Astrocyte-neuron interplay in maladaptive plasticity

Peripheral and central neurobiological effects of botulinum toxin A (BoNT/A) in neuropathic pain: a systematic review

ABSTRACT

Botulinum toxin (BoNT), a presynaptic inhibitor of acetylcholine (Ach) release at the neuromuscular junction (NMJ), is a successful and safe drug for the treatment of several neurological disorders. However, a wide and recent literature review has demonstrated that BoNT exerts its effects not only at the "periphery" but also within the central nervous system (CNS). Studies from animal models, in fact, have shown a retrograde transport to the CNS, thus modulating synaptic function. The increasing number of articles reporting efficacy of BoNT on chronic neuropathic pain (CNP), a complex disease of the CNS, demonstrates that the central mechanisms of BoNT are far from being completely elucidated. In this new light, BoNT might interfere with the activity of spinal, brain stem, and cortical circuitry, modulating excitability and the functional organization of CNS in healthy conditions. Botulinum toxins efficacy on CNP is the result of a wide and complex action on many and diverse mechanisms at the basis of the maladaptive plasticity, the core of the pathogenesis of CNP. This systematic review aims to discuss in detail the BoNT's mechanisms and effects on peripheral and central neuroplasticity, at the basis for the clinical efficacy in CNP syndromes.

Brain-Gut Axis: Invasive and Noninvasive Vagus Nerve Stimulation, Limitations, and Potential Therapeutic Approaches

Inflammatory bowel disease (IBD) is a chronic relapsing condition with no known etiology and is characterized by disrupted gut homeostasis, chronic inflammation, and ulcerative lesions. Although current treatments can reduce disease activity, IBD frequently recurs once treatments are discontinued, indicating that treatments are ineffective in providing long-term remission. The lack of responsiveness and reluctance of some affected persons to take medications because of potential adverse effects has enhanced the need for novel therapeutic approaches. The vagus nerve (VN) is likely important in the pathogenesis of IBD, considering the decreased activity of the parasympathetic nervous system, especially the VN, and the impaired interaction between the enteric nervous system and central nervous system in patients with IBD. Vagus nerve stimulation (VNS) has demonstrated anti-inflammatory effects in various inflammatory disorders, including IBD, by inhibiting the production of inflammatory cytokines by immune cells. It has been suggested that stimulating the vagus nerve to induce its anti-inflammatory effects may be a potential therapeutic approach for IBD. Noninvasive techniques for VNS have been developed. Considering the importance of VN function in the brain-gut axis, VNS is a promising treatment option for IBD. This review discusses the potential therapeutic advantages and drawbacks of VNS, particularly the use of noninvasive transcutaneous auricular vagus nerve stimulation.

Inhibition of astroglial hemichannels ameliorates infrasonic noise induced short-term learning and memory impairment

As a kind of environmental noise, infrasonic noise has negative effects on various human organs. To date, research has shown that infrasound impairs cognitive function, especially the ability for learning and memory. Previously, we demonstrated that impaired learning and memory induced by infrasound was closely related with glia activation; however, the underlying mechanisms remain unclear. Connexin 43 hemichannels (Cx43 HCs), which are mainly expressed in hippocampal astrocytes, are activated under pathological conditions, lending support to the hypothesis that Cx43 HCs might function in the impaired learning and memory induced by infrasound. This study revealed that that blocking hippocampal Cx43 HCs or downregulating hippocampal Cx43 expression significantly alleviated impaired learning and memory induced by infrasound. We also observed that infrasound exposure led to the abundant release of glutamate and ATP through Cx43 HCs. In addition, the abundant release of glutamate and ATP depended on proinflammatory cytokines. Our finds suggested that the enhanced release of ATP and glutamate by astroglial Cx43 HCs may be involved in the learning and memory deficits caused by infrasound exposure.

Long-Term Neuromodulatory Effects of Repetitive Transcranial Magnetic Stimulation (rTMS) on Plasmatic Matrix Metalloproteinases (MMPs) Levels and Visuospatial Abilities in Mild Cognitive Impairment (MCI)

Repetitive transcranial magnetic stimulation (rTMS) is a non-invasive neuromodulation technique that is used against cognitive impairment in mild cognitive impairment (MCI) and Alzheimer's disease (AD). However, the neurobiological mechanisms underlying the rTMS therapeutic effects are still only partially investigated. Maladaptive plasticity, glial activation, and neuroinflammation, including metalloproteases (MMPs) activation, might represent new potential targets of the neurodegenerative process and progression from MCI to AD. In this study, we aimed to evaluate the effects of bilateral rTMS over the dorsolateral prefrontal cortex (DLPFC) on plasmatic levels of MMP1, -2, -9, and -10; MMPs-related tissue inhibitors TIMP1 and TIMP2; and cognitive performances in MCI patients. Patients received high-frequency (10 Hz) rTMS (MCI-TMS, n = 9) or sham stimulation (MCI-C, n = 9) daily for four weeks, and they were monitored for six months after TMS. The plasmatic levels of MMPs and TIMPs and the cognitive and behavioral scores, based on the Repeatable Battery for the Assessment of Neuropsychological Status (RBANS), Beck Depression Inventory II, Beck Anxiety Inventory, and Apathy Evaluation Scale, were assessed at baseline (T0) and after 1 month (T1) and 6 months (T2) since rTMS. In the MCI-TMS group, at T2, plasmatic levels of MMP1, -9, and -10 were reduced and paralleled by increased plasmatic levels of TIMP1 and TIMP2 and improvement of visuospatial performances. In conclusion, our findings suggest that targeting DLPFC by rTMS might result in the long-term modulation of the MMPs/TIMPs system in MCI patients and the neurobiological mechanisms associated with MCI progression to dementia.

Glial Cell Modulation of Dendritic Spine Structure and Synaptic Function

Glia comprise a heterogeneous group of cells involved in the structure and function of the central and peripheral nervous system. Glial cells are found from invertebrates to humans with morphological specializations related to the neural circuits in which they are embedded. Glial cells modulate neuronal functions, brain wiring and myelination, and information processing. For example, astrocytes send processes to the synaptic cleft, actively participate in the metabolism of neurotransmitters, and release gliotransmitters, whose multiple effects depend on the targeting cells. Human astrocytes are larger and more complex than their mice and rats counterparts. Astrocytes and microglia participate in the development and plasticity of neural circuits by modulating dendritic spines. Spines enhance neuronal connectivity, integrate most postsynaptic excitatory potentials, and balance the strength of each input. Not all central synapses are engulfed by astrocytic processes. When that relationship occurs, a different pattern for thin and large spines reflects an activity-dependent remodeling of motile astrocytic processes around presynaptic and postsynaptic elements. Microglia are equally relevant for synaptic processing, and both glial cells modulate the switch of neuroendocrine secretion and behavioral display needed for reproduction. In this chapter, we provide an overview of the structure, function, and plasticity of glial cells and relate them to synaptic maturation and modulation, also involving neurotrophic factors. Together, neurons and glia coordinate synaptic transmission in both normal and abnormal conditions. Neglected over decades, this exciting research field can unravel the complexity of species-specific neural cytoarchitecture as well as the dynamic region-specific functional interactions between diverse neurons and glial subtypes.

