Differential blood-brain barrier breakdown and leucocyte recruitment following excitotoxic lesions in juvenile and adult rats

Role of N-methyl-d-aspartate receptors in anxiety disorder with thyroid lesions

OBJECTIVE

Patients with anxiety disorder (AD) often have structural and functional abnormalities of the thyroid gland, but their specific causes remain unclear. N-methyl- d-aspartate receptors (NMDARs) play an important role in many psychosomatic diseases and tumorigenesis, but there are few reports on the role of NMDARs in AD with thyroid lesions, especially thyroid nodules (TNs).

METHODS

A cross-sectional study was conducted on patients admitted to the hospital with AD (n = 71) as the main diagnosis from April to October 2021. Meanwhile, patients with TNs with no AD (NAD-TN group, n = 20) and healthy subjects (HS group, n = 37) with matched age, sex, and education were randomly collected as controls. Patients with AD were sub-grouped into the AD with TNs (AD-TN group, n = 41) and the AD with no TNs (AD-NTN group, n = 30). The thyroid ultrasound reports, Hamilton Anxiety Scale (HAMA) scores, and the expression of NMDARs and their subunits (NR1, NR2A, and NR2B) and hypothalamic-pituitary-thyroid (HPT) axis-related hormones were analyzed in all subjects. Some patients with TNs underwent surgery and postoperative pathological examination.

RESULTS

Patients with AD showed a lower level of free triiodothyronine (FT3) and higher levels of thyrotropin-releasing hormone (TRH) and NMDARs and their subunits compared to the healthy controls. The expression of the NR2A subunit was higher in the AD-TN group than that in other three groups (AD-NTN, NAD-TN, and HS groups, F = 13.650, p < 0.001). Regression analysis showed that the level of NMDARs was positively correlated with the HAMA scores (B = 1.622, p = 0.029) and the maximum diameter of TNs (B = 3.836, p = 0.005). Immunohistochemical results showed that the NR2A subunit was widely expressed in multinodular goiter (MNG) and papillary thyroid carcinoma (PTC) tissues, while the expression of the NR2B subunit was lower in PTC adjacent and MNG tissues and almost absent in PTC tissues.

CONCLUSION

In a sample of mostly women hospitalized with generalized anxiety disorder (GAD) or panic disorder, abnormal expression of NMDARs is closely related to AD with thyroid lesions, NMDAR subunits may have various activities and exert diverse effects in TNs, and the NR2A subunit may be an important regulator in AD with TNs.

Tryptophan, kynurenine pathway, and diabetic ketoacidosis in type 1 diabetes

Diabetic ketoacidosis (DKA) is a serious complication of complete insulin deficiency and insulin resistance in Type 1 diabetes (T1D). This results in the body producing high levels of serum ketones in an attempt to compensate for the insulin deficiency and decreased glucose utilization. DKA's metabolic and immunologic dysregulation results in gradual increase of systemic and cerebral oxidative stress, along with low grade systemic and cerebral inflammation and the development of pretreatment subclinical BE. During treatment the early progression of oxidative stress and inflammation is hypothesized to advance the possibility of occurrence of crisis of clinical brain edema (BE), which is the most important cause of morbidity and mortality in pediatric DKA. Longitudinal neurocognitive studies after DKA treatment show progressive and latent deficits of cognition and emphasize the need for more effective DKA treatment of this long-standing conundrum of clinical BE, in the presence of systemic osmotic dehydration, metabolic acidosis and immune dysregulation. Candidate biomarkers of several systemic and neuroinflammatory pathways prior to treatment also progress during treatment, such as the neurotoxic and neuroprotective molecules in the well-recognized tryptophan (TRP)/kynurenine pathway (KP) that have not been investigated in DKA. We used LC-MS/MS targeted mass spectrometry analysis to determine the presence and initiation of the TRP/KP at three time points: A) 6-12 hours after initiation of treatment; B) 2 weeks; and C) 3 months following DKA treatment to determine if they might be involved in the pathogenesis of the acute vasogenic complication of DKA/BE. The Trp/KP metabolites TRP, KYN, quinolinic acid (QA), xanthurnenic acid (XA), and picolinic acid (PA) followed a similar pattern of lower levels in early treatment, with subsequent increases. Time point A compared to Time points B and C were similar to the pattern of sRAGE, lactate and pyruvic acid. The serotonin/melatonin metabolites also followed a similar pattern of lower quantities at the early stages of treatment compared to 3 months after treatment. In addition, glutamate, n-acetylglutamate, glutamine, and taurine were all lower at early treatment compared to 3 months, while the ketones 3-hydroxybutaric acid and acetoacetate were significantly higher in the early treatment compared to 3 months. The two major fat metabolites, L-carnitine and acetyl-L-carnitine (ALC) changed inversely, with ALC significantly decreasing at 2 weeks and 3 months compared to the early stages of treatment. Both anthranilic acid (AA) and 3-OH-anthranilic acid (3OH-AA) had overall higher levels in the early stages of treatment (A) compared to Time points (B and C). Interestingly, the levels of AA and 3OH-AA early in treatment were higher in Caucasian females compared to African American females. There were also differences in the metabolite levels of QA and kynurenic acid (KA) between genders and between races that may be important for further development of custom targeted treatments. We hypothesize that the TRP/KP, along with the other inflammatory pathways, is an active participant in the metabolic and immunologic pathogenesis of DKA's acute and chronic insults.

Cerebrospinal Fluid Pleocytosis Not Attributable to Status Epilepticus in First 24 Hours

BACKGROUND

Status epilepticus (SE) has traditionally been thought to cause cerebrospinal fluid (CSF) pleocytosis. However, attributing CSF pleocytosis solely to SE without addressing the underlying etiology may lead to poor outcomes. Leukocyte recruitment to CSF has been shown to peak around 24 hours after prolonged seizures in animal studies, suggesting that CSF pleocytosis within the first 24 hours of SE onset may be due to underlying causes. The goal of this study is to assess if SE is associated with CSF pleocytosis, independent of other causes within the first 24 hours of onset.

METHODS

We completed a historical cohort study of adult patients with SE admitted to the intensive care unit of Vancouver General Hospital between March 2010 and May 2019.

RESULTS

Of the 441 patients admitted with SE during the study period, 107 met our inclusion criteria leading to 111 lumbar punctures (LPs), with 4 patients receiving two LPs. CSF pleocytosis was seen in 12 of 72 patients who underwent an LP within the first 24 hours of SE onset. In all 12 patients, a secondary etiology for the pleocytosis was observed aside from SE. Of the six CSF samples collected after 24 hours of onset that demonstrated pleocytosis, four had no cause for pleocytosis other than SE.

CONCLUSIONS

In all 12 patients with CSF pleocytosis in the first 24 hours of onset of SE, an underlying etiology was identified. Therefore, any pleocytosis noticed within the first 24 hours of onset of refractory SE should not be attributed solely to SE.

Evaluating the safety profile of focused ultrasound and microbubble-mediated treatments to increase blood-brain barrier permeability

INTRODUCTION

Treatment of several diseases of the brain are complicated by the presence of the skull and the blood-brain barrier (BBB). Focused ultrasound (FUS) and microbubble (MB)-mediated BBB treatment is a minimally invasive method to transiently increase the permeability of blood vessels in targeted brain areas. It can be used as a general delivery system to increase the concentration of therapeutic agents in the brain parenchyma.

