Herbal root extracts in Ben-Cha-Moon-Yai remedy attenuated pain-like behaviors and inflammation through the opioid and prostaglandin systems

ETHNOPHARMACOLOGICAL RELEVANCE

Ben-Cha-Moon-Yai (BMY) remedy used in Thai traditional medicine as an anti-inflammatory, analgesic, and antipyretic agent compromises five herbal root extracts of equal weights: Aegle marmelos (L.) Corrêa (AM), Oroxylum indicum (L.) Kurz (OI), Dimocarpus longan Lour. (DL), Dolichandrone serrulata (Wall. ex DC.) Seem. (DS), and Walsura trichostemon Miq. (WT).

AIM OF THE STUDY

To assess the anti-nociceptive and anti-inflammatory effects of the root extracts of all five species of BMY in experimental animal (mouse) models to ensure the rational use of herbal products in Thai traditional medicine.

MATERIALS AND METHODS

Root extracts prepared by ethanol and water extraction were used for the biological assays in animal models at five dose levels: 25, 50,100,200 & 400 mg/kg. The anti-nociceptive activity was evaluated based on hot-plate latency, duration of paw licking induced by formalin, and abdominal writhing induced by acetic acid. Carrageenan- and prostaglandin-induced paw oedema models were used to determine the anti-inflammatory activity.

RESULTS

The oral administration of AM, DS and WT root extracts displayed significant analgesic effects in the hot-plate test, both phases (early and late) of formalin test and acetic-acid induced writhing test at different dose levels. OI and DL only produced significant analgesia in the late phase of the formalin test and writhing test. The pretreatment of animals with the non-selective opioid receptor antagonist naloxone, reverse AM, DS and WT induced-antinociceptive activity. In both carrageenan and prostaglandin-induced paw oedema tests, all five herbal plant root extracts significantly reduced paw oedema at 3 h or more at different dose levels. Rotarod test results showed no effects of five herbal plant root extracts on the balance and the motor coordination at the highest dose level evaluated (400 mg/kg).

CONCLUSION

The root extracts of AM, DS, and WT possess both central and peripheral anti-nociceptive properties, while OI and DL possess only peripheral analgesic properties. All five root extracts own anti-inflammatory properties, which might be due to their activity on the prostaglandin system. Altogether these findings ensure the rational use of BMY remedy in Thai traditional medicine.

Intracerebroventricular administration of CYX-6, a potent μ-opioid receptor agonist, a δ- and κ-opioid receptor antagonist and a biased ligand at μ, δ & κ-opioid receptors, evokes antinociception with minimal constipation and respiratory depression in rats in contrast to morphine

Mu opioid receptor (MOPr) agonists are thought to produce analgesia via modulation of G-protein-coupled intracellular signalling pathways whereas the β-arrestin2 pathway is proposed to mediate opioid-related adverse effects. Here, we report the antinociception, constipation and respiratory depressant profile of CYX-6, a potent MOPr agonist that is also a delta and a kappa opioid receptor (DOPr/KOPr) antagonist and that lacks β-arrestin2 recruitment at each of the MOPr, DOPr and the KOPr. In anaesthetised male Sprague Dawley rats, an intracerebroventricular (i.c.v.) guide cannula was stereotaxically implanted. After 5-7 days post-surgical recovery, rats received a single i.c.v. bolus dose of CYX-6 (3-30 nmol), morphine (100 nmol) or vehicle. Antinociception was assessed using the warm water tail flick test (52.5 ± 0.5 °C). Constipation was assessed using the charcoal meal gut motility test and the castor oil-induced diarrhoea test. Respiratory depression was measured by whole-body plethysmography in awake, freely moving animals, upon exposure to a hypercapnic gas mixture (8% CO2, 21% O2 and 71% N2). The intrinsic pharmacology of CYX-6 given by the i.c.v. route in rats showed that it produced dose-dependent antinociception. It also produced respiratory stimulation rather than depression and it had a minimal effect on intestinal motility in contrast to the positive control, morphine. CYX-6 is an endomorphin-2 analogue that dissociates antinociception from constipation and respiratory depression in rats. Our findings provide useful insight to inform the discovery and development of novel opioid analgesics with a superior tolerability profile compared with morphine.

Differential Tolerance to FTY720-Induced Antinociception in Acute Thermal and Nerve Injury Mouse Pain Models: Role of Sphingosine-1-Phosphate Receptor Adaptation

The immunomodulatory prodrug 2-amino-2-(2-[4-octylphenyl]ethyl)-1,3-propanediol (FTY720), which acts as an agonist for sphingosine-1-phosphate (S1P) receptors (S1PR) when phosphorylated, is proposed as a novel pain therapeutic. In this study, we assessed FTY720-mediated antinociception in the radiant heat tail-flick test and in the chronic constriction injury (CCI) model of neuropathic pain in mice. FTY720 produced antinociception and antiallodynia, respectively, and these effects were dose-dependent and mimicked by the S1PR1-selective agonist CYM-5442. Repeated administration of FTY720 for 1 week produced tolerance to acute thermal antinociception, but not to antiallodynia in the CCI model. S1PR-stimulated [35S]GTPγS autoradiography revealed apparent desensitization of G protein activation by S1P or the S1PR1 agonist 5-[4-phenyl-5-(trifluoromethyl)-2-thienyl]-3-[3-(trifluoromethyl)phenyl]-1,2,4-oxadiazole (SEW-2871) throughout the brain. Similar results were seen in spinal cord membranes, whereby the Emax value of S1PR-stimulated [35S]GTPγS binding was greatly reduced in repeated FTY720-treated mice. These results suggest that S1PR1 is a primary target of FTY720 in alleviating both acute thermal nociception and chronic neuropathic nociception. Furthermore, the finding that tolerance develops to antinociception in the tail-flick test but not in chronic neuropathic pain suggests a differential mechanism of FTY720 action between these models. The observation that repeated FTY720 administration led to desensitized S1PR1 signaling throughout the central nervous system suggests the possibility that S1PR1 activation drives the acute thermal antinociceptive effects, whereas S1PR1 desensitization mediates the following: 1) tolerance to thermal antinociceptive actions of FTY720 and 2) the persistent antiallodynic effects of FTY720 in neuropathic pain by producing functional antagonism of pronociceptive S1PR1 signaling.

Neutrophil elastase inhibition effectively rescued angiopoietin-1 decrease and inhibits glial scar after spinal cord injury

After spinal cord injury (SCI), neutrophil elastase (NE) released at injury site disrupts vascular endothelium integrity and stabilization. Angiopoietins (ANGPTs) are vascular growth factors that play an important role in vascular stabilization. We hypothesized that neutrophil elastase is one of the key determinants of vascular endothelium disruption/destabilization and affects angiopoietins expression after spinal cord injury. To test this, tubule formation and angiopoietins expression were assessed in endothelial cells exposed to different concentrations of recombinant neutropil elastase. Then, the expression of angiopoietin-1, angiopoietin-2, and neutrophil elastase was determined at 3 h and at 1, 3, 5, 7, 14, 21, and 28 days in a clinically relevant model of moderate compression (35 g for 5 min at T10) spinal cord injury. A dichotomy between the levels of angiopoietin-1 and angiopoietin-2 was observed; thus, we utilized a specific neutrophil elastase inhibitor (sivelestat sodium; 30 mg/kg, i.p., b.i.d.) after spinal cord injury. The expression levels of neutropil elastase and angiopoietin-2 increased, and that of angiopoietin-1 decreased after spinal cord injury in rats. The sivelestat regimen, optimized via a pharmacokinetics study, had potent effects on vascular stabilization by upregulating angiopoietin-1 via the AKT pathway and preventing tight junction protein degradation. Moreover, sivelestat attenuated the levels of inflammatory cytokines and chemokines after spinal cord injury and hence subsequently alleviated secondary damage observed as a reduction in glial scar formation and the promotion of blood vessel formation and stabilization. As a result, hindlimb locomotor function significantly recovered in the sivelestat-treated animals as determined by the Basso, Beattie, and Bresnahan scale and footprint analyses. Furthermore, sivelestat treatment attenuated neuropathic pain as assessed by responses to von Frey filaments after spinal cord injury. Thus, our result suggests that inhibiting neutropil elastase by administration of sivelestat is a promising therapeutic strategy to inhibit glial scar and promote functional recovery by upregulating angiopoietin-1 after spinal cord injury.

Zinc involvement in opioid addiction and analgesia--should zinc supplementation be recommended for opioid-treated persons?

INTRODUCTION

Zinc chelators were shown to facilitate some opioid-withdrawal signs in animals. Zinc deficiency, which affects more than 15% the world's population, is also common among opioid consumers and opioid-treated animals exhibit misbalances of zinc distribution.

