Opioid use disorder (OUD) has become a considerable global public health challenge; however, potential medications for the management of OUD that are effective, safe, and nonaddictive are not available. Accumulating preclinical evidence indicates that antagonists of the dopamine D₃ receptor (D₃R) have effects on addiction in different animal models. We have previously reported that YQA14, a D₃R antagonist, exhibits very high affinity and selectivity for D₃Rs over D₂Rs, and is able to inhibit cocaine- or methamphetamine-induced reinforcement and reinstatement in self-administration tests. In the present study, our results illustrated that YQA14 dose-dependently reduced infusions under the fixed-ratio 2 procedure and lowered the breakpoint under the progressive-ratio procedure in heroin self-administered rats, also attenuated heroin-induced reinstatement of drug-seeking behavior. On the other hand, YQA14 not only reduced morphine-induced expression of conditioned place preference but also facilitated the extinguishing process in mice. Moreover, we elucidated that YQA14 attenuated opioid-induced reward or reinforcement mainly by inhibiting morphine-induced up-regulation of dopaminergic neuron activity in the ventral tegmental area and decreasing dopamine release in the nucleus accumbens with a fiber photometry recording system. These findings suggest that D₃R might play a very important role in opioid addiction, and YQA14 may have pharmacotherapeutic potential in attenuating opioid-induced addictive behaviors dependent on the dopamine system.
Rats ; Mice ; Animals ; Analgesics, Opioid ; Dopamine ; Heroin/pharmacology* ; Dopamine Antagonists/pharmacology* ; Receptors, Dopamine D3/metabolism* ; Morphine/pharmacology* ; Behavior, Addictive/drug therapy* ; Self Administration

Microglia are important cells involved in the regulation of neuropathic pain (NPP) and morphine tolerance. Information on their plasticity and polarity has been elucidated after determining their physiological structure, but there is still much to learn about the role of this type of cell in NPP and morphine tolerance. Microglia mediate multiple functions in health and disease by controlling damage in the central nervous system (CNS) and endogenous immune responses to disease. Microglial activation can result in altered opioid system activity, and NPP is characterized by resistance to morphine. Here we investigate the regulatory mechanisms of microglia and review the potential of microglial inhibitors for modulating NPP and morphine tolerance. Targeted inhibition of glial activation is a clinically promising approach to the treatment of NPP and the prevention of morphine tolerance. Finally, we suggest directions for future research on microglial inhibitors.
Humans ; Calcitonin Gene-Related Peptide/antagonists & inhibitors* ; Drug Tolerance ; Hypoglycemic Agents/pharmacology* ; Microglia/physiology* ; MicroRNAs/physiology* ; Minocycline/pharmacology* ; Morphine/pharmacology* ; Neuralgia/etiology* ; Plant Extracts/pharmacology* ; Signal Transduction/physiology*

OBJECTIVETo study the acting mechanism of anti-morphine conditioned place preference (CPP) between aqueous extract of Corydalis yanhusuo and L-THP and compare their effects.

METHODThe CPP model was established by injecting morphine in rats with a increasing dose for 10 days, with the initial dose of 10 g x kg(-1) and the final dose of 100 g x kg(-1), 10 mg x kg(-1) was increased each day, thus 100 mg x kg(-1) was injected by d 10. Having been treated with differential doses (2, 1 and 0.5 g x kg(-1)) of C. yanhusuo (containing L-THP: 0.153, 0.077 and 0.038 mg x kg(-1) respectively) and L-THP (3.76, 1.88 and 0.94 mg x kg(-1)) for six days, the CPP effect in rats was detected. Both colorimetry and immunohistochemistry methods were adopted to detect the content of glutamate neurotransmitter in each brain region and the expression of NR2B in VTA-NAc-PFC neuroanatomical circuit.

RESULTCompared with the physiological saline treatment group, C. yanhusuo (2, 1 g x kg(-1)) and L-THP (3.76 and 1.88 mg x kg(-1)) groups showed a notably shorter retention period of rats in white boxes (morphine-accompanied boxes) (P < 0.05 or P < 0.01) and remarkably lower glutamic acid content in VTA, NAc and PFC and NR2B expression.