Vagus Nerve Stimulation: A Personalized Therapeutic Approach for Crohn's and Other Inflammatory Bowel Diseases

Inflammatory bowel diseases, including Crohn's disease and ulcerative colitis, are incurable autoimmune diseases characterized by chronic inflammation of the gastrointestinal tract. There is increasing evidence that inappropriate interaction between the enteric nervous system and central nervous system and/or low activity of the vagus nerve, which connects the enteric and central nervous systems, could play a crucial role in their pathogenesis. Therefore, it has been suggested that appropriate neuroprosthetic stimulation of the vagus nerve could lead to the modulation of the inflammation of the gastrointestinal tract and consequent long-term control of these autoimmune diseases. In the present paper, we provide a comprehensive overview of (1) the cellular and molecular bases of the immune system, (2) the way central and enteric nervous systems interact and contribute to the immune responses, (3) the pathogenesis of the inflammatory bowel disease, and (4) the therapeutic use of vagus nerve stimulation, and in particular, the transcutaneous stimulation of the auricular branch of the vagus nerve. Then, we expose the working hypotheses for the modulation of the molecular processes that are responsible for intestinal inflammation in autoimmune diseases and the way we could develop personalized neuroprosthetic therapeutic devices and procedures in favor of the patients.

Is non-invasive brain stimulation effective for cognitive enhancement in Alzheimer's disease? An updated meta-analysis

OBJECTIVE

Alzheimer's disease dementia (AD) and its preclinical stage, mild cognitive impairment (MCI), are critical issues confronting the aging society. Non-invasive brain stimulation (NIBS) techniques have the potential to be effective tools for enhancing cognitive functioning. The main objective of our meta-analysis was to quantify and update the status of the efficacy of repetitive Transcranial Magnetic Stimulation (rTMS) and Transcranial Direct Current Stimulation (tDCS) when applied in AD and MCI.

METHODS

The systematic literature search was conducted in PubMed and Web of Science according to PRISMA statement.

RESULTS

Pooled effect sizes (Hedges' g) from 32 studies were analyzed using random effect models. We found both, rTMS and tDCS to have significant immediate cognition-enhancing effect in AD with rTMS inducing also beneficial long-term effects. We found no evidence for synergistic effect of cognitive training with NIBS.

CONCLUSIONS

In AD a clinical recommendation can be made for NEURO-AD^TM system and for high-frequency rTMS over the left dorsolateral prefrontal cortex (DLPFC) as probably effective protocols (B-level of evidence) and for anodal tDCS over the left DLPFC as a possibly effective.

SIGNIFICANCE

According to scientific literature, NIBS may be an effective method for improving cognition in AD and possibly in MCI.

The relationships between neuroglial and neuronal changes in Alzheimer's disease, and the related controversies II:

Since the original description of Alzheimer´s disease (AD), research into this condition has mainly focused on assessing the alterations to neurons associated with dementia, and those to the circuits in which they are involved. In most of the studies on human brains and in many models of AD, the glial cells accompanying these neurons undergo concomitant alterations that aggravate the course of neurodegeneration. As a result, these changes to neuroglial cells are now included in all the "pathogenic cascades" described in AD. Accordingly, astrogliosis and microgliosis, the main components of neuroinflammation, have been integrated into all the pathogenic theories of this disease, as discussed in this part of the two-part monograph that follows an accompanying article on gliopathogenesis and glioprotection. This initial reflection verified the implication of alterations to the neuroglia in AD, suggesting that these cells may also represent therapeutic targets to prevent neurodegeneration. In this second part of the monograph, we will analyze the possibilities of acting on glial cells to prevent or treat the neurodegeneration that is the hallmark of AD and other pathologies. Evidence of the potential of different pharmacological, non-pharmacological, cell and gene therapies (widely treated) to prevent or treat this disease is now forthcoming, in most cases as adjuncts to other therapies. A comprehensive AD multimodal therapy is proposed in which neuronal and neuroglial pharmacological treatments are jointly considered, as well as the use of new cell and gene therapies and non-pharmacological therapies that tend to slow down the progress of dementia.

Regional Development of Glioblastoma: The Anatomical Conundrum of Cancer Biology and Its Surgical Implication

Glioblastoma (GBM) are among the most common malignant central nervous system (CNS) cancers, they are relatively rare. This evidence suggests that the CNS microenvironment is naturally equipped to control proliferative cells, although, rarely, failure of this system can lead to cancer development. Moreover, the adult CNS is innately non-permissive to glioma cell invasion. Thus, glioma etiology remains largely unknown. In this review, we analyze the anatomical and biological basis of gliomagenesis considering neural stem cells, the spatiotemporal diversity of astrocytes, microglia, neurons and glutamate transporters, extracellular matrix and the peritumoral environment. The precise understanding of subpopulations constituting GBM, particularly astrocytes, is not limited to glioma stem cells (GSC) and could help in the understanding of tumor pathophysiology. The anatomical fingerprint is essential for non-invasive assessment of patients’ prognosis and correct surgical/radiotherapy planning.

Altered Spinal Homeostasis and Maladaptive Plasticity in GFAP Null Mice Following Peripheral Nerve Injury

The maladaptive response of the central nervous system (CNS) following nerve injury is primarily linked to the activation of glial cells (reactive gliosis) that produce an inflammatory reaction and a wide cellular morpho-structural and functional/metabolic remodeling. Glial acidic fibrillary protein (GFAP), a major protein constituent of astrocyte intermediate filaments (IFs), is the hallmark of the reactive astrocytes, has pleiotropic functions and is significantly upregulated in the spinal cord after nerve injury. Here, we investigated the specific role of GFAP in glial reaction and maladaptive spinal cord plasticity following sciatic nerve spared nerve injury (SNI) in GFAP KO and wild-type (WT) animals. We evaluated the neuropathic behavior (thermal hyperalgesia, allodynia) and the expression of glial (vimentin, Iba1) and glutamate/GABA system markers (GLAST, GLT1, EAAC1, vGLUT, vGAT, GAD) in lumbar spinal cord sections of KO/WT animals. SNI induced neuropathic behavior in both GFAP KO and WT mice, paralleled by intense microglial reaction (Iba1 expression more pronounced in KO mice), reactive astrocytosis (vimentin increase) and expression remodeling of glial/neuronal glutamate/GABA transporters. In conclusion, it is conceivable that the lack of GFAP could be detrimental to the CNS as it lacks a critical sensor for neuroinflammation and morpho-functional–metabolic rewiring after nerve injury. Understanding the maladaptive morpho-functional changes of glial cells could represent the first step for a new glial-based targeted approach for mechanisms of disease in the CNS.

