Identification of the first noncompetitive SARM1 inhibitors.

Sterile Alpha and Toll Interleukin Receptor Motif-containing protein 1 (SARM1) is a key therapeutic target for diseases that exhibit Wallerian-like degeneration; Wallerian degeneration is characterized by degeneration of the axon distal to the site of injury. These diseases include traumatic brain injury, peripheral neuropathy, and neurodegenerative diseases. SARM1 promotes neurodegeneration by catalyzing the hydrolysis of NAD+ to form a mixture of ADPR and cADPR. Notably, SARM1 knockdown prevents degeneration, indicating that SARM1 inhibitors will likely be efficacious in treating these diseases. Consistent with this hypothesis is the observation that NAD+ supplementation is axoprotective. To identify compounds that block the NAD+ hydrolase activity of SARM1, we developed and performed a high-throughput screen (HTS). This HTS assay exploits an NAD+ analog, etheno-NAD+ (ENAD) that fluoresces upon cleavage of the nicotinamide moiety. From this screen, we identified berberine chloride and zinc chloride as the first noncompetitive inhibitors of SARM1. Though modest in potency, the noncompetitive mode of inhibition, suggests the presence of an allosteric binding pocket on SARM1 that can be targeted for future therapeutic development. Additionally, zinc inhibition and site-directed mutagenesis reveals that cysteines 629 and 635 are critical for SARM1 catalysis, highlighting these sites for the design of inhibitors targeting SARM1.

Wallerian degeneration as a therapeutic target in traumatic brain injury.

PURPOSE OF REVIEW: Diffuse or traumatic axonal injury is one of the principal pathologies encountered in traumatic brain injury (TBI) and the resulting axonal loss, disconnection, and brain atrophy contribute significantly to clinical morbidity and disability. The seminal discovery of the slow Wallerian degeneration mice (Wld) in which transected axons do not degenerate but survive and function independently for weeks has transformed concepts on axonal biology and raised hopes that axonopathies may be amenable to specific therapeutic interventions. Here we review mechanisms of axonal degeneration and also describe how these mechanisms may inform biological therapies of traumatic axonopathy in the context of TBI. RECENT FINDINGS: In the last decade, SARM1 [sterile a and Toll/interleukin-1 receptor (TIR) motif containing 1] and the DLK (dual leucine zipper bearing kinase) and LZK (leucine zipper kinase) MAPK (mitogen-activated protein kinases) cascade have been established as the key drivers of Wallerian degeneration, a complex program of axonal self-destruction which is activated by a wide range of injurious insults, including insults that may otherwise leave axons structurally robust and potentially salvageable. Detailed studies on animal models and postmortem human brains indicate that this type of partial disruption is the main initial pathology in traumatic axonopathy. At the same time, the molecular dissection of Wallerian degeneration has revealed that the decision that commits axons to degeneration is temporally separated from the time of injury, a window that allows potentially effective pharmacological interventions. SUMMARY: Molecular signals initiating and triggering Wallerian degeneration appear to be playing an important role in traumatic axonopathy and recent advances in understanding their nature and significance is opening up new therapeutic opportunities for TBI.

Granulocyte-macrophage colony-stimulating factor improves mouse peripheral nerve regeneration following sciatic nerve crush.

Peripheral nerve injuries severely impair patients' quality of life as full recovery is seldom achieved. Upon axonal disruption, the distal nerve stump undergoes fragmentation, and myelin breaks down; the subsequent regeneration progression is dependent on cell debris removal. In addition to tissue clearance, macrophages release angiogenic and neurotrophic factors that contribute to axon growth. Based on the importance of macrophages for nerve regeneration, especially during the initial response to injury, we treated mice with granulocyte-macrophage colony-stimulating factor (GM-CSF) at various intervals after sciatic nerve crushing. Sciatic nerves were histologically analyzed at different time intervals after injury for the presence of macrophages and indicators of regeneration. Functional recovery was followed by an automated walking track test. We found that GM-CSF potentiated early axon growth, as indicated by the enhanced expression of growth-associated protein at 7 days postinjury. Inducible nitric oxide synthase expression increased at the beginning and at the end of the regenerative process, suggesting that nitric oxide is involved in axon growth and pruning. As expected, GM-CSF treatment stimulated macrophage infiltration, which increased at 7 and 14 days; however, it did not improve myelin clearance. Instead, GM-CSF stimulated early brain-derived neurotrophic factor (BDNF) production, which peaked at 7 days. Locomotor recovery pattern was not improved by GM-CSF treatment. The present results suggest that GM-CSF may have beneficial effects on early axonal regeneration.