AIM

The present study focuses on how zinc ions interfere with opioid dependence/addiction and analgesia, trying to preliminary discuss if zinc supplementation in opioid-users should be recommended in order to reduce the risk of addiction.

METHODS

All relevant literature was searched up to April 2015. The search was performed using the term "zinc" plus combinations of following terms: "opioid receptors", "opioid" or representatives of this class, "addiction", "dependence", "analgesia", and "pain". Human, animal, in vitro studies and reviews were including.

RESULTS

Both human and animal studies revealed decreased serum zinc under opioid-administration conditions, attributed mainly to increased urinary elimination (humans) or redistribution (animals). Moreover, animal studies revealed decreased brain zinc levels in morphine-treated animals, with increased zinc hepatic levels, but also an enhancement of endogenous opioid system activity and a possible reduction of morphine withdrawal by zinc. In vitro studies revealed reduction of opioid ligands binding to receptors by zinc. However, the very few in vivo animal studies on opioid analgesia revealed controversial results, as zinc demonstrated clear analgesic effect, but zinc associated to opioids doesn't result in a potentiation of the analgesic effect.

CONCLUSION

Zinc dietary supplementation in patients treated with opioids for cancer-related chronic pain should be considered, due to the high incidence of zinc deficiency, also well-documented in opioid consumers. The low toxicity of orally-administered zinc also pleads for this idea. The main contra-argument to zinc administration in opioid-treated persons is related to the way zinc influences opioid-induced analgesia.

Interplay between RAS and opioids: opening the Pandora of complexities

Angiotensin and endogenous opioids are important bioactive neuropeptides, which are widely distributed in the brain and peripheral regions to produce diverse biological and neurobiological activities. An endogenous opioid system includes proopiomelanocortin-derived enkephalin, dynorphin and endorphin that act on their specific receptors such as delta (δ), kappa (κ) and mu (μ) receptors. Research evidence demonstrates significant positive as well as negative interactions between renin angiotensin system (RAS) and endogenous opioids in the brain and periphery. The diverse actions of Ang II are possibly mediated indirectly through endogenous opioids, while opioids are also shown to activate RAS components suggesting the up-regulation of each system in concern with each other. On the contrary, there are reports suggesting a negative correlation between RAS and opioid system. Research evidence also supports the notion that Ang II acts as anti-opioid peptide to decrease the actions of opioids. Moreover, opioids-induced decline in angiotensin release and functioning has also been reported. Co-administration of ACE inhibitors with opioids exhibits significant interactions possibly due to decreased metabolism of opioids leading to potentiation of their actions. The present review describes the complexities of positive and negative interactions between RAS and opioids along with possible mechanisms responsible for these interactions.

Physiopathological and therapeutical correlations in alcohol dependence

No doubt, alcoholism represents nowadays the toxicomany with the highest expansion rate among all population groups, being recognized by the specialists from the medical, social, economic and legal field as a true "toxic pandemy". Researchers consider ethanol, this small but highly aggressive molecule, to have supremacy if we were to consider the number of pages dedicated to it worldwide on daily bases, in the medical or any other specialty literature. Nonetheless, the large volume of data regarding ethanol toxicity does not seen to simplify things, on the contrary it points out new information about the its negative effects on human body. Ethanol represents a toxic that is rapidly and completely absorbed in the intestinal tract being distributed to most tissues and organs; ethanol is recognized as an enzymatic inductor of its own metabolization but also of the metabolization of numerous therapeutic agents.

Gonadal steroids differentially modulate the actions of orphanin FQ/nociceptin at a physiologically relevant circuit controlling female sexual receptivity

Orphanin FQ/nociceptin (OFQ/N) inhibits the activity of pro-opiomelanocortin (POMC) neurones located in the hypothalamic arcuate nucleus (ARH) that regulate female sexual behaviour and energy balance. We tested the hypothesis that gonadal steroids differentially modulate the ability of OFQ/N to inhibit these cells via presynaptic inhibition of transmitter release and postsynaptic activation of G protein-gated, inwardly-rectifying K(+) (GIRK)-1 channels. Whole-cell patch clamp recordings were performed in hypothalamic slices prepared from ovariectomised rats. OFQ/N (1 μm) decreased the frequency of miniature excitatory postsynaptic currents (mEPSCs) and miniature inhibitory postsynaptic currents (mIPSCs), and also caused a robust outward current in the presence of tetrodotoxin, in ARH neurones from vehicle-treated animals. A priming dose of oestradiol benzoate (EB; 2 μg) increased basal mEPSC frequency, markedly diminished both the OFQ/N-induced decrease in mEPSC frequency and the activation of GIRK-1 currents, and potentiated the OFQ/N-induced decrease in mIPSC frequency. Steroid treatment regimens that facilitate sexual receptivity reinstate the basal mEPSC frequency, the OFQ/N-induced decrease in mEPSC frequency and the activation of GIRK-1 currents to levels observed in vehicle-treated controls, and largely abolish the ability of OFQ/N to decrease mIPSC frequency. These effects were observed in an appreciable population of identified POMC neurones, almost one-half of which projected to the medial preoptic nucleus. Taken together, these data reveal that gonadal steroids influence the pleiotropic actions of OFQ/N on ARH neurones, including POMC neurones, in a disparate manner. These temporal changes in OFQ/N responsiveness further implicate this neuropeptide system as a critical mediator of the gonadal steroid regulation of reproductive behaviour.

Controlled cross-over study in normal subjects of naloxone-preceding-lactate infusions; respiratory and subjective responses: relationship to endogenous opioid system, suffocation false alarm theory and childhood parental loss

BACKGROUND

The expanded suffocation false alarm theory (SFA) hypothesizes that dysfunction in endogenous opioidergic regulation increases sensitivity to CO2, separation distress and panic attacks. In panic disorder (PD) patients, both spontaneous clinical panics and lactate-induced panics markedly increase tidal volume (TV), whereas normals have a lesser effect, possibly due to their intact endogenous opioid system. We hypothesized that impairing the opioidergic system by naloxone could make normal controls parallel PD patients' response when lactate challenged. Whether actual separations and losses during childhood (childhood parental loss, CPL) affected naloxone-induced respiratory contrasts was explored. Subjective panic-like symptoms were analyzed although pilot work indicated that the subjective aspect of anxious panic was not well modeled by this specific protocol.

METHOD

Randomized cross-over sequences of intravenous naloxone (2 mg/kg) followed by lactate (10 mg/kg), or saline followed by lactate, were given to 25 volunteers. Respiratory physiology was objectively recorded by the LifeShirt. Subjective symptomatology was also recorded.

RESULTS

Impairment of the endogenous opioid system by naloxone accentuates TV and symptomatic response to lactate. This interaction is substantially lessened by CPL.

CONCLUSIONS

Opioidergic dysregulation may underlie respiratory pathophysiology and suffocation sensitivity in PD. Comparing specific anti-panic medications with ineffective anti-panic agents (e.g. propranolol) can test the specificity of the naloxone+lactate model. A screen for putative anti-panic agents and a new pharmacotherapeutic approach are suggested. Heuristically, the experimental unveiling of the endogenous opioid system impairing effects of CPL and separation in normal adults opens a new experimental, investigatory area.

The nociceptin/orphanin FQ system as a target for treating alcoholism

Nociceptin (known also as orphanin FQ) is the most recently discovered member of the endogenous opioid peptide family, albeit nearly 15 years ago. Nociceptin renders or influences many behavioral, psychological and neurobiological processes, including memory, anxiety, stress and reward. Since its discovery, results of a steady stream of studies have suggested that endogenous nociceptin might be involved in responses to addictive drugs, and that targeting the nociceptin system may be beneficial in treating addictions. The current review summarizes and critically appraises those studies, particularly those that point to an application in treating alcoholism. Overall, most, studies suggest that the endogenous nociceptin system has a physiological role in mediating or regulating behavioral responses to alcohol, and that activating nociceptin receptors suppresses ongoing alcohol consumption or reinstatement of responding for alcohol. These findings encourage the development of therapies targeted at the nociceptin system for the treatment of alcoholism in humans, though a minor number of studies showing continuous activation of the nociceptin receptor can produce increased, rather than reduced, alcohol consumption emphasize the necessity of further investigation.

