Reactive gliosis in traumatic brain injury: a comprehensive review

Effects of mitochondrial O-GlcNAcylation in pericytes after mechanical injury

Damage to vascular cells comprise an important part of traumatic brain injury (TBI) but the underlying pathophysiology remains to be fully elucidated. Here, we investigate the loss of O-Linked β-N-acetylglucosamine(O-GlcNAc) modification (O-GlcNAcylation) and mitochondrial disruption in vascular pericytes as a candidate mechanism. In mouse models in vivo, TBI rapidly induces vascular oxidative stress and down-regulates mitochondrial O-GlcNAcylation. In pericytes but not brain endothelial cultures in vitro, mechanical stretch injury down-regulates mitochondrial O-GlcNAcylation. This is accompanied by disruptions in mitochondrial dynamics, comprising a decrease in mitochondrial fusion and an increase in mitochondrial fission proteins. Pharmacologic rescue of endogenous mitochondrial O-GlcNAcylation with an O-GlcNAcase inhibitor Thiamet-G or addition of exogenous O-GlcNAc-enhanced extracellular mitochondria ameliorates the mitochondrial disruption in pericytes damaged by mechanical injury. Finally, in a pericyte-endothelial co-culture model, mechanical injury increased trans-cellular permeability; adding Thiamet-G or O-GlcNAc-enhanced extracellular mitochondria rescued trans-cellular permeability following mechanical injury. These proof-of-concept findings suggest that mitochondrial O-GlcNAcylation in pericytes may represent a novel therapeutic target for ameliorating oxidative stress and vascular damage after mechanical injury following TBI.

Blueprints for healing: central nervous system regeneration in zebrafish and neonatal mice

In adult mammals, including humans, neurons, and axons in the brain and spinal cord are inherently incapable of regenerating after injury. Studies of animals with innate capacity for regeneration are providing valuable insights into the mechanisms driving tissue healing. The aim of this review is to summarize recent data on regeneration mechanisms in the brain and spinal cord of zebrafish and neonatal mice. We infer that elucidating these mechanisms and understanding how and why they are lost in adult mammals will contribute to the development of strategies to promote central nervous system regeneration.

Hybrid membrane-coated Cyclosporine A nanocrystals preventing secondary brain injury via alleviating neuroinflammatory and oxidative stress

Secondary brain injury (SBI), a prevalent complication following traumatic brain injury, remains a critical clinical challenge due to the lack of effective therapeutic interventions. Mitochondrial dysfunction in injured neurons and microglia has been identified as a pivotal driver of SBI pathogenesis. Cyclosporine A (CsA) exerts neuroprotective effects by inhibiting the over opening of the mitochondrial permeability transition pore, thereby preserving mitochondrial dysfunction in both neurons and microglia. These properties render CsA a promising candidate for SBI treatment. However, CsA shows systemic distribution and insufficient central nervous system penetration. In this study, a biomimetic SBI-targeted CsA nanocrystal system (CsA-NC@M-PB) was prepared by using hybrid membranes derived from platelets and microglia. A large amount of CsA-NC@M-PB actively accumulated in the damaged brain tissue in mild SBI mice. Mechanistically, CsA-NC@M-PB effectively attenuated mitochondrial dysfunction in both neuron and microglia, and promoted microglial polarization towards M2 phenotype by suppressing the overproduction of reactive oxygen species. Meanwhile, by suppressing neuroinflammation and enhancing the integrity of the BBB, CsA-NC@M-PB protected neuron from apoptosis and improved directional learning and memory abilities of mild SBI mice. These findings collectively demonstrated that CsA-NC@M-PB was a therapeutically viable strategy for SBI management.

