Synthesis, Biological Evaluation, and SAR Studies of 14ß-phenylacetyl Substituted 17-cyclopropylmethyl-7, 8-dihydronoroxymorphinones Derivatives: Ligands With Mixed NOP and Opioid Receptor Profile.

A series of 14ß-acyl substituted 17-cyclopropylmethyl-7,8-dihydronoroxymorphinone compounds has been synthesized and evaluated for affinity and efficacy for mu (MOP), kappa (KOP), and delta (DOP) opioid receptors and nociceptin/orphanin FQ peptide (NOP) receptors. The majority of the new ligands displayed high binding affinities for the three opioid receptors, and moderate affinity for NOP receptors. The affinities for NOP receptors are of particular interest as most classical opioid ligands do not bind to NOP receptors. The predominant activity in the [35S]GTPγS assay was partial agonism at each receptor. The results are consistent with our prediction that an appropriate 14ß side chain would access a binding site within the NOP receptor and result in substantially higher affinity than displayed by the parent compound naltrexone. Molecular modeling studies, utilizing the recently reported structure of the NOP receptor, are also consistent with this interpretation.

In Vitro and In Vivo Profile of PPL-101 and PPL-103: Mixed Opioid Partial Agonist Analgesics with Low Abuse Potential.

Opiates are still the most effective and widely used treatments for acute and chronic pain. However, the problems associated with morphine and other standard opioid analgesics severely limit their effectiveness in the clinic. PPL-101 and PPL-103 derived from morphine and morphinan ring systems contain a chiral N-substituent, which confers it with a unique combination of high-binding affinities and partial agonist activities at mu, delta, and kappa opioid receptors, leading to unique in vivo pharmacology compared to other conventional opioids. Acute antinociceptive and reward acquisition of PPL-101 and PPL-103 were assessed in mice using the tail flick assay and conditioned place preference (CPP) paradigm, respectively. The reinforcing effects of these compounds were assessed in rats using the self-administration paradigm. In mice, PPL-101 and PPL-103 produced antinociception reaching maximal effects that were equivalent to morphine at approximately 1/3 and 1/10 of morphine's dose, respectively. PPL-101-induced antinociception was attenuated following pretreatment with the kappa antagonist JDTic, but not the mu opioid antagonist beta-FNA. In mice, PPL-101 and PPL-103 produced dose-dependent decreases in activity, similar to other kappa agonists; however, they did not produce conditioned place aversion, and in fact elicited a trend toward CPP. In rats, neither PPL-101 nor PPL-103 were self-administered when substituted for morphine and PPL-101 attenuated morphine self-administration, when administered systemically prior to the self-administration session. Collectively, these results indicate that mixed opioid receptor partial agonists can produce potent antinociceptive activity with a lack of aversion in mice and without being self-administered in rats. Compounds with this profile could be superior analgesics with greatly reduced addiction liability and fewer side-effects compared to traditional opiates.

Cyclooxygenase inhibition targets neurons to prevent early behavioural decline in Alzheimer's disease model mice.

Identifying preventive targets for Alzheimer's disease is a central challenge of modern medicine. Non-steroidal anti-inflammatory drugs, which inhibit the cyclooxygenase enzymes COX-1 and COX-2, reduce the risk of developing Alzheimer's disease in normal ageing populations. This preventive effect coincides with an extended preclinical phase that spans years to decades before onset of cognitive decline. In the brain, COX-2 is induced in neurons in response to excitatory synaptic activity and in glial cells in response to inflammation. To identify mechanisms underlying prevention of cognitive decline by anti-inflammatory drugs, we first identified an early object memory deficit in APPSwe-PS1ΔE9 mice that preceded previously identified spatial memory deficits in this model. We modelled prevention of this memory deficit with ibuprofen, and found that ibuprofen prevented memory impairment without producing any measurable changes in amyloid-ß accumulation or glial inflammation. Instead, ibuprofen modulated hippocampal gene expression in pathways involved in neuronal plasticity and increased levels of norepinephrine and dopamine. The gene most highly downregulated by ibuprofen was neuronal tryptophan 2,3-dioxygenase (Tdo2), which encodes an enzyme that metabolizes tryptophan to kynurenine. TDO2 expression was increased by neuronal COX-2 activity, and overexpression of hippocampal TDO2 produced behavioural deficits. Moreover, pharmacological TDO2 inhibition prevented behavioural deficits in APPSwe-PS1ΔE9 mice. Taken together, these data demonstrate broad effects of cyclooxygenase inhibition on multiple neuronal pathways that counteract the neurotoxic effects of early accumulating amyloid-ß oligomers.