CONCLUSIONBoth C. yanhusuo and L-THP can substantially inhibit the effect of morphine CPP, reduce the increasing glutamic acid content in VTA-NAc-PFC neuroanatomical circuit and down-regulated NR2B expression, which may be one of mechanisms on reducing the effect of morphine CPP. C. yanhusuo preparations containing L-THP (1 x ) showed 24-fold effect of L-THP monomer of single application in terms of the behaviouristics of inhibitory effect on CPP as well as the similarity in terms of transmitter glutamic acid of in VTA-NAc-PFC neuroanatomical circuit and pharmacological mechanism of NR2B.

Animals ; Berberine Alkaloids ; therapeutic use ; Conditioning, Operant ; drug effects ; Corydalis ; chemistry ; Disease Models, Animal ; Dose-Response Relationship, Drug ; Drugs, Chinese Herbal ; therapeutic use ; Humans ; Male ; Morphine ; antagonists & inhibitors ; Morphine Dependence ; drug therapy ; psychology ; Rats ; Rats, Sprague-Dawley

OBJECTIVETo explore the effects of intrathecal injection of neuronal nitric oxide synthase (nNOS) inhibitors 7-Nitroindazole (7-Ni) and inducible nitric oxide synthase(iNOS) inhibitors aminoguanidine (AG) on the behavioral changes of morphine-induced dependent and withdrawal rats; the expression of Fos, nNOS and iNOS in spinal cord.

METHODSTo set up morphine dependence model, rats were subcutaneously injected with morphine (twice a day, for 5 d). The dose of morphine was 10 mg/kg in the first day and was increased by 10 mg/ kg every day. On day 6, 4 h after the injection of morphine (50 mg/kg), morphine withdrawal syndrome was precipitated by an injection of naloxone (4 mg/kg ip). 7-Ni, an nNOS inhibitor or iNOS inhibitors AG were intrathecally injected 30 min before the administration of naloxone respectively. The scores of morphine withdrawal symptom and morphine withdrawal-induced allodynia were observed. One hour after naloxone-precipitated withdrawal, Fos protein expression was assessed by immunohistochemical analysis and Western blot was used to detect the expression of nNOS and iNOS in the rat spinal cord.

RESULTSIntrathecal administration of nNOS inhibitor 7-Ni and iNOS inhibitors AG decreased the scores of morphine withdrawal, attenuated morphine withdrawal-induced allodynia and also inhibited the increase of Fos protein expression in the spinal cord of morphine withdrawal rats. nNOS and iNOS positive neurons in dorsal horn in nNOS group and iNOS group were significantly lower than that in withdrawal group. Compared with withdrawal group, level of nNOS and iNOS protein in spinal cord in nNOS group and iNOS group were significantly lower.

CONCLUSIONIt is suggested that nNOS and iNOS in the spinal cord may contribute to naloxone-precipitated withdrawal in rats and may play different roles in the above-mentioned effect.

Animals ; Guanidines ; pharmacology ; Indazoles ; pharmacology ; Male ; Morphine Dependence ; metabolism ; Naloxone ; pharmacology ; Nitric Oxide Synthase Type I ; antagonists & inhibitors ; metabolism ; Nitric Oxide Synthase Type II ; antagonists & inhibitors ; metabolism ; Rats ; Rats, Sprague-Dawley ; Spinal Cord ; drug effects ; metabolism ; Substance Withdrawal Syndrome ; metabolism

OBJECTIVETo explore the effects of intrathecal injection of mitogen-activated protein kinases inhibitors U0126 on the behavioral changes of morphine-induced dependent and withdrawal rats and the expression of nitric oxide synthase (NOS) in spinal cord.