Polyethylene glycol solutions rapidly restore and maintain axonal continuity, neuromuscular structures, and behaviors lost after sciatic nerve transections in female rats.

Complete severance of major peripheral mixed sensory-motor nerve proximally in a mammalian limb produces immediate loss of action potential conduction and voluntary behaviors mediated by the severed distal axonal segments. These severed distal segments undergo Wallerian degeneration within days. Denervated muscles atrophy within weeks. Slowly regenerating (∼1 mm/day) outgrowths from surviving proximal stumps that often nonspecifically reinnervate denervated targets produce poor, if any, restoration of lost voluntary behaviors. In contrast, in this study using completely transected female rat sciatic axons as a model system, we provide extensive morphometric, immunohistochemical, electrophysiological, and behavioral data to show that these adverse outcomes are avoided by microsuturing closely apposed axonal cut ends (neurorrhaphy) and applying a sequence of well-specified solutions, one of which contains polyethylene glycol (PEG). This "PEG-fusion" procedure within minutes reestablishes axoplasmic and axolemmal continuity and signaling by nonspecifically fusing (connecting) closely apposed open ends of severed motor and/or sensory axons at the lesion site. These PEG-fused axons continue to conduct action potentials and generate muscle action potentials and muscle twitches for months and do not undergo Wallerian degeneration. Continuously innervated muscle fibers undergo much less atrophy compared with denervated muscle fibers. Dramatic behavioral recovery to near-unoperated levels occurs within days to weeks, almost certainly by activating many central nervous system and peripheral nervous system synaptic and other plasticities, some perhaps to a greater extent than most neuroscientists would expect. Negative control transections in which neurorrhaphy and all solutions except the PEG-containing solution are applied produce none of these remarkably fortuitous outcomes observed for PEG-fusion.

Avian axons undergo Wallerian degeneration after injury and stress.

The integrity of long axons is essential for neural communication. Unfortunately, relatively minor stress to a neuron can cause extensive loss of this integrity. Axon degeneration is the cell-intrinsic program that actively deconstructs an axon after injury or damage. Although ultrastructural examination has revealed signs of axon degeneration in vivo, the occurrence and progression of axon degeneration in avian species have not yet been documented in vitro. Here, we use a novel cell culture system with primary embryonic zebra finch retinal ganglion cells to interrogate the properties of avian axon degeneration. First, we establish that both axotomy and a chemically induced injury (taxol and vincristine) are sufficient to initiate degeneration. These events are dependent on a late influx of calcium. In addition, as in mammals, the NAD pathway is involved, since a decrease in NMN with FK866 can reduce degeneration. Importantly, these retinal ganglion cell axons were sensitive to a pressure-induced injury, which may mimic the effect of high intraocular pressure associated with glaucoma. We have demonstrated that avian neurons undergo Wallerian degeneration in response to both physical and chemical injury. Subsequent avian studies will investigate whether blocking the degeneration pathway can protect individuals from neurodegenerative disease.

Adenosine 5'-triphosphate (ATP) inhibits schwann cell demyelination during Wallerian degeneration.

Adenosine 5'-triphosphate (ATP) is implicated in intercellular communication as a neurotransmitter in the peripheral nervous system. In addition, ATP is known as lysosomal exocytosis activator. In this study, we investigated the role of extracellular ATP on demyelination during Wallerian degeneration (WD) using ex vivo and in vivo nerve degeneration models. We found that extracellular ATP inhibited myelin fragmentation and axonal degradation during WD. Furthermore, metformin and chlorpromazine, lysosomal exocytosis antagonists blocked the effect of ATP on the inhibition of demyelination. Thus, these findings indicate that ATP-induced-lysosomal exocytosis may be involved in demyelination during WD.

Blocking the P2X7 receptor improves outcomes after axonal fusion.