High affinity α3ß4 nicotinic acetylcholine receptor ligands AT-1001 and AT-1012 attenuate cocaine-induced conditioned place preference and behavioral sensitization in mice.

Cholinergic signaling via the nicotinic acetylcholine receptors (nAChRs) in the mesolimbic circuitry is involved in the rewarding effects of abused drugs such as cocaine and opioids. In mouse studies, nonselective nAChR antagonist mecamylamine blocks cocaine-induced conditioned place preference (CPP) and behavioral sensitization. Among subtype-selective nAChR antagonists, the ß2-selective antagonist dihydrobetaerythroidine and α7 antagonist methyllycaconitine (MLA), but not MLA alone prevent behavioral sensitization to cocaine. Since the role of the α3ß4 nAChR subtype in the rewarding and behavioral effects of cocaine is unknown, the present study investigated the effect of two potent and selective α3ß4 nAChR ligands, AT-1001 and AT-1012, on the acquisition of cocaine-induced CPP and behavioral sensitization in mice. At 5-30mg/kg, cocaine produced robust CPP, whereas behavioral sensitization of locomotor activity was only observed at the higher doses (20-30mg/kg). Pretreatment with AT-1001 (1-10mg/kg) or AT-1012 (3-10mg/kg) blocked CPP induced by 5mg/kg cocaine, but not by 30mg/kg cocaine. Lower doses of AT-1001 (0.3-1mg/kg) and AT-1012 (1-3mg/kg) did not affect the increase in locomotor activity induced by 5 or 30mg/kg cocaine. But AT-1001, at these doses, blocked locomotor sensitization induced by 30mg/kg cocaine. These results indicate that the α3ß4 nAChR play a role in the rewarding and behavioral effects of cocaine, and that selective α3ß4 nAChR ligands can attenuate cocaine-induced behavioral phenomena. Since the selective α3ß4 nAChR functional antagonist AT-1001 has also been shown to block nicotine self-administration in rats, the present results suggest that α3ß4 nAChRs may be a target for the treatment of cocaine addiction as well as for cocaine-nicotine comorbid addiction.

Varenicline enhances dopamine release facilitation more than nicotine after long-term nicotine treatment and withdrawal.

An important factor contributing to the high relapse rates among smokers is nicotine withdrawal symptoms. Multiple studies suggest that decreased dopamine release in nucleus accumbens plays a key role in withdrawal. However, recent reports showed that long-term nicotine exposure itself also decreases accumbal dopamine release, suggesting that additional mechanisms are involved in withdrawal. Here, we used real-time cyclic voltammetry in brain slices containing the nucleus accumbens to further elucidate the changes in dopamine release linked to nicotine withdrawal. Rats received vehicle or nicotine via the drinking water for 2-3 months. Studies assessing the expression of somatic signs in vehicle-treated, nicotine-treated, and 24-h nicotine withdrawn rats showed that nicotine withdrawal led to a significant increase in somatic signs. Subsequent voltammetry studies showed that long-term nicotine decreased single-pulse-stimulated dopamine release via an interaction at α6ß2* receptors. Nicotine withdrawal led to a partial recovery in α6ß2* receptor-mediated release. In addition, long-term nicotine treatment alone increased dopamine release paired-pulse ratios and this was partially reversed with nicotine removal. We then evaluated the effect of bath-applied nicotine and varenicline on dopamine release. Nicotine and varenicline both decreased single-pulse-stimulated release in vehicle-treated, nicotine-treated, and nicotine withdrawn rats. However, bath-applied varenicline increased paired-pulse ratios to a greater extent than nicotine during long-term nicotine treatment and after its withdrawal. Altogether these data suggest that nicotine withdrawal is associated with a partial restoration of dopamine release measures to control levels and that varenicline's differential modulation of dopamine release may contribute to its mechanism of action.

