[Show abstract][Hide abstract] ABSTRACT: Pulsed radiofrequency (PRF) is effective in the treatment of neuropathic pain in clinical practice. Its application to sites proximal to nerve injury can inhibit the activity of extra-cellular signal-regulated kinase (ERK) for up to 28 days. The spared nerve injury (SNI)+ immPRF group (immediate exposure to PRF for 6 min after SNI) exhibited a greater anti-allodynic effect compared with the control group (SNI alone) or the SNI + postPRF group (application of PRF for 6 min on the 14th day after SNI). Insulin-like growth factor 2 (IGF2) was selected using microarray assays and according to web-based gene ontology annotations in the SNI + immPRF group. An increase in IGF2 and activation of ERK1/2 were attenuated by the immPRF treatment compared with an SNI control group. Using immunofluorescent staining, we detected co-localized phosphorylated ERK1/2 and IGF2 in the dorsal horn regions of rats from the SNI group, where the IGF2 protein predominantly arose in CD11b- or NeuN-positive cells, whereas IGF2 immunoreactivity was not detected in the SNI + immPRF group. Taken together, these results suggest that PRF treatment immediately after nerve injury significantly inhibited the development of neuropathic pain with a lasting effect, most likely through IGF2 down-regulation and the inhibition of ERK1/2 activity primarily in microglial cells.
Preview · Article · Nov 2015 · International Journal of Molecular Sciences
[Show abstract][Hide abstract] ABSTRACT: We had previously demonstrated that excitatory amino acid glutamate plays a role in the progression and severity of knee osteoarthritis (OA), and early hyaluronic acid injection attenuates the OA progression by attenuation of knee joint glutamate level, which was also related to the cystine/glutamate antiporter system X (system XC (-) ) expression. System XC (-) uptakes cystine into chondrocytes for glutathione (GSH) synthesis, but the role of system XC (-) in OA is rarely addressed. Sulfasalazine (SSZ) is a system XC (-) inhibitor; SSZ was applied intra-articularly to study the function of system XC (-) in the development of OA in rats subjected to anterior cruciate ligament transection and medial meniscectomy (ACLT + MMx). Moerover, the system XC (-) activator N-acetylcysteine (NAC) was also applied to verify the role of system XC (-) . The intra-articular injection of SSZ significantly attenuated knee swelling and cartilage destruction in the knees of ACLT + MMx rats and this effect was blocked by NAC. The results showed that inhibition of system XC (-) function can attenuate ACLT + MMx-induced cartilage destruction. In the present study, system XC (-) inhibitor SSZ was shown to reduce glutamate content in synovial fluid and GSH in chondrocytes. It was also showed SSZ could attenuate ACLT + MMx-induced cartilage destruction, and treatment of NAC reversed the protective effect of SSZ. This article is protected by copyright. All rights reserved.
No preview · Article · Oct 2015 · Journal of Orthopaedic Research
[Show abstract][Hide abstract] ABSTRACT: Aims:
The study was to examine the effect of Hylan G-F 20 on the progression of posttraumatic osteoarthritis (PTOA) and the expression of the circadian genes neuronal PAS domain protein 2 (NPAS2) and period 2 (Per2).
We used the anterior cruciate ligament transaction and medial menisectomy (ACLT + MMx) model in Wistar rats. The rats were divided into three groups, the sham-operated group, the Hylan G-F 20-treated group, and the saline-treated group. Rats which underwent ACLT + MMx surgery were injected intraarticulary with, respectively, Hylan G-F 20 or saline once a week for 3 consecutive weeks, starting 7days after surgery. The gross morphology and histopathology of the experimental knee joints were evaluated at the end of week 6. Expression of the NPAS2 and Per2 genes was measured by real-time PCR.
