The neurotrophins BDNF, NT-3, and NGF display distinct patterns of retrograde axonal transport in peripheral and central neurons

Neuron-specific RNA-sequencing reveals different responses in peripheral neurons after nerve injury

Peripheral neurons are heterogeneous and functionally diverse, but all share the capability to switch to a pro-regenerative state after nerve injury. Despite the assumption that the injury response is similar among neuronal subtypes, functional recovery may differ. Understanding the distinct intrinsic regenerative properties between neurons may help to improve the quality of regeneration, prioritizing the growth of axon subpopulations to their targets. Here, we present a comparative analysis of regeneration across four key peripheral neuron populations: motoneurons, proprioceptors, cutaneous mechanoreceptors, and nociceptors. Using Cre/Ai9 mice that allow fluorescent labeling of neuronal subtypes, we found that nociceptors showed the greater regeneration after a sciatic crush, followed by motoneurons, mechanoreceptors, and, finally, proprioceptors. By breeding these Cre mice with Ribotag mice, we isolated specific translatomes and defined the regenerative response of these neuronal subtypes after axotomy. Only 20% of the regulated genes were common, revealing a diverse response to injury among neurons, which was also supported by the differential influence of neurotrophins among neuron subtypes. Among differentially regulated genes, we proposed MED12 as a specific regulator of the regeneration of proprioceptors. Altogether, we demonstrate that the intrinsic regenerative capacity differs between peripheral neuron subtypes, opening the door to selectively modulate these responses.

Brain-Derived Neurotrophic Factor, Nociception, and Pain

This article examines the involvement of the brain-derived neurotrophic factor (BDNF) in the control of nociception and pain. BDNF, a neurotrophin known for its essential role in neuronal survival and plasticity, has garnered significant attention for its potential implications as a modulator of synaptic transmission. This comprehensive review aims to provide insights into the multifaceted interactions between BDNF and pain pathways, encompassing both physiological and pathological pain conditions. I delve into the molecular mechanisms underlying BDNF's involvement in pain processing and discuss potential therapeutic applications of BDNF and its mimetics in managing pain. Furthermore, I highlight recent advancements and challenges in translating BDNF-related research into clinical practice.

Immunohistochemical phenotype of sensory neurons associated with sympathetic plexuses in the trigeminal ganglia of adult nerve growth factor transgenic mice

Following peripheral nerve injury, postganglionic sympathetic axons sprout into the affected sensory ganglia and form perineuronal sympathetic plexuses with somata of sensory neurons. This sympathosensory coupling contributes to the onset and persistence of injury-induced chronic pain. We have documented the presence of similar sympathetic plexuses in the trigeminal ganglia of adult mice that ectopically overexpress nerve growth factor (NGF), in the absence of nerve injury. In this study, we sought to further define the phenotype(s) of these trigeminal sensory neurons having sympathetic plexuses in our transgenic mice. Using quantitative immunofluorescence staining analyses, we show that the invading sympathetic axons specifically target sensory somata immunopositive for several biomarkers: NGF high-affinity receptor tyrosine kinase A (trkA), calcitonin gene-related peptide (CGRP), neurofilament heavy chain (NFH), and P2X purinoceptor 3 (P2X3). Based on these phenotypic characteristics, the majority of the sensory somata surrounded by sympathetic plexuses are likely to be NGF-responsive nociceptors (i.e., trkA expressing) that are peptidergic (i.e., CGRP expressing), myelinated (i.e., NFH expressing), and ATP sensitive (i.e., P2X3 expressing). Our data also show that very few sympathetic plexuses surround sensory somata expressing other nociceptive (pain) biomarkers, including substance P and acid-sensing ion channel 3. No sympathetic plexuses are associated with sensory somata that display isolectin B4 binding. Though the cellular mechanisms that trigger the formation of sympathetic plexus (with and without nerve injury) remain unknown, our new observations yield an unexpected specificity with which invading sympathetic axons appear to target a precise subtype of nociceptors. This selectivity likely contributes to pain development and maintenance associated with sympathosensory coupling.

Enhanced TrkA signaling impairs basal forebrain-dependent behavior

Basal forebrain cholinergic neurons (BFCNs) modulate cognitive functions such as attention, learning and memory. The NGF/TrkA pathway plays an important role in the development and function of BFCNs, although two mouse models conditionally deleting TrkA expression in the central nervous system (CNS) have shown contradictory results. To shed light into this discrepancy, we used a mouse model with a gain-of-function in TrkA receptor signaling. Our results indicate that enhanced TrkA signaling did not alter hippocampal cholinergic innervation, general locomotion or anxiety-related behaviors, but it increases ChAT expression, the number of cholinergic neurons at early postnatal stages and, mutant mice showed impaired motor learning and memory functions. These data demonstrate that proper functioning of the cholinergic system in CNS requires a balanced NGF/TrkA signaling.

Delayed viral vector mediated delivery of neurotrophin-3 improves skilled hindlimb function and stability after thoracic contusion

Intramuscular injection of an Adeno-associated viral vector serotype 1 (AAV1) encoding Neurotrophin-3 (NT3) into hindlimb muscles 24 h after a severe T9 spinal level contusion in rats has been shown to induce lumbar spinal neuroplasticity, partially restore locomotive function and reduce spasms during swimming. Here we investigate whether a targeted delivery of NT3 to lumbar and thoracic motor neurons 48 h following a severe contusive injury aids locomotive recovery in rats. AAV1-NT3 was injected bilaterally into the tibialis anterior, gastrocnemius and rectus abdominus muscles 48-h following trauma, persistently elevating serum levels of the neurotrophin. NT3 modestly improved trunk stability, accuracy of stepping during skilled locomotion, and alternation of the hindlimbs during swimming, but it had no effect on gross locomotor function in the open field. The number of vGlut1⁺ boutons, likely arising from proprioceptive afferents, on gastrocnemius α-motor neurons was increased after injury but normalised following NT3 treatment, suggestive of a mechanism in which functional benefits may be mediated through proprioceptive feedback. Ex vivo MRI revealed substantial loss of grey and white matter at the lesion epicentre but no effect of delayed NT3 treatment to induce neuroprotection. Lower body spasms and hyperreflexia of an intrinsic paw muscle were not reliably induced in this severe injury model suggesting a more complex anatomical or physiological cause to their induction. We have shown that delayed intramuscular AAV-NT3 treatment can promote recovery in skilled stepping and coordinated swimming, supporting a role for NT3 as a therapeutic strategy for spinal injuries potentially through modulation of somatosensory feedback.

Growth factors and molecular-driven plasticity in neurological systems

It has been almost 70 years since the discovery of nerve growth factor (NGF), a period of a dramatic evolution in our understanding of dynamic growth, regeneration, and rewiring of the nervous system. In 1953, the extraordinary finding that a protein found in mouse submandibular glands generated a halo of outgrowing axons has now redefined our concept of the nervous system connectome. Central and peripheral neurons and their axons or dendrites are no longer considered fixed or static "wiring." Exploiting this molecular-driven plasticity as a therapeutic approach has arrived in the clinic with a slate of new trials and ideas. Neural growth factors (GFs), soluble proteins that alter the behavior of neurons, have expanded in numbers and our understanding of the complexity of their signaling and interactions with other proteins has intensified. However, beyond these "extrinsic" determinants of neuron growth and function are the downstream pathways that impact neurons, ripe for translational development and potentially more important than individual growth factors that may trigger them. Persistent and ongoing nuances in clinical trial design in some of the most intractable and irreversible neurological conditions give hope for connecting new biological ideas with clinical benefits. This review is a targeted update on neural GFs, their signals, and new therapeutic ideas, selected from an expansive literature.

Ultrasound Therapy of Injury Site Modulates Gene and Protein Expressions in the Dorsal Root Ganglion in a Sciatic Nerve Crush Injury Rat Model

The aim of this study was to verify the effects of ultrasound on dorsal root ganglion (DRG) neurons at the injury site in a rat model of sciatic nerve crush injury. We evaluated the mRNA expression of neurotrophic and pro-inflammatory factors by quantitative reverse transcription polymerase chain reaction 7 and 14 d post-injury. We also evaluated the protein levels of brain-derived neurotrophic factor (BDNF) 7 and 14 d post-injury. Axon regeneration and motor function analyses were performed 21 days after injury to confirm the facilitative effect of ultrasound on nerve regeneration. In the ultrasound group, BDNF and interleukin-6 mRNA expression of the DRG was significantly reduced 7 d post-injury. Compared with the sham group, the BDNF protein expression of the DRG in the ultrasound group remained at a higher level 14 d post-injury. Motor function, myelinated fiber density and myelin sheath thickness were significantly higher in the ultrasound group than in the sham group 21 d post-injury. These results indicate that ultrasound therapy at the injury site promotes nerve regeneration and modulates gene and protein expression in the DRG of a rat model of a sciatic nerve crush injury.

