Co-administration Of Morphine Research Articles

Restraint stress potentiates sensitivity to the antinociceptive effect of morphine through orexin receptors in the ventral tegmental area

Orexin signaling in the ventral tegmental area (VTA) plays a critical role in stress and addictive behaviors. On the other hand, exposure to stress potentiates behavioral sensitization to drugs of abuse such as morphine. This study aimed to elucidate the role of orexin receptors within the VTA in restraint stress (RS)-induced morphine sensitization. Adult male albino Wistar rats underwent stereotaxic surgery, and two stainless steel guide cannulae were bilaterally implanted into the VTA. Different doses of SB334867 or TCS OX2 29 as orexin-1 (OX1) and orexin-2 (OX2) receptor antagonists were microinjected into the VTA five min before exposure to RS, respectively. A duration of three hours was considered for applying the RS, and 10 min after RS exposure, animals received a subcutaneous injection of an ineffective dose of morphine (1 mg/kg) for three consecutive days followed by a five-day drug/stress-free period. On the ninth day, the tail-flick test evaluated the sensitivity to the antinociceptive effects of morphine. The results demonstrated that the sole application of RS or morphine (1 mg/kg) could not induce morphine sensitization; however, concurrent application of RS and morphine could induce morphine sensitization. Besides, intra-VTA administration of OX1 R or OX2 R antagonists before paired administration of morphine and RS blocked morphine sensitization. The role of OX1 R and OX2 R in the induction of stress-induced morphine sensitization was almost identical. This study provides new insight into the role of orexin signaling in the VTA in the potentiation of morphine sensitization induced by RS and morphine co-administration.

Naloxone could limit morphine hypersensitivity: Considering the molecular mechanisms

BackgroundNaloxone has been used as an opioid antagonist to prevent multiple adverse side effects of opioid-like tolerance and hyperalgesia. This study has investigated naloxone combined with morphine to limit pain hypersensitivity. In addition, the expression of brain-derived neurotrophic factor (BDNF) and K+ Cl− cotransporter2 (KCC2) were also studied. MethodsForty-eight adult male Wistar rats (180–220 g) were divided into eight groups, with six rats in each group. Rats were divided into two tolerance and hyperalgesia groups; the sham group, the morphine group, the treatment group (naloxone along with morphine), and the sham group (naloxone along with saline) for eight consecutive days. Tail-flick test was performed on days 1, 5, and 8, and the plantar test on days 1 and 10. On days 8 and 10, the lumbar segments of the spinal cord were collected, and BDNF and KCC2 expression were analyzed using western blotting and immunohistochemistry, respectively. ResultsResults showed that tolerance and hyperalgesia developed following eight days of repeated morphine injection. BDNF expression significantly increased, but KCC2 was downregulated. Co-administration of naloxone and morphine decreased tolerance and hyperalgesia by decreasing BDNF and increasing KCC2 expression, respectively. ConclusionThis study suggests that BDNF and KCC2 may be candidate molecules for decreased morphine tolerance and hyperalgesia.

Effect of ASP8062 on morphine self-administration and morphine-induced respiratory suppression in monkeys

ASP8062 is an orally available GABAB receptor positive allosteric modulator (PAM). This study assessed the potential of ASP8062 for treating opioid use disorder (OUD). Three rhesus monkeys were pretreated with ASP8062 (0.3, 1 or 3 mg/kg) by oral administration 1 h prior to a 2-h morphine self-administration session (0.03 mg/kg, iv, per injection) under a fixed-ratio 5 schedule. We further examined the potential worsening of morphine-induced respiratory suppression by ASP8062 after coadministration of morphine (10 mg/kg, sc) and ASP8062 (10 mg/kg, po) in cynomolgus monkeys using a custom-made whole-body plethysmograph. Plasma concentrations of ASP8062 (3 or 10 mg/kg, po) were assessed in cynomolgus monkeys using liquid chromatography-tandem mass spectroscopy (LC-MS/MS). ASP8062 at 3 mg/kg, po decreased the morphine self-administrations with significant differences from the vehicle-treated group (IC50 = 0.97 ± 0.36 mg/kg). Exposure levels at 3 mg/kg observed in monkeys were comparable to the clinical exposure levels which positive pharmacodynamic effects were previously shown. Further, ASP8062 did not potentiate morphine-induced respiratory suppression up to exposure levels higher than the clinically relevant dose. ASP8062 may reduce opioid use in OUD patients without affecting respiratory system, providing justification for further ASP8062 development as a potential treatment option for OUD.