AREAS COVERED

Over the past two decades, the safety of using FUS+MBs to deliver agents across the BBB has been interrogated through various methods of imaging, histology, biochemical assays, and behavior analyses. Here we provide an overview of the factors that affect the safety profile of these treatments, describe methods by which FUS+MB treatments are controlled, and discuss data that have informed the assessment of treatment risks.

EXPERT OPINION

There remains a need to assess the risks associated with clinically relevant treatment strategies, specifically repeated FUS+MB treatments, with and without therapeutic agent delivery. Additionally, efforts to develop metrics by which FUS+MB treatments can be easily compared across studies would facilitate a more rapid consensus on the risks associated with this intervention.

Astrocyte Activation and the Calcineurin/NFAT Pathway in Cerebrovascular Disease

Calcineurin (CN) is a Ca2+/calmodulin-dependent protein phosphatase with high abundance in nervous tissue. Though enriched in neurons, CN can become strongly induced in subsets of activated astrocytes under different pathological conditions where it interacts extensively with the nuclear factor of activated T cells (NFATs). Recent work has shown that regions of small vessel damage are associated with the upregulation of a proteolized, highly active form of CN in nearby astrocytes, suggesting a link between the CN/NFAT pathway and chronic cerebrovascular disease. In this Mini Review article, we discuss CN/NFAT signaling properties in the context of vascular disease and use previous cell type-specific intervention studies in Alzheimer's disease and traumatic brain injury models as a framework to understand how astrocytic CN/NFATs may couple vascular pathology to neurodegeneration and cognitive loss.

Markers of immune-mediated inflammation in the brains of young adults and adolescents with type 1 diabetes and fatal diabetic ketoacidosis. Is there a difference?

Due to the limited data on diabetic ketoacidosis and brain edema (DKA/BE) in children/adolescents and the lack of recent data on adults with type 1 diabetes (T1D), we addressed the question of whether neuroinflammation was present in the fatal DKA of adults. We performed immunohistochemistry (IHC) studies on the brains of two young adults with T1D and fatal DKA and compared them with two teenagers with poorly controlled diabetes and fatal DKA. C5b-9, the membrane attack complex (MAC) had significantly greater deposits in the grey and white matter of the teenagers than the young adults (p=0.03). CD59, a MAC assembly inhibitory protein was absent, possibly suppressed by the hyperglycemia in the teenagers but was expressed in the young adults despite comparable average levels of hyperglycemia. The receptor for advanced glycation end products (RAGE) had an average expression in the young adults significantly greater than in the teenagers (p=0.02). The autophagy marker Light Chain 3 (LC3) A/B was the predominant form of programmed cell death (PCD) in the teenage brains. The young adults had high expressions of both LC3A/B and TUNEL, an apoptotic cell marker for DNA fragmentation. BE was present in the newly diagnosed young adult with hyperglycemic hyperosmolar DKA and also in the two teenagers. Our data indicate that significant differences in neuroinflammatory components, initiated by the dysregulation of DKA and interrelated metabolic and immunologic milieu, are likely present in the brains of fatal DKA of teenagers when compared with young adults.

Migration of bone marrow progenitor cells in the adult brain of rats and rabbits

Neurogenesis takes place in the adult mammalian brain in three areas: Subgranular zone of the dentate gyrus (DG); subventricular zone of the lateral ventricle; olfactory bulb. Different molecular markers can be used to characterize the cells involved in adult neurogenesis. It has been recently suggested that a population of bone marrow (BM) progenitor cells may migrate to the brain and differentiate into neuronal lineage. To explore this hypothesis, we injected recombinant SV40-derived vectors into the BM and followed the potential migration of the transduced cells. Long-term BM-directed gene transfer using recombinant SV40-derived vectors leads to expression of the genes delivered to the BM firstly in circulating cells, then after several months in mature neurons and microglial cells, and thus without central nervous system (CNS) lesion. Most of transgene-expressing cells expressed NeuN, a marker of mature neurons. Thus, BM-derived cells may function as progenitors of CNS cells in adult animals. The mechanism by which the cells from the BM come to be neurons remains to be determined. Although the observed gradual increase in transgene-expressing neurons over 16 mo suggests that the pathway involved differentiation of BM-resident cells into neurons, cell fusion as the principal route cannot be totally ruled out. Additional studies using similar viral vectors showed that BM-derived progenitor cells migrating in the CNS express markers of neuronal precursors or immature neurons. Transgene-positive cells were found in the subgranular zone of the DG of the hippocampus 16 mo after intramarrow injection of the vector. In addition to cells expressing markers of mature neurons, transgene-positive cells were also positive for nestin and doublecortin, molecules expressed by developing neuronal cells. These cells were actively proliferating, as shown by short term BrdU incorporation studies. Inducing seizures by using kainic acid increased the number of BM progenitor cells transduced by SV40 vectors migrating to the hippocampus, and these cells were seen at earlier time points in the DG. We show that the cell membrane chemokine receptor, CCR5, and its ligands, enhance CNS inflammation and seizure activity in a model of neuronal excitotoxicity. SV40-based gene delivery of RNAi targeting CCR5 to the BM results in downregulating CCR5 in circulating cells, suggesting that CCR5 plays an important role in regulating traffic of BM-derived cells into the CNS, both in the basal state and in response to injury. Furthermore, reduction in CCR5 expression in circulating cells provides profound neuroprotection from excitotoxic neuronal injury, reduces neuroinflammation, and increases neuronal regeneration following this type of insult. These results suggest that BM-derived, transgene-expressing, cells can migrate to the brain and that they become neurons, at least in part, by differentiating into neuron precursors and subsequently developing into mature neurons.

Western diets induce blood-brain barrier leakage and alter spatial strategies in rats

Western diet (WD) intake induces obesity and metabolic dysfunction. The present study examined the effects of WD on hippocampal-dependent cognitive functioning and blood-brain barrier (BBB) permeability as a function of exposure duration, obesity phenotype, and peripheral markers of energy regulation. The use of hippocampal-dependent "place" or hippocampal-independent "response" strategies in a Y maze was assessed in male rats following 10, 40, and 90 days of WD exposure in diet-induced obese (DIO) rats, in diet resistant (DR) rats that are relatively insensitive to the obesogenic properties of WD, and in chow-fed controls. Insulin, glucose, and BBB permeability throughout several loci in the hippocampus, striatum, and cerebellum were evaluated in relation to duration of WD exposure, obesity phenotype, and type of strategy used. DIO rats had increased body weight and adiposity throughout the study, and elevated 10-day glucose and 90-day insulin levels. Throughout the study, chow-fed and DR rats reliably relied on a place strategy. DIO rats, in contrast, favored a response strategy at the 10- and 90-day time points. BBB leakage was observed in the dorsal striatum and multiple subregions of the hippocampus of DIO, but not DR or chow-fed rats. Increased ventral hippocampal BBB permeability and blood glucose levels were associated with reduced place strategy use. These data indicate that WD-induced BBB leakage is dependent on duration of diet exposure as well as obesity phenotype, and implicates BBB leakage and impaired glucoregulation in behavioral strategy and cognitive performance.