BACKGROUND: Activation of the P2X7 receptor on peripheral neurons causes the formation of pannexin pores, which allows the influx of calcium across the cell membrane. Polyethylene glycol (PEG) and methylene blue have previously been shown to delay Wallerian degeneration if applied during microsuture repair of the severed nerve. Our hypothesis is that by modulating calcium influx via the P2X7 receptor pathway, we could improve PEG-based axonal repair. The P2X7 receptor can be stimulated or inhibited using bz adenosine triphosphate (bzATP) or brilliant blue (FCF), respectively. METHODS: A single incision rat sciatic nerve injury model was used. The defect was repaired using a previously described PEG methylene blue fusion protocol. Experimental animals were treated with 100 µL of 100 µM FCF solution (n = 8) or 100 µL of a 30 µM bzATP solution (n = 6). Control animals received no FCF, bzATP, or PEG. Compound action potentials were recorded prior to transection (baseline), immediately after repair, and 21 d postoperatively. Animals underwent behavioral testing 3, 7, 14, and 21 d postoperatively. After sacrifice, nerves were fixed, sectioned, and immunostained to allow for counting of total axons. RESULTS: Rats treated with FCF showed an improvement compared with control at all time points (n = 8) (P = 0.047, 0.044, 0.014, and 0.0059, respectively). A statistical difference was also shown between FCF and bzATP at d 7 (P < 0.05), but not shown with d 3, 14, and 21 (P > 0.05). CONCLUSIONS: Blocking the P2X7 receptor improves functional outcomes after PEG-mediated axonal fusion.

The effects of adjuvant fibrin sealant on the surgical repair of segmental nerve defects in an animal model.

PURPOSE: Nerve repair after a segmental defect injury remains a challenge for surgeons. Fibrin glue can be used to expedite surgical procedures and maintain proper nerve spatial orientation to potentially optimize recovery, yet surgeons hesitate to use it owing to concerns about fibrin's inhibiting regeneration and increasing scar formation. The purpose of these experiments was to evaluate whether fibrin glue impedes nerve regeneration. METHODS: A critical-size defect of 10 mm was created in 32 Sprague-Dawley rats with 4 different forms of repair: a collagen type-I conduit (n = 8), a collagen type-I conduit filled with fibrin glue (n = 8), an autologous nerve graft (n=8), and an autologous nerve graft with fibrin glue (n = 8). Behavioral tests, including sciatic functional indices, were used to evaluate functional recovery. Neurophysiology, immunohistochemistry, and nerve morphometry were used to critically analyze nerve regeneration. RESULTS: Multiple outcome parameters for nerve regeneration, remyelination, behavior, and electrophysiology were used to determine that the addition of fibrin did not influence recovery for the autograft groups. Similarly, within the conduit group, behavioral tests showed comparable functional recovery and indistinguishable results in compound motor action potential and nerve morphometry. Immunohistochemistry revealed identical degrees of Wallerian degeneration and scarring between conduit groups. CONCLUSIONS: The addition of fibrin to either the conduit or the autograft group did not result in any meaningful differences in recovery. Our data demonstrate that fibrin glue does not impede nerve regeneration or functional recovery after surgical repair of a segmental nerve defect in a rat model. CLINICAL RELEVANCE: The clinical use of fibrin glue as an adjunct with peripheral nerve repair may be considered safe because it does not impair nerve regeneration with critical size defects in an animal model.

Local production of serum amyloid a is implicated in the induction of macrophage chemoattractants in Schwann cells during wallerian degeneration of peripheral nerves.

The elevation of serum levels of serum amyloid A (SAA) has been regarded as an acute reactive response following inflammation and various types of injuries. SAA from the liver and extrahepatic tissues plays an immunomodulatory role in a variety of pathophysiological conditions. Inflammatory cytokines in the peripheral nerves have been implicated in the Wallerian degeneration of peripheral nerves after injury and in certain types of inflammatory neuropathies. In the present study, we found that a sciatic nerve axotomy could induce an increase of SAA1 and SAA3 mRNA expression in sciatic nerves. Immunohistochemical staining showed that Schwann cells are the primary sources of SAA production after nerve injury. In addition, interleukin-6-null mice, but not tumor necrosis factor-α-null mice showed a defect in the production of SAA1 in sciatic nerve following injury. Dexamethasone treatment enhanced the expression and secretion of SAA1 and SAA3 in sciatic nerve explants cultures, suggesting that interleukin-6 and corticosteroids might be major regulators for SAA production in Schwann cells following injury. Moreover, the stimulation of Schwann cells with SAA1 elicited the production of the macrophage chemoattractants, Ccl2 and Ccl3, in part through a G-protein coupled receptor. Our findings suggest that locally produced SAA might play an important role in Wallerian degeneration after peripheral nerve injury.

Arachidonic acid derivatives and their role in peripheral nerve degeneration and regeneration.

