Histochemical Identification of Motor Fascicles Using Cholinesterase Staining in Rats Using a Mixed Nerve Model.

BACKGROUND: Inappropriate matching of motor and sensory fibers after nerve repair or grafting can lead to nerve recovery failure. Identifying the motor and sensory fascicles enables surgeons to match them accurately and correctly align nerve stumps, which is crucial for neural regeneration. Very few methods have been reported to differentiate between the sensory and motor nerve fascicles, and the replicability of these techniques remains unestablished. In this study, we aimed to assess the accuracy of axonal cholinesterase (CE) histochemical staining in distinguishing motor and sensory nerve fibers. METHODS: The femoral and sciatic nerves were harvested from rats. The specimens were immediately cut, frozen in isopentane, and cooled with liquid nitrogen. Nerve serial cross-sections were processed for hematoxylin and eosin staining, followed by CE histochemistry. The staining protocol solutions included acetylthiocholine iodide, phosphate buffer, cobalt sulfate hydrate, potassium phosphate monobasic, sulfuric acid, sodium bicarbonate, glutaraldehyde, and ammonium sulfide. RESULTS: Cross-sections of nerves containing efferent and afferent nerve fibers in segregated fascicles showed that CE activity was confined to motor neurons. A histochemical study revealed that motor fibers with high cholinesterase activity can be differentiated from sensory fibers. The motor branches of the femoral and sciatic nerves showed specific axonal staining, whereas the sensory branch did not show any specific staining. CONCLUSION: CE histochemical staining is a useful technique for distinguishing between motor and sensory nerve fibers. It can be potentially useful in improving the outcomes of nerve grafts or extremity allotransplantation surgery.

Neurotoxins subvert the allosteric activation mechanism of SARM1 to induce neuronal loss.

SARM1 is an inducible TIR-domain NAD+ hydrolase that mediates pathological axon degeneration. SARM1 is activated by an increased ratio of NMN to NAD+, which competes for binding to an allosteric activating site. When NMN binds, the TIR domain is released from autoinhibition, activating its NAD+ hydrolase activity. The discovery of this allosteric activating site led us to hypothesize that other NAD+-related metabolites might activate SARM1. Here, we show the nicotinamide analog 3-acetylpyridine (3-AP), first identified as a neurotoxin in the 1940s, is converted to 3-APMN, which activates SARM1 and induces SARM1-dependent NAD+ depletion, axon degeneration, and neuronal death. In mice, systemic treatment with 3-AP causes rapid SARM1-dependent death, while local application to the peripheral nerve induces SARM1-dependent axon degeneration. We identify 2-aminopyridine as another SARM1-dependent neurotoxin. These findings identify SARM1 as a candidate mediator of environmental neurotoxicity and suggest that SARM1 agonists could be developed into selective agents for neurolytic therapy.

TXNIP, a novel key factor to cause Schwann cell dysfunction in diabetic peripheral neuropathy, under the regulation of PI3K/Akt pathway inhibition-induced DNMT1 and DNMT3a overexpression.

Diabetic peripheral neuropathy (DPN) is the most common complication of diabetes mellitus (DM) and the dysfunction of Schwann cells plays an important role in the pathogenesis of DPN. Thioredoxin-interacting protein (TXNIP) is known as an inhibitor of thioredoxin and associated with oxidative stress and inflammation. However, whether TXNIP is involved in dysfunction of Schwann cells of DPN and the exact mechanism is still not known. In this study, we first reported that TXNIP expression was significantly increased in the sciatic nerves of diabetic mice, accompanied by abnormal electrophysiological indexes and myelin sheath structure. Similarly, in vitro cultured Schwann cells TXNIP was evidently enhanced by high glucose stimulation. Again, the function experiment found that knockdown of TXNIP in high glucose-treated RSC96 cells led to a 4.12 times increase of LC3-II/LC3-I ratio and a 25.94% decrease of cleaved caspase 3/total caspase 3 ratio. Then, DNA methyltransferase (DNMT) inhibitor 5-Aza has been reported to benefit Schwann cell in DPN, and here 5-Aza treatment reduced TXNIP protein expression, improved autophagy and inhibited apoptosis in high glucose-treated RSC96 cells and the sciatic nerves of diabetic mice. Furthermore, DNMT1 and DNMT3a upregulation were found to be involved in TXNIP overexpression in high glucose-stimulated RSC96 cells. Silencing of DNMT1 and DNMT3a effectively reversed high glucose-enhanced TXNIP. Moreover, high glucose-inhibited PI3K/Akt pathway led to DNMT1, DNMT3a, and TXNIP upregulation in RSC96 cells. Knockdown of DNMT1 and DNMT3a prevented PI3K/Akt pathway inhibition-caused TXNIP upregulation in RSC96 cells. Finally, in vivo knockout of TXNIP improved nerve conduction function, increased autophagosome and LC3 expression, and decreased cleaved Caspase 3 and Bax expression in diabetic mice. Taken together, PI3K/Akt pathway inhibition mediated high glucose-induced DNMT1 and DNMT3a overexpression, leading to cell autophagy inhibition and apoptosis via TXNIP protein upregulation in Schwann cells of DPN.