Astroglia-Microglia Cross Talk during Neurodegeneration in the Rat Hippocampus

Brain injury triggers a progressive inflammatory response supported by a dynamic astroglia-microglia interplay. We investigated the progressive chronic features of the astroglia-microglia cross talk in the perspective of neuronal effects in a rat model of hippocampal excitotoxic injury. N-Methyl-D-aspartate (NMDA) injection triggered a process characterized within 38 days by atrophy, neuronal loss, and fast astroglia-mediated S100B increase. Microglia reaction varied with the lesion progression. It presented a peak of tumor necrosis factor-α (TNF-α) secretion at one day after the lesion, and a transient YM1 secretion within the first three days. Microglial glucocorticoid receptor expression increased up to day 5, before returning progressively to sham values. To further investigate the astroglia role in the microglia reaction, we performed concomitant transient astroglia ablation with L-α-aminoadipate and NMDA-induced lesion. We observed a striking maintenance of neuronal death associated with enhanced microglial reaction and proliferation, increased YM1 concentration, and decreased TNF-α secretion and glucocorticoid receptor expression. S100B reactivity only increased after astroglia recovery. Our results argue for an initial neuroprotective microglial reaction, with a direct astroglial control of the microglial cytotoxic response. We propose the recovery of the astroglia-microglia cross talk as a tissue priority conducted to ensure a proper cellular coordination that retails brain damage.

The systemic response to CNS injury

Inflammation within the brain or spinal cord has the capacity to damage neurons and is known to contribute to long-term disability in a spectrum of central nervous system (CNS) pathologies. However, there is a more profound increase in the recruitment of potentially damaging populations of leukocytes to the spinal cord than to the brain after equivalent injuries. Increased levels of inflammatory cytokines and chemokines in the spinal cord underpin this dissimilarity after injury, which also appears to be very sensitive to processes that operate within organs distant from the primary injury site such as the liver, lung and spleen. Indeed, CNS injury per se can generate profound changes in gene expression and the cellularity of these organs, which, as a consequence, gives rise to secondary organ damage. Our understanding of the local inflammatory processes that can damage neurons is becoming clearer, but our understanding of how the peripheral immune system coordinates the response to CNS injury and how any concomitant infections or injury might impact on the outcome of CNS injury is not so well developed. It is clear that the orientation of the response to peripheral challenges, be it a pro- or anti-inflammatory effect, appears to be dependent on the nature and timing of events. Here, the importance of the inter-relationship between inflammation in the CNS and the consequent inflammatory response in peripheral tissues is highlighted.

Nanoparticles for brain drug delivery

The central nervous system, one of the most delicate microenvironments of the body, is protected by the blood-brain barrier (BBB) regulating its homeostasis. BBB is a highly complex structure that tightly regulates the movement of ions of a limited number of small molecules and of an even more restricted number of macromolecules from the blood to the brain, protecting it from injuries and diseases. However, the BBB also significantly precludes the delivery of drugs to the brain, thus, preventing the therapy of a number of neurological disorders. As a consequence, several strategies are currently being sought after to enhance the delivery of drugs across the BBB. Within this review, the recently born strategy of brain drug delivery based on the use of nanoparticles, multifunctional drug delivery systems with size in the order of one-billionth of meters, is described. The review also includes a brief description of the structural and physiological features of the barrier and of the most utilized nanoparticles for medical use. Finally, the potential neurotoxicity of nanoparticles is discussed, and future technological approaches are described. The strong efforts to allow the translation from preclinical to concrete clinical applications are worth the economic investments.

Mast cell activation and neutrophil recruitment promotes early and robust inflammation in the meninges in EAE

The meninges are often considered inert tissues that house the CSF and provide protection for the brain and spinal cord. Yet emerging data demonstrates that they are also active sites of immune responses. Furthermore, the blood-CSF barrier surrounding meningeal blood vessels, together with the blood-brain barrier (BBB), is postulated to serve as a gateway for the pathological infiltration of immune cells into the CNS in multiple sclerosis (MS). Our previous studies using mast cell-deficient (Kit(W/Wv)) mice demonstrated that mast cells resident in the dura mater and pia mater exacerbate experimental autoimmune encephalomyelitis (EAE), a rodent model of MS, by facilitating CNS inflammatory cell influx. Here we examined the underlying mechanisms that mediate these effects. We demonstrate that there are dramatic alterations in immune associated gene expression in the meninges in pre-clinical disease, including those associated with mast cell and neutrophil function. Meningeal mast cells are activated within 24 h of disease induction, but do not directly compromise CNS vascular integrity. Rather, through production of TNF, mast cells elicit an early influx of neutrophils, cells known to alter vascular permeability, into the meninges. These data add to the growing evidence that inflammation in the meninges precedes CNS immune cell infiltration and establish that mast cells are among the earliest participants in these disease-initiating events. We hypothesize that mast cell-dependent neutrophil recruitment and activation in the meninges promotes early breakdown of the local BBB and CSF-blood barrier allowing initial immune cell access to the CNS.

Paclitaxel-induced neuropathic pain is age dependent and devolves on glial response

BACKGROUND

Paclitaxel is an antimitotic antitumour drug highly effective against a broad range of cancers considered refractory to conventional chemotherapy. One of the main serious side effects of paclitaxel treatment is the induction of peripheral neuropathic pain that often diminishes the patient's quality of life. In this study, we evaluated the severity of the neuropathy induced by paclitaxel and the inflammatory reaction in the dorsal horn of the spinal cord in young, adult and aged male CD1 mice.

METHOD

Hyperalgesia to noxious thermal stimulus and allodynia to non-noxious mechanical stimulus were evaluated using the plantar test and the von Frey filament model, respectively. Spinal cord microglia and astrocytes expression was assessed using Iba1 and glial fibrillary acidic protein immunofluorescence staining, respectively.

RESULTS

All groups of mice showed a higher nociceptive reaction to thermal noxious (hyperalgesia) and mechanical non-noxious (allodynia) stimuli after paclitaxel treatment. However, these signs of neuropathy were enhanced in young mice followed by aged animals. Additionally, paclitaxel evoked a marked microglial and astrocytic response in the spinal cord of young and aged mice, whereas this enhanced reactivity was less important in adult mice. Indeed, the most severe glial activation observed in juvenile animals correlated well with major signs of neuropathy in this group of age.

CONCLUSION

Our results demonstrate that paclitaxel-induced neuropathy in mice is an age-dependent phenomenon whose severity devolves on glial response.

Copaiba oil-resin treatment is neuroprotective and reduces neutrophil recruitment and microglia activation after motor cortex excitotoxic injury

The oil-resin of Copaifera reticulata Ducke is used in the Brazilian folk medicine as an anti-inflammatory and healing agent. However, there are no investigations on the possible anti-inflammatory and neuroprotective roles of copaiba oil-resin (COR) after neural disorders. We have investigated the anti-inflammatory and neuroprotective effects of COR following an acute damage to the motor cortex of adult rats. Animals were injected with the neurotoxin N-Methyl-D-Aspartate (NMDA) (n = 10) and treated with a single dose of COR (400 mg/kg, i.p.) soon after surgery (Group 1) or with two daily doses (200 mg/kg, i.p.) during 3 days (Group 2) alter injury. Control animals were treated with vehicle only. COR treatment induced tissue preservation and decreased the recruitment of neutrophils and microglial activation in the injury site compared to vehicle animals. The results suggest that COR treatment induces neuroprotection by modulating inflammatory response following an acute damage to the central nervous system.

