Endogenous nociceptin / orphanin FQ system involvement in hypothalamic-pituitary-adrenal axis responses: relevance to models of inflammation

Nociceptin/orphanin FQ (N/OFQ) peptide and its receptor (NOP) function in the neuromodulation of anxiety, stress and hypothalamic-pituitary-adrenal (HPA) axis activity. We investigated the endogenous NOP system using the selective NOP antagonist, UFP-101, during the HPA axis response to bacterial endotoxin, lipopolysaccharide (LPS). Although i.c.v. N/OFQ (1 microg/rat) had no significant effect on LPS-induced (250 microg/rat i.p) plasma corticosterone release at 30 or 60 min post-i.c.v. injection, i.c.v. UFP-101 (1 microg/rat)/LPS significantly attenuated plasma adrenocorticotrophic hormone and corticosterone at the 30-min time-point compared to i.c.v saline (0.9%)/LPS. Parvocellular paraventricular nucleus (PVN) corticotrophin-releasing factor (CRF) and corticotrophic pro-opiomelanocortin (POMC), but not parvocellular PVN arginine vasopressin (AVP), mRNA expression was significantly increased by LPS compared to non-LPS control. Intracerebroventricular UFP-101/LPS treatment was associated with increased POMC mRNA expression 4 h after injection and a clear trend towards increased parvocellular CRF mRNA. Furthermore, i.c.v. UFP-101 was selectively associated with an LPS-induced increase in parvocellular AVP mRNA, an effect that was absent in the i.c.v saline/LPS group. To determine whether LPS challenge was associated with compensatory changes in N/OFQ precursor or NOP receptor mRNAs, in a separate study, we undertook reverse transcriptase-polymerase chain reaction analysis of preproN/OFQ and NOP transcripts. In support of an endogenous role for central N/OFQ in inflammatory stress, we found that LPS significantly increased preproN/OFQ transcript expression in the hypothalamus 4 h after injection compared to the saline control. No changes in preproN/OFQ mRNA level in the hippocampus or basal forebrain (including bed nucleus of stria terminalis) were seen, albeit at 4 h. LPS was associated with a significant attenuation of NOP mRNA in the basal forebrain at 4 h, possibly as a compensatory response to increased N/OFQ release. Although the exact mechanisms require elucidation, the findings obtained in the present study provide evidence indicating that the endogenous NOP system is involved in the acute HPA axis response to immune challenge.

Effect of nociceptin/orphanin FQ on feeding behavior and hypothalamic neuropeptide expression in layer-type chicks

Nociceptin/orphanin FQ (N/OFQ) was identified in 1995 as the endogenous ligand for the orphan G(i)/G(o)-coupled opioid receptor-like 1 receptor (NOP(1)). Exogenous N/OFQ increases food intake in mammals, but its effect and mode of action in chicks are not fully known. We report herein that N/OFQ (5.0 nmol) has a stimulatory effect on food intake in layer-type chicks over a 2-h period after intracerebroventricular (icv) injection. Thirty minutes after central injection of N/OFQ (5.0 nmol) the concentration of agouti-related protein (AGRP) mRNA in the diencephalon increased, while cocaine- and amphetamine-regulated transcript (CART) mRNA decreased. However, concentrations of neuropeptide Y, proopiomelanocortin and glutamate decarboxylase mRNAs, and of catecholamines and excitatory amino acids were not affected. Simultaneous administration of alpha-melanocyte stimulating hormone (alpha-MSH: 1.0 pmol), a competitor of AGRP, completely blocked the orexigenic effect of N/OFQ (5.0 nmol). These data suggest that N/OFQ functions in layer chicks as an orexigenic peptide in the central nervous system, and that the AGRP and the CART neurons may mediate this function, as in mammals.

Discriminatory synergistic effect of Trp-substitutions in superagonist [(Arg/Lys)(14), (Arg/Lys)(15)]nociceptin on ORL1 receptor binding and activation

ORL1 is an endogenous G protein-coupled receptor for neuropeptide nociceptin. [(R/K)(14), (R/K)(15)]nociceptin is a superagonist that strongly activates the ORL1 receptor. We have previously found that substituting with Trp can reproduce the potentiation induced by Arg or Lys at position 14. In the present study, in order to ensure the effect of Trp-substitution on the activities of [(R/K)(14), (R/K)(15)]nociceptin, we synthesized [W(14), (R/K)(15)]nociceptin and [(R/K)(14), W(15)]nociceptin. [W(14), (R/K)(15)]nociceptin was found to exhibit threefold higher binding activity and 10-fold greater potency in a functional [(35)S]GTPgammaS functional assay as compared to wild-type nociceptin. However, when only Trp was placed in position 15, the resulting analogues, [(R/K)(14), W(15)]nociceptin, showed only a moderate enhancement of binding and biological activity (2-3 fold in both). These results indicate that the placement of Trp at position 14, unlike at position 15, enhances in a synergistic fashion the interaction of nociceptin with the ORL1 receptor. The results indicate that specific interactions feasible for Arg/Lys and Trp in common must be there for aromatic residues in ORL1, thus forming a cation/pi interaction or pi/pi hydrophobic interaction. The necessity for a favorable electrostatic interaction appears strict in position 15.

Spinal nociceptin mediates electroacupuncture-related modulation of visceral sympathoexcitatory reflex responses in rats

The role of nociceptin and its spinal cord neural pathways in electroacupuncture (EA)-related inhibition of visceral excitatory reflexes is not clear. Nociceptin/orphanin FQ (N/OFQ) is an endogenous ligand for a G protein-coupled receptor, called the N/OFQ peptide (NOP) receptor, which has been found to be distributed in the spinal cord. The present study investigated the importance of this system in visceral-cardiovascular reflex modulation during EA. Cardiovascular pressor reflex responses were induced by gastric distension in Sprague-Dawley rats anesthetized by ketamine and xylazine. An intrathecal injection of nociceptin (10 nM) at T1-2 attenuated the pressor responses by 35%, similar to the influence of EA at P 5-6 (42% decrease). An intrathecal injection of the NOP antagonist, [N-Phe(1)]nociceptin(1-13) NH(2), partially reversed the EA response. Pretreatment with the opioid receptor antagonist naloxone did not alter the EA-like inhibitory effect of nociceptin on the pressor reflex, whereas a combination of nociceptin receptor antagonist with naloxone completely abolished the EA response. An intrathecal injection of nociceptin attenuated the pressor responses to the electrical stimulation of the rostral ventrolateral medulla by 46%, suggesting that nociceptin can regulate sympathetic outflow. Furthermore, a bilateral microinjection of NOP antagonist into either the dorsal horn or the intermediolateral column at T1 partially reversed the EA inhibitory effect. These results suggest that nociceptin in the spinal cord mediates part of the EA-related modulation of visceral reflex responses.

Estrogen-dependent, sex-specific modulation of mustard oil-induced secondary thermal hyperalgesia by orphanin FQ in the rat

Activation of opioid receptor-like 1 receptor (ORL(1)) by intrathecal administration of orphanin FQ (OFQ), an endogenous ligand for the ORL(1) receptor, has been shown to produce antinociception. In addition, we have recently shown gonadal hormone-dependent, sex-specific modulation of acute spinal nociception such that estrogen attenuated OFQ-induced antinociception in the female whereas testosterone was required for the expression of antinociception in the male. However, sex-related differences in the role of OFQ under hyperalgesic conditions are unknown. Hence, we investigated whether OFQ produces sex-specific modulation of mustard oil-induced secondary thermal hyperalgesia in the rat. Mustard oil application to the hind limb significantly reduced the tail-flick latencies (TFL) in male, and ovariectomized (OVX), estradiol treated ovariectomized (OVX+E), proestrous (ProE) and diestrous (DiE) females. Intrathecal administration of OFQ not only attenuated mustard oil-induced decrease in TFLs, i.e. reversed hyperalgesia, but also led to a significant increase in TFLs above the baseline, i.e. produced antinociception in male, OVX, and diestrous rats. However, OFQ failed to alter TFLs in proestrous or OVX+E females, thus these two groups with elevated estrogen levels remained hyperalgesic following mustard oil treatment. These findings demonstrate that OFQ modulates mustard oil-induced secondary hyperalgesia in an estrogen-dependent, sex-specific manner.

Effect of Nociceptin/Orphanin FQ (N/OFQ) and isoflurane on the corticosterone secretory response in mice lacking the N/OFQ prepropeptide (ppN/OFQ-/-)

The effects of subcutaneous Nociceptin/Orphanin FQ (N/OFQ) administration on corticosterone (CORT) secretion were determined in male and female wild-type mice and mice lacking the N/OFQ prepropeptide. Additionally the effect of pretreating animals with isoflurane anesthesia to minimize the potential stress of injection was examined. Although N/OFQ itself did not specifically increase CORT levels in males or females of either genotype, injection alone (either vehicle or N/OFQ) or isoflurane exposure both increased CORT levels in all groups. These results demonstrate that N/OFQ does not elevate circulating CORT levels; however the injection process itself results in increased CORT secretion. Pretreatment with isoflurane did not significantly diminish the CORT response to injection, except in wild-type males. In fact, isoflurane exposure alone increased CORT levels above basal values. Additionally, a gender difference was evident; females displayed a greater change of plasma CORT levels than males. Finally, because even saline injection increased CORT levels, we closely investigated another possible non-specific stress effect, i.e. the effect of transporting animals from their home environment in the animal facility to the laboratory on the day of the experiment. Although basal CORT levels were similar to values reported in other studies, circulating CORT levels were elevated in animals transported to the laboratory, even after a 30 min acclimation period. These results indicate that the experimental protocol that is followed when conducting stress experiments needs to be carefully considered.