Very Early Involvement of Innate Immunity in Peripheral Nerve Degeneration in SOD1-G93A Mice.

Recent preclinical and clinical evidence suggest that immune system has a role in the progression and prognosis of Amyotrophic Lateral Sclerosis (ALS), but the identification of a clear mechanism and immune players remains to be elucidated. Here, we have investigated, in 30 and 60 days (presymptomatic) and 120 days (symptomatic) old SOD1-G93A mice, systemic, peripheral, and central innate and adaptive immune and inflammatory response, correlating it with the progression of the neurodegeneration in neuromuscular junction, sciatic nerves, and spinal cord. Surprisingly, we found a very initial (45-60 days) presence of IgG in sciatic nerves together with a gradual enhancement of A20/TNFAIP3 (protein controlling NF-κB signalling) and a concomitantly significant increase and activation of circulating mast cells (MCs) as well as MCs and macrophages in sciatic nerve and an enhancement of IL-6 and IL-10. This immunological frame coincided with a myelin aggregation. The 30-60 days old SOD1-G93A mice didn't show real elements of neuroinflammation and neurodegeneration in spinal cord. In 120 days old mice macrophages and monocytes are widely diffused in sciatic nerves, peripheral neurodegeneration reaches the tip, high circulating levels of TNFα and IL-2 were found and spinal cord exhibits clear signs of neural damage and infiltrating immune cells. Our results underpin a clear immunological disorder at the origin of ALS axonopathy, in which MCs are involved in the initiation and sustaining of inflammatory events. These data cannot be considered a mere epiphenomenon of motor neuron degeneration and reveal new potential selective immune targets in ALS therapy.

Quercetin provides protection against the peripheral nerve damage caused by vincristine in rats by suppressing caspase 3, NF-κB, ATF-6 pathways and activating Nrf2, Akt pathways.

In the present study, the protective effects of quercetin on peripheral neurotoxicity caused by vincristine, which is used effectively in the treatment of various types of cancers, were investigated by using different techniques. In the study, for 12 days, male Sprague Dawley rats were given 25 and 50 mg/kg doses of quercetin orally and were administered a 0.1 mg/kg dose of vincristine (a total cumulative dose of 1.2 mg/kg) intraperitoneally 30 min later. The protein levels of nuclear factor erythroid 2-related factor-2 (Nrf2), heme oxygenase-1 (HO-1), NAD(P)H quinone dehydrogenase-1 (NQO1), glial fibrillary acidic protein (GFAP), and nuclear factor kappa B (NF-κB) were measured with ELISA; the immunopositivity of 8-hydroxy-2'-deoxyguanosine (8-OHdG) and caspase 3 were determined with immunohistochemistry; the mRNA transcript levels of double-stranded RNA-activated protein kinase (PKR)-like ER kinase (PERK), inositol-requiring enzyme-1 (IRE1), activating transcription factor-6 (ATF-6), glucose-regulated protein 78 (GRP78), Bcl-2-associated X protein (Bax), B-cell lymphoma-2 (Bcl-2), caspase 3, protein kinase B1/2 (Akt-1/2), and forkhead box transcription factor, class O1 (FOXO1) were determined with RT-PCR. The reduction of Nrf2 levels and HO-1 and NQO1 activities in the sciatic nerve tissue, the increase in the levels of 8-OHdG, and the increase in the levels of GFAP and NF-κB caused by vincristine was observed to cause oxidative stress, oxidative DNA damage, neuronal cell damage, and inflammation, respectively. Additionally, vincristine was determined to cause ER stress and apoptosis by increasing PERK, IRE1, ATF-6, and GRP78 and caspase 3 and Bax expressions and by decreasing Bcl-2 expressions. Vincristine causing Akt inhibition also shows that it prevents neuronal survival. However, quercetin was determined to relieve oxidative stress, oxidative DNA damage, neuronal cell damage, inflammation, ER stress, and apoptosis caused by vincristine and enable Akt activation. These results show that in rats, quercetin may have a protective effect against peripheral neurotoxicity caused by vincristine.