Spatiotemporal differences in vascular permeability after ischaemic brain damage

To study spatiotemporal differences in vascular permeability, we histologically analysed tracer extravasation, neovessels and reactive astrocytes in a mouse ischaemic brain damage model. On day 1 after damage induction, the extravasation was not associated with the distribution of neovessels or reactive astrocytes. On day 7, the extravasation was limited within the infarct region in which neovessels, but not reactive astrocytes, were observed. However, the extravasation was not observed at peri-infarct region in which both neovessels and reactive astrocytes were observed, suggesting that neovessels had high permeability and reactive astrocytes prevented the extravasation from neovessels. Furthermore, the extravasation was denser in the regions near the surface than in those further in the infarct region, suggesting a spatial heterogeneity in neovascular permeability.

Immunohistological markers for proliferative events, gliogenesis, and neurogenesis within the adult hippocampus

Biologists long believed that, once development is completed, no new neurons are produced in the forebrain. However, as is now firmly established, new neurons can be produced at least in two specific forebrain areas: the subventricular zone (SVZ) and the dentate gyrus (DG) of the hippocampal formation. Neurogenesis within the adult DG occurs constitutively throughout postnatal life, and the rate of neurogenesis within the DG can be altered under various physiological and pathophysiological conditions. The process of adult neurogenesis within the DG is a multi-step process (proliferation, differentiation, migration, targeting, and synaptic integration) that ends with the formation of a post-mitotic functionally integrated new neuron. Various markers are expressed during specific stages of adult neurogenesis. The availability of such markers allows the time-course and fate of newly born cells to be followed within the DG in a detailed and precise fashion. Several of the available markers (e.g., PCNA, Ki-67, PH3, MCM2) are markers for proliferative events, whereas others are more specific for early phases of neurogenesis and gliogenesis within the adult DG (e.g., nestin, GFAP, Sox2, Pax6). In addition, markers are available allowing events to be distinguished that are related to later steps of gliogenesis (e.g., vimentin, BLBP, S100beta) or neurogenesis (e.g., NeuroD, PSA-NCAM, DCX).

Kynurenines and intestinal neurotransmission: the role of N-methyl-D-aspartate receptors

Gastrointestinal neuroprotection involves the net effect of many mechanisms which protect the enteral nervous system and its cells from death, dysfunction or degeneration. Neuroprotection is also a therapeutic strategy, aimed at slowing or halting the progression of primary neuronal loss following acute or chronic diseases. The neuroprotective properties of a compound clearly have implications for an understanding of the mechanism of dysfunctions and for therapeutic approaches in a number of gastrointestinal diseases.This paper focused on the roles of glutamate and N-methyl-D-aspartate (NMDA) receptors in the intrinsic neuronal control of gastrointestinal motility; the consequences of inflammation on gastrointestinal motility changes; and the involvement of tryptophan metabolites (especially kynurenic acid) in the regulatory function of the enteral nervous system and the modulation of the inflammatory response. Common features in the mechanisms of action, illustrative evidence from animal models, and experimental neuroprotective therapies making use of the currently available possibilities are also discussed.Overall, the evidence suggests that gastrointestinal neuroprotection against inflammation and glutamate-induced neurotoxicity may be mediated synergistically through the blockade of NMDA receptors and the inhibition of neuronal nitric oxide synthase activity and xanthine oxidoreductase-dependent superoxide production. These components are likewise significant factors in the pathomechanism of gastrointestinal inflammatory diseases and inflammation-linked motility alterations. Inhibition of the enteric NMDA receptors by kynurenic acid or its analogues may provide a novel option via which to influence intestinal hypermotility and inflammatory processes simultaneously.

Sensorimotor behavioral tests for use in a juvenile rat model of traumatic brain injury: assessment of sex differences

Modeling juvenile traumatic brain injury (TBI) in rodents presents several unique challenges compared to adult TBI, one of which is selecting appropriate sensorimotor behavioral tasks that enable the assessment of the extent of injury and recovery over time in developing animals. To address this challenge, we performed a comparison of common sensorimotor tests in Long-Evans rats of various sizes and developmental stages (postnatal days 16-45, 35-190 g). Tests were compared and selected for their developmental appropriateness, scalability for growth, pre-training requirements, and throughput capability. Sex differences in response to TBI were also assessed. Grid walk, automated gait analysis, rotarod, beam walk, spontaneous forelimb elevation test, and measurement of motor activity using the force-plate actometer were evaluated. Grid walk, gait analysis, and rotarod failed to meet one or more of the evaluation criteria. Beam walk, spontaneous forelimb elevation test, and measurement of motor activity using the force-plate actometer satisfied all criteria and were capable of detecting motor abnormalities in rats subjected to controlled cortical impact on postnatal day 17. No sex differences were detected in the acute effects of TBI or functional recovery during the 28 days after injury using these tests. This demonstrates the utility of these tests for the evaluation of sensorimotor function in studies using rat models of pediatric TBI, and suggests that pre-pubertal males and females respond similarly to TBI with respect to sensorimotor outcomes.

Role of CCR5 and its ligands in the control of vascular inflammation and leukocyte recruitment required for acute excitotoxic seizure induction and neural damage

Chemokines may play a role in leukocyte migration across the blood-brain barrier (BBB) during neuroinflammation and other neuropathological processes, such as epilepsy. We investigated the role of the chemokine receptor CCR5 in seizures. We used a rat model based on intraperitoneal kainic acid (KA) administration. Four months before KA injection, adult rats were given femoral intramarrow inoculations of SV (RNAiR5-RevM10.AU1), which carries an interfering RNA (RNAi) against CCR5, plus a marker epitope (AU1), or its monofunctional RNAi-carrying homologue, SV(RNAiR5). This treatment lowered expression of CCR5 in circulating cells. In control rats, seizures induced elevated expression of CCR5 ligands MIP-1α and RANTES in the microvasculature, increased BBB leakage and CCR5(+) cells, as well as neuronal loss, inflammation, and gliosis in the hippocampi. Animals given either the bifunctional or the monofunctional vector were largely protected from KA-induced seizures, neuroinflammation, BBB damage, and neuron loss. Brain CCR5 mRNA was reduced. Rats receiving RNAiR5-bearing vectors showed far greater repair responses: increased neuronal proliferation, and decreased production of MIP-1α and RANTES. Controls received unrelated SV(BUGT) vectors. Decrease in CCR5 in circulating cells strongly protected from excitotoxin-induced seizures, BBB leakage, CNS injury, and inflammation, and facilitated neurogenic repair.

Intersection between metabolic dysfunction, high fat diet consumption, and brain aging

Deleterious neurochemical, structural, and behavioral alterations are a seemingly unavoidable aspect of brain aging. However, the basis for these alterations, as well as the basis for the tremendous variability in regards to the degree to which these aspects are altered in aging individuals, remains to be elucidated. An increasing number of individuals regularly consume a diet high in fat, with high-fat diet consumption known to be sufficient to promote metabolic dysfunction, although the links between high-fat diet consumption and aging are only now beginning to be elucidated. In this review we discuss the potential role for age-related metabolic disturbances serving as an important basis for deleterious perturbations in the aging brain. These data not only have important implications for understanding the basis of brain aging, but also may be important to the development of therapeutic interventions which promote successful brain aging.

