ro-64-6198 and naloxone-benzoylhydrazone

The endogenous neuropeptide nociceptin (N/OFQ), which mediates its actions via the nociceptin receptor (NOP), is implicated in multiple behavioural and physiological functions. This study examined the effects of the NOP agonists N/OFQ and the synthetic agonist Ro 64-6198, the antagonists NNN and NalBzoH, as well as deletion of the Pronociceptin gene on emotional memory in mice. The animals were tested in the passive avoidance (PA) task, dependent on hippocampal and amygdala functions. N/OFQ injected intraventricularly (i.c.v.) prior to training produced a biphasic effect on PA retention; facilitation at a low dose and impairment at higher doses. Ro 64-6198 also displayed a biphasic effect with memory facilitation at lower doses and impairment at a high dose. None of the agonists influenced PA training latencies. NNN did not significantly modulate retention in the PA task but antagonized the inhibitory effects of N/OFQ. NalBzoH facilitated memory retention in a dose-dependent manner and blocked the impairing effects of N/OFQ. However, neither NNN nor NalBzoH blocked the memory-impairing effects of Ro 64-6198. Finally, the Pnoc knockout mice exhibited enhanced PA retention latencies compared to the wild type mice. The biphasic effect of the natural ligand and Ro 64-6198 and the failure of the antagonists to block the action of Ro 64-6198 indicate complexity in ligand-receptor interaction. These results indicate that brain nociceptin and its NOP has a subtle role in regulation of mechanisms of relevance for treatment of disorders with processing disturbances of aversive events e.g. Alzheimer's disease, anxiety, depression and PTSD.

Topics: Animals; Association Learning; Avoidance Learning; Dose-Response Relationship, Drug; Imidazoles; Injections, Intraventricular; Male; Mice; Mice, Inbred C57BL; Mice, Knockout; Naloxone; Narcotic Antagonists; Nociceptin; Nociceptin Receptor; Opioid Peptides; Peptide Fragments; Receptors, Opioid; Retention, Psychology; Spiro Compounds

This study examines the effects of NOP agonists nociceptin/orphanin FQ (N/OFQ) and Ro 64-6198, NOP antagonists [Nphe(1)]N/OFQ(1-13)-NH(2) Nphe(1) and naloxone benzoylhydrazone (NalBzoH) on spatial memory in NMRI mice and pronociceptin (proNC) knockout (KO) mice using the water maze task. N/OFQ, administered i.c.v. (1, 5 and 10 nmol/mouse) and into hippocampal CA3 (1 nmol/mouse, bilaterally), impaired acquisition and retention in the maze. Impairments were blocked by pre-treatment with Nphe(1) (10 nmol, i.c.v.). Ro 64-6198 (0.1-0.3-1 mg/kg i.p.) also dose-dependently impaired learning. However, pre-treatment with NalBzoH (1 mg/kg, s.c.) failed to modify the effects of Ro 64-6198. Nphe(1) (10 nmol/mouse i.c.v.) and NalBzoH (1 mg/kg, s.c.) by themselves failed to affect maze performance, despite a tendency for enhanced performance. Prepro N/OFQ knockout (ppN/OFQ -/-) showed evidence of improved learning, evident at retention trials and in reversal training. ppN/OFQ -/- mice were not impaired by N/OFQ (10 nmol i.c.v.) in the task, suggesting that changes in postsynaptic NOP receptors may occur in such KO mice. It is concluded that N/OFQ and NOP receptors have an important role in hippocampus-dependent spatial learning and memory, probably by modulation of glutamatergic functions.

Topics: Animals; Central Nervous System Agents; Cognition; Dose-Response Relationship, Drug; Hippocampus; Imidazoles; Male; Maze Learning; Memory; Mice; Mice, Inbred Strains; Mice, Knockout; Naloxone; Narcotic Antagonists; Neuropsychological Tests; Nociceptin; Nociceptin Receptor; Opioid Peptides; Peptide Fragments; Protein Precursors; Random Allocation; Receptors, Opioid; Reversal Learning; Spiro Compounds; Time Factors

1. The ORL1 agonists nociceptin and Ro 64-6198 were compared in their ability to modify spontaneous locomotor activity in male NMRI mice not habituated to the test environment. 2. Higher doses of nociceptin (>5 nmol i.c.v.) reduced whereas lower doses (<1 nmol i.c.v.) stimulated locomotor activity. Both effects were blocked by the putative ORL1 antagonists [NPhe1]nociceptin(1-13)NH2 (10 nmol i.c.v.) and UFP101 (10 nmol, i.c.v.). The effects were also blocked by naloxone benzoylhydrazone (1 mg x kg(-1) s.c.), but not by the nonselective opioid antagonist naloxone (1 mg x kg(-1) s.c.). 3 In contrast to nociceptin, the synthetic ORL1 agonist Ro 64-6198 (0.01-1.0 mg x kg(-1) i.p.) produced monophasic inhibition of locomotor activity, which was insensitive to the treatment with [NPhe1]nociceptin(1-13)NH2 or naloxone benzoylhydrazone. Treatment with UFP101 abolished the locomotor inhibition induced by Ro 64-6198 (1.0 mg x kg(-1)), whereas naloxone (1.0 mg x kg(-1), s.c.) further increased the locomotor-inhibitory effects. 4. Naloxone benzoylhydrazone (0.3; 1.0 and 3.0 mg x kg(-1) s.c.) increased locomotor activity, although the effect was statistically significant only with the highest dose used. 5. Pretreatment with the tyrosine hydroxylase inhibitor H44-68 totally eliminated the motor-stimulatory effects of low doses of nociceptin, probably via dopamine depletion. 6. The results suggest that nociceptin stimulates locomotor activity at low doses if dopamine activity is intact. High doses of nociceptin and all the tested doses of Ro 64-6198 seem to interact with a functionally different subset of ORL1 receptors. In addition, the effects of Ro 64-6198 are modulated by tonic opioid receptor activity.

Topics: Animals; Cerebrospinal Fluid; Dose-Response Relationship, Drug; Drug Combinations; Drug Synergism; Imidazoles; Injections, Intraperitoneal; Injections, Intraventricular; Injections, Subcutaneous; Male; Methods; Methyltyrosines; Mice; Mice, Inbred Strains; Motor Activity; Naloxone; Narcotic Antagonists; Nociceptin; Nociceptin Receptor; Opioid Peptides; Receptors, Opioid; Spiro Compounds; Tyrosine 3-Monooxygenase