Hylan G-F 20 suppressed the articular cartilage destruction and synovitis compared to the saline-treated group. Compared to the sham-operated group, the Hylan G-F 20-treated group showed significantly upregulated expression of NPAS2 in cartilage (2.53±0.08-fold higher; p<0.05) and a non-significant increase in Per2 expression (2.35±1.26-fold higher p=0.28), while the saline-treated group showed significant downregulation of NPAS2 expression and a non-significant decrease in Per2 expression.
Our data suggested that early intraarticular injection of Hylan G-F 20 attenuates the progression of PTOA and significantly upregulates NPAS2 expression. These findings provide a new direction for studying associations between the use of a pharmacological agent, the degenerative process, and circadian gene expression.
[Show abstract][Hide abstract] ABSTRACT: The application of pulsed radiofrequency (PRF) close to the dorsal root ganglia, or peripheral nerves, has been demonstrated to be effective for the treatment of chronic neuropathic pain conditions. The goal of this study was to investigate the analgesic effect of immediate PRF treatment after nerve injury and its possible cellular alterations in the dorsal horn of the spinal cord in rats with spared nerve injury (SNI).
Neuropathic pain was achieved in a SNI neuropathic pain model by ligating and cutting the common peroneal and tibial branches of the left sciatic nerve, leaving the sural nerve intact. Wistar rats were divided into four groups that received different treatments, i.e., SNI and PRF for 6 min at 45 V (SNI + PRF-45 V), at 60 V (SNI + PRF-60 V), SNI alone, and sham groups. After the SNI surgery, each rat was immediately given the PRF treatment (500 kHz, rate of 2 Hz, 20 ms duration, temperature below 42 °C) on the left sciatic nerve 0.3-0.4 cm proximal to the injured site. The behavioral measurements included mechanical allodynia and cold allodynia of the ipsilateral hind paw and were performed during the 28 days that followed the SNI surgery and PRF treatment. Total extracellular signal-regulated kinase 1 and 2 (ERK1/2) and phospho-ERK1/2 were measured using Western blot in the ipsilateral spinal cord from animals in the different groups.
The three groups of rats with nerve injuries manifested a lower paw withdrawal threshold (PWT) in the behavioral measurement of mechanical allodynia and a shorter painful-behavior duration in the cold allodynia test over 28 days. Mechanical allodynia measurement showed that both the PRF-45 V and PRF-60 V treatment groups exhibited a more prominent antiallodynic effect than did the SNI group from days 1 to 28 after surgery. Similarly, in comparison with the SNI group, both the SNI + PRF-45 V and SNI + PRF-60 V groups had significant inhibition on the cold allodynia measurement from days 1 to 28 after surgery. Furthermore, the activation of the extracellular signal-regulated kinase 1 and 2 (ERK1/2) in the ipsilateral spinal dorsal horn of SNI rats was effectively inhibited in the SNI + PRF-45 V and SNI + PRF-60 V groups for 28 days after surgery.
Immediate PRF application on the proximal nerve injury site provided a significant inhibition of neuropathic pain formation, accompanied by the inhibition of ERK activation.
[Show abstract][Hide abstract] ABSTRACT: Background
Glutamate and oxidative stress play important roles after subarachnoid hemorrhage (SAH). The ability to modulate glutamate transporter 1 (GLT-1) and the antioxidative effect of rosiglitazone have been demonstrated. We investigated the neuroprotective effect of rosiglitazone after SAH.
SAH was induced by double blood injection. The rats were randomly divided into sham, SAH + vehicle, and SAH + rosiglitazone groups and treated with dimethyl sulfoxide, dimethyl sulfoxide, and 6 mg/kg of rosiglitazone, respectively, at 2 and 12 h after SAH induction and then daily for 6 days. Cerebrospinal fluid dialysates were collected 30 min before SAH induction and then daily for 7 days for glutamate measurement. Mortality, body weight, and neurological scores were also measured daily. On day 7 after SAH, the wall thickness and the perimeter of the basilar artery (BA), neuron variability, GLT-1 levels, glial fibrillary acidic protein (GFAP) expression and activity, and malondialdehyde, superoxide dismutase, and catalase activities were also evaluated.
