Effects of Glycogen Synthase Kinase 3β and Cyclin-Dependent Kinase 5 Inhibitors on Morphine-Induced Analgesia and Tolerance in Rats

A selective GSK3β inhibitor, tideglusib, decreases intermittent access and binge ethanol self-administration in C57BL/6J mice

Over 10% of the US population over 12 years old meets criteria for Alcohol Use Disorder (AUD), yet few effective, long-term treatments are currently available. Glycogen synthase kinase 3 beta (GSK3β) has been implicated in ethanol behaviors and poses as a potential therapeutic target in the treatment of AUD. Here we investigate the role of tideglusib, a selective GSK3β inhibitor, in ethanol consumption and other behaviors. We have shown tideglusib decreases ethanol consumption in both a model of daily, progressive ethanol intake (two-bottle choice, intermittent ethanol access) and binge-like drinking behavior (drinking-in-the-dark) without effecting water intake. Further, we have shown tideglusib to have no effect on ethanol pharmacokinetics, taste preference, or anxiety-like behavior, though there was a transient increase in total locomotion following treatment. Additionally, we assessed liver health following treatment via serum levels of alanine aminotransferase, aspartate aminotransferase, and alkaline phosphatase and showed no effect on aminotransferase levels though there was a decrease in alkaline phosphatase. RNA sequencing studies revealed a role of GSK3β inhibition via tideglusib on the canonical Wnt signaling pathway, suggesting tideglusib may carry out its effects on ethanol consumption through effects on β-catenin binding to the transcription factors TCF3 and LEF1. The data presented here further implicate GSK3β in alcohol consumption and support the use of tideglusib as a potential therapeutic in the treatment of AUD.

Function of GSK‑3 signaling in spinal cord injury (Review)

Spinal cord injury (SCI) is a major social problem with a heavy burden on patient physiology and psychology. Glial scar formation and irreversible neuron loss are the two key points during SCI progression. During the acute phase of spinal cord injury, glial scars form, limiting the progression of inflammation. However, in the subacute or chronic phase, glial scarring inhibits axon regeneration. Following spinal cord injury, irreversible loss of neurons leads to further aggravation of spinal cord injury. Several therapies have been developed to improve either glial scar or neuron loss; however, few therapies reach the stage of clinical trials and there are no mainstream therapies for SCI. Exploring the key mechanism of SCI is crucial for finding further treatments. Glycogen synthase kinase-3 (GSK-3) is a widely expressed kinase with important physiological and pathophysiological functions in vivo. Dysfunction of the GSK-3 signaling pathway during SCI has been widely discussed for controlling neurite growth in vitro and in vivo, improving the proliferation and neuronal differentiation of endogenous neural stem cells and functional recovery from spinal cord injury. SCI can decrease the phosphorylated (p)/total (t)-GSK-3β ratio, which leads to an increase in apoptosis, whereas treatment with GSK-3 inhibitors can promote neurogenesis. In addition, several therapies for the treatment of SCI involve signaling pathways associated with GSK-3. Furthermore, signaling pathways associated with GSK-3 also participate in the pathological process of neuropathic pain that remains following SCI. The present review summarized the roles of GSK-3 signaling in SCI to aid in the understanding of GSK-3 signaling during the pathological processes of SCI and to provide evidence for the development of comprehensive treatments.

Proteomic Analysis of the Spinal Dorsal Horn in Mice with Neuropathic Pain After Exercise

Purpose

Neuropathic pain (NP) is a chronic pain state with a complex etiology that currently lacks effective treatment in clinical practice. Studies have found that exercise training can alleviate NP hyperalgesia, but the specific mechanism remains unclear. Here, we sought to identify proteins and signaling pathways critical for mediating the effects of treadmill training on NP in a mouse model of spared nerve injury (SNI).

Methods

We used Tandem Mass Tag (TMT) technology for proteins and signaling pathways identification. Functional enrichment analyses were conducted using DAVID and Metascape software. Ingenuity pathway analysis was used to conduct functional annotation and analyze alterations in canonical pathways and molecular networks. Reverse transcription quantitative PCR (RT-qPCR) was used to confirm the results of proteomics analysis.

Results

A total of 270 differentially expressed proteins were screened in the detrained and trained groups (P ≤0.05). Enrichment and ingenuity pathway analysis revealed the effects of treadmill training on autophagy, cAMP-mediated signaling, calcium signaling and NP signaling in dorsal horn nerves. Treadmill training reduced the expression of Akt3, Atf2, Gsk3b, Pik3c3, Ppp2ca, and Sqstm1, and increased the expression of Pik3cb in the autophagic pathway.

Conclusion

Our results suggest that treadmill training may alleviate nociceptive hyperalgesia in NP mice by modulating the autophagic pathway, providing unique mechanistic insights into the analgesic effects of exercise.

Glycogen synthesis kinase-3β involves in the analgesic effect of liraglutide on diabetic neuropathic pain

AIMS

Explore whether Glycogen synthesis kinase-3β (GSK3β) involved in the analgesic effect of liraglutide on diabetic neuropathic pain (DNP).

METHODS

DNP was induced by streptozocin (STZ) in WT and GSK3β(S9A) mice, which carried a constitutively active form of GSK3β. DNP mice were intracerebroventricularly injected with liraglutide 5 weeks after STZ injection. The behavior of neuropathic pain was evaluated 2 h after drugs administration. The microglial activation and the expression of NOD-like receptor protein 3 (NLRP3) in microglia in cortex were evaluated. The role of GSK3β in the inhibitory effect of liraglutide on the NLRP3 inflammasome was explored in BV2 microglia.

RESULTS

Intracerebroventricular administration of liraglutide significantly relieved neuropathic pain and inhibited the activation of cortical microglia in WT mice with DNP. But the effect of liraglutide disappeared in GSK3β(S9A) mice. In BV2 microglia, GSK3β inhibitor significantly suppressed NLRP3 inflammasome activation. And activating GSK3β through GSK3β(S9A) lentivirus significantly blocked the inhibitory effect of liraglutide on NLRP3 inflammasome in BV2 microglia. Intracerebroventricular administration of liraglutide significantly inhibited the expression of NLRP3 in cortex microglia of DNP group in WT mice but failed in GSK3β(S9A) mice.

CONCLUSION

GSK3β involves in the analgesic effect of liraglutide on DNP through NLRP3 inflammasome in microglia.

Long-Term Exposure to Morphine Induces Cross-Tolerance to Acute Antinociceptive Effect of Remifentanil on Somatic and Visceral Stimuli in Rats

Purpose

Remifentanil is one of the most commonly used opioids intraoperatively. Previous reports indicate that long-term use of opioids may lead to cross-tolerance to remifentanil, which poses a challenge in the control of acute pain intraoperatively. However, there is limited information regarding cross-tolerance to remifentanil, especially in visceral pain. Therefore, this study aimed to examine cross-tolerance to remifentanil in somatic and visceral tolerance using morphine-tolerant rats.