Bacterial lipopolysaccharide regulates nociceptin expression in sensory neurons

Nociceptin/orphanin FQ (N/OFQ) is an opioid-related peptide that is markedly up-regulated in sensory neurons in vivo following peripheral inflammation and plays a key role in pain physiology. To identify substances that up-regulate N/OFQ expression in sensory neurons, we carried out an in vitro screen using purified adult mouse dorsal root ganglion (DRG) neurons and identified the potent proinflammatory agent bacterial lipopolysaccharide (LPS) as a very effective inducer of N/OFQ. The robust response of these neurons to LPS enabled us to identify the components of a putative neuronal LPS receptor complex. In contrast to the immune system, where the functional LPS receptor complex is composed of CD-14 together with either MD-2 and TLR4 on myeloid cells or the homologous receptors MD-1 and RP105 on mature B cells, DRG neurons express the unusual combination of CD-14, TLR4, and MD-1. Blocking antibodies against TLR4 and MD-1 prevented induction of N/OFQ by LPS, and, in immunoprecipitation experiments, MD-1 coprecipitated with TLR4. Our findings suggest that LPS regulates N/OFN expression in sensory neurons via a novel combination of LPS receptor components and demonstrate for the first time a direct action of a key initiator of innate immune responses on neurons.

Role of ATP-sensitive potassium channels in the piracetam induced blockade of opioid effects

The present study has been designed to investigate the effect of piracetam on morphine/ buprenorphine-induced antinociception in rats and effect of piracetam on morphine or minoxidil induced relaxation in KCl-precontracted isolated rat aortic ring preparation. Nociceptive threshold was measured by the tail flick test in rats. The cumulative dose responses of morphine or minoxidil were recorded in KCl-precontracted isolated rat aortic ring preparation. Piracetam attenuated buprenorphine-induced antinociception in rats. Piracetam significantly reduced the morphine and minoxidil induced relaxation in KCl precontracted isolated rat aortic ring preparation suggesting that piracetam interferes with opioid receptor and ATP-sensitive potassium channel (KATP) opener mediated responses in vitro. Thus, it may be suggested that piracetam attenuates opioid effects by an opioid receptor-KATP channel linked mechanism.

Dopamine depletion and subsequent treatment with L-DOPA, but not the long-lived dopamine agonist pergolide, enhances activity of the Akt pathway in the rat striatum

Dysregulation of signaling pathways is believed to contribute to Parkinson's disease pathology and l-DOPA-induced motor complications. Long-lived dopamine (DA) agonists are less likely to cause motor complications by virtue of continuous stimulation of DA receptors. In this study, we compared the effects of the unilateral 6-hydroxydopamine lesion and subsequent treatment with l-DOPA and DA agonist pergolide on signaling pathways in rats. Pergolide caused less pronounced behavioral sensitization than l-DOPA (25 mg/kg, i.p., 10 days), particularly at lower dose (0.5 and 0.25 mg/kg, i.p.). Pergolide, but not l-DOPA, reversed lesion-induced up-regulation of preproenkephalin and did not up-regulate preprodynorphine or DA D3 receptor in the lesioned hemisphere. Pergolide was as effective as l-DOPA in reversing the lesion-induced elevation of ERK2 phosphorylation in response to acute apomorphine administration (0.05 mg/kg, s.c.). Chronic l-DOPA significantly elevated the level of Akt phosphorylation at both Thr(308) and Ser(473) and concentration of phosphorylated GSK3alpha, whereas pergolide suppressed the lesion- and/or challenge-induced supersensitive Akt responses. The data indicate that l-DOPA, unlike pergolide, exacerbates imbalances in the Akt pathway caused by the loss of DA. The results support the hypothesis that the Akt pathway is involved in long-term actions of l-DOPA and may be linked to l-DOPA-induced dyskinesia.

Nociceptin (1-13)NH2 inhibits stimulated calcitonin-gene-related-peptide release from primary cultures of rat trigeminal ganglia neurones

In this work we have developed and characterized primary cultures of neonatal rat trigeminal ganglia neurones; calcitonin-gene-related-peptide (CGRP) released from cells was taken as a marker of neuronal function. A significant and consistent increase in CGRP secretion was elicited by non-specific (56 mm KCl or veratridine) or specific (capsaicin) depolarizing stimuli. This paradigm was subsequently used to investigate the effects of nociceptin, an opioid-like peptide involved in central and peripheral control of nociception. We found that the nociceptin analogue nociceptin (1-13)NH2 (NOC) did not affect baseline CGRP release, but it reduced in a concentration-dependent manner CGRP release induced by all tested stimuli. NOC-induced reduction was statistically significant from 0.01 nm onward and achieved maximal effects at 10 nm. Such effects of NOC were seemingly mediated by the activation of specific ORL1 receptors, as a well-known nociceptin antagonist, N(Phe1)nociceptin (1-13)NH2, was able to completely revert NOC inhibition of capsaicin-stimulated CGRP release.

The endogenous opioid system and clinical pain management

The endogenous opioid system is one of the most studied innate pain-relieving systems. This system consists of widely scattered neurons that produce three opioids: beta-endorphin, the met- and leu-enkephalins, and the dynorphins. These opioids act as neurotransmitters and neuromodulators at three major classes of receptors, termed mu, delta, and kappa, and produce analgesia. Like their endogenous counterparts, the opioid drugs, or opiates, act at these same receptors to produce both analgesia and undesirable side effects. This article examines some of the recent findings about the opioid system, including interactions with other neurotransmitters, the location and existence of receptor subtypes, and how this information drives the search for better analgesics. We also consider how an understanding of the opioid system affects clinical responses to opiate administration and what the future may hold for improved pain relief. The goal of this article is to assist clinicians to develop pharmacological interventions that better meet their patient's analgesic needs.

Changes in the beta-endorphin plasma level after repeated treatment with acamprosate in rats selectively bred for high and low alcohol preference

The aim of this study was to evaluate the beta-endorphin (beta-endorphin) plasma level in Warsaw Low Preferring (WLP) and Warsaw high-preferring (WHP) rats after repeated administration of acamprosate, one of most effective drug in the treatment of alcoholism. Treatment with acamprosate in dose 200mg/kg, p.o. for 10 days induced an increase in plasma beta-endorphin levels. A single injection of ethanol also results in the increase of beta-endorphin level. Moreover, it was found that single injection of ethanol to WHP rats resulted in lower increase of plasma beta-endorphin content in rats earlier treated with acamprosate. In WLP rats, repeated acamprosate treatment prevents the ethanol-induced increase in plasma beta-endorphin level. It may be concluded that acamprosate modulates the endogenous opioid system.

Androgen dependence in hamsters: overdose, tolerance, and potential opioidergic mechanisms

Anabolic steroids are drugs of abuse. However, the potential for steroid reward and addiction remains largely unexplored. This study used i.c.v. testosterone self-administration and controlled infusions of testosterone or vehicle in hamsters to explore central mechanisms of androgen overdose. Forty-two hamsters used nose-pokes to self-administer 1 microg/microl testosterone i.c.v. 4 h/day in an operant chamber. During 1-56 days of androgen self-administration, 10 (24%) hamsters died. Deaths correlated with peak daily intake of testosterone. Of the hamsters that self-administered a peak intake of <20 microg/day, there was 100% survival (10/10). Survival decreased to 86% (19/22) when daily testosterone intake peaked at 20-60 microg/day. Only 30% (three of 10) survived when daily testosterone intake exceeded 60 microg/day. Deaths are not due to volume or vehicle because i.c.v. infusions of 80 mul vehicle had no effect. Testosterone overdose resembles opiate intoxication. When male hamsters received infusions of 40 microg testosterone, locomotion (25.1+/-18.8 grid-crossings/10 min), respiration (72.7+/-5.4 breaths/min) and body temperature (33.5+/-0.4 degrees C) were significantly reduced, compared with males receiving vehicle infusions (186.1+/-8.1 crossings/10 min, 117.6+/-1.0 breaths/min, 35.9+/-0.1 degrees C, P<0.05). However, males developed tolerance to continued daily testosterone infusion. After 15 days, locomotion (170.2+/-6.3 crossings), respiration (118.4+/-1.3 breaths/min), and body temperature (35.3+/-0.3 degrees C) in testosterone-infused males were equivalent to that in vehicle controls (P>0.05). The depressive effects of testosterone infusion are blocked by the opioid antagonist, naltrexone. With naltrexone pre-treatment (10 mg/kg s.c.), locomotion (183.7+/-1.8 crossings/10 min), respiration (116.9+/-0.3 breaths/min), and body temperature (36.1+/-0.4 degrees C) during testosterone infusion were equivalent to vehicle controls. Likewise, naltrexone prevents the reinforcing effects of i.c.v. testosterone self-administration. These results indicate that testosterone at high doses causes central autonomic depression, which may be a factor in deaths during self-administration. As well, the depressive effects of large quantities of testosterone may be mediated, at least in part, by an opioidergic mechanism.

Endogenous opioids, µ-opiate receptors and chloroquine-induced pruritus: A double-blind comparison of naltrexone and promethazine in patients with malaria fever who have an established history of generalized chloroquine-induced itching

AIMS

Chloroquine induces a severe generalized pruritus, in predisposed Black African patients, during treatment of malaria fever, and also in some Caucasian patients treated for rheumatological diseases. We have previously shown that chloroquine may release endogenous opioids and/or interact with micro-opiate receptors in rats, and that both histamine and malaria parasite blood density, contribute to the itching severity in malaria fever in humans. The aim of our present study was to assess and compare the antipruritic efficacy of the micro-opiate receptor antagonist, naltrexone, and the antihistamine, promethazine, in chloroquine treated patients with malaria fever.