Effects of regenerative peripheral nerve interface on dorsal root ganglia neurons following peripheral axotomy

Background

Long-term delayed reconstruction of injured peripheral nerves always results in poor recovery. One important reason is retrograde cell death among injured sensory neurons of dorsal root ganglia (DRG). A regenerative peripheral nerve interface (RPNI) was capable of generating new synaptogenesis between the proximal nerve stump and free muscle graft. Meanwhile, sensory receptors within the skeletal muscle can also be readily reinnervated by donor sensory axons, which allows the target muscles to become sources of sensory information for function reconstruction. To date, the effect of RPNI on injured sensory neurons is still unclear. Here, we aim to investigate the potential neuroprotective role of RPNI on sensory DRG neurons after sciatic axotomy in adult rats.

Materials and methods

The sciatic nerves of sixty rats were transected. The rats were randomly divided into three groups following this nerve injury: no treatment (control group, n = 20), nerve stump implantation inside a fully innervated muscle (NSM group, n = 20), or nerve stump implantation inside a free muscle graft (RPNI group, n = 20). At 8 weeks post-axotomy, ipsilateral L4 and L5 DRGs were harvested in each group. Toluidine blue staining was employed to quantify the neuronal densities in DRGs. The neuronal apoptosis index was quantified with TUNEL assay. Western blotting was applied to measure the expressions of Bax, Bcl-2, and neurotrophins (NTs) in ipsilateral DRGs.

Results

There were significantly higher densities of neurons in ipsilateral DRGs of RPNI group than NSM and control groups at 8 weeks post-axotomy (p < 0.01). Meanwhile, neuronal apoptosis index and the expressions of pro-apoptotic Bax within the ipsilateral DRGs were significantly lower in the RPNI group than those in the control and NSM groups (p < 0.05), while the opposite result was observed in the expression of pro-survival Bcl-2. Furthermore, the expressions of NGF, NT-3, BDNF, and GDNF were also upregulated in the ipsilateral DRGs in the RPNI group (p < 0.01).

Conclusion

The present results demonstrate that RPNI could prevent neuronal loss after peripheral axotomy. And the neuroprotection effect has a relationship with the upregulation of NTs in DRGs, such as NGF, NT-3, BDNF, and GDNF. These findings provide an effective therapy for neuroprotection in the delayed repair of the peripheral nerve injury.

The Role of Axonal Transport in Glaucoma

Glaucoma is a neurodegenerative disease that affects the retinal ganglion cells (RGCs) and leads to progressive vision loss. The first pathological signs can be seen at the optic nerve head (ONH), the structure where RGC axons leave the retina to compose the optic nerve. Besides damage of the axonal cytoskeleton, axonal transport deficits at the ONH have been described as an important feature of glaucoma. Axonal transport is essential for proper neuronal function, including transport of organelles, synaptic components, vesicles, and neurotrophic factors. Impairment of axonal transport has been related to several neurodegenerative conditions. Studies on axonal transport in glaucoma include analysis in different animal models and in humans, and indicate that its failure happens mainly in the ONH and early in disease progression, preceding axonal and somal degeneration. Thus, a better understanding of the role of axonal transport in glaucoma is not only pivotal to decipher disease mechanisms but could also enable early therapies that might prevent irreversible neuronal damage at an early time point. In this review we present the current evidence of axonal transport impairment in glaucomatous neurodegeneration and summarize the methods employed to evaluate transport in this disease.

Retrograde Axonal Transport of Neurotrophins in Basal Forebrain Cholinergic Neurons

Axonal transport is key for the survival and function of all neurons. This process is especially important in basal forebrain cholinergic neurons due to their extremely long and diffuse axonal projections. These neurons are critical for learning and memory and degenerate rapidly in age-related neurodegenerative disorders like Alzheimer's and Parkinson's disease. The vulnerability of these neurons to age-related neurodegeneration may be partially attributed to their reliance on retrograde axonal transport for neurotrophic support. Unfortunately, little is known about the molecular biology underlying the retrograde transport dynamics of these neurons due to the difficulty associated with their maintenance in vitro. Here, we outline a protocol for culturing primary rodent basal forebrain cholinergic neurons in microfluidic chambers, devices designed specifically for the study of axonal transport in vitro. We outline protocols for labeling neurotrophins and tracking neurotrophin transport in these neurons. Our protocols can also be used to study axonal transport in other types of primary neurons such as cortical and hippocampal neurons.

Peripherally delivered Adeno-associated viral vectors for spinal cord injury repair

Via the peripheral and autonomic nervous systems, the spinal cord directly or indirectly connects reciprocally with many body systems (muscular, intengumentary, respiratory, immune, digestive, excretory, reproductive, cardiovascular, etc). Accordingly, spinal cord injury (SCI) can result in catastrophe for multiple body systems including muscle paralysis affecting movement and loss of normal sensation, as well as neuropathic pain, spasticity, reduced fertility and autonomic dysreflexia. Treatments and cure for an injured spinal cord will likely require access of therapeutic agents across the blood-CNS (central nervous system) barrier. However, some types of repair within the CNS may be possible by targeting treatment to peripherally located cells or by delivering Adeno-Associated Viral vectors (AAVs) by peripheral routes (e.g., intrathecal, intravenous). This review will consider some future possibilities for SCI repair generated by therapeutic peripheral gene delivery. There are now six gene therapies approved worldwide as safe and effective medicines of which three were created by modification of the apparently nonpathogenic Adeno-Associated Virus. One of these AAVs, Zolgensma, is injected intrathecally for treatment of spinal muscular atrophy in children. One day, delivery of AAVs into peripheral tissues might improve recovery after spinal cord injury in humans; we discuss experiments by us and others delivering transgenes into nerves or muscles for sensorimotor recovery in animal models of SCI or of stroke including human Neurotrophin-3. We also describe ongoing efforts to develop AAVs that are delivered to particular targets within and without the CNS after peripheral administration using capsids with improved tropisms, promoters that are selective for particular cell types, and methods for controlling the dose and duration of expression of a transgene. In conclusion, in the future, minimally invasive administration of AAVs may improve recovery after SCI with minimal side effects.

TGFβ-Neurotrophin Interactions in Heart, Retina, and Brain

Ischemic insults to the heart and brain, i.e., myocardial and cerebral infarction, respectively, are amongst the leading causes of death worldwide. While there are therapeutic options to allow reperfusion of ischemic myocardial and brain tissue by reopening obstructed vessels, mitigating primary tissue damage, post-infarction inflammation and tissue remodeling can lead to secondary tissue damage. Similarly, ischemia in retinal tissue is the driving force in the progression of neovascular eye diseases such as diabetic retinopathy (DR) and age-related macular degeneration (AMD), which eventually lead to functional blindness, if left untreated. Intriguingly, the easily observable retinal blood vessels can be used as a window to the heart and brain to allow judgement of microvascular damages in diseases such as diabetes or hypertension. The complex neuronal and endocrine interactions between heart, retina and brain have also been appreciated in myocardial infarction, ischemic stroke, and retinal diseases. To describe the intimate relationship between the individual tissues, we use the terms heart-brain and brain-retina axis in this review and focus on the role of transforming growth factor β (TGFβ) and neurotrophins in regulation of these axes under physiologic and pathologic conditions. Moreover, we particularly discuss their roles in inflammation and repair following ischemic/neovascular insults. As there is evidence that TGFβ signaling has the potential to regulate expression of neurotrophins, it is tempting to speculate, and is discussed here, that cross-talk between TGFβ and neurotrophin signaling protects cells from harmful and/or damaging events in the heart, retina, and brain.