Opioid-induced microbial dysbiosis disrupts irinotecan (CPT-11) metabolism and increases gastrointestinal toxicity in a murine model.

Opioids are commonly used for the management of cancer-associated pain and chemotherapy-induced diarrhoea. The chemotherapeutic irinotecan (CPT-11) causes severe gastrointestinal (GI) toxicity due to deconjugation of inactive metabolite SN-38 glucuronide (SN-38G) by bacterial β-glucuronidases to the active 7-ethyl-10-hydroxycamptothecin (SN-38). Opioids are known to cause gut microbial dysbiosis, this study evaluated whether CPT-11 anti-tumour efficacy and GI toxicity are exacerbated by opioid co-administration. Eight-week-old C57BL/6 male mice were co-administration with CPT-11 ± opioid. 16S rRNA sequencing was used for gut microbiome analysis. LC-MS analyses of plasma and intestinal extracts were performed to investigate the pharmacokinetic profile of CPT-11. Histological analysis and quantitative real-time polymerase chain reaction were used to determine the severity of intestinal tissue damage. Human liver microsome In vitro assay was performed to confirm the effects of opioids on CPT-11 metabolism. Gut microbiome analysis showed that morphine treatment induced enrichment of β-glucuronidase-producing bacteria in the intestines of CPT-11-treated mice, resulting in SN-38 accumulation and exacerbation of GI toxicity in the small intestine. Oral administration of both antibiotics and glucuronidase inhibitor protected mice against GI toxicity induced with CPT-11 and morphine co-administration, implicating a microbiome-dependent mechanism. Additionally, morphine and loperamide decreased the plasma concentration of SN-38 and compromised CPT-11 anti-tumour efficacy, this seemed to be microbiome independent. Gut microbiota play a significant role in opioid and chemotherapeutic agent drug-drug interactions. Inhibition of gut microbial glucuronidase may also prevent adverse GI effects of CPT-11 in patients on opioids.

Effects of the Co-Administration of Morphine and Lipopolysaccharide on Toll-Like Receptor-4/Nuclear Factor Kappa β Signaling Pathway of MDA-MB-231 Breast Cancer Cells.

The Toll-like receptor 4 (TLR4) gene promotes migration in adenocarcinoma cells. Morphine is an agonist for TLR4 that has a dual role in cancer development. The promoter or inhibitor role of morphine in cancer progression remains controversial. This study aims to evaluate the effects of morphine on the TLR4, myeloid differentiation primary response protein 88-dependent (MyD88), and nuclear factor-kappa B (NF-κB) expressions in the human MDA-MB-231 breast cancer cell line. The cells were examined after 24 hours of incubation with morphine using the Boyden chamber system. TLR4, MyD88, and NF-κB mRNA expressions were assessed using quantitative real-time polymerase chain reaction (RT-PCR). The concentration of interleukin-2 beta was also measured using the ELISA assay. According to the findings, three doses of morphine (0.25, 1.25, and 0.025 μM) increased the expression of the TLR4 and NF-κB genes, whereas no significant change was observed in the mRNA expression of MyD88. Furthermore, treatment with morphine and lipopolysaccharide (LPS) significantly decreased the expression of TLR4, MyD88, and NF-κB. However, no significant change was observed in interleukin 2 beta concentration. These findings confirmed the excitatory effects of morphine on TRL4 expression and the MYD88 signaling pathway in vitro.