Rosiglitazone improved survival (relative risk = 0.325) and neurological functions and reduced neuronal degeneration (5.7 ± 0.8 vs. 10.0 ± 0.9; P
No preview · Article · Jul 2014 · Neurocritical Care
[Show abstract][Hide abstract] ABSTRACT: As known, long-term morphine infusion leads to tolerance. We previously demonstrated that both co-infusion and post-administration of ultra-low dose (±)-naloxone restores the antinociceptive effect of morphine in morphine-tolerant rats. However, whether the mechanism of the action of ultra-low dose (±)-naloxone is through opioid receptors or not. Therefore, in the present study, we further investigated the effect of ultra-low dose (+)-naloxone, it does not bind to opioid receptors, on the antinociceptive effect of morphine.
Male Wistar rats were implanted with one or two intrathecal (i.t.) catheters; one catheter was connected to a mini-osmotic pump, used for morphine (15 μg/h), ultra-low dose (+)-naloxone (15 pg/h), morphine plus ultra-low dose (+)-naloxone (15 pg/h) or saline (1 μl/h) infusion for 5 days. On day 5, either ultra-low dose (+)-naloxone (15 pg) or saline (5 μl) was injected via the other catheter immediately after discontinued morphine or saline infusion. Three hours later, morphine (15 μg in 5 μl saline) or saline were given intrathecally. All rats received nociceptive tail-flick test every 30 min for 120 min after morphine challenge at different temperature (45∼52 °C, respective).
Our results showed that, both co-infusion and post-treatment of ultra-low dose (+)-naloxone with morphine preserves the antinociceptive effect of morphine. Moreover, in the post administration rats, ultra-low dose (+)-naloxone further enhances the antinociceptive effect of morphine.
This study provides an evidence for ultra-low dose (+)-naloxone as a therapeutic adjuvant for patients who need long-term opioid administration for pain management.
No preview · Article · Dec 2013 · Journal of the Formosan Medical Association
[Show abstract][Hide abstract] ABSTRACT: Glutamate homeostasis and microglia activation play an important role in the development and maintenance of neuropathic pain. We designed this investigation to examine whether ultra-low dose naloxone administered alone or in combination with morphine could alter the concentration of the excitatory amino acids (EAAs) glutamate and aspartate, as well as the expression of tumor necrosis factor-α (TNF-α) and its receptors (TNFR1 and TNFR2) in the spinal cord dorsal horn of rats with partial sciatic nerve transection (PST).
Male Wistar rats underwent intrathecal catheter implantation for drug delivery and were divided in 7 groups: sham-operated + saline (sham), PST + saline (S), PST + 15 ng naloxone (n), PST + 15 µg naloxone (N), PST + 10 µg morphine (M), PST + 15 ng naloxone + 10 µg morphine (Mn), PST + 15 µg naloxone + 10 µg morphine (MN). Thermal withdrawal latency and mechanical withdrawal threshold, TNF-α and TNFR expression in the spinal cord and dorsal root ganglia, and EAAs glutamate and aspartate concentration in cerebrospinal fluid dialysates were measured.
Ten days after PST, rats developed hyperalgesia (P < 0.0001) and allodynia (P < 0.0001), and increased TNF-α (P < 0.0001) and TNFR1 expression (P = 0.0009) were measured in the ipsilateral spinal cord dorsal horn. The antihyperalgesic and antiallodynic effects of morphine (10 μg) were abolished by high-dose naloxone (15 μg; P = 0.0031) but enhanced by ultra-low dose naloxone (15 ng; P = 0.0015), and this was associated with a reduction of TNF-α (P < 0.0001) and TNFR1 (P = 0.0009) expression in the spinal cord dorsal horn and EAAs concentration (glutamate: P = 0.0001; aspartate: P = 0.004) in cerebrospinal fluid dialysate. Analysis of variance (ANOVA) or Student t test with Bonferroni correction were used for statistical analysis.