Methods

Six male Sprague-Dawley rats were allocated to the morphine and saline groups each. Tolerance to the antinociceptive effect of morphine was induced in rats in the morphine group. Remifentanil was continuously infused intravenously at 10 mcg/kg/min for 120 min to assess cross-tolerance from morphine to remifentanil. The antinociceptive effects on somatic and visceral nociceptive stimuli were measured using the tail-flick (TF) and colorectal distension (CD) tests, respectively. The antinociceptive efficacy was evaluated by converting the response threshold to the percentage maximal possible effect (%MPE).

Results

Remifentanil increased the %MPE in the morphine and saline groups in both the tests; however, the increase in %MPE was attenuated significantly in the morphine group compared with that in the saline group at 60, 90, and 120 min (all P < 0.01) in the TF test and at 90 and 120 min in the CD test (all P <0.05).

Conclusion

Our results indicate that morphine-tolerant rats exhibit cross-tolerance to remifentanil's acute antinociceptive effects on somatic and visceral stimuli. Cross-tolerance to remifentanil should be considered in the perioperative management of patients using morphine.

Pharmacological Chaperones Attenuate the Development of Opioid Tolerance

Opioids are potent analgesics widely used to control acute and chronic pain, but long-term use induces tolerance that reduces their effectiveness. Opioids such as morphine bind to mu opioid receptors (MORs), and several downstream signaling pathways are capable of inducing tolerance. We previously reported that signaling from the endoplasmic reticulum (ER) contributed to the development of morphine tolerance. Accumulation of misfolded proteins in the ER induced the unfolded protein response (UPR) that causes diverse pathological conditions. We examined the effects of pharmacological chaperones that alleviate ER stress on opioid tolerance development by assessing thermal nociception in mice. Pharmacological chaperones such as tauroursodeoxycholic acid and 4-phenylbutyrate suppressed the development of morphine tolerance and restored analgesia. Chaperones alone did not cause analgesia. Although morphine administration induced analgesia when glycogen synthase kinase 3β (GSK3β) was in an inactive state due to serine 9 phosphorylation, repeated morphine administration suppressed this phosphorylation event. Co-administration of chaperones maintained the inactive state of GSK3β. These results suggest that ER stress may facilitate morphine tolerance due to intracellular crosstalk between the UPR and MOR signaling. Pharmacological chaperones may be useful in the management of opioid misuse.

Lithium reverses the effect of opioids on eNOS/nitric oxide pathway in human umbilical vein endothelial cells

The main challenge of pain management with opioids is development of acute and chronic analgesic tolerance. Several studies on neuronal cells have focused on the molecular mechanisms involved in tolerance such as cyclic AMP (cAMP) activation, and nitric oxide (NO) pathway. However, the effects of opioids on non-neuronal cells and tolerance development have been poorly investigated. Lithium chloride is a glycogen synthase kinase 3β (GSK-3β) inhibitor and exert its effects through modulation of nitric oxide pathway. In this study we examined the effect of lithium on acute/chronic morphine and methadone administration in endothelial cells which express mu opioid receptors. Human umbilical vein endothelial cells (HUVECs) were treated with different doses of morphine, methadone, and lithium for six and 48 h. Then we evaluated cell viability, nitrite and cyclic AMP levels, as well as the expression of endothelial nitric oxide synthase (eNOS) protein using Immunocytochemistry (ICC) assay and phosphorylated GSK-3β enzyme by western blot analysis in cells. Both chronic morphine and methadone treatment increased NO level and eNOS expression in HUVECs. Morphine induced cAMP overproduction after 48 h exposure with cells. Lithium pretreatment (10 mM) in both morphine and methadone received groups significantly reduced nitrite and cAMP levels as well as eNOS expression as compared to the control. The decreased amount of phospho GSK-3β due to the opioid exposure was increased following lithium treatment. Tolerance like pattern may occur in non-neuronal cells with opioid receptors and this study clearly revealed the attenuation of morphine and methadone tolerance like behavior by lithium treatment in HUVECs.

Glycogen Synthase Kinase 3β in Cancer Biology and Treatment

Glycogen synthase kinase (GSK)3β is a multifunctional serine/threonine protein kinase with more than 100 substrates and interacting molecules. GSK3β is normally active in cells and negative regulation of GSK3β activity via phosphorylation of its serine 9 residue is required for most normal cells to maintain homeostasis. Aberrant expression and activity of GSK3β contributes to the pathogenesis and progression of common recalcitrant diseases such as glucose intolerance, neurodegenerative disorders and cancer. Despite recognized roles against several proto-oncoproteins and mediators of the epithelial–mesenchymal transition, deregulated GSK3β also participates in tumor cell survival, evasion of apoptosis, proliferation and invasion, as well as sustaining cancer stemness and inducing therapy resistance. A therapeutic effect from GSK3β inhibition has been demonstrated in 25 different cancer types. Moreover, there is increasing evidence that GSK3β inhibition protects normal cells and tissues from the harmful effects associated with conventional cancer therapies. Here, we review the evidence supporting aberrant GSK3β as a hallmark property of cancer and highlight the beneficial effects of GSK3β inhibition on normal cells and tissues during cancer therapy. The biological rationale for targeting GSK3β in the treatment of cancer is also discussed at length.

The day-night differences in ERK1/2, GSK3β activity and c-Fos levels in the brain, and the responsiveness of various brain structures to morphine

As with other drugs or pharmaceuticals, opioids differ in their rewarding or analgesic effects depending on when they are applied. In the previous study, we have demonstrated the day/night difference in the sensitivity of the major circadian clock in the suprachiasmatic nucleus to a low dose of morphine, and showed the bidirectional effect of morphine on pERK1/2 and pGSK3β levels in the suprachiasmatic nucleus depending on the time of administration. The main aim of this study was to identify other brain structures that respond differently to morphine depending on the time of its administration. Using immunohistochemistry, we identified 44 structures that show time-of-day specific changes in c-Fos level and activity of ERK1/2 and GSK3β kinases in response to a single dose of 1 mg/kg morphine. Furthermore, comparison among control groups revealed the differences in the spontaneous levels of all markers with a generally higher level during the night, that is, in the active phase of the day. We thus provide further evidence for diurnal variations in the activity of brain regions outside the suprachiasmatic nucleus indicated by the temporal changes in the molecular substrate. We suggest that these changes are responsible for generating diurnal variation in the reward behavior or analgesic effect of opioid administration.

The Potential Role of Glycogen Synthase Kinase-3β in Neuropathy-Induced Apoptosis in Spinal Cord

Introduction:

Glycogen Synthase Kinase-3β (GSK-3β) participates in several signaling pathways and plays a crucial role in neurodegenerative diseases, inflammation, and neuropathic pain. The ratio of phosphorylated GSK-3β over total GSK-3β (p-GSK-3β/t-GSK-3β) is reduced following nerve injury. Apoptosis is a hallmark of many neuronal dysfunctions in the context of neuropathic pain. Thus, this study aimed to evaluate the contribution of p-GSK-3β/t-GSK-3β ratio in spinal dorsal horn apoptosis following peripheral nerve injury.