AT-1001: a high-affinity α3ß4 nAChR ligand with novel nicotine-suppressive pharmacology.

BACKGROUND AND PURPOSE: The α3ß4 subtype of nicotinic acetylcholine receptors (nAChRs) has been implicated in mediating nicotine reinforcement processes. AT-1001 has been recently described as a high-affinity and selective α3ß4 nAChR antagonist that blocks nicotine self-administration in rats. The aim of this study was to investigate the mechanism of action underlying the nicotine-suppressive effects of AT-1001. EXPERIMENTAL APPROACH: Effects of AT-1001 were determined using in vitro assays and rat models of nicotine addiction, and compared with varenicline. KEY RESULTS: AT-1001 and its analogue AT-1012 were functionally selective as antagonists for α3ß4 over α4ß2 nAChRs, but not to the same extent as the binding selectivity, and had partial agonist activity at α3ß4 nAChRs. In contrast, varenicline was a partial agonist at α4ß2, a weak agonist at α3ß4 and inhibited α4ß2 at a much lower concentration than it inhibited α3ß4 nAChRs. AT-1001 and varenicline also had very different in vivo properties. Firstly, AT-1001 did not exhibit reinforcing properties per se while varenicline was self-administered. Secondly, systemic treatment with AT-1001 did not induce reinstatement of nicotine seeking but rather attenuated reinstatement induced by varenicline, as well as nicotine. Finally, unlike varenicline, AT-1001 selectively blocked nicotine self-administration without altering alcohol lever pressing as assessed in an operant co-administration paradigm. CONCLUSIONS AND IMPLICATIONS: These findings describe a more complex AT-1001 in vitro profile than previously appreciated and provide further support for the potential of AT-1001 and congeners as clinically useful compounds for smoking cessation, with a mechanism of action distinct from currently available medications.

Designing bifunctional NOP receptor-mu opioid receptor ligands from NOP-receptor selective scaffolds. Part II.

The nociceptin opioid receptor (NOP) and its endogenous peptide ligand nociceptin/orphanin FQ have been shown to modulate the pharmacological effects of the classical opioid receptor system. Suppression of opioid-induced reward associated with mu-opioid receptor (MOP)-mediated analgesia, without decreasing anti-nociceptive efficacy, can potentially be achieved with NOP agonists having bifunctional agonist activity at MOP, to afford 'non-addicting' analgesics. In Part II of this series, we describe a continuing structure-activity relationship (SAR) study of the NOP-selective piperidin-4-yl-1,3-dihydroindol-2-one scaffold, to obtain bifunctional activity at MOP, and a suitable ratio of NOP/MOP agonist activity that produces a non-addicting analgesic profile. The SAR reported here is focused on the influence of various piperidine nitrogen aromatic substituents on the ratio of binding affinity and intrinsic activity at both the NOP and MOP receptors.

Retrodialysis of N/OFQ into the nucleus accumbens shell blocks cocaine-induced increases in extracellular dopamine and locomotor activity.