Chronic intracerebroventricular infusion of nociceptin/orphanin FQ produces body weight gain by affecting both feeding and energy metabolism in mice

Nociceptin/orphanin FQ (N/OFQ), an endogenous ligand for opioid receptor-like 1 (ORL1), is involved in various central functions, such as pain, psychological stress, locomotor activity, learning and memory, and feeding regulation. Of these functions, the role of N/OFQ in the regulation of feeding has been suggested by the fact that the central administration of N/OFQ leads to feeding behavior. However, the manner in which N/OFQ influences body weight control and subsequent obesity is unclear. To clarify the involvement of N/OFQ in the development of obesity, we evaluated the effects of intracerebroventricular infusion of N/OFQ on food intake and body weight in C57BL/6J mice that were fed a regular chow diet or moderately high-fat (MHF) diet (32.6% kcal fat). N/OFQ significantly increased food intake and body weight both in the regular diet- and MHF diet-fed mice, and these changes were more apparent in the MHF diet-fed mice. When we performed a pair-feeding study in N/OFQ intracerebroventricularly infused mice, N/OFQ did not cause body weight gain but increased white adipose tissue weight and plasma leptin, insulin, and cholesterol levels. N/OFQ reduced rectal temperature in pair-fed mice, in keeping with decreased UCP1 mRNA expression in brown adipose tissue. These results suggest that N/OFQ contributes to the development of obesity not only by inducing hyperphagia but also by decreasing energy expenditure.

Involvement of NMDA receptor in nociceptive effects elicited by intrathecal [Tyr6] gamma2-MSH(6-12), and the interaction with nociceptin/orphanin FQ in pain modulation in mice

The mas-related genes (Mrgs, also known as sensory neuron-specific receptors, SNSRs) are specifically expressed in small diameter sensory neurons in the trigeminal and dorsal root ganglia, suggesting an important role of the receptors in pain transmission. The present study aimed to investigate the underlying mechanism of the nociceptive effects after activation of MrgC, and the interaction between MrgC and N/OFQ-NOP receptor system in modulation of nociception in mice. Intrathecal (i.t.) administration of [Tyr(6)] gamma2-MSH(6-12), the most potent agonist for MrgC receptor, produced a significant hyperalgesic response as assayed by tail withdrawal test and a series of characteristic nociceptive responses, including biting, licking and scratching, in a dose-dependent manner (0.01-10 pmol and 0.01-10 nmol, respectively) in mice. These pronociceptive effects induced by [Tyr(6)] gamma2-MSH(6-12) were inhibited dose-dependently by co-injection of competitive NMDA receptor antagonist D-APV, non-competitive NMDA receptor antagonist MK-801, and nitric oxide (NO) synthase inhibitor L-NAME. However, the tachykinin NK(1) receptor antagonist L-703,606, and tachykinin NK(2) receptor antagonist MEN-10,376, had no influence on pronociceptive effects elicited by [Tyr(6)] gamma2-MSH(6-12). In other groups, [Tyr(6)] gamma2-MSH(6-12)-induced nociceptive responses were bidirectionally regulated by the co-injection of N/OFQ. N/OFQ inhibited nociceptive responses at high doses (0.01-1 nmol), but potentiated the behaviors at low doses (1 fmol-3 pmol). Furthermore, both hyperalgesia and nociceptive responses were enhanced after the co-administration with NOP receptor antagonist [Nphe(1)]N/OFQ(1-13)-NH(2). These results suggest that intrathecal [Tyr(6)] gamma2-MSH(6-12)-induced pronociceptive effects may be mediated through NMDA receptor-NO system in the spinal cord, and demonstrate the interaction between MrgC and N/OFQ-NOP receptor system in pain transmission.

Inhibition of serotonin outflow by nociceptin/orphaninFQ in dorsal raphe nucleus slices from normal and stressed rats: Role of corticotropin releasing factor

In the dorsal raphe nucleus (DRN) many inputs converge and interact to modulate serotonergic neuronal activity and the behavioral responses to stress. The effects exerted by two stress-related neuropeptides, corticotropin releasing factor (CRF) and nociceptin/orphaninFQ (N/OFQ), on the outflow of [(3)H]5- hydroxytryptamine were investigated in superfused rat dorsal raphe nucleus slices. Electrical stimulation (100 mA, 1 ms for 2 min) evoked a frequency-dependent peak of [(3)H]5- hydroxytryptamine outflow, which was sodium and calcium-dependent. Corticotropin releasing factor (1-100 nM), concentration-dependently inhibited the stimulation (3 Hz)-evoked [(3)H]5-hydroxytryptamine outflow; the inhibition by 30 nM corticotropin releasing factor (to 68 +/- 5.7%) was prevented both by the non selective CRF receptor antagonist alpha-helicalCRF(9-41) (alpha-HEL) (300 nM) and by the CRF(1) receptor antagonist antalarmin (ANT) (100 nM). The CRF(2) agonist urocortin II (10 nM) did not modify [(3)H]5- hydroxytryptamine outflow, ruling out the involvement of CRF(2) receptors. Bicuculline (BIC), a GABAA antagonist (10 microM), prevented the inhibitory effect of corticotropin releasing factor (30 nM), supporting the hypothesis that the inhibition was mediated by increased gamma-aminobutyric acid (GABA) release. Nociceptin/ orphaninFQ (1 nM-1 microM) exerted an antalarmin- and bicuculline-insensitive inhibition on [(3)H]5- hydroxytryptamine outflow, with the maximum at 100 nM (to 63+/- 4.2%), antagonized by the NOP receptor antagonist UFP-101 (1 microM). Dorsal raphe nucleus slices prepared from rats exposed to 15 min of forced swim stress displayed a reduced [(3)H]5-hydroxytryptamine outflow, in part reversed by antalarmin and further inhibited by nociceptin/orphaninFQ. These findings indicate that (i) both corticotropin releasing factor and nociceptin/orphaninFQ exert an inhibitory control on dorsal raphe nucleus serotonergic neurons; (ii) the inhibition by corticotropin releasing factor involves gamma-aminobutyric acid neurons; (iii) nociceptin/ orphaninFQ inhibits dorsal raphe nucleus serotonin system in a corticotropin releasing factor- and gamma-aminobutyric acid-independent manner; (iv) nociceptin/orphaninFQ modulation is still operant in slices prepared from stressed rats. The nociceptin/orphaninFQ-NOP receptor system could represent a new target for drugs effective in stress-related disorders.

Nociceptin-induced modulation of human T cell function

There is an accumulating evidence for the immunoregulatory role of the neuropeptide, nociceptin/orphanin FQ (N/OFQ) however its role on T cell function requires elucidation. This study has demonstrated an inhibitory role for N/OFQ on SEB-activated T cell function. N/OFQ decreases T cell proliferation, which is abrogated when the costimulatory receptors CD80 and CD86 are blocked. In addition, evidence suggests that the immunoregulatory cytokines TGF-beta, IFN-gamma and nitric oxide (NO) are involved in the N/OFQ effect. N/OFQ also, through involvement of IFN and NO, induces the expression of the immunosuppressive modulator indoleamine 2,3-dioxygenase (IDO), suggesting a central role for IDO in the N/OFQ effect on T cell proliferation. The data presented in this report indicate a multi-faceted mechanism of action used by N/OFQ to modulate T cell function.

The hypothalamus-pituitary-adrenal axis does not influence the protective effects of nociceptin/orphanin FQ on the rat gastric mucosa

The participation of hypothalamus-pituitary-adrenal axis in the gastroprotective effects of nociceptin/orphanin FQ (N/OFQ) has been investigated. Gastric mucosal lesions were induced by intragastric administration of 50% ethanol, 1 ml/rat. Rats received N/OFQ either by the intracerebroventricular (icv) route, at 3 microg/rat, or by the intraperitoneal (ip) route, at 10 microg/kg, 30 min before ethanol administration. The protective effect of icv and ip administered N/OFQ was assessed in adrenalectomized rats and in rats pretreated with the glucocorticoid receptor antagonist, mifepristone, or with the CRF receptor antagonist, alpha-helical CRF(9-41). The damaging effect of ethanol was apparently not influenced by adrenalectomy. N/OFQ markedly reduced macroscopically and histologically assessed gastric mucosal damage. The extent of reduction by N/OFQ was comparable in adrenalectomized and in sham-operated rats, with either icv or ip route of administration. Pretreatment with mifepristone, both icv (80 microg/rat) and ip (10 mg/kg) injected, did not modify the response to icv and ip N/OFQ. Pretreatment with alpha-helical CRF(9-41) (25 microg/rat icv or 250 microg/kg ip), had no effect on the reduction of gastric damage produced by icv or ip N/OFQ. Present findings suggest that the gastroprotective effects of N/OFQ on ethanol-induced damage do not involve the endocrine pathway through the HPA axis.

Nociceptin/orphanin FQ-induced food intake and cocaine amphetamine regulated transcript gene expression in strains derived from rats prone (WOKW) and resistant (Dark Agouti) to metabolic syndrome

In previous work, we observed that N/OFQ-induced hyperphagia is greater in DA rats, animals resistant to metabolic syndrome, than in WOKW animals, which are prone to this disease. We attributed this difference to the fact that these two strains have different Cart gene sequences and expression. As a preliminary approach to pursue this hypothesis, the present work focused on Cart gene expression by developing from DA and WOKW rats various congenic animals with exchanges of metabolic syndrome-related QTL's of different chromosomes (3, 5, 10 and 16), and analyzing their N/OFQ-induced (2.1, 4.2, and 8.4nmol/rat) food intake in terms of their CART gene expression and N/OFQ hypothalamic immunostaining. Two groupings emerged, the first, with strains 3a, 3b, and 5a with elevated N/OFQ-induced feeding similar to that of the DA rats, and the second, with strains 16 and 10, with lower feeding, like the WOKW rats. There was a perfect correlation between Cart gene expression and N/OFQ-induced feeding data at 30min for the strains DA, 3a, 3b, 5 in the first group, and 16 and WOKW for the second, but not for strain 10. As expected, the strains with low content of Cart gene expression had elevated N/OFQ-induced feeding, but contrary to expectations, strain 10, with the lowest Cart gene expression, exhibited low N/OFQ-induced feeding, on the order of that of the WOKW rats. A comparable trend was observed with N/OFQ hypothalamic immunostaining. This anomaly may be due to other satiety-related factors involved in N/OFQ-induced feeding.