METHODSAll the rats were divided into 4 groups: control group, dependent group, withdrawal group, U0126 group (5 microg). Global withdrawal score, Touch evoked agitation scores (TEA score), immunohistochemical and Western blot technique were undertaken to evaluate behavioral changes and expression of FOS, nNOS and iNOS in spinal cord respectively.

RESULTSThe results showed that intrathecal administration of U0126 significantly alleviated withdrawal symptom, withdrawal scores of U0126 group (22.5 +/- 4.09) were significantly lower than than those of withdrawal group (28.6 +/- 4.89) (P < 0.05). TEA scores of withdrawal group were 13.5 +/- 2.55, which were significantly higher than those of U0126 group (10.0 +/- 2.76, P < 0.05). Fos-like positive neurons in dorsal horn of withdrawal group were 380 +/- 71, which were higher than those of U0126 group(287 +/- 54, P < 0.05). Also nNOS and iNOS positive neurons in dorsal horn of U0126 group were 180 +/- 32, 10.8 +/- 2.8 respectively, which were significantly lower than that of withdrawal group (239 +/- 45, 16.8 +/- 5.1, P < 0.05). Compared with withdrawal group, levels of nNOS and iNOS protein in spinal cord of U0126 group were significantly lower.

CONCLUSIONMEK inhibitors could alleviate withdrawal symptom of morphine-induced dependent rats and could suppress expression of NOS in spinal cord, and extracellular signal-regulate kinase (ERK) might involve the expression of NOS in spinal cord.

Animals ; Behavior, Animal ; drug effects ; Butadienes ; pharmacology ; Enzyme Inhibitors ; pharmacology ; Extracellular Signal-Regulated MAP Kinases ; metabolism ; Male ; Mitogen-Activated Protein Kinases ; antagonists & inhibitors ; Morphine ; adverse effects ; Morphine Dependence ; metabolism ; Nitric Oxide Synthase ; metabolism ; Nitriles ; pharmacology ; Rats ; Rats, Sprague-Dawley ; Spinal Cord ; metabolism ; Substance Withdrawal Syndrome ; metabolism

The purpose of this study is to determine 1) whether morphine postconditiong (MPostC) can attenuate the intercellular adhesion molecules-1 (ICAM-1) expression after reoxygenation injury and 2) the subtype(s) of the opioid receptors (ORs) that are involved with MPostC. Human umbilical vein endothelial cells (HUVECs) were subjected to 6 hr anoxia followed by 12 hr reoxygenation. Three morphine concentrations (0.3, 3, 30 microM) were used to evaluate the protective effect of MPostC. We also investigated blockading the OR subtypes' effects on MPostC by using three antagonists (a micro-OR antagonist naloxone, a kappa-OR antagonist nor-binaltorphimine, and a delta-OR antagonist naltrindole) and the inhibitor of protein kinase C (PKC) chelerythrine. As results, the ICAM-1 expression was significantly reduced in the MPostC (3, 30 microM) groups compared to the control group at 1, 6, 9, and 12 hours reoxygenation time. As a consequence, neutrophil adhesion was also decreased after MPostC. These effects were abolished by coadministering chelerythrine, nor-binaltorphimine or naltrindole, but not with naloxone. In conclusion, it is assumed that MPostC could attenuate the expression of ICAM-1 on endothelial cells during reoxygenation via the kappa and delta-OR (opioid receptor)-specific pathway, and this also involves a PKC-dependent pathway.
Animals ; Benzophenanthridines/pharmacology ; Endothelial Cells/cytology/*drug effects/*metabolism ; Endothelium, Vascular/cytology ; Humans ; Intercellular Adhesion Molecule-1/genetics/*metabolism ; Morphine/*pharmacology ; Naloxone/pharmacology ; Naltrexone/analogs & derivatives/pharmacology ; Narcotic Antagonists/pharmacology ; Narcotics/*pharmacology ; Protein Isoforms/metabolism ; Protein Kinase C/antagonists & inhibitors/metabolism ; Receptors, Opioid/metabolism ; Reperfusion Injury/*metabolism ; Signal Transduction/physiology ; Umbilical Veins/cytology

OBJECTIVETo investigate the effects of clobenpropit and histidine on reinstatement of morphine-induced conditioned place preference (CPP) in rats.

