Pre- and postsynaptic inhibition by nociceptin in guinea pig small intestinal myenteric plexus in vitro.
Actions of nociceptin on electrical and synaptic behavior of morphologically and neurochemically identified neurons in the guinea pig duodenal myenteric plexus were studied with conventional techniques. Nociceptin hyperpolarized the membrane potential in 104 of 121 AH-type and 28 of 51 S-type neurons with an EC(50) of 11.9 +/- 1.2 nM. Increased K(+) conductance accounted for the hyperpolarizing responses that were blocked by pertussis toxin and unaffected by naloxone. The selective opioid receptor-like (ORL)(1) receptor antagonist [Phe(1)-psi(CH(2)-NH)-Gly(2)]nociceptin(1--13)-NH(2) suppressed the nociceptin-evoked responses while behaving like a partial agonist. The nonselective ORL(1) antagonist naloxone benzoylhydrazone competitively suppressed nociceptin actions with a pA(2) value of 5.8. Nociceptin acted at presynaptic inhibitory receptors to suppress fast excitatory nicotinic postsynaptic potentials in 25 of 30 neurons (EC(50) = 22.5 +/- 4.4 nM) and slow synaptic excitation in 38 of 45 neurons (EC(50) = 15.1 +/- 1.6 nM). Presynaptic inhibitory action of nociceptin was unaffected by naloxone and was antagonized by [Phe(1)-psi(CH(2)-NH)-Gly(2)]nociceptin(1--13)-NH(2) or naloxone benzoylhydrazone. The results suggest that nociceptin acts both pre- and postsynaptically by activating an ORL(1) receptor that is distinct from typical naloxone-sensitive opioid receptors.
Liu
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S
Department of Physiology and Cell Biology, College of Medicine and Public Health, Ohio State University, Columbus, Ohio 43210.
Hu
H Z
HZ
Ren
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J
Gao
C
C
Gao
N
N
Lin
Z
Z
Xia
Y
Y
Wood
J D
JD
D000818:Animals; D004305:Dose-Response Relationship, Drug; D004744:Enkephalin, Methionine / Q000494:pharmacology; D019706:Excitatory Postsynaptic Potentials / Q000187:drug effects; D006168:Guinea Pigs; D066298:In Vitro Techniques; D007421:Intestine, Small / Q000294:innervation*; D008297:Male; D009197:Myenteric Plexus / Q000166:cytology*; D009270:Naloxone / Q000031:analogs & derivatives / Q000494:pharmacology; D009292:Narcotic Antagonists / Q000494:pharmacology; D018847:Opioid Peptides / Q000494:pharmacology*; D010446:Peptide Fragments / Q000494:pharmacology; D011957:Receptors, Opioid / Q000378:metabolism; D012701:Serotonin / Q000494:pharmacology; D009435:Synaptic Transmission / Q000187:drug effects*; D014665:Vasodilator Agents / Q000494:pharmacology*; D000094942:Nociceptin Receptor; D000097629:Nociceptin
D004744:Enkephalin, Methionine; D009270:Naloxone; D009292:Narcotic Antagonists; D018847:Opioid Peptides; D010446:Peptide Fragments; D011957:Receptors, Opioid; D012701:Serotonin; D014665:Vasodilator Agents; D000094942:Nociceptin Receptor; D000097629:Nociceptin; C403776:nociceptin-(1-13)-NH2, NPhe(1)-; C058380:naloxone benzoylhydrazone