Immediate inhibition of spinal secretory phospholipase A2 prevents the pain and elevated spinal neuronal hyperexcitability and neuroimmune regulatory genes that develop with nerve root compression.

Cervical nerve root injury induces a host of inflammatory mediators in the spinal cord that initiate and maintain neuronal hyperexcitability and pain. Secretory phospholipase A2 (sPLA2) is an enzyme that has been implicated as a mediator of pain onset and maintenance in inflammation and neural injury. Although sPLA2 modulates nociception and excitatory neuronal signaling in vitro, its effects on neuronal activity and central sensitization early after painful nerve root injury are unknown. This study investigated whether inhibiting spinal sPLA2 at the time of nerve root compression (NRC) modulates the pain, dorsal horn hyperexcitability, and spinal genes involved in glutamate signaling, nociception, and inflammation that are seen early after injury. Rats underwent a painful C7 NRC injury with immediate intrathecal administration of the sPLA2 inhibitor thioetheramide-phosphorlycholine. Additional groups underwent either injury alone or sham surgery. One day after injury, behavioral sensitivity, spinal neuronal excitability, and spinal cord gene expression for glutamate receptors (mGluR5 and NR1) and transporters (GLT1 and EAAC1), the neuropeptide substance P, and pro-inflammatory cytokines (TNFα, IL1α, and IL1ß) were assessed. Treatment with the sPLA2 inhibitor prevented mechanical allodynia, attenuated neuronal hyperexcitability in the spinal dorsal horn, restored the proportion of spinal neurons classified as wide dynamic range, and reduced genes for mGluR5, substance P, IL1α, and IL1ß to sham levels. These findings indicate spinal regulation of central sensitization after painful neuropathy and suggest that spinal sPLA2 is implicated in those early spinal mechanisms of neuronal excitability, perhaps via glutamate signaling, neurotransmitters, or inflammatory cascades.

AMP-Activated Protein Kinase Activation in Dorsal Root Ganglion Suppresses mTOR/p70S6K Signaling and Alleviates Painful Radiculopathies in Lumbar Disc Herniation Rat Model.

STUDY DESIGN: Animal experiment: a rat model of lumbar disc herniation (LDH) induced painful radiculopathies. OBJECTIVE: To investigate the role and mechanism of AMP-activated protein kinase (AMPK) in dorsal root ganglia (DRG) neurons in LDH-induced painful radiculopathies. SUMMARY OF BACKGROUND DATA: Overactivation of multiple pain signals in DRG neurons triggered by LDH is crucial to the development of radicular pain. AMPK is recognized as a cellular energy sensor, as well as a pain sensation modulator, but its function in LDH-induced pain hypersensitivity remains largely unknown. METHODS: The LDH rat model was established by autologous nucleus pulposus transplantation into the right lumbar 5 (L5) nerve root. At different time points after AMPK agonist metformin (250 mg/kg/d) or mammalian target of rapamycin (mTOR) inhibitor rapamycin (5 mg/kg) intraperitoneal administration, thermal and mechanical sensitivity were evaluated by measuring paw withdrawal latency (PWL) and 50% paw withdrawal thresholds (PWT). The levels of AMPK, mTOR, and p70S6K phosphorylation were determined by Western blot. We also investigated the proportion of p-AMPK positive neurons in the right L5 DRG neurons using immunofluorescence. RESULTS: LDH evoked persistent thermal hyperalgesia and mechanical allodynia on the ipsilateral paw, as indicated by the decreased PWL and 50% PWT. These pain hypersensitive behaviors were accompanied with significant inhibition of AMPK and activation of mTOR in the associated DRG neurons. Pharmacological activation of AMPK in the DRG neurons not only suppressed mTOR/p70S6K signaling, but also alleviated LDH-induced pain hypersensitive behaviors. CONCLUSION: We provide a molecular mechanism for the activation of pain signals based on AMPK-mTOR axis, as well as an intervention strategy by targeting AMPK-mTOR axis in LDH-induced painful radiculopathies. LEVEL OF EVIDENCE: N/A.

Intracisternal administration of NR2 subunit antagonists attenuates the nociceptive behavior and p-p38 MAPK expression produced by compression of the trigeminal nerve root.