Hijacking Dorsal Raphe to Improve Metabolism and Depression-Like Behaviors via BDNF Gene Transfer in Mice

Moods and metabolism modulate each other. High comorbidity of depression and metabolic disorders, such as diabetes and obesity, poses a great challenge to treat such conditions. Here we report the therapeutic efficacy of brain-derived neurotrophic factor (BDNF) by gene transfer in the dorsal raphe nucleus (DRN) in a chronic unpredictable mild stress model (CUMS) of depression and models of diabetes and obesity. In CUMS, BDNF-expressing mice displayed antidepressant- and anxiolytic-like behaviors, which are associated with augmented serotonergic activity. Both in the diet-induced obesity model (DIO) and in db/db mice, BDNF ameliorated obesity and diabetes, which may be mediated by enhanced sympathetic activity not involving DRN serotonin. Chronic activation of DRN neurons via chemogenetic tools produced similar effects as BDNF in DIO mice. These results established the DRN as a key nexus in regulating depression-like behaviors and metabolism, which can be exploited to combat comorbid depression and metabolic disorders via BDNF gene transfer.

Enhanced T-type calcium channel 3.2 activity in sensory neurons contributes to neuropathic-like pain of monosodium iodoacetate-induced knee osteoarthritis

The monosodium iodoacetate knee osteoarthritis model has been widely used for the evaluation of osteoarthritis pain, but the pathogenesis of associated chronic pain is not fully understood. The T-type calcium channel 3.2 (Ca_V3.2) is abundantly expressed in the primary sensory neurons, in which it regulates neuronal excitability at both the somata and peripheral terminals and facilitates spontaneous neurotransmitter release at the spinal terminals. In this study, we investigated the involvement of primary sensory neuron-Ca_V3.2 activation in monosodium iodoacetate osteoarthritis pain. Knee joint osteoarthritis pain was induced by intra-articular injection of monosodium iodoacetate (2 mg) in rats, and sensory behavior was evaluated for 35 days. At that time, knee joint structural histology, primary sensory neuron injury, and inflammatory gliosis in lumbar dorsal root ganglia, and spinal dorsal horn were examined. Primary sensory neuron-T-type calcium channel current by patch-clamp recording and Ca_V3.2 expression by immunohistochemistry and immunoblots were determined. In a subset of animals, pain relief by Ca_V3.2 inhibition after delivery of Ca_V3.2 inhibitor TTA-P2 into sciatic nerve was investigated. Knee injection of monosodium iodoacetate resulted in osteoarthritis histopathology, weight-bearing asymmetry, sensory hypersensitivity of the ipsilateral hindpaw, and inflammatory gliosis in the ipsilateral dorsal root ganglia, sciatic nerve, and spinal dorsal horn. Neuronal injury marker ATF-3 was extensively upregulated in primary sensory neurons, suggesting that neuronal damage was beyond merely knee-innervating primary sensory neurons. T-type current in dissociated primary sensory neurons from lumbar dorsal root ganglia of monosodium iodoacetate rats was significantly increased, and Ca_V3.2 protein levels in the dorsal root ganglia and spinal dorsal horn ipsilateral to monosodium iodoacetate by immunoblots were significantly increased, compared to controls. Perineural application of TTA-P2 into the ipsilateral sciatic nerve alleviated mechanical hypersensitivity and weight-bearing asymmetry in monosodium iodoacetate osteoarthritis rats. Overall, our findings demonstrate an elevated Ca_V3.2 expression and enhanced function of primary sensory neuron-T channels in the monosodium iodoacetate osteoarthritis pain. Further study is needed to delineate the importance of dysfunctional primary sensory neuron-Ca_V3.2 in osteoarthritis pain.

Retinal Ganglion Cell Transplantation: Approaches for Overcoming Challenges to Functional Integration

As part of the central nervous system, mammalian retinal ganglion cells (RGCs) lack significant regenerative capacity. Glaucoma causes progressive and irreversible vision loss by damaging RGCs and their axons, which compose the optic nerve. To functionally restore vision, lost RGCs must be replaced. Despite tremendous advancements in experimental models of optic neuropathy that have elucidated pathways to induce endogenous RGC neuroprotection and axon regeneration, obstacles to achieving functional visual recovery through exogenous RGC transplantation remain. Key challenges include poor graft survival, low donor neuron localization to the host retina, and inadequate dendritogenesis and synaptogenesis with afferent amacrine and bipolar cells. In this review, we summarize the current state of experimental RGC transplantation, and we propose a set of standard approaches to quantifying and reporting experimental outcomes in order to guide a collective effort to advance the field toward functional RGC replacement and optic nerve regeneration.

Ipsilateral BDNF mRNA expression in the motor cortex positively correlates with motor function of the affected forelimb after intracerebral hemorrhage

Intracerebral hemorrhage (ICH) is a subtype of stroke that causes major motor impairments. Brain-derived neurotrophic factor (BDNF) is known to have important roles in neuroplasticity and beneficially contributes to stroke recovery. This study aimed to characterize BDNF expression in the motor cortex after ICH and investigate the relationship between cortical BDNF expression and behavioral outcomes using an ICH rat model. Wistar rats were divided into two groups: a SHAM group (n = 7) and an ICH group (n = 8). ICH was induced by the injection of collagenase into the left striatum near the internal capsule. For behavioral assessments, the cylinder test and open field test were performed before surgery and 3 days, 1 week, 2 weeks, and 4 weeks after surgery. Following the behavioral assessments at 4 weeks, BDNF expression in the ipsilateral and contralateral motor cortex was assayed using RT-PCR and ELISA methods. There was no significant difference in either cortical BDNF mRNA or protein expression levels between the SHAM and ICH groups. However, the asymmetry index of BDNF mRNA expression between the ipsilateral and contralateral hemispheres shifted to the ipsilateral hemisphere after ICH. Furthermore, the ipsilateral cortical BDNF mRNA expression level positively correlated with motor function in the affected forelimb after ICH. This study describes for the first time that cortical BDNF mRNA expression is related to post-ICH motor impairment. These results highlight the importance of assessing the interhemispheric laterality of BDNF expression and could help develop novel treatment strategies for BDNF-dependent recovery after ICH.

BDNF Protein and BDNF mRNA Expression of the Medial Prefrontal Cortex, Amygdala, and Hippocampus during Situational Reminder in the PTSD Animal Model

Whether BDNF protein and BDNF mRNA expression of the medial prefrontal cortex (mPFC; cingulated cortex area 1 (Cg1), prelimbic cortex (PrL), and infralimbic cortex (IL)), amygdala, and hippocampus (CA1, CA2, CA3, and dentate gyrus (DG)) was involved in fear of posttraumatic stress disorder (PTSD) during the situational reminder of traumatic memory remains uncertain. Footshock rats experienced an inescapable footshock (3 mA, 10 s), and later we have measured fear behavior for 2 min in the footshock environment on the situational reminder phase. In the final retrieval of situational reminder, BDNF protein and mRNA levels were measured. The results showed that higher BDNF expression occurred in the Cg1, PrL, and amygdala. Lower BDNF expression occurred in the IL, CA1, CA2, CA3, and DG. BDNF mRNA levels were higher in the mPFC and amygdala but lower in the hippocampus. The neural connection analysis showed that BDNF protein and BDNF mRNA exhibited weak connections among the mPFC, amygdala, and hippocampus during situational reminders. The present data did not support the previous viewpoint in neuroimaging research that the mPFC and hippocampus revealed hypoactivity and the amygdala exhibited hyperactivity for PTSD symptoms. These findings should be discussed with the previous evidence and provide clinical implications for PTSD.

Neuroprotective Effect of Vascular Endothelial Growth Factor on Motoneurons of the Oculomotor System

Vascular endothelial growth factor (VEGF) was initially characterized as a potent angiogenic factor based on its activity on the vascular system. However, it is now well established that VEGF also plays a crucial role as a neuroprotective factor in the nervous system. A deficit of VEGF has been related to motoneuronal degeneration, such as that occurring in amyotrophic lateral sclerosis (ALS). Strikingly, motoneurons of the oculomotor system show lesser vulnerability to neurodegeneration in ALS compared to other motoneurons. These motoneurons presented higher amounts of VEGF and its receptor Flk-1 than other brainstem pools. That higher VEGF level could be due to an enhanced retrograde input from their target muscles, but it can also be produced by the motoneurons themselves and act in an autocrine way. By contrast, VEGF’s paracrine supply from the vicinity cells, such as glial cells, seems to represent a minor source of VEGF for brainstem motoneurons. In addition, ocular motoneurons experiment an increase in VEGF and Flk-1 level in response to axotomy, not observed in facial or hypoglossal motoneurons. Therefore, in this review, we summarize the differences in VEGF availability that could contribute to the higher resistance of extraocular motoneurons to injury and neurodegenerative diseases.