Maternal sciatic nerve administered bupivacaine induces hippocampal cell apoptosis in offspring.

BACKGROUND: Bupivacaine, an amid-type local anesthetic, is widely used for clinical patients especially in pregnant women. In addition to neurotoxicity effect of bupivacaine, it can cross the placenta, accumulates in this tissue and retained in fetal tissues. Nevertheless, whether bupivacaine can cause neurotoxicity in fetus remains unclear. Hence, this study was design to investigate the effects of maternal bupivacaine use on fetus hippocampal cell apoptosis and the possible related mechanism. METHODS: On day 15 of pregnancy, sciatic nerve of pregnant wistar rat (180-200 g) were exposed by lateral incision of the right thigh and 0.2 ml of bupivacaine was injected. After their delivery, we randomly selected one male offspring of every mother. On day 30 after of their birth, the rat's hippocampi were isolated for molecular studies. Western blotting was used to examine the expression of cleaved caspase-3, caspase-8 and p-Akt in fetal hippocampus. RESULTS: Our results showed that maternal bupivacaine use caused a significant increment of cleaved caspase-3 and caspase-8 expression in fetal hippocampus compared with the sham group. In addition, maternally administered bupivacaine could significantly decrease hippocampal P.Akt/T.Akt ratio which was concurrent with an increment of cleaved caspase-3 and caspase-8 expression. CONCLUSION: Our data suggest that maternal bupivacaine use increases fetal hippocampal cell apoptosis markers such as caspase 8 and cleaved caspase 3, at least in part, via inhibiting the Akt activation.

The fibroblast-derived protein PI16 controls neuropathic pain.

Chronic pain is a major clinical problem of which the mechanisms are incompletely understood. Here, we describe the concept that PI16, a protein of unknown function mainly produced by fibroblasts, controls neuropathic pain. The spared nerve injury (SNI) model of neuropathic pain increases PI16 protein levels in fibroblasts in dorsal root ganglia (DRG) meninges and in the epi/perineurium of the sciatic nerve. We did not detect PI16 expression in neurons or glia in spinal cord, DRG, and nerve. Mice deficient in PI16 are protected against neuropathic pain. In vitro, PI16 promotes transendothelial leukocyte migration. In vivo, Pi16-/- mice show reduced endothelial barrier permeability, lower leukocyte infiltration and reduced activation of the endothelial barrier regulator MLCK, and reduced phosphorylation of its substrate MLC2 in response to SNI. In summary, our findings support a model in which PI16 promotes neuropathic pain by mediating a cross-talk between fibroblasts and the endothelial barrier leading to barrier opening, cellular influx, and increased pain. Its key role in neuropathic pain and its limited cellular and tissue distribution makes PI16 an attractive target for pain management.

Membrane metallo-endopeptidase is dispensable for repair after nerve injury.

Membrane metallo-endopeptidase (MME), also known as neprilysin (NEP), has been of interest for its role in neurodegeneration and pain due to its ability to degrade ß-amyloid and substance-P, respectively. In addition to its role in the central nervous system, MME has been reported to be expressed in the peripheral system, specifically in the inner and outer border of myelinating fibers, in the Schmidt-Lantermann cleft and in the paranodes. Recently, mutations of this gene have been associated with Charcot-Marie-Tooth Type 2 (CMT2). Peripheral nerve morphometry in mice lacking MME previously showed minor abnormalities in aged animals in comparison to CMT2 patients. We found that MME expression was dysregulated after nerve injury in a Neuregulin-1 dependent fashion. We therefore explored the hypothesis that MME may have a role in remyelination. In the naïve state in adulthood we did not find any impairment in myelination in MME KO mice. After nerve injury the morphological outcome in MME KO mice was indistinguishable from WT littermates in terms of axon regeneration and remyelination. We did not find any difference in functional motor recovery. There was a significant difference in sensory function, with MME KO mice starting to recover response to mechanical stimuli earlier than WT. The epidermal reinnnervation, however, was unchanged and this altered sensitivity may relate to its known function in cleaving the peptide substance-P, known to sensitise nociceptors. In conclusion, although MME expression is dysregulated after nerve injury in a NRG1-dependent manner this gene is dispensable for axon regeneration and remyelination after injury.