Methods:

In this study, adult male Wistar rats (220–250 g) underwent Spinal Nerve Ligation (SNL) surgery. Mechanical allodynia and thermal hyperalgesia were assessed before the surgery (day 0); then, every other day up to day 8. GSK-3β selective inhibitor, AR-014418 [0.3 mg/kg, Intraperitoneal (IP)] was administrated 1 h prior to SNL on day 0, then daily up to the day 8. The GSK-3β activity and apoptosis in the lumbar section (L4, L5, or L6) of the study rat’s spinal cord were assessed by immunohistochemical and Terminal Deoxynucleotidyl Transferase dUTP Nick End Labeling (TUNEL) staining, respectively on day 8 post-SNL.

Results:

Following the SNL, the mechanical allodynia and thermal hyperalgesia increased on day 2 up to day 8 post-SNL. The ratio of p-GSK-3β/t-GSK-3β decreased, and the number of apoptotic cells increased in the spinal dorsal horn on day 8. However, AR-A014418 administration could increase the p-GSK-3β/t-GSK-3β ratio and decreased apoptosis in the SNL rats. In addition, AR-A014418 decreased the mechanical allodynia from day 4 up to day 8; however, it did not affect thermal hyperalgesia.

Conclusion:

The study findings suggested that increasing the p-GSK-3β/t-GSK-3β ratio might be a helpful strategy for reducing the apoptotic cells and subsequent neuropathic pain during peripheral nerve injury.

Glycogen Synthase Kinase 3β in the Ventral Hippocampus is Important for Cocaine Reward and Object Location Memory

The ventral hippocampus is a component of the neural circuitry involved with context-associated memory for reward and generation of appropriate behavioral responses to context. Glycogen synthase kinase 3 beta (GSK3β) has been linked to the maintenance of synaptic plasticity, contextual memory retrieval, and is involved in the reconsolidation of cocaine-associated contextual memory. In this study, the effects of targeted downregulation of GSK3β in the ventral hippocampus were examined on a series of behavioral tests for assessing drug reward-context association and non-reward related memory. The Cre/loxP site-specific recombination system was used to knockdown GSK3β through bilateral stereotaxic delivery of an adeno-associated virus expressing Cre-recombinase (AAV-Cre) into the ventral hippocampus of adult mice homozygous for a floxed GSK3β allele. GSK3β floxed mice injected with AAV-Cre had a loss of 56-75% of GSK3β in the ventral hippocampus and displayed diminished development of cocaine conditioned place preference, but not morphine place preference as compared with wild-type mice injected with AAV-Cre or GSK3β floxed mice injected with a control virus, AAV-GFP. Impaired object location memory was observed in mice with GSK3β downregulation in the ventral hippocampus, but novel object recognition remained intact. These results indicate that GSK3β signaling in the ventral hippocampus is differentially involved in the formation of place-drug reward association dependent upon drug class. Additionally, ventral hippocampal GSK3β signaling is important in detection of discrete spatial cues, but not recognition memory for objects.

Supraphysiologic-dose anabolic-androgenic steroid use: A risk factor for dementia?

Supraphysiologic-dose anabolic-androgenic steroid (AAS) use is associated with physiologic, cognitive, and brain abnormalities similar to those found in people at risk for developing Alzheimer's Disease and its related dementias (AD/ADRD), which are associated with high brain β-amyloid (Aβ) and hyperphosphorylated tau (tau-P) protein levels. Supraphysiologic-dose AAS induces androgen abnormalities and excess oxidative stress, which have been linked to increased and decreased expression or activity of proteins that synthesize and eliminate, respectively, Aβ and tau-P. Aβ and tau-P accumulation may begin soon after initiating supraphysiologic-dose AAS use, which typically occurs in the early 20s, and their accumulation may be accelerated by other psychoactive substance use, which is common among non-medical AAS users. Accordingly, the widespread use of supraphysiologic-dose AAS may increase the numbers of people who develop dementia. Early diagnosis and correction of sex-steroid level abnormalities and excess oxidative stress could attenuate risk for developing AD/ADRD in supraphysiologic-dose AAS users, in people with other substance use disorders, and in people with low sex-steroid levels or excess oxidative stress associated with aging.

In vitro evaluation of effects of metformin on morphine and methadone tolerance through mammalian target of rapamycin signaling pathway

The chronic use of opioids leads to tolerance, psychological, and physical dependence that limits their use as an effective long-term pain control. Several studies have shown that mammalian target of rapamycin (mTOR) plays a crucial role in the development of opioid tolerance. Metformin activates 5' adenosine monophosphate-activated protein kinase (AMPK) which directly suppresses the mTOR complex 1 signaling pathway. On the other hand, metformin can also inhibit mTOR directly and in an AMPK-independent manner. Thus, in the current study, we aimed to investigate the effects of metformin on the development of morphine and/or methadone-induced tolerance in human glioblastoma (T98G) cell line. We examined the effects of chronic treatment of morphine and/or methadone in the presence or absence of metformin with or without AMPK inhibitor (dorsomorphin hydrochloride) on levels of nitric oxide and cyclic adenosine monophosphate (cAMP), phosphorylated and dephosphorylated ribosomal protein S6 kinase β-1 (S6K1) and 4E-binding protein 1 (4E-BP1) in T98G cells. Pretreatment of cells with metformin (40 µM) with or without AMPK inhibitor (dorsomorphin hydrochloride; 1 µM) before adding of morphine (2.5 µM) or methadone (1 µM) revealed a protective effects on the development of opioid tolerance. Prior administration of metformin reversed the elevation of nitric oxide levels induced by morphine (p < 0.001) and methadone (p < 0.001) and also prevented the raise of cAMP levels induced by morphine in T98G cells (p < 0.05). Contribution of mTOR signaling pathway in metformin-induced effect was shown by the inhibition of phosphorylation of S6K1 and 4E-BP1, the downstream targets of mTOR. mTOR activation suppresses opioid-induced antinociception, and its activity has also been increased during opioid tolerance.

Suppression of RGSz1 function optimizes the actions of opioid analgesics by mechanisms that involve the Wnt/β-catenin pathway

Regulator of G protein signaling z1 (RGSz1), a member of the RGS family of proteins, is present in several networks expressing mu opioid receptors (MOPRs). By using genetic mouse models for global or brain region-targeted manipulations of RGSz1 expression, we demonstrated that the suppression of RGSz1 function increases the analgesic efficacy of MOPR agonists in male and female mice and delays the development of morphine tolerance while decreasing the sensitivity to rewarding and locomotor activating effects. Using biochemical assays and next-generation RNA sequencing, we identified a key role of RGSz1 in the periaqueductal gray (PAG) in morphine tolerance. Chronic morphine administration promotes RGSz1 activity in the PAG, which in turn modulates transcription mediated by the Wnt/β-catenin signaling pathway to promote analgesic tolerance to morphine. Conversely, the suppression of RGSz1 function stabilizes Axin2-Gαz complexes near the membrane and promotes β-catenin activation, thereby delaying the development of analgesic tolerance. These data show that the regulation of RGS complexes, particularly those involving RGSz1-Gαz, represents a promising target for optimizing the analgesic actions of opioids without increasing the risk of dependence or addiction.