Expression of Concern: Epidural Co-Administration of Dexmedetomidine and Levobupivacaine Improves the Gastrointestinal Motility Function after Colonic Resection in Comparison to Co-Administration of Morphine and Levobupivacaine.

Expression of Concern: Epidural Co-Administration of Dexmedetomidine and Levobupivacaine Improves the Gastrointestinal Motility Function after Colonic Resection in Comparison to Co-Administration of Morphine and Levobupivacaine.

Enhanced anxiolytic and analgesic effectiveness or a better safety profile of morphine and tramadol combination in cholestatic and addicted mice.

The involvement of the opioidergic system on anxiolytic and antinociceptive responses induced by cholestasis was investigated in cholestatic and addicted mice. Elevated plus-maze and tail-flick devices were used to assess anxiety and pain levels, respectively. The data indicated that induction of cholestasis and injection of opioid drugs including morphine and tramadol enhanced %OAT and %OAE but naloxone reduced %OAT and %OAE in the sham-operated and bile duct ligation (BDL) mice. Induction of cholestasis and addiction to morphine and tramadol prolonged tail-flick latency, which was reversed by naloxone. Coadministration of morphine and tramadol enhanced anxiolytic and analgesic effects in the sham-operated and BDL mice. It seems (a) cholestasis and addiction affect anxiety and pain behaviors, (b) μ-opioid receptors play a key role in anxiolytic and analgesic effects induced by cholestasis, and (c) cotreatment with morphine and tramadol augmented the effectiveness of them for induction of anxiolytic and analgesic effects both in cholestatic and addicted mice.

Intrathecal Co-administration of Morphine Facilitated the Anti-nociceptive of Bupivacaine in a Rat Model of Acute Postoperative Pain.

Introduction: Bupivacaine is one of the commonly used agents for spinal anaesthesia. Moreover, co-administration with morphine can likely increase its anti-nociceptive effect bringing about a reduction in the required dose of bupivacaine. Though this has been observed clinically, preclinical studies on the efficacy of this drug combination are lacking.Methods: Sprague Dawley rats, previously implanted with intrathecal catheters, were administered either bupivacaine (30 mcg) or morphine (30 mcg) or both bupivacaine and morphine (15 mcg each). These doses were determined following prior evaluation of different doses of bupivacaine (3, 10 and 30 mcg). Rats were subjected to hind paw incision under isoflurane anaesthesia, 15 min after drug administration. Anti-nociception was evaluated by estimating mechanical allodynia in a fixed peri-incisional area using von Frey filaments. This was done 4 h after the incision.Results: Both bupivacaine and morphine attenuated allodynia though morphine was more effective. Co-administration of both drugs at half the doses increased the antinociceptive effect of bupivacaine to the 30 mcg dose level.Conclusion: The underlying reason for this enhanced anti-nociception could be the different neural mechanisms responsible for anti-nociception. Local anaesthetics inhibit the generation of action potentials by blocking sodium channels whereas opioids like morphine act through G-protein coupled mu opioid receptor-linked closure of calcium channels in presynaptic terminals. In conclusion, the addition of morphine can facilitate bupivacaine’s anti-nociceptive effect following intrathecal administration. This information could have clinical relevance in the treatment of postoperative pain.

Acetic acid-induced nociception modulates sociability in adult zebrafish: Influence on shoaling behavior in heterogeneous groups and social preference