BACKGROUND: We investigated the role of the central NMDA receptor NR2 subunits in the modulation of nociceptive behavior and p-p38 MAPK expression in a rat model with compression of the trigeminal nerve root. To address this possibility, changes in air-puff thresholds and pin-prick scores were determined following an intracisternal administration of NR2 subunit antagonists. We also examined effects of NR2 subunit antagonists on the p-p38 MAPK expression. RESULTS: Experiments were carried out using male Sprague-Dawley rats weighing (200-230 g). Compression of the trigeminal nerve root was performed under pentobarbital sodium (40 mg/kg) anesthesia. Compression of the trigeminal nerve root produced distinct nociceptive behavior such as mechanical allodynia and hyperalgesia. Intracisternal administration of 10 or 20 µg of D-AP5 significantly increased the air-puff threshold and decreased the pin-prick scores in a dose-dependent manner. The intracisternal administration of PPPA (1, 10 µg), or PPDA (5, 10 µg) increased the air-puff threshold and decreased the pin-prick scores ipsilateral as well as contralateral to the compression of the trigeminal root. Compression of the trigeminal nerve root upregulated the expression of p-p38 MAPK in the ipsilateral medullary dorsal horn which was diminished by D-AP5, PPPA, PPDA, but not Ro25-6981. CONCLUSIONS: Our findings suggest that central NMDA receptor NR2 subunits play an important role in the central processing of trigeminal neuralgia-like nociception in rats with compression of the trigeminal nerve root. Our data further indicate that the targeted blockade of NR2 subunits is a potentially important new treatments strategy for trigeminal neuralgia-like nociception.

[Effect of the heat shock protein 27 on NOS expression of spinal cord anterior hornmotoneurons after brachial plexus avulsion].

AIM: To observe the effect of heat shock protein 27 (Hsp27) on nitric oxide synthase (NOS) of spinal cord anterior horn after brachial plexus roots avulsion. METHODS: Sixty male adult Wistar rats were divided into control and experiment groups at random. The experiment group subjected to heat shock under 45 degrees C for 15 min, and maintained under 42 degrees C for 20 min subsequently. After recovering 24 h under the room temperature, the nerves of brachial plexus were avulsion with microhemostatic forcep. In a span from 12 h to 7 d, these animals were killed at different time. But the control group only received the surgery of the nerve roots of brachial plexus avulsion. The freeze sections of spinal cord were stained by NADPH-d histochemistry, HSP27 immunohistochemical. RESULTS: (1) In experiment group, the motoneuron began to express NOS abundantly at 12 h after avulsion (A=0.13625). Then the NOS-positive neurons declined quickly, but in control group, the motoneuron began to express NOS at the 5th day after lesion. (2) Hsp27 begin to show the peak at 1 d in experiment and control groups, but the experiment group were more strong than the control group. CONCLUSION: Hsp27 inhibited NOS of motoneuron after avulsion and brought into full play the cytoprotection.

Electroacupuncture inhibits cyclooxygenase-2 up-regulation in rat spinal cord after spinal nerve ligation.

Electroacupuncture (EA) has long been used to treat pain including neuropathic pain, but its mechanisms remain to be delineated. Since cyclooxygenase-2 (COX-2) has been reported to increase in the spinal dorsal horn following spinal nerve ligation (SNL) and it may play a role in the neuropathic pain, we hereby tested the hypothesis that EA may affect COX-2 expression and hence neuropathic nociception after SNL. The results showed that EA (2 Hz) can significantly reduce mechanical and thermal hypersensitivity following lumbar L5 SNL in rats. Immunostaining demonstrated suppression of COX-2 expression in the spinal L4-L6 dorsal horn after EA. The present results suggest that EA may alleviate neuropathic hypersensitivity by, at least partially, inhibiting COX-2 expression in the spinal cord.

Reduced hyperalgesia in homozygous carriers of a GTP cyclohydrolase 1 haplotype.

BACKGROUND: Carriers of a particular haplotype of the GTP cyclohydrolase gene (GCH1) had less pain after surgery for chronic lumbar radiculopathy and a decreased sensitivity to some experimental mechanical pain stimuli. Ex-vivo, GCH1 upregulation and BH4 production after forskolin stimulation were reduced, while baseline BH4 concentrations were not affected. This suggested that the haplotype may mainly exert its modulating function when the GCH1 system is provoked. The present study aimed at (i) testing this hypothesis and (ii) independently reproducing the pain-decreasing effects of a particular GCH1 haplotype having been previously associated with pain protection. METHODS: Experimental pain models with sensitization (local skin inflammation, dermal capsaicin application) and without sensitization (punctate pressure, blunt pressure, thermal and electrical pain) were assessed in 10 homozygous and 22 non-carriers of the particular GCH1 haplotype reportedly associated with pain protection. GCH1, iNOS upregulation and BH4 production were assessed ex-vivo in white blood cells after lipopolysaccharide stimulation for 24 h. RESULTS: Carriers of the particular GCH1 haplotype addressed in this study had higher thresholds to punctate mechanical pain (von Frey hairs) following local skin inflammation (18.1+/-11.3 vs. 9+/-2.8 g; p=0.005) and, to a lesser degree, to heat pain following capsaicin sensitization (35.2+/-0.9 vs. 36.6+/-2.4 degrees C; p=0.026). In contrast, heat and pressure thresholds and tolerance to electrical stimulation in pain models without sensitization did not differ among the genotypes. GCH1, BH4 and iNOS upregulation in white blood cells after lipopolysaccharide stimulation were decreased in carriers of the GCH1 haplotype, which verified that the genotype groups differed with respect to regulation of the biopterin pathway. CONCLUSIONS: This study verifies previous results that decreased GCH1 function or inducibility as a result of genetic polymorphisms protects against pain. This study extents previous results by showing that this pain protection is mainly conferred under conditions of hyperalgesia resulting from sensitization, supporting specific functions of BH4 in relation to particular aspects of pain.