Casein kinase 1-epsilon deletion increases mu opioid receptor-dependent behaviors and binge eating1

Genetic and pharmacological studies indicate that casein kinase 1 epsilon (Csnk1e) contributes to psychostimulant, opioid, and ethanol motivated behaviors. We previously used pharmacological inhibition to demonstrate that Csnk1e negatively regulates the locomotor stimulant properties of opioids and psychostimulants. Here, we tested the hypothesis that Csnk1e negatively regulates opioid and psychostimulant reward using genetic inhibition and the conditioned place preference assay in Csnk1e knockout mice. Similar to pharmacological inhibition, Csnk1e knockout mice showed enhanced opioid-induced locomotor activity with the mu opioid receptor agonist fentanyl (0.2 mg/kg i.p.) as well as enhanced sensitivity to low-dose fentanyl reward (0.05 mg/kg). Interestingly, female knockout mice also showed a markedly greater escalation in consumption of sweetened palatable food - a behavioral pattern consistent with binge eating that also depends on mu opioid receptor activation. No difference was observed in fentanyl analgesia in the 52.5°C hot plate assay (0-0.4 mg/kg), naloxone conditioned place aversion (4 mg/kg), or methamphetamine conditioned place preference (0-4 mg/kg). To identify molecular adaptations associated with increased drug and food behaviors in knockout mice, we completed transcriptome analysis via mRNA sequencing of the striatum. Enrichment analysis identified terms associated with myelination and axon guidance and pathway analysis identified a differentially expressed gene set predicted to be regulated by the Wnt signaling transcription factor, Tcf7l2. To summarize, Csnk1e deletion increased mu opioid receptor-dependent behaviors, supporting previous studies indicating an endogenous negative regulatory role of Csnk1e in opioid behavior.

Molecular mechanisms underlying the positive role of treadmill training in locomotor recovery after spinal cord injury

OBJECTIVES

This study aimed to investigate the molecular mechanisms underlying the positive role of treadmill training (TMT) in locomotor recovery.

METHODS

GSE52763 microarray data were downloaded from GEO database, which was collected from the lumbar spinal cord samples of three groups of mice: mice subjected to contusive injury and killed 1 week after injury (I1), mice subjected to injury and killed 3 weeks after injury (I3), and mice subjected to injury and TMT beginning at week 1 and lasting until week 3 (T3). Differential expression analysis between I3 and I1, between T3 and I1 and between T3 and I3 were performed by T-test using R/LIMMA. Genes with |log₂FC (fold change)|>0.58 and P-value<0.05 were considered as differentially expressed genes (DEGs). Specific I3 vs I1 DEGs and T3 vs I1 DEGs were screened. Then TMT-induced specific DEGs were subject to functional and pathway enrichment analysis using DAVID online tool. Protein-protein interaction (PPI) analysis was also carried out using the STRING database.

RESULTS

Finally, 82 upregulated DEGs and 297 downregulated DEGs were found specifically induced by TMT. Specific upregulated DEGs were mostly enriched in response to organic substance and morphogenesis-related events, and specific downregulated DEGs were related to positive regulation of transcription. ATP2A1, PRKACA, ITPR2 and so on had high connection degree in the PPI network of the specific upregulated DEGs; FOS, GSK3B and so on had high degrees in the PPI network of the specific downregulated DEGs.

CONCLUSION

ATP2A1, C-FOS and GSK3B may have critical roles in the positive role of TMT in locomotor recovery.

Decreased Activity in Neuropathic Pain Form and Gene Expression of Cyclin-Dependent Kinase5 and Glycogen Synthase Kinase-3 Beta in Soleus Muscle of Wistar Male Rats

BACKGROUND

The relationship between decreased activity/neuropathic pain and gene expression alterations in soleus muscle has remained elusive.

OBJECTIVES

In this experimental study, we investigated the effects of decreased activity in neuropathic pain form on Cyclin-Dependent Kinase 5 (CDK5) and Glycogen Synthase Kinase-3 β (GSK-3β) gene expression in soleus muscle of rats.

MATERIALS AND METHODS

Twelve male Wistar rats were randomly divided into three groups: (1) tight ligation of the L5 spinal nerve (SNL: n = 4); (2) sham surgery (Sham: n = 4), and (3) control (C: n = 4). The threshold to produce a withdrawal response to a mechanical and thermal stimulus was measured using von Frey filaments and radiation heat apparatus, respectively. Following 4 weeks after surgery, the left soleus muscle was removed and mRNA levels were determined by real-time Polymerase Chain Reaction (PCR).

RESULTS

Compared to control animals, L5 ligated animals developed mechanical and heat hypersensitivity during total period of study. Soleus muscle weight as well as CDK5 mRNA levels (less than ~ 0.4 fold) was decreased and GSK-3β mRNA levels (up to ~ 7 folds) increased in L5 ligated animals.

CONCLUSIONS

These results showed enhanced muscle atrophy processes following peripheral nerve damage and might provide a useful approach to study underlying muscle mechanisms associated with clinical neuropathic pain syndromes.

GSK3β-activation is a point of convergence for HIV-1 and opiate-mediated interactive neurotoxicity

Infection of the CNS with HIV-1 occurs rapidly after primary peripheral infection. HIV-1 can induce a wide range of neurological deficits, collectively known as HIV-1-associated neurocognitive disorders. Our previous work has shown that the selected neurotoxic effects induced by individual viral proteins, Tat and gp120, and by HIV(+) supernatant are enhanced by co-exposure to morphine. This mimics co-morbid neurological effects observed in opiate-abusing HIV(+) patients. Although there is a correlation between opiate drug abuse and progression of HIV-1-associated neurocognitive disorders, the mechanisms underlying interactions between HIV-1 and opiates remain obscure. Previous studies have shown that HIV-1 induces neurotoxic effects through abnormal activation of GSK3β. Interestingly, expression of GSK3β has shown to be elevated in brains of young opiate abusers indicating that GSK3β is also linked to neuropathology seen with opiate-abusing patients. Thus, we hypothesize that GSK3β activation is a point of convergence for HIV- and opiate-mediated interactive neurotoxic effects. Neuronal cultures were treated with supernatant from HIV-1SF162-infected THP-1 cells, in the presence or absence of morphine and GSK3β inhibitors. Our results show that GSK3β inhibitors, including valproate and small molecule inhibitors, significantly reduce HIV-1-mediated neurotoxic outcomes, and also negate interactions with morphine that result in cell death, suggesting that GSK3β-activation is an important point of convergence and a potential therapeutic target for HIV- and opiate-mediated neurocognitive deficits.