Due to the recognition of fishes as sentient beings, the zebrafish (Danio rerio) has become an emergent animal model system to investigate the biological processes of nocifensive responses. Here, we aimed to characterize the zebrafish social behavior in a nociception-based context. For this purpose, using a three-dimensional analysis of heterogeneous shoals, we investigated the main behavioral responses in two 6-min trials: before (baseline) and after a single intraperitoneal (i.p) injection of 10 μL phosphate-buffered saline (PBS) (control), acetic acid 5% (AA), morphine 2.5 mg/kg (MOR) or acetic acid 5% plus morphine 2.5 mg/kg (AA + MOR) in one subject from a four-fish shoal. The social preference of individuals for tanks with shoals of fish treated with PBS, 5 % AA, or to an empty aquarium was also tested. We verified that AA administration disrupted the shoal homogeneity by eliciting dispersion of the treated fish with simultaneous clustering of non-manipulated fish. In general, morphine coadministration protected against AA-induced behavioral changes. The social preference test revealed a clear preference to conspecifics (PBS and AA) over an empty tank. However, a prominent preference for PBS- over AA-treated shoal was verified. Overall, our novel findings show that nociception can modulate zebrafish sociability, possibly due to the visual recognition of nocifensive responses. Although future studies are needed to elucidate how nociception modulates zebrafish social behavior, our results contribute to improve the welfare assessment of zebrafish shoals under distinct experimental manipulations.

Morphine with or without Acepromazine in Horses: A Kinematic Evaluation.

Simple SummaryMorphine is an opioid agonist drug and produces a significant analgesic effect in horses but besides the evidenced analgesic effect, the use of morphine is not routine due to the potential excitatory effects described in the literature. To minimize these effects, neuroleptanalgesia, or the combination of opioids and sedative drugs, is encouraged. Our aim was to describe changes occurring in the locomotor pattern after co-administration of a tranquilizer, acepromazine, and morphine in horses. Six mature horses were used and received four different treatments with saline solution, morphine, acepromazine, or a combination of morphine and acepromazine. A three-dimensional accelerometric device was used to collect data and objectivize those findings moreover the sedative effect of the treatments was also measured. Significant differences were observed when comparing all the treatments in the majority of accelerometric variables, except the regularity of the pattern, some energetic parameters, and tranquilization. An evident counteraction of the effects caused by both morphine and acepromazine was observed. Due to these effects, the possibility of adding acepromazine to an additional analgesic treatment with morphine in the clinical setting ensures the absence of the supplemental instability caused by other sedatives and minimizes the potential opioid excitatory effects.The objective was to demonstrate walking locomotor pattern alterations after co-administration of acepromazine and morphine in horses. Six mature horses receiving four different treatments were used. Treatments consisted of a single dose of saline solution, 0.2 mg/kg bwt of morphine hydrochloride, 0.02 mg/kg bwt of acepromazine maleate, and a combination of 0.2 mg/kg bwt of morphine hydrochloride with 0.02 mg/kg bwt of acepromazine maleate. A three-dimensional accelerometric device was used to collect data. Walking tests were performed 10 min prior to injection, and then at 5, 10, 15, and 20 min after the injection, and then every 10 min for 3 h. Eight variables were calculated including stride kinematic, coordination, and energetic parameters; moreover ground-to-lip distance (GLD), as a tranquilization parameter, was also measured. A significant interaction was observed in all the variables studied but regularity, mediolateral power, the propulsive part of the power, and the GLD. An evident counteraction of the effects caused by both, opioids and phenothiazines, in the gait pattern was observed. The co-administration of acepromazine and morphine could allow a safe opiate administration while minimizing the possible central nervous system (CNS) excitation and reducing potential locomotor adverse effects.

Assessing the synergistic effects of morphine and MP‐III‐024 co‐administration: enhanced antinociception with reduced side effects

