The type 1 interleukin 1 receptor is not required for the death of murine hippocampal dentate granule cells and microglia activation

Neuroprotective effects of ex vivo-expanded regulatory T cells on trimethyltin-induced neurodegeneration in mice

Background

Trimethyltin (TMT) is a potent neurotoxicant that leads to hippocampal neurodegeneration. Regulatory T cells (Tregs) play an important role in maintaining the immune balance in the central nervous system (CNS), but their activities are impaired in neurodegenerative diseases. In this study, we aimed to determine whether adoptive transfer of Tregs, as a living drug, ameliorates hippocampal neurodegeneration in TMT-intoxicated mice.

Methods

CD4⁺CD25⁺ Tregs were expanded in vitro and adoptively transferred to TMT-treated mice. First, we explored the effects of Tregs on behavioral deficits using the Morris water maze and elevated plus maze tests. Biomarkers related to memory formation, such as cAMP response element-binding protein (CREB), protein kinase C (PKC), neuronal nuclear protein (NeuN), nerve growth factor (NGF), and ionized calcium binding adaptor molecule 1 (Iba1) in the hippocampus were examined by immunohistochemistry after killing the mouse. To investigate the neuroinflammatory responses, the polarization status of microglia was examined in vivo and in vitro using real-time reverse transcription polymerase chain reaction (rtPCR) and Enzyme-linked immunosorbent assay (ELISA). Additionally, the inhibitory effects of Tregs on TMT-induced microglial activation were examined using time-lapse live imaging in vitro with an activation-specific fluorescence probe, CDr20.

Results

Adoptive transfer of Tregs improved spatial learning and memory functions and reduced anxiety in TMT-intoxicated mice. Additionally, adoptive transfer of Tregs reduced neuronal loss and recovered the expression of neurogenesis enhancing molecules in the hippocampi of TMT-intoxicated mice. In particular, Tregs inhibited microglial activation and pro-inflammatory cytokine release in the hippocampi of TMT-intoxicated mice. The inhibitory effects of TMT were also confirmed via in vitro live time-lapse imaging in a Treg/microglia co-culture system.

Conclusions

These data suggest that adoptive transfer of Tregs ameliorates disease progression in TMT-induced neurodegeneration by promoting neurogenesis and modulating microglial activation and polarization.

Intranasal Administration of Mesenchymal Stem Cell Secretome Reduces Hippocampal Oxidative Stress, Neuroinflammation and Cell Death, Improving the Behavioral Outcome Following Perinatal Asphyxia

Perinatal Asphyxia (PA) is a leading cause of motor and neuropsychiatric disability associated with sustained oxidative stress, neuroinflammation, and cell death, affecting brain development. Based on a rat model of global PA, we investigated the neuroprotective effect of intranasally administered secretome, derived from human adipose mesenchymal stem cells (MSC-S), preconditioned with either deferoxamine (an hypoxia-mimetic) or TNF-α+IFN-γ (pro-inflammatory cytokines). PA was generated by immersing fetus-containing uterine horns in a water bath at 37 °C for 21 min. Thereafter, 16 μL of MSC-S (containing 6 μg of protein derived from 2 × 10⁵ preconditioned-MSC), or vehicle, were intranasally administered 2 h after birth to asphyxia-exposed and control rats, evaluated at postnatal day (P) 7. Alternatively, pups received a dose of either preconditioned MSC-S or vehicle, both at 2 h and P7, and were evaluated at P14, P30, and P60. The preconditioned MSC-S treatment (i) reversed asphyxia-induced oxidative stress in the hippocampus (oxidized/reduced glutathione); (ii) increased antioxidative Nuclear Erythroid 2-Related Factor 2 (NRF2) translocation; (iii) increased NQO1 antioxidant protein; (iv) reduced neuroinflammation (decreasing nuclearNF-κB/p65 levels and microglial reactivity); (v) decreased cleaved-caspase-3 cell-death; (vi) improved righting reflex, negative geotaxis, cliff aversion, locomotor activity, anxiety, motor coordination, and recognition memory. Overall, the study demonstrates that intranasal administration of preconditioned MSC-S is a novel therapeutic strategy that prevents the long-term effects of perinatal asphyxia.