Nociceptin (N/OFQ) has been implicated in a variety of neurological disorders, most notably in reward processes and drug abuse. N/OFQ suppresses extracellular dopamine in the nucleus accumbens (NAc) after intracerebroventricular injection. This study sought to examine the effects of retrodialyzed N/OFQ on the cocaine-induced increase in extracellular dopamine levels in the NAc, as well as locomotor activity, in freely moving rats. 1.0µM, 10µM, and 1mM N/OFQ, in the NAc shell, significantly suppressed the cocaine-induced dopamine increase in the NAc, while N/OFQ alone had no significant effect on dopamine levels. Co-delivery of the selective NOP receptor antagonist SB612111 ([(-)-cis-1-Methyl-7-[[4-(2,6-dichlorophenyl)piperidin-1-yl]methyl]-6,7,8,9-tetrahydro-5H-benzocyclohepten-5-ol] reversed the N/OFQ suppression of cocaine-induced dopamine in the NAc, suggesting that this is an NOP receptor-mediated effect. Using a novel system to assess locomotion, we measured various motor activities of the animals with simultaneous microdialysis from the home cage. Cocaine produced an expected increase in total activity, including horizontal movement and rearing behavior. Retrodialysis of N/OFQ with cocaine administration affected all motor activities, initially showing no effect on behavior, but over time inhibiting cocaine-induced motor behaviors. These results suggest that N/OFQ can act directly in the NAc shell to block cocaine-induced increases in extracellular dopamine levels. Extracellular dopamine and locomotor activity can be dissociated within the NAc and may reflect motor output differences in shell versus core regions of the NAc. These studies confirm the widespread involvement of NOP receptors in drug addiction and further validate the utility of an NOP receptor agonist as a medication for treatment of drug addiction.

Rodent motor and neuropsychological behaviour measured in home cages using the integrated modular platform SmartCage™.

1. To facilitate investigation of diverse rodent behaviours in rodents' home cages, we have developed an integrated modular platform, the SmartCage(™) system (AfaSci, Inc. Burlingame, CA, USA), which enables automated neurobehavioural phenotypic analysis and in vivo drug screening in a relatively higher-throughput and more objective manner. 2, The individual platform consists of an infrared array, a vibration floor sensor and a variety of modular devices. One computer can simultaneously operate up to 16 platforms via USB cables. 3. The SmartCage(™) detects drug-induced increases and decreases in activity levels, as well as changes in movement patterns. Wake and sleep states of mice can be detected using the vibration floor sensor. The arousal state classification achieved up to 98% accuracy compared with results obtained by electroencephalography and electromyography. More complex behaviours, including motor coordination, anxiety-related behaviours and social approach behaviour, can be assessed using appropriate modular devices and the results obtained are comparable with results obtained using conventional methods. 4. In conclusion, the SmartCage(™) system provides an automated and accurate tool to quantify various rodent behaviours in a 'stress-free' environment. This system, combined with the validated testing protocols, offers powerful a tool kit for transgenic phenotyping and in vivo drug screening.

AT-1001: a high affinity and selective α3ß4 nicotinic acetylcholine receptor antagonist blocks nicotine self-administration in rats.

Genomic and pharmacologic data have suggested the involvement of the α3ß4 subtype of nicotinic acetylcholine receptors (nAChRs) in drug seeking to nicotine and other drugs of abuse. In order to better examine this receptor subtype, we have identified and characterized the first high affinity and selective α3ß4 nAChR antagonist, AT-1001, both in vitro and in vivo. This is the first reported compound with a Ki below 10 nM at α3ß4 nAChR and >90-fold selectivity over the other major subtypes, the α4ß2 and α7 nAChR. AT-1001 competes with epibatidine, allowing for [³H]epibatidine binding to be used for structure-activity studies, however, both receptor binding and ligand-induced Ca²âº flux are not strictly competitive because increasing ligand concentration produces an apparent decrease in receptor number and maximal Ca²âº fluorescence. AT-1001 also potently and reversibly blocks epibatidine-induced inward currents in HEK cells transfected with α3ß4 nAChR. Importantly, AT-1001 potently and dose-dependently blocks nicotine self-administration in rats, without affecting food responding. When tested in a nucleus accumbens (NAcs) synaptosomal preparation, AT-1001 inhibits nicotine-induced [³H]dopamine release poorly and at significantly higher concentrations compared with mecamylamine and conotoxin MII. These results suggest that its inhibition of nicotine self-administration in rats is not directly due to a decrease in dopamine release from the NAc, and most likely involves an indirect pathway requiring α3ß4 nAChR. In conclusion, our studies provide further evidence for the involvement of α3ß4 nAChR in nicotine self-administration. These findings suggest the utility of this receptor as a target for smoking cessation medications, and highlight the potential of AT-1001 and congeners as clinically useful compounds.