Heme Oxygenase 1 in Schwann Cells Regulates Peripheral Nerve Degeneration Against Oxidative Stress.

During Wallerian degeneration, Schwann cells lose their characteristic of myelinating axons and shift into the state of developmental promyelinating cells. This recharacterized Schwann cell guides newly regrowing axons to their destination and remyelinates reinnervated axons. This Schwann cell dynamics during Wallerian degeneration is associated with oxidative events. Heme oxygenases (HOs) are involved in the oxidative degradation of heme into biliverdin/bilirubin, ferrous iron, and carbon monoxide. Overproduction of ferrous iron by HOs increases reactive oxygen species, which have deleterious effects on living cells. Thus, the key molecule for understanding the exact mechanism of Wallerian degeneration in the peripheral nervous system is likely related to oxidative stress-mediated HOs in Schwann cells. In this study, we demonstrate that demyelinating Schwann cells during Wallerian degeneration highly express HO1, not HO2, and remyelinating Schwann cells during nerve regeneration decrease HO1 activation to levels similar to those in normal myelinating Schwann cells. In addition, HO1 activation during Wallerian degeneration regulates several critical phenotypes of recharacterized repair Schwann cells, such as demyelination, transdedifferentiation, and proliferation. Thus, these results suggest that oxidative stress in Schwann cells after peripheral nerve injury may be regulated by HO1 activation during Wallerian degeneration and oxidative-stress-related HO1 activation in Schwann cells may be helpful to study deeply molecular mechanism of Wallerian degeneration.

"Adjusting internal organs and dredging channel" electroacupuncture treatment prevents the development of diabetic peripheral neuropathy by downregulating glucose-related protein 78 (GRP78) and caspase-12 in streptozotocin-diabetic rats.

BACKGROUND: The clinical efficacy of electroacupuncture in treating diabetic peripheral neuropathy (DPN) is significant, but the underlying mechanism of action is not clear. Considering that glucose-regulated protein 78 (GRP78) and caspase-12 are major proteins participating in cell apoptosis, we investigated the effects of "adjusting internal organs and dredging channel" electroacupuncture therapy on GRP78 and caspase-12 levels in streptozotocin (STZ)-diabetic rats to elucidate the mechanism of action. METHODS: Rats were first divided into two groups: one group was rendered diabetic with a single injection of 50 mg/kg STZ, whereas the other normal control group was injected with an equivalent volume of citrate buffer. The STZ-diabetic rats were randomly divided into three groups: model control and electroacupuncture- and mecobalamin-treated groups. After 12 weeks treatment, the therapeutic efficacy of electroacupuncture was assessed using sciatic nerves isolated from rats. In the electroacupuncture group, rats were treated by electroacupuncture for 20 minutes once daily for 6 days each week, with 1 day off, for 12 consecutive weeks. The selected acupressure points include bilateral acupressure points of BL13 (Fehu), BL20 (Pishu), BL23 (Shenshu), LI4 (Hegu), LR3 (faichong), ST36 (Zusanli), and SP6 (Sanyiniiao). Acupressure points were stimulated using a HuaTuo SDZ-V Electric Acupuncture Therapy Apparatus. The acupressure points of BL13 and BL23, as well as SP6 and LR3, were connected on the same side with a dilatational wave of 3 Hz (frequency ratio of 1 : 5) to stimulate the parts of the body to the extent that could be tolerated by the rat. As for the mecobalamin-treated groups, mecobalamin was administrated to rats intragastrically at a dose of 20 mg/kg once daily for 12 consecutive weeks. Immunofluorescence and western blot analysis were used to determine GRP78 and caspase-12 levels in sciatic nerves. In addition, cell apoptosis in sciatic nerves was determined using the terminal deoxyribonucleotidyl transferase-mediated dUTP-digoxigenin nick end-labeling (TUNEL) assay. RESULTS: Electroacupuncture markedly reduced the pathological injury to sciatic nerves in STZ-diabetic rats. Moreover, electroacupuncture significantly downregulated GRP78 and caspase-12 and reduced cell apoptosis of sciatic nerves in DPN rats. CONCLUSIONS: Electroacupuncture improved DPN by downregulating GRP78 and caspase-12 and reducing cell apoptosis of sciatic nerves in STZ-diabetic rats, and further inhibited the occurrence of endoplasmic reticulum stress, thus preventing sciatic nerve injuries.