Glycogen synthase kinase 3 beta regulates glial glutamate transporter protein expression in the spinal dorsal horn in rats with neuropathic pain

Dysfunctional glial glutamate transporters and over production of pro-inflammatory cytokines (including interleukin-1β, IL-1β) are two prominent mechanisms by which glial cells enhance neuronal activities in the spinal dorsal horn in neuropathic pain conditions. Endogenous molecules regulating production of IL-1β and glial glutamate functions remain poorly understood. In this study, we revealed a dynamic alteration of GSK3β activities and its role in regulating glial glutamate transporter 1 (GLT-1) protein expression in the spinal dorsal horn and nociceptive behaviors following the nerve injury. Specifically, GSK3β was expressed in both neurons and astrocytes in the spinal dorsal horn. GSK3β activities were suppressed on day 3 but increased on day 10 following the nerve injury. In parallel, protein expression of GLT-1 in the spinal dorsal horn was enhanced on day 3 but reduced on day 10. In contrast to these time-dependent changes, the activation of astrocytes and over-production of IL-1β were found on both day 3 and day 10. Meanwhile, thermal hyperalgesia was observed from day 2 through day 10 and mechanical allodynia from day 4 through day 10. Pre-emptive pharmacological inhibition of GSK3β activities significantly ameliorated thermal hyperalgesia and mechanical allodynia at the late stage but did not have effects at the early stage. These were accompanied with the suppression of GSK3β activities, prevention of decreased GLT-1 protein expression, inhibition of astrocytic activation, and reduction of IL-1β in the spinal dorsal horn on day 10. These data indicate that the increased GSK3β activity in the spinal dorsal horn is attributable to the downregulation of GLT-1 protein expression in neuropathic rats at the late stage. Further, we also demonstrated that the nerve-injury-induced thermal hyperalgesia on day 10 was transiently suppressed by pharmacological inhibition of GSK3β. Our study suggests that GSK3β may be a potential target for the development of analgesics for chronic neuropathic pain.

Inhibition of glycogen synthase kinase-3β prevents remifentanil-induced hyperalgesia via regulating the expression and function of spinal N-methyl-D-aspartate receptors in vivo and vitro

A large number of experimental and clinical studies have confirmed that brief remifentanil exposure can enhance pain sensitivity presenting as opioid-induced hyperalgesia (OIH). N-methyl-D-aspartate (NMDA) receptor antagonists have been reported to inhibit morphine analgesic tolerance in many studies. Recently, we found that glycogen synthase kinase-3β (GSK-3β) modulated NMDA receptor trafficking in a rat model of remifentanil-induced postoperative hyperalgesia. In the current study, it was demonstrated that GSK-3β inhibition prevented remifentanil-induced hyperalgesia via regulating the expression and function of spinal NMDA receptors in vivo and in vitro. We firstly investigated the effects of TDZD-8, a selective GSK-3β inhibitor, on thermal and mechanical hyperalgesia using a rat model of remifentanil-induced hyperalgesia. GSK-3β activity as well as NMDA receptor subunits (NR1, NR2A and NR2B) expression and trafficking in spinal cord L4-L5 segments were measured by Western blot analysis. Furthermore, the effects of GSK-3β inhibition on NMDA-induced current amplitude and frequency were studied in spinal cord slices by whole-cell patch-clamp recording. We found that remifentanil infusion at 1 μg·kg(-1)·min(-1) and 2 μg·kg(-1)·min(-1) caused mechanical and thermal hyperalgesia, up-regulated NMDA receptor subunits NR1 and NR2B expression in both membrane fraction and total lysate of the spinal cord dorsal horn and increased GSK-3β activity in spinal cord dorsal horn. GSK-3β inhibitor TDZD-8 significantly attenuated remifentanil-induced mechanical and thermal hyperalgesia from 2 h to 48 h after infusion, and this was associated with reversal of up-regulated NR1 and NR2B subunits in both membrane fraction and total lysate. Furthermore, remifentanil incubation increased amplitude and frequency of NMDA receptor-induced current in dorsal horn neurons, which was prevented with the application of TDZD-8. These results suggest that inhibition of GSK-3β can significantly ameliorate remifentanil-induced hyperalgesia via modulating the expression and function of NMDA receptors, which present useful insights into the mechanistic action of GSK-3β inhibitor as potential anti-hyperalgesic agents for treating OIH.

Inhibition of glycogen synthase kinase 3β activity with lithium prevents and attenuates paclitaxel-induced neuropathic pain

Paclitaxel (taxol) is a first-line chemotherapy-drug used to treat many types of cancers. Neuropathic pain and sensory dysfunction are the major toxicities, which are dose-limiting and significantly reduce the quality of life in patients. Two known critical spinal mechanisms underlying taxol-induced neuropathic pain are an increased production of pro-inflammatory cytokines including interleukin-1β (IL-1β) and suppressed glial glutamate transporter activities. In this study, we uncovered that increased activation of glycogen synthase kinase 3beta (GSK3β) in the spinal dorsal horn was concurrently associated with increased protein expressions of GFAP, IL-1β and a decreased protein expression of glial glutamate transporter 1 (GLT-1), as well as the development and maintenance of taxol-induced neuropathic pain. The enhanced GSK3β activities were supported by the concurrently decreased AKT and mTOR activities. The changes of all these biomarkers were basically prevented when animals received pre-emptive lithium (a GSK3β inhibitor) treatment, which also prevented the development of taxol-induced neuropathic pain. Further, chronic lithium treatment, which began on day 11 after the first taxol injection, reversed the existing mechanical and thermal allodynia induced by taxol. The taxol-induced increased GSK3β activities and decreased AKT and mTOR activities in the spinal dorsal horn were also reversed by lithium. Meanwhile, protein expressions of GLT-1, GFAP and IL-1β in the spinal dorsal horn were improved. Hence, suppression of spinal GSK3β activities is a key mechanism used by lithium to reduce taxol-induced neuropathic pain, and targeting spinal GSK3β is an effective approach to ameliorate GLT-1 expression and suppress the activation of astrocytes and IL-1β over-production in the spinal dorsal horn.

The Role of Glycogen Synthase Kinase 3 Beta in Neuroinflammation and Pain

Neuroinflammation is a crucial mechanism related to many neurological diseases. Extensive studies in recent years have indicated that dysregulation of Glycogen Synthase Kinase 3 Beta (GSK3β) contributes to the development and progression of these disorders through regulating the neuroinflammation processes. Inhibitors of GSK3β have been shown to be beneficial in many neuroinflammatory disease models including Alzheimer's disease, multiple sclerosis and AIDS dem entia complex. Glial activation and elevated pro-inflammation cytokines (signs of neuroinflammation) in the spinal cord have been widely recognized as a pivotal mechanism underlying the development and maintenance of many types of pathological pain. The role of GSK3β in the pathogenesis of pain has recently emerged. In this review, we will first review the GSK3β structure, regulation, and mechanisms by which GSK3βregulates inflammation. We will then describe neuroinflammationin general and in specific types of neurological diseases and the potential beneficial effects induced by inhibiting GSK3β. Finally, we will provide new evidence linking aberrant levels of GSK3β in the development of pathological pain.

