Intrathecal midazolam regulates spinal AMPA receptor expression and function after nerve injury in rats

Reduced excitatory neurotransmission in the hippocampus after inflammation and sevoflurane anaesthesia

Background

Inflammation and general anaesthesia likely contribute to perioperative neurocognitive disorders, possibly by causing a neuronal imbalance of excitation and inhibition. We showed previously that treatment with lipopolysaccharide (LPS) and sevoflurane causes a sustained increase in a tonic inhibitory conductance in the hippocampus; however, whether excitatory neurotransmission is also altered remains unknown. The goal of this study was to examine excitatory synaptic currents in the hippocampus after treatment with LPS and sevoflurane. Synaptic plasticity in the hippocampus, a cellular correlate of learning and memory, was also studied.

Methods

Mice were injected with vehicle or LPS (1 mg kg-1 i.p.), and after 24 h they were then exposed to vehicle or sevoflurane (2.3%; 2 h). Hippocampal slices were prepared 48 h later. Excitatory synaptic currents were recorded from pyramidal neurones. Long-term potentiation (LTP) and long-term depression (LTD) were studied in the Schaffer collateral-cornu ammonis 1 pathway.

Results

The amplitude of miniature excitatory postsynaptic currents (EPSCs) was reduced after LPS+sevoflurane (P<0.001), whereas that of spontaneous EPSCs was unaltered, as evidenced by cumulative distribution plots. The frequency, area, and kinetics of both miniature and spontaneous EPSCs were unchanged, as were LTP and LTD.

Conclusions

The reduced amplitude of miniature EPSCs, coupled with the previously reported increase in tonic inhibition, indicates that the combination of LPS and sevoflurane markedly disrupts the balance of excitation and inhibition. Restoring this balance by pharmacologically enhancing excitatory neurotransmission and inhibiting the tonic current may represent an effective therapeutic option for perioperative neurocognitive disorders.

Different effects of dexmedetomidine and midazolam on the expression of NR2B and GABAA-α1 following peripheral nerve injury in rats

Neuropathic pain is a complex, chronic pain condition and the treatment is a major clinical challenge. Recent studies have shown that two FDA approved drugs dexmedetomidine (DEX) and midazolam (MZL), may be useful in treating neuropathic pain, but the mechanism is not fully dementated. Here, we investigated the effects and mechanisms of DEX and MZL treatment in the peripheral nerve injury model. Intramuscular injection with DEX and MZL attenuated the development of mechanical allodynia and thermal hyperalgesia in rats with chronic constriction injury (CCI). Concurrently, the expression of NMDA receptor subunit 2B (NR2B), GABA (A) receptor subunit alpha1 (GABAA-α1), and Sonic Hedgehog (SHH) displayed different temporal patterns in the thalamus and the ipsilateral dorsal horn of the spinal cord after CCI. Such that (1) NR2B expression was decreased on day 1 and 14, whereas GABAA-α1 expression was increased on day 1 in the thalamus, and NR2B expression was decreased on day 1, whereas GABAA-α1 expression was increased on day 1 and day 30 in the ipsilateral spinal cord dorsal horn after DEX treatment. (2) NR2B expression was increased on day 1, then decreased on day 14 and returned to baseline on day30, whereas GABAA-α1 expression was no significant changes on day 1, 14, 30 in the thalamus, and NR2B expression was decreased on day 14 and 30, whereas GABAA-α1 expression was no changes on day 1 and 14 but increased on day 30 after MZL treatment. Furthermore, the mechanical allodynia was significantly attenuated after PUR administration. Meanwhile the expression of NR2B was significantly decreased, and the expression of GABAA-α1 was significantly increased, in the thalamus and in the ipsilateral spinal cord dorsal horn when detected on postoperative day 1, 7, and 14. Our findings indicate that DEX and MZL have different mechanisms in CCI rats, suggesting different strategies could be considered in managing neuropathic pain in different individuals. © 2018 IUBMB Life, 70(2):143-152, 2018.

