G Protein Activation and Cyclic AMP Modulation by Naloxone Benzoylhydrazone in Distinct Layers of Rat Olfactory Bulb
Overview
Authors
Affiliations
1 Naloxone benzoylhydrazone (NalBzoH) has initially been developed as an agonist of the pharmacologically defined kappa3-opioid receptor and has recently been employed as an antagonist at the opioid receptor-like (ORL1) receptor. In the present study, we investigated the ability of NalBzoH to elicit agonist-like effects on receptor signalling in distinct layers of rat olfactory bulb, a brain region where we have demonstrated the presence of opioid and ORL1 receptors coupled to both stimulation and inhibition of cyclic AMP formation. 2 In membranes of the olfactory nerve-glomerular layer (ON-GL), external plexiform layer (EPL) and granule cell layer (GRL), NalBzoH elicited a concentration-dependent stimulation of guanosine-5'-O-(3-[35S]-thio)triphosphate ([35S]GTPgammaS) binding with pEC50 values ranging from 7.36 to 7.86, whereas the kappa1-opioid receptor agonists (-)-U-50,488 and U-69,593 were inactive. 3 In membranes of GRL, but not ON-GL and EPL, NalBzoH stimulated basal adenylyl cyclase activity by 40% with a pEC50 of 8.14, and significantly potentiated the net enzyme stimulation elicited by corticotropin-releasing hormone and pituitary adenylate cyclase-activating peptide 38. Pertussis toxin prevented the NalBzoH stimulations of [35S]GTPgammaS binding and adenylyl cyclase activity. 4 In membranes of EPL and GRL, but not ON-GL, NalBzoH elicited a concentration-dependent inhibition of forskolin-stimulated adenylyl cyclase activity with pEC50 values of 8.07 and 8.08, respectively. 5 At concentrations that completely blocked the actions of nociceptin/orphanin FQ (N/OFQ), the ORL1 receptor antagonists CompB and [Nphe1]N/OFQ(1-13)NH2 failed to antagonize either the stimulatory or the inhibitory effect of NalBzoH on cyclic AMP formation. Similarly, the kappa1-opioid receptor antagonist nor-binaltorphimine counteracted the NalBzoH effects with relatively low potencies (pKi values=7.67-8.09). 6 Conversely, the selective delta-opioid receptor antagonist TIPP (pKi=9.10) and the selective mu-opioid receptor antagonist CTAP (pKi=8.27) reduced the inhibitory effect of NalBzoH by 70 and 30%, respectively. Moreover, TIPP and CTAP potently inhibited the NalBzoH stimulation of cyclic AMP, each antagonist maximally causing 50% blockade of the agonist response. 7These data demonstrate that in the olfactory bulb NalBzoH activates receptor signalling by acting through delta- and mu-opioid receptors and independently of ORL1 and kappa1-opioid receptors.
Burns J, Kroll D, Feldman D, Kure Liu C, Manza P, Wiers C Front Psychiatry. 2019; 10:626.
PMID: 31620026 PMC: 6759955. DOI: 10.3389/fpsyt.2019.00626.
Molecular Pharmacology of δ-Opioid Receptors.
Gendron L, Cahill C, Von Zastrow M, Schiller P, Pineyro G Pharmacol Rev. 2016; 68(3):631-700.
PMID: 27343248 PMC: 4931872. DOI: 10.1124/pr.114.008979.
G protein-coupled receptor heteromerization: a role in allosteric modulation of ligand binding.
Gomes I, IJzerman A, Ye K, Maillet E, Devi L Mol Pharmacol. 2011; 79(6):1044-52.
PMID: 21415307 PMC: 3102551. DOI: 10.1124/mol.110.070847.
Agonist activity of naloxone benzoylhydrazone at recombinant and native opioid receptors.
Olianas M, Concas D, Onali P Br J Pharmacol. 2006; 147(4):360-70.
PMID: 16402046 PMC: 1616995. DOI: 10.1038/sj.bjp.0706601.
Has the sun set on kappa3-opioid receptors?.
Connor M, Kitchen I Br J Pharmacol. 2006; 147(4):349-50.
PMID: 16402044 PMC: 1616993. DOI: 10.1038/sj.bjp.0706603.