The role of nitric oxide in diabetes-induced changes of morphine tolerance in rats

Differential expression of H19, BC1, MIAT1, and MALAT1 long non-coding RNAs within key brain reward regions after repeated morphine treatment

Morphine-induced analgesic tolerance and dependence are significant limits of pain control; however, the exact molecular mechanisms underlying morphine tolerance and dependence have remained unclear. The role of long non-coding RNAs (lncRNAs) in morphine tolerance and dependence is yet to be determined. We aimed to explore the association of specific lncRNAs expression in key brain reward regions after repeated injection of morphine. Male Wistar rats received subcutaneous injections of twice-daily morphine (10 mg/kg) or saline (1 mL/kg) for eight days. On day 8 of the repeated injections, induction of morphine analgesic tolerance and dependence was confirmed through a hotplate test and a naloxone-precipitated withdrawal analysis, respectively. Expression of H19, BC1, MIAT1, and MALAT1 lncRNAs was determined from the midbrain, striatum, hypothalamus, prefrontal cortex (PFC), and hippocampus by real-time PCR on day 8 of the repeated injections. The H19 expression was significantly different between morphine-treated and control saline-treated rats in all investigated areas except for the hippocampus. The BC1 expression significantly altered in the midbrain, hypothalamus, and hippocampus, but not in the striatum and PFC after repeated morphine treatment. The MIAT1 and MALAT1 expression site-specifically altered in the midbrain, hypothalamus, and striatum; however, no significant changes were detected in their expression in the PFC and hippocampus after repeated morphine treatment. We conclude that alterations in the expression of these lncRNAs in the brain reward regions especially in the midbrain, striatum and hypothalamus may have critical roles in the development of morphine dependence and tolerance, which need to be considered in future researches.

The Mechanisms Involved in Morphine Addiction: An Overview

Opioid use disorder is classified as a chronic recurrent disease of the central nervous system (CNS) which leads to personality disorders, co-morbidities and premature death. It develops as a result of long-term administration of various abused substances, along with morphine. The pharmacological action of morphine is associated with its stimulation of opioid receptors. Opioid receptors are a group of G protein-coupled receptors and activation of these receptors by ligands induces significant molecular changes inside the cell, such as an inhibition of adenylate cyclase activity, activation of potassium channels and reductions of calcium conductance. Recent data indicate that other signalling pathways also may be involved in morphine activity. Among these are phospholipase C, mitogen-activated kinases (MAP kinases) or β-arrestin. The present review focuses on major mechanisms which currently are considered as essential in morphine activity and dependence and may be important for further studies.

Role of hydrogen sulfide in skeletal muscle biology and metabolism

Hydrogen sulfide (H2S) is a novel endogenous gaseous signal transducer (gasotransmitter). Its emerging role in multiple facets of inter- and intra-cellular signaling as a metabolic, inflammatory, neuro and vascular modulator has been increasingly realized. Although H2S is known for its effects as an anti-hypertensive, anti-inflammatory and anti-oxidant molecule, the relevance of these effects in skeletal muscle biology during health and during metabolic syndromes is unclear. H2S has been implicated in vascular relaxation and vessel tone enhancement, which might lead to mitigation of vascular complications caused by the metabolic syndromes. Metabolic complications may also lead to mitochondrial remodeling by interfering with fusion and fission, therefore, leading to mitochondrial mitophagy and skeletal muscle myopathy. Mitochondrial protection by H2S enhancing treatments may mitigate deterioration of muscle function during metabolic syndromes. In addition, H2S might upregulate uncoupling proteins and might also cause browning of white fat, resulting in suppression of imbalanced cytokine signaling caused by abnormal fat accumulation. Likewise, as a source for H(+) ions, it has the potential to augment anaerobic ATP synthesis. However, there is a need for studies to test these putative H2S benefits in different patho-physiological scenarios before its full-fledged usage as a therapeutic molecule. The present review highlights current knowledge with regard to exogenous and endogenous H2S roles in skeletal muscle biology, metabolism, exercise physiology and related metabolic disorders, such as diabetes and obesity, and also provides future directions.