Adhesion-Related Pathways and Functional Polarization of Astrocytes in Traumatic Brain Injury: Insights from Single-cell RNA Sequencing

Traumatic brain injury (TBI) induces profound functional heterogeneity in astrocytes, yet the regulatory mechanisms underlying this diversity remain poorly understood. In this study, we analyzed single-cell RNA sequencing data from the cortex and hippocampus of TBI mouse models to characterize astrocyte subtypes and their functional dynamics. We identified two major reactive subtypes: A1 astrocytes, enriched in inflammatory response, synaptic regulation, and neurodegenerative disease-related pathways; and A2 astrocytes, enriched in lipid metabolism, extracellular matrix (ECM) remodeling, and phagosome formation pathways. These functional differences were consistently observed across datasets with varying injury severities. Notably, adhesion-related pathways-including gap junctions, adherens junctions, and calcium-dependent adhesion-showed significant subtype-specific expression patterns and temporal shifts. Pseudotime trajectory analysis further suggested a potential transition between A1 and A2 states, accompanied by dynamic regulation of adhesion-related genes. Our findings highlight the complex and context-dependent roles of astrocytes in TBI and propose cell adhesion as a key modulator of astrocyte functional polarization.

Cerebellar pathology in forensic and clinical neuroscience

Recent research underscores the cerebellum's growing importance in forensic science and neurology, showing its functions extend beyond motor control, especially in identifying causes of death. Critical neuropathological markers including alpha-synuclein and tau protein aggregates, cellular degeneration, inflammation, and vascular changes are vital for identifying neurodegenerative diseases, injuries, and toxic exposures. Advanced forensic methods, such as Magnetic resonance imaging (MRI), immunohistochemistry, and molecular analysis, have greatly improved the accuracy of diagnoses. Promising new therapies, including neuroprotective agents like resveratrol and transcranial magnetic stimulation (TMS), offer potential in treating cerebellar disorders. The cerebellum's vulnerability to toxins, drugs, and traumatic brain injuries (TBIs) highlights its forensic relevance. Moreover, advancements in genetic diagnostics, such as next-generation sequencing and CRISPR-Cas9, are enhancing the understanding and treatment of genetic conditions like Joubert syndrome and Dandy-Walker malformation. These findings emphasize the need for further research into cerebellar function and its broader significance in both forensic science and neurology.

SLC1A4 and Serine Homeostasis: Implications for Neurodevelopmental and Neurodegenerative Disorders

The solute carrier family 1 member 4 (SLC1A4) gene encodes a neutral amino acid transporter, also referred to as alanine-serine-cysteine transporter 1, ASCT1, that helps maintain amino acid balance in the brain and periphery. In the brain, SLC1A4 plays an important role in transporting levo (L) and dopa (D) isomers of serine. L-serine is required for many cellular processes, including protein and sphingolipid synthesis, while D-serine is a co-agonist required for normal neurotransmission through N-methyl-D-aspartate receptors. Through its roles transporting L-serine across the blood-brain barrier and regulating synaptic D-serine levels, SLC1A4 helps establish and maintain brain health across the lifespan. This review examines the role of SLC1A4 in neurodevelopment and neurodegeneration and assesses the therapeutic potential of serine supplementation to treat neurodevelopmental symptoms associated with mutations in SLC1A4, as well as schizophrenia, depression, traumatic brain injury, and Alzheimer's and Parkinson's diseases.

Glutamate uptake is transiently compromised in the perilesional cortex following controlled cortical impact

Glutamate, the primary excitatory neurotransmitter in the central nervous system (CNS), is regulated by the excitatory amino acid transporters glutamate transporter 1 (GLT-1) and glutamate aspartate transporter (GLAST). Following traumatic brain injury, extracellular glutamate levels increase, contributing to excitotoxicity, circuit dysfunction, and morbidity. Increased neuronal glutamate release and compromised astrocyte-mediated uptake contribute to elevated glutamate, but the mechanistic and spatiotemporal underpinnings of these changes are not well established. Using the controlled cortical impact model of TBI and iGluSnFR glutamate imaging, we quantified extracellular glutamate dynamics after injury. Three days postinjury, glutamate release was increased, and glutamate uptake and GLT-1 expression were reduced. Seven and 14 days postinjury, glutamate dynamics were comparable between sham and controlled cortical impact animals. Changes in peak glutamate response were unique to specific cortical layers and proximity to injury. This was likely driven by increases in glutamate release, which was spatially heterogeneous, rather than reduced uptake, which was spatially uniform. The astrocyte K+ channel, Kir4.1, regulates activity-dependent slowing of glutamate uptake. Surprisingly, Kir4.1 was unchanged after controlled cortical impact and accordingly, activity-dependent slowing of glutamate uptake was unaltered. This dynamic glutamate dysregulation after traumatic brain injury underscores a brief period in which disrupted glutamate uptake may contribute to dysfunction and highlights a potential therapeutic window to restore glutamate homeostasis.