METHODSThe persistence, extinction and reinstatement of morphine-induced CPP were established.In clobenpropit group three different doses of clobenpropit (2, 5 and 10 microg/rat, i.c.v.) were administered 15 min after morphine (1 mg/kg, i.p.) was injected. In histidine group histidine (100, 200, 500 mg/kg) was given 1 h prior to morphine treatment (1 mg/kg i.p).

RESULTThe CPP was reinstated by priming injection of 1 mg/kg morphine. Clobenpropit (5, 10 microg/rat) significantly inhabited the reinstatement by a priming dose of morphine-induced CPP compared with the morphine control group; histidine (100, 200, 500 mg/kg) significantly inhibited the reinstatement in a dose-dependent manner.

CONCLUSIONClobenpropit and histidine inhibit the revival of morphine-induced CPP in a dose dependent manner, indicating that endogenous histamine may inhibit relapse of morphine to some extent.

Animals ; Conditioning, Operant ; drug effects ; Histidine ; metabolism ; Imidazoles ; pharmacology ; Male ; Morphine Dependence ; physiopathology ; Random Allocation ; Rats ; Rats, Sprague-Dawley ; Receptors, Cell Surface ; antagonists & inhibitors ; Substance Withdrawal Syndrome ; physiopathology ; Thiourea ; analogs & derivatives ; pharmacology

The possible characteristics of spinal interaction between sildenafil (phosphodiesterase 5 inhibitor) and morphine on formalin-induced nociception in rats was examined. Then the role of the opioid receptor in the effect of sildenafil was further investigated. Catheters were inserted into the intrathecal space of male Sprague-Dawley rats. For induction of pain, 50 microliter of 5% formalin solution was applied to the hindpaw. Isobolographic analysis was used for the evaluation of drug interaction between sildenafil and morphine. Furthermore, naloxone was intrathecally given to verify the involvement of the opioid receptor in the antinociception of sildenafil. Both sildenafil and morphine produced an antinociceptive effect during phase 1 and phase 2 in the formalin test. The isobolographic analysis revealed an additive interaction after intrathecal delivery of the sildenafil-morphine mixture in both phases. Intrathecal naloxone reversed the antinociception of sildenafil in both phases. These results suggest that sildenafil, morphine, and the mixture of the two drugs are effective against acute pain and facilitated pain state at the spinal level. Thus, the spinal combination of sildenafil with morphine may be useful in the management of the same state. Furthermore, the opioid receptor is contributable to the antinocieptive mechanism of sildenafil at the spinal level.
Analgesics/*administration & dosage ; Analgesics, Opioid/*administration & dosage ; Animals ; Behavior, Animal/drug effects ; Dose-Response Relationship, Drug ; Drug Synergism ; Formaldehyde/toxicity ; Injections, Spinal ; Male ; Morphine/*administration & dosage ; Naloxone/administration & dosage ; Narcotic Antagonists/administration & dosage ; Pain/chemically induced/therapy ; Pain Measurement/drug effects ; Phosphodiesterase Inhibitors/*administration & dosage ; Piperazines/*administration & dosage ; Purines/administration & dosage ; Rats ; Rats, Sprague-Dawley ; Sulfones/*administration & dosage ; Time Factors

BACKGROUNDOpioid preconditioning (PC) reduces anoxia/reoxygenation (A/R) injury to various cells. However, it remains unclear whether opioid-induced delayed PC would show anti-apoptotic effects on pulmonary artery endothelial cells (PAECs) suffering from A/R injury. The present study was conducted to elucidate this issue and to investigate the potential mechanism of opioid-induced delayed PC.