Ultra-low dose naloxone enhances the antihyperalgesia and antiallodynia effects of morphine in PST rats, possibly by reducing TNF-α and TNFR1 expression, and EAAs concentrations in the spinal dorsal horn. Ultra-low dose naloxone may be a useful adjuvant for increasing the analgesic effect of morphine in neuropathic pain conditions.
No preview · Article · Dec 2013 · Anesthesia and analgesia
[Show abstract][Hide abstract] ABSTRACT: Object:
Baicalein has been shown to offer neuroprotection in the ischemic brain, but its effect in subarachnoid hemorrhage (SAH) is unknown. The authors used a double-hemorrhage model to study the role of early baicalein treatment in SAH.
Subarachnoid hemorrhage was induced in male Wistar rats through a repeat injection of autologous blood at a 48-hour interval. Rats subjected or not subjected to SAH received a 30-mg/kg baicalein injection 3 hours after SAH and daily for 6 consecutive days, and results were compared with those obtained in vehicle-treated control rats. Mortality of the rats was recorded. Neurological outcome was assessed daily. Cerebrospinal fluid dialysates were collected and examined for glutamate concentrations. Cerebral vasospasm (CVS), brain water content, neuron variability, expression of glutamate transporter-1 (GLT-1), immunoreactivity of astrocyte, and level of malondialdehyde, activities of superoxide dismutase (SOD), and catalase in brain tissues content were determined on post-SAH Day 7.
Mortality rate, neuronal degeneration, brain water content, and CVS were decreased and neurological function improved in the baicalein-treated rats. Baicalein increased astrocyte activity and preserved GLT-1, which attenuated the glutamate surge after SAH. Baicalein also provided antioxidative stress by preserving activities of SOD and catalase and decreased malondialdehydelevel after SAH. The glutamate, body weight, neurological scores, and glial fibrillary acidic protein activity were significantly correlated. The CVS was correlated with neuronal degeneration, and GLT-1 was correlated with oxidative stress.
Early baicalein treatment attenuated CVS and limited neurological injury following SAH. These data may indicate clinical utility for baicalein as an adjunct therapy to reduce brain injury and improve patient outcomes.
Full-text · Article · May 2013 · Journal of Neurosurgery
[Show abstract][Hide abstract] ABSTRACT: Background/purpose:
In a recent study, we found that baicalin exhibited a potent analgesic effect on carrageenan-evoked thermal hyperalgesia. The underlining mechanisms may be associated with inhibition of inflammatory mediator overproduction, including proinflammatory cytokines, nitric oxide (NO), and prostaglandin E2 (PGE2). In the present study, we examined the effect of baicalin on the antinociceptive effect of morphine and histone deacetylase 1 (HDAC1) expression in the spinal cord dorsal horn in neuropathic pain rats.
Neuropathic pain was induced by tight ligation of the left L5 spinal nerve of the rats. An intrathecal catheter was implanted for drug administration. Nociception was assessed by using the plantar test with the Hargreaves radiant heat apparatus, and the von Frey test with the dynamic plantar anesthesiometer. Spinal cords were removed for histone acetyl-H3 and HDAC1 western blot analysis at the end of the nociceptive assessment.
The results showed that hyperalgesia and allodynia were observed in the spinal nerve ligated (SNL) left hindlimb; it was companied by histone-H3 deacetylation and HDAC1 overexpression on the ipsilateral side of the spinal cord dorsal horn. Intrathecal injection of baicalin (10 μg) significantly attenuated the allodynia and hyperalgesia, and enhanced the antinociceptive effect of morphine (15 μg). Moreover, baicalin reversed the histone-H3 acetylation and suppressed HDAC1 expression on the ipsilateral side of the spinal cord dorsal horn of SNL rats.
The present findings suggest that baicalin can ameliorate neuropathic pain by suppressing HDAC1 expression and preventing histone-H3 acetylation in the spinal cord dorsal horn of SNL rats.