Zimelidine attenuates the development of tolerance to morphine-induced antinociception

OBJECTIVES

The aim of this study was to investigate effect of zimelidine (a serotonin reuptake inhibitor) on morphine-induced tolerance in rats.

MATERIALS AND METHODS

Male Wistar albino rats weighing 160-180 g were used in these experiments (n=72). A 3-day cumulative dosing regimen was used for the induction of morphine tolerance. To constitute of morphine tolerance, animals received morphine twice daily for 3 days. After the last dose morphine was injected on the fourth day, morphine tolerance was evaluated. The analgesic effects of zimelidine (15 mg/kg; i.p.) and morphine (5 mg/kg) were considered at 30-min time intervals (0, 30, 60, 90 and 120 min) by tail-flick and hot-plate analgesiometer (n=6 in each experimental group).

RESULTS

The results showed that zimelidine significantly attenuated the development and expression of morphine tolerance. The maximal antinociceptive effect of zimelidine was obtained at the 60 minutes measurements in the zimelidine group and at the 30 minutes measurements in the morphine tolerant group by the tail-flick and hot-plate tests. Administration of zimelidine with morphine showed additive analgesic effect.

CONCLUSION

In conclusion, our results show that zimelidine reduces the development of tolerance to morphine-induced antinociception in rats.

The inhibition of the nitric oxide-cGMP-PKG-JNK signaling pathway avoids the development of tolerance to the local antiallodynic effects produced by morphine during neuropathic pain

Tolerance to the local antiallodynic effects of morphine, DPDPE ([D-Pen(2),D-Pen(5)]-Enkephalin) or JWH-015 ((2-methyl-1-propyl-1H-indol-3-yl)-1-naphthalenylmethanone) after their repeated administration during neuropathic pain was evaluated. The role of the nitric oxide-cGMP-protein kinase G (PKG)-c-Jun N-terminal kinase (JNK) signaling pathway on the peripheral morphine-induced tolerance after the chronic constriction of sciatic nerve in mice was also assessed. The mechanical and thermal antiallodynic effects produced by a high dose of morphine, DPDPE or JWH-015 subplantarly administered daily from days 10 to 20 after nerve injury were estimated with the von Frey filaments and cold plate tests. The antiallodynic effects of the repeated administration of morphine combined with a sub-analgesic dose of a selective inducible nitric oxide synthase (NOS2) (L-N(6)-(1-iminoethyl)-lysine; L-NIL), L-guanylate cyclase (1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one; ODQ), PKG ((Rp)-8-(para-chlorophenylthio)guanosine-3',5'-cyclic monophosphorothioate; Rp-8-pCPT-cGMPs) or JNK (anthra[1,9-cd]pyrazol-6(2H)-one; SP600125) inhibitor from days 10 to 20 after injury were also evaluated. The repeated administration of morphine, but not DPDPE or JWH-015, produced a rapid development of tolerance to its mechanical and thermal antiallodynic effects in sciatic nerve-injured mice. The co-administration of morphine with L-NIL, ODQ, Rp-8-pCPT-cGMPs or SP600125 avoided the development of morphine antiallodynic tolerance after nerve injury. These findings reveal that the repeated local administration of DPDPE or JWH-015 did not induce antinociceptive tolerance after sciatic nerve injury-induced neuropathic pain. Our data also indicate that the peripheral nitric oxide-cGMP-PKG-JNK signaling pathway participates in the development of morphine tolerance after nerve injury and propose the inactivation of this pathway as a promising strategy to avoid morphine tolerance during neuropathic pain.

Protective effect and potential mechanism of Ginkgo biloba extract EGb 761 on STZ-induced neuropathic pain in rats