After peripheral nerve injury, a process of axonal degradation, debris clearance, and subsequent regeneration is initiated by complex local signaling, called Wallerian degeneration (WD). This process is in part mediated by neuroglia as well as infiltrating inflammatory cells and regulated by inflammatory mediators such as cytokines, chemokines, and the activation of transcription factors also related to the inflammatory response. Part of this neuroimmune signaling is mediated by the innate immune system, including arachidonic acid (AA) derivatives such as prostaglandins and leukotrienes. The enzymes responsible for their production, cyclooxygenases and lipooxygenases, also participate in nerve degeneration and regeneration. The interactions between signals for nerve regeneration and neuroinflammation go all the way down to the molecular level. In this paper, we discuss the role that AA derivatives might play during WD and nerve regeneration, and the therapeutic possibilities that arise.

[Mechanism of axonal degeneration: from molecular signaling to the development of therapeutic applications].

Neurons communicate with other cells via long processes, i.e., axons and dendrites, functionally and morphologically specialized tree-like structures. Formation and maintenance of such processes play a crucial role in neuronal functions. Axons are particularly important for construction of neuronal network, and, together with synapses at the end of them, play a central role in transmission of information. Axonal degeneration, a phenomenon that once formed axons lose structural integrity, is most typically observed as "Wallerian degeneration", in which injured axonal segment (distal to the site of injury) degenerates. Different forms of axonal degeneration are also observed in a variety of contexts, including pathogenesis and progression of different neurodegenerative disorders, as well as neuronal network formation during development. Thus, understanding of regulatory mechanism of axonal degeneration is important in many aspects, such as for clarification of neuronal morphogenesis mechanism, and for development of neuroprotective therapy against neurological disorders. Here, I discuss recent progress in the research field of axonal degeneration mechanism.

Sarm1 haploinsufficiency or low expression levels after antisense oligonucleotides delay programmed axon degeneration.

Activation of the pro-degenerative protein SARM1 after diverse physical and disease-relevant injuries causes programmed axon degeneration. Original studies indicate that substantially decreased SARM1 levels are required for neuroprotection. However, we demonstrate, in Sarm1 haploinsufficient mice, that lowering SARM1 levels by 50% delays programmed axon degeneration in vivo after sciatic nerve transection and partially prevents neurite outgrowth defects in mice lacking the pro-survival factor NMNAT2. In vitro, the rate of degeneration in response to traumatic, neurotoxic, and genetic triggers of SARM1 activation is also slowed. Finally, we demonstrate that Sarm1 antisense oligonucleotides decrease SARM1 levels by more than 50% in vitro, which delays or prevents programmed axon degeneration. Combining Sarm1 haploinsufficiency with antisense oligonucleotides further decreases SARM1 levels and prolongs protection after neurotoxic injury. These data demonstrate that axon protection occurs in a Sarm1 gene dose-responsive manner and that SARM1-lowering agents have therapeutic potential, making Sarm1-targeting antisense oligonucleotides a promising therapeutic strategy.

Neuroprotection without immunomodulation is not sufficient to reduce first relapse severity in experimental autoimmune encephalomyelitis.

OBJECTIVES: Multiple sclerosis can be characterized by a strong neuroinflammatory and progressive neurodegenerative component leading to prolonged disability. The synthetic compound R(+)WIN55,212-2 is reported to be neuroprotective at moderate doses and both neuroprotective and immunomodulatory at high doses, most likely due to differences in receptor affinities. In order to investigate the effects of neuroprotection and immunomodulation in an animal model of multiple sclerosis, we examined the impact of increasing concentrations of R(+)WIN55,212-2 on the inflammatory profile in CNS during first relapse and related this to demyelination, axonal degeneration and relapse severity. METHODS: Experimental autoimmune encephalomyelitis was induced in Dark Agouti rats and treatment with R(+)WIN55,212-2 was initiated at symptom debut. The animals were scored clinically throughout the experiment, and axonal degeneration, demyelination, T cells, microglia/macrophages, TNF-alpha, IL-12, IFN-gamma, IL-10 and the T(H)17 response were estimated at the peak of the first relapse. RESULTS: Treatment with high-dose R(+)WIN55,212-2 (10 and 20 mg/kg) significantly improved the clinical performance of the animals during relapse. Interestingly, treatment at any dosage did not affect the brain levels of TNF-alpha, IL-12 and IFN-gamma (T(H)1 response), whereas high-dose cannabinoid treatment reduced the number of T cells and microglia/macrophages in addition to the T(H)17 response. At the same time, we observed a significant reduction in axonal degeneration in all treatment groups whereas only high-dose treatment resulted in reduced demyelination. CONCLUSION: High-dose R(+)WIN55,212-2 treatment reduces demyelination and axonal degeneration and has immunomodulatory effects which significantly improve clinical performance, whereas a reduction in axonal degeneration on its own, induced by 5 mg/kg R(+)WIN55,212-2, has no impact on first relapse severity.