No preview · Article · May 2013 · Journal of the Formosan Medical Association
[Show abstract][Hide abstract] ABSTRACT: A tourniquet is commonly used in limb surgery. Tourniquet inflation after a period of time may produce painful sensation. While the mechanisms of tourniquet-induced pain are still unknown, two components, pressure and ischemia, have been proposed. In this study, in vivo microdialysis was used to detect changes in intrathecal glutamate, an excitatory amino acid highly relevant to pain transmission, following hindlimb tourniquet application and femoral artery occlusion in the rat.
Male Wistar rats were used. For the tourniquet study, 6 rats of the study group received 30 minutes right hindlimb tourniquet inflation and another 6 rats as the control group received only tourniquet application without inflation. In the femoral artery occlusion study, 6 rats of the study group received 30 minutes right femoral artery occlusion and another 6 rats as the control group received only sham operation without femoral artery occlusion. Cerebrospinal fluid dialysates were collected prior to, during, and after tourniquet application or femoral artery occlusion. Glutamate was measured by HPLC.
A significant increase in intrathecal glutamate release was found during the tourniquet inflation period, and it returned to baseline after tourniquet deflation. No change of glutamate release was noted during femoral artery occlusion or after femoral artery reperfusion.
The intrathecal glutamate release was increased by the hindlimb tourniquet inflation, but not influenced by femoral artery occlusion in the rat.
No preview · Article · May 2013 · Journal of the Formosan Medical Association
[Show abstract][Hide abstract] ABSTRACT: The purpose of this preliminary study was to examine whether collateral meridian (CM) therapy was feasible in treating knee osteoarthritis (OA) pain.
Twenty-eight patients with knee OA and knee pain were randomly allocated to 2 groups. The CM group patients received CM therapy, whereas the control patients received placebo treatment for knee pain relief. Patients in the CM group received 2 CM treatments weekly for 3 weeks. The outcome measures were pain intensity on a visual analog scale, and knee function was determined using the Western Ontario and McMaster Universities Osteoarthritis Index.
In the CM group, the posttreatment visual analog scale and Western Ontario and McMaster Universities Osteoarthritis Index scores were lower than those of the control group; a significant reduction in pain intensity (P = .02, P = .01, respectively) and improvement in knee function (P = .04, P = .03, respectively) were shown in the CM group at the second and third week.
Collateral meridian therapy may be feasible and effective for knee OA pain relief and knee function recovery. Therefore, additional randomized control trials are warranted.
No preview · Article · Feb 2013 · Journal of manipulative and physiological therapeutics
[Show abstract][Hide abstract] ABSTRACT: Opioids have been used as potent analgesics in clinics for decades; however, their long-term administration leads to tolerance. Two possible mechanisms for drug tolerance are postulated as within-system and between-systems adaptation. The within-system tolerance is involved in the signal transduction of opioid receptors, including downregulation of opioid receptors, uncoupling of G-protein from opioid receptors, and β-arrestin recruitment to opioid receptors, which causes receptor desensitization and internalization/endocytosis. The between-systems tolerance comprehends the glutamatergic receptor system and glial activation with the release of proinflammatory cytokines, and thus the analgesic effect of morphine is reduced. Tumor necrosis factor-α (TNF-α) is a vital proinflammatory cytokine and exerts either a neurotoxic or neuroprotective effect on different diseases of the central nervous system. TNF-α has also been demonstrated to correlate with neuronal plasticity via activation of spinal glial cells and enhancement of glutamatergic transmission. Previous studies had revealed an increased expression of TNF-α in morphine tolerance. This review article focuses on the role of TNF-α in neuroinflammation and the glutamatergic receptor system in morphine tolerance. It may provide another adjuvant therapy for morphine tolerance, which extends the effectiveness of opioids in clinical pain management.
[Show abstract][Hide abstract] ABSTRACT: An intravenous bolus of fentanyl often induces a cough reflex. This study investigates whether priming with rocuronium can effectively attenuate fentanyl-induced coughing.
