Development Of Morphine-induced Analgesic Tolerance Research Articles

Chronic morphine induces cyclic adenosine monophosphate formation and hyperpolarization-activated cyclic nucleotide-gated channel expression in the spinal cord of mice

Chronic morphine exposure persistently activates Gαi/o protein-coupled receptors and enhances adenylyl cyclase (AC) activity, which can increase cyclic adenosine monophosphate (cAMP) production. Direct binding of cAMP to the cytoplasmic site on hyperpolarization-activated cyclic nucleotide-gated (HCN) channels increases the probability of channel opening. HCN channels play a prominent role in chronic pain the disease that shares some common mechanisms with opioid tolerance. This compensatory AC activation may be responsible for the induction of morphine-induced analgesic tolerance. We investigated spinal cAMP formation and expression of HCN2 in the spinal cord, and observed the effect of AC inhibition on the induction of morphine analgesic tolerance. We found that chronic morphine-induced antinociceptive tolerance increased spinal cAMP formation and the expression of spinal HCN2. Inhibition of spinal AC partially blocked chronic morphine-induced cAMP formation and prevented the induction of morphine-induced analgesic tolerance. Inhibition of HCN2 also showed a partial preventive effect on morphine-induced tolerance, hypothermia tolerance and also the right-shift of the dose-response curve. We conclude that repeated morphine treatment increases AC activity and cAMP formation, and also spinal HCN2 expression, blockade of AC or HCN2 can prevent the development of morphine-induced analgesic tolerance.

Blockade of peripheral nociceptive signal input relieves the formation of spinal central sensitization and retains morphine efficacy in a neuropathic pain rat model

Neural plasticity, especially central sensitization, is essential for developing and maintaining neuropathic pain. Unfortunately, the analgesic potency of morphine is greatly reduced in animal models and patients with neuropathic pain. We hypothesized that pre-activation of spinal N-methyl-d-aspartate receptors (NMDARs) by agonist or neuropathic pain facilitated the development of morphine-induced analgesic tolerance. We therefore investigated the effects of spinal NMDAR activation, induced by neuropathic pain, on the development of morphine-induced analgesic tolerance in male Sprague-Dawley rats. Four days of chronic constriction injury (CCI) induced upregulation of spinal NR1. Once established, spinal central sensitization accelerated the development of morphine-induced analgesic tolerance. Continuous ropivacaine infusion prevented CCI-induced increases in spinal Substance P (SP), NR1, and TRPV1. Blockade of peripheral nociceptive inputs prevented chronic morphine-induced increases in spinal SP, NR1, and TRPV1 and a rightward shift of the morphine dose-response curve in the CCI model. These findings suggest that pre-activation of spinal NMDARs contributes to central sensitization and potentiates the development of morphine-induced analgesic tolerance. Interruption of the peripheral nociceptive inputs during the induction phase could prevent spinal central sensitization and retain morphine efficacy, thereby delaying the development of morphine-induced tolerance in patients with neuropathic conditions.

Evaluation of the effects of metformin administration on morphine tolerance in mice

Opioids are used in clinical practice to relieve moderate to severe pain. Prolonged use of opioids can lead to a situation of analgesic tolerance and dependence. Several mechanisms are involved in the tolerance to analgesic opioids, including desensitization or internalization of the opioid receptor, elevation of cAMP levels, microglial activation and neuroinflammation, elevation of spinal mTOR activity and change in the expression of some proteins involved in tolerance, such as nNOS. Activation of the AMPK pathway inhibits mTOR and p38 MAPK ameliorating neuroinflammation and tolerance induced by morphine. Metformin, a potent antidiabetic agent, can also activate AMPK.Morphine tolerance was induced in mice by intraperitoneal administration three times daily at 08:00, 11.00 and 16.00 h of 50, 50 and 75 mg/kg morphine, respectively during four days. On the fifth day mice received a single injection of morphine 50 mg/kg. To evaluate the effects of metformin in development of morphine-induced analgesic tolerance a group of mice received metformin (10 mg/kg) 45 min before each morphine administration. Tail flick and hot plate tests were performed to estimate analgesic latency on days 1, 3 and 5. At five days, the animals were sacrificed, the brain dissected and nitrite levels determined.Chronic metformin administration significantly increased the analgesic latency on days 3 and 5 compared to the morphine group in hot plate test and in tail flick test. Chronic and acute metformin administration significantly decreased nitric oxide level compare to morphine group. The present results revealed that metformin attenuated analgesic tolerance induced by repeated intraperitoneal injections of morphine in mice.