Dysregulation of Metabolic Peptides in the Gut-Brain Axis Promotes Hyperinsulinemia, Obesity, and Neurodegeneration

Metabolic peptides can influence metabolic processes and contribute to both inflammatory and/or anti-inflammatory responses. Studies have shown that there are thousands of metabolic peptides, made up of short chains of amino acids, that the human body produces. These peptides are crucial for regulating many different processes like metabolism and cell signaling, as they bind to receptors on various cells. This review will cover the role of three specific metabolic peptides and their roles in hyperinsulinemia, diabetes, inflammation, and neurodegeneration, as well as their roles in type 3 diabetes and dementia. The metabolic peptides glucagon-like peptide 1 (GLP-1), gastric inhibitor polypeptide (GIP), and pancreatic peptide (PP) will be discussed, as dysregulation within their processes can lead to the development of various inflammatory and neurodegenerative diseases. Research has been able to closely investigate the connections between these metabolic peptides and their links to the gut-brain axis, highlighting changes made in the gut that can lead to dysfunction in processes in the brain, as well as changes made in the brain that can lead to dysregulation in the gut. The role of metabolic peptides in the development and potentially reversal of diseases such as obesity, hyperinsulinemia, and type 2 diabetes will also be discussed. Furthermore, we review the potential links between these conditions and neuroinflammation and the development of neurodegenerative diseases like dementia, specifically Parkinson's disease and Alzheimer's disease.

Retinal Inflammation and Reactive Müller Cells: Neurotrophins' Release and Neuroprotective Strategies

Millions of people worldwide suffer from retinal disorders. Retinal diseases require prompt attention to restore function or reduce progressive impairments. Genetics, epigenetics, life-styling/quality and external environmental factors may contribute to developing retinal diseases. In the physiological retina, some glial cell types sustain neuron activities by guaranteeing ion homeostasis and allowing effective interaction in synaptic transmission. Upon insults, glial cells interact with neuronal and the other non-neuronal retinal cells, at least in part counteracting the biomolecular changes that may trigger retinal complications and vision loss. Several epigenetic and oxidative stress mechanisms are quickly activated to release factors that in concert with growth, fibrogenic and angiogenic factors can influence the overall microenvironment and cell-to-cell response. Reactive Müller cells participate by secreting neurotrophic/growth/angiogenic factors, cytokines/chemokines, cytotoxic/stress molecules and neurogenic inflammation peptides. Any attempt to maintain/restore the physiological condition can be interrupted by perpetuating insults, vascular dysfunction and neurodegeneration. Herein, we critically revise the current knowledge on the cell-to-cell and cell-to-mediator interplay between Müller cells, astrocytes and microglia, with respect to pro-con modulators and neuroprotective/detrimental activities, as observed by using experimental models or analyzing ocular fluids, altogether contributing a new point of view to the field of research on precision medicine.