Opioid analgesics are critical for acute and chronic pain management, but important side effects—including tolerance, constipation, respiratory depression, and abuse liability—limit their safety and utility. To provide patients with safer analgesic options, it is critically important to identify of new pharmacotherapeutic strategies to treat pain. Activation of µ‐opioid receptors (MORs) in central and peripheral nociceptive pathways mediates opioid analgesia and their critical side effects. Antinociception can also be achieved via selective enhancement of GABAergic signaling at ionotropic GABAA receptors. α2 and α3 subunit‐containing GABAA receptors (α2/α3GABAA), which are co‐expressed with MORs in dorsal horn spinal pathways important to nociceptive transmission, can be selectively targeted with novel imidazodiazepine positive allosteric modulators (PAMs), such as MP‐III‐024, which produces antinociceptive effects with limited behavioral disruption. MP‐III‐024 co‐administered with morphine produces synergistic antinociceptive and anti‐hyperalgesic effects. In this study, we evaluated whether MP‐III‐024/morphine co‐administration produces sub‐additive or synergistic effects in behavioral tests sensitive to morphine side effects. Herein we report that co‐administration of MP‐III‐024/morphine at a 0.94/1 ratio (synergistic in models of antinociception) produced sub‐additive effects in morphine‐induced hyperlocomotion and in measures of behavioral disruption in food‐maintained operant responding. Ongoing studies are evaluating the effects of MP‐III‐024/morphine co‐administration on tolerance in the hot plate test and in conditioned place preference. These experiments are the first comprehensive preclinical analyses of a dual MOR‐α2/α3GABAA pharmacotherapy strategy which may increase the therapeutic window between desirable opioid analgesic effects and side effects.

Modulation of Morphine Analgesia, Antinociceptive Tolerance, and Mu-Opioid Receptor Binding by the Cannabinoid CB2 Receptor Agonist O-1966.

Acutely, non-selective cannabinoid (CB) agonists have been shown to increase morphine antinociceptive effects, and we and others have also demonstrated that non-selective CB agonists attenuate morphine antinociceptive tolerance. Activation of cannabinoid CB2 receptors reverses allodynia and hyperalgesia in models of chronic pain, and co-administration of morphine with CB2 receptor selective agonists has been shown to be synergistic. CB2 receptor activation has also been shown to reduce morphine-induced hyperalgesia in rodents, an effect attributed to CB2 receptor modulation of inflammation. In the present set of experiments, we tested both the acute and chronic interactions between morphine and the CB2 receptor selective agonist O-1966 treatments on antinociception and antinociceptive tolerance in C57Bl6 mice. Co-administration of morphine and O-1966 was tested under three dosing regimens: simultaneous administration, morphine pre-treated with O-1966, and O-1966 pre-treated with morphine. The effects of O-1966 on mu-opioid receptor binding were determined using [3H]DAMGO and [35S]GTPγS binding assays, and these interactions were further examined by FRET analysis linked to flow cytometry. Results yielded surprising evidence of interactions between the CB2 receptor selective agonist O-1966 and morphine that were dependent upon the order of administration. When O-1966 was administered prior to or simultaneous with morphine, morphine antinociception was attenuated and antinociceptive tolerance was exacerbated. When O-1966 was administered following morphine, morphine antinociception was not affected and antinociceptive tolerance was attenuated. The [35S]GTPγS results suggest that O-1966 interrupts functional activity of morphine at the mu-opioid receptor, leading to decreased potency of morphine to produce acute thermal antinociceptive effects and potentiation of morphine antinociceptive tolerance. However, O-1966 administered after morphine blocked morphine hyperalgesia and led to an attenuation of morphine tolerance, perhaps due to well-documented anti-inflammatory effects of CB2 receptor agonism.

Co-administration of morphine and levamisole increases death risk, produces neutropenia and modifies antinociception in mice.