Roles of neural stem cells and adult neurogenesis in adolescent alcohol use disorders

This review discusses the contributions of a newly considered form of plasticity, the ongoing production of new neurons from neural stem cells, or adult neurogenesis, within the context of neuropathologies that occur with excessive alcohol intake in the adolescents. Neural stem cells and adult neurogenesis are now thought to contribute to the structural integrity of the hippocampus, a limbic system region involved in learning, memory, behavioral control, and mood. In adolescents with alcohol use disorders (AUDs), the hippocampus appears to be particularly vulnerable to the neurodegenerative effects of alcohol, but the role of neural stem cells and adult neurogenesis in alcoholic neuropathology has only recently been considered. This review encompasses a brief overview of neural stem cells and the processes involved in adult neurogenesis, how neural stem cells are affected by alcohol, and possible differences in the neurogenic niche between adults and adolescents. Specifically, what is known about developmental differences in adult neurogenesis between the adult and adolescent is gleaned from the literature, as well as how alcohol affects this process differently among the age groups. Finally, this review suggests differences that may exist in the neurogenic niche between adults and adolescents and how these differences may contribute to the susceptibility of the adolescent hippocampus to damage. However, many more studies are needed to discern whether these developmental differences contribute to the vulnerability of the adolescent to developing an AUD.

Evaluation of N-benzyl-N-[11C]methyl-2- (7-methyl-8-oxo-2-phenyl-7,8-dihydro-9H-purin-9-yl)acetamide ([11C]DAC) as a novel translocator protein (18 kDa) radioligand in kainic acid-lesioned rat

The aim of this study was to evaluate N-benzyl-N-[11C]methyl-2-(7-methyl-8-oxo-2-phenyl-7,8-dihydro-9H-purin-9-yl)acetamide ([11C]DAC) as a new translocator protein (18 kDa) [TSPO, formerly known as the peripheral-type benzodiazepine receptor (PBR)] positron emission tomography (PET) ligand in normal mice and unilateral kainic acid (KA)-lesioned rats. DAC is a derivative of AC-5216, which is a potent and selective PET ligand for the clinical investigation of TSPO. The binding affinity and selectivity of DAC for TSPO were similar to those of AC-5216, and DAC was less lipophilic than AC-5216. The distribution pattern of [11C]DAC was in agreement with TSPO distribution in rodents. No radioactive metabolite of [11C]DAC was found in the mouse brain, although it was metabolized rapidly in mouse plasma. Using small-animal PET, we examined the in vivo binding of [11C]DAC for TSPO in KA-lesioned rats. [11C]DAC and [11C]AC-5216 exhibited similar brain uptake in the lesioned and nonlesioned striatum, respectively. The binding of [11C]DAC to TSPO was increased significantly in the lesioned striatum, and [(11)C]DAC showed good contrast between the lesioned and nonlesioned striatum (the maximum ratio was about threefold). In displacement experiments, the uptake of [11C]DAC in the lesioned striatum was eventually blocked using an excess of either unlabeled DAC or PK11195 injected. [11C]DAC had high in vivo specific binding to TSPO in the injured rat brain. Therefore, [11C]DAC is a useful PET ligand for TSPO imaging, and its specific binding to TSPO is suitable as a new biomarker for brain injury.

Chronic hypoperfusion increases claudin-3 immunoreactivity in rat brain

Chronic hypoperfusion-induced changes in blood-brain barrier (BBB) tight junction components have not been well studied. In the present study, we investigated the temporal profiles of claudin-3 (a BBB tight junction element) and myleoperoxidase (MPO, a marker of neutrophil infiltration) in the cortical and thalamic regions of rat brain subjected to chronic cerebral hypoperfusion. Chronic cerebral hypoperfusion was induced by an occlusion of two common carotid arteries and the immunoreactivity of claudin-3 or MPO was determined at 1, 2, 3, or 6 weeks after the occlusion. A typical pattern of BBB breakdown was observed from 2 weeks of the occlusion in cortical and thalamic regions based on Evans Blue leakage. Claudin-3 immunoreactivity was increased only in cortical regions after 2 weeks of occlusion. However, after 3 weeks of occlusion, marked increases in claudin-3 immunoreactivity were observed in both cortical and thalamic regions (P<0.05), which persisted for at least 6 weeks after the occlusion despite a slight reduction. In contrast, MPO immunoreactivity was increased only in the thalamic regions after 2 weeks of occlusion. But the pattern of MPO immunoreactivity at 3 and 6 weeks after the occlusion was same as claudin-3. At these time points, MPO immunoreactivity was significantly increased in both cortical and thalamic regions (P<0.05). These results show that chronic cerebral hypoperfusion increases the immunoreactivity of claudin-3 and neutrophil infiltration in cortical and thalamic regions of the brain, and demonstrate changes in BBB tight junction status during chronic cerebral hypoperfusion.

Acute astrocyte activation in brain detected by MRI: new insights into T(1) hypointensity

Increases in the T(1) of brain tissue, which give rise to dark or hypointense areas on T(1)-weighted images using magnetic resonance imaging (MRI), are common to a number of neuropathologies including multiple sclerosis (MS) and ischaemia. However, the biologic significance of T(1) increases remains unclear. Using a multiparametric MRI approach and well-defined experimental models, we have experimentally induced increases in tissue T(1) to determine the underlying cellular basis of such changes. We have shown that a rapid acute increase in T(1) relaxation in the brain occurs in experimental models of both low-flow ischaemia induced by intrastriatal injection of endothelin-1 (ET-1), and excitotoxicity induced by intrastriatal injection of N-methyl-D-aspartate (NMDA). However, there appears to be no consistent correlation between increases in T(1) relaxation and changes in other MRI parameters (apparent diffusion coefficient, T(2) relaxation, or magnetisation transfer ratio of tissue water). Immunohistochemically, one common morphologic feature shared by the ET-1 and NMDA models is acute astrocyte activation, which was detectable within 2 h of intracerebral ET-1 injection. Pretreatment with an inhibitor of astrocyte activation, arundic acid, significantly reduced the spatial extent of the T(1) signal change induced by intrastriatal ET-1 injection. These findings suggest that an increase in T(1) relaxation may identify the acute development of reactive astrocytes within a central nervous system lesion. Early changes in T(1) may, therefore, provide insight into acute and reversible injury processes in neurologic patients, such as those observed before contrast enhancement in MS.

Solutes, but not cells, drain from the brain parenchyma along basement membranes of capillaries and arteries: significance for cerebral amyloid angiopathy and neuroimmunology

Elimination of interstitial fluid and solutes plays a role in homeostasis in the brain, but the pathways are unclear. Previous work suggests that interstitial fluid drains along the walls of arteries.

AIMS

to define the pathways within the walls of capillaries and arteries for drainage of fluid and solutes out of the brain.