Protein pathway analysis to study development-dependent effects of acute and repeated trimethyltin (TMT) treatments in 3D rat brain cell cultures

Trimethyltin is an organometallic compound, described to be neurotoxic and to trigger neuroinflammation and oxidative stress. Previous studies associated TMT with the perturbation of mitochondrial function, or neurotransmission. However, the mechanisms of toxicity may differ depending on the duration of exposure and on the stage of maturation of brain cells. This study aim at elucidating whether the toxicity pathways triggered by a known neurotoxicant (TMT) differs depending on cell maturation stage or duration of exposure. To this end omics profiling of immature and differentiated 3D rat brain cell cultures exposed for 24 h or 10 days (10-d) to 0.5 and 1 μM of TMT was performed to better understand the underlying mechanisms of TMT associated toxicity. Proteomics identified 55 and 17 proteins affected by acute TMT treatment in immature and differentiated cultures respectively, while 10-day treatment altered 96 proteins in immature cultures versus 353 in differentiated. The results suggest different sensitivity to TMT depending on treatment duration and cell maturation. In accordance with known TMT mechanisms oxidative stress and neuroinflammation was observed after 10-d treatment at both maturation stages, whereas the neuroinflammatory process was more prominent in differentiated cultures than in the immature, no development-dependent difference could be detected for oxidative stress or synaptic neurodegeneration. Pathway analysis revealed that both vesicular trafficking and the synaptic machinery were strongly affected by 10-d TMT treatment in both maturation stages, as was GABAergic and glutamatergic neurotransmission. This study shows that omics approaches combined with pathway analysis constitutes an improved tool-set in elucidating toxicity mechanisms.

NLRP3 inflammasome activation is involved in trimethyltin-induced neuroinflammation

Trimethyltin (TMT), a neurotoxic organotin compound, is selectively localized within the limbic system. The mechanisms of TMT-induced hippocampal neurodegeneration include inflammatory responses, oxidative stress, and neuronal death. Increasing evidence shows that the inflammatory response, mediated by activated inflammasomes, is involved in apoptosis and cellular dysfunction during brain injury. This study aimed to assess the role of the nucleotide-binding oligomerization domain-like receptor pyrin-domain-containing protein 3 (NLRP3) inflammasome in TMT-induced central nervous system (CNS) injury. In addition, the mechanisms underlying TMT neurotoxicity are similar to those involved in the pathogenesis of multiple neurodegenerative diseases; hence, a study on TMT cytotoxicity may be informative for the understanding of human CNS diseases. Microglia were significantly activated in the rat hippocampal dentate gyrus after TMT treatment. The mRNA expression of pro-inflammatory cytokines, interleukin-1β and interleukin-18, was induced both in vitro and in vivo. TMT treatment activated the NLRP3 inflammasome in the microglial cell line BV2. NLRP3 RNA interference significantly protected these cells from TMT-induced neuroinflammation. Our results demonstrate that the NLRP3 inflammasome is a key mediator of neuroinflammation and plays an important role in TMT-induced neuroinflammation.

In vitro models to study insulin and glucocorticoids modulation of trimethyltin (TMT)-induced neuroinflammation and neurodegeneration, and in vivo validation in db/db mice

Brain susceptibility to a neurotoxic insult may be increased in a compromised health status, such as metabolic syndrome. Both metabolic syndrome and exposure to trimethyltin (TMT) are known to promote neurodegeneration. In combination the two factors may elicit additive or compensatory/regulatory mechanisms. Combined effects of TMT exposure (0.5-1 μM) and mimicked metabolic syndrome-through modulation of insulin and glucocorticoid (GC) levels-were investigated in three models: tridimensional rat brain cell cultures for neuron-glia effects; murine microglial cell line BV-2 for a mechanistic analysis of microglial reactivity; and db/db mice as an in vivo model of metabolic syndrome. In 3D cultures, low insulin condition significantly exacerbated TMT's effect on GABAergic neurons and promoted TMT-induced neuroinflammation, with increased expression of cytokines and of the regulator of intracellular GC activity, 11β-hydroxysteroid dehydrogenase 1 (11β-Hsd1). Microglial reactivity increased upon TMT exposure in medium combining low insulin and high GC. These results were corroborated in BV-2 microglial cells where lack of insulin exacerbated the TMT-induced increase in 11β-Hsd1 expression. Furthermore, TMT-induced microglial reactivity seems to depend on mineralocorticoid receptor activation. In diabetic BKS db mice, a discrete exacerbation of TMT neurotoxic effects on GABAergic neurons was observed, together with an increase of interleukin-6 (IL-6) and of basal 11β-Hsd1 expression as compared to controls. These results suggest only minor additive effects of the two brain insults, neurotoxicant TMT exposure and metabolic syndrome conditions, where 11β-Hsd1 appears to play a key role in the regulation of neuroinflammation and of its protective or neurodegenerative consequences.