Effect of neonatal nociceptin or nocistatin imprinting on the brain concentration of biogenic amines and their metabolites

Noradrenaline (NA), dopamine (DA), homovanillic acid (HA), serotonin (5HT) and 5-hydroxyindole acetic acid (5HIAA) content of five brain regions (hypothalamus, hippocampus, brainstem, striatum and frontal cortex) and the cerebrospinal fluid (CSF) was measured in adult (three months old) male and female rats treated neonatally with a single dose of 10 microg nociceptin (NC) or 10 microg nocistatin (NS) for hormonal imprinting. The biogenic amine and metabolite content of cerebrospinal fluid was also determined. In NC treated animals the serotonergic, dopaminergic as well as noradrenergic systems were influenced by the imprinting. The 5HT level increased in hypothalamus, the 5HIAA tissue levels were found increased in hypothalamus. Hippocampus and striatum and the HVA levels increased highly significantly in brainstem. Dopamine level decreased significantly in striatum, however in frontal cortex both noradrenalin and 5HIAA level decreased. Nevertheless, in NS-treated rats decreased NA tissue levels were found in hypothalamus, brainstem and frontal cortex. Decreased DA levels were found in the hypothalamus, brainstem and striatum. NS imprinting resulted in decreased HVA level, but increased one in the brainstem. The 5HT levels decreased in the hypothalamus, brainstem, striatum and frontal cortex, while 5HIAA content of CSF, and frontal cortex decreased, and that of hypothalamus, hippocampus and striatum increased. There was no significant difference between genders except in the 5HT tissue levels of NC treated rats. Data presented show that neonatal imprinting both by NC and NS have long-lasting and brain area specific effects. In earlier experiments endorphin imprinting also influenced the serotonergic system suggesting that during labour release of pain-related substances may durably affect the serotonergic (dopaminergic, adrenergic) system which can impress the animals' later behavior.

1-Benzyl-N-[3-[spiroisobenzofuran-1(3H),4'-piperidin-1-yl]propyl]pyrrolidine-2-carboxamide (Compound 24) antagonizes NOP receptor-mediated potassium channel activation in rat periaqueductal gray slices

Nociceptin/orphanin FQ (N/OFQ) peptide (NOP) receptor, the fourth member of opioid receptor family, shares 60-70% homology with traditional opioid receptors but displays little affinity for opioids. This receptor was implicated in many neurological functions and its functional heterogeneity has been proposed. Therefore, it is imperative to develop and characterize new ligands for NOP receptors. 1-Benzyl-N-[3-[spiroisobenzofuran-1(3H),4'-piperidin-1-yl]propyl]pyrrolidine-2-carboxamide (Compound 24) is a new non-peptide ligand of NOP receptor having antagonistic actions in cloned and peripheral NOP receptors. In this study, we quantitatively characterized its effect on the native NOP receptors in the midbrain slices containing ventrolateral periaqueductal gray (vlPAG), a region with dense NOP receptors and involved in pain regulation. In vlPAG neurons, N/OFQ induced G-protein-coupled inwardly rectifying potassium (GIRK) current through NOP receptors. Compound 24, at 0.3-10 microM, attenuated N/OFQ-induced GIRK current concentration-dependently. The antagonistic potency of Compound 24 in vlPAG neurons (IC(50): 2.6+/-0.6 microM) was, however, lower than that obtained in mouse vas deferens preparations or expressed human NOP receptors. The action kinetic of Compound 24 was slower than [Nphe(1), Arg(14), Lys(15)]N/OFQ-NH(2) (UFP-101), a peptide antagonist, in the same preparation. Compound 24 had no intrinsic agonistic activity at NOP receptors at the concentration up to 10 microM. However, at concentrations higher than 3 microM, it also attenuated the GIRK current induced by [D-Ala(2), N-Me-Phe(4), Gly(5)-ol]-enkephalin, a mu-opioid receptor agonist. It is concluded that Compound 24 acts as a pure antagonist at the native NOP receptors in the vlPAG with moderate potency and selectivity.

Neurobiological mechanisms of placebo responses

Expectations, positive or negative, are modulating factors influencing behavior. They are also thought to underlie placebo effects, potentially impacting perceptions and biological processes. We used sustained pain as a model to determine the neural mechanisms underlying placebo-induced analgesia and affective changes in healthy humans. Subjects were informed that they could receive either an active agent or an inactive compound, similar to routine clinical trials. Using PET and the mu-opioid selective radiotracer [(11)C]carfentanil we demonstrate placebo-induced activation of opioid neurotransmission in a number of brain regions. These include the rostral anterior cingulate, orbitofrontal and dorsolateral prefrontal cortex, anterior and posterior insula, nucleus accumbens, amygdala, thalamus, hypothalamus, and periaqueductal grey. Some of these regions overlap with those involved in pain and affective regulation but also motivated behavior. The activation of endogenous opioid neurotransmission was further associated with reductions in pain report and negative affective state. Additional studies with the radiotracer [(11)C]raclopride, studies labeling dopamine D2/3 receptors, also demonstrate the activation of nucleus accumbens dopamine during placebo administration under expectation of analgesia. Both dopamine and opioid neurotransmission were related to expectations of analgesia and deviations from those initial expectations. When the activity of the nucleus accumbens was probed with fMRI using a monetary reward expectation paradigm, its activation was correlated with both dopamine, opioid responses to placebo in this region and the formation of placebo analgesia. These data confirm that specific neural circuits and neurotransmitter systems respond to the expectation of benefit during placebo administration, inducing measurable physiological changes.

Intrinsic and synaptic long-term depression of NTS relay of nociceptin- and capsaicin-sensitive cardiopulmonary afferents hyperactivity

The nucleus tractus solitarius (NTS) in the caudal medulla is a gateway for a variety of cardiopulmonary afferents important for homeostatic regulation and defense against airway and cardiovascular insults and is a key central target potentially mediating the response habituation to these inputs. Here, whole-cell and field population action potential recordings and infrared imaging in rat brainstem slices in vitro revealed a compartmental pain-pathway-like organization of capsaicin-facilitated vs. nocistatin-facilitated/nociceptin-suppressed neuronal clusters in an NTS region, which receives cardiopulmonary A- and C-fiber afferents with differing capsaicin sensitivities. All capsaicin-sensitive neurons and a fraction of nociceptin-sensitive neurons expressed N-methyl-D: -aspartate (NMDA) receptor-dependent synaptic long-term depression (LTD) following afferent stimulation. All neurons also expressed activity-dependent decrease of excitability (intrinsic LTD), which converted to NMDA receptor-dependent intrinsic long-term potentiation after GABA(A) receptor blockade. Thus, distinct intrinsic and synaptic LTD mechanisms in the NTS specific to the relay of A- or C-fiber afferents may underlie the response habituation to persistent afferents hyperactivity that are associated with varying physiologic challenges and cardiopulmonary derangements-including hypertension, chronic cough, asthmatic bronchoconstriction, sustained elevated lung volume in chronic obstructive pulmonary disease or in continuous positive-airway-pressure therapy for sleep apnea, metabolic acidosis, and prolonged exposure to hypoxia at high altitude.

Central administration of Orphanin FQ inhibits GnRH secretion by ORL1 receptor in the median eminence of freely moving ovariectomized rats

OBJECTIVE

This study aimed to investigate the possible role of Orphanin FQ (OFQ) in the regulation of hypo-thalamic gonadotropin-releasing hormone (GnRH) secretion.

METHODS

The method of push-pull perfusion and radioimmuno-assay (RIA) were adopted to examine the secretory profile of GnRH in the median eminence (ME) in freely moving ovari-ectomized (OVX) rats after intracerebroventricular (icv) injection of OFQ and/or [Nphe(1)]NC(1-13)NH(2) (NC13), a competitive antagonists of the opioid receptor-like 1 receptor (ORL1 receptor).

RESULTS

GnRH release from ME significantly decreased from 40 min to 80 min after the administration of 20 and 200 nmol OFQ in OVX rats (P < 0.05). This inhibitory effect of 20 nmol OFQ could be abolished by pretreatment with equal dose of NC13. More interestingly, GnRH secretion from ME was increased markedly 60 min after icv injection of 100 and 200 nmol NC13 (P < 0.05).

CONCLUSION

Our results suggested central administration of OFQ could inhibit the release of GnRH in the ME of hypothalamus through ORL1 receptor, providing further in vivo evidence supporting the role of OFQ in the control of GnRH secretion.

Further studies on the pharmacological features of the nociceptin/orphanin FQ receptor ligand ZP120

ZP120 is a nociceptin/orphanin FQ (N/OFQ) peptide receptor (NOP) ligand. In previous studies, the effects of ZP120 were found to be sensitive to J-113397 in mouse tissues while resistant to UFP-101 in rat tissues. The aim of this study was to further investigate the ZP120 pharmacological profile using mouse and rat preparations, J-113397 and UFP-101, as well as NOP receptor knockout (NOP(-/-)) mice. Electrically stimulated mouse and rat vas deferens were used to characterize the pharmacology of ZP120 in vitro. For in vivo studies the tail-withdrawal assay was performed in wild type (NOP(+/+)) and NOP knockout (NOP(-/-)) mice. In the mouse and rat vas deferens ZP120 mimicked the effects of N/OFQ showing higher potency but lower maximal effects. In both preparations, J-113397 antagonized N/OFQ and ZP120 effects showing similar pK(B) values ( approximately 7.8). UFP-101 antagonized the actions of N/OFQ (pK(B) values approximately 7.3) but did not modify the effects of ZP120. The inhibitory effects of N/OFQ and ZP120 were no longer evident in vas deferens tissues taken from NOP(-/-) mice. In NOP(+/+) mice subjected to the tail-withdrawal assay, ZP120 (1 nmol) mimicked the pronociceptive action of N/OFQ (10 nmol), producing longer lasting effects. The effects of both peptides were absent in NOP(-/-) animals. The NOP receptor ligand ZP120 is a high potency NOP selective partial agonist able to evoke long-lasting effects; its diverse antagonist sensitivity in comparison with N/OFQ may derive from different modality of binding to the NOP receptor.