The study involved 260 participants, aged between 18 and 80 years of age, who were undergoing various elective surgeries. They were randomly assigned to two groups. Patients in the study group (the rocuronium group) were treated with intravenous (IV) 0.06 mg/kg rocuronium, whereas those in the control group were treated with the same volume of normal saline. Fentanyl (1.5 μg/kg IV, given over 2 seconds) was administered 30 seconds after the injection of rocuronium or normal saline. We recorded the number of coughs for 1 minute after the fentanyl injection.
Patients in the rocuronium group showed a significantly lower incidence of coughing (8.5% vs. 23.1%, in the control group; p < 0.05) and a milder severity of cough in comparison with the patients in the control group.
Pretreatment with IV rocuronium (0.06 mg/kg) suppressed the cough reflex induced by fentanyl. Therefore, priming with rocuronium may be a clinically useful method for preventing fentanyl-induced cough.
[Show abstract][Hide abstract] ABSTRACT: Epigenetic reprogramming may have a possible role in neuropathic pain development; the present study examined the global patterns of lysine histone modification. In this serial study we analyzed the levels of histone 3 lysine 4 monomethylation, histone 3 lysine 4 dimethylation, and histone 3 lysine 9 trimethylation in pertussis toxin (PTX)-induced thermal hyperalgesic rat spinal cords.
Male Wistar rats implanted with an intrathecal catheter received a single intrathecal PTX (1μg in 5μl saline) injection. Four days later, they were randomly assigned to receive either a single injection of saline, or ultra-low-dose naloxone (15ng in 5μl saline), followed by morphine (10μg in 5μl saline) injection 30 minutes later.
The results showed that PTX injection induced thermal hyperalgesia and significant increase of global histone methylation in the spinal cords. Intrathecal morphine alone did not affect the thermal hyperalgesia and global histone methylation. In contrast, intrathecal administration of ultra-low-dose naloxone plus morphine significantly attenuated the PTX-induced thermal hyperalgesia and down-regulated the global histone methylation.
The results suggest that ultra-low-dose naloxone might be clinical valuable for neuropathic pain management via regulating global histone modification.
[Show abstract][Hide abstract] ABSTRACT: Ultra-low dose naloxone has been shown to restore the antinociceptive effect of morphine in pertussis toxin (PTX)-treated rats by suppressing spinal microglia activation and inhibiting inflammatory cytokine expression. This study was further investigated the mechanism by which ultra-low dose naloxone promotes analgesia in pertussis toxin-treated rats.
Male Wistar rats were implanted with an intrathecal (i.t.) catheter and injected either saline or PTX (1 μg). Four days later, rats randomly received either saline, or ultra-low dose naloxone, or recombinant rat interleukin-10 (rrIL-10) (1 μg) injection followed by saline or morphine (10 μg) 30 min later. In some experiments, mouse anti-rat IL-10 antibody (10 μg) was injected intrathecally into PTX injected rats daily on days 4, 5, 6, and 7. On day 7, ultra-low dose naloxone was given 1h after antibody injection with or without subsequent morphine injection.
PTX injection induced notable thermal hyperalgesia and mechanical allodynia. Injection of ultra-low dose naloxone preserved the antinociceptive effect of morphine in PTX-treated rats and associated an increasing of IL-10 protein expression. Intrathecal injection rrIL-10 alone or in combination with morphine, not only reversed mechanical allodynia but also partially restored the antinociceptive effect of morphine; injection of anti-rat IL-10 antibody attenuated the effect of morphine plus ultra-low dose naloxone on mechanical allodynia and completely inhibited the antinociceptive effect of morphine.
These results indicate that intrathecal ultra-low dose naloxone induces IL-10 expression in spinal neuron and microglia, which suppresses PTX-induced neuroinflammation and restores the antinociceptive effect of morphine.
[Show abstract][Hide abstract] ABSTRACT: In the present study, we examined the effects and mechanisms of the Chinese herb resveratrol on attenuation of morphine tolerance in rats.