The Effect of Aromatherapy with the Essential Oil of Orange on Pain and Vital Signs of Patients with Fractured Limbs Admitted to the Emergency Ward: A Randomized Clinical Trial

BACKGROUND AND OBJECTIVE

Pain is an emotional and unpleasant experience associated with actual or potential tissue damage. The literature shows no study on the effect of aromatherapy with the essential oil of orange on unpleasant feelings of patients with fractured limbs. In this regard, this paper aims at studying the effect of aromatherapy with the essential oil of orange on patients with fractured limbs admitted to the emergency ward.

METHODS

Sixty patients admitted to the emergency ward of Vali-e-Asr Hospital were selected by purposive sampling method and then were divided into two groups of control and experiment by block method. This study was done in one shift work (morning or afternoon). Four drops of the orange oil were poured on a pad and were pinned with a plastic pin to the patient's collar, about 20 cm distant from head. The old pad was replaced by the new one every 1 h. The patients' pain and vital signs were checked every 1 h for at last 6 h. The data were analyzed by SPSS Version 21.

RESULTS

Forty (66.7%) patients were male and twenty (33.3%) were female. Their age average was 37.93 ± 18.19 years old. The most fractured cases were in the scapular (11 patients [18.3%]). Friedman test showed that pain in the experiment group (P = 0.0001) decreased significantly rather than the control group (0.339). However, in vital signs, there could be found that no significant change between the two groups was seen.

CONCLUSION

Aromatherapy with orange oil can relieve pain in patients with fractured limbs but has no effect on their vital signs. Therefore, aromatherapy with orange oil can be used as a complementary medicine in these patients.

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

Objectives

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

Methods

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

Key findings

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

Conclusions

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

The efficacy of different doses of Midazolam added to Lidocaine for upper extremity Bier block on the sensory and motor block characteristics and postoperative pain

Objective:

This study was designed to evaluate the effect of different doses of midazolam on anesthesia and analgesia quality when added to lidocaine during the intravenous regional anesthesia (IVRA).

Methods:

One hundred and forty patients underwent hand surgery were randomly allocated into four groups to receive 3 mg/kg lidocaine 2% diluted with saline to a total volume of 40 mL in the control Group L-C (n = 35), 30 μg/kg midazolam plus 3 mg/kg lidocaine 2% diluted with saline to a total volume of 40 mL in the midazolam Group L-M₁ (n = 35), 40 μg/kg midazolam plus 3 mg/kg 2% lidocaine diluted with saline to a total volume of 40 mL in the midazolam Group L-M₂ (n = 35), and 50 μg/kg midazolam plus 3 mg/kg lidocaine 2% diluted with saline to a total volume of 40 mL in the midazolam Group L-M₃ (n = 35). Sensory and motor block and recovery times, tourniquet pain, intra-operative analgesic requirement, and visual analog scale (VAS) scores were recorded.

Findings:

Onset time of sensory and motor block in L-M₃ Group was shorter than the L-M₂ and L-M₁ and L-C Groups (P < 0.001). Furthermore, prolonged sensory (P = 0.005) and motor recovery time (P = 0.001) in L-M₃ were longer than the other groups. Intra-operative VAS score and intra-operative fentanyl consumption in L-M₃ were lower than the other groups (P < 0.001). The numbers of patients needed to pethidine in Group L-M₃ were significantly less compared with the other groups (P = 0.035). VAS scores were significantly lower in Group L-M₃ in different time intervals in the postoperative period compared with the other groups (P < 0.001).

Conclusion:

Addition of 50 μg/kg midazolam for IVRA (Group L-M₃) enhanced intra-operative analgesia and improved anesthesia quality better than other groups receiving lower midazolam doses as well as a control group.

Injury-Dependent and Disability-Specific Lumbar Spinal Gene Regulation following Sciatic Nerve Injury in the Rat