Spinal cytochrome P450c17 plays a key role in the development of neuropathic mechanical allodynia: Involvement of astrocyte sigma-1 receptors.

While evidence indicates that sigma-1 receptors (Sig-1Rs) play an important role in the induction of peripheral neuropathic pain, there is limited understanding of the role that the neurosteroidogenic enzymes, which produce Sig-1R endogenous ligands, play during the development of neuropathic pain. We examined whether sciatic nerve injury upregulates the neurosteroidogenic enzymes, cytochrome P450c17 and 3ß-hydroxysteroid dehydrogenase (3ß-HSD), which modulate the expression and/or activation of Sig-1Rs leading to the development of peripheral neuropathic pain. Chronic constriction injury (CCI) of the sciatic nerve induced a significant increase in the expression of P450c17, but not 3ß-HSD, in the ipsilateral lumbar spinal cord dorsal horn at postoperative day 3. Intrathecal administration of the P450c17 inhibitor, ketoconazole during the induction phase of neuropathic pain (day 0 to day 3 post-surgery) significantly reduced the development of mechanical allodynia and thermal hyperalgesia in the ipsilateral hind paw. However, administration of the 3ß-HSD inhibitor, trilostane had no effect on the development of neuropathic pain. Sciatic nerve injury increased astrocyte Sig-1R expression as well as dissociation of Sig-1Rs from BiP in the spinal cord. These increases were suppressed by administration of ketoconazole, but not by administration of trilostane. Co-administration of the Sig-1R agonist, PRE084 restored the development of mechanical allodynia originally suppressed by the ketoconazole administration. However, ketoconazole-induced inhibition of thermal hyperalgesia was not affected by co-administration of PRE084. Collectively these results demonstrate that early activation of P450c17 modulates the expression and activation of astrocyte Sig-1Rs, ultimately contributing to the development of mechanical allodynia induced by peripheral nerve injury.

Dual leucine zipper kinase is required for mechanical allodynia and microgliosis after nerve injury.

Neuropathic pain resulting from nerve injury can become persistent and difficult to treat but the molecular signaling responsible for its development remains poorly described. Here, we identify the neuronal stress sensor dual leucine zipper kinase (DLK; Map3k12) as a key molecule controlling the maladaptive pathways that lead to pain following injury. Genetic or pharmacological inhibition of DLK reduces mechanical hypersensitivity in a mouse model of neuropathic pain. Furthermore, DLK inhibition also prevents the spinal cord microgliosis that results from nerve injury and arises distant from the injury site. These striking phenotypes result from the control by DLK of a transcriptional program in somatosensory neurons regulating the expression of numerous genes implicated in pain pathogenesis, including the immune gene Csf1. Thus, activation of DLK is an early event, or even the master regulator, controlling a wide variety of pathways downstream of nerve injury that ultimately lead to chronic pain.

The deletion of dicer in mature myelinating glial cells causes progressive axonal degeneration but not overt demyelination in adult mice.