Endothelin-1 increases Na+-K+-2Cl- cotransporter-1 expression in cultured astrocytes and in traumatic brain injury model: An involvement of HIF1α activation

Na+-K+-2Cl- cotransporter-1 (NKCC1) is present in brain cells, including astrocytes. The expression of astrocytic NKCC1 increases in the acute phase of traumatic brain injury (TBI), which induces brain edema. Endothelin-1 (ET-1) is a factor that induces brain edema and regulates the expression of several pathology-related genes in astrocytes. In the present study, we investigated the effect of ET-1 on NKCC1 expression in astrocytes. ET-1 (100 nM)-treated cultured astrocytes showed increased NKCC1 mRNA and protein levels. The effect of ET-1 on NKCC1 expression in cultured astrocytes was reduced by BQ788 (1 μM), an ETB antagonist, but not by FR139317 (1 μM), an ETA antagonist. The involvement of ET-1 in NKCC1 expression in TBI was examined using a fluid percussion injury (FPI) mouse model that replicates the pathology of TBI with high reproducibility. Administration of BQ788 (15 nmol/day) decreased FPI-induced expressions of NKCC1 mRNA and protein, accompanied with a reduction of astrocytic activation. FPI-induced brain edema was attenuated by BQ788 and NKCC1 inhibitors (azosemide and bumetanide). ET-1-treated cultured astrocytes showed increased mRNA and protein expression of hypoxia-inducible factor-1α (HIF1α). Immunohistochemical observations of mouse cerebrum after FPI showed co-localization of HIF1α with GFAP-positive astrocytes. Increased HIF1α expression in the TBI model was reversed by BQ788. FM19G11 (an HIF inhibitor, 1 μM) and HIF1α siRNA suppressed ET-induced increase in NKCC1 expression in cultured astrocytes. These results indicate that ET-1 increases NKCC1 expression in astrocytes through the activation of HIF1α.

Omega-3 Fatty Acids and Traumatic Injury in the Adult and Immature Brain

Background/Objectives: Traumatic brain injury (TBI) can lead to substantial disability and health loss. Despite its importance and impact worldwide, no treatment options are currently available to help protect or preserve brain structure and function following injury. In this review, we discuss the potential benefits of using omega-3 polyunsaturated fatty acids (O3 PUFAs) as therapeutic agents in the context of TBI in the paediatric and adult populations. Methods: Preclinical and clinical research reports investigating the effects of O3 PUFA-based interventions on the consequences of TBI were retrieved and reviewed, and the evidence presented and discussed. Results: A range of animal models of TBI, types of injury, and O3 PUFA dosing regimens and administration protocols have been used in different strategies to investigate the effects of O3 PUFAs in TBI. Most evidence comes from preclinical studies, with limited clinical data available thus far. Overall, research indicates that high O3 PUFA levels help lessen the harmful effects of TBI by reducing tissue damage and cell loss, decreasing associated neuroinflammation and the immune response, which in turn moderates the severity of the associated neurological dysfunction. Conclusions: Data from the studies reviewed here indicate that O3 PUFAs could substantially alleviate the impact of traumatic injuries in the central nervous system, protect structure and help restore function in both the immature and adult brains.

Agathisflavone Modulates Reactive Gliosis After Trauma and Increases the Neuroblast Population at the Subventricular Zone

BACKGROUND

Reactive astrogliosis and microgliosis are coordinated responses to CNS insults and are pathological hallmarks of traumatic brain injury (TBI). In these conditions, persistent reactive gliosis can impede tissue repopulation and limit neurogenesis. Thus, modulating this phenomenon has been increasingly recognized as potential therapeutic approach.

METHODS

In this study, we investigated the potential of the flavonoid agathisflavone to modulate astroglial and microglial injury responses and promote neurogenesis in the subventricular zone (SVZ) neurogenic niche. Agathisflavone, or the vehicle in controls, was administered directly into the lateral ventricles in postnatal day (P)8-10 mice by twice daily intracerebroventricular (ICV) injections for 3 days, and brains were examined at P11.