METHODS

Fluorescent soluble tracers, dextran (3 kDa) and ovalbumin (40 kDa), and particulate fluospheres (0.02 microm and 1.0 microm in diameter) were injected into the corpus striatum of mice. Brains were examined from 5 min to 7 days by immunocytochemistry and confocal microscopy.

RESULTS

soluble tracers initially spread diffusely through brain parenchyma and then drain out of the brain along basement membranes of capillaries and arteries. Some tracer is takenf up by vascular smooth muscle cells and by perivascular macrophages. No perivascular drainage was observed when dextran was injected into mouse brains following cardiac arrest. Fluospheres expand perivascular spaces between vessel walls and surrounding brain, are ingested by perivascular macrophages but do not appear to leave the brain even following an inflammatory challenge with lipopolysaccharide or kainate.

CONCLUSIONS

capillary and artery basement membranes act as 'lymphatics of the brain' for drainage of fluid and solutes; such drainage appears to require continued cardiac output as it ceases following cardiac arrest. This drainage pathway does not permit migration of cells from brain parenchyma to the periphery. Amyloid-beta is deposited in basement membrane drainage pathways in cerebral amyloid angiopathy, and may impede elimination of amyloid-beta and interstitial fluid from the brain in Alzheimer's disease. Soluble antigens, but not cells, drain from the brain by perivascular pathways. This atypical pattern of drainage may contribute to partial immune privilege of the brain and play a role in neuroimmunological diseases such as multiple sclerosis.

Diffuse axonal damage, myelin impairment, astrocytosis and inflammatory response following microinjections of NMDA into the rat striatum

White matter damage and inflammatory response are important secondary outcomes after acute neural disorders. Nevertheless, a few studies addressed the temporal outcomes of these pathological events using non-traumatic models of acute brain injury. In the present study, we describe acute inflammatory response and white matter neuropathology between 1 and 7 days after acute excitotoxic striatal damage. Twenty micrometer sections were stained by hematoxylin and eosin technique for gross histopathological analysis and immunolabed for neutrophils (anti-mbs-1), activated macrophages/microglia (anti-ed1), astrocytes (anti-gfap), damaged axons (anti-betaapp) and myelin basic protein (MBP). Recruitment peak of neutrophils and macrophages occurred at 1 and 7 days post-nmda injection, respectively. Diffuse damaged axons (beta-app + end-bulbs) were apparent at 7 days, concomitant with progressive myelin impairment and astrocytosis. Further studies using electron microscopy and blockers of inflammatory response and glutamatergic receptors should be performed to confirm and address the mechanisms of white matter damage following an excitotoxic lesion.

Characterization of monocyte chemoattractant protein-1 expression following a kainate model of status epilepticus

Brain injury due to seizure induces a robust inflammatory response that involves multiple factors. Although the expression of chemokines has been identified as a part of this response, there are remaining questions about their relative contribution to seizure pathogenesis. To address this, we report the expression profile of the chemokine, monocyte chemoattractant protein-1 (MCP-1, CCL2), during kainate-induced seizure in the rat hippocampus. Furthermore, we compare MCP-1 expression to the temporal profile of blood-brain barrier (BBB) permeability and immune cell recruitment at the injury site, since both of these events have been linked to MCP-1. We find that BBB permeability increased prior to upregulation of MCP-1, while MCP-1 upregulation and immune cell recruitment occurred concurrently, 7-13 h after opening of the BBB. Our findings support the following conclusions: (1) BBB opening to large proteins does not require MCP-1 upregulation; (2) Leukocyte immigration is not sufficient to induce BBB opening to large proteins; (3) MCP-1 upregulation likely mediates recruitment of macrophages/microglia and granulocytes during seizure injury, thus warranting further investigation of this chemokine.

Differential patterns of inflammatory response, axonal damage and myelin impairment following excitotoxic or ischemic damage to the trigeminal spinal nucleus of adult rats

Inflammatory response, axonal damage and demyelination are important components of the pathophysiology of acute neurodegenerative diseases. We have investigated the outcome of these pathological events following an excitotoxic or an ischemic damage to the spinal nucleus of adult rats at 1 and 7 days postinjury. Microinjections of 80 nmol of NMDA or 40 pmol of endothelin-1 into the rat spinal nucleus induced differential histopathological events. NMDA injection induced intense tissue loss in the gray matter (GM) without significant tissue loss in the white matter (WM). There was a mild inflammatory response, with recruitment of a few neutrophils and macrophages. Axonal damage was present in the GM following NMDA injection, with negligible axonal damage in the WM. Myelin impairment was apparent at 7 days. Microinjections of endothelin-1 into the same region induced lesser tissue loss than NMDA injections, concomitant with an intense inflammatory response characterized by recruitment of macrophages, but not of neutrophils. There were more axonal damage and early myelin impairment after endothelin-1 injection. These results were confirmed by quantitative analysis. Microcysts were present in the WM of the trigeminothalamic tract at 7 days following injection of endothelin-1. These results show that an ischemic damage to the spinal nucleus affects both GM and WM with more bystander inflammation, axonal damage and myelin impairment, while excitotoxic damage induces effects more restricted to the GM. These pathological events may occur following acute damage to the human brain stem and can be an important contributing factor to the underlying functional deficits.

Immunohistological markers for staging neurogenesis in adult hippocampus

Neurogenesis in the adult dentate gyrus (DG) of the hippocampus occurs constitutively throughout postnatal life, and the rate of neurogenesis within the DG can be altered under various physiological and pathophysiological conditions. Adult neurogenesis includes the process in which the division of a precursor cell takes place and the multi-step process (proliferation, differentiation, migration, targeting, and synaptic integration) that ends with the formation of a postmitotic functionally integrated new neuron. During specific time-frames of adult neurogenesis, various markers are expressed that correlate with the differentiation steps along the pathway from early progenitor cells to newly generated postmitotic neurons within the DG. Markers that are currently widely used for the investigation of adult hippocampal neurogenesis are: glial fibrillary acidic protein, nestin, Pax6, NeuroD, PSA-NCAM, doublecortin, TUC-4, Tuj-1, and calretinin. The discovery and development of specific markers that allow the time-course and fate of neurons to be followed during adult neurogenesis in a detailed and precise fashion are not only helpful for gaining further insights into the genesis of new neurons in the hippocampus, but also might be applicable to the development of strategies for therapeutic interventions.

Loss of the atypical inflammatory response in juvenile and aged rats

Epidemiological evidence indicates that the severity of many human neuropathologies is often age-related, and this also appears true in rodent models of human disease. In this study, we examined the inflammatory response within the brain to the archetypal pro-inflammatory cytokines interleukin-1beta (IL-1beta) or tumour necrosis factor-alpha (TNF-alpha). We assessed how the cerebral vasculature changes with age and whether any structural alterations are associated with altered cytokine sensitivities. Six hours after equivalent microinjections of IL-1beta or TNF-alpha, 3-week-old juvenile and 18-month-old aged rats displayed increased leucocyte recruitment, blood-brain barrier (BBB) breakdown, and a loss of specificity in the populations of leucocytes recruited when compared with the restricted profile observed in 2-month-old young adult rat brain. The expression of the tight junction protein claudin-1 was absent in those vessels where neutrophils were being actively recruited. To determine whether changes in the structure of the BBB might be responsible for the increased susceptibility observed at either end of the age spectrum, we compared the number of claudin-1 positive vessels in the unchallenged brain to the total number of vessels. Virtually all vessels in the young adult brain express claudin-1, but a significant proportion of vessels are claudin-1 negative in the juvenile rat brain. In the aged rat brain, the overall number of vessels is markedly reduced, but the majority of these still appear to be claudin-1 positive. The pattern of claudin-1 expression together with the change in vessel density indicates that the properties of the BBB change with age, and, despite similarities, the underlying cause of the heightened inflammatory response in the juvenile and in the aged brain is likely to differ. Indeed, the spatial characteristics of the cytokine-induced BBB breakdown are different at either end of the age spectrum. These studies identify two periods within the lifespan of a rat where susceptibility to pro-inflammatory mediators is dramatically increased.

