Nor-binaltorphimine Dihydrochloride Research Articles

100 Hz Electroacupuncture Alleviated Chronic Itch and GRPR Expression Through Activation of Kappa Opioid Receptors in Spinal Dorsal Horn.

BackgroundClinical studies have shown that electroacupuncture (EA) alleviates chronic itch. Gastrin-releasing peptide receptor (GRPR) and dynorphin (DYN) in the spinal dorsal horn positively or negatively regulate itch, respectively. However, which frequency of EA is effective on relieving chronic itch and reducing the expression of GRPR, whether DYN-A in the spinal cord is involved in the underlying mechanism of the antipruritus effect of EA remains unknown.MethodsThe mixture of acetone and diethyl ether (1:1) [designated as AEW (acetone/diethyl ether and water) treatment] was used to induce the dry skin model of chronic itch. EA was applied to Quchi (LI11) and Hegu (LI4). Western blot was used to detect the expression of GRPR and DYN-A. Immunofluorescence was used to detect the expression of DYN-A.ResultsThe AEW administration induced remarkable spontaneous scratching, enhanced the expression of GRPR, and reduced the expression of DYN-A. Compared with the sham EA, 2 Hz EA, or 15 Hz EA group, 100 Hz EA was the most effective frequency for relieving chronic itch, reducing the expression of GRPR, and increasing the expression of DYN-A in the cervical dorsal horn. Furthermore, intraperitoneal injection of kappa opioid receptors (KORs) antagonist nor-Binaltorphimine dihydrochloride (nor-BNI) significantly reversed the effect of 100 Hz EA on the inhibition of both itching behavior and GRPR expression.ConclusionEA at 100 Hz is the most effective frequency that inhibits chronic itch and GRPR expression through activation of KORs in the spinal dorsal horn, which can effectively guide the clinical treatment and improve the antipruritic effect of acupuncture.

The Opioid Interactions of the Antipsychotic Medications Risperidone and Amisulpride in Mice and Their Potential Use in the Treatment of Other Non-Psychotic Medical Conditions.

Pain is defined as an unpleasant sensory and emotional experience associated with actual or potential tissue damage. The opioid epidemic in the USA has highlighted the need for alternative treatments for pain. Following reports on the opioid interactions of various antipsychotic medications, we speculated that the involvement of the opioid system in some of the antipsychotics' mechanism of action may suggest their potential use in the treatment of pain. Risperidone is a neuroleptic with a potent dopamine D2 and serotonin 5-HT2 receptor-blocking activity as well as a high affinity for adrenergic and histamine H1 receptors. Amisulpride is a neuroleptic which selectively blocks dopamine D2 and D3 receptors. Both had a potent antinociceptive effect on ICR mice tested with a tail flick assay. That effect on both medications was antagonized by naloxone, indicating that at least some of the antinociceptive effects were mediated by an opioid mechanism of action. Further investigation found that β-Funaltrexamine hydrochloride (β-FNA), naloxonazine, and nor-Binaltorphimine dihydrochloride (nor-BNI) reversed the antinociceptive effect of both risperidone and amisulpride. Naltrindole at a dose that blocked [D-Pen2,D-Pen5]enkephalin (DPDPE, δ analgesia) blocked notably amisplride effect and only partially reversed that of risperidone. Risperidone induced an antinociceptive effect, implying involvement of μ and κ-opioid and δ-opioid mechanisms. Amisulpride-induced antinociception was mediated through selective involvement of all three opioid receptor subtypes. These findings emphasize the need for clinical trials to assess the possibility of extending the spectrum of medications available for the treatment of pain.

Low-Threshold Mechanosensitive VGLUT3-Lineage Sensory Neurons Mediate Spinal Inhibition of Itch by Touch.

