The spinal nitric oxide involved in the inhibitory effect of midazolam on morphine-induced analgesia tolerance

Contribution of Opioid and Nitrergic Systems to m-Trifluoromethyl diphenyl Diselenide Attenuates Morphine-Induced Tolerance in Mice

m-Trifluoromethyl diphenyl diselenide (TFDD) has antinociceptive and antidepressant-like properties and attenuates morphine withdrawal signs in mice. This study investigated if TFDD affects the development of morphine tolerance to its antinociceptive and antidepressant-like effects in mice. We also investigated whether TFDD modulates signaling pathways related to morphine tolerance, including the opioid receptors and some parameters of the nitrergic system. Male adult Swiss mice received morphine alone (5 mg/kg, subcutaneous) and in combination with TFDD (10 mg/kg, intragastric) for 7 days. Mice were subjected to hot plate and forced swim tests on days 1, 3, 5, and 7 of the experimental protocol. Repeated TFDD administrations avoided tolerance development mediated by morphine, including its antinociceptive and antidepressant-like effects. A single morphine dose increased MOR and NOx but decreased iNOS contents in the mouse cerebral cortex. In turn, single morphine and TFDD co-administration restored the MOR and iNOS protein levels. On the other hand, morphine repeated doses enhanced DOR and reduced MOR and NOx contents, whereas the morphine and TFDD association reestablished DOR and NOx levels in the mouse cerebral cortex. In conclusion, some opioid and nitrergic system parameters might contribute to TFDD attenuation of antinociceptive and antidepressant-like tolerance induced by morphine in mice.

Nitric oxide modulates tapentadol antinociceptive tolerance and physical dependence

Tapentadol, an analgesic with a dual mechanism of action, involving both μ-opioid receptor agonism and noradrenaline reuptake inhibition (MOP-NRI), was designed for the treatment of moderate to severe pain. However, the widely acknowledged risk of analgesic tolerance and development of physical dependence following sustained opioid use may hinder their effectiveness. One of the possible mechanisms behind these phenomena are alterations in nitric oxide synthase (NOS) system activity. The aim of the study was to investigate the tolerance and dependence potential of tapentadol in rodent models and to evaluate the possible role of nitric oxide (NO) in these processes. Our study showed that chronic tapentadol treatment resulted in tolerance to its antinociceptive effects to an extent similar to tramadol, but much less than morphine. A single injection of a non-selective NOS inhibitor, N^G-nitro-L-arginine (L-NOArg), reversed the tapentadol tolerance. In dependence studies, repeated administration of L-NOArg attenuated naloxone-precipitated withdrawal in tapentadol-treated mice, whereas a single injection of L-NOArg was ineffective. Biochemical analysis revealed that tapentadol decreased nNOS protein levels in the dorsal root ganglia of rats following 31 days of treatment, while no significant changes were found in iNOS and eNOS protein expression. Moreover, pre-treatment with L-NOArg augmented tapentadol antinociception in an opioid- and α₂-adrenoceptor-dependent manner. In conclusion, our data suggest that the NOS system plays an important role in the attenuation of tapentadol-induced tolerance and withdrawal. Thus, inhibition of NOS activity can serve as a promising treatment option for long-term tapentadol use by extending its effectiveness and improving the side-effects profile.

Venlafaxine inhibits naloxone-precipitated morphine withdrawal symptoms: Role of inflammatory cytokines and nitric oxide

