Repeated administration of orexin into the thalamic paraventricular nucleus inhibits the development of morphine-induced analgesia

Background: Hypothalamic neuropeptides, orexins, play pivotal roles in nociception and pain modulation. Objective: In this study, we investigated the effect of the administration of orexin into the paraventricular nucleus (PVT) on the development of morphine-induced analgesia in rats. Method. Male Wistar rats weighing 250-300 g received subcutaneous (s.c.) chronic morphine (6, 16, 26, 36, 46, 56 and 66 mg/kg, 2 ml/kg) at an interval of 24 hours for 7 days. Animals were divided into two experimental groups in which the orexin (100 μM, 200 nl) and its vehicle were microinjected into the PVT nucleus for 7 days before each morphine injection. Then, the formalin test was performed for the assessment of pain-related behaviors. Results: The results demonstrated that the rats pretreated by intra-PVT orexin exhibited higher pain-related behaviors than the morphine-treated group. The analgesic effects of morphine were significantly lower in orexin plus morphine-treated rats than the vehicle plus morphine-treated ones. Conclusion: Our findings suggested that the animals receiving the prolonged intra-PVT application of orexin before morphine injection demonstrated a significant increase in the development of nociceptive behaviors in all phases. Therefore, the present study highlighted a new area of the brain involved in the effect of orexin on analgesia induced by morphine.

Pharmacological blockade of neurokinin1 receptor restricts morphine-induced tolerance and hyperalgesia in the rat

Objectives The most notable adverse side effects of chronic morphine administration include tolerance and hyperalgesia. This study investigated the involvement of dorsal root ganglion (DRG) protein kinase Cɛ (PKCɛ) expression during chronic morphine administration and also considered the relationship between DRG PKCɛ expression and the substance P- neurokinin1 receptor (SP- NK1R) activity. Methods Thirty-six animals were divided into six groups (n=6) in this study. In the morphine and sham groups, rats received 10 µg intrathecal (i.t.) morphine or saline for eight consecutive days, respectively. Behavioral tests were performed on days 1 and 8 before and after the first injections and then 48 h after the last injection (day 10). In the treatment groups, rats received NK1R antagonist (L-732,138, 25 µg) daily, either alone or 10 min before a morphine injection, Sham groups received DMSO alone or 10 min before a morphine injection. Animals were sacrificed on days 8 and 10, and DRG PKCɛ and SP expression were analyzed by western blot and immunohistochemistry techniques, respectively. Results Behavioral tests indicated that tolerance developed following eight days of chronic morphine injection. Hyperalgesia was induced 48 h after the last morphine injection. Expression of SP and PKCɛ in DRG significantly increased in rats that developed morphine tolerance on day 8 and hyperalgesia on day 10, respectively. NK1R antagonist (L-732,138) not only blocked the development of hyperalgesia and the increase of PKCɛ expression but also alleviated morphine tolerance. Conclusions Our results provide evidence that DRG PKCɛ and SP-NK1R most likely participated in the generation of morphine tolerance and hyperalgesia. Pharmacological inhibition of SP-NK1R activity in the spinal cord suggests a role for NK1R and in restricting some side effects of chronic morphine. All experiments were performed by the National Institute of Health (NIH) Guidelines for the Care and Use of Laboratory Animals (NIH Publication No. 80-23, revised1996) and were approved by the Animal Ethics Committee of Shahid Beheshti University of Medical Sciences, Tehran, Iran (IR.SBMU.MSP.REC.1396.130).

Neural basis of opioid-induced respiratory depression and its rescue

Opioid-induced respiratory depression (OIRD) causes death following an opioid overdose, yet the neurobiological mechanisms of this process are not well understood. Here, we show that neurons within the lateral parabrachial nucleus that express the µ-opioid receptor (PBLOprm1 neurons) are involved in OIRD pathogenesis. PBLOprm1 neuronal activity is tightly correlated with respiratory rate, and this correlation is abolished following morphine injection. Chemogenetic inactivation of PBLOprm1 neurons mimics OIRD in mice, whereas their chemogenetic activation following morphine injection rescues respiratory rhythms to baseline levels. We identified several excitatory G protein–coupled receptors expressed by PBLOprm1 neurons and show that agonists for these receptors restore breathing rates in mice experiencing OIRD. Thus, PBLOprm1 neurons are critical for OIRD pathogenesis, providing a promising therapeutic target for treating OIRD in patients.

Study protocol for a randomised, placebo-controlled, single-blind phase II study of the efficacy of morphine for dyspnoea in patients with interstitial lung disease (JORTC-PAL 15)

IntroductionDyspnoea is common in patients with interstitial lung disease (ILD) and often refractory to conventional treatment. Little is known about the efficacy of systemic morphine for dyspnoea in patients with ILD. The aim of this study is to estimate the efficacy of a single subcutaneous morphine injection for dyspnoea in patients with ILD.Methods and analysisWe will conduct a multicentre, prospective, randomised, placebo-controlled, single-blinded phase II study of a single subcutaneous morphine injection for dyspnoea in patients with ILD. In patients with ILD who have dyspnoea at rest refractory to conventional treatment will be eligible for participation in this study. The morphine dose will be 2 mg. The primary endpoint is changes in dyspnoea intensity from baseline to 60 min after treatment as measured using an 11-point Numerical Rating Scale and compared between the morphine and placebo groups.Ethics and disseminationEthical approval has been obtained by the Osaka City University Certified Review Board. The results of this study will be submitted for publication in an international peer-reviewed journal and the findings will be presented at international scientific conferences.Trial registration numberjRCTs051190030; pre-results.

