Pharmacological profiles of presynaptic nociceptin/orphanin FQ receptors modulating 5-hydroxytryptamine and noradrenaline release in the rat neocortex

Abstract

1. The pharmacological profiles of presynaptic nociceptin/orphanin FQ (N/OFQ) peptide receptors (NOP) modulating 5-hydroxytryptamine (5-HT) and noradrenaline (NE) release in the rat neocortex were characterized in a preparation of superfused synaptosomes challenged with 10 mM KCl. 2. N/OFQ concentration-dependently inhibited K +-evoked [ 3H]-5-HT and [ 3H]-NE overflow with similar potency (pEC 50 ∼7.9 and ∼7.7, respectively) and efficacy (maximal inhibition ∼40%). 3. N/OFQ (0.1 μM) inhibition of [ 3H]-5-HT and [ 3H]-NE overflow was antagonized by selective NOP receptor antagonists of peptide ([Nphe 1]N/OFQ(1-13)NH 2 and UFP-101; 10 and 1 μM, respectively) and non-peptide (J-113397 and JTC-801; both 0.1 μM) nature. Antagonists were routinely applied 3 min before N/OFQ. However, a 21 min pre-application time was necessary for J-113397 and JTC-801 to prevent N/OFQ inhibition of [ 3H]-NE overflow. 4. The NOP receptor ligand [Phe 1Ψ(CH 2-NH)Gly 2]N/OFQ(1-13)NH 2 ([F/G]N/OFQ(1-13)NH 2; 3 μM) did not affect K +-evoked [ 3H]-NE but inhibited K +-evoked [ 3H]-5-HT overflow in a UFP-101 sensitive manner. [F/G]N/OFQ(1-13)NH 2 antagonized N/OFQ actions on both neurotransmitters. 5. The time-dependency of JTC-801 action was studied in CHO cells expressing human NOP receptors. N/OFQ inhibited forskolin-stimulated cAMP accumulation and JTC-801, tested at different concentrations (0.1-10 μM) and pre-incubation times (0, 40 and 90 min), antagonized this effect in a time-dependent manner. The Schild-type analysis excluded a competitive type of antagonism. 6. We conclude that presynaptic NO receptors inhibiting 5-HT and NE release in the rat neocortex have similar pharmacological profiles. Nevertheless, they can be differentiated pharmacologically on the basis of responsiveness to [E/G]N/OFQ(1-13)NH 2 and time-dependent sensitivity towards non-peptide antagonists.