Matrix metalloproteinases, purinergic signaling, and epigenetics: hubs in the spinal neuroglial network following peripheral nerve injury

Activation of glial cells (reactive gliosis) and the purinergic pathway, together with metalloproteinase (MMP)-induced remodeling of the neural extracellular matrix (nECM), drive maladaptive changes in the spinal cord following peripheral nerve injury (PNI). We evaluated the effects on spinal maladaptive plasticity through administration of oxidized ATP (oxATP), an antagonist of P2X receptors (P2XR), and/or GM6001, an inhibitor of MMPs, in rats following spared nerve injury (SNI) of the sciatic nerve. With morpho-molecular techniques, we demonstrated a reduction in spinal reactive gliosis and changes in the neuro-glial-nECM crosstalk via expression remodeling of P2XR, nerve growth factor (NGF) receptors (TrkA and p75), and histone deacetylase 2 (HDAC2) after treatments with oxATP/GM6001. Altogether, our data suggest that MMPs and purinergic inhibition have a modulatory impact on key proteins in the neuro-glial-nECM network, acting at different levels from intracellular signaling to epigenetic modifications.

Ultra-high field neuroimaging in psychosis: A narrative review

Schizophrenia and related psychoses are complex neuropsychiatric diseases representing dysconnectivity across multiple scales, through the micro (cellular), meso (brain network), manifest (behavioral), and social (interpersonal) levels. In vivo human neuroimaging, particularly at ultra-high field (UHF), offers unprecedented opportunity to examine multiscale dysconnectivity in psychosis. In this review, we provide an overview of the literature to date on UHF in psychosis, focusing on microscale findings from magnetic resonance spectroscopy (MRS), mesoscale studies on structural and functional magnetic resonance imaging (fMRI), and multiscale studies assessing multiple neuroimaging modalities and relating UHF findings to behavior. We highlight key insights and considerations from multiscale and longitudinal studies and provide recommendations for future research on UHF neuroimaging in psychosis.

Time dependent alteration of locomotor behavior in rat with acute liver failure induced cerebellar neuroinflammation and neuro-astroglial damage

Hepatic encephalopathy (HE) is a neurophysiological syndrome secondary to acute or chronic liver failure. Studies showed that HE patients exhibit a deficit in motor coordination, which may result from cerebellar functional impairment. The aim of this study is to assess the time-dependent alteration of locomotor behavior and the glial and neuronal alteration in rat with acute HE induced chemically. The study was carried out in male Sprague-Dawley rats with thioacetamide (TAA) induced acute liver failure at different stages 12 h, 24 h and 36 h. Hepatic and renal functions were assessed via various biochemical and histopathological examinations, while the cerebellum and the midbrain were examined using histology and immunohistochemistry for tyrosine hydroxylase (TH), cyclooxygenase-2 (COX-2) and glial fibrillary acidic protein (GFAP). We used as well, the open field test and the Rotarod test for assessing the locomotor activity and coordination. Our data showed a progressive loss of liver function and a progressive alteration in locomotor behavior and motor coordination in acute HE rats. In the cerebellum, we noted an increase in the degeneration of cerebellar Purkinje neurons parallel to increased COX-2 immunoreactivity together with astrocytic morphology and density changes. Likewise, in substantia nigra pars compacta, TH levels were reduced. We showed through the current study, a progressive deterioration in locomotor behavior in acute HE rats, as a result of Purkinje neurons death and a deficient dopaminergic neurotransmission, together with the morpho-functional astroglial modifications involving the oxidative stress and neuroinflammation.

Inhibition of plasminogen/plasmin system retrieves endogenous nerve growth factor and adaptive spinal synaptic plasticity following peripheral nerve injury

Dysfunctions of the neuronal-glial crosstalk and/or impaired signaling of neurotrophic factors represent key features of the maladaptive changes in the central nervous system (CNS) in neuroinflammatory as neurodegenerative disorders. Tissue plasminogen activator (tPA)/plasminogen (PA)/plasmin system has been involved in either process of maturation and degradation of nerve growth factor (NGF), highlighting multiple potential targets for new therapeutic strategies. We here investigated the role of intrathecal (i.t.) delivery of neuroserpin (NS), an endogenous inhibitor of plasminogen activators, on neuropathic behavior and maladaptive synaptic plasticity in the rat spinal cord following spared nerve injury (SNI) of the sciatic nerve. We demonstrated that SNI reduced spinal NGF expression, induced spinal reactive gliosis, altering the expression of glial and neuronal glutamate and GABA transporters, reduced glutathione (GSH) levels and is associated to neuropathic behavior. Beside the increase of NGF expression, i.t. NS administration reduced reactive gliosis, restored synaptic homeostasis, GSH levels and reduced neuropathic behavior. Our results hereby highlight the essential role of tPA/PA system in the synaptic homeostasis and mechanisms of maladaptive plasticity, sustaining the beneficial effects of NGF-based approach in neurological disorders.

The Glioblastoma Microenvironment: Morphology, Metabolism, and Molecular Signature of Glial Dynamics to Discover Metabolic Rewiring Sequence

Different functional states determine glioblastoma (GBM) heterogeneity. Brain cancer cells coexist with the glial cells in a functional syncytium based on a continuous metabolic rewiring. However, standard glioma therapies do not account for the effects of the glial cells within the tumor microenvironment. This may be a possible reason for the lack of improvements in patients with high-grade gliomas therapies. Cell metabolism and bioenergetic fitness depend on the availability of nutrients and interactions in the microenvironment. It is strictly related to the cell location in the tumor mass, proximity to blood vessels, biochemical gradients, and tumor evolution, underlying the influence of the context and the timeline in anti-tumor therapeutic approaches. Besides the cancer metabolic strategies, here we review the modifications found in the GBM-associated glia, focusing on morphological, molecular, and metabolic features. We propose to analyze the GBM metabolic rewiring processes from a systems biology perspective. We aim at defining the crosstalk between GBM and the glial cells as modules. The complex networking may be expressed by metabolic modules corresponding to the GBM growth and spreading phases. Variation in the oxidative phosphorylation (OXPHOS) rate and regulation appears to be the most important part of the metabolic and functional heterogeneity, correlating with glycolysis and response to hypoxia. Integrated metabolic modules along with molecular and morphological features could allow the identification of key factors for controlling the GBM-stroma metabolism in multi-targeted, time-dependent therapies.