Diabetes induced neuropathic pain is recognized as one of the most difficult types of pain to treat with conventional analgaesics. EGb 761 is a standardized extract of Ginkgo biloba that has analgaesic and antiinflammatory properties and modulatory effects on key pain-related molecules. We examined the effect of EGb 761 on streptozotocin (STZ)-induced neuropathic pain behaviours and assessed its mechanism of action. Streptozotocin (20 mg/kg i.p for 5 days) was administered to induce experimental diabetes. Pain hypersensitivity to radiant heat was measured using the Dynamic Plantar Aesthesiometer to test the pain threshold. Diabetic rats exhibited mechanical allodynia and thermal hyperanalgaesia after the third week of STZ injection and concomitantly increased thiobarbituric acid reactive substance and nitric oxide concentration. The antioxidant enzymes level of superoxide dismutase and catalase was markedly reduced in STZ-diabetic rats (p < 0.05). Systemic administration of EGb 761 (25, 50 and 100 mg/kg), starting after the third week following STZ injection, dose-dependently reversed STZ-induced thermal hyperanalgaesia and mechanical allodynia. Moreover, it reduced oxidonitrosative stress and concomitantly restored the level of antioxidant enzymes (p < 0.05) as compared with untreated diabetic rats. These results suggest that EGb 761 attenuated STZ-induced neuropathic pain behaviours by inhibiting oxidative and nitrosative stress and may constitute a new approach for treatment of painful diabetic neuropathy.

Possible mechanism of protective effect of thalidomide in STZ-induced-neuropathic pain behavior in rats

INTRODUCTION

Diabetes-induced neuropathic pain is recognized as one of the most difficult type of pain to treat and conventional analgesics are well known to be partially effective or associated with potential toxicity. Recently, it has been demonstrated that thalidomide, besides its teratogenic potential, reduced chronic pain in an SNL experimental pain model.

OBJECTIVE

The present study was designed to investigate the effect of thalidomide on streptozotocin (STZ)-induced neuropathic pain in rats.

MATERIALS AND METHODS

Streptozotocin (20 mg/kg, i.p, daily × 4 days) was administered to induce diabetes in the rats. Nociceptive latency was measured using tail-flick and paw-withdrawal test. Thermal hyperalgesia and mechanical allodynia were measured using planter test and dynamic aesthesiometer (Ugo-Basile, Italy), respectively. Urinary and serum nitrite concentration was estimated using Greiss reagent method. Spleen homogenate supernatant was prepared from spleen of 28th day diabetic rats and administered to normal rats (400 ul, i.v) daily for 28 days.

RESULTS

Pain threshold progressively decreased in STZ-treated rats, as compared with control rats. 3 weeks after induction of diabetes, the rat exhibited thermal hyperalgesia and mechanical allodynia. The analgesic effect of morphine (8 mg/kg, s.c.) was significantly decreased in both diabetic and in SHS-treated non-diabetic rats. Administration of thalidomide (25 and 50 mg/kg, i.p), a TNF-α inhibitor, significantly prevented hyperglycemia-induced thermal hyperalgesia and mechanical allodynia and also attenuated the increase in serum and urinary nitrite concentration, as compared with untreated diabetic rats. Also, thalidomide (25 and 50 mg/kg, i.p) 1 h before or concurrently with morphine significantly restored the analgesic effect of morphine in diabetic rats.

CONCLUSION

It may be concluded that thalidomide has a beneficial effect in neuropathic pain by decreasing cytokines (TNF-α) and nitric oxide level and may provide a novel promising therapeutic approach for managing painful diabetic neuropathy.

Effects of alpha 2-adrenoceptor agonists dexmedetomidine and guanfacine on morphine analgesia and tolerance in rats

BACKGROUND

Alpha 2 (α(2))-adrenoceptor agonists may be useful for their potential to increase or prolong opioid analgesia while attenuating the development of opioid tolerance. The purpose of this study was to investigate the effects of dexmedetomidine and guanfacine (α(2)-adrenoceptor agonists) on morphine analgesia and tolerance in rats.

METHODS

Adult male Wistar albino rats weighing 195-205 g were used. To constitute morphine tolerance, animals received morphine (50 mg/kg) once daily for 3 days. After the last dose of morphine had been injected on day 4, morphine tolerance was evaluated by analgesia tests. The analgesic effects of dexmedetomidine (20 ug/kg), guanfacine (0.5 mg/kg), MK-467 (0.25 mg/kg), and morphine were estimated at 30-min intervals (0, 30, 60, 90, and 120 min) by tail-flick and hot-plate analgesia tests.