Innocuous mechanical stimuli, such as rubbing or stroking the skin, relieve itch through the activation of low-threshold mechanoreceptors. However, the mechanisms behind this inhibition remain unknown. We presently investigated whether stroking the skin reduces the responses of superficial dorsal horn neurons to pruritogens in male C57BL/6J mice. Single-unit recordings revealed that neuronal responses to chloroquine were enhanced during skin stroking, and this was followed by suppression of firing below baseline levels after the termination of stroking. Most of these neurons additionally responded to capsaicin. Stroking did not suppress neuronal responses to capsaicin, indicating state-dependent inhibition. Vesicular glutamate transporter 3 (VGLUT3)-lineage sensory nerves compose a subset of low-threshold mechanoreceptors. Stroking-related inhibition of neuronal responses to chloroquine was diminished by optogenetic inhibition of VGLUT3-lineage sensory nerves in male and female Vglut3-cre/NpHR-EYFP mice. Conversely, in male and female Vglut3-cre/ChR2-EYFP mice, optogenetic stimulation of VGLUT3-lineage sensory nerves inhibited firing responses of spinal neurons to pruritogens after the termination of stimulation. This inhibition was nearly abolished by spinal delivery of the κ-opioid receptor antagonist nor-binaltorphimine dihydrochloride, but not the neuropeptide Y receptor Y1 antagonist BMS193885. Optogenetic stimulation of VGLUT3-lineage sensory nerves inhibited pruritogen-evoked scratching without affecting mechanical and thermal pain behaviors. Therefore, VGLUT3-lineage sensory nerves appear to mediate inhibition of itch by tactile stimuli.SIGNIFICANCE STATEMENT Rubbing or stroking the skin is known to relieve itch. We investigated the mechanisms behind touch-evoked inhibition of itch in mice. Stroking the skin reduced the activity of itch-responsive spinal neurons. Optogenetic inhibition of VGLUT3-lineage sensory nerves diminished stroking-evoked inhibition, and optogenetic stimulation of VGLUT3-lineage nerves inhibited pruritogen-evoked firing. Together, our results provide a mechanistic understanding of touch-evoked inhibition of itch.

Discovery of small molecules that normalize the transcriptome and enhance cysteine cathepsin activity in progranulin-deficient microglia

Patients with frontotemporal dementia (FTD) resulting from granulin (GRN) haploinsufficiency have reduced levels of progranulin and exhibit dysregulation in inflammatory and lysosomal networks. Microglia produce high levels of progranulin, and reduction of progranulin in microglia alone is sufficient to recapitulate inflammation, lysosomal dysfunction, and hyperproliferation in a cell-autonomous manner. Therefore, targeting microglial dysfunction caused by progranulin insufficiency represents a potential therapeutic strategy to manage neurodegeneration in FTD. Limitations of current progranulin-enhancing strategies necessitate the discovery of new targets. To identify compounds that can reverse microglial defects in Grn-deficient mouse microglia, we performed a compound screen coupled with high throughput sequencing to assess key transcriptional changes in inflammatory and lysosomal pathways. Positive hits from this initial screen were then further narrowed down based on their ability to rescue cathepsin activity, a critical biochemical readout of lysosomal capacity. The screen identified nor-binaltorphimine dihydrochloride (nor-BNI) and dibutyryl-cAMP, sodium salt (DB-cAMP) as two phenotypic modulators of progranulin deficiency. In addition, nor-BNI and DB-cAMP also rescued cell cycle abnormalities in progranulin-deficient cells. These data highlight the potential of a transcription-based platform for drug screening, and advance two novel lead compounds for FTD.

Spexin/NPQ Induces FBJ Osteosarcoma Oncogene (Fos) and Produces Antinociceptive Effect against Inflammatory Pain in the Mouse Model

Spexin/NPQ is a novel highly conserved neuropeptide. It has a widespread expression in the periphery and central nervous system. However, the effects of central spexin on acute inflammatory pain are still unknown. This study explored the mechanisms and effects of supraspinal spexin on inflammatory pain. The results from the mouse formalin test show that i.c.v. administration of spexin decreased licking/biting time during the late and early phases. The nonamidated spexin had no effect on pain response. The antinociception of spexin was blocked by galanin receptor 3 antagonist SNAP 37889. The Galr3 and Adcy4 mRNA levels in the brain were increased after injection with spexin. The antinociceptive effects of spexin were completely reversed by opioid receptor antagonist naloxone and κ-opioid receptor antagonist nor-binaltorphimine dihydrochloride. Spexin up-regulated the dynorphin and κ-opioid receptor gene and protein expression. PCR array assay and real-time PCR analysis show that spexin up-regulated the mRNA level of the FBJ osteosarcoma oncogene (Fos). T-5224, the inhibitor of c FBJ osteosarcoma oncogene (c-Fos)/activator protein 1 (AP-1), blocked the increased mRNA level of Pdyn and Oprk1 induced by spexin. I.C.V. spexin (2.43 mg/kg) increased the number of c-Fos-positive neurons in most subsections of periaqueductal gray. In addition, in the acetic acid-induced writhing test, i.c.v. spexin produced an antinociceptive effect. Our results indicate that spexin might be a novel neuropeptide with an antinociceptive effect against acute inflammatory pain.