Neurobiological After-Effects of Low Intensity Transcranial Electric Stimulation of the Human Nervous System: From Basic Mechanisms to Metaplasticity

Non-invasive low-intensity transcranial electrical stimulation (tES) of the brain is an evolving field that has brought remarkable attention in the past few decades for its ability to directly modulate specific brain functions. Neurobiological after-effects of tES seems to be related to changes in neuronal and synaptic excitability and plasticity, however mechanisms are still far from being elucidated. We aim to review recent results from in vitro and in vivo studies that highlight molecular and cellular mechanisms of transcranial direct (tDCS) and alternating (tACS) current stimulation. Changes in membrane potential and neural synchronization explain the ongoing and short-lasting effects of tES, while changes induced in existing proteins and new protein synthesis is required for long-lasting plastic changes (LTP/LTD). Glial cells, for decades supporting elements, are now considered constitutive part of the synapse and might contribute to the mechanisms of synaptic plasticity. This review brings into focus the neurobiological mechanisms and after-effects of tDCS and tACS from in vitro and in vivo studies, in both animals and humans, highlighting possible pathways for the development of targeted therapeutic applications.

Endoplasmic reticulum chaperone BiP/GRP78 knockdown leads to autophagy and cell death of arginine vasopressin neurons in mice

The immunoglobulin heavy chain binding protein (BiP), also referred to as 78-kDa glucose-regulated protein (GRP78), is a pivotal endoplasmic reticulum (ER) chaperone which modulates the unfolded protein response under ER stress. Our previous studies showed that BiP is expressed in arginine vasopressin (AVP) neurons under non-stress conditions and that BiP expression is upregulated in proportion to the increased AVP expression under dehydration. To clarify the role of BiP in AVP neurons, we used a viral approach in combination with shRNA interference for BiP knockdown in mouse AVP neurons. Injection of a recombinant adeno-associated virus equipped with a mouse AVP promoter and BiP shRNA cassette provided specific BiP knockdown in AVP neurons of the supraoptic (SON) and paraventricular nuclei (PVN) in mice. AVP neuron-specific BiP knockdown led to ER stress and AVP neuronal loss in the SON and PVN, resulting in increased urine volume due to lack of AVP secretion. Immunoelectron microscopy of AVP neurons revealed that autophagy was activated through the process of AVP neuronal loss, whereas no obvious features characteristic of apoptosis were observed. Pharmacological inhibition of autophagy by chloroquine exacerbated the AVP neuronal loss due to BiP knockdown, indicating a protective role of autophagy in AVP neurons under ER stress. In summary, our results demonstrate that BiP is essential for the AVP neuron system.

Roadmap for Stroke: Challenging the Role of the Neuronal Extracellular Matrix

Stroke is a major challenge in modern medicine and understanding the role of the neuronal extracellular matrix (NECM) in its pathophysiology is fundamental for promoting brain repair. Currently, stroke research is focused on the neurovascular unit (NVU). Impairment of the NVU leads to neuronal loss through post-ischemic and reperfusion injuries, as well as coagulatory and inflammatory processes. The ictal core is produced in a few minutes by the high metabolic demand of the central nervous system. Uncontrolled or prolonged inflammatory response is characterized by leukocyte infiltration of the injured site that is limited by astroglial reaction. The metabolic failure reshapes the NECM through matrix metalloproteinases (MMPs) and novel deposition of structural proteins continues within months of the acute event. These maladaptive reparative processes are responsible for the neurological clinical phenotype. In this review, we aim to provide a systems biology approach to stroke pathophysiology, relating the injury to the NVU with the pervasive metabolic failure, inflammatory response and modifications of the NECM. The available data will be used to build a protein–protein interaction (PPI) map starting with 38 proteins involved in stroke pathophysiology, taking into account the timeline of damage and the co-expression scores of their RNA patterns The application of the proposed network could lead to a more accurate design of translational experiments aiming at improving both the therapy and the rehabilitation processes.

The fifth cranial nerve in headaches

The fifth cranial nerve is the common denominator for many headaches and facial pain pathologies currently known. Projecting from the trigeminal ganglion, in a bipolar manner, it connects to the brainstem and supplies various parts of the head and face with sensory innervation. In this review, we describe the neuroanatomical structures and pathways implicated in the sensation of the trigeminal system. Furthermore, we present the current understanding of several primary headaches, painful neuropathies and their pharmacological treatments. We hope that this overview can elucidate the complex field of headache pathologies, and their link to the trigeminal nerve, to a broader field of young scientists.

Dual roles of astrocytes in plasticity and reconstruction after traumatic brain injury

Traumatic brain injury (TBI) is one of the leading causes of fatality and disability worldwide. Despite its high prevalence, effective treatment strategies for TBI are limited. Traumatic brain injury induces structural and functional alterations of astrocytes, the most abundant cell type in the brain. As a way of coping with the trauma, astrocytes respond in diverse mechanisms that result in reactive astrogliosis. Astrocytes are involved in the physiopathologic mechanisms of TBI in an extensive and sophisticated manner. Notably, astrocytes have dual roles in TBI, and some astrocyte-derived factors have double and opposite properties. Thus, the suppression or promotion of reactive astrogliosis does not have a substantial curative effect. In contrast, selective stimulation of the beneficial astrocyte-derived molecules and simultaneous attenuation of the deleterious factors based on the spatiotemporal-environment can provide a promising astrocyte-targeting therapeutic strategy. In the current review, we describe for the first time the specific dual roles of astrocytes in neuronal plasticity and reconstruction, including neurogenesis, synaptogenesis, angiogenesis, repair of the blood-brain barrier, and glial scar formation after TBI. We have also classified astrocyte-derived factors depending on their neuroprotective and neurotoxic roles to design more appropriate targeted therapies.

Gliosis and Neurodegenerative Diseases: The Role of PET and MR Imaging

Glial activation characterizes most neurodegenerative and psychiatric diseases, often anticipating clinical manifestations and macroscopical brain alterations. Although imaging techniques have improved diagnostic accuracy in many neurological conditions, often supporting diagnosis, prognosis prediction and treatment outcome, very few molecular imaging probes, specifically focused on microglial and astrocytic activation, have been translated to a clinical setting. In this context, hybrid positron emission tomography (PET)/magnetic resonance (MR) scanners represent the most advanced tool for molecular imaging, combining the functional specificity of PET radiotracers (e.g., targeting metabolism, hypoxia, and inflammation) to both high-resolution and multiparametric information derived by MR in a single imaging acquisition session. This simultaneity of findings achievable by PET/MR, if useful for reciprocal technical adjustments regarding temporal and spatial cross-modal alignment/synchronization, opens still debated issues about its clinical value in neurological patients, possibly incompliant and highly variable from a clinical point of view. While several preclinical and clinical studies have investigated the sensitivity of PET tracers to track microglial (mainly TSPO ligands) and astrocytic (mainly MAOB ligands) activation, less studies have focused on MR specificity to this topic (e.g., through the assessment of diffusion properties and T2 relaxometry), and only few exploiting the integration of simultaneous hybrid acquisition. This review aims at summarizing and critically review the current state about PET and MR imaging for glial targets, as well as the potential added value of hybrid scanners for characterizing microglial and astrocytic activation.