RESULTS

Our findings indicate that dexmedetomidine and guanfacine attenuated the expression of morphine tolerance. In addition, administration of dexmedetomidine with morphine increased morphine analgesia. On the contrary, data suggested that MK-467 (an α(2)-adrenoceptor antagonist) decreased morphine analgesia and increased morphine tolerance in analgesia tests.

CONCLUSION

In conclusion, we observed that co-injection of dexmedetomidine or guanfacine with morphine attenuated the expression of tolerance to the analgesic effect of morphine and that dexmedetomidine enhanced the morphine analgesia.

The nitric oxide-cGMP signaling pathway plays a significant role in tolerance to the analgesic effect of morphine

Although the phenomenon of opioid tolerance has been widely investigated, neither opioid nor nonopioid mechanisms are completely understood. The aim of the present study was to investigate the role of the nitric oxide (NO)-cyclic guanosine monophosphate (cGMP) pathway in the development of morphine-induced analgesia tolerance. The study was carried out on male Wistar albino rats (weighing 180-210 g; n = 126). To develop morphine tolerance, animals were given morphine (50 mg/kg; s.c.) once daily for 3 days. After the last dose of morphine was injected on day 4, morphine tolerance was evaluated. The analgesic effects of 3-(5'-hydroxymethyl-2'-furyl)-1-benzylindazole (YC-1), BAY 41-2272, S-nitroso-N-acetylpenicillamine (SNAP), N(G)-nitro-L-arginine methyl ester (L-NAME), and morphine were considered at 15 or 30 min intervals (0, 15, 30, 60, 90, and 120 min) by tail-flick and hot-plate analgesia tests (n = 6 in each study group). The results showed that YC-1 and BAY 41-2272, a NO-independent activator of soluble guanylate cyclase (sGC), significantly increased the development and expression of morphine tolerance, and L-NAME, a NO synthase (NOS) inhibitor, significantly decreased the development of morphine tolerance. In conclusion, these data demonstrate that the nitric oxide-cGMP signal pathway plays a pivotal role in developing tolerance to the analgesic effect of morphine.

Synthesis, conformation, and biological characterization of a sugar derivative of morphine that is a potent, long-lasting, and nontolerant antinociceptive

A synthetic mannoside derivative, namely, 6-morphinyl-alpha-D-mannopyranoside, shows a naloxone-reversible antinociception that is 100-fold more potent and twice as long lasting compared to morphine when administered intraperitoneally to rats in paw pressure and tail flick tests. The compound does not produce tolerance and binds to rat mu opioid receptors with twice the affinity of morphine. NMR studies suggest that differences of activity between the derivative and its parent compound M6G might be related to their differing molecular dynamic behavior.

Analytical chemistry of nitric oxide

Nitric oxide (NO) is the focus of intense research primarily because of its wide-ranging biological and physiological actions. To understand its origin, activity, and regulation, accurate and precise measurement techniques are needed. Unfortunately, analytical assays for monitoring NO are challenged by NO's unique chemical and physical properties, including its reactivity, rapid diffusion, and short half-life. Moreover, NO concentrations may span the picomolar-to-micromolar range in physiological milieus, requiring techniques with wide dynamic response ranges. Despite such challenges, many analytical techniques have emerged for the detection of NO. Herein, we review the most common spectroscopic and electrochemical methods, with a focus on the underlying mechanism of each technique and on approaches that have been coupled with modern analytical measurement tools to create novel NO sensors.

Endogenous opiates and behavior: 2007

This paper is the thirtieth consecutive installment of the annual review of research concerning the endogenous opioid system. It summarizes papers published during 2007 that studied the behavioral effects of molecular, pharmacological and genetic manipulation of opioid peptides, opioid receptors, opioid agonists and opioid antagonists. The particular topics that continue to be covered include the molecular-biochemical effects and neurochemical localization studies of endogenous opioids and their receptors related to behavior, and the roles of these opioid peptides and receptors in pain and analgesia; stress and social status; tolerance and dependence; learning and memory; eating and drinking; alcohol and drugs of abuse; sexual activity and hormones, pregnancy, development and endocrinology; mental illness and mood; seizures and neurologic disorders; electrical-related activity and neurophysiology; general activity and locomotion; gastrointestinal, renal and hepatic functions; cardiovascular responses; respiration and thermoregulation; and immunological responses.