Allodynia, hyperalgesia and spontaneous pain are cardinal sensory signs of neuropathic pain. Clinically, many neuropathic pain patients experience affective-motivational state changes, including reduced familial and social interactions, decreased motivation, anhedonia and depression which are severely debilitating. In earlier studies we have shown that sciatic nerve chronic constriction injury (CCI) disrupts social interactions, sleep-wake-cycle and endocrine function in one third of rats, a subgroup reliably identified six days after injury. CCI consistently produces allodynia and hyperalgesia, the intensity of which was unrelated either to the altered social interactions, sleep-wake-cycle or endocrine changes. This decoupling of the sensory consequences of nerve injury from the affective-motivational changes is reported in both animal experiments and human clinical data. The sensory changes triggered by CCI are mediated primarily by functional changes in the lumbar dorsal horn, however, whether lumbar spinal changes may drive different affective-motivational states has never been considered. In these studies, we used microarrays to identify the unique transcriptomes of rats with altered social behaviours following sciatic CCI to determine whether specific patterns of lumbar spinal adaptations characterised this subgroup. Rats underwent CCI and on the basis of reductions in dominance behaviour in resident-intruder social interactions were categorised as having Pain & Disability, Pain & Transient Disability or Pain alone. We examined the lumbar spinal transcriptomes two and six days after CCI. Fifty-four ‘disability-specific’ genes were identified. Sixty-five percent were unique to Pain & Disability rats, two-thirds of which were associated with neurotransmission, inflammation and/or cellular stress. In contrast, 40% of genes differentially regulated in rats without disabilities were involved with more general homeostatic processes (cellular structure, transcription or translation). We suggest that these patterns of gene expression lead to either the expression of disability, or to resilience and recovery, by modifying local spinal circuitry at the origin of ascending supraspinal pathways.

Differential roles of hippocampal glutamatergic receptors in neuropathic anxiety-like behavior after partial sciatic nerve ligation in rats

BACKGROUND

Neuropathic pain evoked by nerve injury is frequently accompanied by deterioration of emotional behaviors, but the underlying signaling mechanisms remain elusive. Glutamate (Glu) is the major mediator of excitatory synaptic transmission throughout the brain, and abnormal activity of the glutamatergic system has been implicated in the pathophysiology of pain and associated emotional comorbidities. In this study we used the partial sciatic nerve ligation (PSNL) model of neuropathic pain in rats to characterize the development of anxiety-like behavior, the expression of glutamatergic receptors, and the phosphorylation of extracellular signal-regulated kinase (ERK) in the hippocampus, the region that encodes memories related to emotions.

RESULTS

We found that the mechanical withdrawal threshold was significantly reduced and an anxiety-like behavior was increased as determined via open field tests and elevated plus-maze tests at 28 days after injury. No significant differences were found in the ratio of sucrose preference and immobility time detected by sucrose preference tests and forced swimming tests respectively, possibly due to the timing factor. The expression of N-methyl-D-aspartate (NMDA) receptor subtypes NR1 and NR2B, but not NR2A, GluR1, or GluR2 (the main subtype of the α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid [AMPA] receptor) in the hippocampus of injured rats was significantly reduced. Moreover, PSNL resulted in decreased phosphorylation of ERK1/2 in the hippocampus. Intriguingly, treatment with D-serine (a co-agonist of NMDA receptor, 1 g/kg intraperitoneally) reduced the anxiety-like behavior but not the mechanical hypersensitivity induced by PSNL.

CONCLUSIONS

PSNL can induce significant anxiety-like but not depression-like behavior, and trigger down-regulation of NMDA but not AMPA receptors in the hippocampus at 28 days after injury.

Midazolam exacerbates morphine tolerance and morphine-induced hyperactive behaviors in young rats with burn injury

Midazolam and morphine are often used in pediatric intensive care unit (ICU) for analgesia and sedation. However, how these two drugs interact behaviorally remains unclear. Here, we examined whether (1) co-administration of midazolam with morphine would exacerbate morphine tolerance and morphine-induced hyperactive behaviors, and (2) protein kinase C (PKC) would contribute to these behavioral changes. Male rats of 3-4 weeks old were exposed to a hindpaw burn injury. In Experiment 1, burn-injured young rats received once daily saline or morphine (10mg/kg, subcutaneous, s.c.), followed 30min later by either saline or midazolam (2mg/kg, intraperitoneal, i.p.), for 14 days beginning 3 days after burn injury. In Experiment 2, young rats with burn injury were administered with morphine (10mg/kg, s.c.), midazolam (2mg/kg, i.p.), and chelerythrine chloride (a non-specific PKC inhibitor, 10nmol, intrathecal) for 14 days. For both experiments, cumulative morphine anti-nociceptive dose-response (ED50) was tested and hyperactive behaviors such as jumping and scratching were recorded. Following 2 weeks of each treatment, ED50 dose was significantly increased in rats receiving morphine alone as compared with rats receiving saline or midazolam alone. The ED50 dose was further increased in rats receiving both morphine and midazolam. Co-administration of morphine and midazolam also exacerbated morphine-induced hyperactive behaviors. Expression of the NR1 subunit of the N-methyl-d-aspartate (NMDA) receptor and PKCγ in the spinal cord dorsal horn (immunohistochemistry; Western blot) was upregulated in burn-injured young rats receiving morphine alone or in combination with midazolam, and chelerythrine prevented the development of morphine tolerance. These results indicate that midazolam exacerbated morphine tolerance through a spinal NMDA/PKC-mediated mechanism.