Gene and cell therapy for the nucleus basalis of Meynert with NGF in Alzheimer's disease

There is currently no effective treatment for the most common of the dementia disorders, Alzheimer's disease (AD). It has been known for decades that the central cholinergic system is important for memory. The cholinergic neurons in the basal forebrain with its cortical and hippocampal projections degenerate in AD and thus contribute to the cognitive decline characteristic of AD. This knowledge led to the development of the currently approved treatment for AD, with inhibitors of acetylcholine-esterase targeting the cholinergic system with beneficial but mild effects. In recent years, other approaches to influence the degenerating cholinergic system in AD focusing on nerve growth factor (NGF) have been undertaken. NGF is required for the survival and function of the basal forebrain cholinergic neurons, the most important being the nucleus basalis of Meynert (nbM). Since there is a lack of NGF and its receptors in the AD forebrain, the hypothesis is that local delivery of NGF to the nbM could revive the cholinergic circuitry and thereby restore cognitive functions. Since NGF does not pass through the blood-brain barrier, approaches involving cerebral injections of genetically modified cells or viral vectors or implantation of encapsulated cells in the nbM in AD patients have been used. These attempts have been partially successful but also have limitations, which are presented and discussed here. In conclusion, these trials point to the importance of further development of NGF-related therapies in AD.

The BDNF-Increasing Allele is Associated With Increased Proportion of Fast-Twitch Muscle Fibers, Handgrip Strength, and Power Athlete Status

Guilherme, JPLF, Semenova, EA, Borisov, OV, Kostryukova, ES, Vepkhvadze, TF, Lysenko, EA, Andryushchenko, ON, Andryushchenko, LB, Lednev, EM, Larin, AK, Bondareva, EA, Generozov, EV, and Ahmetov, II. The BDNF-increasing allele is associated with increased proportion of fast-twitch muscle fibers, handgrip strength, and power athlete status. J Strength Cond Res XX(X): 000-000, 2020-The brain-derived neurotrophic factor (BDNF) is involved in neurogenesis and formation of regenerated myofibers following injury or damage. A recent study suggested that the BDNF overexpression increases the proportion of fast-twitch muscle fibers, while the BDNF deletion promotes a fast-to-slow transition. The purpose of this study was to evaluate the association between the BDNF gene rs10501089 polymorphism (associated with blood BDNF levels), muscle fiber composition, and power athlete status. Muscle fiber composition was determined in 164 physically active individuals (113 men, 51 women). BDNF genotype and allele frequencies were compared between 508 Russian power athletes, 178 endurance athletes, and 190 controls. We found that carriers of the minor A-allele (the BDNF-increasing allele) had significantly higher percentage of fast-twitch muscle fibers than individuals homozygous for the G-allele (males: 64.3 [7.8] vs. 50.3 [15.8]%, p = 0.0015; all subjects: 64.1 ± 7.9 vs. 49.6 ± 14.7%, p = 0.0002). Furthermore, the A-allele was associated (p = 0.036) with greater handgrip strength in a sub-group of physically active subjects (n = 83) and over-represented in power athletes compared with controls (7.7 vs. 2.4%, p = 0.0001). The presence of the A-allele (i.e., AA+AG genotypes) rather than GG genotype increased the odds ratio of being a power athlete compared with controls (odds ratio [OR]: 3.43, p = 0.00071) or endurance athletes (OR: 2.36, p = 0.0081). In conclusion, the rs10501089 A-allele is associated with increased proportion of fast-twitch muscle fibers and greater handgrip strength, and these may explain, in part, the association between the AA/AG genotypes and power athlete status.

Facial Nerve Repair by Muscle-Vein Conduit in Rats: Functional Recovery and Muscle Reinnervation

The facial nerve is the most frequently damaged nerve in head and neck traumata. Repair of interrupted nerves is generally reinforced by fine microsurgical techniques; nevertheless, regaining all functions is the exception rather than the rule. The so-called "postparalytic syndrome," which includes synkinesia and altered blink reflexes, follows nerve injury. The purpose of this study was to examine if nerve-gap repair using an autologous vein filled with skeletal muscle would improve axonal regeneration, reduce neuromuscular junction polyinnervation, and improve the recovery of whisking in rats with transected and sutured right buccal branches of the facial nerve. Vibrissal motor performance was studied with the use of a video motion analysis. Immunofluorescence was used to visualize and analyze target muscle reinnervation. The results taken together indicate a positive effect of muscle-vein-combined conduit (MVCC) on the improvement of the whisking function after reparation of the facial nerve in rats. The findings support the recent suggestion that a venal graft with implantation of a trophic source, such as autologous denervated skeletal muscle, may promote the monoinnervation degree and ameliorate coordinated function of the corresponding muscles.

Expression of brain-derived neurotrophic factor in the lateral geniculate body of monocular form deprivation amblyopic kittens

PURPOSE

The present study compared the expression of brain-derived neurotrophic factor (BDNF) in the lateral geniculate body between form deprivation amblyopia kittens and normal kittens to examine the significance of BDNF in the lateral geniculate body in the pathogenesis of amblyopia.

METHODS

Twenty kittens were divided into control group (n = 10) and deprivation group (n = 10). A black opaque eye mask was placed to cover the right eye of the deprivation group. Pattern visual-evoked potentials (PVEPs) were detected weekly in all kittens .After the kittens in the deprivation group developed monocular amblyopia, the lateral geniculate bodies of all kittens were removed. The expression of BDNF in the lateral geniculate body of the two groups was compared by immunohistochemistry and Western blotting.

RESULTS

The latency of the P100 wave in the right eye of the deprivation group was longer than that of the left eye and that of the right eye of the control group (p < 0.05), and the amplitude decreased (p < 0.05). The number and average optical density of BDNF-positive cells in the deprivation group were lower than those in the control group (p < 0.05), and the expression of BDNF in the deprivation group was lower than that in the control group (p < 0.05).

CONCLUSIONS

The expression of BDNF in the lateral geniculate body of the amblyopic kittens decreased, and the decrease in BDNF promoted the development of amblyopia. These results demonstrate that BDNF in the lateral geniculate body plays an important role in visual development.

Muscle Injury Induces Postoperative Cognitive Dysfunction

Postoperative cognitive dysfunction (POCD) is a major complication affecting patients of any age undergoing surgery. This syndrome impacts everyday life up to months after hospital discharge, and its pathophysiology still remains unclear. Translational research focusing on POCD is based on a wide variety of rodent models, such as the murine tibial fracture, whose severity can limit mouse locomotion and proper behavioral assessment. Besides, influence of skeletal muscle injury, a lesion encountered in a wide range of surgeries, has not been explored in POCD occurrence. We propose a physical model of muscle injury in CX3CR1^GFP/+ mice (displaying green fluorescent microglial cells) to study POCD, with morphological, behavioral and molecular approaches. We highlighted: alteration of short- and long-term memory after muscle regeneration, wide microglial reactivity in the brain, including hippocampus area, 24 hours after muscle injury, and an alteration of central brain derived neurotrophic factor (BDNF) and nerve growth factor (NGF) balance, 28 days after muscle injury. Our results suggest for the first time that muscle injury can have early as well as late impacts on the brain. Our CX3CR1^GFP/+ model can also facilitate microglial investigation, more specifically their pivotal role in neuroinflammation and synaptic plasticity, in the pathophysiology of POCD.

Neuroprotective effects of brain-derived neurotrophic factor against amyloid beta 1-40-induced retinal and optic nerve damage

Brain-derived neurotrophic factor (BDNF) could be considered a potential neuroprotective therapy in amyloid beta (Aβ)-associated retinal and optic nerve degeneration. Hence, in this study we investigated the neuroprotective effect of BDNF against Aβ1-40-induced retinal and optic nerve injury. In this study, exposure to Aβ1-40 was associated with retinal and optic nerve injury. TUNEL staining showed significant reduction in the apoptotic cell count in the BDNF-treated group compared with Aβ1-40 group. H&E-stained retinal sections also showed a striking reduction in neuronal cells in the ganglion cell layer (GCL) of retinas fourteen days after Aβ1-40 exposure. By contrast, number of retinal cells was preserved in the retinas of BDNF-treated animals. After Aβ1-40 exposure, visible axonal swelling was observed in optic nerve sections. However, the BDNF-treated group showed fewer changes in optic nerve; axonal swelling was less frequent and less marked. In the present study, exposure to Aβ was associated with oxidative stress, whereas levels of retinal glutathione (GSH), superoxide dismutase (SOD) and catalase were significantly increased in BDNF-treated than in Aβ1-40-treated rats. Both visual object recognition tests using an open-field arena and a Morris water maze showed that BDNF improved rats' ability to recognise visual cues (objects with different shapes) after Aβ1-40 exposure, thus demonstrating that the visual performance of rats was relatively preserved following BDNF treatment. In conclusion, intravitreal treatment with BDNF prevents Aβ1-40-induced retinal cell apoptosis and axon loss in the optic nerve of rats by reducing retinal oxidative stress and restoring retinal BDNF levels.