Peptides derived from the prohormone proNPQ/spexin are potent central modulators of cardiovascular and renal function and nociception.

Computational methods have led two groups to predict the endogenous presence of a highly conserved, amidated, 14-aa neuropeptide called either spexin or NPQ. NPQ/spexin is part of a larger prohormone that contains 3 sets of RR residues, suggesting that it could yield more than one bioactive peptide; however, no in vivo activity has been demonstrated for any peptide processed from this precursor. Here we demonstrate biological activity for two peptides present within proNPQ/spexin. NPQ/spexin (NWTPQAMLYLKGAQ-NH(2)) and NPQ 53-70 (FISDQSRRKDLSDRPLPE) have differing renal and cardiovascular effects when administered intracerebroventricularly or intravenously into rats. Intracerebroventricular injection of NPQ/spexin produced a 13 ± 2 mmHg increase in mean arterial pressure, a 38 ± 8 bpm decrease in heart rate, and a profound decrease in urine flow rate. Intracerebroventricular administration of NPQ 53-70 produced a 26 ± 9 bpm decrease in heart rate with no change in mean arterial pressure, and a marked increase in urine flow rate. Intraventricular NPQ/spexin and NPQ 53-70 also produced antinociceptive activity in the warm water tail withdrawal assay in mice (ED(50)<30 and 10 nmol for NPQ/spexin and NPQ 53-70, respectively). We conclude that newly identified peptides derived from the NPQ/spexin precursor contribute to CNS-mediated control of arterial blood pressure and salt and water balance and modulate nociceptive responses.

Differential effects of nociceptin/orphanin FQ (NOP) receptor agonists in acute versus chronic pain: studies with bifunctional NOP/µ receptor agonists in the sciatic nerve ligation chronic pain model in mice.

1-(1-Cyclooctylpiperidin-4-yl)-indolin-2-one (SR14150) and 1-(1-(2,3,3a,4,5,6-hexahydro-1H-phenalen-1-yl)piperidinl-4-yl)-indolin-2-one (SR16835) are moderately selective nociceptin/orphanin FQ (NOP) receptor agonists. In the [(35)S]guanosine 5'-O-(3-thiotriphosphate) assay in vitro, SR14150 is a partial agonist at both the NOP and µ-opioid receptors, whereas SR16835 is a full agonist at the NOP receptor and has low efficacy at µ receptors. These compounds were tested for antinociceptive and antiallodynic activity, using mice in chronic pain, subsequent to spinal nerve ligation (SNL) surgery. When administered subcutaneously to mice after SNL surgery, SR14150 but not SR16835 increased tail-flick latency, which was blocked by the opioid antagonist naloxone, but not by the NOP receptor antagonist (-)-cis-1-methyl-7-[[4-(2,6-dichlorophenyl)piperidin-1-yl]methyl]-6,7,8,9-tetrahydro-5H-benzocyclohepten-5-ol (SB-612111). In contrast, both SR14150 and SR16835 had antiallodynic activity when mechanical allodynia was measured with von Frey monofilaments. This effect was completely blocked by SB-612111 but not by naloxone. On the other hand, morphine antinociception and antiallodynia were both blocked by naloxone and potentiated by SB-612111. These results indicate that, in mice, circuitry mediating antinociceptive activity in acute and chronic pain states is different. It is possible that during a chronic pain state, an up-regulated NOP system in the spinal cord leads to NOP receptor-mediated antiallodynia, which is blocked by NOP antagonists. However, supraspinal up-regulation could lead to an attenuation of morphine antinociception and antiallodynia, which can be alleviated by an NOP receptor antagonist. Thus, although neither NOP agonists nor antagonists are effective as analgesics in acute pain, they may have efficacy as analgesics, either alone or in combination with morphine, for treatment of chronic pain.