The effects of the sympathetic nerves on lumbar radicular pain: a behavioural and immunohistochemical study.

A rat model of lumbar root constriction with an additional sympathectomy in some animals was used to assess whether the sympathetic nerves influenced radicular pain. Behavioural tests were undertaken before and after the operation. On the 28th post-operative day, both dorsal root ganglia and the spinal roots of L4 and L5 were removed, frozen and sectioned on a cryostat (8 microm to 10 microm). Immunostaining was then performed with antibodies to tyrosine hydroxylase (TH) according to the Avidin Biotin Complex method. In order to quantify the presence of sympathetic nerve fibres, we counted TH-immunoreactive fibres in the dorsal root ganglia using a light microscope equipped with a micrometer graticule (10 x 10 squares, 500 mm x 500 mm). We counted the squares of the graticule which contained TH-immunoreactive fibres for each of five randomly-selected sections of the dorsal root ganglia. The root constriction group showed mechanical allodynia and thermal hyperalgesia. In this group, TH-immunoreactive fibres were abundant in the ipsilateral dorsal root ganglia at L5 and L4 compared with the opposite side. In the sympathectomy group, mechanical hypersensitivity was attenuated significantly. We consider that the sympathetic nervous system plays an important role in the generation of radicular pain.

The role of ERK activation in the neuronal excitability in the chronically compressed dorsal root ganglia.

We examined the roles of phosphorylation of extracellular signal-regulated protein kinases (pERK) in regulating the excitability of neurons in the dorsal root ganglion (DRG) after chronic compression. A chronic compression of DRG (CCD) induced a significant increase in pERK in intact L4/L5 DRGs of rats as assessed by Western blot analysis. The treatment of U0126, the mitogen-activated protein kinase (MAPK) kinase 1/2 inhibitor, suppressed excitability in CCD-injured DRG neurons but not in naïve DRG neurons. Furthermore, the inhibition of ERK signaling increased A-type fast inactivating potassium current. Taken together, the excitation of CCD neurons might be attributed to the CCD-induced activation of ERK, which suppressed the A-type fast inactivating potassium conductance in CCD neurons.

Survival of injured spinal motoneurons in adult rat upon treatment with glial cell line-derived neurotrophic factor at 2 weeks but not at 4 weeks after root avulsion.

We conducted a study of whether treatment with glial cell line-derived neurotrophic factor (GDNF) initiated at 2 or 4 weeks after spinal-root avulsion could promote survival and regulate neuronal nitric oxide synthase (nNOS) expression in adult rat spinal motoneurons. By 6 weeks after root avulsion, the treatment given at 2 weeks not only increased motoneuron survival (86.1% vs. 27.9%), but also reversed the atrophy of injured motoneurons and increased their somatic size (101.3% vs. 52.9%) in comparison to the untreated control group of animals. All surviving motoneurons in the GDNF-treated group showed immunoreactivity for choline acetyltransferase. In contrast, GDNF treatment at 4 weeks post-injury failed to promote motoneuron survival (33.1% vs. 27.9%) at 6 weeks compared to the control group. Both the 2- and 4-week post-injury treatments downregulated nNOS expression. This finding suggests that injured adult motoneurons die shortly (a few weeks in the rat) after root avulsion injury, but can be saved from degeneration by treatment within the proper time frame after injury, which in the case of GDNF treatment in rats, appears to be within 2 weeks of the avulsion injury of the spinal root. These findings provide useful information for choosing the best time frame for the potential clinical treatment of brachial plexus avulsion.

Activation of extracellular signal-regulated protein kinase in the dorsal root ganglion following inflammation near the nerve cell body.