Acute normobaric hypoxia does not affect the simultaneous exercise-induced increase in circulating BDNF and GDNF in young healthy men: A feasibility study

Physical exercise has a neuromodulatory effect on the central nervous system (CNS) partially by modifying expression of neuropeptides produced and secreted by neurons and glial cells, among which the best examined are brain-derived neurotrophic factor (BDNF) and glial cell line-derived neurotrophic factor (GDNF). Because both neurotrophins can cross the brain-blood barrier (BBB), their blood levels indirectly reflect their production in the CNS. Moreover, both neuropeptides are involved in modulation of dopaminergic and serotoninergic system function. Because limited information is available on the effects of exercise to volition exhaustion and acute hypoxia on CNS, BDNF and GDNF formation, the aims of the present study were to verify whether 1) acute exercise to exhaustion in addition to neurons also activates glial cells and 2) additional exposure to acute normobaric moderate hypoxia affects their function. In this feasibility study we measured blood concentrations of BDNF, GDNF, and neuropeptides considered as biomarkers of brain damage (bFGF, NGF, S100B, GFAP) in seven sedentary healthy young men who performed a graded exercise test to volitional exhaustion on a cycle ergometer under normoxic (N) and hypoxic conditions: 2,000 m (H2; FiO2 = 16.6%) and 3,000 m altitude (H3; FiO2 = 14.7%). In all conditions serum concentrations of both BDNF and GDNF increased immediately after cessation of exercise (p<0.01). There was no effect of condition or interaction (condition x time of measurement) and exercise on any of the brain damage biomarkers: bFGF, NGF, S100B, GFAP. Moreover, in N (0<0.01) and H3 (p<0.05) exercise caused elevated serum 5-HT concentration. The results suggest that a graded effort to volitional exhaustion in normoxia, as well as hypoxia, simultaneously activates both neurons and astrocytes. Considering that s100B, GFAP, bFGF, and NGF (produced mainly by astrocytes) are markers of brain damage, it can be assumed that a maximum effort in both conditions is safe for the CNS.

Retrograde axonal transport of BDNF and proNGF diminishes with age in basal forebrain cholinergic neurons

Basal forebrain cholinergic neurons (BFCNs) are critical for learning and memory and degenerate early in Alzheimer's disease (AD). BFCNs depend for their survival and function on nerve growth factor (NGF) and brain-derived neurotrophic factor (BDNF), which are retrogradely transported from BFCN targets. Age is the greatest risk factor for developing AD, yet the influence of age on BFCN axonal transport is poorly understood. To model aging, embryonic rat basal forebrain or cortical neurons were cultured in microfluidic chambers. Senescence-associated beta-galactosidase staining indicated an aging phenotype only in BFCNs cultured for 18+ days in vitro. BDNF axonal transport impairments were observed exclusivley in aged BFCNs. BFCNs displayed robust proNGF transport, which also diminished with in vitro age. The expression of NGF receptor tropomyosin-related kinase-A and BDNF receptor tropomyosin-related kinase-B also decreased significantly with in vitro age in BFCNs only. These results suggest a unique vulnerability of BFCNs to age-induced transport deficits. These deficits, coupled with the reliance of BFCNs on neurotrophin transport, may explain their vulnerability to age-related neurodegenerative disorders like AD.

Overground gait training promotes functional recovery and cortical neuroplasticity in an incomplete spinal cord injury model

AIM

Evidence suggests that task-specific gait training improves locomotor impairments in people with incomplete spinal cord injury (SCI); however, plastic changes in brain areas remain poorly understood. The aim of this study was to examine the possible effects of a task-specific overground gait training on locomotor recovery and neuroplasticity markers in the cortex, cerebellum, and lumbar spinal cord in an experimental model of incomplete-SCI.

MAIN METHODS

Using a blind, basic experimental design, 24 adult Wistar rats underwent a surgical procedure and were allocated into sham, non-trained SCI (SCI), and trained SCI (Tr-SCI) groups. On postoperative day 14, trained animals started a 4-week overground gait training program. All groups were subjected to weekly assessment of locomotor recovery of the hind limbs. On postoperative day 40, brain and lumbar spinal cord structures were dissected and processed for biochemical analysis of the synaptophysin, microtubule-associated protein 2 (MAP-2), and brain-derived neurotrophic factor (BDNF).

KEY FINDINGS

Tr-SCI group showed greater locomotor function recovery compared with non-trained SCI from the postoperative day 21 (p < 0.05). The training was able to improve the neuroplasticity markers synaptophysin, MAP-2, and BDNF expressions in motor cortex (p < 0.05), but not in the cerebellum and in the spinal cord for trained SCI group compared to non-trained.

SIGNIFICANCE

Task-specific overground gait training improves locomotor recovery in a rat model of incomplete thoracic-SCI. Furthermore, training promotes motor cortex plasticity, evidenced for increasing expression of the neuroplasticity markers that may support the functional recovery.

ProNGF and Neurodegeneration in Alzheimer's Disease

Profound and early basal forebrain cholinergic neuron (BFCN) degeneration is a hallmark of Alzheimer's disease (AD). Loss of synapses between basal forebrain and hippocampal and cortical target tissue correlates highly with the degree of dementia and is thought to be a major contributor to memory loss. BFCNs depend for their survival, connectivity and function on the neurotrophin nerve growth factor (NGF) which is retrogradely transported from its sites of synthesis in the cortex and hippocampus. The form of NGF found in human brain is proNGF. ProNGF binds to the NGF receptors TrkA and p75^NTR, but it binds more strongly to p75^NTR and more weakly to TrkA than does mature NGF. This renders proNGF more sensitive to receptor balance than mature NGF. In the healthy brain, where BFCNs express both TrkA and p75^NTR, proNGF is neurotrophic, activating TrkA-dependent signaling pathways such as MAPK and Akt-mTOR and eliciting cell survival and neurite outgrowth. However, if TrkA is lost or if p75^NTR is increased, proNGF activates p75^NTR-dependent apoptotic pathways such as JNK. This receptor sensitivity serves as a neurotrophic/apoptotic switch that eliminates BFCNs that cannot maintain TrkA/p75^NTR balance and therefore synaptic connections with their targets. TrkA is increasingly lost in mild cognitive impairment (MCI) and AD. In addition, proNGF accumulates at BFCN terminals in cortex and hippocampus, reducing the amount of trophic factor that reaches BFCN cell bodies. The loss of TrkA and accumulation of proNGF occur early in MCI and correlate with cognitive impairment. Increased levels of proNGF and reduced levels of TrkA lead to BFCN neurodegeneration and eventual p75NTR-dependent apoptosis. In addition, in AD BFCNs suffer from reduced TrkA-dependent retrograde transport which reduces neurotrophic support. Thus, BFCNs are particularly vulnerable to AD due to their dependence upon retrograde trophic support from proNGF signaling and transport.

Innovative Therapy for Alzheimer's Disease-With Focus on Biodelivery of NGF

Alzheimer’s disease (AD) is a progressive neurodegenerative disorder associated with abnormal protein modification, inflammation and memory impairment. Aggregated amyloid beta (Aβ) and phosphorylated tau proteins are medical diagnostic features. Loss of memory in AD has been associated with central cholinergic dysfunction in basal forebrain, from where the cholinergic circuitry projects to cerebral cortex and hippocampus. Various reports link AD progression with declining activity of cholinergic neurons in basal forebrain. The neurotrophic molecule, nerve growth factor (NGF), plays a major role in the maintenance of cholinergic neurons integrity and function, both during development and adulthood. Numerous studies have also shown that NGF contributes to the survival and regeneration of neurons during aging and in age-related diseases such as AD. Changes in neurotrophic signaling pathways are involved in the aging process and contribute to cholinergic and cognitive decline as observed in AD. Further, gradual dysregulation of neurotrophic factors like NGF and brain derived neurotrophic factor (BDNF) have been reported during AD development thus intensifying further research in targeting these factors as disease modifying therapies against AD. Today, there is no cure available for AD and the effects of the symptomatic treatment like cholinesterase inhibitors (ChEIs) and memantine are transient and moderate. Although many AD treatment studies are being carried out, there has not been any breakthrough and new therapies are thus highly needed. Long-term effective therapy for alleviating cognitive impairment is a major unmet need. Discussion and summarizing the new advancements of using NGF as a potential therapeutic implication in AD are important. In summary, the intent of this review is describing available experimental and clinical data related to AD therapy, priming to gain additional facts associated with the importance of NGF for AD treatment, and encapsulated cell biodelivery (ECB) as an efficient tool for NGF delivery.