Opioid-induced neuroinflammation plays a role in the development of opioid physical dependence. Moreover, nitric oxide (NO) has been implicated in several oxidative and inflammatory pathologies. Here, we sought to determine whether treatment with venlafaxine during the development of morphine dependence could inhibit naloxone-precipitated withdrawal symptoms. The involvement of neuro-inflammation related cytokines, oxidative stress, and L-arginine (L-arg)-NO pathway in these effects were also investigated. Mice received morphine (50 mg/kg/daily; s.c.), plus venlafaxine (5 and 40 mg/kg, i.p.) once a day for 3 consecutive days. In order to evaluate the possible role of L-arg-NO on the effects caused by venlafaxine, animals received L-arg, L-NAME or aminoguanidine with venlafaxine (40 mg/kg, i.p.) 30 min before each morphine injection for 3 consecutive days. On 4^th day of experiment, behavioral signs of morphine-induced physical dependence were evaluated after i.p. naloxone injection. Then, brain levels of tissue necrosis factor-alpha (TNF-α), interleukin-1-beta (IL-1β), interleukin-6 (IL-6), interleukin-10 (IL-10), brain-derived neurotrophic factor (BDNF), NO and oxidative stress factors including; total thiol, malondialdehyde (MDA) contents and glutathione peroxidase (GPx) activity were determined. Co-administration of venlafaxine (40 mg/kg) with morphine not only inhibited the naloxone-precipitated withdrawal signs including jumping and weight loss, but also reduced the up-regulation of TNF-α, IL-1β, IL-6, NO and MDA contents in mice brain tissue. However, repeated administration of venlafaxine inhibited the decrease in the brain levels of BDNF, total thiol and GPx. Pre-administration of L-NAME and aminoguanidine improved, while L-arg antagonized the venlafaxine-induced effects. These results provide evidences that venlafaxine could be used as a candidate drug to inhibit morphine withdrawal through the involvement of inflammatory cytokines and l-arginine-NO in mice.

The effect of metformin on morphine analgesic tolerance and dependence in rats

Opiate tolerance and dependence is a worldwide public health problem and gives a significant burden to society. The aim of this study was to evaluate the effects of metformin (MET) on development and expression of morphine tolerance and dependence in rats. For induction of tolerance, morphine sulfate was injected (10 mg/kg, twice a day, s.c.) for 7 days. Animals received metformin (5 and 50 mg/kg, orally, daily) during the examination period for assessing the development of morphine tolerance and dependence. In order to evaluate the expression of morphine tolerance and dependence, single doses of MET (5 and 50 mg/kg, orally) were administered on day 7. Tail flick test was performed to assess the induction of morphine tolerance. For evaluation of morphine dependence, naloxone-induced jumping (5 mg/kg, s.c.) was monitored. Our results showed that 7 days coadministration of 50 mg/kg of MET significantly reduced the development of morphine analgesic tolerance versus morphine + saline treated rats (P < 0.001). Treatment with 50 mg/kg MET reduced the incidence and frequency of jumping in naloxone injected animals (P < 0.01). It is notable that single dose administration of MET, did not prevent the expression of analgesic tolerance and physical dependence to morphine. Based on these results, it can be concluded that MET attenuates the development of morphine analgesic tolerance and dependence in rats.

Pharmacokinetics cannot explain the increased effective dose requirement for morphine and midazolam in rats during their extended administration alone or in combination

Objectives

Chronic administration of morphine and midazolam, alone or in combination, can induce tolerance to their effects. Data showed that co-administration of morphine and midazolam increased effective dose requirement of morphine, exceeding that observed with morphine alone.

Methods

To elucidate the pharmacokinetic component to the tolerance, we administered midazolam (2 mg/kg) and morphine (10 mg/kg) alone or their combination daily to rats for 12 days followed by a pharmacokinetic study on day 13. On the study day, each animal received a single bolus dose of 5 mg/kg morphine, and 2 mg/kg of midazolam 30 s later. Multiple blood samples were obtained for 6 h. Plasma drug concentrations were assayed by mass spectrometry optimized for small samples.

Key findings

Mean morphine clearance was as follows: 22.2, 27.2, 26.0 and 23.4 l/h per kg in the saline–saline, saline–midazolam, saline–morphine and midazolam–morphine groups, respectively. Corresponding midazolam clearances were 32.8, 23.0, 22.2 and 31.1 l/h per kg. ANOVA indicated no significant differences among the four groups in the clearances, half-lives, and volumes of distribution. Morphine and midazolam clearances were significantly correlated (R2 = 0.48, P &lt; 0.001).

Conclusions

This animal model suggests that altered pharmacokinetics cannot explain tolerance evidenced as increased dose requirement for morphine or midazolam, when administered alone or combination, for extended periods.