Nociceptin/orphanin FQ peptide receptor agonist Ac-RYYRWKKKKKKK-NH2 (ZP120) induces antinatriuresis in rats by stimulation of amiloride-sensitive sodium reabsorption

The aim of the present study was to examine the mechanisms responsible for the antinatriuretic effect of the selective, peripherally acting, nociceptin/orphanin FQ peptide (NOP) receptor partial agonist Ac-RYYRWKKKKKKK-NH(2) (ZP120). Using immunohistochemistry, we showed that in the cortex NOP receptors are expressed in the distal convoluted tubules, the connecting tubules, and the collecting ducts. Using clearance techniques, we evaluated renal excretory function during acute administration of ZP120 (1 nmol/kg/min) in chronically catheterized, conscious rats (n = 8/group). To examine the hypothesis that ZP120 induces direct renal effects by modifying the activity of sodium transporters in the distal convoluted tubules or in the collecting ducts, ZP120-induced antinatriuresis was examined during coadministration of an inhibitor of the NaCl cotransporter, bendroflumethiazide, or a blocker of the epithelial sodium channel, amiloride, respectively. ZP120 produced a marked antinatriuresis [fractional excretion of sodium (FE(Na)): ZP120, 0.3 +/- 0.1% versus control, 0.9 +/- 0.1%; p < 0.05] in sodium-replete rats. The natriuretic response to amiloride was significantly increased in ZP120-treated rats compared with controls (DeltaFE(Na): ZP120, 1.1 +/- 0.2% versus control, 0.5 +/- 0.2%; p < 0.01), whereas the effect of BFTZ was equal in ZP120-treated rats and controls. These results suggest that ZP120 exerts a direct renal NOP receptor-mediated stimulatory effect on the epithelial sodium channel in the collecting ducts.

Distinct effects of nociceptin analogs on scopolamine-induced memory impairment in mice

Nociceptin, also known as orphanin FQ, binds to opioid receptor like-1 (NOP) receptors. Nociceptin and NOP receptor play important roles in several physiological functions in the central nervous system. We reported that although high doses of nociceptin impaired learning and memory and these effects were blocked by nocistatin, naloxone benzoylhydrazone and [NPhe(1)]nociceptin(1-13)NH(2), low doses of nociceptin improved scopolamine- or mecamylamine-induced impairment of learning and memory, and these ameliorating effects were not blocked by these antagonists. In the present study, to confirm our previous findings, the effects of [Arg(14), Lys(15)]nociceptin and [(pF)Phe(4)]nociceptin(1-13)NH(2), highly potent and long-lasting nociceptin analogs, on the memory impairment induced by scopolamine using the Y-maze and step-down type passive avoidance tests were investigated. [Arg(14), Lys(15)]Nociceptin (0.1 and/or 1 pmol/mouse, i.c.v.) significantly improved impairment of memory function. Although this analog was about 30 times more potent than nociceptin, the doses ameliorating these memory impairments were comparable to those of the natural ligand nociceptin. The ameliorating effects of [Arg(14), Lys(15)]nociceptin were not blocked by an NOP receptor antagonist, [NPhe(1)]nociceptin(1-13)NH(2). Interestingly, another potent nociceptin analog, [(pF)Phe(4)]nociceptin(1-13)NH(2) could not improve impairment of memory function. These results confirmed that there are novel mechanisms underlying these ameliorating effects and these seem not to be mediated via an NOP receptor.

Nociceptin produces antinociception after spinal administration in amphibians

Nociceptin, also known as orphanin FQ, is a opioid-like neuropeptide that mediates its effects at the nociceptin receptor, a member of the G protein-coupled receptor superfamily. In mammals, nociceptin produces analgesia after spinal administration, however the role of nociceptin and nociceptin receptors in the modulation of noxious stimuli in non-mammalian species has not been examined. In an amphibian pain model using the acetic acid test with Rana pipiens, nociceptin and nociceptin1-13 amide produced dose-dependent antinociception (1-100 nmol), blocked by the nociceptin antagonist, [Nphe1]-nociceptin1-13 amide (30 nmol), but not the opioid antagonist, naltrexone (100 nmol/g, s.c.). Conversely, the antinociceptive effects of micro, delta, and kappa opioid receptor agonists were not blocked by the nociceptin antagonist. Nociceptin and nociceptin1-13 amide were the least potent of the opioid agonists tested. These studies demonstrate that spinal nociceptin receptors and not opioid receptors mediate the antinociceptive effect of nociceptin. Considered with previous findings, these behavioral data supports a role for nociceptin inhibition of spinal nociception in amphibians and perhaps all vertebrates.

Nociceptin/orphanin FQ modulates motor behavior and primary motor cortex output through receptors located in substantia nigra reticulata

This study was set to investigate whether motor effects of nociceptin/orphanin FQ (N/OFQ) can be related to changes in primary motor cortex output. N/OFQ injected i.c.v. biphasically modulated motor performance, low doses being facilitating and higher ones inhibitory. These effects were counteracted by the N/OFQ receptor antagonist [Nphe(1) Arg(14),Lys(15)]N/OFQ-NH(2) (UFP-101) confirming the specificity of N/OFQ action. However, UFP-101 alone facilitated motor performance, suggesting that endogenous N/OFQ inhibits motor function. N/OFQ and UFP-101 injected into the substantia nigra reticulata but not motor cortex replicated these effects, suggesting motor responses were mediated by subcortical circuits involving the basal ganglia. Intracortical microstimulation technique showed that i.c.v. N/OFQ also biphasically modulated motor cortex excitability and movement representation. Low N/OFQ doses caused a leftward shift of threshold distribution curve in the forelimb area without affecting the number of effective sites. Conversely, high N/OFQ doses increased unresponsive and reduced excitable (movement) sites in vibrissa but not forelimb area. However, increased threshold currents and rightward shift of threshold distribution curve were observed in both areas, suggesting an overall inhibitory effect on cortical motor output. UFP-101 alone evoked effects similar to low N/OFQ doses, suggesting tonic inhibitory control over forelimb movement by endogenous N/OFQ. As shown in behavioral experiments, these effects were replicated by intranigral, but not intracortical, N/OFQ or UFP-101 injections. We conclude that N/OFQ receptors located in the substantia nigra reticulata mediate N/OFQ biphasic control over motor behavior, possibly through changes of primary motor cortex output.

Nocistatin and nociceptin given centrally induce opioid-mediated gastric mucosal protection

Nociceptin (N/OFQ) and nocistatin (NST) are two endogenous neuropeptides derived from the same precursor protein, preproN/OFQ. The aim of the present work was to study the effect of NST on the ethanol-induced mucosal damage compared with that of N/OFQ following intracerebroventricular (i.c.v.) administration in the rat and to analyze the mechanism of the gastroprotective action. It was found that both NST and N/OFQ reduced the mucosal lesions in the same dose range (0.2-1 nmol i.c.v.), but in higher doses (2-5 nmol i.c.v.) the gastroprotective effect of both peptides was highly diminished. The gastroprotective effect of N/OFQ (1 nmol), but not that of NST (1 nmol), was reduced by the selective nociceptin receptor antagonist J-113397 (69 nmol i.c.v.). Similarly, decrease of the gastroprotective effect was observed after the combination of NST (1 nmol) with N/OFQ (0.6 or 1 nmol). However, addition of the gastroprotective effects was observed, when lower dose (0.2 nmol) of NST was given prior to N/OFQ (0.6 nmol). The gastroprotective effect of both N/OFQ and NST was antagonized by naloxone (27 nmol), beta-funaltrexamine (20 nmol), naltrindole (5 nmol) and norbinaltorphimine (14 nmol), the mu-, delta- and kappa-opioid receptor antagonists, respectively, given i.c.v. The mucosal protection was significantly decreased after bilateral cervical vagotomy. The present findings suggest that NST similar to N/OFQ, may also induce gastric mucosal protective action initiated centrally in a vagal-dependent mechanism. Opioid component is likely to be involved in the gastroprotective effect of both NST and N/OFQ.

Involvement of ORL1 receptor and ERK kinase in the orphanin FQ-induced nociception in the nucleus accumbens of rats

Nociceptin/orphanin FQ (N/OFQ) is a heptadecapeptide, which has been identified as an endogenous ligand of the opioid receptor-like (ORL1) receptor. The present study investigated the nociceptive effect of intra-nucleus accumbens (intra-NAc) injection of OFQ, and the involvement of ERK pathway in such effect. Intra-NAc injection of OFQ (0.1, 0.5, 1 nmol) dose-dependently decreased the nociceptive thresholds on the hindpaw withdrawal response to thermal and mechanical stimulation in rats. Moreover, the intra-NAc injection of OFQ-induced decreases in HWLs were antagonized by intra-NAc injection of (Nphe(1))nociceptin(1-13)NH(2), an antagonist of ORL1 receptor, in a dose-dependent way. Furthermore, the OFQ-induced nociception could be attenuated by pretreatment with the mitogen-activated protein kinase/ERK kinase (MEK) inhibitor 1,4-diamino-2,3-dicyano-1,4-bis(2-aminopheylthio)butadiene (U0126). Our results demonstrate that OFQ induces nociceptive effects in NAc. The effect was blocked by the antagonist (Nphe(1))nociceptin(1-13)NH(2) and attenuated by U0126, suggesting that the activation of ERK pathways is involved in the OFQ-induced nociceptive effect in the NAc of rats.