METHODS

A double-blind, randomized, parallel group comparison of the chloroquine-induced pruritus intensity and time profile in patients with parasitologically proven malaria fever, who were pretreated with a single dose of either naltrexone 50 mg or promethazine 25 mg orally (six patients each). All patients had an established history of severe pruritus following chloroquine treatment of malaria fever. A self-assessed itching severity score was undertaken at 0, 6, 12, 24, 48 and 72 h after initial chloroquine dosing, and the areas under the pruritus-intensity time curve AUCP0-72 h was determined in each patient and correlated to the malaria parasite density in blood.

RESULTS

Both naltrexone and promethazine subjectively reduced itching severity compared with prior historical experience. One patient on naltrexone and two on promethazine never experienced any itching. There was no statistically significant treatment effect, but a significant time effect (P = 0.001, F = 4.77 d.f. 5) by two-way repeated measures ANOVA. The AUCP for naltrexone was 82 +/- 25 units/h, and 57 +/- 34 units/h for promethazine [95% confidence interval for the difference being -73 to 123]. However, the malaria parasite density in the naltrexone group (740 +/- 178 microl(-1)) tended to be higher than in the promethazine group 314 +/- 69 microl(-1) (P = 0.056, 95% confidence interval for the difference being -15 to 866 microl(-1)). Correction of the AUCP for malaria parasite density (parasite pruritogenic index, AUCP. units/h/parasites/microl blood) tended to be lower with naltrexone 9.1 +/- 2.6 than with promethazine 12.2 +/- 7.0 There was a highly significant and positive correlation between the malaria parasite density and the AUCP0-72 h, on naltrexone (r2 = 0.78, P = 0.040) and promethazine (r2 = 0.93, P = 0.008). However, comparison of regressions revealed that the slope of the regression was significantly steeper with promethazine 0.48 than naltrexone 0.12 (P = 0.006, t = 4.2), with the intercepts showing a trend to a difference (P = 0.086).

CONCLUSION

Naltrexone exerted an antipruritic action, at least to a similar extent to promethazine in patients with chloroquine-induced itching in malaria fever. However, the relationship between parasite density and resultant pruritus was significantly different between naltrexone and promethazine. Thus, micro-opiate receptors/and or endogenous opioids may contribute to chloroquine itching in malaria fever, in humans, in accord with animal experimental findings. Malaria parasite density in blood is a strong determinant of itching severity in patients predisposed to chloroquine-induced pruritus.

Effect of intrathecal nocistatin on nociceptin/orphanin FQ analgesia in chronic constriction injury rat

Nocistatin and nociceptin/orphanin FQ (N/OFQ) are two neuropeptides derived from the same precursor protein, prepronociceptin (ppOFQ), and exhibit different effects on spinal neurotransmission. Nocistatin does not bind to nociceptin/orphanin FQ peptide receptor (NOP), but intrathecal (i.t.) nocistatin has been reported to block the analgesic effect of i.t. N/OFQ. In this study, we investigated the effect of i.t. nocistatin on N/OFQ analgesia to radiant thermal stimuli in chronic constriction injury (CCI) rat. Firstly, to investigate the analgesic effect of N/OFQ, different doses of N/OFQ (3, 10, 30 microg) were intrathecally injected and foot withdrawal latency (FWL) to radiant heat was recorded. It is observed that 3 microg N/OFQ had no effect on FWL, 10 and 30 microg N/OFQ significantly increased FWL of CCI rat. Then, 10 microg N/OFQ, 10 microg nocistatin and a drug cocktail including 10 microg N/OFQ and 10 microg nocistatin were intrathecally injected. The results showed that FWL significantly decreased after using N/OFQ and nocistatin compared with using only N/OFQ, and 10 microg nocistatin had no effect on FWL versus control, suggesting that this dose of nocistatin per se had no effect on the pain threshold of CCI rat, but could block the analgesic effect of N/OFQ. These results indicated that i.t. N/OFQ dose-relatedly depressed thermal hyperalgesia produced by CCI and nocistatin could block N/OFQ analgesia at spinal level in CCI rat.

Effects of single and dual administration of cocaine and ethanol on opioid and ORL1 receptor expression in rat CNS: an autoradiographic study

The co-abuse of cocaine and ethanol is common among human addicts and has been reported to produce a stronger increase of euphoria as compared to either drug given alone. Both cocaine and ethanol increase the extracellular dopamine concentration in the nucleus accumbens, a terminal region in the mesolimbic dopamine pathway. In addition, both cocaine and ethanol affect the endogenous opioid system, which in turn alters the activity of the mesolimbic dopamine pathway. We have carried out quantitative autoradiography mapping of the opioid receptors as well as the opioid receptor-like 1 receptor in the brains of rats treated with both single and dual cocaine and ethanol. Rats received acute cocaine, ethanol or both drugs in combination. Ethanol alone or in combination with cocaine modulated the receptor densities in rat central nervous system. The kappa receptor densities were generally decreased, while both the mu and the opioid receptor-like 1 receptors were up-regulated. The mu opioid receptor levels were mainly increased in non-cortical regions, whereas the opioid receptor-like 1 receptors were increased in cortical structures. No changes in delta opioid receptors were observed. Cocaine alone did not influence the receptor levels in any of the treatment groups.

The nociceptin/orphanin FQ/NOP receptor system as a target for treatment of alcohol abuse: a review of recent work in alcohol-preferring rats

The intracerebroventricular administration of the 17 amino acid peptide nociceptin/orphanin FQ (N/OFQ), the endogenous ligand of the NOP receptor (previously referred to as ORL-1 or OP4 receptor), reduces voluntary 10% ethanol intake in genetically selected Marchigian Sardinian alcohol-preferring (msP) rats. Studies aimed at the pharmacological characterization of the receptor, which mediates the effect, have shown that the C-terminal 13 amino acid sequence is crucial for activity and that the selective NOP receptor antagonist [Nphe(1)]N/OFQ(1-13)NH(2) blocks the effect of N/OFQ on ethanol drinking. In place conditioning studies, N/OFQ abolishes the conditioned place preference (CPP) induced by ethanol in msP rats, or by morphine in nonselected Wistar rats; these findings suggest that N/OFQ is able to abolish the rewarding properties of ethanol and morphine. Moreover, N/OFQ inhibits reinstatement of alcohol-seeking behavior induced to electric footshock stress, as well as reinstatement of alcohol-seeking behavior induced by ethanol-paired cues. Together, these findings suggest that N/OFQ and its receptor may represent an interesting target for pharmacological treatment of alcohol abuse.

Neuroimmunotherapy of untreatable metastatic solid tumors with subcutaneous low-dose interleukin-2, melatonin and naltrexone: modulation of interleukin-2-induced antitumor immunity by blocking the opioid system

OBJECTIVES

The preliminary applications of the psychoneuroimmunological knowledges to the treatment of human diseases have confirmed the possibility to amplify IL-2-dependent anticancer immunity by the pineal hormone melatonin (MLT) or by opioid antagonist, such as naltrexone (NTX), which act by activating TH1 lymphocytes or suppressing TH2 lymphocytes, respectively. At present, however, there are no data about the immunobiological effects of a concomitant administration of both MLT and NTX on IL-2-induced anticancer immunity. This preliminary study was carried out to evaluate whether the association of NTX may further enhance the lymphocytosis induced by the neuroimmunotherapy with IL-2 plus MLT.

MATERIALS & METHODS

The study included 14 consecutive untreatable metastatic solid tumor patients. According to a cross-over randomized study, the patients were treated during two consecutive immunotherapeutic cycles at 21-day intervals with IL-2 plus MLT alone or with IL-2 plus MLT plus NTX. IL-2 was injected subcutaneously at 3 MIU/day for 6 days/week for 4 weeks, MLT was given orally at 20 mg /day in the evening every day, and NTX was given orally at 100 mg in the morning every next day. For the immune evaluation, venous blood samples were drawn before the onset of treatment and at weekly intervals.

RESULTS

Lymphocyte mean number significantly increased after both IL-2 plus MLT and IL-2 plus MLT plus NTX. However, the concomitant administration of NTX induced a significantly higher increase in lymphocyte mean number with respect to that achieved with IL-2 plus MLT alone. In contrast, the increase in eosinophil mean number was significantly higher on IL-2 plus MLT alone.