Reduction in labor pain by intrathecal midazolam as an adjunct to sufentanil

BACKGROUND

Anesthesia today has strived to decrease labor pain in a tolerable and controllable fashion. Intrathecal midazolam has been introduced as an adjunct to analgesics. The study was planned to assess the efficacy, safety and duration of analgesia produced by intrathecal midazolam adjunct to sufentanil in decreasing labor pain.

METHODS

In a randomized clinical trial 80 parturient included in the study. The two groups were matched for age, cervical dilation, gravid, gestational age, and other demographic characteristics. Combination of sufentanil and midazolam administered intrathecally to experimental group and compared to sufentanil group. Time to reach maximum block, and pain score was measured and recorded.

RESULTS

Groups were matched for age and weight and other demographic characteristic. No significant adverse effect was seen in both groups including decrease in Apgar score. Duration of analgesia was 92.0 ± 12.7 in sufentanil group and 185.2 ± 15.2 minutes in midazolam and sufentanil group which was significantly different (P = 0.002). Numeric rating scale score was significantly lower in midazolam group compare to sufentanil group at 120 min (P = 0.01), 150 min (P = 0.0014), and 180 min (P = 0.001).

CONCLUSIONS

Intrathecal midazolam as an adjunct to opioid could significantly enhance analgesia in labor pain with no significant adverse effect. Intrathecal injection of midazolam is an appropriate alternative to parenteral or epidural analgesia in small hospital settings.

Leptin enhances NMDA-induced spinal excitation in rats: A functional link between adipocytokine and neuropathic pain

Recent studies have shown that leptin (an adipocytokine) played an important role in nociceptive behavior induced by nerve injury, but the cellular mechanism of this action remains unclear. Using the whole-cell patch-clamp recording from rat's spinal cord slices, we showed that superfusion of leptin onto spinal cord slices dose-dependently enhanced N-methyl-d-aspartate (NMDA) receptor-mediated currents in spinal cord lamina II neurons. At the cellular level, the effect of leptin on spinal NMDA-induced currents was mediated through the leptin receptor and the JAK2/STAT3 (but not PI3K or MAPK) pathway, as the leptin effect was abolished in leptin receptor-deficient (db/db) mice and inhibited by a JAK/STAT inhibitor. Moreover, we demonstrated in naïve rats that a single intrathecal administration of leptin enhanced spontaneous biting, scratching, and licking behavior induced by intrathecal NMDA and that repeated intrathecal administration of leptin elicited thermal hyperalgesia and mechanical allodynia, which was attenuated by the noncompetitive NMDA receptor antagonist MK-801. Intrathecal leptin also upregulated the expression of NMDA receptors and pSTAT3 within the rat's spinal cord dorsal horn, and intrathecal MK-801 attenuated this leptin effect as well. Our data demonstrate a relationship between leptin and NMDA receptor-mediated spinal neuronal excitation and its functional role in nociceptive behavior. Since leptin contributes to nociceptive behavior induced by nerve injury, the present findings suggest an important cellular link between the leptin's spinal effect and the NMDA receptor-mediated cellular mechanism of neuropathic pain. A functional link is demonstrated between leptin, an adipocytokine, and the cellular mechanisms of neuropathic pain via enhancement of function and expression of spinal N-methyl-d-aspartate receptors.

Quality of lidocaine analgesia with and without midazolam for intravenous regional anesthesia

PURPOSE

Midazolam has analgesic effects mediated by gamma aminobutyric acid-A receptors. This study was designed to evaluate the effect of midazolam on anesthesia and analgesia quality when added to lidocaine for intravenous regional anesthesia (IVRA).