Venlafaxine prevents morphine antinociceptive tolerance: The role of neuroinflammation and the l-arginine-nitric oxide pathway

Opioid-induced neuroinflammation and the nitric oxide (NO) signal-transduction pathway are involved in the development of opioid analgesic tolerance. The antidepressant venlafaxine (VLF) modulates NO in nervous tissues, and so we investigated its effect on induced tolerance to morphine, neuroinflammation, and oxidative stress in mice. Tolerance to the analgesic effects of morphine were induced by injecting mice with morphine (50 mg/kg) once a day for three consecutive days; the effect of co-administration of VLF (5 or 40 mg/kg) with morphine was similarly tested in a separate group. To determine if the NO precursor l-arginine hydrochloride (l-arg) or NO are involved in the effects rendered by VLF, animals were pre-treated with l-arg (200 mg/kg), or the NO synthesis inhibitors N(ω)-nitro-l-arginine methyl ester (L-NAME; 30 mg/kg) or aminoguanidine hydrochloride (AG; 100 mg/kg), along with VLF (40 mg/kg) for three days before receiving morphine for another three days. Nociception was assessed with a hot-plate test on the fourth day, and the concentration of tumor necrosis factor alpha (TNF-α), interleukin-1beta (IL-1β), interleukin-6 (IL-6), interleukin-10, brain-derived neurotrophic factor, NO, and oxidative stress factors such as total thiol, malondialdehyde content, and glutathione peroxidase (GPx) activity in the brain was also determined. Co-administration of VLF with morphine attenuated morphine-induced analgesic tolerance and prevented the upregulation of proinflammatory cytokines (TNF-α, IL-1β, and IL-6), NO, and malondialdehyde in brains of mice with induced morphine tolerance; chronic VLF administration inhibited this decrease in brain-derived neurotrophic factor, total thiol, and GPx levels. Moreover, repeated administration of l-arg before receipt of VLF antagonized the effects induced by VLF, while L-NAME and AG potentiated these effects. VLF attenuates morphine-induced analgesic tolerance, at least partly because of its anti-inflammatory and antioxidative properties. VLF also appears to suppress the development of morphine-induced analgesic tolerance through an l-arg–NO-mediated mechanism.

Gene Expression Profile of Calcium/Calmodulin-Dependent Protein Kinase IIα in Rat Spinal Cord and Midbrain During Induction of Morphine Analgesic Tolerance

Background: Calcium/calmodulin-dependent protein kinase IIα (CamKIIα) may modulate the function of mu-opioid receptors by phosphorylation and therefore, be involved in development of morphine-induced analgesic tolerance. Objectives: The current study aimed to examine changes in gene expression of CamKIIα in the lumbosacral cord and midbrain during induction of morphine analgesic tolerance. Materials and Methods: Male Wistar rats weighing 250 - 300 g were used. Two groups of rats (n = 6 per group) received saline (1 mL/kg) or morphine (10 mg/mL/kg) twice-daily for eight days, and induction of morphine analgesic tolerance was assessed using a hotplate test on days one, four and eight of the injections. The lumbosacral spinal cord and midbrain were also dissected in six independent groups (n = 4 per group) on days one, four and eight of saline or morphine injections to examine changes in gene expression of CamKIIα with a semi-quantitative reverse transcription polymerase chain reaction (RT-PCR) method. Results: The result of the hotplate test showed that the rats receiving repeated injections of morphine developed tolerance and exhibited significant decrease in antinociception on days four and eight of the injections compared to that of day one (P < 0.001). The result of gene expression in the lumbosacral cord showed no significant changes in the CamKIIα gene expression on days one and eight but its expression significantly increased by 102 % on day four of the injections (P < 0.01). In addition, the CamKIIα gene expression in the midbrain showed no significant changes on days one and four, but it significantly decreased by 67 % on day eight of morphine injection (P < 0.01). Conclusions: It can be concluded that changes in the CamKIIα gene expression in the lumbosacral cord and midbrain during repeated injections of morphine may be differently associated with induction of morphine tolerance.