Structural determinants of opioid and NOP receptor activity in derivatives of buprenorphine.

The unique pharmacological profile of buprenorphine has led to its considerable success as an analgesic and as a treatment agent for drug abuse. Activation of nociceptin/orphanin FQ peptide (NOP) receptors has been postulated to account for certain aspects of buprenorphine's behavioral profile. In order to investigate the role of NOP activation further, a series of buprenorphine analogues has been synthesized with the aim of increasing affinity for the NOP receptor. Binding and functional assay data on these new compounds indicate that the area around C20 in the orvinols is key to NOP receptor activity, with several compounds displaying higher affinity than buprenorphine. One compound, 1b, was found to be a mu opioid receptor partial agonist of comparable efficacy to buprenorphine but with higher efficacy at NOP receptors.

The first universal opioid ligand, (2S)-2-[(5R,6R,7R,14S)-N-cyclopropylmethyl-4,5-epoxy-6,14-ethano-3-hydroxy-6-methoxymorphinan-7-yl]-3,3-dimethylpentan-2-ol (BU08028): characterization of the in vitro profile and in vivo behavioral effects in mouse models of acute pain and cocaine-induced reward.

Certain behavioral features of buprenorphine, including a bell-shaped curve for antinociception and attenuation of alcohol consumption, are thought to be mediated by activation of nociceptin/orphanin FQ peptide (NOP) receptors, despite moderate affinity and low efficacy at NOP receptors. We hypothesized that ligands with buprenorphine's physical properties, but possessing increased NOP receptor affinity and efficacy, would improve the profile as a drug abuse medication and reduce addiction liability. Using this strategy, we designed several compounds with universally high affinity, i.e., less than 10 nM at µ, δ, κ, and NOP receptors. Among these, (2S)-2-[(5R,6R,7R,14S)-N-cyclopropylmethyl-4,5-epoxy-6,14-ethano-3-hydroxy-6-methoxymorphinan-7-yl]-3,3-dimethylpentan-2-ol (BU08028) has high affinity at all opioid receptors and increased NOP receptor efficacy in vitro in the [³5S]GTPγS binding assay, however, while still being a partial agonist. In vivo, BU08028 was evaluated in an acute thermal antinociception assay, for its ability to induce conditioned place preference (CPP), and for its effect on cocaine-induced CPP. BU08028 is a very potent long-lasting analgesic. It produces an increase in locomotor activity and a significant CPP. As a pretreatment to cocaine, BU08028 does not alter cocaine CPP but causes a further increase in cocaine-induced locomotor activity. The analgesic, rewarding, and stimulant effects are probably caused by µ receptor stimulation. It is likely that with BU08028, a partial agonist at both NOP and µ receptors, µ-mediated activity overpowers NOP-mediated effects. Thus, it is possible that a different buprenorphine analog that is a universal high-affinity opioid ligand but with "full agonist" activity at NOP may counteract traditional opioid-mediated effects such as antinociception and reward.

Comparison of the antinociceptive and antirewarding profiles of novel bifunctional nociceptin receptor/mu-opioid receptor ligands: implications for therapeutic applications.