Opioid receptors mediate inotropic and depressor effects of apelin in rats with 2K1C-induced chronic renovascular hypertension.

Apelin receptors (APJ) cross-talk with other G-protein-coupled receptors. However, the role of APJ interaction with opioid receptors (OPR) on the cardiovascular effects of apelin in hypertension is not clear. Renovascular hypertension was induced by placing a Plexiglas clip on the left kidney of rats. After 16weeks, F13A (an APJ antagonist), naloxone (a general OPR inhibitor), and nor-binaltorphimine dihydrochloride (nor-BNI; a selective inhibitor of KOR) were given prior to injections of apelin at doses of 40 and 60μg/kg. The arterial systolic/diastolic blood pressure and left ventricular contractility responses were then evaluated. The arterial systolic/diastolic blood pressure in sham and 2K1C rats was 110/71mmHg and 171/124mmHg, respectively. The hypotensive effects of apelin at both doses were inhibited by F13A and naloxone. Nor-BNI completely inhibited the effects of apelin 40 on arterial pressure, and decreased the effects of 60μg/kg. KOR inhibition also prevented the compensation for the decrease in the left ventricle +dp/dt max and -dp/dt max caused by apelin 60. The simultaneous inhibition of OPR and APJ reduced arterial pressure and increased cardiac contractility. Findings showed that the OPR, particularly KOR, mediate the inotropic, lusitropic, and depressor effects of apelin. The interaction of the OPR and APJ augments the inotropic and vasodepressor effects of apelin. This interaction may have potential clinical applications in cardiac failure since opioids are currently used in the treatment of myocardial infarction and stroke, and apelin has been introduced as a potential therapeutic agent in cardiovascular complications.

Mu and kappa opioid receptors of the periaqueductal gray stimulate and inhibit thermogenesis, respectively, during psychological stress in rats.

The periaqueductal gray matter (PAG) is rich in mu and kappa opioid receptors, and this system is involved in thermoregulation, analgesia, and defensive behaviors. No study approached the involvement of the PAG opioids in body temperature (Tb) regulation during psychological stress such as restraint. Because activation of mu and kappa receptors increases and reduces Tb, respectively, we tested the hypothesis that they exert excitatory and inhibitory modulation, respectively, of the restraint-induced fever in rats. To this end, Tb, heat loss index (HLI, inference for peripheral vasoconstriction/vasodilation), and oxygen consumption (inference for thermogenesis) were monitored in unanesthetized rats, restrained or unrestrained, before and after intra-PAG microinjection of the selective mu opioid receptor antagonist (D-Phe-Cys-Tyr-D-Trp-Arg-Thr-Pen-Thr-NH2 cyclic, CTAP; 1 and 10μg/100nL) or the selective kappa opioid receptor antagonist (nor-binaltorphimine dihydrochloride, nor-BNI; 1 and 4μg/100nL) or saline (100nL). CTAP and nor-BNI did not change the Tb or HLI of euthermic animals. During restraint, Tb increased (1.0±0.1°C) in all groups; however, this effect was lower in those animals treated with CTAP and higher in animals treated with nor-BNI. The HLI decreased during restraint and increased after animals were released, but this response was not affected by any treatment. Restraint stress increased oxygen consumption (35.9±3.9% elevation), but this response was diminished by CTAP and overstimulated by nor-BNI. Confirming our hypothesis, the results indicate that the mu and kappa opioid receptors in the PAG of rats play a pyrogenic and antipyretic role, respectively, during fever induced by restraint by affecting the thermogenic but not the heat conservation effector.

The differential effects of low and high doses of apelin through opioid receptors on the blood pressure of rats with renovascular hypertension.

The apelin/APJ system has an important role in the regulation of vascular tone and blood pressure. Opioid receptors (OPRs) are also important cardiovascular regulators and exert many of their effects by modulating the function of other G-protein-coupled receptors. The aim of this study was to analyze the interaction of apelin and the opioid system with respect to vascular responses to apelin in rats with renovascular hypertension (two-kidney, one clip (2K1C)). Homodynamic studies were carried out in 2K1C rats. Naloxone (a nonselective OPR inhibitor) or nor-binaltorphimine dihydrochloride (norBNI, a kappa OPR inhibitor) and signaling pathway inhibitors PTX (a Gi path inhibitor) and chelerythrine (a protein kinase C (PKC) inhibitor) were administered before apelin at 20 and 40 μg kg-1. Apelin at 20 and 40 μg kg-1 decreased the systolic blood pressure by 15% and 20%, respectively (P<0.05). The pressure drop caused by apelin 20 was inhibited by naloxone, norBNI and PTX, but it was not affected by chelerythrine. The pressure drop caused by apelin 40 was augmented by naloxone and chelerythrine, and it was not affected by norBNI or PTX. The lowering effect of apelin 20 on blood pressure is exerted through OPRs and stimulation of Gi and PKC pathways. However, apelin 40 functions independently of OPRs, Gi and PKC. This dose-dependent differential effect of apelin may have potential clinical applications as opioids are currently used, and apelin has been introduced as a potential therapeutic agent in cardiovascular complications.