Nociceptin/orphanin FQ causes non-quantal slowing of respiratory rhythm in brainstem-spinal cord preparation from newborn rat

Nociceptin/orphanin FQ (N/OFQ) is the endogenous agonist of the N/OFQ peptide receptor, an inhibitory G protein-coupled receptor. N/OFQ acts as a neuromodulator to depress respiratory rhythm in the brainstem. Although the mechanisms of respiratory rhythm generation remain poorly understood, the pre-inspiratory neuron (Pre-I) and the pre-Bötzinger complex (preBötC) inspiratory neuron (Insp) network in the rostral ventrolateral medulla (RVLM) have been proposed to be essential for respiratory rhythm generation. Opioids presumably cause quantal slowing via selective depression of preBötC Insps. However, it is unclear whether N/OFQ depresses respiratory rhythm via the same mechanism. In this study, using in vitro newborn rat en bloc preparations, we examined the slowing pattern of N/OFQ (quantal or non-quantal) and the effects of N/OFQ on the extracellularly recorded discharge of Pre-Is and Insps in the RVLM. N/OFQ caused non-quantal slowing with a synchronous decrease in burst rates of Insps and of C4 discharge whereas the intraburst spike number in Insps remained unchanged. It also caused a significant decrease in burst rates and intraburst spike numbers in Pre-Is, while the 1:1 coupling of Pre-Is bursts to C4 bursts was preserved. When superfusate K(+) was elevated from 6.2 to 11.2mM, Pre-I activity was increasingly uncoupled from C4 bursts. After the application of N/OFQ in a high [K(+)] superfusate, the 1:1 coupling of Pre-Is to C4 bursts was restored. We conclude that N/OFQ suppresses burst and spike generation of Pre-Is, and that suppression of Pre-Is activity with synchronous coupling to the Insps network contributes to N/OFQ-induced non-quantal slowing.

Activation of nociceptin/orphanin FQ-NOP receptor system inhibits tyrosine hydroxylase phosphorylation, dopamine synthesis, and dopamine D(1) receptor signaling in rat nucleus accumbens and dorsal striatum

Nociceptin/orphanin FQ (N/OFQ) has been reported to inhibit dopamine (DA) release in basal ganglia mainly by acting on NOP receptors in substantia nigra and ventral tegmental area. We investigated whether N/OFQ could affect DA transmission by acting at either DA nerve endings or DA-targeted post-synaptic neurons. In synaptosomes of rat nucleus accumbens and striatum N/OFQ inhibited DA synthesis and tyrosine hydroxylase (TH) phosphorylation at Ser40 via NOP receptors coupled to inhibition of the cAMP/protein kinase A pathway. Immunofluorescence studies showed that N/OFQ preferentially inhibited phospho-Ser40-TH in nucleus accumbens shell and that in this subregion NOP receptors partly colocalized with either TH or DA D(1) receptor positive structures. In accumbens and striatum N/OFQ inhibited DA D(1) receptor-stimulated cAMP formation, but failed to affect either adenosine A(2A) or DA D(2) receptor regulation of cAMP. In accumbens slices, N/OFQ inhibited DA D(1)-induced phosphorylation of NMDA and alpha-amino-3-hydroxy-5-methylisoxazole-4-propionate glutamate receptors, whereas in primary cultures of accumbal cells, which were found to coexpress NOP and DA D(1) receptors, N/OFQ curtailed DA D(1) receptor-induced cAMP-response element-binding protein phosphorylation. Thus, in accumbens and striatum N/OFQ exerts an inhibitory constraint on DA transmission by acting on either pre-synaptic NOP receptors inhibiting TH phosphorylation and DA synthesis or post-synaptic NOP receptors selectively down-regulating DA D(1) receptor signaling.

Coupling specificity of NOP opioid receptors to pertussis-toxin-sensitive Galpha proteins in adult rat stellate ganglion neurons using small interference RNA

The opioid receptor-like 1 (NOP or ORL1) receptor is a G-protein-coupled receptor the endogenous ligand of which is the heptadecapeptide, nociceptin (Noc). NOP receptors are known to modulate pain processing at spinal, supraspinal, and peripheral levels. Previous work has demonstrated that NOP receptors inhibit N-type Ca2+ channel currents in rat sympathetic stellate ganglion (SG) neurons via pertussis toxin (PTX)-sensitive Galphai/o subunits. However, the identification of the specific Galpha subunit that mediates the Ca2+ current modulation is unknown. The purpose of the present study was to examine coupling specificity of Noc-activated NOP receptors to N-type Ca2+ channels in SG neurons. Small interference RNA (siRNA) transfection was employed to block the expression of PTX-sensitive Galpha subunits. RT-PCR results showed that siRNA specifically decreased the expression of the intended Galpha subunit. Evaluation of cell surface protein expression and Ca2+ channel modulation were assessed by immunofluorescence staining and electrophysiological recordings, respectively. Furthermore, the presence of mRNA of the intended siRNA target Galpha protein was examined by RT-PCR experiments. Fluorescence imaging showed that Galphai1, Galphai3, and Galphao were expressed in SG neurons. The transfection of Galphai1-specific siRNA resulted in a significant decrease in Noc-mediated Ca2+ current inhibition, while silencing of either Galphai3 or Galphao was without effect. Taken together, these results suggest that in SG neurons Galphai1 subunits selectively couple NOP receptors to N-type Ca2+ channels.

Effect and mechanism of nociceptin/orphanin FQ reversing multi-drug resistance in K562/ADM cell

OBJECTIVE

To investigate the effect and mechanism of nociceptin/orphanin FQ (OFQ) reversing multi-drug resistance of K562/ADM cells in vitro.

METHODS

MTT assay, Wright staining, flow cytometry, transmission electron microscope and gel electrophoresis were used to evaluate the effect and mechanism of OFQ in reversing multi-drug resistance of K562/ADM cells.

RESULTS

OFQ could time-dependently reverse the ADM resistance of K562/ADM cell. After treatment with OFQ (1 x 10(-7) mol x L(-1)), K562/ADM cells were cultured for 24, 48 and 72 h. The reversal index (RI) was 1.33, 1.42 and 1.53, respectively. Furthermore, OFQ significantly increased the intracellular accumulation of ADM in K562/ADM cells and percentage apoptosis in K562/ADM cells. OFQ down-regulated the level of P-gp time-dependently, while the level of Fas and FasL were up-regulated. There were evidently significant differences compared with the control (P < 0.01). After treating K562/ADM cells with OFQ (1 x 10(-7) mol x L(-1)) and ADM (20 microg x ml(-1)) for 48 hours, the cells showed apoptotic nuclear fragmentation, which was characterized by the appearance of a DNA ladder pattern in genomic DNA gel electrophoresis.

CONCLUSION

OFQ can reverse the ADM resistance of K562/ADM cells. The mechanism involves OFQ up-regulating the expression of Fas/FasL, down-regulating the level of P-gp, and decreasing the intracellular level of calcium in K562/ADM cells.

Involvement of the GABA/benzodiazepine receptor in the axiolytic-like effect of nociceptin/orphanin FQ

We investigated the mechanism underlying the anxiolytic actions of the neuropeptide nociceptin/orphanin FQ (N/OFQ) with an elevated plus-maze test. In mice, intracerebroventricular (i.c.v.) infusions of N/OFQ (0.1 and 0.32 nmol) led to an increase in time spent in the open arms (anxiolytic-like effects). A non-peptidyl N/OFQ receptor (NOP) antagonist, J-113397(1-{(3R,4R)-1-cyclooctylmethyl-3-hydroxymethyl-4-piperidyl}-3-ethyl-1,3-dihydro-2H-benzimidazol-2-one), (1.0 and 3.2 mg/kg, s.c.) blocked the increase induced by N/OFQ. On the other hand, a benzodiazepine receptor antagonist, flumazenil, (10 mg/kg, i.p.) and a GABAA receptor antagonist, (+)-bicuculline, (5.6 mg/kg, i.p.) also inhibited the increase induced by N/OFQ. In rats, microinfusions of N/OFQ (10 and 32 pmol) into the amygdala led to an increase in time spent in the open arms. However, intracranial infusions of N/OFQ (10-100 pmol) into the dorsal hippocampus did not affect the time spent in the open arms. These findings suggest that the anxiolytic-like effects of N/OFQ may be related to the GABA/benzodiazepine system in the amygdala.

Central and peripheral role of the nociceptin/orphaninFQ system on normal and disturbed colonic motor function and faecal pellet output in the rat

In this study, seeking further information on the role of the nociceptin/orphanin FQ (N/OFQ)-ergic system in normal and disturbed colonic motor function in rats, we compared the colonic effects of UFP-112, a novel highly potent agonist, with those of N/OFQ. When injected intracerebroventricularly (i.c.v.) and intraperitoneally (i.p.), UFP-112 and N/OFQ increased bead expulsion time in a statistically significant and dose-related manner and reduced the percentage of rats with castor oil-induced diarrhoea. UFP-112 showed greater efficacy, higher potency and longer-lasting inhibitory effects than N/OFQ, and pretreatment with UFP-101, a selective antagonist, blocked the N/OFQ analogue-induced responses in both tests. When injected i.c.v., UFP-112 and N/OFQ inhibited corticotrophin releasing factor- and restrain stress-stimulated faecal pellet excretion significantly and in a dose-related manner. Conversely, when injected peripherally both peptides significantly inhibited colonic propulsive motility but did so in a non-dose-related manner. In conclusion, these findings indicate that, in the rat, the central and peripheral N/OFQ systems have an inhibitory role in modulating distal colonic propulsive motility under physiological and pathological conditions. UFP-112 therefore promises to be a useful pharmacological tool for investigating the role of the N/OFQ system in motor functions in the distal colonic tract under physiological and pathological conditions.