Inflammation of the primary afferent proximal to the dorsal root ganglion (DRG) and the DRG itself is known to produce radicular pain. Here, we examined pain-related behaviors and the activation of extracellular signal-regulated protein kinase (ERK) in the DRG after inflammation near the DRG somata. Inflammation of the L4/5 nerve roots and DRG induced by complete Freund's adjuvant (CFA) produced mechanical allodynia on the ipsilateral hindpaw and induced an increase in the phosphorylation of ERK, mainly in tyrosine kinase (trk) A-expressing small- and medium-size neurons. This CFA-induced increase in ERK phosphorylation was mediated through trk receptors, because intrathecal treatment with the tyrosine kinase inhibitor, K252a, reduced the activation of ERK. On the other hand, an increase in brain-derived neurotrophic factor (BDNF) mRNA/protein in the DRG concomitant with the ERK activation was also observed. Furthermore, we found that nerve growth factor (NGF) injection directly into the L4/5 nerve roots and DRG produced mechanical allodynia, and an increase in the phosphorylation of ERK and BDNF expression in the DRG, but the mitogen-activated protein kinase (MAPK) kinase1/2 inhibitor, U0126, inhibited the effects induced by NGF. Therefore, we suggest that after inflammation near the cell body, NGF synthesized within the nerve root and DRG induces BDNF expression through trkA receptors and intracellular ERK-MAPK. The activation of MAPK in the primary afferents may be involved in the pathophysiological mechanisms of inflammation-induced radiculopathy and MAPK pathways in the primary afferents may be potential targets for pharmacological intervention for neuropathic pain produced by inflammation near the DRG somata.

The role of steroids and their effects on phospholipase A2. An animal model of radiculopathy.

STUDY DESIGN: The possible role of phospholipase A2 in an animal model for lumbar radiculopathy and mechanisms of epidural steroid injections were studied. OBJECTIVES: To clarify the pathophysiologic mechanism of the recently proved animal model for lumbar radiculopathy and to characterize further the mechanisms of action of steroids. SUMMARY OF BACKGROUND DATA: There have been several reported animal models of peripheral neuropathy. Recently an animal model that shows reliable behavioral and neurochemical changes was proposed, and epidural steroid injections in this model were effective in the reduction of thermal hyperalgesia and allodynia. METHOD: In a behavioral study, 24 rats were divided into 4 groups: Group I, loose ligature of the left L4 and L5 nerve roots with 4-0 chromic gut sutures and an epidural injection of 0.1 mL of saline at 3 days after surgery; Group II, same as Group I but with an epidural injection of 0.1 mL of betamethasone on the day before the operation; Group II, same as Group II except injection at 1 day after surgery; Group IV, same as Group II except injection at 3 days after surgery. To test the phospholipase A2 activity in the nerve roots and dorsal root ganglia after the operation, eight rats were killed at given intervals. Analysis of variance techniques were used to test behavioral pattern changes and phospholipase A2 activity across time in each group. RESULTS: Thermal hyperalgesia reached its maximal point at 3 weeks after surgery in Group I, but in steroid injection groups, the recovery from hyperalgesia was faster than in Group I. However, there was no significant difference in recovery time among steroid injection groups. The level of phospholipase A2 activity was at its maximum at 1 week after surgery in Groups I and IV. It showed a steady reduction in the steroid group, whereas it remained relatively high and dropped rapidly after 3 weeks in the saline-treated group, and returned to the level of a normal nerve root at 6 weeks after surgery. CONCLUSION: These results suggest that the behavioral pattern changes observed in the irritated nerve root model are caused in part by a high level of phospholipase A2 activity initiated by inflammation, and that the mechanism of action of epidural steroid injection in this model is inhibition of phospholipase A2 activity.

Superoxide dismutase activity in cerebrospinal fluid and its relation to compression of the lumbosacral nerve root.

In the pathophysiology of lumbosacral radiculopathy, inflammation of the nerve root is of critical importance. Additionally, free radicals have been shown to be associated with some inflammatory process. This study was designed to investigate whether free radicals participate in the pathophysiology of nerve root involvement. We measured superoxide dismutase (SOD) activity in cerebrospinal fluid (CSF) of 31 patients with unilateral lumbosacral radiculopathy caused by a herniated disc using electron spin resonance (ESR) spectrometry. Then SOD activity was compared with the type of nerve root compression as seen on preoperative myelography. SOD activity in the normal control group was 7U/ml, while that in the hernia group remarkably decreased. The concentration gradient of SOD activity was different between central herniation and centrolateral herniation. Our findings indicate that free radicals are generated after nerve root compression. Under severe deficiency of SOD activity in CSF, serum SOD penetrates into CSF after further compression. In addition, SOD in CSF may play an important role in protecting against nerve root involvement.

[Determination of fucokinase activity in the blood of schizophrenic patients]. / Bestimmung der Fukokinaseaktivität im Blut schizophrener Patienten.

An investigation was conducted into whether dopamine induces an alteration in the fucolysation of glycoproteins, starting from the dopamine hypothesis of schizophrenia and taking the fucokinase activity determined in erythrocytes of schizophrenic patients as parameter. As with patients with "schizoaffective psychosis" and those with manic-depressive disorders, who were likewise examined, it was found that the enzyme activity of schizophrenic patients was no different than that found in the blood of a control group.