κ Opioid receptors in the nucleus accumbens shell mediate escalation of methamphetamine intake.

Given that the κ opioid receptor (KOR) system has been implicated in psychostimulant abuse, we evaluated whether the selective KOR antagonist norbinaltorphimine dihydrochloride (nor-BNI) would attenuate the escalation of methamphetamine (METH) intake in an extended-access self-administration model. Systemic nor-BNI decreased the escalation of intake of long-access (LgA) but not short-access (ShA) self-administration. nor-BNI also decreased elevated progressive-ratio (PR) breakpoints in rats in the LgA condition and continued to decrease intake after 17 d of abstinence, demonstrating that the effects of a nor-BNI injection are long lasting. Rats with an ShA history showed an increase in prodynorphin immunoreactivity in both the nucleus accumbens (NAc) core and shell, but LgA animals showed a selective increase in the NAc shell. Other cohorts of rats received nor-BNI directly into the NAc shell or core and entered into ShA or LgA. nor-BNI infusion in the NAc shell, but not NAc core, attenuated escalation of intake and PR responding for METH in LgA rats. These data indicate that the development and/or expression of compulsive-like responding for METH under LgA conditions depends on activation of the KOR system in the NAc shell and suggest that the dynorphin-KOR system is a central component of the neuroplasticity associated with negative reinforcement systems that drive the dark side of addiction.

The role of kappa opioid receptors in stress-induced reinstatement of alcohol seeking in rats.

IntroductionStress is related to heavy alcohol use and relapse in alcoholics. Using the reinstatement model, we have shown that corticotropin-releasing factor (CRF) underlies stress-induced relapse to alcohol seeking in laboratory rodents. Little is known about how other neurotransmitters interact with CRF in these effects. Dynorphin and its receptor (kappa opioid receptor, KOR) are involved in stress responses and in alcohol seeking. KOR and CRF receptors (CRF R) may interact in the production of stress-related behaviors but it is not known whether this interaction is involved in reinstatement of alcohol seeking.MethodsMale Long Evans rats were trained to self-administer alcohol (12% w/v). After extinction of responding, we determined the effects of the KOR agonist, U50,488 (2.5, 5 mg/kg) on reinstatement of alcohol seeking, and their sensitivity to the selective KOR antagonist nor-binaltorphimine dihydrochloride (nor-BNI) (10 mg/kg) administered at different times before U50,488. We then examined the effects of nor-BNI on reinstatement induced by the stressor yohimbine (1.25 mg/kg) and on reinstatement induced by exposure to alcohol-associated cues. Finally, we determined whether CRF R1 blockade with antalarmin (10, 20 mg/kg) attenuates alcohol seeking induced by U50,488.ResultsU50,488 reinstated alcohol seeking. Prior treatment with nor-BNI 2, but not 24 h before administration of U50,488 or yohimbine blocked reinstatement induced by these drugs. Cue-induced reinstatement was blocked by nor-BNI administered 2 h prior to testing. Finally, U50,488-induced reinstatement was blocked by antalarmin.ConclusionsThese data further support a role for KOR in reinstatement of alcohol seeking under nonstress and stressful conditions and that KOR and CRF R interact in these effects.