GABA(A) signalling is involved in N/OFQ anxiolytic-like effects but not in nocistatin anxiogenic-like action as evaluated in the mouse elevated plus maze

Nociceptin/orphanin FQ (N/OFQ) and nocistatin are two neuropeptides originated from the same precursor prepronociceptin/orphanin FQ (ppN/OFQ). N/OFQ is the endogenous ligand of the NOP receptor, while the target of action of nocistatin is still unknown. N/OFQ modulates various biological functions, including anxiety. Conversely, nocistatin either behaves as a functional N/OFQ antagonist or evokes per se effects opposite to those of N/OFQ. Here we investigated the interaction between the anxiolytic-like effects of N/OFQ and the anxiogenic-like action of nocistatin with those evoked by GABA(A) receptor ligands in the mouse elevated plus maze. The anxiogenic-like effects of the GABA(A) receptor antagonist pentylenetetrazol (20mg/kg; intraperitoneal, i.p.) were abolished by the co-treatment with N/OFQ (10pmol; intracerebroventricular, i.c.v.) while potentiated by the administration of nocistatin (0.01pmol; i.c.v.). The anxiolytic-like effects of the benzodiazepine receptor agonist diazepam (0.75mg/kg, i.p.) were reversed by nocistatin (0.1pmol; i.c.v.), whereas signs of sedation were observed when mice were co-treated with diazepam and N/OFQ (3pmol). Interesting enough, the i.p. treatment with flumazenil (1mg/kg) blocked the anxiolytic-like effects of N/OFQ (10pmol; i.c.v.), but not the anxiogenic effect elicited by nocistatin. Collectively, our findings suggest that the effects on anxiety elicited by pentylenetetrazol and diazepam can be counteracted or potentiated in the presence of N/OFQ and nocistatin. In addition, the effects on anxiety of N/OFQ, but not nocistatin, appear to be dependent on the benzodiazepine site of the GABA(A) receptor.

Orphanin FQ and glutamate connection in the regulation of gonadotropin-releasing hormone secretion in the preoptic area of conscious male rats

Utilizing the method of push-pull perfusion and radioimmunoassay (RIA), the secretory profile of gonadotropin-releasing hormone (GnRH) in the preoptic area (POA) and serum-luteinizing hormone (LH) levels were examined in conscious male rats after administration of [Nphe(1)]NC(1-13)NH(2), a competitive antagonists of the opioid receptor-like 1 receptor (ORL1 receptor) which is endogenous receptor for Orphanin FQ (OFQ). Glutamate release in the POA was also measured by high-performance liquid chromatography (HPLC) after perfusion of [Nphe(1)]NC(1-13)NH(2), i.e. NC13. The results showed that GnRH secretion from the POA and serum LH levels was increased significantly 40 min and 60 min, respectively after perfusion of 2 and 20 mmol/L NC13 in freely moving male rats (p<0.05). Pretreatment with a glutamate, N-methyl-D-aspartate (NMDA) receptor antagonist (MK-801, s.c., 0.2 mg/kg) abolished the increase of GnRH release in the POA induced by 2 mmol/L NC13. Additionally, 20 mmol/L NC13 significantly enhanced glutamate release in the POA at 40 min post-perfusion in a dose-dependent manner. These findings suggest that hypothalamic OFQ/ORL1 receptor system plays a role in the physiological inhibitory control of GnRH secretion in the POA of male rats, and provide evidence for involvement of an OFQ and glutamate pathway in the control of GnRH secretion.

Dysregulation of nociceptin/orphanin FQ activity in the amygdala is linked to excessive alcohol drinking in the rat

BACKGROUND

Alcoholism is a complex behavioral disorder in which interactions between stressful life events and heritable susceptibility factors contribute to the initiation and progression of disease. Neural substrates of these interactions remain largely unknown. Here, we examined the role of the nociceptin/orphanin FQ (N/OFQ) system, with an animal model in which genetic selection for high alcohol preference has led to co-segregation of elevated behavioral sensitivity to stress (Marchigian Sardinian alcohol-preferring [msP]).

METHODS

The msP and Wistar rats trained to self-administer alcohol received central injections of N/OFQ. In situ hybridization and receptor binding assays were also performed to evaluate N/OFQ receptor (NOP) function in naïve msP and Wistar rats.

RESULTS

Intracerebroventricular (ICV) injection of N/OFQ significantly inhibited alcohol self-administration in msP but not in nonselected Wistar rats. The NOP receptor messenger RNA expression and binding was upregulated across most brain regions in msP compared with Wistar rats. However, in msP rats [(35)S]GTPgammaS binding revealed a selective impairment of NOP receptor signaling in the central amygdala (CeA). Ethanol self-administration in msP rats was suppressed after N/OFQ microinjection into the CeA but not into the bed nucleus of the stria terminalis or the basolateral amygdala.

CONCLUSIONS

These findings indicate that dysregulation of N/OFQ-NOP receptor signaling in the CeA contributes to excessive alcohol intake in msP rats and that this phenotype can be rescued by local administration of pharmacological doses of exogenous N/OFQ. Data are interpreted on the basis of the anti-corticotropin releasing factor (CRF) actions of N/OFQ and the significance of the CRF system in promoting excessive alcohol drinking in msP rats.

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.

Neuropeptide FF receptors antagonist, RF9, attenuates opioid-evoked hypothermia in mice

The present study used the endpoint of hypothermia to investigate opioid and neuropeptide FF (NPFF) interactions in conscious animals. Both opioid and NPFF systems played important roles in thermoregulation, which suggested a link between opioid receptors and NPFF receptors in the production of hypothermia. Therefore, we designed a study to investigate the relationship between opioid and NPFF in control of thermoregulation in mice. The selective NPFF receptors antagonist RF9 (30nmol) injected into the third ventricle failed to induce significant effect, but it completely antagonized the hypothermia of NPFF (45 nmol) after cerebral administration in mice. In addition, RF9 (30 nmol) co-injected i.c.v. in the third ventricle reduced the hypothermia induced by morphine (5nmol,) or nociceptin/orphanin FQ (N/OFQ) (2 nmol). Neither the classical opioid receptors antagonist naloxone (10 nmol) nor NOP receptor antagonist [Nphe(1)]NC(1-13)NH(2) (7.5 nmol) reduced the hypothermia induced by the central injection of NPFF at dose of 45 nmol. Co-injected with a low dose of NPFF (5 nmol), the hypothermia of morphine (5 nmol) or N/OFQ (2 nmol) was not modified. These results suggest that NPFF receptors activation is required for opioid to produce hypothermia. In contrast, NPFF-induced hypothermia is mainly mediated by its own receptors, independent of opioid receptors in the mouse brain. This interaction, quantitated in the present study, is the first evidence that NPFF receptors mediate opioid-induced hypothermia in conscious animals.

Nociceptin attenuates methamphetamine abstinence-induced withdrawal-like behavior in planarians

Planarians display a concentration-related reduction in locomotor activity when amphetamine, cocaine, cannabinoid, or benzodiazepine exposure is abruptly discontinued. In the present study, we tested the hypothesis that abrupt discontinuation of methamphetamine would also cause withdrawal-like behavior in planarians and that the withdrawal-like behavior would be prevented by nociceptin, which has been shown to modulate the effects of methamphetamine in mammals. We observed a concentration-related reduction of locomotor behavior when planarians exposed to methamphetamine (0.1-100 microM) were tested in drug-free water. The withdrawal-like behavior was abolished when methamphetamine (10 microM)-exposed planarians were placed into water containing nociceptin (10 microM) or when planarians co-exposed to methamphetamine (10 microM) and nociceptin (10 microM) were placed into drug-free water. The effects of nociceptin were abolished in the presence of a nociceptin receptor antagonist, JTC-801 (1 microM). Planarians did not display a change in locomotor behavior during exposure to nociceptin (10 microM) or JTC-801 (1 microM) by themselves. These results (1) reveal a functional interaction between nociceptin and methamphetamine in planarians and (2) provide evidence that nociceptin blocks methamphetamine-induced withdrawal-like behavior in planarians through a JTC-801-sensitive mechanism.

Differential cardiovascular effects of synthetic peptides derived from endomorphin-1 in anesthetized rats

Previously, five synthetic peptides derived from endomorphin-1 (Tyr1-Pro2-Trp3-Phe4-NH2, EM-1), including Tyr-D-Ala-Trp-p-Cl-Phe-NH2 (HDAPC), Tyr-D-Ala-Trp-Phe-NH2 (HDADC), Nalpha-amidino-Tyr-D-Ala-Trp-p-Cl-Phe-NH2 (GDAPC), Nalpha-amidino-Tyr-D-Ala-Trp-Phe-NH2 (GDADC) and Nalpha-amidino-Tyr-D-Pro-Gly-Trp-p-Cl-Phe-NH2 (GBDPC), were described to elicit analgesia by subcutaneous administration with enhanced metabolic stabilities. To further our knowledge of the influences of particular modification on the pharmacological activities of EM-1, the present study was undertaken to investigate cardiovascular effects of these peptides in anesthetized rats by intravenous injection. Our results showed that the four D-Ala-containing peptides decreased the systemic arterial pressure (SAP) and heart rate (HR) through a naloxone-sensitive mechanism. Different patterns, potencies and durations of cardiovascular effects were observed among these peptides. When compared to EM-1, the hemodynamic responses to these four tetrapeptides were significantly lower in magnitude but much longer in duration. Surprisingly, intravenous administration of the only pentapeptide GBDPC produced fairly prolonged hypertensive and tachycardiac effects, which was naloxone-insensitive, thus providing evidence that changes in the primary structure of a peptide can profoundly affect its pharmacological activity. Comparisons of the cardiovascular effects between these peptides showed that each modification introduced into EM-1, including N-amidination, chloro-halogenation and unnatural amino acid substitution, played a role in the influence on the cardiovascular regulation of these peptides.