Emergence of SARM1 as a Potential Therapeutic Target for Wallerian-type Diseases.

Wallerian degeneration is a neuronal death pathway that is triggered in response to injury or disease. Death was thought to occur passively until the discovery of a mouse strain, i.e., Wallerian degeneration slow (WLDS), which was resistant to degeneration. Given that the WLDS mouse encodes a gain-of-function fusion protein, its relevance to human disease was limited. The later discovery that SARM1 (sterile alpha and toll/interleukin receptor [TIR] motif-containing protein 1) promotes Wallerian degeneration suggested the existence of a pathway that might be targeted therapeutically. More recently, SARM1 was found to execute degeneration by hydrolyzing NAD+. Notably, SARM1 knockdown or knockout prevents neuron degeneration in response to a range of insults that lead to peripheral neuropathy, traumatic brain injury, and neurodegenerative disease. Here, we discuss the role of SARM1 in Wallerian degeneration and the opportunities to target this enzyme therapeutically.

NMDA receptor blockade with memantine attenuates white matter injury in a rat model of periventricular leukomalacia.

Hypoxia-ischemia (H/I) in the premature infant leads to white matter injury termed periventricular leukomalacia (PVL), the leading cause of subsequent neurological deficits. Glutamatergic excitotoxicity in white matter oligodendrocytes (OLs) mediated by cell surface glutamate receptors (GluRs) of the AMPA subtype has been demonstrated as one factor in this injury. Recently, it has been shown that rodent OLs also express functional NMDA GluRs (NMDARs), and overactivation of these receptors can mediate excitotoxic OL injury. Here we show that preterm human developing OLs express NMDARs during the PVL period of susceptibility, presenting a potential therapeutic target. The expression pattern mirrors that seen in the immature rat. Furthermore, the uncompetitive NMDAR antagonist memantine attenuates NMDA-evoked currents in developing OLs in situ in cerebral white matter of immature rats. Using an H/I rat model of white matter injury, we show in vivo that post-H/I treatment with memantine attenuates acute loss of the developing OL cell surface marker O1 and the mature OL marker MBP (myelin basic protein), and also prevents the long-term reduction in cerebral mantle thickness seen at postnatal day 21 in this model. These protective doses of memantine do not affect normal myelination or cortical growth. Together, these data suggest that NMDAR blockade with memantine may provide an effective pharmacological prevention of PVL in the premature infant.

Combination therapy of lovastatin and rolipram provides neuroprotection and promotes neurorepair in inflammatory demyelination model of multiple sclerosis.

Drug combination therapies for central nervous system (CNS) demyelinating diseases including multiple sclerosis (MS) are gaining momentum over monotherapy. Over the past decade, both in vitro and in vivo studies established that statins (HMG-CoA reductase inhibitors) and rolipram (phosphodiesterase-4 inhibitor; blocks the degradation of intracellular cyclic AMP) can prevent the progression of MS in affected individuals via different mechanisms of action. In this study, we evaluated the effectiveness of lovastatin (LOV) and rolipram (RLP) in combination therapy to promote neurorepair in an inflammatory CNS demyelination model of MS, experimental autoimmune encephalomyelitis (EAE). Combination treatment with suboptimal doses of these drugs in an established case of EAE (clinical disease score > or = 2.0) significantly attenuated the infiltration of inflammatory cells and protected myelin sheath and axonal integrity in the CNS. It was accompanied with elevated level of cyclic AMP and activation of its associated protein kinase A. Interestingly, combination treatment with these drugs impeded neurodegeneration and promoted neurorepair in established EAE animals (clinical disease score > or = 3.5) as verified by quantitative real-time polymerase chain reaction, immunohistochemistry and electron microscopic analyses. These effects of combination therapy were minimal and/or absent with either drug alone in these settings. Together, these data suggest that combination therapy with LOV and RLP has the potential to provide neuroprotection and promote neurorepair in MS, and may have uses in other related CNS demyelinating diseases.