Myelinating glial cells (MGCs), oligodendrocytes (OLs) in the central nervous system (CNS) and Schwann cells (SCs) in the peripheral nervous system (PNS), generate myelin sheaths that insulate axons. After myelination is completed in adulthood, MGC functions independent from myelin are required to support axon survival, but the underlying mechanisms are still unclear. Dicer is a key enzyme that is responsible for generating functional micro-RNAs (miRNAs). Despite the importance of Dicer in initiating myelination, the role of Dicer in mature MGCs is still unclear. Here, Dicer was specifically deleted in mature MGCs in 2-month old mice (PLP-CreERT; Dicer fl/fl) by tamoxifen administration. Progressive motor dysfunction was observed in the Dicer conditional knockout mice, which displayed hind limb ataxia at 3 months post recombination that deteriorated into paralysis within 5 months. Massive axonal degeneration/atrophy in peripheral nerves was responsible for this phenomenon, but overt demyelination was not observed in either the CNS or PNS. In contrast to the PNS, signs of axonal degeneration were not observed in the CNS of these animals. We induced a Dicer deletion in oligodendroglia at postnatal day 5 in NG2-CreERT; Dicer fl/fl mice to evaluate whether Dicer expression in OLs is essential for axonal survival. Dicer deletion in oligodendroglia did not cause motor dysfunction at the age of 7 months. Neither axonal atrophy nor demyelination was observed in the CNS. Based on our results, Dicer expression in SCs is required to maintain axon integrity in adult PNS, and Dicer is dispensable for maintaining myelin sheaths in MGCs.

Effect of Sciatic Nerve Transection on acetylcholinesterase activity in spinal cord and skeletal muscles of the bullfrog Lithobates catesbeianus / Efeito da Secção do Nervo Isquiático sobre a atividade da acetilcolinesterase em medula espinal e músculos esqueléticos da rã-touro Lithobates catesbeianus

Abstract Sciatic nerve transection (SNT), a model for studying neuropathic pain, mimics the clinical symptoms of "phantom limb", a pain condition that arises in humans after amputation or transverse spinal lesions. In some vertebrate tissues, this condition decreases acetylcholinesterase (AChE) activity, the enzyme responsible for fast hydrolysis of released acetylcholine in cholinergic synapses. In spinal cord of frog Rana pipiens, this enzyme's activity was not significantly changed in the first days following ventral root transection, another model for studying neuropathic pain. An answerable question is whether SNT decreases AChE activity in spinal cord of frog Lithobates catesbeianus, a species that has been used as a model for studying SNT-induced neuropathic pain. Since each animal model has been created with a specific methodology, and the findings tend to vary widely with slight changes in the method used to induce pain, our study assessed AChE activity 3 and 10 days after complete SNT in lumbosacral spinal cord of adult male bullfrog Lithobates catesbeianus. Because there are time scale differences of motor endplate maturation in rat skeletal muscles, our study also measured the AChE activity in bullfrog tibial posticus (a postural muscle) and gastrocnemius (a typical skeletal muscle that is frequently used to study the motor system) muscles. AChE activity did not show significant changes 3 and 10 days following SNT in spinal cord. Also, no significant change occurred in AChE activity in tibial posticus and gastrocnemius muscles at day 3. However, a significant decrease was found at day 10, with reductions of 18% and 20% in tibial posticus and gastrocnemius, respectively. At present we cannot explain this change in AChE activity. While temporally different, the direction of the change was similar to that described for rats. This similarity indicates that bullfrog is a valid model for investigating AChE activity following SNT.

Resumo A transecção do nervo isquiático (SNT), um modelo para estudar dor neuropática, simula os sintomas clínicos do "membro fantasma", uma condição dolorosa que ocorre nos humanos após amputação ou secção completa da medula espinal. Essa condição muda a atividade da acetilcolinesterase (AChE), a enzima responsável pela rápida hidrólise da acetilcolina liberada nas sinapses colinérgicas, em alguns tecidos de vertebrados. Em medula espinal de rã Rana pipiens, a atividade da AChE não foi significativamente alterada nos primeiros dias após a secção da raiz ventral, outro modelo para o estudo da dor neuropática. Uma questão ainda não respondida é se a SNT diminui a atividade da AChE na medula espinal de rã Lithobates catesbeianus, uma espécie que vem sendo usada como modelo em estudos da dor neuropática induzida por SNT. Como cada modelo animal é criado a partir de metodologia específica, e seus resultados tendem a variar com pequenas mudanças na metodologia de indução da dor, o presente estudo avaliou a atividade da AChE em medula espinal lombossacral de rã-touro Lithobates catesbeianus, adultos, machos, 3 e 10 dias após a completa SNT. Como há diferenças temporais na maturação de placas motoras em músculos esqueléticos de ratos, nosso estudo ainda demonstrou, na rã-touro, os efeitos da SNT sobre a atividade da AChE nos músculos esqueléticos tibial posticus, um músculo postural, e gastrocnêmio, um músculo frequentemente usado em estudos do sistema motor. A atividade da AChE não mudou significativamente na medula espinal aos 3 e 10 dias após a SNT. Nos músculos, a atividade não alterou significativamente aos 3 dias após a lesão, mas reduziu de forma significativa aos 10 dias após a SNT. Aos 10 dias, a diminuição foi 18% no músculo tibial posticus e 20% no gastrocnêmio. No momento, nós não temos explicação para essa mudança na atividade da AChE. Embora temporalmente diferente, o sentido da mudança é similar ao que é descrito em ratos. Esta similaridade torna a rã-touro um modelo válido para se estudar questões ainda não respondidas da SNT sobre a AChE.