RESULTS

In the controls, ICV injection caused glial reactivity along the needle track, characterised immunohistochemically by increased astrocyte expression of glial fibrillary protein (GFAP) and the number of Iba-1+ microglia at the lesion site. Treatment with agathisflavone decreased GFAP expression, reduced both astrocyte reactivity and the number of Iba-1+ microglia at the core of the lesion site and the penumbra, and induced a 2-fold increase on the ratio of anti-inflammatory CD206+ to pro-inflammatory CD16/32+ microglia. Notably, agathisflavone increased the population of neuroblasts (GFAP+ type B cells) in all SVZ microdomains by up to double, without significantly increasing the number of neuronal progenitors (DCX+).

CONCLUSIONS

Although future studies should investigate the underlying molecular mechanisms driving agathisflavone effects on microglial polarization and neurogenesis at different timepoints, these data indicate that agathisflavone could be a potential adjuvant treatment for TBI or central nervous system disorders that have reactive gliosis as a common feature.

ALS-like pathology diminishes swelling of spinal astrocytes in the SOD1 animal model

Astrocytes are crucial for the functioning of the nervous system as they maintain the ion homeostasis via volume regulation. Pathological states, such as amyotrophic lateral sclerosis (ALS), affect astrocytes and might even cause a loss of such functions. In this study, we examined astrocytic swelling/volume recovery in both the brain and spinal cord of the SOD1 animal model to determine the level of their impairment caused by the ALS-like pathology. Astrocyte volume changes were measured in acute brain or spinal cord slices during and after exposure to hyperkalemia. We then compared the results with alterations of extracellular space (ECS) diffusion parameters, morphological changes, expression of the Kir4.1 channel and the potassium concentration measured in the cerebrospinal fluid, to further disclose the link between potassium and astrocytes in the ALS-like pathology. Morphological analysis revealed astrogliosis in both the motor cortex and the ventral horns of the SOD1 spinal cord. The activated morphology of SOD1 spinal astrocytes was associated with the results from volume measurements, which showed decreased swelling of these cells during hyperkalemia. Furthermore, we observed lower shrinkage of ECS in the SOD1 spinal ventral horns. Immunohistochemical analysis then confirmed decreased expression of the Kir4.1 channel in the SOD1 spinal cord, which corresponded with the diminished volume regulation. Despite astrogliosis, cortical astrocytes in SOD1 mice did not show alterations in swelling nor changes in Kir4.1 expression, and we did not identify significant changes in ECS parameters. Moreover, the potassium level in the cerebrospinal fluid did not deviate from the physiological concentration. The results we obtained thus suggest that ALS-like pathology causes impaired potassium uptake associated with Kir4.1 downregulation in the spinal astrocytes, but based on our data from the cortex, the functional impairment seems to be independent of the morphological state.

HISTOLOGICAL COMPARISON OF REPEATED MILD WEIGHT DROP AND LATERAL FLUID PERCUSSION INJURY MODELS OF TRAUMATIC BRAIN INJURY IN FEMALE AND MALE RATS

ABSTRACT

In preclinical traumatic brain injury (TBI) research, the animal model should be selected based on the research question and outcome measures of interest. Direct side-by-side comparisons of different injury models are essential for informing such decisions. Here, we used immunohistochemistry to compare the outcomes from two common models of TBI, lateral fluid percussion (LFP) and repeated mild weight drop (rmWD) in adult female and male Wistar rats. Specifically, we measured the effects of LFP and rmWD on markers of cerebrovascular and tight junction disruption, neuroinflammation, mature neurons, and perineuronal nets in the cortical site of injury, cortex adjacent to injury, dentate gyrus, and the CA 2/3 area of the hippocampus. Animals were randomized into the LFP or rmWD group. On day 1, the LFP group received a craniotomy, and on day 4, injury (or sham procedure; randomly assigned). The rmWD animals underwent either injury or isoflurane only (randomly assigned) on each of those 4 days. Seven days after injury, brains were harvested for analysis. Overall, our observations revealed that the most significant disruptions were evident in response to LFP, followed by craniotomy only, whereas rmWD animals showed the least residual changes compared with isoflurane-only controls, supporting consideration of rmWD as a mild injury. LFP led to longer-lasting disruptions, perhaps more representative of moderate TBI. We also report that craniotomy and LFP produced greater disruptions in females relative to males. These findings will assist the field in the selection of animal models based on target severity of postinjury outcomes and support the inclusion of both sexes and appropriate control groups.