Glycogen synthase kinase-3β contributes to remifentanil-induced postoperative hyperalgesia via regulating N-methyl-D-aspartate receptor trafficking

BACKGROUND

Although remifentanil provides perfect analgesia during surgery, postoperative hyperalgesia after remifentanil administration might be a challenge to anesthesiologists. The trafficking and activation of N-methyl-D-aspartate (NMDA) receptors have a pivotal role in the development and maintenance of remifentanil-induced postoperative hyperalgesia. However, the underlying mechanisms of hyperalgesia are poorly elucidated. We designed the present study to examine the hypothesis that glycogen synthase kinase (GSK)-3β could contribute to remifentanil-induced postoperative hyperalgesia via regulating NMDA receptor trafficking in the spinal cord.

METHODS

Using a rat model of remifentanil-induced postoperative hyperalgesia, we first tested thermal and mechanical hyperalgesia at baseline (24 hours before incision) and 2, 6, 24, and 48 hours after remifentanil infusion. GSK-3β mRNA and protein expression and NMDA receptor subunits (NR1, NR2A, and NR2B) trafficking in the spinal cord L4-L6 segments were then measured using real-time polymerase chain reaction and Western blot analysis. Furthermore, we investigated the effects of TDZD-8, a selective GSK-3β inhibitor, on remifentanil-induced postoperative hyperalgesia and NMDA receptor subunits trafficking.

RESULTS

Remifentanil induced significant postoperative hyperalgesia, as indicated by increased paw withdrawal latencies and thresholds to thermal and mechanical stimulation, which were markedly improved by pretreatment with TDZD-8. Moreover, remifentanil infusion increased the expression of GSK-3β mRNA and protein as well as the GSK-3β activity in the spinal cord. More importantly, intraoperative infusion of remifentanil increased NMDA receptor subunits (NR1 and NR2B) trafficking from the intracellular pool to surface pool in the spinal cord, which was significantly attenuated by TDZD-8.

CONCLUSION

The above results suggest that activation of GSK-3β contributes to remifentanil-induced postoperative hyperalgesia via regulating NMDA receptor subunits (NR1 and NR2B) trafficking in the spinal cord. Inhibition of GSK-3β may be an effective novel option for the treatment of remifentanil-induced postoperative hyperalgesia.

Disruption of δ-opioid receptor phosphorylation at threonine 161 attenuates morphine tolerance in rats with CFA-induced inflammatory hypersensitivity

OBJECTIVE

Our previous study identified Threonine 161 (Thr-161), located in the second intracellular loop of the δ-opioid receptor (DOR), as the only consensus phosphorylation site for cyclin-dependent kinase 5 (Cdk5). The aim of this study was to assess the function of DOR phosphorylation by Cdk5 in complete Freund's adjuvant (CFA)-induced inflammatory pain and morphine tolerance.

METHODS

Dorsal root ganglion (DRG) neurons of rats with CFA-induced inflammatory pain were acutely dissociated and the biotinylation method was used to explore the membrane localization of phosphorylated DOR at Thr-161 (pThr-161-DOR), and paw withdrawal latency was measured after intrathecal delivery of drugs or Tat-peptide, using a radiant heat stimulator in rats with CFA-induced inflammatory pain.

RESULTS

Both the total amount and the surface localization of pThr-161-DOR were significantly enhanced in the ipsilateral DRG following CFA injection. Intrathecal delivery of the engineered Tat fusion-interefering peptide corresponding to the second intracellular loop of DOR (Tat-DOR-2L) increased inflammatory hypersensitivity, and inhibited DOR- but not µ-opioid receptor-mediated spinal analgesia in CFA-treated rats. However, intrathecal delivery of Tat-DOR-2L postponed morphine antinociceptive tolerance in rats with CFA-induced inflammatory pain.

CONCLUSION

Phosphorylation of DOR at Thr-161 by Cdk5 attenuates hypersensitivity and potentiates morphine tolerance in rats with CFA-induced inflammatory pain, while disruption of the phosphorylation of DOR at Thr-161 attenuates morphine tolerance.

Cdk5: An Emerging Kinase in Pain Signaling

Pain is an important survival mechanism for an organism. It can turn into severe mental and physical disorder however, if the molecular and/or cellular pathways involved in pain signaling are altered. Chronic pain is characterized by an altered pain perception that includes allodynia (a response to a normally non-noxious stimulus) and hyperalgesia (an exaggerated response to a normally noxious stimulus). Past few years of pain research has been mainly focused on precise understanding of the molecular and cellular nociceptive signatures altered during chronic pain, so that more effective pain relievers can be developed. The importance of protein kinases in normal cellular homeostasis and disease pathogenesis has evolved rapidly in the past few decades. The recent advancement defining the role of multiple protein kinases in regulating neuronal plasticity and pain sensitization has gained enough attention of pharmaceutical industry to develop specific and selective kinase inhibitors as analgesics. Cyclin-dependent kinase 5 (Cdk5) is one such emerging kinase in pain biology. We will discuss here the recent advancement and therapeutic potential of Cdk5 in pain signaling.

BiP, an endoplasmic reticulum chaperone, modulates the development of morphine antinociceptive tolerance

Morphine is a potent analgesic, but the molecular mechanism for tolerance formation after repeated use is not fully understood. Binding immunoglobulin protein (BiP) is an endoplasmic reticulum (ER) chaperone that is central to ER function. We examined knock-in mice expressing a mutant BiP with the retrieval sequence deleted in order to elucidate physiological processes that are sensitive to BiP functions. We tested the thermal antinociceptive effect of morphine in heterozygous mutant BiP mice in a hot plate test. Paw withdrawal latencies before and after a single administration of morphine were not significantly different between the wild-type and mutant BiP mice. Repeated morphine administration caused the development of morphine tolerance in the wild-type mice. The activation of glycogen synthase kinase 3b (GSK-3b) was associated with morphine tolerance, because an inhibitor of GSK-3β prevented it. On the other hand, the mutant BiP mice showed less morphine tolerance, and the activation of GSK-3b was suppressed in their brain. These results suggest that BiP may play an important role in the development of morphine tolerance. Furthermore, we found that a chemical chaperone which improves ER protein folding capacity also attenuated the development of morphine tolerance in wild-type mice, suggesting a possible clinical application of chemical chaperones in preventing morphine tolerance.

Nociceptive behavior following hindpaw burn injury in young rats: response to systemic morphine

OBJECTIVE

Develop a burn injury model in young age rats.

BACKGROUND

Management of pain after burn injury in pediatric patients is an unresolved clinical issue.

METHODS

A burn injury model in young rats of 3-4 weeks old was developed by briefly immersing the dorsal part of the right hindpaw in a hot water bath (85°C) for 12 seconds under pentobarbital anesthesia.