CONCLUSIONS

This preliminary study shows that the association of NTX further amplifies the lymphocytosis obtained by IL-2 plus MLT. Since the lymphocytosis represents the most important favourable prognostic variable predicting the anticancer efficacy of IL-2 immunotherapy, it is probable that a cancer neuroimmunotherapy with IL-2 plus both MLT and NTX to activate TH1 and suppress TH2 cells respectively, may deserve more promising results in the treatment of human neoplasms according to the psychoneuroimnunological knowledge.

Venlafaxine and mirtazapine: different mechanisms of antidepressant action, common opioid-mediated antinociceptive effects--a possible opioid involvement in severe depression?

The efficacy of each antidepressant available has been found equal to that of amitriptyline in double-blind studies as far as mild to moderate depression is involved. However, it seems that some antidepressants are more effective than others in the treatment of severe types of depression (i.e., delusional depression and refractory depression). Following studies regarding the antinociceptive mechanisms of various antidepressants, we speculate that the involvement of the opioid system in the antidepressants' mechanism of action may be necessary, in order to prove effective in the treatment of severe depression. Among the antidepressants of the newer generations, that involvement occurs only with venlafaxine (a presynaptic drug which blocks the synaptosomal uptake of noradrenaline and serotonin and, to a lesser degree, of dopamine) and with mirtazapine (a postsynaptic drug which enhances noradrenergic and 5-HT1A-mediated serotonergic neurotransmission via antagonism of central alpha-auto- and hetero-adrenoreceptors). When mice were tested with a hotplate analgesia meter, both venlafaxine and mirtazapine induced a dose-dependent, naloxone-reversible antinociceptive effect following ip administration. Summing up the various interactions of venlafaxine and mirtazapine with opioid, noradrenergic and serotonergic agonists and antagonists, we found that the antinociceptive effect of venlafaxine is influenced by opioid receptor subtypes (mu-, kappa1- kappa3- and delta-opioid receptor subtypes) combined with the alpha2-adrenergic receptor, whereas the antinociceptive effect of mirtazapine mainly involves mu- and kappa3-opioid mechanisms. This opioid profile of the two drugs may be one of the explanations to their efficacy in severe depression, unlike the SSRIs and other antidepressants which lack opioid activity.

The anxiolytic effect of acute ethanol or diazepam exposure is unaltered in mu-opioid receptor knockout mice

Previous researchers demonstrate an opioidergic involvement in the anxiolytic and rewarding actions of ethanol and diazepam. Therefore, to further characterize the role of the opioid system in the anxiolytic action of ethanol and diazepam, normal (C57BL/6J), hybrid (B6129F1) and mu-opioid receptor knockout mice were given i.p. ethanol (0, 1.0 or 1.6 g/kg) or diazepam (1.5 mg/kg). The anxiolytic properties of these agents were then tested in the elevated plus-maze. Additional ethanol-treated mu-opioid receptor knockout mice (1 g/kg) were pretreated with the kappa-opioid receptor antagonist nor-BNI (0 or 3 mg/kg) to assess the involvement of kappa-opioid activity in ethanol's anxiolytic actions. The anxiolytic action of ethanol and diazepam in the mu-opioid receptor knockout mouse did not differ from the effects obtained in normal mice and pretreatment with nor-BNI did not significantly attenuate ethanol's actions in mu-opioid receptor knockout mice. Thus, the anxiolytic actions of ethanol and diazepam appear to be independent of opioid system activity in the mu-opioid receptor knockout mouse.

Naloxone improves arterial blood pressure and hypoxic ventilatory depression, but not survival, of rats during acute hypoxia

OBJECTIVE

To investigate the effects of naloxone and morphine during acute hypoxia.

DESIGN

Prospective, randomized animal study.

SETTING

University laboratory.

SUBJECTS

Twenty-eight adult male Sprague Dawley rats, weighing 300-350 g.

INTERVENTIONS

The rats were implanted with a femoral catheter and subcutaneous electrodes for electrocardiogram recording and were randomly assigned to receive morphine (5 mg/kg), naloxone (5 mg and 10 mg/kg), or normal saline (control) (n = 7 in each). Fifteen minutes after intraperitoneal injection of the drug, each rat was exposed to hypoxic gas (5% oxygen, 95% N2) for 70 mins. Hypoxic survival time was measured. Mean arterial pressure (MAP), arterial pH, Paco2, Pao2, and base excess were measured before injection (baseline), 14 mins after injection (H0), and 6 mins (H1), 33 mins (H2), and 48 mins (H3) after exposure to hypoxia.

MEASUREMENTS AND MAIN RESULTS

Hypoxic survival was similar between the naloxone 5 mg/kg and control groups (p = .183), significantly lower in the naloxone 10 mg/kg group (p < .01), and significantly higher in the morphine 5 mg/kg group (p < .05) compared with controls. MAP significantly decreased in all groups. However, at H2-H3, MAP was better preserved in both naloxone groups and was lower in the morphine group compared with controls. Paco2 was maintained higher at H0-H3 in the morphine group and lower at H2-H3 in both naloxone groups compared with controls.

CONCLUSION

During acute hypoxia, naloxone preserves arterial blood pressure and attenuates hypoxic ventilatory depression by antagonizing endogenous opiates, but it does not improve hypoxic survival. In contrast, morphine, which enhances the action of endogenous opiates, does improve hypoxic survival. The acute hypoxic tolerance of morphine may be partly attributable to a depression of oxygen consumption, increased cerebral blood flow secondary to high Paco2, and protective actions mediated by delta-opioid receptors.

Early exposure to chronic variable stress facilitates the occurrence of anhedonia and enhanced emotional reactions to novel stressors: reversal by naltrexone pretreatment

The present research studied the influence of an early chronic variable stress (CVS) paradigm - an animal model of depression - on behavioral responses to subsequent environmental challenges suggested to model anhedonia and emotional reactions such as anxiety and fear. In order to explore a potential involvement of an endogenous opiate mechanism - presumably activated during CVS exposure - in the development of such behavioral reactions, in all experiments rats were administered naltrexone (NAL, 2 mg/kg, i.p.) or vehicle (VH) prior to each daily stressor of the CVS procedure. Animals were exposed to CVS and 1 week later tested for sucrose preference (1%) in a free choice paradigm after the presentation or not of a 90-min restraint period. Only CVS treated animals that were later exposed to restraint showed a reduction of sucrose preference, this reduction was absent when CVS rats were pretreated previously with NAL. Moreover, CVS rats were one week later tested on the elevated plus maze (EPM) and in their conditioned and unconditioned freezing response to a single shock session. Early chronic stress resulted in an anxiogenic behavior in the EPM and in an enhanced conditioned and unconditioned freezing which were all abolished by NAL pretreatment. These behavioral findings suggest that the potential activation of an endogenous opiate mechanism during CVS participates in the development of anhedonia and exaggerated emotional reactions in response to subsequent stressful experiences.

Anabolic androgenic steroids affects alcohol intake, defensive behaviors and brain opioid peptides in the rat

The present study investigated whether a relationship exists between nandrolone decanoate and voluntary ethanol intake in laboratory rats. Animals were subjected to daily subcutaneous injections with nandrolone decanoate (15 mg/kg) during 2 weeks. One group of animals was tested for voluntary alcohol intake 1 week after the end of the 2-week treatment period and another group received alcohol 3 weeks after the treatment. In addition, assessment of defensive behaviors and immunoreactivity (ir) levels of the brain opioid peptides dynorphin B and Met-enkephalin-Arg-Phe (MEAP) were performed. The nandrolone decanoate-treated animals were significantly more aggressive and showed lower fleeing and freeezing reaction than the oil-treated controls. Treatment with nandrolone decanoate enhanced voluntary alcohol intake, regardless if it was presented 1 or 3 weeks after end of the treatment period. These animals had a decreased activity of dynorphin B-ir in the nucleus accumbens, decreased levels of MEAP-ir in the periaqueductal gray (PAG) and higher levels of MEAP-ir in the hypothalamus compared to controls. In line with previous studies, this suggests that the altered dynorphin B-ir activity may promote the rewarding effects of ethanol and thereby increasing alcohol intake, whereas MEAP-ir may be associated with the ability to control the aggressive reaction. Abuse of nandrolone decanoate may thus constitute a risk factor for increased alcohol consumption and defensive aggression. In human, this constellation of behavioral symptoms is closely related to acts of crimes and violence and is often observed among those abusing anabolic androgenic steroids.