The nociceptin receptor (NOPr), a member of the opioid receptor family, is a target for the treatment of pain and drug abuse. Nociceptin/orphanin FQ (N/OFQ), the endogenous peptide for NOPr, not only modulates opioid antinociception, but also blocks the rewarding effects of several abused drugs, such as morphine, cocaine, and amphetamine. We hypothesized that NOPr agonists, with bifunctional activity at the mu-opioid receptor (MOPr), may function as nonaddicting analgesics or as drug abuse medications. Bifunctional small-molecule NOPr agonists possessing different selectivities and efficacies at MOPr were evaluated in an acute thermal antinociception assay, and for their ability to induce conditioned place preference (CPP) and their effect on morphine-induced CPP. 1-(1-Cyclooctylpiperidin-4-yl)-indolin-2-one) (SR14150), a high-affinity NOPr partial agonist, with low MOPr affinity and efficacy, produced analgesia that was naloxone-reversible. SR14150 did not induce CPP alone, nor did it attenuate morphine-induced CPP. 3-Ethyl-1-(1-(4-isopropylcyclohexyl)piperidin-4-yl)-indolin-2-one (SR16507), which has high affinity for both NOPr and MOPr, full agonist activity at NOPr, and partial agonist activity at MOPr, was also a potent analgesic and produced CPP alone, but also modestly attenuated morphine CPP. 1-(1-(2,3,3a,4,5,6-hexahydro-1H-phenalen-1-yl)piperidinl-4-yl)-indolin-2-one (SR16835), a NOPr full agonist and low-affinity MOPr partial agonist, was not antinociceptive, did not produce CPP alone, but attenuated morphine CPP. Our results suggest that NOPr full-agonist activity is required to modulate opioid-induced reward, whereas a bifunctional NOPr/MOPr partial agonist profile may be suitable as a nonaddicting analgesic. The opioid-modulating effects of the NOPr ligands may be used effectively to produce better medications for treatment of drug abuse and pain.

Nociceptin/orphanin FQ receptor activation attenuates antinociception induced by mixed nociceptin/orphanin FQ/mu-opioid receptor agonists.

Activation of brain nociceptin/orphanin FQ (NOP) receptors leads to attenuation of mu-opioid receptor (MOP receptor)-mediated antinociception. Buprenorphine, a high-affinity partial MOP receptor agonist also binds to NOP receptors with 80 nM affinity. The buprenorphine-induced inverted U-shaped dose-response curve for antinociception may be due to NOP receptor activation, given that, in the presence of the NOP receptor antagonist, 1-[(3R,4R)-1-cyclooctylmethyl-3-hydroxymethyl-4-piperidyl]-3-ethyl-1,3-dihydro-2H-benzimidazol-2-one (J113397), or in NOP receptor knockout mice, buprenorphine has a steeper dose-response curve and acts as a full agonist. To further explore the involvement of the direct activation of NOP receptors by buprenorphine and other compounds that activate both NOP and MOP receptors, the antinociceptive effects of 1-(1-(2,3,3alpha,4,5,6-hexahydro-1H-phenalen-1-yl)piperidin-4-yl)-indolin-2-one. (SR16435), 3-ethyl-1-(1-(4-isopropylcyclohexyl)piperidin-4-yl)-indolin-2-one (SR16507), buprenorphine, pentazocine, and morphine, compounds with varying levels of MOP and NOP receptor affinity and efficacy, were assessed in mice using the tail-flick assay. The ability of the selective NOP receptor antagonist (-)-cis-1-methyl-7-[[4-(2,6-dichlorophenyl)piperidin-1-yl]methyl]-6,7,8,9-tetrahydro-5H-benzocyclohepten-5-ol (SB-612111) to potentiate antinociception induced by the above compounds was examined to investigate whether activation of NOP receptors leads to attenuation of MOP receptor-mediated antinociception. SB-612111 potentiated antinociception induced by buprenorphine and the other mixed NOP/MOP receptor agonists SR16435 and SR16507. However, SB-612111 had no effect on pentazocine or morphine antinociception, two compounds with no NOP receptor-binding affinity. These results further support the hypothesis that activation of NOP receptors can lead to attenuation of MOP receptor-mediated antinociception elicited by mixed NOP/MOP receptor compounds such as buprenorphine, SR16435, and SR16507 and that, although buprenorphine has low efficacy in vitro, it has significant NOP receptor agonist activity in vivo.

Activity of new NOP receptor ligands in a rat peripheral mononeuropathy model: potentiation of morphine anti-allodynic activity by NOP receptor antagonists.