The purine nucleosides adenosine and guanosine delay axonal degeneration in vitro.

Axonal degeneration is a key component of many neurodegenerative diseases. Injured axons undergo a program of self-destruction termed Wallerian degeneration that is an active, well-regulated process. The pathways leading to axon fragmentation are uncharacterized, but experiments with wld(s) mutant mice led to the discovery that over-expression of NMN adenylyltransferase 1 or treatment with NAD(+) can inhibit axonal degeneration. In this study, we show that the purine nucleosides adenosine and guanosine, but not inosine, inhibit injury-induced axonal degeneration in cultured dorsal root ganglia neurons. Axons can be preserved by adding adenosine within 6 h of the axonal injury. The presence of adenosine was required continuously after the injury to maintain axonal protection. Together these results suggest that adenosine does not alter the neuronal response to injury, but instead inhibits a local axonal pathway necessary for the commitment and/or execution of the axon destructive program.

The future of multiple sclerosis treatment.

Recent years have seen considerable evolution and increasing sophistication of our concepts of the pathophysiology of multiple sclerosis. These new notions include the increased recognition of the importance of extralesional pathology, of the interplay between inflammation and neurodegenerative changes, pathophysiological heterogeneity and additional immune cell populations contributing to disease. These advances have driven the development and evaluation of new therapeutic strategies and outcome measures for clinical trials. A sizeable number of new immunomodulatory and immunosuppressive agents are under development and attracting great attention. These may offer potential advantages over existing treatments in terms of convenience and efficacy, but certain agents may raise safety concerns. In addition, neuroprotective and repair strategies are beginning to be considered. Not all of these agents will eventually be marketed but they will all help us gain insight into the pathophysiology of multiple sclerosis and decipher the mechanisms that underlie its heterogeneity. The place that these therapies will come to occupy in future years will depend on their relative benefits and risks.

New options for early treatment of multiple sclerosis.

It is now possible to diagnose patients with multiple sclerosis earlier than previously due to the integration of MRI parameters into the diagnostic criteria. This provides a window of opportunity to treat patients with disease-modifying treatments before clinically-manifest tissue destruction and disability has emerged. There are a number of reasons to believe that such early treatment will be particularly beneficial. For example, immunopathological studies have shown that the irreversible axonal damage that underlies accumulation of disability occurs very early in the course of the disease. In addition, natural history studies demonstrate that frequent relapses and accumulation of a high T2 lesion load in the first years following diagnosis are predictive of long-term disability outcome. Treating patients early, after a clinically isolated neurological syndrome suggestive of multiple sclerosis, appears to have a greater impact on relapse frequency than when treatment is initiated later in the disease course. The latest data comes from the PreCISe study, a placebo-controlled randomised study of glatiramer acetate in patients with a clinically isolated syndrome. The study showed that this treatment significantly reduced the risk of conversion to clinically definite multiple sclerosis, with the quartile time for conversion being prolonged by more than one year in the glatiramer acetate cohort compared to placebo-treated patients. The safety and tolerability of glatiramer acetate in this relatively healthy and independent patient population was acceptable and consistent with its known safety profile in patients with relapsing remitting multiple sclerosis. An application for an extension of the approved indication of glatiramer acetate to the treatment of patients with a first clinical event suggestive of multiple sclerosis has been filed with the regulatory authorities.

Protective effect of BDNF against beta-amyloid induced neurotoxicity in vitro and in vivo in rats.

We examined the potential protective effect of BDNF against beta-amyloid-induced neurotoxicity in vitro and in vivo in rats. In neuronal cultures, BDNF had specific and dose-response protective effects on neuronal toxicity induced by Abeta(1-42) and Abeta(25-35). It completely reversed the toxic action induced by Abeta(1-42) and partially that induced by Abeta(25-35). These effects involved TrkB receptor activation since they were inhibited by K252a. Catalytic BDNF receptors (TrkB.FL) were localized in vitro in cortical neurons (mRNA and protein). In in vivo experiments, Abeta(25-35) was administered into the indusium griseum or the third ventricle and several parameters were measured 7 days later to evaluate potential Abeta(25-35)/BDNF interactions, i.e. local measurement of BDNF release, number of hippocampal hilar cells expressing SRIH mRNA and assessment of the corpus callosum damage (morphological examination, pyknotic nuclei counting and axon labeling with anti-MBP antibody). We conclude that BDNF possesses neuroprotective properties against toxic effects of Abeta peptides.