Basal levels and alcohol-induced changes in nociceptin/orphanin FQ, dynorphin, and enkephalin levels in C57BL/6J mice

In order to investigate the involvement of the opioid and nociceptin/orphanin FQ (N/OFQ) system in alcohol drinking behaviour, N/OFQ and the opioid peptides dynorphin B (DYNB) and Met-enkephalin-Arg(6) Phe(7) (MEAP) were examined in the alcohol-preferring C57BL/6J mice. Basal peptide levels were compared in the brain and the pituitary gland with basal levels in the alcohol-avoiding DBA/2J mice. Furthermore, the effects of chronic alcohol self-administration on peptides were studied in the C57BL/6J mice. Compared to the DBA/2J mice, C57BL/6J mice had low immunoreactive (ir) levels of DYNB and MEAP in the nucleus accumbens, the hippocampus, and the substantia nigra, low ir-DYNB levels in the striatum and low ir-MEAP levels in the frontal cortex. Higher ir-DYNB levels in the pituitary gland and in the periaqueductal gray (PAG) and higher ir-N/OFQ levels in the frontal cortex and in the hippocampus were detected in C57BL/6J mice compared to the DBA/2J mice. After 4 weeks of voluntary alcohol consumption, only minor changes in steady-state peptide levels were identified. However, 5 days after the alcohol-drinking period, lower levels of all peptides were detected in the ventral tegmental area and ir-DYNB levels were also lower in the amygdala and in the substantia nigra. Twenty-one days after cessation of alcohol self-administration, the opioid peptides in alcohol-consuming C57BL/6J mice were lower in the PAG, the N/OFQ was lower in the frontal cortex and DYNB was higher in the amygdala and substantia nigra as compared to control C57BL/6J mice. This study demonstrates strain differences between C57BL/6J mice and DBA/2J mice that could contribute to divergent drug-taking behaviour, and it also demonstrates time- and structure-specific changes in neuropeptide levels after alcohol self-administration in the C57BL/6J mice.

The nociceptin/orphanin FQ receptor antagonist, [Nphe1]NC(1-13)NH2, potentiates morphine analgesia

Nociceptin/orphanin FQ (NC) and its receptor (OP4) represent a novel peptide/receptor system which has been implicated in the regulation of various central functions, including pain. The aim of the present study was to explore the involvement of the endogenous NC/OP4 system in the modulation of opioid analgesia using the selective OP4 receptor antagonist [Nphe1]NC(1-13)NH2. Experiments were performed in mice exposed to acute as well as chronic treatment with morphine. [Nphe1]NC(1-13)NH2, injected i.c.v. at 30 nmol, strongly potentiated the analgesic effect of supraspinal morphine (1 nmol, i.c.v.) while it only slightly increased the antinociceptive activity of morphine given systemically (5 mg/kg, s.c.). [Nphe1]NC(1-13)NH, (30 nmol, i.c.v.) also potentiated morphine analgesia in mice made tolerant to the opiate (30 mg/kg/day for 4 days). These findings implicate the endogenous NC signaling as a modulator of morphine analgesia and tolerance.

Effects of repeated nicotine administration and footshock stress on rat mesoprefrontal dopamine systems: Evidence for opioid mechanisms

We have examined the effects of nicotine pre-treatment on mesoprefrontal dopamine (DA) function in the presence and absence of acute stress, and the involvement of endogenous opiate peptide systems (EOPS). Acute electrical footshock stress preferentially increases DA utilization in medial prefrontal cortex (mPFC) compared to nucleus accumbens (NAS) and striatal terminal fields, and this is correlated with profound locomotor immobility. Our recent studies have demonstrated that repeated, but not acute, nicotine pre-treatment significantly reduced mPFC DA utilization and footshock stress-induced immobility responses. There is increasing evidence that the biochemical and behavioral effects of nicotine are mediated by EOPS, and we hypothesized that the stress-reducing effects of repeated nicotine administration in these studies were mediated by EOPS. Accordingly, rats pre-treated subcutaneously with repeated nicotine were given a single dose of the opiate receptor antagonist naloxone (0.1-10.0 mg/kg, i.p.) or saline as a co-treatment with nicotine or saline 10 min prior to acute footshock stress. Naloxone had no effects on non-stressed or acute footshock stress-induced mPFC DA utilization, but dose-dependently antagonized repeated nicotine's attenuation of stress-induced mesoprefrontal DA utilization and immobility responses. Furthermore, naloxone dose-dependently blocked repeated nicotine's augmentation of accumbal DA utilization. These results suggest that EOPS may be involved in mediating repeated nicotine administration effects on mesoprefrontal dopaminergic and immobility responses to acute footshock stress.

Upregulation of an opioid-mediated antinociceptive mechanism in transgenic mice over-expressing substance P in the spinal cord

In transgenic mice expressing ectopic substance P fibres in the spinal white matter, a normally innocuous mechanical stimulus induces hyperalgesia and allodynia which are reversed by substance P and N-methyl-D-aspartate receptor antagonists. This period of enhanced excitation is followed by a rebound overshoot in these animals. As previous evidence indicates opioid mechanisms in a similar rebound in normal animals, the present study was done to determine the effects of systemic administration of morphine and the opiate receptor antagonist, naloxone, on the stimulus-induced responses in the tail withdrawal reflex. Once baseline reaction times had been taken, different combinations of saline, naloxone and morphine were administered intraperitoneally to transgenic and control mice of either sex. A mechanical conditioning stimulus of 450g was then applied to the tip of the tail for 2s. This stimulus was innocuous in control mice given saline or naloxone, but provoked a nociceptive response in transgenic mice given these compounds. In control and transgenic mice, following morphine administration there was an antinociceptive effect. In control mice the subsequent mechanical stimulus had no effect. However, in transgenic mice the mechanical stimulus produced a further antinociception. Naloxone blocked the effect of morphine and the subsequent conditioning stimulus in both control and transgenic mice. The results indicate that while morphine is equally effective on the withdrawal reflex in both types of animal, in the transgenic mice morphine reveals an intrinsic, naloxone-sensitive antinociceptive mechanism. The data are interpreted to suggest that over-expression of substance P or some other factor in the spinal cord of transgenic mice is associated with the up-regulation or facilitation of an opiate-mediated intrinsic antinociceptive mechanism. This is a novel observation because the genetic manipulation in this transgenic mouse results in a transient over-expression of nerve growth factor during development that leads to the formation of ectopic primary afferent fibres in the spinal cord containing substance P. These fibres persist indefinitely after the nerve growth factor levels return to normal. Opioid mechanisms, which are likely of dorsal horn origin, do not fall under the direct influence of nerve growth factor mechanisms and therefore the intriguing possibility is raised that opioid mechanisms in the spinal cord are regulated at least in part by substance P-related mechanisms.

Antinociceptive role of galanin in periaqueductal grey of rats with experimentally induced mononeuropathy

The present study was performed in rats with experimentally induced mononeuropathy after left common sciatic nerve ligation. The hindpaw withdrawal latencies to thermal and mechanical stimulation increased significantly after intra-periaqueductal grey injection of 2 or 3nmol, but not 1nmol of galanin in rats with mononeuropathy. Intraperitoneal administration of 4.5mg/kg morphine induced significant increases in hindpaw withdrawal latencies to both noxious stimulation, which were attenuated by following intra-periaqueductal grey injection of 2nmol of the galanin antagonist galantide. Furthermore, the antinociceptive effect induced by intra-periaqueductal grey injection of 26.6nmol of morphine was attenuated significantly by following intra-periaqueductal gray administration of 2nmol of galantide. The results demonstrated that in periaqueductal grey galanin plays an antinociceptive role in rats with mononeuropathy and galanin is involved in the mechanisms of opioid-induced antinociception.

Extremely low frequency magnetic fields can either increase or decrease analgaesia in the land snail depending on field and light conditions

Results of prior investigations with opioid peptide mediated antinociception or analgaesia have suggested that these extremely low frequency (ELF) magnetic field effects are described by a resonance mechanism rather than mechanisms based on either induced currents or magnetite. Here we show that ELF magnetic fields (141-414 microT peak) can, in a manner consistent with the predictions of Lednev's parametric resonance model (PRM) for the calcium ion, either (i) reduce, (ii) have no effect on, or (iii) increase endogenous opioid mediated analgaesia in the land snail, Cepaea nemoralis. When the magnetic fields were set to parameters for the predictions of the PRM for the potassium ion, opioid-peptide mediated analgaesia increased and there was evidence of antagonism by the K(+) channel blocker, glibenclamide. Furthermore, these effects were dependent on the presence of light; the effects were absent in the absence of light. These observed increases and decreases in opioid analgaesia are largely consistent with the predictions of Lednev's PRM.

Paraventricular nucleus injections of naloxone methiodide inhibit NPY's effects on energy substrate utilization

Microinjection of neuropeptide Y (NPY) into the paraventricular nucleus (PVN) of the hypothalamus stimulates eating and increases respiratory quotient. In contrast, administration of opioid receptor antagonists reduces food intake and suppresses NPY-induced feeding. The present study examined whether naloxone methiodide, an opioid antagonist, would suppress the potentiation of NPY on energy substrate utilization, when injected into the PVN. Naloxone methiodide was injected at doses of 0.1 and 1.0 g, 10 min prior to NPY treatment. NPY was administered immediately prior to the start of the nocturnal period and RQ was determined using an open-circuit calorimeter. Doses of 50 and 100 pmol NPY alone evoked reliable increases in RQ within 30min of treatment. Following naloxone methiodide pretreatment, the stimulatory action of NPY was significantly attenuated. These data indicate that opioid receptors in the PVN influence the action of NPY on energy substrate utilization.