Neuroimaging of Narcolepsy and Primary Hypersomnias

Advances in neuroimaging open up the possibility for new powerful tools to be developed that potentially can be applied to clinical populations to improve the diagnosis of neurological disorders, including sleep disorders. At present, the diagnosis of narcolepsy and primary hypersomnias is largely limited to subjective assessments and objective measurements of behavior and sleep physiology. In this review, we focus on recent neuroimaging findings that provide insight into the neural basis of narcolepsy and the primary hypersomnias Kleine-Levin syndrome and idiopathic hypersomnia. We describe the role of neuroimaging in confirming previous genetic, neurochemical, and neurophysiological findings and highlight studies that permit a greater understanding of the symptoms of these sleep disorders. We conclude by considering some of the remaining challenges to overcome, the existing knowledge gaps, and the potential role for neuroimaging in understanding the pathogenesis and clinical features of narcolepsy and primary hypersomnias.

Neurons, Glia, Extracellular Matrix and Neurovascular Unit: A Systems Biology Approach to the Complexity of Synaptic Plasticity in Health and Disease

The synaptic cleft has been vastly investigated in the last decades, leading to a novel and fascinating model of the functional and structural modifications linked to synaptic transmission and brain processing. The classic neurocentric model encompassing the neuronal pre- and post-synaptic terminals partly explains the fine-tuned plastic modifications under both pathological and physiological circumstances. Recent experimental evidence has incontrovertibly added oligodendrocytes, astrocytes, and microglia as pivotal elements for synapse formation and remodeling (tripartite synapse) in both the developing and adult brain. Moreover, synaptic plasticity and its pathological counterpart (maladaptive plasticity) have shown a deep connection with other molecular elements of the extracellular matrix (ECM), once considered as a mere extracellular structural scaffold altogether with the cellular glue (i.e., glia). The ECM adds another level of complexity to the modern model of the synapse, particularly, for the long-term plasticity and circuit maintenance. This model, called tetrapartite synapse, can be further implemented by including the neurovascular unit (NVU) and the immune system. Although they were considered so far as tightly separated from the central nervous system (CNS) plasticity, at least in physiological conditions, recent evidence endorsed these elements as structural and paramount actors in synaptic plasticity. This scenario is, as far as speculations and evidence have shown, a consistent model for both adaptive and maladaptive plasticity. However, a comprehensive understanding of brain processes and circuitry complexity is still lacking. Here we propose that a better interpretation of the CNS complexity can be granted by a systems biology approach through the construction of predictive molecular models that enable to enlighten the regulatory logic of the complex molecular networks underlying brain function in health and disease, thus opening the way to more effective treatments.

Regional brain susceptibility to neurodegeneration: what is the role of glial cells?

The main pathological feature of the neurodegenerative diseases is represented by neuronal death that represents the final step of a cascade of adverse/hostile events. Early in the neurodegenerative process, glial cells (including astrocytes, microglial cells, and oligodendrocytes) activate and trigger an insidious neuroinflammatory reaction, metabolic decay, blood brain barrier dysfunction and energy impairment, boosting neuronal death. How these mechanisms might induce selective neuronal death in specific brain areas are far from being elucidated. The last two decades of neurobiological studies have provided evidence of the main role of glial cells in most of the processes of the central nervous system, from development to synaptogenesis, neuronal homeostasis and integration into, highly specific neuro-glial networks. In this mini-review, we moved from in vitro and in vivo models of neurodegeneration to analyze the putative role of glial cells in the early mechanisms of neurodegeneration. We report changes of transcriptional, genetic, morphological, and metabolic activity in astrocytes and microglial cells in specific brain areas before neuronal degeneration, providing evidence in experimental models of neurodegenerative disorders, including Parkinson's and Alzheimer's diseases. Understanding these mechanisms might increase the insight of these processes and pave the way for new specific glia-targeted therapeutic strategies for neurodegenerative disorders.

Selective Vulnerability of Basal Ganglia: Insights into the Mechanisms of Bilateral Striatal Necrosis

Selective neuronal death in neurodegenerative disorders represents the final step of a cascade of events, including neuroinflammation, regional-specific reactive gliosis, changes of brain-blood barrier structure and functions, metabolic failure and mitochondrial energy impairment. Bilateral striatal necrosis is usually reported in inherited mitochondrial disorders, suggesting a pathogenetic role of the energy impairment by mitochondrial dysfunction. We investigated mechanisms of the selective striatal degeneration, comparing clinical findings of a patient with an acquired bilateral striatal necrosis and experimental data of a selective basal ganglia degenerative model in rats. In a 70-year-old patient affected by severe parkinsonian syndrome triggered by persistent metabolic acidosis, brain MRI revealed bilateral cystic-lacunar necrosis of basal ganglia. Immunohistochemistry of rat brain sections after single intraperitoneal administration (60 mg/kg) of the mitochondrial toxin 3-nitropropionic acid (3-NP) revealed (i) selective bilateral striatal necrotic/cavitary lesions, (ii) degeneration of striatal medium spiny neurons, (iii) evidence of synaptic and transcriptional dysfunction, and (iv) reactive gliosis (activated microglia and astrocytes) in the striatum. Our data provide an intriguing hypothesis for the selective neuronal degeneration in the striatum, claiming that selective mitochondrial energy impairment associated to loco-regional neuroinflammation and reactive gliosis might contribute to synaptic dysfunction and excitotoxicity that ultimately lead to neuronal degeneration.

The Relationship Between Neuroimmunity and Bipolar Disorder: Mechanism and Translational Application

Neuroimmune system may be involved in the pathological process of bipolar disorder (BD), but the essential association is not fully understood. Accumulating evidence has shown that BD involves the activation of immune cells and the release of inflammatory substances in the central nerve system (CNS). Meanwhile, neuroimmune responses also interact with other hypothesis of the etiology of BD that are widely recognized, such as neurotransmitter systems, neuroendocrine systems, neurotrophic factors, and oxidative stress. Simultaneously, related genes and immune changes in peripheral blood vary with it. Overall, neuroimmunity may play an important role in the pathogenesis of BD, and the inflammatory cytokines, especially interleukin-6 and tumor necrosis factor-alpha, have potential value for the clinical diagnosis and prognosis of BD, as well as predicting the therapeutic effects of drugs. Large-scale studies are needed to extend the evidence on neuroimmunity in BD, and to examine its clinical value for applications such as early prediction and treatment.