METHODS

Forty patients undergoing hand surgery were randomly assigned to two groups to receive IVRA. The control group received 3 mg/kg lidocaine 2% w/v diluted with saline to a total volume of 40 ml, and the midazolam group received an additional 50 μg/kg midazolam. Sensory and motor block onset and recovery times, tourniquet pain, intraoperative analgesic requirements, sedation, and anesthesia quality were recorded. Postoperative pain and sedation scores, time to first analgesic requirements, analgesic use in the first 24 h, and side effects were noted.

RESULTS

Sensory and motor block onset and recovery times did not differ significantly between groups. Tourniquet pain scores were lower at 10, 15, 20, and 30 min (P < 0.0001) in the midazolam group. Three (15%) patients in the midazolam group required fentanyl for tourniquet pain compared with thirteen (65%) patients in the control group (P = 0.02). Patients in both groups received fentanyl once. Midazolam group showed that significantly less patients required diclofenac for postoperative analgesia (P < 0.01) and analgesic-free period during first postoperative 24 h was significantly longer (726.8 ± 662.8 min vs. 91.0 ± 35.9 min, P < 0.0001). Postoperative pain scores were lower (P < 0.0001) and sedation scores higher (P < 0.05) for the first 2 h in the midazolam group.

CONCLUSION

Addition of midazolam to lidocaine for IVRA improves anesthesia quality and enhances intraoperative and postoperative analgesia without causing side effects.

Acetazolamide and midazolam act synergistically to inhibit neuropathic pain

Treatment of neuropathic pain is a major clinical challenge that has been met with minimal success. After peripheral nerve injury, a decrease in the expression of the K-Cl cotransporter KCC2, a major neuronal Cl(-) extruder, leads to pathologic alterations in GABA(A) and glycine receptor function in the spinal cord. The down-regulation of KCC2 is expected to cause a reduction in Cl(-) extrusion capacity in dorsal horn neurons, which, together with the depolarizing efflux of HCO(3)(-) anions via GABA(A) channels, would result in a decrease in the efficacy of GABA(A)-mediated inhibition. Carbonic anhydrases (CA) facilitate intracellular HCO(3)(-) generation and hence, we hypothesized that inhibition of CAs would enhance the efficacy of GABAergic inhibition in the context of neuropathic pain. Despite the decrease in KCC2 expression, spinal administration of benzodiazepines has been shown to be anti-allodynic in neuropathic conditions. Thus, we also hypothesized that spinal inhibition of CAs might enhance the anti-allodynic effects of spinally administered benzodiazepines. Here, we show that inhibition of spinal CA activity with acetazolamide (ACT) reduces neuropathic allodynia. Moreover, we demonstrate that spinal co-administration of ACT and midazolam (MZL) act synergistically to reduce neuropathic allodynia after peripheral nerve injury. These findings indicate that the combined use of CA inhibitors and benzodiazepines may be effective in the clinical management of neuropathic pain in humans.

Ionotropic glutamate receptors in spinal nociceptive processing

Glutamate is the predominant excitatory transmitter used by primary afferent synapses and intrinsic neurons in the spinal cord dorsal horn. Accordingly, ionotropic glutamate receptors mediate basal spinal transmission of sensory, including nociceptive, information that is relayed to supraspinal centers. However, it has become gradually more evident that these receptors are also crucially involved in short- and long-term plasticity of spinal nociceptive transmission, and that such plasticity have an important role in the pain hypersensitivity that may result from tissue or nerve injury. This review will cover recent findings on pre- and postsynaptic regulation of synaptic function by ionotropic glutamate receptors in the dorsal horn and how such mechanisms contribute to acute and chronic pain.