Stroke Recovery in Rats after 24-Hour-Delayed Intramuscular Neurotrophin-3 Infusion

Objective

Neurotrophin‐3 (NT3) plays a key role in the development and function of locomotor circuits including descending serotonergic and corticospinal tract axons and afferents from muscle and skin. We have previously shown that gene therapy delivery of human NT3 into affected forelimb muscles improves sensorimotor recovery after stroke in adult and elderly rats. Here, to move toward the clinic, we tested the hypothesis that intramuscular infusion of NT3 protein could improve sensorimotor recovery after stroke.

Methods

Rats received unilateral ischemic stroke in sensorimotor cortex. To simulate a clinically feasible time to treatment, 24 hours later rats were randomized to receive NT3 or vehicle by infusion into affected triceps brachii for 4 weeks using implanted catheters and minipumps.

Results

Radiolabeled NT3 crossed from the bloodstream into the brain and spinal cord in rodents with or without strokes. NT3 increased the accuracy of forelimb placement during walking on a horizontal ladder and increased use of the affected arm for lateral support during rearing. NT3 also reversed sensory impairment of the affected wrist. Functional magnetic resonance imaging during stimulation of the affected wrist showed spontaneous recovery of peri‐infarct blood oxygenation level–dependent signal that NT3 did not further enhance. Rather, NT3 induced neuroplasticity of the spared corticospinal and serotonergic pathways.

Interpretation

Our results show that delayed, peripheral infusion of NT3 can improve sensorimotor function after ischemic stroke. Phase I and II clinical trials of NT3 (for constipation and neuropathy) have shown that peripheral high doses are safe and well tolerated, which paves the way for NT3 as a therapy for stroke. ANN NEUROL 2019;85:32–46.

Influencing mechanism of magnolol on expression of BDNF and Bax in rats with cerebral ischemic stroke

The impact of magnolol on cerebral ischemic stroke in rats and the molecular mechanism were explored. Sprague-Dawley rat models were studied. Cerebral indexes, hematoxylin and eosin staining, TUNEL staining assay, reverse transcription-polymerase chain reaction (RT-PCR) and western blotting were applied. The cerebral index in model group was significantly higher than that in sham operation group, and the cerebral index was obviously decreased after magnolol administration. Inflammatory cells accumulated in the brain tissue of rats in the model group. Abundant apoptotic cells were produced in the model group, which was overtly improved after rats were given magnolol. RT-PCR and western blot analysis showed that expression of mRNA and protein of brain-derived neurotrophic factor (BDNF) were distinctly decreased in model group, and increased after rats were given magnolol; while mRNA and protein expression of Bcl-2-associated X protein (Bax) were significantly raised in model group, and reduced after rats were given magnolol. The results showed that there were statistically significant differences in expression of BDNF and Bax among sham operation, model and magnolol administration groups (p<0.01). In conclusion, magnolol can increase the expression of BDNF and decrease the expression of Bax, thereby inhibiting apoptosis to protect the nerves, and magnolol can improve cerebral ischemic stroke in rats.

Brain-Derived Neurotrophic Factor (BDNF): Novel Insights into Regulation and Genetic Variation

Since its discovery, brain-derived neurotrophic factor (BDNF) has spawned a literature that now spans 35 years of research. While all neurotrophins share considerable overlap in sequence homology and their processing, BDNF has become the most widely studied neurotrophin because of its broad roles in brain homeostasis, health, and disease. Although research on BDNF has produced thousands of articles, there remain numerous long-standing questions on aspects of BDNF molecular biology and signaling. Here we provide a comprehensive review, including both a historical narrative and a forward-looking perspective on advances in the actions of BDNF within the brain. We specifically review BDNF’s gene structure, peptide composition (including domains, posttranslational modifications and putative motif sites), mechanisms of transport, signaling pathway recruitment, and other recent developments including the functional effects of genetic variation and the discovery of a new BDNF prodomain ligand. This body of knowledge illustrates a highly conserved and complex role for BDNF within the brain, that promotes the idea that the neurotrophin biology of BDNF is diverse and that any disease involvement is likely to be equally multifarious.

The histology, physiology, neurochemistry and circuitry of the substantia gelatinosa Rolandi (lamina II) in mammalian spinal cord

The substantia gelatinosa Rolandi (SGR) was first described about two centuries ago. In the following decades an enormous amount of information has permitted us to understand - at least in part - its role in the initial processing of pain and itch. Here, I will first provide a comprehensive picture of the histology, physiology, and neurochemistry of the normal SGR. Then, I will analytically discuss the SGR circuits that have been directly demonstrated or deductively envisaged in the course of the intensive research on this area of the spinal cord, with particular emphasis on the pathways connecting the primary afferent fibers and the intrinsic neurons. The perspective existence of neurochemically-defined sets of primary afferent neurons giving rise to these circuits will be also discussed, with the proposition that a cross-talk between different subsets of peptidergic fibers may be the structural and functional substrate of additional gating mechanisms in SGR. Finally, I highlight the role played by slow acting high molecular weight modulators in these gating mechanisms.

Time- and dose-related effects of amyloid beta1-40 on retina and optic nerve morphology in rats

PURPOSE

Amyloid beta (Aβ) is known to contribute to the pathophysiology of retinal neurodegenerative diseases such as glaucoma. Effects of intravitreal Aβ(1-42) on retinal and optic nerve morphology in animal models have widely been studied but not those of Aβ(1-40). Hence, we evaluated the time- and dose-related effects of intravitreal Aβ(1-40) on retinal and optic nerve morphology. Since oxidative stress and brain derived neurotrophic factor (BDNF) are associated with Aβ-induced neuronal damage, we also studied dose and time-related effects of Aβ(1-40) on retinal oxidative stress and BDNF levels.

MATERIALS AND METHODS

Five groups of rats were intravitreally administered with vehicle or Aβ(1-40) in doses of 1.0, 2.5, 5 and 10 nmol. Animals were sacrificed and eyes were enucleated at weeks 1, 2 and 4 post-injection. The retinae were subjected to morphometric analysis and TUNEL staining. Optic nerve sections were stained with toluidine blue and were graded for neurodegenerative effects. The estimation of BDNF and markers of oxidative stress in retina were done using ELISA technique.

RESULTS AND CONCLUSIONS

It was observed that intravitreal Aβ(1-40) causes significant retinal and optic nerve damage up to day 14 post-injection and there was increasing damage with increase in dose. However, on day 30 post-injection both the retinal and optic nerve morphology showed a trend towards normalization. The observations made for retinal cell apoptosis, retinal glutathione, superoxide dismutase activity and BDNF were in accordance with those of morphological changes with deterioration till day 14 and recovery by day 30 post-injection. The findings of this study may provide a guide for selection of appropriate experimental conditions for future studies.

Conditional Depletion of Hippocampal Brain-Derived Neurotrophic Factor Exacerbates Neuropathology in a Mouse Model of Alzheimer's Disease

Damage occurring to noradrenergic neurons in the locus coeruleus (LC) contributes to the evolution of neuroinflammation and neurodegeneration in a variety of conditions and diseases. One cause of LC damage may be loss of neurotrophic support from LC target regions. We tested this hypothesis by conditional unilateral knockout of brain-derived neurotrophic factor (BDNF) in adult mice. To evaluate the consequences of BDNF loss in the context of neurodegeneration, the mice harbored familial mutations for human amyloid precursor protein and presenilin-1. In these mice, BDNF depletion reduced tyrosine hydroxylase staining, a marker of noradrenergic neurons, in the rostral LC. BDNF depletion also reduced noradrenergic innervation in the hippocampus, the frontal cortex, and molecular layer of the cerebellum, assessed by staining for dopamine beta hydroxylase. BDNF depletion led to an increase in cortical amyloid plaque numbers and size but was without effect on plaque numbers in the striatum, a site with minimal innervation from the LC. Interestingly, cortical Iba1 staining for microglia was reduced by BDNF depletion and was correlated with reduced dopamine beta hydroxylase staining. These data demonstrate that reduction of BDNF levels in an LC target region can cause retrograde damage to LC neurons, leading to exacerbation of neuropathology in distinct LC target areas. Methods to reduce BDNF loss or supplement BDNF levels may be of value to reduce neurodegenerative processes normally limited by LC noradrenergic activities.