Levamisole is a veterinary anthelmintic drug and a common adulterant of misused drugs. This study analyses the lethal, antinociceptive and haematological effects produced by acute or repeated levamisole administration by itself or combined with morphine. Independent groups of male Swiss Webster mice were i.p. injected with 100 mg/kg morphine, 31.6mg/kg levamisole (lethal doses at 10%, LD10 ) or the same doses combined. Naloxone pretreatment (10mg/kg, i.p.) prevented morphine-induced death, as did 2.5mg/kg, i.p. mecamylamine with levamisole. Co-administration of levamisole and morphine (Lvm + Mor) increased lethality from 10% to 80%. This augmented effect was prevented by 30 mg/kg, i.p. naloxone and reduced with 10mg/kg naloxone plus 2.5mg/kg, i.p. mecamylamine. In independent groups of mice, 17.7mg/kg, i.p. levamisole antagonized the acute morphine's antinociceptive effect evaluated in the tail-flick test. Repeated 17.7mg/kg levamisole administration (2×/day/3weeks) did not affect tolerance development to morphine (10mg/kg, 3×/day/1week). Blood samples obtained from mice repeatedly treated with levamisole showed leukopenia and neutropenia. Morphine also produced neutropenia, increased erythrocyte count and other related parameters (e.g. haemoglobin). Lvm + Mor had similar effects on leukocyte and neutrophil counts to those seen with levamisole only, but no erythrocyte-related alterations were evident. Blood chemistry analysis did not indicate liver damage but suggested some degree of electrolyte balance impairment. In conclusion, Lvm + Mor increased death risk, altered morphine-induced antinociceptive effects and produced haematologic abnormalities. The importance of studying combinations of drugs of abuse lies in the fact that drug users frequently combine drugs, which are commonly adulterated.

Chemokine CXCL10 regulates pain behaviors via PI3K-AKT signaling pathway in mice

The analgesic efficacy of morphine can be affected by a variety of factors. Our previous studies demonstrated that chemokine (CXC motif) ligand 10 (CXCL10) could induce algesia directly and attenuate the analgesic effect produced by a single dose of morphine. However, the underlying mechanism remains unclear. In the present study, we aimed to further investigate the mechanism of CXCL10-mediated inhibition on morphine analgesic effect. According to our findings, recombinant CXCL10 protein (rmCXCL10) could increase the phosphorylation of serine-threonine kinase AKT reduced by morphine in spinal cord. Blocking AKT activation by phosphoinositide 3-kinase (PI3K) inhibitor could effectively attenuate CXCL10-induced algesia, and reverse the decrease of paw withdrawal thresholds caused by the co-administration of morphine and rmCXCL10. Furthermore, rmCXCL10 could enhance the spinal expression of pro-inflammatory cytokines, including TNF-α, IL-6, and IL-1β, which could be blocked by PI3K inhibitor. In summary, these findings suggest that PI3K-AKT signaling pathway mediates the effect of CXCL10 on the regulation of morphine analgesia and the release of cytokines in spinal cord. Our study provides a new insight into the mechanism of chemokine-relative pain regulation.

Magnesium and Morphine in the Treatment of Chronic Neuropathic Pain-A Biomedical Mechanism of Action.

The effectiveness of opioids in the treatment of neuropathic pain is limited. It was demonstrated that magnesium ions (Mg2+), physiological antagonists of N-methyl-D-aspartate receptor (NMDAR), increase opioid analgesia in chronic pain. Our study aimed to determine the molecular mechanism of this action. Early data indicate the cross-regulation of µ opioid receptor (MOR) and NMDAR in pain control. Morphine acting on MOR stimulates protein kinase C (PKC), while induction of NMDAR recruits protein kinase A (PKA), leading to a disruption of the MOR-NMDAR complex and promoting functional changes in receptors. The mechanical Randall-Selitto test was used to assess the effect of chronic Mg2+ and morphine cotreatment on streptozotocin-induced hyperalgesia in Wistar rats. The level of phosphorylated NMDAR NR1 subunit (pNR1) and phosphorylated MOR (pMOR) in the periaqueductal gray matter was determined with the Western blot method. The activity of PKA and PKC was examined by standard enzyme immunoassays. The experiments showed a reduction in hyperalgesia after coadministration of morphine (5 mg/kg intraperitoneally) and Mg2+ (40 mg/kg intraperitoneally). Mg2+ administered alone significantly decreased the level of pNR1, pMOR, and activity of both tested kinases. The results suggest that blocking NMDAR signaling by Mg2+ restores the MOR-NMDAR complex and thus enables morphine analgesia in neuropathic rats.

Dopamine receptors in the anterior cingulate cortex implicate in nicotine enhanced morphine analgesia.