Dual effect of cAMP agonist on ameliorative function of PKA inhibitor in morphine-dependent mice

The present study shows interactive effects of bucladesine (db-cAMP) as a cyclic adenosine monophosphate (cAMP) agonist and H-89 as a protein kinase A (PKA) inhibitor on naloxone-induced withdrawal signs in morphine-dependent mice. Animals were treated subcutaneously with morphine thrice daily with doses progressively increased from 50 to 125 mg/kg. A last dose of morphine (50 mg/kg) was administered on the 4th day. Several withdrawal signs were precipitated by intraperitoneal (i.p.) administration of naloxone (5 mg/kg). Different doses of bucladesine (50, 100, 200 nm/mouse) and H-89 (0.05, 0.5, 1, 5 mg/kg) were administered (i.p.) 60 min before naloxone injection. In combination groups, bucladesine was injected 15 min before H-89 injection. Single administration of H-89 (0.5, 1, 5 mg/kg) and bucladesine (50, 100 nm/mouse) significantly attenuated prominent behavioral signs of morphine withdrawal. Lower doses of bucladesine (50, 100 nm/mouse) in combination with H-89 (0.05 mg/kg) increased the inhibitory effects of H-89 on withdrawal signs while in high dose (200 nm/mouse) decreased the ameliorative function of H-89 (0.05 mg/kg) in morphine-dependent animals. It is concluded that H-89 and bucladesine could affect morphine withdrawal syndrome via possible interaction with cyclic nucleotide messengering systems, protein kinase A signaling pathways, and modified related neurotransmitters.

Functional differences between neurochemically defined populations of inhibitory interneurons in the rat spinal dorsal horn

In order to understand how nociceptive information is processed in the spinal dorsal horn we need to unravel the complex synaptic circuits involving interneurons, which constitute the vast majority of the neurons in laminae I-III. The main limitation has been the difficulty in defining functional populations among these cells. We have recently identified 4 non-overlapping classes of inhibitory interneuron, defined by expression of galanin, neuropeptide Y (NPY), neuronal nitric oxide synthase (nNOS) and parvalbumin, in the rat spinal cord. In this study we demonstrate that these form distinct functional populations that differ in terms of sst(2A) receptor expression and in their responses to painful stimulation. The sst(2A) receptor was expressed by nearly all of the nNOS- and galanin-containing inhibitory interneurons but by few of those with NPY and none of the parvalbumin cells. Many galanin- and NPY-containing cells exhibited phosphorylated extracellular signal-regulated kinases (pERK) after mechanical, thermal or chemical noxious stimuli, but very few nNOS-containing cells expressed pERK after any of these stimuli. However, many nNOS-positive inhibitory interneurons up-regulated Fos after noxious thermal stimulation or injection of formalin, but not after capsaicin injection. Parvalbumin cells did not express either activity-dependent marker following any of these stimuli. These results suggest that interneurons belonging to the NPY, nNOS and galanin populations are involved in attenuating pain, and for NPY and nNOS cells this is likely to result from direct inhibition of nociceptive projection neurons. They also suggest that the nociceptive inputs to the nNOS cells differ from those to the galanin and NPY populations.

Pioglitazone potentiates development of morphine-dependence in mice: possible role of NO/cGMP pathway

Peroxizome proliferator-activated receptor gamma (PPARγ) is highly expressed in the central nervous system where it modulates numerous gene transcriptions. Nitric oxide synthase (NOS) expression could be modified by simulation of PPARγ which in turn activates nitric oxide (NO)/soluble guanylyl-cyclase (sGC)/cyclic guanosine mono phosphate (cGMP) pathway. It is well known that NO/cGMP pathway possesses pivotal role in the development of opioid dependence and this study is aimed to investigate the effect of PPARγ stimulation on opioid dependence in mice as well as human glioblastoma cell line. Pioglitazone potentiated naloxone-induced withdrawal syndrome in morphine dependent mice in vivo. While selective inhibition of PPARγ, neuronal NOS or GC could reverse the pioglitazone-induced potentiation of morphine withdrawal signs; sildenafil, a phosphodiesterase-5 inhibitor amplified its effect. We also showed that nitrite levels in the hippocampus were significantly elevated in pioglitazone-treated morphine dependent mice. In the human glioblastoma (U87) cell line, rendered dependent to morphine, cAMP levels did not show any alteration after chronic pioglitazone administration while cGMP measurement revealed a significant rise. We were unable to show a significant alteration in neuronal NOS mRNA expressions by pioglitazone in mice hippocampus or U87 cells. Our results suggest that pioglitazone has the ability to enhance morphine-dependence and to augment morphine withdrawal signs. The possible pathway underlying this effect is through activation of NO/GC/cGMP pathway.