Molecular Mechanisms That Contribute to Bone Marrow Pain

Pain associated a bony pathology puts a significant burden on individuals, society, and the health-care systems worldwide. Pathology that involves the bone marrow activates sensory nerve terminal endings of peripheral bone marrow nociceptors, and is the likely trigger for pain. This review presents our current understanding of how bone marrow nociceptors are influenced by noxious stimuli presented in pathology associated with bone marrow. A number of ion channels and receptors are emerging as important modulators of the activity of peripheral bone marrow nociceptors. Nerve growth factor (NGF) sequestration has been trialed for the management of inflammatory bone pain (osteoarthritis), and there is significant evidence for interaction of NGF with bone marrow nociceptors. Activation of transient receptor potential cation channel subfamily V member 1 sensitizes bone marrow nociceptors and could contribute to increased sensitivity of patients to noxious stimuli in various bony pathologies. Acid-sensing ion channels sense changes to tissue pH in the bone marrow microenvironment and could be targeted to treat pathology that involves acidosis of the bone marrow. Piezo2 is a mechanically gated ion channel that has recently been reported to be expressed by most myelinated bone marrow nociceptors and might be a target for treatments directed against mechanically induced bone pain. These ion channels and receptors could be useful targets for the development of peripherally acting drugs to treat pain of bony origin.

Regulatory role of NGFs in neurocognitive functions

Nerve growth factors (NGFs), especially the prototype NGF and brain-derived neurotrophic factor (BDNF), have a diverse array of functions in the central nervous system through their peculiar set of receptors and intricate signaling. They are implicated not only in the development of the nervous system but also in regulation of neurocognitive functions like learning, memory, synaptic transmission, and plasticity. Evidence even suggests their role in continued neurogenesis and experience-dependent neural network remodeling in adult brain. They have also been associated extensively with brain disorders characterized by neurocognitive dysfunction. In the present article, we aimed to make an exhaustive review of literature to get a comprehensive view on the role of NGFs in neurocognitive functions in health and disease. Starting with historical perspective, distribution in adult brain, implied molecular mechanisms, and developmental basis, this article further provides a detailed account of NGFs’ role in specified neurocognitive functions. Furthermore, it discusses plausible NGF-based homeostatic and adaptation mechanisms operating in the pathogenesis of neurocognitive disorders and has presents a survey of such disorders. Finally, it elaborates on current evidence and future possibilities in therapeutic applications of NGFs with an emphasis on recent research updates in drug delivery mechanisms. Conclusive remarks of the article make a strong case for plausible role of NGFs in comprehensive regulation of the neurocognitive functions and pathogenesis of related disorders and advocate that future research should be directed to explore use of NGF-based mechanisms in the prevention of implicated diseases as well as to target these molecules pharmacologically.

Extraocular Motor System Exhibits a Higher Expression of Neurotrophins When Compared with Other Brainstem Motor Systems

Extraocular motoneurons resist degeneration in diseases such as amyotrophic lateral sclerosis. The main objective of the present work was to characterize the presence of neurotrophins in extraocular motoneurons and muscles of the adult rat. We also compared these results with those obtained from other cranial motor systems, such as facial and hypoglossal, which indeed suffer neurodegeneration. Immunocytochemical analysis was used to describe the expression of nerve growth factor, brain-derived neurotrophic factor and neurotrophin-3 in oculomotor, trochlear, abducens, facial, and hypoglossal nuclei of adult rats, and Western blots were used to describe the presence of neurotrophins in extraocular, facial (buccinator), and tongue muscles, which are innervated by the above-mentioned motoneurons. In brainstem samples, brain-derived neurotrophic factor was present both in extraocular and facial motoneuron somata, and to a lesser degree, in hypoglossal motoneurons. Neurotrophin-3 was present in extraocular motor nuclei, while facial and hypoglossal motoneurons were almost devoid of this protein. Finally, nerve growth factor was not present in the soma of any group of motoneurons, although it was present in dendrites of motoneurons located in the neuropil. Neuropil optical density levels were higher in extraocular motoneuron nuclei when compared with facial and hypoglossal nuclei. Neurotrophins could be originated in target muscles, since Western blot analyses revealed the presence of the three molecules in all sampled muscles, to a larger extent in extraocular muscles when compared with facial and tongue muscles. We suggest that the different neurotrophin availability could be related to the particular resistance of extraocular motoneurons to neurodegeneration.

CNS Gene Therapy and a Nexus of Complexity: Systems and Biology at a Crossroads

Gene therapy is a potentially promising new treatment for neurodegenerative disorders such as Alzheimer's disease (AD), which has been difficult to treat with conventional therapeutics. Viral vector-mediated somatic gene therapy is a rapidly developing methodology for providing never before achieved capability to deliver specific genes to the CNS in a highly localized and controlled manner. With the advent and refinements of this technology one focus is directed to which genes are the most appropriate to select for specific disease indications. Nerve growth factor (NGF), a potent survival factor for critical cell populations that degenerate in AD, has been chosen already for clinical gene therapy trials in human AD patients. Much knowledge about the pathophysiological underpinnings of AD is still lacking to make clear which patients may benefit from a gene therapy approach. Moreover, a detailed understanding of sustained NGF action in the normal and diseased CNS needs to be resolved before conclusions can be drawn regarding the utility of NGF gene therapy. Systematic efforts to acquire this new knowledge should compel clinically and biologically sophisticated efforts to advance gene therapy for neurodegenerative diseases.

Transplants of Neurotrophin-Producing Autologous Fibroblasts Promote Recovery of Treadmill Stepping in the Acute, Sub-Chronic, and Chronic Spinal Cat

Adult cats show limited spontaneous locomotor capabilities following spinal transection, but recover treadmill stepping with body-weight-supported training. Delivery of neurotrophic factors such as brain-derived neurotrophic factor (BDNF) and neurotrophic factor 3 (NT-3) can substitute for body-weight-supported training, and promotes a similar recovery in a shorter period of time. Autologous cell grafts would negate the need for the immunosuppressive agents currently used with most grafts, but have not shown functional benefits in incomplete spinal cord injury models and have never been tested in complete transection or chronic injury models. In this study, we explored the effects of autologous fibroblasts, prepared from the individual cats and modified to produce BDNF and NT-3, on the recovery of locomotion in acute, sub-chronic and chronic full-transection models of spinal injury. Fourteen female cats underwent complete spinal transection at T11/T12. Cats were separated into four groups: sham graft at the time of injury, and BDNF and NT-3 producing autologous fibroblasts grafted at the time of injury, 2 weeks after injury, or 6 weeks after injury. Kinematics were recorded 3 and 5 weeks after cell graft. Additional kinematic recordings were taken for some cats until 12 weeks post-graft. Eleven of 12 cats with neurotrophin-producing grafts recovered plantar weight-bearing stepping at treadmill speeds from 0.3 to 0.8 m/sec within 5 weeks of grafting, whereas control cats recovered poor quality stepping at low speeds only (≤ 0.4 m/sec). Further, kinematic measures in cats with grafts were closer to pre-transection values than those for controls, and recovery was maintained up to 12 weeks post-grafting. Our results show that not only are autologous neurotrophin-producing grafts effective at promoting recovery of locomotion, but that delayed delivery of neurotrophins does not diminish the therapeutic effect, and may improve outcome.

Differential expression of cytoskeletal regulatory factors in the adolescent prefrontal cortex: Implications for cortical development

The prevalence of depression, anxiety, schizophrenia, and drug and alcohol use disorders peaks during adolescence. Further, up to 50% of "adult" mental health disorders emerge in adolescence. During adolescence, the prefrontal cortex (PFC) undergoes dramatic structural reorganization, in which dendritic spines and synapses are refined, pruned, and stabilized. Understanding the molecular mechanisms that underlie these processes should help to identify factors that influence the development of psychiatric illness. Here we briefly discuss the anatomical connections of the medial and orbital prefrontal cortex (mPFC and OFC, respectively). We then present original findings suggesting that dendritic spines on deep-layer excitatory neurons in the mouse mPFC and OFC prune at different adolescent ages, with later pruning in the OFC. In parallel, we used Western blotting to define levels of several cytoskeletal regulatory proteins during early, mid-, and late adolescence, focusing on tropomyosin-related kinase receptor B (TrkB) and β1-integrin-containing receptors and select signaling partners. We identified regional differences in the levels of several proteins in early and midadolescence that then converged in early adulthood. We also observed age-related differences in TrkB levels, both full-length and truncated isoforms, Rho-kinase 2, and synaptophysin in both PFC subregions. Finally, we identified changes in protein levels in the dorsal and ventral hippocampus that were distinct from those in the PFC. We conclude with a general review of the manner in which TrkB- and β1-integrin-mediated signaling influences neuronal structure in the postnatal brain. Elucidating the role of cytoskeletal regulatory factors throughout adolescence may identify critical mechanisms of PFC development. © 2016 Wiley Periodicals, Inc.