Centrally administered apelin-13 induces depression-like behavior in mice

Apelin, a novel bioactive peptide highly concentrated in the brain, is identified as the endogenous ligand for angiotensin-like 1 receptor (APJ). The present study was designed to investigate the effect of apelin-13 on emotion-related behavior using the forced swimming test (FST) and tail suspension test (TST). Intracerebroventricular (i.c.v.) administration of apelin-13 (0.3, 1 and 3μg/mouse) dose-dependently increased the immobility time in the FST and TST, compared with control group. However, the APJ receptor antagonist apelin-13(F13A) (0.3-10μg/mouse, i.c.v.) had no influence on immobility time in the FST. The increase of immobility time induced by apelin-13 was significantly blocked by apelin-13(F13A), non-selective opioid receptor antagonist naloxone and κ-opioid receptor antagonist nor-binaltorphimine dihydrochloride (nor-BNI), respectively, but not the non-selective corticotrophin-releasing factor (CRF) receptor antagonist α-helical CRF(9-41) in the FST. In order to eliminate the possibility of a false-positive result in the FST or TST, spontaneous activity and motor function were checked. The results demonstrate that apelin-13 alone or antagonists co-administered with apelin-13 did influence spontaneous activity counts. And apelin-13 had no effect on the motor behavior in the rotarod test and wire hanging test. These results indicate that centrally administered apelin-13 elicited depression-like behavior in mice, which was mediated via APJ receptor and κ-opioid receptor, but not CRF receptor.

Perivascular Expression and Potent Vasoconstrictor Effect of Dynorphin A in Cerebral Arteries

BackgroundNumerous literary data indicate that dynorphin A (DYN-A) has a significant impact on cerebral circulation, especially under pathophysiological conditions, but its potential direct influence on the tone of cerebral vessels is obscure. The aim of the present study was threefold: 1) to clarify if DYN-A is present in cerebral vessels, 2) to determine if it exerts any direct effect on cerebrovascular tone, and if so, 3) to analyze the role of κ-opiate receptors in mediating the effect.Methodology/Principal FindingsImmunohistochemical analysis revealed the expression of DYN-A in perivascular nerves of rat pial arteries as well as in both rat and human intraparenchymal vessels of the cerebral cortex. In isolated rat basilar and middle cerebral arteries (BAs and MCAs) DYN-A (1–13) and DYN-A (1–17) but not DYN-A (1–8) or dynorphin B (DYN-B) induced strong vasoconstriction in micromolar concentrations. The maximal effects, compared to a reference contraction induced by 124 mM K+, were 115±6% and 104±10% in BAs and 113±3% and 125±9% in MCAs for 10 µM of DYN-A (1–13) and DYN-A (1–17), respectively. The vasoconstrictor effects of DYN-A (1–13) could be inhibited but not abolished by both the κ-opiate receptor antagonist nor-Binaltorphimine dihydrochloride (NORBI) and blockade of Gi/o-protein mediated signaling by pertussis toxin. Finally, des-Tyr1 DYN-A (2–13), which reportedly fails to activate κ-opiate receptors, induced vasoconstriction of 45±11% in BAs and 50±5% in MCAs at 10 µM, which effects were resistant to NORBI.Conclusion/SignificanceDYN-A is present in rat and human cerebral perivascular nerves and induces sustained contraction of rat cerebral arteries. This vasoconstrictor effect is only partly mediated by κ-opiate receptors and heterotrimeric Gi/o-proteins. To our knowledge our present findings are the first to indicate that DYN-A has a direct cerebral vasoconstrictor effect and that a dynorphin-induced vascular action may be, at least in part, independent of κ-opiate receptors.

Local Kappa Opioid Receptor Activation Decreases Temporomandibular Joint Inflammation

In an attempt to decrease central side effects associated with the use of opioids, some strategies have been developed by targeting peripheral opioid receptors. In this context, kappa receptors are of major interest, since, in contrast to other opioid receptors, their activation is not associated with potent peripheral side effects. We have recently demonstrated that local activation of kappa opioid receptors significantly decreases formalin-induced temporomandibular joint nociception; however, whether it also decreases temporomandibular joint inflammation is not known. To address this issue, we evaluated if a specific kappa opioid receptor agonist, U50,488 (trans-(1S,2S)-3,4-dichloro-N-methyl-N-[2-(1-pyrrolidinyl)cyclohexyl] benzeneacetamide hydrochloride hydrate), administered into the temporomandibular joint decreases formalin-induced plasma extravasation and neutrophil migration. Ipsilateral, but not contralateral, administration of U50,488 into the temporomandibular joint blocked formalin-induced plasma extravasation and neutrophil migration in a dose-dependent manner. This anti-inflammatory effect was reversed by the ipsilateral, but not contralateral, administration of the kappa opioid receptor antagonist nor-BNI (nor-binaltorphimine dihydrochloride). This study demonstrates that local activation of kappa opioid receptors decreases two important parameters of temporomandibular joint inflammation, that is, plasma extravasation and neutrophil migration, in a dose-dependent and antagonist-reversible manner. This anti-inflammatory effect taken together with the potent antinociceptive effect, suggests that drugs targeting peripheral kappa opioid receptors are promising for the treatment of inflammatory temporomandibular joint pain and probably, other articular pain conditions with an inflammatory basis.