Increased frequency of AMP-activated protein kinase-positive spinal motor neurons after sciatic nerve injury in a mouse model.

The role of AMP-activated protein kinase (AMPK) in the regulation of energy metabolism and the control of skeletal muscle regeneration post injury has been described previously. It remains unknown whether this metabolic sensor plays a role in the mechanism of axonal regeneration post injury. In this study, we used a sciatic nerve crushed mouse model to detect the expression of AMPK in sciatic nerve and spinal motor neurons at 1 week, 2 weeks and 3 weeks after injury by immunofluorescence staining. Electrophysiological and histopathological studies were used to confirm the nerve injury and regeneration. Our results showed that frequency of AMPK-positive spinal motor neurons was significantly higher on day 7 after sciatic nerve crush (SNC) and peaked on day 14. No expression of AMPK was detected in axons of the sciatic nerve before and after the injury. Taken together, our study suggested a possible role of AMPK in the mechanism of motor nerve regeneration after injury.

Hyperglycemia-induced Bcl-2/Bax-mediated apoptosis of Schwann cells via mTORC1/S6K1 inhibition in diabetic peripheral neuropathy.

Schwann cell apoptosis is one of the characteristics of diabetic peripheral neuropathy (DPN). The mammalian target of rapamycin (mTOR) is a multifunctional signaling pathway that regulates cell apoptosis in various types of tissues and cells. To investigate whether the mTOR pathway is involved in cell apoptosis in the Schwann cells of DPN, diabetic mice and rat Schwann cells (RSC96) were chosen to detect phospho-mTOR (Ser 2448), phospho-S6K1 (Thr 389), phospho-4EBP1 (Thr 37/46), Bcl-2, Bax and cleaved caspase-3 by diverse pathological and biological techniques. The results showed that phospho-mTOR (Ser 2448) was decreased in the sciatic nerves of diabetic mice, concomitant with decreased Bcl-2, increased Bax, cleaved caspase-3 and cell apoptosis. In addition, high glucose treatment for 72 h caused a 35.95% decrease in the phospho-mTOR (Ser 2448)/mTOR ratio, a 65.50% decrease in the phospho-S6K1 (Thr 389)/S6K1 ratio, a 3.67-fold increase in the Bax/Bcl-2 ratio and a 1.47-fold increase in the cleaved caspase-3/caspase-3 ratio. Furthermore, mTORC1 inhibition, rather than mTORC2 inhibition, resulted in mitochondrial controlled apoptosis in RSC96 cells by silencing RAPTOR or RICTOR. Again, suppression of the mTORC1 pathway by a chemical inhibitor led to mitochondrial controlled apoptosis in cultured RSC96 cells in vitro. By contrast, activation of the mTORC1 pathway with MHY1485 prevented decreased phospho-S6K1 (Thr 389) levels caused by high glucose and cell apoptosis. Additionally, constitutive activation of S6K1 avoided high glucose-induced cell apoptosis in RSC96 cells. In summary, our findings suggest that activating mTORC1/S6K1 signaling in Schwann cells may be a promising strategy for the prevention and treatment of DPN.

Insulin-induced upregulation of lipoprotein lipase in Schwann cells during diabetic peripheral neuropathy.

