orphanin FQ ([H-3]Noc/OFQ). In each layer, the presence of high-and low-affinity binding sites, with K -D values in the picomolar and nanomolar range, respectively, was detected. The binding of [H-3]Noc/OFQ was displaced by unlabelled Noc/OFQ, but not b y opioid antagonists. In each layer, Noc/OFQ significantly stimulated [S-35 ]GTP gammaS binding with nanomolar potencies. In ON-G layer, Noc/OFQ inhibi ted basal adenylyl cyclase activity and the enzyme stimulations by corticot ropin releasing hormone (CRH), Ca2+/calmodulin (Ca2+/CaM) and forskolin (FS K). In EP layer, Noc/OFQ inhibited Ca2+/CaM-and FSK-stimulated enzyme activ ities. Conversely, in GR layer the peptide stimulated basal cyclase activit y and potentiated the enzyme activation by CRH. The Noc/OFQ stimulation was counteracted by the GDP-bound form of the alpha subunit of transducin and was mimicked by transducin Br subunits. In the same tissue layer, Ca2+/CaM- and FSK-stimulated enzyme activities were inhibited. Naloxone failed to ant agonize all the actions of Noc/OFQ. Western blot and RT-PCR analysis reveal ed the expression of Ca2+-insensitive and -sensitive adenylyl cyclases in t he three layers. These results demonstrate that in rat main olfactory bulb ORL1 receptors can differentially affect distinct forms of adenylyl cyclase in a layer specific manner.