The neurotrophin receptor signaling endosome: Where trafficking meets signaling

Neurons are the largest cells in the body and form subcellular compartments such as axons and dendrites. During both development and adulthood building blocks must be continually trafficked long distances to maintain the different regions of the neuron. Beyond building blocks, signaling complexes are also transported, allowing for example, axons to communicate with the soma. The critical roles of signaling via ligand-receptor complexes is perhaps best illustrated in the context of development, where they are known to regulate polarization, survival, axon outgrowth, dendrite development, and synapse formation. However, knowing 'when' and 'how much' signaling is occurring does not provide the complete story. The location of signaling has a significant impact on the functional outcomes. There are therefore complex and functionally important trafficking mechanisms in place to control the precise spatial and temporal aspects of many signal transduction events. In turn, many of these signaling events affect trafficking mechanisms, setting up an intricate connection between trafficking and signaling. In this review we will use neurotrophin receptors, specifically TrkA and TrkB, to illustrate the cell biology underlying the links between trafficking and signaling. Briefly, we will discuss the concepts of how trafficking and signaling are intimately linked for functional and diverse signaling outputs, and how the same protein can play different roles for the same receptor depending on its localization. © 2017 Wiley Periodicals, Inc. Develop Neurobiol 77: 419-437, 2017.

The Contribution of Spatial and Temporal Molecular Networks in the Induction of Long-term Memory and Its Underlying Synaptic Plasticity

The ability to form long-lasting memories is critical to survival and thus is highly conserved across the animal kingdom. By virtue of its complexity, this same ability is vulnerable to disruption by a wide variety of neuronal traumas and pathologies. To identify effective therapies with which to treat memory disorders, it is critical to have a clear understanding of the cellular and molecular mechanisms which subserve normal learning and memory. A significant challenge to achieving this level of understanding is posed by the wide range of distinct temporal and spatial profiles of molecular signaling induced by learning-related stimuli. In this review we propose that a useful framework within which to address this challenge is to view the molecular foundation of long-lasting plasticity as composed of unique spatial and temporal molecular networks that mediate signaling both within neurons (such as via kinase signaling) as well as between neurons (such as via growth factor signaling). We propose that evaluating how cells integrate and interpret these concurrent and interacting molecular networks has the potential to significantly advance our understanding of the mechanisms underlying learning and memory formation.

Prolongation of Relaxation Time in Extraocular Muscles With Brain Derived Neurotrophic Factor in Adult Rabbit

PURPOSE

We tested the hypothesis that short-term treatment with brain derived neurotrophic factor (BDNF) would alter the contractile characteristics of rabbit extraocular muscle (EOM).

METHODS

One week after injections of BDNF in adult rabbit superior rectus muscles, twitch properties were determined in treated and control muscles in vitro. Muscles were also examined for changes in mean cross-sectional areas, neuromuscular junction size, and percent of myofibers expressing specific myosin heavy chain isoforms, and sarcoendoplasmic reticulum calcium ATPases (SERCA) 1 and 2.

RESULTS

Brain derived neurotrophic factor-treated muscles had prolonged relaxation times compared with control muscles. Time to 50% relaxation, time to 100% relaxation, and maximum rate of relaxation were increased by 24%, 27%, and 25%, respectively. No significant differences were seen in time to peak force, twitch force, or maximum rate of contraction. Brain derived neurotrophic factor treatment significantly increased mean cross-sectional areas of slow twitch and tonic myofibers, with increased areas ranging from 54% to 146%. Brain derived neurotrophic factor also resulted in an increased percentage of slow twitch myofibers in the orbital layers, ranging from 54% to 77%, and slow-tonic myofibers, ranging from 44% to 62%. No significant changes were seen SERCA1 or 2 expression or in neuromuscular junction size.

CONCLUSIONS

Short-term treatment with BDNF significantly prolonged the duration and rate of relaxation time and increased expression of both slow-twitch and slow-tonic myosin-expressing myofibers without changes in neuromuscular junctions or SERCA expression. The changes induced by BDNF treatment might have potential therapeutic value in dampening/reducing uncontrolled eye oscillations in nystagmus.

Molecular examination of bone marrow stromal cells and chondroitinase ABC-assisted acellular nerve allograft for peripheral nerve regeneration

The present study aimed to evaluate the molecular mechanisms underlying combinatorial bone marrow stromal cell (BMSC) transplantation and chondroitinase ABC (Ch-ABC) therapy in a model of acellular nerve allograft (ANA) repair of the sciatic nerve gap in rats. Sprague Dawley rats (n=24) were used as nerve donors and Wistar rats (n=48) were randomly divided into the following groups: Group I, Dulbecco's modified Eagle's medium (DMEM) control group (ANA treated with DMEM only); Group II, Ch-ABC group (ANA treated with Ch-ABC only); Group III, BMSC group (ANA seeded with BMSCs only); Group IV, Ch-ABC + BMSCs group (Ch-ABC treated ANA then seeded with BMSCs). After 8 weeks, the expression of nerve growth factor, brain-derived neurotrophic factor and vascular endothelial growth factor in the regenerated tissues were detected by reverse transcription-quantitative polymerase chain reaction and immunohistochemistry. Axonal regeneration, motor neuron protection and functional recovery were examined by immunohistochemistry, horseradish peroxidase retrograde neural tracing and electrophysiological and tibialis anterior muscle recovery analyses. It was observed that combination therapy enhances the growth response of the donor nerve locally as well as distally, at the level of the spinal cord motoneuron and the target muscle organ. This phenomenon is likely due to the propagation of retrograde and anterograde transport of growth signals sourced from the graft site. Collectively, growth improvement on the donor nerve, target muscle and motoneuron ultimately contribute to efficacious axonal regeneration and functional recovery. Thorough investigation of molecular peripheral nerve injury combinatorial strategies are required for the optimization of efficacious therapy and full functional recovery following ANA.

The interaction between NGF-induced hyperalgesia and acid-provoked pain in the infrapatellar fat pad and tibialis anterior muscle of healthy volunteers

BACKGROUND

Tissue pH is lowered in inflamed tissues, and the increased proton concentration activates acid-sensing ion channels (ASICs), contributing to pain and hyperalgesia. ASICs can be upregulated by nerve growth factor (NGF). The aim of this study was to investigate two new human experimental pain models combining NGF- and acid-induced pain in a randomized, controlled, double-blind study.

METHODS

In experiment 1, volunteers (N = 16) received an injection of either NGF or isotonic saline in each infrapatellar fat pad (IFP). One day after 5 mL of phosphate-buffered acidic saline was infused into each IFP at a rate of 20 mL/h. In experiment 2, the tibialis anterior (TA) muscle of additional volunteers (N = 16) was examined, following the same procedure except that the volume and infusion rate of acid were different (10 mL, 30 mL/h). Continuous pain ratings were recorded during and after acid infusions. In addition, soreness scores on a Likert scale and pressure pain thresholds (PPTs) were assessed.

RESULTS

The PPT of the IFP was significantly decreased at the NGF injection site on day 1, but acid-provoked pain ratings and the change in PPT from pre- to postinfusion between the knees were similar. In the muscle pain model, local mechanical hyperalgesia developed 3 h after the NGF injection and a significant additional decrease in PPT was found after acid infusion compared to preinfusion.

CONCLUSIONS

NGF sensitization in the IFP was not facilitated by acid, whereas an acid-provoked enhancement of muscle hyperalgesia was found. NGF sensitization of adipose tissue responds differently to acid provocation compared to muscle tissue.

SIGNIFICANCE

Quantification of two novel pain models combining NGF and acid. Hyperalgesia developed after NGF injection in the infrapatellar fat pad, but it was not facilitated by acid provocation. Contrary, NGF-induced hyperalgesia in muscle tissue was enhanced by acid.