MicroRNAs Are Involved in the Development of Morphine-Induced Analgesic Tolerance and Regulate Functionally Relevant Changes in Serpini1.

Long-term opioid treatment results in reduced therapeutic efficacy and in turn leads to an increase in the dose required to produce equivalent pain relief and alleviate break-through or insurmountable pain. Altered gene expression is a likely means for inducing long-term neuroadaptations responsible for tolerance. Studies conducted by our laboratory (Tapocik et al., 2009) revealed a network of gene expression changes occurring in canonical pathways involved in neuroplasticity, and uncovered miRNA processing as a potential mechanism. In particular, the mRNA coding the protein responsible for processing miRNAs, Dicer1, was positively correlated with the development of analgesic tolerance. The purpose of the present study was to test the hypothesis that miRNAs play a significant role in the development of analgesic tolerance as measured by thermal nociception. Dicer1 knockdown, miRNA profiling, bioinformatics, and confirmation of high value targets were used to test the proposition. Regionally targeted Dicer1 knockdown (via shRNA) had the anticipated consequence of eliminating the development of tolerance in C57BL/6J (B6) mice, thus supporting the involvement of miRNAs in the development of tolerance. MiRNA expression profiling identified a core set of chronic morphine-regulated miRNAs (miR's 27a, 9, 483, 505, 146b, 202). Bioinformatics approaches were implemented to identify and prioritize their predicted target mRNAs. We focused our attention on miR27a and its predicted target serpin peptidase inhibitor clade I (Serpini1) mRNA, a transcript known to be intricately involved in dendritic spine density regulation in a manner consistent with chronic morphine's consequences and previously found to be correlated with the development of analgesic tolerance. In vitro reporter assay confirmed the targeting of the Serpini1 3′-untranslated region by miR27a. Interestingly miR27a was found to positively regulate Serpini1 mRNA and protein levels in multiple neuronal cell lines. Lastly, Serpini1 knockout mice developed analgesic tolerance at a slower rate than wild-type mice thus confirming a role for the protein in analgesic tolerance. Overall, these results provide evidence to support a specific role for miR27a and Serpini1 in the behavioral response to chronic opioid administration (COA) and suggest that miRNA expression and mRNA targeting may underlie the neuroadaptations that mediate tolerance to the analgesic effects of morphine.

Does modulation of spinal N-methyl-d-aspartic acid receptor by pre-activation accelerate the development of morphine tolerance?

Repeated morphine administration usually leads to a number of neuroadaptive processes, including tolerance and sensitization. However, research has shown that the induction and maintenance of central sensitization is dependent on N-methyl-d-aspartic acid receptor (NMDAR) activation. Chronic morphine exposure has been shown to result in spinal sensitization and activation of spinal NMDARs. Chronic morphine treatment and the activation of spinal NMDARs may be synergistic and form a closed loop that may worsen the development of morphine analgesic tolerance and spinal sensitization. Inhibition of NMDARs with an antagonist could effectively alleviate the development of morphine analgesic tolerance. So, what is the effect of modulating spinal NMDAR activation with exogenous agonists or neuropathic input on the development of morphine-induced analgesic tolerance? Our hypothesis is that chronic morphine treatment may worsen the already activation of spinal NMDARs and spinal sensitization after agonist application or neuropathic input to shorten the process of morphine-induced analgesic tolerance.