Kappa opioid receptors mediate where fear is expressed following extinction training

Six experiments used a within-subjects renewal design to examine the involvement of kappa opioid receptors (KORs) in regulating the expression and recovery of extinguished fear. Rats were trained to fear a tone conditioned stimulus (CS) via pairings with foot shock in a distinctive context (A). This was followed by extinction training of the CS in a second context (B). Finally, all rats were tested for fear to the tone in the extinction context (ABB) and the training (ABA) or a novel (ABC) context. Intracerebroventricular (ICV) infusion of the KOR antagonist nor-binaltorphimine dihydrochloride (nor-BNI) dose-dependently prevented ABA renewal of fear, but had no effect on the expression of ABC renewal, the expression of extinction, or the expression of nonextinguished fear. Conversely, pretest infusion of the KOR agonist U50,488 hydrochloride (U50,488) selectively facilitated the expression of ABA renewal and had no effect on the expression of extinction. Pretest infusion of nor-BNI had no effect on the expression of context-specific latent inhibition. Collectively, these results suggest that KORs gate the expression of fear following extinction training and may comprise a critical neuropeptide component of the circuitry underlying context-dependent expression of fear.

μ-Opioid receptors in the nucleus accumbens shell region mediate the effects of amphetamine on inhibitory control but not impulsive choice.

Acute challenges with psychostimulants such as amphetamine affect impulsive behavior in both animals and humans. With regard to amphetamine, it is important to unravel how this drug affects impulsivity since it is not only a widely abused recreational drug but also regularly prescribed to ameliorate maladaptive impulsivity. Therefore, we studied the effects of amphetamine in two rat models of impulsivity, the five-choice serial reaction time task and the delayed-reward task, providing measures of inhibitory control and impulsive choice, respectively. We focused on the role of opioid receptor activation in amphetamine-induced impulsivity as there is ample evidence indicating an important role for endogenous opioids in several behavioral and neurochemical effects of amphetamine. Results showed that amphetamine-induced inhibitory control deficits were dose-dependently attenuated by the preferential μ-opioid receptor antagonist naloxone, but not by the selective δ-opioid receptor antagonist naltrindole or κ-opioid receptor antagonist nor-BNI (nor-binaltorphimine dihydrochloride). In contrast, naloxone did not affect amphetamine-induced improvements in impulsive decision making. Naloxone also completely prevented inhibitory control deficits induced by GBR 12909 [1-(2-[bis(4-fluorophenyl)methoxy] ethyl)-4-(3-phenylpropyl)piperazine dihydrochloride], a selective dopamine transporter inhibitor. Intracranial infusions of naloxone, the selective μ-opioid receptor antagonist CTAP (H-D-Phe-Cys-Tyr-D-Trp-Arg-Thr-Pen-Thr-NH(2)), morphine, and the selective μ-opioid receptor agonist DAMGO ([D-Ala(2),N-Me-Phe(4),Gly(5)-ol]-enkephalin acetate salt) revealed that μ-opioid receptor activation in the shell rather than the core subregion of the nucleus accumbens (NAc) modulates inhibitory control and subserves the effect of amphetamine thereon. Together, these results indicate an important role for NAc shell μ-opioid receptors in the regulation of inhibitory control, probably via an interaction between these receptors and the mesolimbic dopamine system.

Role of preoptic opioid receptors in the body temperature reduction during hypoxia

Evidence indicates that endogenous opioids play a role in body temperature (Tb) regulation in mammals but no data exist about the involvement of the specific opioid receptors, mu, kappa and delta, in the reduction of Tb induced by hypoxia. Thus, we investigated the participation of these opioid receptors in the anteroventral preoptic region (AVPO) in hypoxic decrease of Tb. To this end, Tb of unanesthetized Wistar rats was monitored by temperature data loggers before and after intra-AVPO microinjection of the selective kappa-opioid receptor antagonist nor-binaltorphimine dihydrochloride (nor-BNI; 0.1 and 1.0 μg/100 nL/animal), the selective mu-opioid receptor antagonist D-Phe-Cys-Tyr-D-Trp-Arg-Thr-Pen-Thr-NH 2 cyclic (CTAP; 0.1 and 1.0 μg/100 nL/animal), and the selective delta-opioid receptor antagonist Naltrindole (0.06 and 0.6 μg/100 nL/animal) or saline (vehicle, 100 nL/animal), during normoxia and hypoxia (7% inspired O 2). Under normoxia, no effect of opioid antagonists on Tb was observed. Hypoxia induced Tb to reduce in vehicle group, a response that was inhibited by the microinjection intra-AVPO of nor-BNI. In contrast, CTAP and Naltrindole did not change Tb during hypoxia but caused a longer latency for the return of Tb to the normoxic values just after low O 2 exposure. Our results indicate the kappa-opioid receptor in the AVPO is important for the reduction of Tb during hypoxia while the mu and delta receptors are involved in the increase of Tb during normoxia post-hypoxia.