ATP-gated K(+) channel openers enhance opioid antinociception: indirect evidence for the release of endogenous opioid peptides

The ATP-gated K(+) channel openers - diazoxide, levcromakalim and morphine - enhance K(+) efflux by opening ATP-gated K(+) channels, thereby inducing cell hyperpolarization. Hyperpolarization decreases intracellular Ca(2+) levels, which leads to a decrease in neurotransmitter release contributing to the antinociceptive effects of the drugs. Previous findings implicate the release of endogenous opioids as the mediator of the antinociceptive effects of ATP-gated K(+) channel openers. Diazoxide and levcromakalim, administered intracerebroventricularly (i.c.v.), produced dose-dependent antinociception as determined by the tail-flick method ¿ED(50) 44 microg/mouse [95% confidence limits (CLs) from 28 to 68 microg/mouse] for diazoxide¿. Glyburide (10 microg/mouse), an ATP-gated K(+) channel antagonist, attenuated the effects of diazoxide, levcromakalim and morphine. Diazoxide- and levcromakalim-induced antinociception were both antagonized by CTOP (D-Phe-Cys-Tyr-D-Trp-Orn-Thr-Pen-Thr amide), a mu-opioid receptor selective antagonist, and ICI 174,864 (N, N-diallyl-Tyr-Aib-Aib-Phe-Leu), a delta-opioid receptor antagonist, but were differentially attenuated by the kappa-opioid receptor antagonist, nor-Binaltorphimine. Combinations of inactive doses of the K(+) channel openers and opioid receptor agonists produced significant antinociceptive enhancement. Diazoxide (2 microg/mouse) shifted morphine's dose-response curve 47-fold, while levcromakalim (0.1 microg/mouse) shifted the curve 27-fold. The dose-response curve of kappa-opioid receptor agonist U50,488H (trans-(+/-)-3, 4 Dichloro-N-[2-(1-pyrrolidinyl)-cyclohexyl] benzeneacetamide methane sulfonate) was shifted 106-fold by diazoxide in a parallel manner, while levcromakalim administration increased the potency of U50,488H by 15-fold. Diazoxide shifted the dose-response curve of the delta-opioid receptor agonist, DPDPE [(D-Pen(2,5))-enkephalin], leftward in a non-parallel manner, while DPDPE was 6-fold more potent when combined with levcromakalim. We hypothesize that endogenous opioids mediate ATP-gated K(+) channel opener-induced antinociception and enhancement of opioids.

Synergistic interactions of endogenous opioids and cannabinoid systems

Cannabinoids and opioids are distinct drug classes historically used in combination to treat pain. Delta(9)-THC, an active constituent in marijuana, releases endogenous dynorphin A and leucine enkephalin in the production of analgesia. The endocannabinoid, anandamide (AEA), fails to release dynorphin A. The synthetic cannabinoid, CP55,940, releases dynorphin B. Neither AEA nor CP55,940 enhances morphine analgesia. The CB1 antagonist, SR141716A, differentially blocks Delta(9)-THC versus AEA. Tolerance to Delta(9)-THC, but not AEA, involves a decrease in the release of dynorphin A. Our preclinical studies indicate that Delta(9)-THC and morphine can be useful in low dose combination as an analgesic. Such is not observed with AEA or CP55,940. We hypothesize the existence of a new CB receptor differentially linked to endogenous opioid systems based upon data showing the stereoselectivity of endogenous opioid release. Such a receptor, due to the release of endogenous opioids, may have significant impact upon the clinical development of cannabinoid/opioid combinations for the treatment of a variety of types of pain in humans.

Zinc and water intake in rats: investigation of adrenergic and opiatergic central mechanisms

We have demonstrated that central administration of zinc in minute amounts induces a significant antidipsogenic action in dehydrated rats as well as in rats under central cholinergic and angiotensinergic stimulation. Here we show that acute third ventricle injections of zinc also block water intake induced by central ss-adrenergic stimulation in Wistar rats (190-250 g). Central inhibition of opioid pathways by naloxone reverses the zinc-induced antidipsogenic effect in dehydrated rats. After 120 min, rats receiving third ventricle injections of isoproterenol (160 nmol/rat) exhibited a significant increase in water intake (5.78 +/- 0.54 ml/100 g body weight) compared to saline-treated controls (0.15 +/- 0.07 ml/100 g body weight). Pretreatment with zinc (3.0, 30.0 and 300.0 pmol/rat, 45 min before isoproterenol injection) blocked water intake in a dose-dependent way. At the highest dose employed a complete blockade was demonstrable (0.54 +/- 0.2 ml/100 g body weight). After 120 min, control (NaAc-treated) dehydrated rats, as expected, exhibited a high water intake (7.36 +/- 0.39 ml/100 g body weight). Central administration of zinc blocked this response (2.5 +/- 0.77 ml/100 g body weight). Naloxone pretreatment (82.5 nmol/rat, 30 min before zinc administration) reverted the water intake to the high levels observed in zinc-free dehydrated animals (7.04 +/- 0.56 ml/100 g body weight). These data indicate that zinc is able to block water intake induced by central ss-adrenergic stimulation and that zinc-induced blockade of water intake in dehydrated rats may be, at least in part, due to stimulation of central opioid peptides.

Effects of three peptidase inhibitors, amastatin, captopril and phosphoramidon, on the hydrolysis of [Met5]-enkephalin-Arg6-Phe7 and other opioid peptides

The contents of [Met5]-enkephalin-Arg6-Phe7 (met-enk-RF) and its six hydrolysis products: Y, YG, YGG, YGGF, YGGFM, and YGGFMR were estimated after incubating met-enk-RF with either a guinea-pig ileal or striatal membrane fraction for various times at 37 degrees C. After 45 min incubation with either ileal or striatal membranes, met-enk-RF was completely hydrolyzed, yielding Y as the major product. Incubation with either membrane preparation for 60 min in the presence of the aminopeptidase inhibitor amastatin hydrolyzed 90 or 92% of met-enk-RF, respectively, with YGG being the major product. If the dipeptidyl carboxypeptidase I inhibitor captopril is also included in the incubation, met-enk-RF hydrolysis decreases by about half for both membranes, with YGG remaining the major product. Inclusion of three peptidase inhibitors, amastatin, captopril, and phosphoramidon (inhibition of endopeptidase-24.11) further reduced met-enk-hydrolysis, with 87% or more remaining intact. This shows that met-enk-RF was mainly hydrolyzed by three enzymes, amastatin-sensitive aminopeptidase, captopril-sensitive dipeptidyl carboxypeptidase I and phosphoramidon-sensitive endopeptidase-24.11, in both ileal and striatal membranes. Additionally, estimations of [Leu5]-enkephalin (leu-enk), alpha- and beta-neoendorphins (alpha- and beta-neoends), and dynorphin B (dyn B) contents after incubating the individual peptides with striatal membrane for 60 min in the presence of the three peptidase inhibitors showed that 98, 32, 5, and 23%, respectively, remained intact. Our previous studies together with the data obtained here show that one group of endogenous opioid peptides: met-enk, leu-enk, met-enk-RF, met-enk-RGL, and dyn A-(1-8) are largely or almost exclusively hydrolyzed by the three enzymes, amastatin-sensitive aminopeptidase, captopril-sensitive dipeptidyl carboxypeptidase I, and phosphoramidon-sensitive endopeptidase-24.11, and indicate that an unidentified fourth enzyme(s) is involved in the hydrolysis of another group of peptides: alpha-neoend, beta-neoend, and dyn B.

[The endogenous opioid system tonically activates the locomotor neurons in the mollusk Lymnaea stagnalis]

Keeping specimens of the pond snail Lymnaea stagnalis in the aqueous solution of the opiate antagonist naloxone (0.1 mM) or naltrexone (0.1 mM) resulted in a suppression of motor activity, and, particularly, in a decrease in the rate of ciliary locomotion. The activity of ciliomotor serotonergic neurons of the Pedal A cluster was intracellularly recorded in preparations of isolated ganglia. Naloxone (0.1 mM) suppressed, whereas the opiate agonists morphine (0.1 mM) and DAGO (0.05 mM) accelerated the synaptically driven firing of the Pedal A neurons both in preparations of the entire CNS and isolated pedal ganglia. The obtained results testify to the occurrence of tonic activatory influence of the endogenous opioids on the ciliomotor pedal neurons of snails and suggest that this influence is, at least partially, mediated by their synaptic input.