Fangchinoline inhibited the antinociceptive effect of morphine in mice

Fangchinoline (FAN), a non-specific calcium antagonist, is a major alkaloidal component of the creeper Stephania tetrandra S. Moore (or fenfangji). It has been shown to possess antagonistic activity on morphine-induced antinociception in mice. This study was undertaken to assess the antagonistic mechanism. The results demonstrated that FAN (IP) attenuated morphine (SC)-induced antinociception in a dose-dependent manner with significant effect at doses of 30 and 60mg/kg body wt. (IP) in the tail-flick test but not the tail-pinch tests, carried out in mice. This antagonism was abolished by pretreatment with a serotonin precursor, 5-hydroxytryptophan (5-HTP, IP), but not by pretreatment with a noradrenaline precursor, L-dihydroxyphenylalanine (L-DOPA, IP) in the tail-flick test. On the other hand, the development of morphine-induced analgesic tolerance was not prevented by FAN. These results suggest that the serotonergic pathway may be involved in the antagonism of morphine-induced antinociception by FAN and, in agreement with other reports, also indicates the possible dissociation of the morphine analgesic effect from its tolerance-development mechanism.

Antagonism of morphine-induced antinociception by tetrandrine is dependent on serotonergic mechanisms

1Tetrandrine (TET), a non-specific calcium antagonist, inhibited morphine-induced antinociception in the tail-flick test in mice. This study was undertaken to assess the mechanism of the antagonism of morphine-induced antinociception by TET. Morphine-induced antinociception was prevented by pretreatment with TET in the tail-flick but not in the tail-pinch tests carried out in mice and this antagonism was abolished by pretreatment of a serotonin precursor, 5-hydroxytryptophan (5-HTP), but not by the pretreatment of a noradrenaline precursor, L-dihydroxyphenylalanine (L-DOPA), in the tail-flick test. These results indicate that serotonergic mechanisms are involved in the antagonism of morphine-induced antinociception by TET. On the other hand, the development of morphine-induced analgesic tolerance was not prevented by TET. This result, in agreement with other reports, also indicates the possible dissociation of morphine analgesic effect from its tolerance-inducing effect. In addition, TET suppressed the 5-hydroxytryptamine (5-HT)-induced head twtch response. This result provides additional evidence that TET may modulate serotonergic function and the antagonism of morphine-induced antinociception by TET is dependent on serotonergic mechanisms.

Antinarcotic effects of the velvet antler water extract on morphine in mice

The present study was undertaken to investigate the antinarcotic effects of velvet antler water extract (VAWE) from Cervus elaphus on morphine. Morphine-induced analgesic action was measured by tail-flick method. Morphine-induced hyperactivity and reverse tolerance were evidenced by measuring the enhanced ambulatory activity using a tilting-type ambulometer. Dopamine (DA) receptor supersensitivity in mice displaying morphine-induced reverse tolerance was evidenced by the enhanced response in ambulatory activity to the DA agonist, apomorphine. The repeated administration of VAWE significantly inhibits the development of morphine-induced analgesic tolerance, physical dependence, reverse tolerance and postsynaptic DA receptor supersensitivity. But a single administration of VAWE did neither antagonize morphine-induced analgesia nor inhibit morphine-induced hyperactivity. From the above results, it is presumed that VAWE may be useful for prevention and therapy of the adverse actions of morphine caused by the repeated administration of morphine.

Repression of RNA transcription during the development of analgesic tolerance to morphine

SEVERAL reports suggest that RNA and protein synthesis are important for the development of morphine-induced analgesic tolerance and dependency1–4. Following up these reports, we have examined the effect of chronic morphine drugging on the intracellular site of RNA synthesis-nuclear chromatin. We found that brain chromatin from rats tolerant to morphine, synthesised RNA more slowly than that from non-tolerant rats5. This effect was not caused by the direct action of morphine and was found to be associated in the chromatin complex with a protein which is believed to regulate RNA synthesis. Since we may have identified, in part, a mechanism by which morphine-induced analgesic tolerance develops, we looked for a chronological relationship between the development of morphine-induced analgesic tolerance and the effect on brain chromatin RNA synthesis.