Enhancement of morphine-induced antinociception after electroconvulsive shock in mice

Electroconvulsive therapy (ECT) has been applied for chronic pain for decades. The amounts of opioids to treat pain are sometimes reduced after a series of ECT. The effect of ECT on morphine-induced analgesia and its mechanism underlying the reduction of morphine requirement has yet to be clarified. Therefore, we administered electroconvulsive shocks (ECS) to mice and investigated the antinociceptive effect of morphine in a hot plate test. We examined the expression level of µ-opioid receptor in the thalami of mice 25 h after administration of ECS compared to the thalami of mice without ECS administration using western blotting. ECS disturbed the development of a decrease in the percentage of maximal possible effect (%MPE), which was observed 24 h after a morphine injection, when ECS was applied 25, 23, 21, and 12 h before the second administration of morphine. We also examined the effect of ECS on the dose-response curve of %MPE to morphine-antinociception. Twenty-five hours after ECS, the dose-response curve was shifted to the left, and the EC50 of morphine given to ECS-pretreated mice decreased by 30.1% compared to the mice that were not pretreated with ECS. We also found that the expression level of µ-opioid receptors was significantly increased after ECS administration. These results confirm previous clinical reports showing that ECT decreased the required dose of opioids in neuropathic pain patients and suggest the hypothesis that this effect of ECT works through the thalamus.

Effect of Jujube Extract on Acetylcholinesterase Activity and Oxidative Stress in Morphine-treated Male Rats

Background: One of the mechanisms associated with morphine neurotoxicity is oxidative stress. Jujube fruit extract may reduce oxidative stress due to its antioxidant properties. Objective: This study aims to investigate the protective effect of jujube fruit extract on the Acetylcholinesterase (AchE) activity and oxidative stress in the cortex and serum of morphine-treated male rats. Materials and Methods: In this experimental study, 42 male Wistar rats were randomly divided into six groups of 7 which were given oral administration of jujube extract (100 and 200 mg/kg) and intraperitoneal injection of 0.5 mg/kg morphine for 30 days. After blood collection, separation of the serum, and homogenization of brain tissue, the activities of Catalase (CAT), AchE, and Superoxide Dismutase (SOD) enzymes were assessed. Collected data were analyzed using one-way ANOVA. Results: Oral administration of jujube extract at doses of 100 and 200 mg/kg significantly increased the activity of AchE, CAT, and SOD in the serum and cortex of rats compared to morphine injection (P<0.01). Oral administration of 200 mg/kg jujube extract plus morphine injection significantly increased the activity of cortical AchE compared to morphine injection alone (P<0.01). Conclusion: Jujube extract can prevent the side effects of morphine in the cortex by increasing antioxidant activity.

Neural basis of opioid-induced respiratory depression and its rescue

Opioid-induced respiratory depression (OIRD) causes death following an opioid overdose, yet the neurobiological mechanisms of this process are not well understood. Here, we show that neurons within the lateral parabrachial nucleus that express the μ-opioid receptor (PBLOprm1 neurons) are involved in OIRD pathogenesis. PBLOprm1 neuronal activity is tightly correlated with respiratory rate, and this correlation is abolished following morphine injection. Chemogenetic inactivation of PBLOprm1 neurons mimics OIRD in mice, whereas their chemogenetic activation following morphine injection rescues respiratory rhythms to baseline levels. We identified several excitatory G-protein coupled receptors expressed by PBLOprm1 neurons and show that agonists for these receptors restore breathing rates in mice experiencing OIRD. Thus, PBLOprm1 neurons are critical for OIRD pathogenesis, providing a promising therapeutic target for treating OIRD in patients.

Investigating the effect of Ultra-low dose naloxone on spinal BDNF and KCC2 cotransporter in morphine tolerant and hyperalgesia rats

Background: Chronic opioids administration could lead to several side effects including morphine tolerance and opioid induced hyperalgesia (OIH). Tolerance and hyperalgesia to opiates reduce their effectiveness in the treatment of severe pain. Although the mechanisms are unclear. Recently, we have shown that repeated morphine treatments induced increases in spinal PKCᵧ and GAT-1 expression. In this study we investigate the BDNF and KCC2 expression through ultra-low dose of naloxone coadministration of morphine.Results: In morphine group, rats received 10 mg i.p. morphine and in treatment group 15ng ultra-low dose of naloxone with morphine for consecutive 8 days. Behavioral tests were performed on day 1 before and after the morphine injection, day 5, 8 (tolerance test) and 10, 48h after last morphine injection (opioid induced hyperalgesia OIH test). A number of rats were sacrificed on day 8 and others on day 10, then expression of BDNF and KCC2 were analyzed by western blot and immunohistochemistry techniques, respectively. Behavioral tests suggested that following 8 days of chronic morphine injection tolerance developed. OIH was shown 48 hours after the last morphine injection. Expression of BDNF significantly was increased and KCC2 downregulated in rats that developed morphine tolerance and OIH respectively. Ultra-low dose of naloxone by decreasing BDNF and increasing KCC2 was able to suppress development of OIH and alleviated morphine tolerance.Conclusions: Our data suggest that BDNF and KCC2 maybe candidate molecules which are involved in tolerance and OIH. Ultra- low dose of naloxone along morphine might be a valuable therapeutic potential for controlling hypersensitivity following chronic morphine administration.