Male Wistar rats were implanted with 2 intrathecal catheters; one catheter was connected to a mini-osmotic pump, used for either morphine (15 μg/h) or saline (1 μL/h) infusion for 5 days. On day 5, resveratrol (7.5, 15, 30, or 60 μg), dimethyl sulfoxide (5 μL), or saline (5 μL) was injected via the other catheter immediately after the discontinued morphine infusion. Three hours later, intrathecal morphine (15 μg in 5 μL saline) was given. All rats received the nociceptive tail-flick test every 30 minutes for 120 minutes after the morphine challenge.
Long-term morphine infusion induced antinociceptive tolerance and up-regulated N-methyl-d-aspartate receptor (NMDAR) subunit NR1 and NR2B expression in the synaptosome fraction of the tolerant spinal cord dorsal horn. Resveratrol pretreatment provided a significant antinociceptive effect of morphine in morphine-tolerant rats, and it was associated with reversal of the up-regulated NR1 and NR2B subunits in the synaptosome fraction of morphine-tolerant rat spinal cords. NR1/NR2B-specific antagonist ifenprodil treatment produced a similar effect as that of resveratrol. Furthermore, an increase of postsynaptic density-95/NR1/NR2B complex immunoprecipitation in morphine-tolerant rat spinal cord was also inhibited by resveratrol pretreatment. Moreover, chronic morphine infusion activated glial cells with an increase of proinflammatory cytokine tumor necrosis factor-α, interleukin-1β, and interleukin-6 mRNA expression in morphine-tolerant rat spinal cords and these effects were suppressed by resveratrol pretreatment before the morphine challenge.
Resveratrol attenuates morphine tolerance by inhibiting neuroinflammation and down-regulating NMDAR NR1 and NR2B subunit expression. Resveratrol regulates the NMDAR expression, which might be involved in a loss of scaffolding postsynaptic density-95 protein.
No preview · Article · Jun 2012 · Anesthesia and analgesia
[Show abstract][Hide abstract] ABSTRACT: The tricyclic antidepressant amitriptyline binds with high affinity to N-methyl-d-aspartate receptors (NMDARs) and inhibits NMDAR-mediated events. Activation of the postsynaptic density protein-95 (PSD-95)/NMDAR-mediated downstream signaling cascade, including neuronal nitric oxide synthase (nNOS) and protein kinase gamma (PKCγ), has been shown to be involved in morphine tolerance. The present study examined the potential effect of amitriptyline on chronic morphine infusion-induced spinal PSD-95/NMDAR/nNOS/PKCγ signaling in morphine tolerance. Male Wistar rats were implanted with an intrathecal catheter and received an intrathecal infusion of saline or amitriptyline (15 μg/h), morphine+saline (tolerance induction, 15 μg/h), or morphine+amitriptyline for 5 days. Co-administration of amitriptyline with morphine not only preserved the antinociceptive effect of morphine, but also attenuated astrocyte activation in the rat spinal cord dorsal horn. On day 5 after drug infusion, increased expression and phosphorylation of spinal membrane NMDAR NR1 subunit and expression of PSD-95 were observed following chronic morphine infusion and these effects were attenuated by amitriptyline co-infusion. Upregulation of NMDAR-induced intracellular nNOS expression was also inhibited by amitriptyline co-infusion in chronic morphine-infused rats. Furthermore, amitriptyline co-infusion significantly inhibited morphine-induced PKCγ expression in both the cytosol and membrane of spinal neurons. These findings suggest that the attenuation of morphine tolerance caused by amitriptyline is due to downregulation of NMDAR NR1 subunit expression in the synaptosomal membrane accompanied by decreased expression of the scaffolding protein PSD-95. The effects of amitriptyline in attenuating astrocyte activation and reversing tolerance to morphine may be due, at least in part, to inhibition of the PSD-95/NMDAR NR1/nNOS/PKCγ signaling cascade.
No preview · Article · Apr 2012 · Behavioural brain research