Neuro-Immune Hemostasis: Homeostasis and Diseases in the Central Nervous System

Coagulation and the immune system interact in several physiological and pathological conditions, including tissue repair, host defense, and homeostatic maintenance. This network plays a key role in diseases of the central nervous system (CNS) by involving several cells (CNS resident cells, platelets, endothelium, and leukocytes) and molecular pathways (protease activity, complement factors, platelet granule content). Endothelial damage prompts platelet activation and the coagulation cascade as the first physiological step to support the rescue of damaged tissues, a flawed rescuing system ultimately producing neuroinflammation. Leukocytes, platelets, and endothelial cells are sensitive to the damage and indeed can release or respond to chemokines and cytokines (platelet factor 4, CXCL4, TNF, interleukins), and growth factors (including platelet-derived growth factor, vascular endothelial growth factor, and brain-derived neurotrophic factor) with platelet activation, change in capillary permeability, migration or differentiation of leukocytes. Thrombin, plasmin, activated complement factors and matrix metalloproteinase-1 (MMP-1), furthermore, activate intracellular transduction through complement or protease-activated receptors. Impairment of the neuro-immune hemostasis network induces acute or chronic CNS pathologies related to the neurovascular unit, either directly or by the systemic activation of its main steps. Neurons, glial cells (astrocytes and microglia) and the extracellular matrix play a crucial function in a “tetrapartite” synaptic model. Taking into account the neurovascular unit, in this review we thoroughly analyzed the influence of neuro-immune hemostasis on these five elements acting as a functional unit (“pentapartite” synapse) in the adaptive and maladaptive plasticity and discuss the relevance of these events in inflammatory, cerebrovascular, Alzheimer, neoplastic and psychiatric diseases. Finally, based on the solid reviewed data, we hypothesize a model of neuro-immune hemostatic network based on protein–protein interactions. In addition, we propose that, to better understand and favor the maintenance of adaptive plasticity, it would be useful to construct predictive molecular models, able to enlighten the regulating logic of the complex molecular network, which belongs to different cellular domains. A modeling approach would help to define how nodes of the network interact with basic cellular functions, such as mitochondrial metabolism, autophagy or apoptosis. It is expected that dynamic systems biology models might help to elucidate the fine structure of molecular events generated by blood coagulation and neuro-immune responses in several CNS diseases, thereby opening the way to more effective treatments.

MiR-20a Plays a Key Regulatory Role in the Repair of Spinal Cord Dorsal Column Lesion via PDZ-RhoGEF/RhoA/GAP43 Axis in Rat

Spinal cord injury (SCI) causes sensory dysfunctions such as paresthesia, dysesthesia, and chronic neuropathic pain. MiR-20a facilitates the axonal outgrowth of the cortical neurons. However, the role of miR-20a in the axonal outgrowth of primary sensory neurons and spinal cord dorsal column lesion (SDCL) is yet unknown. Therefore, the role of miR-20a post-SDCL was investigated in rat. The NF-200 immunofluorescence staining was applied to observe whether axonal outgrowth of dorsal root ganglion (DRG) neurons could be altered by miR-20a or PDZ-RhoGEF modulation in vitro. The expression of miR-20a was quantized with RT-PCR. Western blotting analyzed the expression of PDZ-RhoGEF/RhoA/GAP43 axis after miR-20a or PDZ-RhoGEF was modulated. The spinal cord sensory conduction function was assessed by somatosensory-evoked potentials and tape removal test. The results demonstrated that the expression of miR-20a decreased in a time-dependent manner post-SDCL. The regulation of miR-20a modulated the axonal growth and the expression of PDZ-RhoGEF/RhoA/GAP43 axis in vitro. The in vivo regulation of miR-20a altered the expression of miR-20a-PDZ-RhoGEF/RhoA/GAP43 axis and promoted the recovery of ascending sensory function post-SDCL. The results indicated that miR-20a/PDZ-RhoGEF/RhoA/GAP43 axis is associated with the pathophysiological process of SDCL. Thus, targeting the miR-20a/PDZ-RhoGEF /RhoA/GAP43 axis served as a novel strategy in promoting the sensory function recovery post-SCI.

The Perineuronal 'Safety' Net? Perineuronal Net Abnormalities in Neurological Disorders

Perineuronal nets (PNN) are extracellular matrix (ECM) assemblies that preferentially ensheath parvalbumin (PV) expressing interneurons. Converging evidence indicates that PV cells and PNN are impaired in a variety of neurological disorders. PNN development and maintenance is necessary for a number of processes within the CNS, including regulation of GABAergic cell function, protection of neurons from oxidative stress, and closure of developmental critical period plasticity windows. Understanding PNN functions may be essential for characterizing the mechanisms of altered cortical excitability observed in neurodegenerative and neurodevelopmental disorders. Indeed, PNN abnormalities have been observed in post-mortem brain tissues of patients with schizophrenia and Alzheimer’s disease. There is impaired development of PNNs and enhanced activity of its key regulator matrix metalloproteinase-9 (MMP-9) in Fragile X Syndrome, a common genetic cause of autism. MMP-9, a protease that cleaves ECM, is differentially regulated in a number of these disorders. Despite this, few studies have addressed the interactions between PNN expression, MMP-9 activity and neuronal excitability. In this review, we highlight the current evidence for PNN abnormalities in CNS disorders associated with altered network function and MMP-9 levels, emphasizing the need for future work targeting PNNs in pathophysiology and therapeutic treatment of neurological disorders.

Tau pathology and neurochemical changes associated with memory dysfunction in an optimised murine model of global cerebral ischaemia - A potential model for vascular dementia?

Cerebral ischemia is known to be a major cause of death and the later development of Alzheimer's disease and vascular dementia. However, ischemia induced cellular damage that initiates these diseases remain poorly understood. This is primarily due to lack of clinically relevant models that are highly reproducible. Here, we have optimised a murine model of global cerebral ischaemia with multiple markers to determine brain pathology, neurochemistry and correlated memory deficits in these animals. Cerebral ischaemia in mice was induced by bilateral common carotid artery occlusion. Following reperfusion, the mice were either fixed with 4% paraformaldehyde or decapitated under anaesthesia. Brains were processed for Western blotting or immunohistochemistry for glial (GLT1) and vesicular (VGLUT1, VGLUT2) glutamate transporters and paired helical filament (PHF1) tau. The PHF1 tau is the main component of neurofibrillary tangle, which is the pathological hallmark of Alzheimer's disease and vascular dementia. The novel object recognition behavioural assay was used to investigate the functional cognitive consequences in these mice. The results show consistent and selective neuronal and glial cell changes in the hippocampus and the cortex together with significant reductions in GLT1 (***P < 0.001), VGLUT1 (**P < 0.01) and VGLUT2 (***P < 0.001) expressions in the hippocampus in occluded mice as compared to sham-operated animals. These changes are associated with increased PHF1 (***P < 0.0001) protein and a significant impairment of performance (*p < 0.0006, N = 6/group) in the novel object recognition test. This model represents a useful tool for investigating cellular, biochemical and molecular mechanisms of global cerebral ischaemia and may be an ideal preclinical model for vascular dementia.