Enhanced hippocampal neurodegeneration after traumatic or kainate excitotoxicity in GFAP-null mice

Astrocytes perform a variety of functions in the adult central nervous system. Recent evidence suggests that the upregulation of glial fibrillary acidic protein (GFAP), an astrocyte-specific intermediate filament component, is a biological marker of neurotoxicity after cerebral injury. We herein compared the response to traumatic brain injury or kainic acid (KA)-induced neurotoxicity in GFAP knockout (GFAP-KO) and wild-type (WT) mice. Seventy-two hours after injury, all GFAP-KO mice showed hippocampal CA3 neurodegeneration, whereas WT mice did not show neurodegeneration. Seventy-two hours after KA administration, GFAP-KO mice were more susceptible to KA-induced seizures and had an increased number of pyknotic damaged CA3 neurons than did WT mice. These results indicate that GFAP plays a crucial role in pyramidal neuronal survival after injury or KA-induced neurotoxicity.

Differential expression of extracellular matrix and adhesion molecule genes in the brain of juvenile versus adult mice in responses to intracerebroventricular administration of IL-1

OBJECTIVE

Intracerebroventricular (ICV) injection of interleukin-1 (IL-1) stimulates the recruitment of leukocytes into the central nervous system at different time points in juvenile versus adult mice. Our results showed that leukocytes entered brain parenchyma at 8 and 16 h after injection in juvenile and adult mice, respectively. This study compares the differential gene expression patterns of extracellular matrix and adhesion molecules in the brain of juvenile and adult mice.

METHODS

We analyzed these gene expressions in mice brains by microarray and real-time PCR at 2 and 8 h after ICV IL-1.

RESULTS

After ICV IL-1, the following genes were significantly upregulated in both juvenile and adult mice: LAMbeta1-1, MMP17, TGFbeta, THBS3 and VCAM1 were upregulated at 2 h after injection; LAMbeta1-1 and TGFbeta were upregulated at 8 h. Additional changes were found in adult mice only: CNTN1, ECM1, ICAM1 and LAMalpha4 were upregulated at 2 h after injection; COL4alpha1, MMP3 and VCAM1 were upregulated at 8 h; TIMP4 was downregulated. Comparing juvenile and adult mice, real-time PCR analysis showed that there was more induction of TGFbeta at 8 h and a stronger downregulation of TIMP4 at 2 h after injection in juvenile mice. Higher expression of MMP17 was found in juvenile mice, compared to adult mice, at both 2 and 8 h after injection.

CONCLUSIONS

These data show distinct expression patterns of molecules related to the extracellular matrix and adhesion molecules in juvenile versus adult mice, and suggest that increased expression of MMP17 and TGFbeta and decreased expression of TIMP4 may contribute to the accelerated recruitment of leukocytes into the central nervous system in juvenile animals.

Depletion of neutrophils reduces neuronal degeneration and inflammatory responses induced by quinolinic acidin vivo

The use of anti-neutrophil serum (anti-PMN) to induce neutropenia has been assessed for neuroprotection, modulation of microgliosis and astrogliosis, effects on oxidative stress, and intactness of blood-brain barrier (BBB) following injection of the excitotoxin quinolinic acid (QUIN) into rat striatum. At 1 day following QUIN injection, considerable striatal neurodegeneration was measured (Fluoro-Jade B marker). At this time, marked microgliosis (OX-42 marker) and astrogliosis (GFAP marker) were evident in QUIN-injected striatum. Treatment of QUIN-injected animals with anti-PMN protected neurons (48% reduction of striatal neuron loss) and inhibited microgliosis (61% reduction) and astrogliosis (43% reduction) compared with QUIN injection alone. Anti-PMN treatment was effective in decreasing levels of superoxide anions (by 42%) compared with QUIN alone; in addition, expressions of the neutrophil enzyme myeloperoxidase and the neutrophil oxidant 3-chlorotyrosine were markedly reduced (by 79 and 72%, respectively) with neutrophil depletion. QUIN-induced leakiness in BBB was indicated by elevated striatal levels of the blood protein fibrinogen, a result confirmed using Evans blue dye; anti-PMN was effective in reducing BBB permeability. Measurements from QUIN-injected animals directly confirmed anti-PMN efficacy in diminishing numbers of circulating neutrophils. Longer term neuroprotection and reduced microgliosis were also observed at 7 days post-injection of anti-PMN; at this time, anti-PMN-treated rats also demonstrated an improved apomorphine-induced rotational performance. We conclude that anti-PMN treatment could serve as a novel strategy to prevent leakiness to BBB, reduce gliosis, and protect striatal neurons in excitotoxin-injected brain.

Characterization of human monocyte-derived microglia-like cells

Microglial cells are central to brain immunity and intervene in many human neurological diseases. The aim of this study was to develop a convenient cellular model for human microglial cells, suitable for HIV studies. Microglia derive from the hematogenous myelomonocytic lineage, possibly as a distinct subpopulation but in any case able to invade the CNS, proliferate, and differentiate into ameboid and then ramified microglia in the adult life. We thus attempted to derive microglia-like cells from human monocytes. When cultured with astrocyte-conditioned medium (ACM), monocytes acquired a ramified morphology, typical of microglia. They overexpressed substance P and the calcium binding protein Iba-1 and dimly expressed class II MHC, three characteristics of microglial cells. Moreover, they also expressed a potassium inward rectifier current, another microglia-specific feature. These monocyte-derived microglia-like cells (MDMi) were CD4(+)/CD14(+), evocative of an activated microglia phenotype. When treated with lipopolysaccharide (LPS), MDMi lost their overexpression of substance P, which returned to untreated monocyte-derived macrophage (MDM) level. Compared with MDM, MDMi expressed higher CD4 but lower CCR5 levels; they could be infected by HIV-1(BaL), but produced less virus progeny than MDM did. This model of human microglia may be an interesting alternative to primary microglia for large scale in vitro HIV studies and may help to better understand HIV-associated microgliosis and chronic inflammation in the brain.