Diabetic peripheral neuropathy (DPN) is one of the major complications associated with diabetes. It is characterized by the degeneration of the myelin sheath around axons, referred to as demyelination. Such demyelinations are often caused by reduced lipid component of the myelin sheath. Since, lipoprotein lipase (LPL) provides the lipid for myelin sheath by hydrolysing the triglyceride rich lipoproteins, and also helps in the uptake of lipids by the Schwann cells (SCs) for its utilization, LPL is considered as the important factor in the regeneration of myelin sheath during diabetic neuropathy. Earlier reports from our laboratory have provided the insights of insulin and its receptor in SCs during diabetic neuropathy. In order to evaluate the long term effect of insulin on lipid metabolism during diabetic neuropathy, in this study, we analyzed the expression of LPL in SCs under normal, high glucose and insulin treated conditions. A decrease in the expression of LPL was observed in SCs of high glucose condition and it was reversed upon insulin treatment. Histochemical observations of sciatic nerve of insulin treated neuropathy subjects showed the improved nerve morphology, signifying the importance of insulin in restoring the pathophysiology of diabetic neuropathy.

Nitric Oxide Synthase (NOS) Isoform Expression after Peripheral Nerve Transection in Mice.

Localization of the nitric oxide (NO)-producing enzyme, nitric oxide synthase (NOS), and its functions are currently being investigated in several tissues and organs. It has been suggested that NO is involved in nerve cell death and the development of neurodegenerative disease. The purpose of this study was to immunohistochemically investigate expression of NOS to clarify its function in the degeneration and regeneration of transected mouse sciatic nerve. Scattered neuronal NOS (nNOS)-positive Schwann cells observed on the central side of the stump on day 1 after transection showed an increase in number on day 7. None were observed at the stump on day 14, however. Expression of nNOS was observed in axons extending from the stump. The number of nNOS-positive axons increased on day 21. Inducible NOS was expressed in inflammatory cells at the stump on day 1. This positive reaction subsequently weakened by day 7, however. Endothelial NOS was expressed in blood vessels at the stump on day 7, but decreased thereafter. The results of the present study suggest that NO is involved in the proliferation and migration of Schwann cells, as well as in axon regeneration at an early stage following nerve transection.

Class IIa histone deacetylases link cAMP signaling to the myelin transcriptional program of Schwann cells.

Schwann cells respond to cyclic adenosine monophosphate (cAMP) halting proliferation and expressing myelin proteins. Here we show that cAMP signaling induces the nuclear shuttling of the class IIa histone deacetylase (HDAC)-4 in these cells, where it binds to the promoter and blocks the expression of c-Jun, a negative regulator of myelination. To do it, HDAC4 does not interfere with the transcriptional activity of MEF2. Instead, by interacting with NCoR1, it recruits HDAC3 and deacetylates histone 3 in the promoter of c-Jun, blocking gene expression. Importantly, this is enough to up-regulate Krox20 and start Schwann cell differentiation program-inducing myelin gene expression. Using conditional knockout mice, we also show that HDAC4 together with HDAC5 redundantly contribute to activate the myelin transcriptional program and the development of myelin sheath in vivo. We propose a model in which cAMP signaling shuttles class IIa HDACs into the nucleus of Schwann cells to regulate the initial steps of myelination in the peripheral nervous system.

Reactive oxygen species regulate axonal regeneration through the release of exosomal NADPH oxidase 2 complexes into injured axons.

Reactive oxygen species (ROS) contribute to tissue damage and remodelling mediated by the inflammatory response after injury. Here we show that ROS, which promote axonal dieback and degeneration after injury, are also required for axonal regeneration and functional recovery after spinal injury. We find that ROS production in the injured sciatic nerve and dorsal root ganglia requires CX3CR1-dependent recruitment of inflammatory cells. Next, exosomes containing functional NADPH oxidase 2 complexes are released from macrophages and incorporated into injured axons via endocytosis. Once in axonal endosomes, active NOX2 is retrogradely transported to the cell body through an importin-ß1-dynein-dependent mechanism. Endosomal NOX2 oxidizes PTEN, which leads to its inactivation, thus stimulating PI3K-phosporylated (p-)Akt signalling and regenerative outgrowth. Challenging the view that ROS are exclusively involved in nerve degeneration, we propose a previously unrecognized role of ROS in mammalian axonal regeneration through a NOX2-PI3K-p-Akt signalling pathway.