It is well known that the anterior cingulate cortex (ACC) plays an important role in acute pain perception. In the present study, we aimed to investigate the possible involvement of the ACC dopamine D1 and D2 receptors in nicotine plus morphine-induced analgesia. The ACC's of adult male Wistar rats were bilaterally cannulated bystereotaxic instrument and the tail-flick test was used to measure the thermal pain threshold. The results indicated that subcutaneous (s.c.) injection of nicotine (0.3mg/kg) potentiated the analgesic response of intraperitoneal (i.p.) administration of morphine (3mg/kg). Systemic administration of the same doses of nicotine or morphine alone had no effect on tail-flick latency. Intra-ACC administration of apomorphine (0.3-0.9μg/rat), the non-selective D1/D2 receptors agonist, plus ineffective doses of nicotine (0.1mg/kg, s.c.) plus morphine (3mg/kg, i.p) induced analgesia in rats. In addition, the analgesia induced with co-administration of nicotine and morphine was inhibited via intra-ACC administration of SCH23390 (0.5-1μg/rat) or sulpiride (0.5-2μg/rat), the selective antagonists of D1 or D2 receptors, respectively. The intra-ACC microinjection of the same doses of drugs alone had no effect on tail-flick latency. Cubic interpolation analysis also confirmed that activation or inactivation of the ACC D1 and D2 receptors by different doses of drugs can modulate the nicotine-morphine analgesic response. The findings suggest that the ACC has an important role in acute thermal pain perception and modulates the analgesia induced by nicotine plus morphine via dopaminergic receptors.

Comparing Benzodiazepines-morphine-induced Respiratory Depression by Analyzing Respiratory Pattern in Rats

Background and Aim: Opioid and benzodiazepine family drugs are concurrently used in various patients. Considering the respiratory depressant effects of both classes, in this study, we investigated the effect of coadministration of morphine and several widely used benzodiazepines in the clinic on the rate of respiratory depression in rats. Methods & Materials: Seventy adult male Wistar rats were randomly divided into 10 groups; morphine, midazolam, diazepam, lorazepam, alprazolam, morphine-midazolam, morphine-diazepam, morphine-lorazepam, and morphine-alprazolam. Respiration signal was recorded using whole-body plethysmography 15 minutes after the intraperitoneal injection of the drugs. The respiratory pattern was examined using several parameters; the mean value of inter-breath interval and the respiratory rate, as well as the coefficient of variation and sample entropy analysis of inter-breath interval. Ethical Considerations: This study was approved by the Ethics Committee of Arak University of Medical Sciences (Code: IR.ARAKMU.REC.1397.327). Results: Analyzing respiratory data revealed that injecting the anxiolytic dose of alprazolam, and the combination of morphine-alprazolam and morphine-midazolam, altered the respiratory pattern. Such changes were associated with a decrease in the number of breaths and an increase in the inter-breath interval in the explored test animals, compared with the controls. The obtained data also indicated that morphine-midazolam injection increased the variability of the breathing pattern; such an alternation was associated with increased irregularity and decreased coefficient of variation of the inter-breath interval. Conclusion: The present research results suggested that the short-term injection of morphine-midazolam changes the respiratory pattern more severely than morphine combined with other benzodiazepines.

Restraint Stress Potentiated Morphine Sensitization: Involvement of Dopamine Receptors within the Nucleus Accumbens.