The effect of new NOP receptor agonists and antagonists in the rat chronic constriction injury model was investigated. Intraperitoneally administered NOP receptor agonist SR14150 and antagonists SR16430 and SR14148, had no effect on mechanical allodynia when given alone. The nonselective NOP/mu-opioid receptor agonist SR16435, however, produced an anti-allodynic response, similar to morphine and reversible by naloxone. Notably, co-administration of the NOP receptor antagonists potentiated the anti-allodynic activity of both morphine and SR16435. Increased levels of the NOP receptor are implicated in the reduced efficacy of morphine in neuropathic pain. Our results suggest the utility of NOP receptor antagonists for potentiating opioid efficacy in chronic pain.

Rodent models of nicotine reward: what do they tell us about tobacco abuse in humans?

Tobacco products are widely abused in humans, and it is assumed that nicotine is the key substrate in these products that produces addiction. Based on this assumption, several pre-clinical studies have utilized animal models to measure various aspects of nicotine addiction. Most of this work has focused on behavioral measures of nicotine and how other variables contribute to these effects. Here we discuss the most commonly used animal models including, self-administration (SA), place conditioning (PC), and the intracranial self-stimulation (ICSS) paradigms in rodents. The strengths, limitations and procedural variables of these models are reviewed, followed by a discussion of how the animal models have been used to study factors such as age, sex, stress, and the effects of tobacco products other than nicotine. These factors are discussed in light of their influences on human tobacco abuse. The rodent models are evaluated in the context of face, predictive, and construct validity, and we propose that inclusion of factors such as age, sex, stress and other constituents of tobacco aside from nicotine can increase the utility of these animal models by more closely mimicking human tobacco abuse.

Hypocretin/orexin and nociceptin/orphanin FQ coordinately regulate analgesia in a mouse model of stress-induced analgesia.

Stress-induced analgesia (SIA) is a key component of the defensive behavioral "fight-or-flight" response. Although the neural substrates of SIA are incompletely understood, previous studies have implicated the hypocretin/orexin (Hcrt) and nociceptin/orphanin FQ (N/OFQ) peptidergic systems in the regulation of SIA. Using immunohistochemistry in brain tissue from wild-type mice, we identified N/OFQ-containing fibers forming synaptic contacts with Hcrt neurons at both the light and electron microscopic levels. Patch clamp recordings in GFP-tagged mouse Hcrt neurons revealed that N/OFQ hyperpolarized, decreased input resistance, and blocked the firing of action potentials in Hcrt neurons. N/OFQ postsynaptic effects were consistent with opening of a G protein-regulated inwardly rectifying K+ (GIRK) channel. N/OFQ also modulated presynaptic release of GABA and glutamate onto Hcrt neurons in mouse hypothalamic slices. Orexin/ataxin-3 mice, in which the Hcrt neurons degenerate, did not exhibit SIA, although analgesia was induced by i.c.v. administration of Hcrt-1. N/OFQ blocked SIA in wild-type mice, while coadministration of Hcrt-1 overcame N/OFQ inhibition of SIA. These results establish what is, to our knowledge, a novel interaction between the N/OFQ and Hcrt systems in which the corticotropin-releasing factor and N/OFQ systems coordinately modulate the Hcrt neurons to regulate SIA.

Genetics of nicotine dependence and pharmacotherapy.

Nicotine dependence is substantially heritable. Several regions across the genome have been implicated in containing genes that confer liability to nicotine dependence and variation in individual genes has been associated with nicotine dependence. Smoking cessation measures are also heritable, and measured genetic variation is associated with nicotine dependence treatment efficacy. Despite significant strides in the understanding of the relative contribution of genetic and environmental factors to nicotine dependence and treatment, emergent challenges necessitate interdisciplinary coordinated effort for effective problem solving. These challenges include refinement of the nicotine dependence phenotype, better understanding of the dynamic interplay between genes and environment in nicotine dependence etiology, application and development of molecular and statistical methodology that can adequately address vast amounts of data, and continuous translational cross-talk.