RESULTS

Burn injury, but not sham control, induced nociceptive behaviors (mechanical allodynia, thermal hyperalgesia) when examined on post-injury day 2, 4, and 7. In burn-injured rats, there was the upregulated expression of the NR1 subunit of the N-methyl-d-aspartate (NMDA) receptor, Akt1, Akt2, and protein kinase C γ (PKCγ), but downregulated expression of neuronal nitric oxide synthase (NOS), inducible NOS, and glycogen synthase kinase-3β, within the spinal cord dorsal horn ipsilateral to burn injury. Moreover, intraperitoneal administration of a clinically available NMDA receptor antagonist dextromethorphan (30 mg/kg, once daily × 7 days beginning on day 7 after burn injury) attenuated mechanical allodynia and thermal hyperalgesia in burn-injured rats. Different from our previous finding in adult burn-injured rats; however, burn injury in young rats of this age did not spontaneously shift the morphine antinociceptive response curve to the right within the dose range used in the study when exposed to morphine for the first time, suggesting that the development of intrinsic tolerance to morphine antinociception may be different from adult rats following burn injury.

CONCLUSIONS

Our data suggest that this model may be used to explore the mechanisms of burn injury-induced nociception in young rats and to differentiate the sequelae from burn injury between adult and young rats under certain experimental conditions.

The antinociceptive effects of AR-A014418, a selective inhibitor of glycogen synthase kinase-3 beta, in mice

We investigated the antinociceptive effects of AR-A014418, a selective inhibitor of glycogen synthase kinase-3β (GSK-3β) in mice. A 30-minute pretreatment with AR-A014418 (.1 and 1 mg/kg, intraperitoneal [ip]) inhibited nociception induced by an ip injection of acetic acid. AR-A014418 pretreatment (.1 and .3 mg/kg, ip) also decreased the late (inflammatory) phase of formalin-induced licking, without affecting responses of the first (neurogenic) phase. In a different set of experiments, AR-A014418 (.1-10 μg/site) coinjected intraplantarly (ipl) with formalin inhibited the late phase of formalin-induced nociception. Furthermore, AR-A014418 administration (1 and 10 ng/site, intrathecal [it]) inhibited both phases of formalin-induced licking. In addition, AR-A014418 coinjection (10 ng/site, it) inhibited nociception induced by glutamate, N-methyl-D-aspartate (NMDA), (±)-1-aminocyclopentane-trans-1,3-dicarboxylic acid (trans-ACPD), tumor necrosis factor-alpha (TNF-α), and interleukin-1beta (IL-1β) by 47 ± 12%, 48 ± 11%, 31 ± 8%, 46 ± 13%, and 44 ± 11%, respectively. In addition, a 30-minute pretreatment with NP031115 (3 and 10 mg/kg, ip), a different GSK-3 β inhibitor, also attenuated the late phase of formalin-induced nociception. Collectively, these results provide convincing evidence that AR-A014418, given by local, systemic, and central routes, produces antinociception in several mouse models of nociception. The AR-A014418-dependent antinociceptive effects were induced by modulation of the glutamatergic system through metabotropic and ionotropic (NMDA) receptors and the inhibition of the cytokine (TNF-α and IL-1β) signaling.

PERSPECTIVE

These results suggest that GSK-3β may be a novel pharmacological target for the treatment of pain.

Effects of repeated morphine treatment on the antinociceptive effects, intestinal absorption, and efflux from intestinal epithelial cells of morphine

The present study was conducted to investigate the effects of repeated treatment with morphine on the drug's antinociceptive effects, intestinal absorption, and transepithelial transport. The antinociceptive effects of morphine in rats were markedly decreased after repeated oral administration of the drug for 5 d, indicating the development of tolerance. In the morphine-tolerant rats, intestinal absorption of morphine was determined using the in situ loop method. Absorption of morphine from the jejunum was significantly decreased after repeated administration. The permeability of human intestinal epithelial Caco-2 cells was increased in the efflux direction after repeated treatment. The repeated administration of morphine also reduced the cellular accumulation and efflux of P-glycoprotein substrates ([(3)H]vincristine and rhodamine123) from Caco-2 cells, suggesting that it enhances P-glycoprotein-mediated efflux in Caco-2 cells. These results suggest that repeated use enhances the efflux of morphine in the epithelial cells of the small intestine, subsequently decreasing its intestinal absorption.

Molecular Roles of Cdk5 in Pain Signaling

Injury and inflammation trigger activation of several critical cellular pathways in nociceptive signaling in the peripheral nervous system, but their precise molecular mechanisms have not been clearly defined. Cyclin-dependent kinase 5 (Cdk5), a serine/threonine kinase, is mainly expressed in the post-mitotic neurons, and has many important roles in the development, functions and pathophysiology of diseases of the nervous system. Although many functional roles of Cdk5 have been identified in neurons, its precise role in pain signaling has not been well determined. Experimental inflammation in the hind paws of mice resulted in increased mRNA and protein levels of Cdk5 and its activator p35, as well as the Cdk5 activity in nociceptive neurons (Pareek et al., 2006). Furthermore, we also identified that Cdk5 phosphorylates transient receptor potential vanilloid 1 (TRPV1), a key receptor that modulates agonist-induced calcium influx in the neurons (Pareek et al., 2007). We subsequently demonstrated that inflammation triggers increase in Cdk5 activity through activation of early growth response 1 (Egr-1) and p35 expression by tumor necrosis factor alpha (TNF-α) (Utreras et al., 2009). These findings suggest that Cdk5 plays an important role in pain signaling and therefore Cdk5 and its activators are potentially important drug targets for development of novel analgesics to treat neuropathic pain.

The discovery of a selective, small molecule agonist for the MAS-related gene X1 receptor

The novel 7-transmembrane receptor MrgX1 is located predominantly in the dorsal root ganglion and has consequently been implicated in the perception of pain. Here we describe the discovery and optimization of a small molecule agonist and initial docking studies of this ligand into the receptor in order to provide a suitable lead and tool compound for the elucidation of the physiological function of the receptor.

Enhancement by grapefruit juice of morphine antinociception

The aim of this study was to investigate the effect of grapefruit juice intake on the antinociception of morphine in rats. The antinociception of morphine (30 mg/kg, per os (p.o.)) was significantly enhanced by the oral administration of grapefruit juice (2 ml/rat). Further, the effect of grapefruit juice was examined in morphine-tolerant rats. The repeated administration of morphine (100 mg/kg p.o.) for 5 d caused a marked decrease in the antinociception, indicating the development of morphine-tolerance. In the morphine-tolerant rats, oral administration of grapefruit juice potentiated significantly the antinociceptive effect of morphine. To examine the pharmacokinetics of morphine after the repeated treatment with morphine for 5 d, microdialysis probes were implanted into the jugular vein and spinal intrathecal space in rats. The morphine concentrations in the blood and intrathecal cerebrospinal fluid (CSF) were gradually decreased by the repeated treatment with morphine. The grapefruit juice treatment significantly increased the blood concentration of morphine in morphine-tolerant rats. These results suggest that oral administration of grapefruit juice enhances the morphine antinociception by increasing the intestinal absorption of this agent.