Systematic analysis of axonal damage and inflammatory response in different white matter tracts of acutely injured rat spinal cord

The mechanisms of white matter (WM) damage during secondary degeneration are a fundamental issue in the pathophysiology of central nervous system (CNS) diseases. Our main goal was to describe the pattern of an acute inflammatory response and secondary damage to axons in different WM tracts of acutely injured rat spinal cord. Adult rats were deeply anesthetized and injected with 20 nmol of NMDA into the spinal cord ventral horn on T7. Animals were perfused after survival times of 1 day, 3 days and 7 days. Ten micrometer sections were submitted to immunocytochemical analysis for activated macrophages/microglia, neutrophils and damaged axons. There were inflammatory response and progressive tissue destruction of ventral WM (VWM) with formation of microcysts in both VWM and lateral WM (LWM). In the VWM, the number of beta-amyloid precursor protein (beta-APP) end-bulbs increased from 1 day with a peak at 3 days, decreasing by 7 days following the injection. APP end-bulbs were present in the dorsal WM (DWM) at 3 days survival time but were not in the LWM. Electron microscopic analysis revealed different degrees of myelin disruption and axonal pathology in the vacuolated WM up to 14 mm along the rostrocaudal axis. Quantitative analysis revealed a significant loss of medium and large axons (P < 0.05), but not of small axons (P > 0.05). Our results suggest that bystander axonal damage and myelin vacuolation are important secondary component of the pathology of WM tracts following rat SCI. Further studies are needed to understand the mechanisms of these pathological events.

Age-related gadolinium-enhancement of MRI brain lesions in multiple sclerosis

There is evidence that inflammatory processes in multiple sclerosis (MS) are age-dependent. In this study we evaluated the impact of aging on gadolinium (Gd) enhancement of brain magnetic resonance imaging (MRI) lesions in MS patients. Pre- and post-contrast MRI scans, acquired using a standardized procedure by the same MRI scanner, at least 1 month far from clinical relapse or steroid treatment, were examined in 200 disease-modifying treatment free MS patients. Seventy-three patients (36.5%) showed at least one enhancing lesion. Age at MRI examination (p=0.0001), disease duration (p=0.002) and EDSS score were significantly (p=0.02) lower, whereas relapse rate in the preceding 2 years was higher (p=0.003) in patients with enhancing lesions than in patients with unenhancing scans. Multivariate logistic analysis showed that current age was the variable better predicting Gd enhancement (p=0.004). The odds ratios were 0.95 (CI: 0.92-0.98) for each year of patient's age and 0.64 (CI: 0.48-0.87) for each age decade. The main changes in enhancement risk occurred after 35 years of age. Multivariate Poisson regression model showed that relapse rate in the preceding 2 years (p<0.0001) and current age (p=0.0003) were the best predictors of the number of enhancing lesions. This information can be used to increase the statistical power of clinical trials using Gd-enhancing lesions as an outcome measure.

Alterations in blood-brain barrier ICAM-1 expression and brain microglial activation after lambda-carrageenan-induced inflammatory pain

Previous studies showed that peripheral inflammatory pain increased blood-brain barrier (BBB) permeability and altered tight junction protein expression and the delivery of opioid analgesics to the brain. What remains unknown is which pathways and mediators during peripheral inflammation affect BBB function and structure. The current study investigated effects of lambda-carrageenan-induced inflammatory pain (CIP) on BBB expression of ICAM-1. We also examined the systemic contribution of a number of proinflammatory cytokines and microglial activation in the brain to elucidate pathways involved in BBB disruption during CIP. We investigated ICAM-1 RNA and protein expression levels in isolated rat brain microvessels after CIP using RT-PCR and Western blot analyses, screened inflammatory cytokines during the time course of inflammation, assessed white blood cell counts, and probed for BBB and central nervous system stimulation and leukocyte transmigration using immunohistochemistry and flow cytometry. Results showed an early increase in ICAM-1 RNA and protein expression after CIP with no change in circulating levels of several proinflammatory cytokines. Changes in ICAM-1 protein expression were noted at 48 h. Immunohistochemistry showed that the induction of ICAM-1 was region specific with increased expression noted in the thalamus and frontal and parietal cortices, which directly correlated with increased expression of activated microglia. The findings of the present study were that CIP induces increased ICAM-1 mRNA and protein expression at the BBB and that systemic proinflammatory mediators play no apparent role in the early response (1-6 h); however, brain region-specific increases in microglial activation suggest a potential for a central-mediated response.

Blood-derived dendritic cells in an acute brain injury

Dendritic cells (DC), while absent from the normal CNS parenchyma, have been demonstrated in delayed type hypersensitivity (DTH), experimental allergic encephalomyelitis (EAE), and some MS lesions. We demonstrate that an acute excitotoxic lesion results in DC recruitment to the brain, with maximal cells between days 3 and 5. Clodronate liposome-mediated depletion of cerebral perivascular macrophages does not prevent recruitment of DC; however, a lesion in a whole-body irradiated animal does not show evidence of DC recruitment. We conclude that DC are recruited to an excitotoxic lesion from a blood-derived cell population. This may have implications for neuropathologies involving DC recruitment.

The therapeutic potential of CXC chemokine blockade in acute inflammation in the brain

Mammalian neurones of the central nervous system (CNS) are terminally differentiated, and there is little endogenous capacity of the CNS to repair itself. Peripheral tissue injury, disease or infection results in a stereotypical inflammatory response to protect the host from pathogens and to promote tissue repair. However, collateral or 'bystander' damage is characteristic of any inflammatory response. Thus, it is apparent that the CNS has evolved mechanisms to regulate tightly the acute inflammatory response, and in particular to restrict the recruitment of neutrophils, in an attempt to protect itself from the potentially damaging consequences of inflammation in the brain. However, neutrophils are not always excluded from the brain. Indeed, they are found in large numbers in the brain parenchyma following traumatic lesions, stroke lesions, and in rodents, during the 'window of susceptibility'. Therapy targeted at blocking excitotoxic cell death has not successfully transferred from rodent models of stroke to human stroke patients. Restricting leukocyte entry to the brain, thereby inhibiting the inflammatory response, may prove to be a more practical therapeutic approach. The evidence presented in this review suggests that antagonising the effects of CXC chemokines may represent one route to achieve this goal.

Differential regulation of type I and type II interleukin-1 receptors in focal brain inflammation

Most pathologies of the brain have an inflammatory component, associated with the release of cytokines such as interleukin-1beta (IL-1beta) from resident and infiltrating cells. The IL-1 type I receptor (IL-1RI) initiates a signalling cascade but the type II receptor (IL-1RII) acts as a decoy receptor. Here we have investigated the expression of IL-1beta, IL-1RI and IL-1RII in distinct inflammatory lesions in the rat brain. IL-1beta was injected into the brain to generate an inflammatory lesion in the absence of neuronal cell death whereas neuronal death was specifically induced by the microinjection of N-methyl-D-aspartate (NMDA). Using TaqMan RT-PCR and ELISA, we observed elevated de novo IL-1beta synthesis 2 h after the intracerebral microinjection of IL-1beta; this de novo IL-1beta remained elevated 24 h later. There was a concomitant increase in IL-1RI mRNA but a much greater increase in IL-1RII mRNA. Immunostaining revealed that IL-1RII was expressed on brain endothelial cells and on infiltrating neutrophils. In contrast, although IL-1beta and IL-1RI were elevated to similar levels in response to NMDA challenge, the response was delayed and IL-1RII mRNA expression was unchanged. The lesion-specific expression of IL-1 receptors suggests that the receptors are differentially regulated in a manner not directly related to the endogenous level of IL-1 in the CNS.