Nocistatin inhibits 5‐hydroxytryptamine release in the mouse neocortex via presynaptic G i/o protein linked pathways

Background and purpose: Nocistatin (NST) is a neuropeptide generated from cleavage of the nociceptin/orphanin FQ (N/OFQ) precursor. Evidence has been presented that NST acts as a functional antagonist of N/OFQ, although NST receptor and transduction pathways have not yet been identified. We previously showed that N/OFQ inhibited [ 3 H]5‐hydroxytryptamine ([ 3 H]5‐HT) release from mouse cortical synaptosomes via activation of NOP receptors. We now investigate whether NST regulates [ 3 H]5‐HT release in the same preparation. Experimental approach: Mouse and rat cerebrocortical synaptosomes in superfusion, preloaded with [ 3 H]5‐HT and stimulated with 1 min pulses of 10 mM KCl, were used. Key results: Bovine NST (b‐NST) inhibited the K + ‐induced [ 3 H]5‐HT release, displaying similar efficacy but lower potency than N/OFQ. b‐NST action underwent concentration‐dependent and time‐dependent desensitization, and was not prevented either by the NOP receptor antagonist [Nphe 1 Arg 14 ,Lys 15 ]N/OFQ(1‐13)‐NH 2 (UFP‐101) or by the non‐selective opioid receptor antagonist, naloxone. Contrary to N/OFQ, b‐NST reduced [ 3 H]5‐HT release from synaptosomes obtained from NOP receptor knockout mice. However, both N/OFQ and NST were ineffective in synaptosomes pre‐treated with the G i/o protein inhibitor, Pertussis toxin. NST‐N/OFQ interactions were also investigated. Co‐application of maximal concentrations of both peptides did not result in additive effects, whereas pre‐application of maximal b‐NST concentrations partially attenuated N/OFQ inhibition. Conclusions and implications: We conclude that b‐NST inhibits [ 3 H]5‐HT release via activation of G i/o protein linked pathways, not involving classical opioid receptors and the NOP receptor. The present data strengthen the view that b‐NST is, per se , a biologically active peptide endowed with agonist activity. British Journal of Pharmacology (2007) 152 , 549–555; doi: 10.1038/sj.bjp.0707377 ; published online 9 July 2007