The role of cyclo-oxygenase inhibitors in attenuating opioid-induced tolerance, hyperalgesia, and dependence

There is no denying that opioids are the most important analgesic drugs which are widely used in clinical situations. Still, prolonged administration of these drugs can cause to reduce their analgesic efficacy due to the development of tolerance. These drugs can also cause induction of hyperalgesia. In addition, long-term administration of opioids through reinforcing- and rewarding pathways of limbic system can result in expression of opioid dependence with the unintended consequences of opioid abuse/misuse and finally opioid addiction. As studies show, over-activity in cyclo-oxygenase pathways and production of prostaglandins due to long-term exposures of opioid have a critical role in the development of tolerance to antinociceptive effect of opioid, hyperalgesia, and opioid dependence. The present study aims at suggesting the hypothesis that through blending a non-steroid anti-inflammatory drug with opioid actively causes reduction in unwanted effects of opioid i.e. by inhibition of opioid-induced cyclo-oxygenase overactivity whereas it is well-known that the combination therapy via reducing opioid dosage reduces the unwanted effects.

Expression of nitric oxide synthase isoforms in the dorsal horn of monoarthritic rats: effects of competitive and uncompetitive N-methyl-D-aspartate antagonists

Chronic pain is associated with N-methyl-D-aspartate (NMDA) receptor activation and downstream production of nitric oxide, which has a pivotal role in multisynaptic local circuit nociceptive processing in the spinal cord. The formation of nitric oxide is catalyzed by three major nitric oxide synthase (NOS) isoforms (neuronal, nNOS; inducible, iNOS; endothelial, eNOS), which are increased in the spinal cord of rodents subjected to some tonic and chronic forms of experimental pain. Despite the important role of NOS in spinal cord nociceptive transmission, there have been no studies exploring the effect of NMDA receptor blockade on NOS expression in the dorsal horn during chronic pain. Furthermore, NOS isoforms have not been fully characterized in the dorsal horn of animals subjected to arthritic pain. The aim of this work was therefore to study the expression of nNOS, iNOS and eNOS in the dorsal horns of monoarthritic rats, and the modifications in NOS expression induced by pharmacological blockade of spinal cord NMDA receptors. Monoarthritis was produced by intra-articular injection of complete Freund's adjuvant into the right tibio-tarsal joint. At week 4, monoarthritic rats were given either the competitive NMDA antagonist (±)-3-(2-carboxypiperazin-4-yl)-propyl-1-phosphonic acid (CPP) or the uncompetitive NMDA antagonist ketamine. After 6 and 24 hours, animals were killed and posterior quadrants of the lumbar spinal cord were dissected. Sample tissues were homogenized and subjected to immunoblotting with anti-nNOS, anti-iNOS or anti-eNOS monoclonal antibodies. The nNOS isoform, but not the iNOS and eNOS isoforms, were detected in the dorsal horns of control rats. Monoarthritis increased the expression of nNOS, iNOS and eNOS in the dorsal horns ipsilateral and contralateral to the inflamed hindpaw. Intrathecal administration of CPP and ketamine reduced nNOS expression in monoarthritic rats but increased the expression of iNOS and eNOS. Results suggest that blockade of spinal cord NMDA receptors produces complex regulatory changes in the expression of NOS isoforms in monoarthritic rats that may be relevant for nitridergic neuronal/glial mechanisms involved in the pathophysiology of monoarthritis and in the pharmacological response to drugs interacting with NMDA receptors.