Attenuation of morphine tolerance by minocycline and pentoxifylline in naive and neuropathic mice

We have previously demonstrated that glial inhibitors reduce the development of allodynia and hyperalgesia, potentiating the effect of a single morphine dose in a neuropathic pain model. This study explores the effects of two glial activation inhibitors, minocycline and pentoxifylline, on the development of tolerance to morphine in naive and chronic constriction injury (CCI)-exposed mice. Administration of morphine to naive (20 mg/kg; i.p.) and CCI-exposed mice (40 mg/kg; i.p.) twice daily resulted in tolerance to its anti-nociceptive effect after 6 days. Injections of morphine were combined with minocycline (30 mg/kg, i.p.) or pentoxifylline (20 mg/kg, i.p.) administered as two preemptive doses before first morphine administration in naive or pre-injury in CCI-exposed mice, and repeated twice daily 30 min before each morphine administration. With treatment, development of morphine tolerance was delayed by 5 days (from 6 to 11 days), as measured by the tail-flick test in naive and by tail-flick, von Frey, and cold plate tests in CCI-exposed mice. Western blot analysis of CD11b/c and GFAP protein demonstrated that minocycline and pentoxifylline, at doses delaying development of tolerance to morphine analgesia, significantly diminished the morphine-induced increase in CD11b/c protein level. We found that repeated systemic administration of glial inhibitors significantly delays development of morphine tolerance by attenuating the level of this microglial marker under normal and neuropathic pain conditions. Our results support the idea that targeting microglial activation during morphine therapy/treatment is a novel and clinically promising method for enhancing morphine's analgesic effects, especially in neuropathic pain.

Protein kinases and addiction

Although drugs of abuse have different chemical structures and interact with different protein targets, all appear to usurp common neuronal systems that regulate reward and motivation. Addiction is a complex disease that is thought to involve drug-induced changes in synaptic plasticity due to alterations in cell signaling, gene transcription, and protein synthesis. Recent evidence suggests that drugs of abuse interact with and change a common network of signaling pathways that include a subset of specific protein kinases. The best studied of these kinases are reviewed here and include extracellular signal-regulated kinase, cAMP-dependent protein kinase, cyclin-dependent protein kinase 5, protein kinase C, calcium/calmodulin-dependent protein kinase II, and Fyn tyrosine kinase. These kinases have been implicated in various aspects of drug addiction including acute drug effects, drug self-administration, withdrawal, reinforcement, sensitization, and tolerance. Identifying protein kinase substrates and signaling pathways that contribute to the addicted state may provide novel approaches for new pharmacotherapies to treat drug addiction.

Sustained cardioprotection: exploring unconventional modalities

Since Murry et al. [Murry, C.E., Jennings, R.B., Reimer, K.A., 1986. Preconditioning with ischemia: a delay of lethal cell injury in ischemic myocardium. Circulation. 74, 1124-36.] initially reported on the powerful protective effects of ischemic preconditioning (PC), a plethora of experimental investigations have identified varied preconditioning protocols or mimetics to achieve cardioprotection. These stimuli predominantly act via archetypal mediators identified in associated signalling studies (including PI3-K, Akt, PKC, mitochondrial K(ATP) channels). Despite an intense research effort over the last 20 years, there remains a paucity of evidence that this protective paradigm is clinically exploitable. This may arise due to a number of drawbacks to conventional protection, including effects of age, disease, and interactions with other pharmacological agents. This encourages investigation of alternate strategies that trigger protection via unconventional signalling (distinct from conventional PC) and/or mediate sustained shifts in ischemic tolerance in hearts of varying age and disease status. This review considers briefly drawbacks to conventional PC, and focuses on alternate strategies for generating prolonged states of cardiac protection.

Regulation of ERK1/2 phosphorylation by acute and chronic morphine - implications for the role of cAMP-responsive element binding factor (CREB)-dependent and Ets-like protein-1 (Elk-1)-dependent transcription; small interfering RNA-based strategy

Extracellular signal-regulated kinases (ERKs) have been shown to be activated by opioids and functionally linked to addiction. Morphine-associated changes in ERK activity seem to be the characteristic features of opioid action. In this study, we observed a rapid and severe increase in ERK1/2 activity after a 5 min morphine treatment of HEK-MOR cells (transfected with the rat mu-opioid receptor MOR1) expressing mu-opioid receptor. Cellular adaptations to chronic (72 h) morphine treatment were manifested by a slight and sustained increase in ERK1/2 activity. Withdrawal caused by an opioid receptor antagonist - naloxone - attenuated phosphorylation of ERK1/2. Little information is available on the precise mechanism of ERK activity regulation. Using RNA interference technology, we generated stably transfected cells with silenced expression of cAMP-responsive element binding factor (CREB) and Ets-like protein-1 (Elk-1) transcription factors, which are known targets for activated ERK1/2. In these cells, ERK1/2 activity regulation was altered. Silencing of CREB or Elk-1 significantly increased ERK activation observed after 5 min of morphine stimulation. The initial level of activated ERKs in these cells was also augmented. Moreover, the cellular response to withdrawal signals and chronic opioid treatment was diminished. These differences suggest that both CREB-dependent and Elk-1-dependent transcription contribute to the expression of proteins regulating morphine-induced ERK activity (particular phosphatases, upstream kinases or their activatory proteins).

Endogenous opiates and behavior: 2006

This paper is the 29th consecutive installment of the annual review of research concerning the endogenous opioid system, now spanning 30 years of research. It summarizes papers published during 2006 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 neurological disorders (Section 11); electrical-related activity and neurophysiology (Section 12); general activity and locomotion (Section 13); gastrointestinal, renal and hepatic functions (Section 14); cardiovascular responses (Section 15); respiration and thermoregulation (Section 16); and immunological responses (Section 17).

The complex p25/Cdk5 kinase in neurofibrillary degeneration and neuronal death: the missing link to cell cycle

Emergence of the cell cycle hypothesis in neurodegenerative disease comes from the numerous lines of evidence showing a tight link between "cell cycle-like reactivation" and neuronal death. Terminally differentiated neurons remain in G0 phase and display, compared to proliferating cells, an opposite regulation pattern of cell cycle markers in that most of the key activators and inhibitors are respectively down- and up-regulated. It has been clearly established that any experimental attempt to force terminally differentiated neurons to divide ultimately leads to their death. Conversely, cell cycle blockade in experimental models of neuronal death is able to rescue neurons. Hence, cell cycle deregulation is certainly among mechanisms governing neuronal death. However, many questions remain unresolved, especially those related to which molecular mechanisms trigger cell cycle deregulation and how this deregulation leads to cell death. In the present review, we focus on neurodegeneration in Alzheimer's disease and discuss the cell cycle deregulation related to this neurodegenerative pathology. Finally, we emphasize the role of p25/Cdk5 kinase complex in this pathological process through retinoblastoma protein phosphorylation and derepression of E2F-responsive genes and other actors such as cdc2, cyclins, and MCM proteins.