A two-center prospective cohort study of serum RIP-3 as a potential biomarker in relation to severity and prognosis after severe traumatic brain injury

Receptor-interacting protein kinase-3 (RIP-3) is a key component for inducing necroptosis following acute brain injury. Purpose of this study is to unveil whether serum RIP-3 levels are related to severity and clinical outcomes after human severe traumatic brain injury (sTBI). In this two-center prospective cohort study, serum RIP-3 levels were detected in 127 healthy controls coupled with 127 sTBI patients. The prognostic indicators encompassed posttraumatic 180-day mortality, overall survival and poor prognosis (defined as extended Glasgow outcome scale scores of 1-4). The prognosis associations were verified via multivariate analysis. There was a significant incremental serum RIP-3 levels in patients with sTBI, relative to the controls. RIP-3 levels of patients were independently correlated with Rotterdam Computed Tomography (CT) scores and Glasgow coma scale (GCS) scores, as well as were independently predictive of mortality, overall survival and poor prognosis. Mortality and poor prognosis were effectively predicted by serum RIP-3 levels under the receiver operating characteristic curve. Linear relationships between RIP-3 levels and their risks were verified. Mortality and poor prognosis models of serum RIP-3 levels combined with GCS and Rotterdam CT scores displayed efficient predictive abilities. The two models were graphically represented, which were of clinical stability and value by employing the calibration and decision curves. Increased serum RIP-3 levels after sTBI are closely linked to heightened trauma severity and poor prognosis, signifying that serum RIP-3 may be an encouraging biomarker for evaluating severity and predicting clinical outcome of sTBI.

An In Vivo Model of Propionic Acid-Rich Diet-Induced Gliosis and Neuro-Inflammation in Mice (FVB/N-Tg(GFAPGFP)14Mes/J): A Potential Link to Autism Spectrum Disorder

Evidence shows that Autism Spectrum Disorder (ASD) stems from an interplay of genetic and environmental factors, which may include propionic acid (PPA), a microbial byproduct and food preservative. We previously reported that in vitro treatment of neural stem cells with PPA leads to gliosis and neuroinflammation. In this study, mice were exposed ad libitum to a PPA-rich diet for four weeks before mating. The same diet was maintained through pregnancy and administered to the offspring after weaning. The brains of the offspring were studied at 1 and 5 months postpartum. Glial fibrillary acidic protein (astrocytic marker) was significantly increased (1.53 ± 0.56-fold at 1 M and 1.63 ± 0.49-fold at 5 M) in the PPA group brains. Tubulin IIIβ (neuronal marker) was significantly decreased in the 5 M group. IL-6 and TNF-α expression were increased in the brain of the PPA group (IL-6: 2.48 ± 1.25-fold at 5 M; TNF-α: 2.84 ± 1.16-fold at 1 M and 2.64 ± 1.42-fold, at 5 M), while IL-10 was decreased. GPR41 and p-Akt were increased, while PTEN (p-Akt inhibitor) was decreased in the PPA group. The data support the role of a PPA-rich diet in glia over-proliferation and neuro-inflammation mediated by the GPR41 receptor and PTEN/Akt pathway. These findings strongly support our earlier study on the role of PPA in ASD.

Anisotropy component of DTI reveals long-term neuroinflammation following repetitive mild traumatic brain injury in rats

BACKGROUND

This study aimed to investigate the long-term effects of repetitive mild traumatic brain injury (rmTBI) with varying inter-injury intervals by measuring diffusion tensor metrics, including mean diffusivity (MD), fractional anisotropy (FA), and diffusion magnitude (L) and pure anisotropy (q).