Neuron-glia Interaction as a Possible Pathophysiological Mechanism of Bipolar Disorder

Accumulating evidence has shown the importance of glial cells in the neurobiology of bipolar disorder. Activated microglia and inflammatory cytokines have been pointed out as potential biomarkers of bipolar disorder. Indeed, recent studies have shown that bipolar disorder involves microglial activation in the hippocampus and alterations in peripheral cytokines, suggesting a potential link between neuroinflammation and peripheral toxicity. These abnormalities may also be the biological underpinnings of outcomes related to neuroprogression, such as cognitive impairment and brain changes. Additionally, astrocytes may have a role in the progression of bipolar disorder, as these cells amplify inflammatory response and maintain glutamate homeostasis, preventing excitotoxicity. The present review aims to discuss neuron-glia interactions and their role in the pathophysiology and treatment of bipolar disorder.

Neuro-Coagulopathy: Blood Coagulation Factors in Central Nervous System Diseases

Blood coagulation factors and other proteins, with modulatory effects or modulated by the coagulation cascade have been reported to affect the pathophysiology of the central nervous system (CNS). The protease-activated receptors (PARs) pathway can be considered the central hub of this regulatory network, mainly through thrombin or activated protein C (aPC). These proteins, in fact, showed peculiar properties, being able to interfere with synaptic homeostasis other than coagulation itself. These specific functions modulate neuronal networks, acting both on resident (neurons, astrocytes, and microglia) as well as circulating immune system cells and the extracellular matrix. The pleiotropy of these effects is produced through different receptors, expressed in various cell types, in a dose- and time-dependent pattern. We reviewed how these pathways may be involved in neurodegenerative diseases (amyotrophic lateral sclerosis, Alzheimer's and Parkinson's diseases), multiple sclerosis, ischemic stroke and post-ischemic epilepsy, CNS cancer, addiction, and mental health. These data open up a new path for the potential therapeutic use of the agonist/antagonist of these proteins in the management of several central nervous system diseases.

Arachidonic acid containing phosphatidylcholine increases due to microglial activation in ipsilateral spinal dorsal horn following spared sciatic nerve injury

Peripheral nerve injury induces substantial molecular changes in the somatosensory system that leads to maladaptive plasticity and cause neuropathic pain. Understanding the molecular pathways responsible for the development of neuropathic pain is essential to the development of novel rationally designed therapeutics. Although lipids make up to half of the dry weight of the spinal cord, their relation with the development of neuropathic pain is poorly understood. We aimed to elucidate the regulation of spinal lipids in response to neuropathic peripheral nerve injury in mice by utilizing matrix-assisted laser desorption/ionization imaging mass spectrometry, which allows visualization of lipid distribution within the cord. We found that arachidonic acid (AA) containing [PC(diacyl-16:0/20:4)+K]⁺ was increased temporarily at superficial ipsilateral dorsal horn seven days after spared nerve injury (SNI). The spatiotemporal changes in lipid concentration resembled microglia activation as defined by ionized calcium binding adaptor molecule 1 (Iba1) immunohistochemistry. Suppression of microglial function through minocycline administration resulted in attenuation of hypersensitivity and reduces [PC(diacyl-16:0/20:4)+K]⁺ elevation in the spinal dorsal horn. These data suggested that AA containing [PC(diacyl-16:0/20:4)+K]⁺ is related to hypersensitivity evoked by SNI and implicate microglial cell activation in this lipid production.

Matrix Metalloproteinases, Neural Extracellular Matrix, and Central Nervous System Pathology

The functionality and stability of the central nervous system (CNS) pabulum, called neural extracellular matrix (nECM), is paramount for the maintenance of a healthy network. The loosening or the damage of the scaffold disrupts synaptic transmission with the consequent imbalance of the neurotransmitters, reactive cells invasion, astrocytosis, new matrix deposition, digestion of the previous structure and ultimately, maladaptive plasticity with the loss of neuronal viability. nECM is constantly affected by CNS disorders, particularly in chronic modifying such as neurodegenerative disease, or in acute/subacute with chronic sequelae, like cerebrovascular and inflammatory pathology. Matrix metalloproteinases (MMPs) are the main interfering agent of nECM, guiding the balance of degradation and new deposition of proteins such as proteoglycans and glycoproteins, or glycosaminoglycans, such as hyaluronic acid. Activation of these enzymes is modulated by their physiologic inhibitors, the tissue inhibitors of MMPs or via other proteases inhibitors, as well as genetic or epigenetic up- or downregulation through molecular interaction or receptor activation. The appropriate understanding of the pathways underlying nECM modifications in CNS pathology is probably one of the pivotal future directions to identify the healthy brain network and subsequently design new therapies to interfere with the progression of the CNS disease and eventually find appropriate therapies.

(Putative) sex differences in neuroimmune modulation of memory

The neuroimmune system is significantly sexually dimorphic, with sex differences evident in the number and activation states of microglia, in the activation of astrocytes, and in cytokine release and function. Neuroimmune cells and signaling are now recognized as critical for many neural functions throughout the life span, including synaptic plasticity and memory function. Here we address the question of how cytokines, astrocytes, and microglia contribute to memory, and specifically how neuroimmune modulation of memory differentially affects males and females. Understanding sex differences in both normal memory processes and dysregulation of memory in psychiatric and neurological disorders is critical for developing treatment and preventive strategies for memory disorders that are effective for both men and women. © 2016 Wiley Periodicals, Inc.

Mild traumatic brain injury-induced hippocampal gene expressions: The identification of target cellular processes for drug development

BACKGROUND

Neurological dysfunction after traumatic brain injury (TBI) poses short-term or long-lasting health issues for family members and health care providers. Presently there are no approved medicines to treat TBI. Epidemiological evidence suggests that TBI may cause neurodegenerative disease later in life. In an effort to illuminate target cellular processes for drug development, we examined the effects of a mild TBI on hippocampal gene expression in mouse.