Central inhibition of opioid receptor subtypes and its effect on haemorrhagic hypotension in conscious sheep

To investigate the contribution of cerebral mu-, kappa- and delta-opioid receptors in causing the hypotension, bradycardia and renal hypoperfusion evoked by haemorrhage. Adult conscious ewes were bled continuously from a jugular vein until mean arterial blood pressure (MAP) was reduced to below 50 mmHg. Starting 30 min before and continuing until 60 min after haemorrhage either artificial cerebrospinal fluid (control), d-Phe-Cys-Tyr-d-Trp-Orn-Thr-Pen-Thr-NH(2) (CTOP micro-receptor antagonist), ICI 174,864 (delta-receptor antagonist) or nor-binaltorphimine dihydrochloride (nor-BNI, kappa-receptor antagonist) were infused intracerebroventricularly. In a randomized crossover fashion the effect of antagonizing one central opioid receptor subtype was compared to control experiments in the same animal (n = 6 in all groups). Compared to corresponding controls, nor-BNI and ICI 174,864 significantly increased the haemorrhage volume needed to reduce MAP to below 50 mmHg (+4.7 mL kg(-1), SD 1.8 and +3.1 mL kg(-1), SD 3.0 respectively). In the nor-BNI group this was accompanied by a significantly augmented tachycardia before MAP fell. Both nor-BNI and ICI 174,864 also postponed haemorrhagic bradycardia and prolonged adequate blood flow to the kidney. The infusions did not affect the circulation per se or the recovery after haemorrhage. The micro-opioid receptor blockade had no effect on baseline circulation or the response to haemorrhage. Activation of kappa- and delta-opioid receptors adjacent to the ventricular compartment contributes to initiating haemorrhagic hypotension and bradycardia in conscious sheep. However, other parts of the brain and different receptors are likely to play a role as well.

Sex differences in opioid-mediated pain inhibitory mechanisms during the interphase in the formalin test

Many chronic pain conditions are more prevalent in women than men and both fundamental and clinical research supports the implication of endogenous pain inhibitory mechanisms. The goal of this study was to verify if sex differences on endogenous pain inhibitory mechanisms during the formalin test are opioidergic and modulated by sex hormones. Formalin tests were performed with naloxone hydrochloride, a non-selective opioid antagonist in intact and gonadectomized Sprague–Dawley rats of both sexes. Considering the sexual dimorphisms we found, where naloxone preferentially blocked the interphase in female rats, injections of all the possible combinations of μ- (naltrexone hydrochloride), δ- (naltrindole hydrochloride) and κ-selective antagonists (norbinaltorphimine dihydrochloride) were given to evaluate the contribution of these opioid-receptor subtypes to the inhibitory mechanism during the interphase in intact females. Finally, the systemic administration of naloxone methiodide and intrathecal administration of naloxone hydrochloride in intact females allowed us to verify if the action of endogenous opioids that are liberated during the interphase takes place at the periphery or spinally, respectively. The results show that the interphase was almost completely inhibited by naloxone in females while it produced only a slight blockade in males. These results permitted us to conclude that opioids play a major role in the pain inhibitory mechanism of the interphase in females while a non-opioid mechanism seems to be responsible for this inhibitory pathway in males. Using gonadectomized animals of both sexes, we demonstrated the modulation of the opioidergic system of the interphase by sex hormones. The administration of different combinations of selective antagonists for μ-, κ- and δ-opioid receptors in intact females permitted us to conclude that only the combination of κ- and δ-selective antagonists significantly blocked the interphase. The same result was obtained with the combination of the three antagonists, confirming the results with systemic naloxone hydrochloride. Finally, intrathecal administration permitted us to support that the action of naloxone is primarily at the spinal level, even if a supraspinal action cannot be ruled out. These results are of particular interest in showing sexual dimorphisms in endogenous pain modulation mechanisms during the interphase of the formalin test. A clearer understanding of the difference between male and female endogenous pain inhibitory pathways should lead to a better understanding of the role of endogenous pain modulation deficits in certain chronic pain conditions.