Bee venom injection produces a peripheral anti-inflammatory effect by activation of a nitric oxide-dependent spinocoeruleus pathway

Our recent data, obtained using a zymosan-induced inflammatory air pouch model in mice, have demonstrated that subcutaneous bee venom (BV) injection into the hind limb selectively activates the contralateral brain stem locus coeruleus (LC) and then via a descending noradrenergic pathway and subsequent adrenal medullary catecholamine release induces a potent anti-inflammatory effect. While the efferent limb of this BV-induced neuroimmune anti-inflammatory pathway is well documented, the afferent limb of this pathway is poorly understood. In particular the spinal mechanisms involved with BV activation of the LC are currently unknown. Spinal nitric oxide (NO) and its synthase (NOS) have been shown to play an important role in the transmission and amplification of neuronal information from the spinal cord to the brain stem. In the present study we evaluated whether spinal NO plays a role in BV-induced LC activation, since we have previously shown that LC activation underlies this 'BV-induced anti-inflammatory effect' (BVAI) using the mouse air pouch model. Intrathecal (i.t.) pretreatment with l-nitro arginine methyl ester (l-NAME, non-selective NOS inhibitor), hemoglobin (NO scavenger) or 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one (ODQ, soluble guanylate cyclase inhibitor) abolished BVAI on zymosan-induced leukocyte migration into the air pouch. Moreover, i.t. injection of l-N-iminoethyl-lysine (l-NIL, inducible NOS inhibitor), but not 7-nitroindazole (7-NI, neuronal NOS inhibitor), also inhibited BVAI. BV injection significantly increased both the number of Fos immunoreactive neurons and tyrosine hydroxylase-Fos double labeling neurons in the contralateral LC in zymosan-induced inflamed mice. Importantly this increase in Fos expression in the LC was also completely inhibited by i.t. injection of l-NIL, but not by i.t. injection of 7-NI. Collectively these results indicate that spinal NO generated from inducible NOS is involved in the BV-induced LC activation that underlies BVAI.

Endogenous opiates and behavior: 2005

This paper is the 28th consecutive installment of the annual review of research concerning the endogenous opioid system, now spanning over a quarter-century of research. It summarizes papers published during 2005 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 (Section 2), and the roles of these opioid peptides and receptors in pain and analgesia (Section 3); stress and social status (Section 4); tolerance and dependence (Section 5); learning and memory (Section 6); eating and drinking (Section 7); alcohol and drugs of abuse (Section 8); sexual activity and hormones, pregnancy, development and endocrinology (Section 9); mental illness and mood (Section 10); seizures and neurologic disorders (Section 11); electrical-related activity, neurophysiology and transmitter release (Section 12); general activity and locomotion (Section 13); gastrointestinal, renal and hepatic functions (Section 14); cardiovascular responses (Section 15); respiration and thermoregulation (Section 16); immunological responses (Section 17).

Cross talk between nitric oxide and ERK1/2 signaling pathway in the spinal cord mediates naloxone-precipitated withdrawal in morphine-dependent rats

Our recent study has shown activation of spinal extracellular signal-regulated kinase-1 and -2 (ERK1/2), a member of the mitogen-activated protein kinase (MAPK) family, contributes to naloxone-precipitated withdrawal and withdrawal-induced spinal neuronal sensitization in morphine-dependent rats. However, the mechanism and significance of the spinal ERK1/2 activation during morphine dependence and withdrawal remain unknown. In this study, we reported that intrathecal (i.t.) pretreatment with either the non-selective nitric oxide synthase (NOS) inhibitor N(G)-nitro-L-arginine methyl ester (L-NAME), neuronal NOS (nNOS) inhibitor 7-nitro indazole (7-NI), or the inducible NOS (iNOS) inhibitor aminoguanidine (AG), could reduce morphine withdrawal-induced increase of phospho-ERK1/2 (pERK1/2) expression in the rat spinal cord. On the other hand, attenuation of the spinal ERK phosphorylation by the MAPK kinase (MEK) inhibitor U0126 also could inhibit the increase of nNOS and iNOS expression in the spinal cord of morphine withdrawal rats. Inhibitory expression of pERK1/2 by i.t. NOS inhibitor L-NAME, 7-NI or AG and of nNOS and iNOS by i.t. U0126 in the spinal cord were accompanied by decreased scores of morphine withdrawal and the inhibited spinal Fos protein (a maker for neuronal excitation or activation) expression induced by morphine withdrawal. These findings suggest cross talk between nitric oxide (NO) and the ERK1/2 signaling pathway mediates morphine withdrawal and withdrawal-induced spinal neuronal sensitization in morphine-dependent rats.