Proteome of synaptosome-associated proteins in spinal cord dorsal horn after peripheral nerve injury

Peripheral nerve injury may lead to neuroadaptive changes of cellular signals in spinal cord that are thought to contribute to central mechanisms underlying neuropathic pain. Here we used a 2-DE-based proteomic technique to determine the global expression changes of synaptosome-associated proteins in spinal cord dorsal horn after unilateral fifth spinal nerve injury (SNI). The fifth lumbar dorsal horns ipsilateral to SNI or sham surgery were harvested on day 14 post-surgery, and the total soluble and synaptosomal fractions were isolated. The proteins derived from the synaptosomal fraction were resolved by 2-DE. We identified 27 proteins that displayed different expression levels after SNI, including proteins involved in transmission and modulation of noxious information, cellular metabolism, membrane receptor trafficking, oxidative stress, apoptosis, and degeneration. Six of the 27 proteins were chosen randomly and further validated in the synaptosomal fraction by Western blot analysis. Unexpectedly, Western blot analysis showed that only one protein in the total soluble fraction exhibited a significant expression change after SNI. The data indicate that peripheral nerve injury changes not only protein expression but also protein subcellular distribution in dorsal horn cells. These changes might participate in the central mechanism that underlies the maintenance of neuropathic pain.

Midazolam administration reverses thermal hyperalgesia and prevents gamma-aminobutyric acid transporter loss in a rodent model of neuropathic pain

BACKGROUND

Loss of gamma-aminobutyric acid (GABA) inhibition in the spinal dorsal horn may contribute to neuropathic pain. Here we examined whether systemic administration of the benzodiazepine midazolam would alleviate thermal hyperalgesia due to chronic constriction injury (CCI) of the sciatic nerve.

METHODS

Hyperalgesia was evaluated with the thermal paw withdrawal latency test before, and 3 and 7 days after CCI. Animals randomly received, via osmotic minipump infusion, midazolam (2.0 mg x kg(-1) x h(-1)), flumazenil (0.004 mg x kg(-1) x h(-1)), midazolam plus flumazenil at the same doses, or saline (0.01 mg x kg(-1) x h(-1)). Four groups of sham-operated rats (surgery without nerve ligation) received matched treatments. Levels of the GABA transporter 1 (GAT-1) in the lumbar spinal dorsal horn were estimated using western immunoblots 7 days after surgery.

RESULTS

Saline-treated CCI rats developed thermal hyperalgesia on Day 3 with a more pronounced effect on Day 7. Continuous midazolam infusion prevented thermal hyperalgesia on both days. The antihyperalgesic effect of midazolam was reversed by the coadministration of flumazenil. Infusion of flumazenil alone had no effect on the thermal hyperalgesia in CCI rats. Sham-operated rats treated with saline, midazolam, or midazolam plus flumazenil exhibited no thermal hyperalgesia. Unexpectedly, thermal paw withdrawal latency in sham animals treated with flumazenil alone was significantly decreased. Changes in GAT-1 levels paralleled the behavior. Midazolam prevented the CCI-associated decreases, and flumazenil reversed midazolam's effect. Flumazenil alone did not modify GAT-1 levels in CCI animals but in sham animals the transporter levels were significantly reduced.

CONCLUSIONS

GABA inhibition plays an important role in neuropathic pain. Continuous systemic benzodiazepine administration may prove effective in alleviating neuropathic pain.

Role of alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionate (AMPA) receptor subunit GluR1 in spinal dorsal horn in inflammatory nociception and neuropathic nociception in rat

The present study aims to investigate changes of spinal cord AMPA receptor GluR1 and its phosphorylation in inflammatory and neuropathic pain. Complete Freund's adjuvant (CFA) injection into the hind paw produced inflammatory thermal hyperalgesia that was assessed by decreased response latency to radiant heat; spinal nerve ligation (SNL) was used to induce mechanical allodynia that was evaluated with von Frey hairs. By method of Western blot, expression of GluR1 (the main subunit of the AMPA receptor) and its phosphorylated forms at serine 845 (pGluR1-Ser845) and at serine 831 (pGluR1-Ser831) in the spinal dorsal horn was observed. It was found that the expression of pGluR1-Ser845 and pGluR1-Ser831 increased significantly at 1 h after CFA injection, reached peak at 4 h and returned to the normal control level at 24 h, while no significant change was detected in GluR1 itself. In contrast, neither GluR1 nor pGluR1 showed any significant change in rats following SNL. These results suggest that phosphorylated GluR1 (pGluR1-Ser845 and pGluR1-Ser831) might play a role in the induction of inflammatory but not neuropathic pain.