Roles of Opiate in Lower Urinary Tract Dysfunction Associated With Spinal Cord Injury in Rats

It has been reported that the opiate receptor system in the spinal cord is involved in bladder and urethral function. We determined whether U-50488 (trans-3,4-dichloro-N-methyl-N-[2-(1-pyrrolidinyl)-cyclohexyl]-benzeneacetamide), a kappa opioid receptor agonist, could decrease detrusor-sphincter dyssynergia (DSD) and, thus, improve voiding efficiency in conscious, spinal cord injured (SCI) rats. Experiments were done in female Sprague-Dawley rats in which the spinal cord was completely transected at the T6-8 level 4 weeks prior to performing cystometry while conscious and held in a restraining cage. Experiments were also performed in normal spinal cord rats. Saline was infused (0.1 ml per minute) via the cystostomy catheter into the bladder. Voiding efficiency was determined by measuring voided and residual volumes. After performing a control cystometrogram increasing doses of U-50488 (0.01, 0.1, 1 and 10 mg/kg) were administered intravenously at 1-hour intervals. The effects of nor-binaltorphimine dihydrochloride, a kappa opioid receptor antagonist, on U-50488 induced changes in voiding parameters were also examined. A high dose of U-50488 (1 to 10 mg/kg) significantly decreased contraction amplitude and bladder capacity (p <0.01 to 0.05) in normal spinal cord and SCI rats. A low dose of U-50488 (0.01 mg/kg) increased voiding efficiency by 32.7% without decreasing bladder capacity in SCI rats. Nor-binaltorphimine hydroparameters counteracted the effect of U-50488 induced changes. These results suggest that the kappa opioid receptor system is related to DSD caused by spinal cord injury. The kappa opioid receptor agent is believed to have therapeutic potential for treating DSD associated with SCI.

Kappa-opioid receptor selectivity for ischemic neuroprotection with BRL 52537 in rats.

Kappa-opioid receptors (KOR) have been implicated in neuroprotection from ischemic neuronal injury, but less work has been performed with transient focal cerebral ischemia to determine the role of KOR during reperfusion. We tested the effects of a selective and specific KOR agonist, BRL 52537 hydrochloride [(+/-)-1-(3,4-dichlorophenyl)acetyl-2-(1-pyrrolidinyl)methylpiperidine], and the standard KOR antagonist, nor-binaltorphimine dihydrochloride [nor-BNI; 17,17'-(dicyclopropylmethyl)-6,6',7,7'-6,6'-imino-7,7'-binorphinan-3,4',14,14'-tetrol], on functional and histological outcome after transient focal ischemia in the rat. By use of the intraluminal filament technique, halothane-anesthetized adult male Wistar rats were subjected to 2 h of middle cerebral artery occlusion confirmed by laser Doppler flowmetry. In a blinded, randomized fashion, rats were treated with 1). saline (vehicle) 15 min before reperfusion followed by saline at reperfusion for 22 h, 2). saline 15 min before reperfusion followed by BRL 52537 (1 mg x kg(-1) x h(-1)) at reperfusion for 22 h, 3). saline 15 min before reperfusion followed by nor-BNI (1 mg x kg(-1) x h(-1)) at reperfusion for 22 h, or 4) nor-BNI (1 mg/kg) 15 min before reperfusion followed by BRL 52537 (1 mgx kg(-1)x h(-1)) and nor-BNI (1 mg x kg(-1) x h(-1)) at reperfusion for 22 h. Infarct volume (percentage of ipsilateral structure) analyzed at 4 days of reperfusion was significantly attenuated in saline/BRL 52537 rats (n = 8; cortex, 10.2% +/- 4.3%; caudoputamen [CP], 23.8% +/- 6.7%) (mean +/- SEM) compared with saline/saline treatment (n = 8; cortex, 28.6% +/- 4.9%; CP, 53.3% +/- 5.8%). Addition of the specific KOR antagonist nor-BNI to BRL 52537 completely prevented the neuroprotection (n = 7; cortex, 28.6% +/- 5.3%; CP, 40.9% +/- 6.2%) conferred by BRL 52537. BRL 52537 did not produce postischemic hypothermia. These data demonstrate that KORs may provide a therapeutic target during early reperfusion after ischemic stroke. The neuroprotective effect of selective kappa-opioid agonists in transient focal ischemia is via a selective action at the kappa-opioid receptors.