Sensitization to psychostimulant drugs, as well as morphine, subjected to cross-sensitization with stress. The development of morphine sensitization is associated with enhancements in dopamine overflow in the Nucleus accumbens (NAc). This study aimed to examine the role of accumbal D1/D2-like dopamine receptors in restraint stress (RS) induced sensitization to morphine antinociceptive effects. Adult male Wistar rats weighing 220-250 g underwent stereotaxic surgery. Two stainless steel guide cannulae were bilaterally implanted, 1 mm above the NAc injection site. Different solutions of SCH-23390, as a D1-like receptor antagonist or sulpiride, as a D2-like receptor antagonist, were microinjected into the NAc five min before exposure to RS. Restraint stress lasted for 3 h, 10 min after RS termination; animals received a subcutaneous injection of morphine (1 mg/kg) for 3 consecutive days. The procedure was followed by a 5-day drug and/or stress-free period. After that, on the 9th day, the nociceptive response was evaluated by the tail-flick test. The results revealed that intra-NAc administration of D1/D2-like dopamine receptor antagonists, SCH-23390 or sulpiride, respectively, blocked morphine sensitization-induced by RS and morphine co-administration in rats for three consecutive days. This work provides new insight into the determinant role of accumbal dopamine receptors in morphine sensitization produced by RS-morphine co-administration.

Isobolographic analysis reveals antinociceptive synergism between Phα1β recombinant toxin and morphine in a model of cancer pain in C57BL/6J mice.

Background:Phoneutria nigriventer venom contains Phα1β. This toxin and its recombinant form have a remarkable analgesic potential that is associated with blockage of voltage-gated calcium channels and TRPA1 receptors. Although morphine is a mainstay drug to treat moderate and severe pain related to cancer, it has serious and dose-limiting side effects. Combining recombinant Phα1β and morphine to treat pain is an interesting approach that has been gaining attention. Therefore, a quantitative and reliable method to establish the strength of the antinociceptive interaction between these two substances is necessary. The present study was designed to investigate the nature of the functional antinociceptive (analgesic) interaction between Phα1β recombinant toxin and morphine in a model of cancer pain.Methods:Melanoma was produced by intraplantar inoculation of B16-F10 cells into the right paw of C57BL/6J mice. Von Frey filaments measured the paw-withdrawal threshold after intrathecal administration of morphine, recombinant Phα1β, and their combination. Thermal hyperalgesia was assessed using Hargreaves apparatus. The degree of interaction was evaluated using isobolographic analysis. Spontaneous and forced motor performance was assessed with the open-field and rotarod tests, respectively.Results:Co-administration of recombinant Phα1β and morphine synergistically reverses the melanoma-induced mechanical hyperalgesia. The potency of the mixture, measured as the effective dose to reach 50% of maximum possible effect (MPE) in ameliorating mechanical hyperalgesia, was about twice fold higher than expected if the interaction between morphine and recombinant Phα1β was merely additive. Treatment with the combination at doses necessary to reach 50% of MPE caused no spontaneous nor forced motor alterations.Conclusion:The combinatorial use of recombinant Phα1β and morphine allows significant and effective dose reduction of both agents, which has translational potential for opioid-sparing approaches in pain management related to cancer.

The Positive and Negative Outcome of Morphine and Disulfiram Subacute Co-Administration in Rats in the Absence of Ethanol Challenge.

Recently, a well-known anti-alcohol agent, disulfiram (DSF), has gain much interest, as it was found to be effective in the treatment of cocaine abusers, thus also giving hope for patients addicted to opioids and other illicit drugs. Therefore, this study was aimed to investigate the possible outcome that might occur within the subacute co-administration of both morphine (MRF) and DSF in rats, but in the absence of ethanol challenge. As observed, intraperitoneal DSF dose-dependently enhanced MRF-mediated analgesia with the maximal efficacy at a dose of 100 mg/kg. Furthermore, MRF-induced tolerance and aggressive behavior were significantly reduced by DSF (100 mg/kg, i.p.) in comparison to MRF solely. Nonetheless, significant blood biochemical markers of hepatotoxicity were found (i.e., alteration in the levels of glutathione, blood urea nitrogen, etc.), following a combination of both drugs. Likewise, histological analysis of liver tissue revealed severe changes in the group of DSF + MRF, which includes swelling, cell death, damage to certain vessels, and hemorrhages into the liver parenchyma. Our findings indicate that DSF should be used with extreme caution, especially within the course of subacute concomitant use with MRF, as several possible side effects may take place.