Suppression of CCL2/MCP-1 and CCL5/RANTES expression by nociceptin in human monocytes

The receptor designated Opioid Receptor-Like 1 (ORL1) is abundantly expressed in the central nervous system (CNS) as well as by cells of the immune system. While much is known about the function of ORL1 in the CNS, there is little information in the literature about the role of ORL1 in the immune response. There have been numerous reports documenting the effects of GPCR activation on the expression of chemokines crucial in mediating inflammatory events in biological systems. The aim of the present work was to examine the effect of nociceptin administration on the pro-inflammatory chemokine expression of human monocytes. We report here that human CD14(+) monocytes expresses the mRNA for ORL1. Our results also demonstrate that nociceptin can suppress the production of CCL2/MCP-1 and CCL5/RANTES chemokine protein in both primary CD14(+) human monocytes and monocyte-like cell lines. However, nociceptin does not appear to regulate the expression of these chemokines at the level of transcription, as CCL2/MCP-1 and CCL5/RANTES mRNA levels following nociceptin treatment of monocytes were essentially normal. Although the mechanism of chemokine regulation by nociceptin is as yet unknown, it is evident that the ORL1/nociceptin system plays a role in regulating chemotactic responses of leukocytes through chemokine suppression. Finally, these data may provide the initial basis for the development of ORL1 agonists and antagonists for therapeutic treatment of inflammatory disease.

[Dmt1, d-1-Nal3]morphiceptin, a novel opioid peptide analog with high analgesic activity

The morphiceptin-derived peptide [Dmt1, d-1-Nal3]morphiceptin, labeled mu-opioid receptor (MOP) with very high affinity and selectivity in the receptor binding assays. In the mouse hot plate test, [Dmt1, d-1-Nal3]morphiceptin given intracerebroventricularly (i.c.v.) produced profound supraspinal analgesia, being approximately 100-fold more potent than the endogenous MOP receptor ligand, endomorphin-2. The antinociceptive effect of this new analog lasted up to 120min. Thus, [Dmt1, d-1-Nal3]morphiceptin is an interesting and extraordinarily potent analgesic, raising the possibility of novel approaches in the design of clinically useful drugs for pain treatment.

Endogenous nociceptin (orphanin FQ) suppresses basal hedonic state and acute reward responses to methamphetamine and ethanol, but facilitates chronic responses

The opioid peptide nociceptin (orphanin FQ) suppresses drug reward, drug self-administration, and impedes some of the processes believed to underlie the transition to addiction. As virtually all previous studies have used administration of nociceptin receptor agonists to evaluate the role of nociceptin on addiction-like behavior, the current study used a pharmacological (nociceptin receptor antagonist) and genetic (nociceptin receptor knockout mice) approach to elucidate the role of endogenous nociceptin. The nociceptin receptor antagonist UFP-101 induced a modest place preference, and enhanced the conditioned place preference induced by methamphetamine. In agreement with this, nociceptin receptor knockout mice had slightly enhanced methamphetamine and ethanol conditioned place preferences compared to wild-type mice. This effect did not appear to depend on differences in learning ability, as nociceptin receptor knockout mice had slightly weaker-conditioned place aversions to lithium chloride, the kappa-opioid receptor agonist, U50488H, and the general opiate antagonist, naloxone. The development of behavioral sensitization to methamphetamine was lower in nociceptin receptor knockout mice, and attenuated by UFP-101 administration to wild-type mice. Additionally, ethanol consumption and preference in a two-bottle choice test was lower in nociceptin receptor knockout mice, though ethanol-stimulated locomotion was stronger. Whereas the rewarding effect of methamphetamine and ethanol following chronic treatment, as measured by place conditioning, strengthened in wild-type mice, this effect was absent in nociceptin receptor knockout mice. These results suggest that endogenous N/OFQ suppresses basal and drug-stimulated increases in hedonic state, and plays either a permissive or facilitatory role in the development of addiction.

Nociceptin receptor impairs recognition memory via interaction with NMDA receptor-dependent mitogen-activated protein kinase/extracellular signal-regulated kinase signaling in the hippocampus

Strong evidence suggests a role for nociceptin/orphanin FQ (N/OFQ) neuropeptide and its receptor (NOP) in cognition. However, the signaling mechanisms underlying N/OFQ modulation of memory are less understood. Here, we show that intracerebroventricular or intrahippocampal infusions of N/OFQ impair long-term memory formation in the mouse object recognition task. The synthetic NOP receptor agonist, (1S,3aS)-8-(2,3,3a,4,5,6-hexahydro-1H-phenalen-1-yl)-1-phenyl-1,3,8-triaza-spiro[4.5]decan-4-one (Ro64-6198), administered systemically, also produced amnesic effects that were blocked by coinfusion of the NOP receptor antagonist, [Nphe1,Arg14,Lys15]nociceptin-NH2 (UFP-101), into the dorsal hippocampus. In contrast, Ro64-6198 had no effect on short-term memory or recall performances. Immunoblotting analysis revealed a strong suppressive action of Ro64-6198 on learning-induced upregulation of hippocampal extracellular signal-regulated kinase (ERK) phosphorylation, which is crucial for long-term information storage. Accordingly, pharmacological inhibition of ERK activation after systemic injection of SL327 [alpha-[amino[(4-aminophenyl)thio]methylene]-2-(trifluoromethyl)benzene acetonitrile], a selective inhibitor of the upstream kinase MEK (mitogen-activated protein kinase kinase), abolished long-term recognition memory formation. The noncompetitive NMDA receptor antagonist (+)-5-methyl-10,11-dihydro-5H-dibenzo [a,d]cyclohepten-5,10-imine maleate (MK-801), given systemically, also suppressed ERK activation and disrupted recognition memory. In contrast, no effect of MK-801 was observed on recall, as for Ro64-6198. When administered concurrently at subthreshold doses, Ro64-6198 and MK-801 synergistically suppressed hippocampal ERK activation and impaired long-term memory formation. Under resting conditions, neither Ro64-6198 nor MK-801 affected spontaneous ERK activity in the hippocampus at the amnesic doses whereas at higher doses, only MK-801 had a suppressive effect. We conclude that N/OFQ-NOP receptor system negatively regulates long-term recognition memory formation through hippocampal ERK signaling mechanisms. This modulation may in part take place by inhibiting glutamatergic function at the NMDA receptor.

Role of nociceptin/orphanin FQ and the pseudopeptide [Phe1Psi(CH2NH)Gly2]-nociceptin(1-13)-NH2 and their interaction with classic opioids in the modulation of thermonociception in the land snail Helix aspersa

The role in nociception of nociceptin/orphanin FQ (N/OFQ) and its receptor, the opioid receptor-like 1 (NOP), remains unclear because this peptide has been implicated in both suppression and enhancement of nociception. The present work characterises the effects of N/OFQ and the NOP receptor antagonist, the pseudopeptide [Phe(1)Psi(CH(2)NH)Gly(2)]-nociceptin(1-13)-NH(2) (Phe(1)Psi), on thermonociception in the snail Helix aspersa using the hot plate assay. Additionally, the possible interaction of each of these compounds with morphine or dynorphin A(1-17) and naloxone was studied. Compounds were administered into the hemocoel cavity of H. aspersa and the latency to the aversive withdrawal behaviour recorded. Dose-response and time course curves were done. N/OFQ and naloxone produced a similar dose-dependent pronociceptive effect; however, N/OFQ reached its peak effect earlier and was 30 times more potent than naloxone. [Phe(1)Psi(CH(2)NH)Gly(2)]-nociceptin(1-13)-NH(2) and the opioid agonists, morphine and dynorphin A(1-17) produced antinociception with a similar efficacy, but [Phe(1)Psi(CH(2)NH)Gly(2)]-nociceptin(1-13)-NH(2) reached its peak effect more rapidly and lasted longer than that of dynorphin A(1-17) and morphine. [Phe(1)Psi(CH(2)NH)Gly(2)]-nociceptin(1-13)-NH(2) was 50 times less potent than dynorphin A(1-17), but 30 times more potent than morphine. N/OFQ significantly reduced morphine and dynorphin A(1-17)-induced antinociception. Combined administration of low doses of [Phe(1)Psi(CH(2)NH)Gly(2)]-nociceptin(1-13)-NH(2) and morphine or dynorphin A(1-17) produced a potent antinociceptive effect. Sub-effective doses of naloxone and N/OFQ also synergised to produce pronociception. Data suggest that these two opioid classes regulate nociception through parallel systems. The H. aspersa model appears as a valuable experimental preparation to continue the study of these opioid receptor systems.

Effects of nociceptin/orphanin FQ in the acquisition of contextual and tone fear conditioning in rats

Nociceptin, or orphanin FQ (N/OFQ), the endogenous ligand of NOP receptors, is known to regulate learning and memory processes. To verify the role of N/OFQ in the acquisition of contextual (CFC) and tone fear conditioning (TFC), Wistar male rats received intracerebroventricular injections of N/OFQ (0.1-5.0 nmol) before training, and were tested 24 and 48 hr later to access the freezing response to context and tone, respectively. The intermediate doses (1.0 and 2.5 nmol) impaired the CFC test, sparing TFC. The highest dose (5.0 nmol) reduced freezing during both tests, a result that may be due to nonspecific effects. The posttraining injection of N/OFQ (1 or 5 nmol) did not interfere with CFC and TFC, suggesting a specific effect of the peptide in acquisition processes. Moreover, the impairment observed with N/OFQ (1 nmol) in CFC cannot be attributed to a state-dependent learning because it was not reversed by its pretest administration. The data support the negative role of N/OFQ in the acquisition of aversively motivated tasks, which encompass a spatial component and depend on the hippocampus.