METHODS

Eighteen rats were randomly divided into three groups: short-interval rmTBI (n = 6), long-interval rmTBI (n = 6), and sham controls (n = 6). MD, FA, L, and q values were analyzed from longitudinal diffusion tensor imaging at days 50 and 90 after rmTBI. Immunohistochemical staining against neurons, astrocytes, microglia, and myelin was performed. Analysis of variance, Pearson correlation coefficient, and simple linear regression model were used.

RESULTS

At day 50 post-rmTBI, lower cortical FA and q values were shown in the short-interval group (p ≤ 0.038). In contrast, higher FA and q values were shown for the long-interval group (p ≤ 0.039) in the corpus callosum. In the ipsilesional external capsule and internal capsule, no significant changes were found in FA, while lower L and q values were shown in the short-interval group (p ≤ 0.028) at day 90. The q values in the external capsule and internal capsule were negatively correlated with the number of microglial cells and the total number of astroglial cells (p ≤ 0.035).

CONCLUSION

Tensor scalar measurements, such as L and q values, are sensitive to exacerbated chronic injury induced by rmTBI with shorter inter-injury intervals and reflect long-term astrogliosis induced by the cumulative injury.

RELEVANCE STATEMENT

Tensor scalar measurements, including L and q values, are potential DTI metrics for detecting long-term and subtle injury following rmTBI; in particular, q values may be used for quantifying remote white matter (WM) changes following rmTBI.

KEY POINTS

The alteration of L and q values was demonstrated after chronic repetitive mild traumatic brain injury. Changing q values were observed in the impact site and remote WM. The lower q values in the remote WM were associated with astrogliosis.

Water channels in the brain and spinal cord-overview of the role of aquaporins in traumatic brain injury and traumatic spinal cord injury

Knowledge about the mechanisms underlying the fluid flow in the brain and spinal cord is essential for discovering the mechanisms implicated in the pathophysiology of central nervous system diseases. During recent years, research has highlighted the complexity of the fluid flow movement in the brain through a glymphatic system and a lymphatic network. Less is known about these pathways in the spinal cord. An important aspect of fluid flow movement through the glymphatic pathway is the role of water channels, especially aquaporin 1 and 4. This review provides an overview of the role of these aquaporins in brain and spinal cord, and give a short introduction to the fluid flow in brain and spinal cord during in the healthy brain and spinal cord as well as during traumatic brain and spinal cord injury. Finally, this review gives an overview of the current knowledge about the role of aquaporins in traumatic brain and spinal cord injury, highlighting some of the complexities and knowledge gaps in the field.

A Pilot Study on a Possible Mechanism behind Olfactory Dysfunction in Parkinson's Disease: The Association of TAAR1 Downregulation with Neuronal Loss and Inflammation along Olfactory Pathway

Parkinson's disease (PD) is characterized not only by motor symptoms but also by non-motor dysfunctions, such as olfactory impairment; the cause is not fully understood. Our study suggests that neuronal loss and inflammation in brain regions along the olfactory pathway, such as the olfactory bulb (OB) and the piriform cortex (PC), may contribute to olfactory dysfunction in PD mice, which might be related to the downregulation of the trace amine-associated receptor 1 (TAAR1) in these areas. In the striatum, although only a decrease in mRNA level, but not in protein level, of TAAR1 was detected, bioinformatic analyses substantiated its correlation with PD. Moreover, we discovered that neuronal death and inflammation in the OB and the PC in PD mice might be regulated by TAAR through the Bcl-2/caspase3 pathway. This manifested as a decrease of anti-apoptotic protein Bcl-2 and an increase of the pro-apoptotic protein cleaved caspase3, or through regulating astrocytes activity, manifested as the increase of TAAR1 in astrocytes, which might lead to the decreased clearance of glutamate and consequent neurotoxicity. In summary, we have identified a possible mechanism to elucidate the olfactory dysfunction in PD, positing neuronal damage and inflammation due to apoptosis and astrocyte activity along the olfactory pathway in conjunction with the downregulation of TAAR1.