METHODSCultured porcine PAECs underwent 16-hour anoxia followed by 1-hour reoxygenation 24 hours after pretreatment with saline (NaCl; 0.9%) or morphine (1 micromol/L). To determine the underlying mechanism, a non-selective K(ATP) channel inhibitor glibenclamide (Glib; 10 micromol/L), a nitric oxide (NO) synthase blocker NG-nitro-L-arginine methyl ester (L-NAME; 100 micromol/L), and an opioid receptor antagonist naloxone (Nal; 10 micromol/L) were given 30 minutes before the A/R load. The percentage of apoptotic cells was assessed by terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling (TUNEL) staining. eNOS mRNA level was measured by real-time polymerase chain reaction (PCR). NO content of PAECs supernatants was measured with the Griess reagent.

RESULTSCompared to the A/R PAECs, morphine-induced delayed PC significantly reduced PAECs apoptosis ((18.1 +/- 1.9)% vs (5.5 +/- 0.3)%; P < 0.05), increased NO release ((11.4 +/- 1.3) micromol/L vs (20.5 +/- 2.1) micromol/L, P < 0.05), and up-regulated eNOS gene expression nearly 9 times (P < 0.05). The anti-apoptosis effect of morphine was abolished by pretreatment with Glib, L-NAME and Nal, but the three agent-selves did not aggravate the A/R injury. Furthermore, L-NAME and Nal offset the enhanced release of NO caused by pretreatment with morphine.

CONCLUSIONSMorphine-induced delayed PC prevents A/R injury of PAECs. This effect may be mediated by activation of K(ATP) channel via opioid receptor and NO signaling pathways.

Analgesics, Opioid ; pharmacology ; Animals ; Apoptosis ; drug effects ; Cell Hypoxia ; Cells, Cultured ; Endothelial Cells ; cytology ; drug effects ; metabolism ; Enzyme Inhibitors ; pharmacology ; Glyburide ; pharmacology ; In Situ Nick-End Labeling ; Morphine ; pharmacology ; NG-Nitroarginine Methyl Ester ; pharmacology ; Naloxone ; pharmacology ; Narcotic Antagonists ; pharmacology ; Nitric Oxide ; metabolism ; Nitric Oxide Synthase Type III ; antagonists & inhibitors ; genetics ; metabolism ; Oxygen ; pharmacology ; Pulmonary Artery ; cytology ; RNA, Messenger ; genetics ; metabolism ; Reverse Transcriptase Polymerase Chain Reaction ; Swine

AIMTo determine whether testosterone is involved in morphine withdrawal syndrome (WS).

METHODSIn order to induce dependency, rats were treated with subcutaneous injection of morphine (days 1-2, 5 mg/kg; days 3-5, 7.5 mg/kg; days 6-8, 10 mg/kg), and after the last dose of morphine (day 8) WS was induced by intraperitoneal injection of naloxone (1 mg/kg). Wet dog shake (WDS), abdomen writhing (AW), and jumps (J) were recorded as indicators of WS.

RESULTSThe severity of WDS, AW, and J in male rats was greater than that in females. Accordingly, in 4-week castrated and flutamide-treated (10 mg/kg/day for 8 days, i.p.) male rats, WDS, AW, and J were significantly decreased compared to male control rats. Testosterone replacement therapy (10 mg/kg/day for 8 days, i.m.) in 4-week castrated rats restored the severity of WDS, AW, and J behaviors to the level of non-castrated male rats, whereas testosterone potentiated the WDS behavior in non-castrated male rats.

CONCLUSIONIt can be concluded that testosterone might be effectively involved in morphine WS.

Androgen Antagonists ; pharmacology ; Androgens ; pharmacology ; physiology ; Animals ; Behavior, Animal ; Female ; Flutamide ; pharmacology ; Male ; Morphine ; pharmacology ; Morphine Dependence ; physiopathology ; Naloxone ; pharmacology ; Narcotic Antagonists ; pharmacology ; Narcotics ; pharmacology ; Orchiectomy ; Rats ; Rats, Wistar ; Severity of Illness Index ; Substance Withdrawal Syndrome ; physiopathology ; Testosterone ; pharmacology ; physiology