Effects of endotoxin on neurally-mediated gastric acid secretion in the rat

The effects of a peripheral administration of E. coli endotoxin on neurally-mediated gastric acid secretion and the role of endogenous opioids or PAF receptors in endotoxin effects have been evaluated in the continuously perfused stomach of the anaesthetized rat. Gastric acid secretion stimulated by distension (20 cm H2O) was reduced dose-dependently by single intravenous bolus injection of endotoxin (0.1-10 microg kg(-1)). Doses of 5 microg kg(-1) induced a peak reduction of distension-stimulated acid output and significantly reduced the secretory response induced by an intravenous bolus of 2-deoxy-D-glucose (150 mg kg(-1)). This dose of endotoxin did not significantly modify mean systemic arterial blood pressure throughout the experimental period. Pretreatment with the opioid receptor antagonist naloxone (1 mg kg(-1) , i.v.) or the platelet-activating factor (PAF) receptor antagonist WEB 2086 (2 mg kg(-1), i.v.) did not reverse the inhibitory effects of endotoxin (5 microg kg(-1) , i.v.) on acid secretion stimulated by both distension and 2-deoxy-D-glucose. These findings suggest that endotoxin-induced acute inhibition of neurally-mediated acid responses, stimulated by gastric distension or administration of 2-deoxy-D-glucose, do not involve the activation of endogenous opioids or PAF receptors.

Sucrose ingestion causes opioid analgesia

The intake of saccharin solutions for relatively long periods of time causes analgesia in rats, as measured in the hot-plate test, an experimental procedure involving supraspinal components. In order to investigate the effects of sweet substance intake on pain modulation using a different model, male albino Wistar rats weighing 180-200 g received either tap water or sucrose solutions (250 g/l) for 1 day or 14 days as their only source of liquid. Each rat consumed an average of 15.6 g sucrose/day. Their tail withdrawal latencies in the tail-flick test (probably a spinal reflex) were measured immediately before and after this treatment. An analgesia index was calculated from the withdrawal latencies before and after treatment. The indexes (mean +/- SEM, N = 12) for the groups receiving tap water for 1 day or 14 days, and sucrose solution for 1 day or 14 days were 0.09 +/- 0.04, 0.10 +/- 0.05, 0.15 +/- 0.08 and 0.49 +/- 0.07, respectively. One-way ANOVA indicated a significant difference (F(3, 47) = 9.521, P < 0.001) and the Tukey multiple comparison test (P < 0.05) showed that the analgesia index of the 14-day sucrose-treated animals differed from all other groups. Naloxone-treated rats (N = 7) receiving sucrose exhibited an analgesia index of 0.20 +/- 0.10 while rats receiving only sucrose (N = 7) had an index of 0.68 +/- 0.11 (t = 0.254, 10 degrees of freedom, P < 0.03). This result indicates that the analgesic effect of sucrose depends on the time during which the solution is consumed and extends the analgesic effects of sweet substance intake, such as saccharin, to a model other than the hot-plate test, with similar results. Endogenous opioids may be involved in the central regulation of the sweet substance-produced analgesia.

A comparison between microwave irradiation and decapitation: basal levels of dynorphin and enkephalin and the effect of chronic morphine treatment on dynorphin peptides

Opioid peptides were analysed in tissue extracts of various brain structures and the pituitary gland from rats sacrificed by microwave irradiation, and compared with peptide levels in tissue extracts from decapitated rats. Dynorphin A, dynorphin B and Leu-enkephalinArg6, derived from prodynorphin, and Met-enkephalinArg6Phe7 from proenkephalin, were measured. Basal immunoreactive levels of dynorphin A and B were consistently higher in extracts from microwave-irradiated rats, whereas in these extracts immunoreactive levels of Leu-enkephalinArg6, an endogenous metabolite of dynorphin peptides, were either lower than, the same as or higher than in decapitated rats. Immunoreactive levels of Met-enkephalinArg6Phe7 were higher in microwave-irradiated rats. Effects of morphine treatment on prodynorphin peptide levels were evaluated and compared with previous findings in decapitated rats. Dynorphin immunoreactive levels were higher in the nucleus accumbens and striatum of morphine-tolerant rats than in corresponding areas in saline-treated rats. These results indicate tissue-specific metabolism of prodynorphin peptides and show that metabolism of opioid peptides occurs during the dissection procedure after decapitation of the rat even though precautions are taken to minimize degradation.

[The role of endogenous opioid peptides in the mechanisms of the antiarrhythmic effect of adaptation]

A decrease in severity and incidence rate of the epinephrine- or CaCl2-induced arrhythmias was found in the rats adapted to stress. An increase of the beta-endorphin and enkephalin levels was revealed in the brain areas, heart, suprarenal glands and in the blood plasma of such rats. Naloxone eliminated the antiarrhythmic effect of the adaptation, as well as D-kyotorphin. The antiarrhythmic effect seems to result from an increase of the endogenous opioid peptides level.

[A comparison of the frequency of the Straub tail elevation reaction as a measure of the activity of the endogenous opiate system in rats of different strains]

Stress-induced and exploratory activity-related Straub tail elevation was studied as a probable measure of endogenous opiate system activity in rats from catalepsy-susceptible GC strain as well as PM+ and PM- strains bred from Wistar stock for the presence and absence of predisposition to a stereotyped hyperkinesis with pendulum-like movements. All the three strains were characterized by lower incidence of Straub tail elevation than in the control Wistar stock. Moreover, the PM+ strain demonstrated a lower incidence of the studied reaction than PM- the difference between the strains being manifested during exploratory activity but not in immobilization stress.

[The participation of opioids in the antinociceptive effect induced by the stimulation of hypothalamic "pleasure zones" in 20- to 30-day-old rabbits]

The involvement of opioid peptides in the mediation of inhibitory influences of the positive reinforcement system ("reward areas") on the evoked potential (EPs) recorded in the thalamic parafascicular complex (CM-Pf) in response to the nociceptive electrodermal stimulation of the hind paw in 20-30 day rabbits has been studied. Electrical stimulation of "reward areas" identified in the preliminary behavioural experiments inhibited the EPs. The systemic injection of naloxone potentiated the antinociceptive effect of "reward areas" stimulation in 75% of cases under the incomplete inhibition of EPs (the decrease of EPs amplitude) but decreased its inhibitory effect in 87% of cases under the complete inhibition of EPs. Naloxone did not change the inhibitory effect of "reward areas" stimulation suggesting to the relationship of analgesic "reward areas" function with nonopioid mechanisms too. On the basis of the comparison of the present data and the ones obtained before it can be inferred that opioid mechanism in realization of antinociceptive influence of "reward areas" stimulation on EPs in CM-Pf is more important for 20-30 day rabbits compared with 41-60 day ones. The correlation of the phenomenon under investigation with the formation of neurotransmitter systems has been discussed.

Spectroscopic features of native and bleached opio-melanins

Opioid peptides can be converted by tyrosinase into melanin-like compounds, in which the peptide moiety is retained. Such pigments, named opio-melanins, exhibit a characteristic absorption spectrum with a maximum at about 330 nm and a different solubility behaviour with respect to dopa-melanin, being completely soluble in hydrophylic solvents at neutral and basic pH. Opio-melanins precipitate in aqueous solutions below pH 5.0, and show apparent pKa values of 3.1, 3.6 and 4.4 for Tyr-Gly-melanin, Tyr-Gly-Gly-melanin and leuenk-melanin, respectively. The concomitant oxidation of dopa and opioid peptides by tyrosinase produces mixed polymers, showing the distinctive absorption peak at 330 nm. In the dark, in the pH range 5.5-7.0 the pigments are completely stable, whereas H2O2 addition provokes a slight degradation. At higher pH values or under simulated solar illumination with or without hydrogen peroxide, bleaching occurs more rapidly than in dopa-melanin. Upon photoirradiation the absorption spectrum of opio-melanins undergoes a marked variation, the peak at 330 nm being replaced by a broad shoulder in the range 280-350 nm. The absorption spectra of native and bleached pigments and the extent of opio-melanins degradation by bleaching agents, confirm the hypothesis that the different initial structure of the precursors accounts for a final diverse polymeric architecture of these pigments with respect to dopa-melanin.

Possible evidence of angiotensin II and endogenous opioid modulation of novelty-induced rearing in the rat

Rats treated with captopril (CAP, 10mg/kg i.p.) naltrexone (Nalx 0.1 mg/kg i.p) and saralasine (100 micrograms/kg i.p) displayed significantly less novelty-induced rearing (NIR) compared to saline injected animals. Naltrexone potentiated the inhibitory effect of CAP on NIR. Pretreatment with NALX did not alter SARA-induced decrease in NIR. It is suggested that the endogenous release of AII and/or opioids somehow modulate basal rearing activity.