METHODS

mTBI was induced in a closed head, weight drop-system in mice (ICR). Animals were anesthetized and subjected to mTBI (30g). Fourteen days after injury the ipsilateral hippocampus was utilized for cDNA gene array studies. mTBI animals were compared with sham-operated animals. Genes regulated by TBI were identified to define TBI-induced physiological/pathological processes. mTBI regulated genes were divided into functional groupings to provide gene ontologies. Genes were further divided to identify molecular/cellular pathways regulated by mTBI.

RESULTS

Numerous genes were regulated after a single mTBI event that mapped to many ontologies and molecular pathways related to inflammation and neurological physiology/pathology, including neurodegenerative disease.

CONCLUSIONS

These data illustrate diverse transcriptional changes in hippocampal tissues triggered by a single mild injury. The systematic analysis of individual genes that lead to the identification of functional categories, such as gene ontologies and then molecular pathways, illustrate target processes of relevance to TBI pathology. These processes may be further dissected to identify key factors that can be evaluated at the protein level to highlight possible treatments for TBI in human disease and potential biomarkers of neurodegenerative processes.

Modulation of Matrix Metalloproteinases Activity in the Ventral Horn of the Spinal Cord Re-stores Neuroglial Synaptic Homeostasis and Neurotrophic Support following Peripheral Nerve Injury

Modulation of extracellular matrix (ECM) remodeling after peripheral nerve injury (PNI) could represent a valid therapeutic strategy to prevent maladaptive synaptic plasticity in central nervous system (CNS). Inhibition of matrix metalloproteinases (MMPs) and maintaining a neurotrophic support could represent two approaches to prevent or reduce the maladaptive plastic changes in the ventral horn of spinal cord following PNI. The purpose of our study was to analyze changes in the ventral horn produced by gliopathy determined by the suffering of motor neurons following spared nerve injury (SNI) of the sciatic nerve and how the intrathecal (i.t.) administration of GM6001 (a MMPs inhibitor) or the NGF mimetic peptide BB14 modulate these events. Immunohistochemical analysis of spinal cord sections revealed that motor neuron disease following SNI was associated with increased microglial (Iba1) and astrocytic (GFAP) response in the ventral horn of the spinal cord, indicative of reactive gliosis. These changes were paralleled by decreased glial aminoacid transporters (glutamate GLT1 and glycine GlyT1), increased levels of the neuronal glutamate transporter EAAC1, and a net increase of the Glutamate/GABA ratio, as measured by HPLC analysis. These molecular changes correlated to a significant reduction of mature NGF levels in the ventral horn. Continuous i.t. infusion of both GM6001 and BB14 reduced reactive astrogliosis, recovered the expression of neuronal and glial transporters, lowering the Glutamate/GABA ratio. Inhibition of MMPs by GM6001 significantly increased mature NGF levels, but it was absolutely ineffective in modifying the reactivity of microglia cells. Therefore, MMPs inhibition, although supplies neurotrophic support to ECM components and restores neuro-glial transporters expression, differently modulates astrocytic and microglial response after PNI.

Neurological Diseases from a Systems Medicine Point of View

The difficulty to understand, diagnose, and treat neurological disorders stems from the great complexity of the central nervous system on different levels of physiological granularity. The individual components, their interactions, and dynamics involved in brain development and function can be represented as molecular, cellular, or functional networks, where diseases are perturbations of networks. These networks can become a useful research tool in investigating neurological disorders if they are properly tailored to reflect corresponding mechanisms. Here, we review approaches to construct networks specific for neurological disorders describing disease-related pathology on different scales: the molecular, cellular, and brain level. We also briefly discuss cross-scale network analysis as a necessary integrator of these scales.

Characteristic Changes of Astrocyte and Microglia in Rat Striatum Induced by 3-NP and MCAO

Our previous studies had confirmed that both 3-NP and MCAO induced the behavioral defect as well as striatal neuronal injury and loss in experimental rats. This study aimed to examine different response forms of striatal astrocyte and microglia in 3-NP and MCAO rat models. The present results showed that the immunoreaction for GFAP was extremely weak in the lesioned core of striatum, but in the transition zone of 3-NP model and the penumbra zone of MCAO model, GFAP+ cells showed strong hypertrophic and proliferative changes. Statistical analysis for the number, size and integral optical density (IOD) of GFAP+ cells showed significant differences when compared with their controls and compared between the core and the transition zone or the penumbra zone, respectively, but no differences between the 3-NP and MCAO groups. However, Iba-1+ cells showed obvious hypertrophy and proliferation in the injured striatum in the 3-NP and the MCAO models, especially in the transition zone of 3-NP model and the penumbra zone of MCAO model. These Iba-1+ cells displayed two characteristic forms as branching cells with thick processes and amoeboid cells with thin processes. Statistical analysis showed that the number, size and IOD of Iba-1+ cells were significantly increased in the cores and the transition zone of 3-NP group and the penumbra zone of MCAO group than that of the controls, and the immune response of Iba-1 was stronger in the MCAO group than in the 3-NP group. The present results suggested that characteristic responses of astrocyte and microglia in the 3-NP and the MCAO models display their different effects on the pathological process of brain injury.

Astrocytes and Microglia-Mediated Immune Response in Maladaptive Plasticity is Differently Modulated by NGF in the Ventral Horn of the Spinal Cord Following Peripheral Nerve Injury

Reactive astrocytes and activated microglia are the key players in several pathophysiologic modifications of the central nervous system. We used the spared nerve injury (SNI) of the sciatic nerve to induce glial maladaptive response in the ventral horn of lumbar spinal cord and examine its role in the remodeling of the tripartite synapse plasticity. Imaging the ventral horn revealed that SNI was associated with both an early microglial and astrocytic activation, assessed, respectively, by analysis of Iba1 and GFAP expression. Microglia, in particular, localized peculiarly surrounding the motor neurons somata. Perineuronal astrocytes, which play a key role in maintaining the homeostasis of neuronal circuitry, underwent a substantial phenotypic change following peripheral axotomy, producing reactive gliosis. The gliosis was associated with the reduction of glial aminoacid transporters (GLT1 and GlyT1) and increase of neuronal glutamate transporter EAAC1. Although the expression of GABAergic neuronal marker GAD65/67 showed no change, glutamate increase, as demonstrated by HPLC analysis, shifted the excitatory/inhibitory balance as showed by the net increase of the glutamate/GABA ratio. Moreover, endogenous NGF levels were altered in SNI animals and not restored by the intrathecal NGF administration. This treatment reverted phenotypic changes associated with reactive astrocytosis, but failed to modify microglia activation. These findings on one hand confirm the correlation between gliopathy and maladaptive plasticity of the spinal synaptic circuitry, on the other hand add new data concerning the complex peculiar behavior of different glial cells in neuronal degenerative processes, defining a special role of microglia in sustaining the inflammatory response.