Quantitative study of [(pF)Phe4,Arg14,Lys15]nociceptin/orphanin FQ-NH2 (UFP-102) at NOP receptors in rat periaqueductal gray slices

The nociceptin/orphanin FQ (N/OFQ) peptide (NOP) receptor is a novel member of the opioid receptor family with little affinity for traditional opioids. This receptor and its endogenous ligand, N/OFQ, are widely distributed in the brain and are implicated in many physiological functions including pain regulation. [(pF)Phe(4),Arg(14),Lys(15)]N/OFQ-NH(2) (UFP-102) is a newly developed peptide agonist of NOP receptors. In this study, we quantitatively investigated the effect of UFP-102 at native NOP receptors of the ventrolateral periaqueductal gray (PAG), a crucial midbrain area involved in pain regulation and enriched with NOP receptors, using blind patch-clamp whole-cell recording technique in rat brain slices. UFP-102, like N/OFQ, induced an outward current in ventrolateral PAG neurons and increased the membrane current elicited by a hyperpolarization ramp from -60 to -140 mV. The current induced by UFP-102 was characterized with inward rectification and had a reversal potential near the equilibrium potential of K(+) ions, indicating that UFP-102 activates G-protein coupled inwardly rectifying K(+) channels. The effect of UFP-102 was concentration-dependent with the maximal effect similar to that of N/OFQ. The EC(50) value was 11+/-2 nM, which is 5 fold lower than that of N/OFQ. The effect of UFP-102 was not affected by naloxone while competitively antagonized by UFP-101 ([Nphe(1),Arg(14),Lys(15)]N/OFQ-NH(2)), a potent NOP receptor antagonist, with a pA(2) value of 6.7. These results suggest that UFP-102 is a full agonist at the postsynaptic NOP receptors of the midbrain of rats and is 5 fold more potent than N/OFQ.

Role of amygdaloid nuclei in the anxiolytic-like effect of nociceptin/orphanin FQ in rats

We investigated the mechanism underlying the anxiolytic actions of the neuropeptide nociceptin/orphanin FQ (N/OFQ) using the elevated plus-maze test and T-maze test. Microinfusions of N/OFQ (10 or 32pmol) into the central amygdala (ACE) increased the time spent in the open arms of the elevated plus-maze (anxiolytic-like effects), whereas microinfusions of N/OFQ (10, 32 or 100 pmol) into the basolateral amygdala (ABL) did not affect the time spent in the open arms. Moreover, microinfusions of N/OFQ (32 pmol) into the ACE impaired escape performance from the open arms of the elevated T-maze (anxiolytic-like effects), but did not change inhibitory avoidance of the open arms. A non-peptidyl N/OFQ receptor (NOP) antagonist, J-113397(1-[(3R,4R)-1-cyclooctylmethyl-3-hydroxymethyl-4-piperidyl]-3-ethyl-1,3-dihydro-2H-benzimidazol-2-one) (10 mg/kg, s.c.), blocked the anxiolytic-like effects induced by N/OFQ. These results indicate that the anxiolytic-like effects of N/OFQ might be due to impaired escape performance from the open arms and it implicates the N/OFQ system within the ACE in the mediation of panic action.

[Delayed effect of exorphins on learning of albino rat pups]

The delayed effect of food-derived opioid peptides (exorphins) after chronic administration on postnatal days 1-14 on the learning of albino rat pups has been studied. Heptapeptide YPFPGPI (beta-casomorphin-7), pentapeptide YPLDL (rubiscolin-5) and pentapeptide YPISL (exorphin C) improved the development of the conditioned foraging reflex in a complex maze. Hexapeptide PFPGPI lacking the N-terminal tyrosine proved inefficient. Only beta-casomorphin-7 had an effect (negative) on passive avoidance conditioning. The obtained data confirm that exorphins (particularly, milk-derived beta-casomorphins) can have significant and long-term effects on the environmental adaptation of young mammals.

Effects of nociceptin on the spread and seizure activity in the rat amygdala kindling model: their correlations with 3H-leucyl-nociceptin binding

The effects with pretreatment with nociceptin (0.03-30nmol, i.c.v.) were evaluated on the threshold for eliciting afterdischarge (ADT), generation and spread of seizure activity and postictal depression in rats with kindling stimulation. Nociceptin produced a decrease in ADT (32-45%) in rats with partial seizures (PS, stage II-III), and an increase (61-92%) in rats with generalized seizures (GS, kindled state). Nociceptin did not modify the behavioral changes, spike frequency and duration of afterdischarge elicited at ADT in both experimental groups. In rats with GS, nociceptin enhanced postictal depression (34-44%) evaluated with a recycling paradigm. Autoradiography experiments revealed enhanced nociceptin opioid receptor (NOP) binding in medial amygdala (22-26%), frontal (21-23%) and entorhinal (27-32%) cortices, and reduced binding in the substantia nigra pars compacta (28%) and medial central gray (29%) of rats with PS. The GS group displayed significant decreased NOP binding (40-70%) in most of the brain areas evaluated. These results suggest that nociceptin facilitates ictal activity in rats with PS, whereas in animals with GS, it induces inhibitory effects on ADT and enhances the postictal period. These effects correlate with significant changes in NOP binding.

Opioids and migration, chemotaxis, invasion, and adhesion of human cancer cells

This study was designed to examine the role of opioids on cell migration, chemotaxis, invasion, and adhesion, with an emphasis on whether the opioid growth factor (OGF, [Met(5)]-enkephalin) or the opioid antagonist naltrexone (NTX) impacts any or all of these processes. Drug concentrations of OGF and NTX known to depress or stimulate, respectively, cell proliferation and growth were analyzed. Three different human cancers (pancreatic, colon, and squamous cell carcinoma of the head and neck), represented by seven different cancer cell lines (PANC-1, MIA PaCa-2, BxPC-3, CAL-27, SCC-1, HCT-116, and HT-29), were evaluated. In addition, the influence of a variety of other natural and synthetic opioids on cell motility, invasion, and adhesion was assessed. Positive and negative controls were included for comparison. OGF and NTX at concentrations of 10(-4) to 10(-6)M, and dynorphin A1-8, beta-endorphin, endomorphin-1, endomorphin-2, leucine enkephalin, [D-Pen(2,5)]-enkephalin (DPDPE), [D-Ala(2), MePhe(4), Glycol(5)]-enkephalin (DAMGO), morphine, and U69,593 at concentrations of 10(-6)M, did not alter cell migration, chemotaxis, or invasion of any cancer cell line. OGF and NTX at a concentration of 10(-6)M, and incubation for 24 or 72h, did not change adhesion of these cancer cells to collagen I, collagen IV, fibronectin, laminin, or vitronectin. Moreover, all other opioids tested at 10(-6)M concentrations and for 24h had no effect on adhesion. These results indicate that the inhibitory or stimulatory actions of OGF and NTX, respectively, on cell replication and growth are independent of cell migration, chemotaxis, invasion, and adhesive properties. Moreover, a variety of other exogenous and endogenous opioids, many specific for the micro, delta, or kappa opioid receptors, also did not alter these biological processes, consonant with previous observations of a lack of effects of these compounds and their receptors on the biology of cancer cells.

Roles of the bed nucleus of stria terminalis and of the amygdala in N/OFQ-mediated anxiety and HPA axis activation

Nociceptin/orphanin FQ (N/OFQ) is an opioid-related neuropeptide that is widely distributed in limbic regions of the brain. After intracerebroventricular (icv) injections in rodents, N/OFQ produces elevations in hypothalamic-pituitary-adrenal (HPA) axis activity, and has been reported to produce both anxiogenic and anxiolytic actions. We examined the neuroanatomical basis of these effects with injections of N/OFQ (0.01-1.0nmol) into the lateral ventricle, the amygdala, and the bed nucleus of stria terminalis (BNST) in independent groups of well-handled rats under low stress conditions. Anxiety-related behaviors were evaluated in a neophobic test of anxiety. The latency to enter, total time spent in, and number of entries into an unfamiliar open field and its central zone were measured. After the open field testing, plasma samples were obtained for analysis of HPA axis activity. The N/OFQ-treated rats displayed more anxiety-related behaviors than vehicle-treated rats did with all three of the injection types. However, these effects were greater and more consistent after the icv injections (0.01-1.0nmol) than they were after the amygdala (0.10-1.0nmol) or BNST (1.0nmol) injections. The icv and BNST injections also produced elevations in circulating corticosterone, indicating that the HPA axis was activated in these rats. Intra-amygdaloid injections did not affect corticosterone levels during the open field testing. These results indicate that the amygdala and BNST participate in the anxiogenic behavioral effects of N/OFQ. However, since the most potent effects were seen after icv N/OFQ injections, the anxiogenic and HPA axis-activating effects of N/OFQ appear to occur through additive actions in multiple limbic (and perhaps cortical and brainstem) sites.

Regulation of nociceptin/orphaninFQ secretion by immune cells and functional modulation of interleukin-2

Previous research has demonstrated that numerous populations of immune cell, including lymphocytes, synthesize nociceptin (N/OFQ) precursor mRNA although little is known regarding the immunological role of N/OFQ. In the present study we have demonstrated significant effects of mitogens, pro-inflammatory cytokines, cyclic AMP analogues, glucocorticoids and CRF on N/OFQ secretion by rat splenocytes in vitro. N/OFQ (10(-14) to 10(-10)M) was also shown to inhibit proliferation of Con A-activated splenocytes and production of IL-2 in vitro. In summary we have shown how a variety of stimuli relevant to inflammation can regulate endogenous N/OFQ secretion by splenocytes in vitro. We also suggest that N/OFQ may promote anti-inflammatory actions via suppression of IL-2 in vivo.