Toxin-Induced Experimental Models of Learning and Memory Impairment

Animal models for learning and memory have significantly contributed to novel strategies for drug development and hence are an imperative part in the assessment of therapeutics. Learning and memory involve different stages including acquisition, consolidation, and retrieval and each stage can be characterized using specific toxin. Recent studies have postulated the molecular basis of these processes and have also demonstrated many signaling molecules that are involved in several stages of memory. Most insights into learning and memory impairment and to develop a novel compound stems from the investigations performed in experimental models, especially those produced by neurotoxins models. Several toxins have been utilized based on their mechanism of action for learning and memory impairment such as scopolamine, streptozotocin, quinolinic acid, and domoic acid. Further, some toxins like 6-hydroxy dopamine (6-OHDA), 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) and amyloid-β are known to cause specific learning and memory impairment which imitate the disease pathology of Parkinson's disease dementia and Alzheimer's disease dementia. Apart from these toxins, several other toxins come under a miscellaneous category like an environmental pollutant, snake venoms, botulinum, and lipopolysaccharide. This review will focus on the various classes of neurotoxin models for learning and memory impairment with their specific mechanism of action that could assist the process of drug discovery and development for dementia and cognitive disorders.

Trimethyltin-induced hippocampal neurodegeneration: A mechanism-based review

Trimethyltin (TMT), a toxic organotin compound, induces neurodegeneration selectively involving the limbic system and especially prominent in the hippocampus. Neurodegeneration-associated behavioral abnormalities, such as hyperactivity, aggression, cognitive deficits, and epileptic seizures, occur in both exposed humans and experimental animal models. Previously, TMT had been used generally in industry and agriculture, but the use of TMT has been limited because of its dangers to people. TMT has also been used to make a promising in vivo rodent model of neurodegeneration because of its region-specific characteristics. Several studies have demonstrated that TMT-treated animal models of epileptic seizures can be used as tools for researching hippocampus-specific neurotoxicity as well as the molecular mechanisms leading to hippocampal neurodegeneration. This review summarizes the in vivo and in vitro underlying mechanisms of TMT-induced hippocampal neurodegeneration (oxidative stress, inflammatory responses, and neuronal death/survival). Thus, the present review may be helpful to provide general insights into TMT-induced neurodegeneration and approaches to therapeutic interventions for neurodegenerative diseases, including temporal lobe epilepsy.

Secret talk between adipose tissue and central nervous system via secreted factors-an emerging frontier in the neurodegenerative research

First seen as a storage organ, the white adipose tissue (WAT) is now considered as an endocrine organ. WAT can produce an array of bioactive factors known as adipokines acting at physiological level and playing a vital role in energy metabolism as well as in immune response. The global effect of adipokines in metabolic activities is well established, but their impact on the physiology and the pathophysiology of the central nervous system (CNS) remains poorly defined. Adipokines are not only produced by the WAT but can also be expressed in the CNS where receptors for these factors are present. When produced in periphery and to affect the CNS, these factors may either cross the blood brain barrier (BBB) or modify the BBB physiology by acting on cells forming the BBB. Adipokines could regulate neuroinflammation and oxidative stress which are two major physiological processes involved in neurodegeneration and are associated with many chronic neurodegenerative diseases. In this review, we focus on four important adipokines (leptin, resistin, adiponectin, and TNFα) and one lipokine (lysophosphatidic acid-LPA) associated with autotaxin, its producing enzyme. Their potential effects on neurodegeneration and brain repair (neurogenesis) will be discussed. Understanding and regulating these adipokines could be an interesting lead to novel therapeutic strategy in order to counteract neurodegenerative disorders and/or promote brain repair.

Glial activation with concurrent up-regulation of inflammatory mediators in trimethyltin-induced neurotoxicity in mice

Trimethyltin (TMT), a potent neurotoxic chemical, causes dysfunction and neuroinflammation in the brain, particularly in the hippocampus. The present study assessed TMT-induced glial cell activation and inflammatory cytokine alterations in the mouse hippocampus, BV-2 microglia, and primary cultured astrocytes. In the mouse hippocampus, TMT treatment significantly increased the expression of glial cell markers, including the microglial marker ionized calcium-binding adapter molecule 1 and the astroglial marker glial fibrillary acidic protein. The expression of M1 and M2 microglial markers (inducible nitric oxide synthase [iNOS] and CD206, respectively) and pro-inflammatory cytokines (interleukin [IL]-1β, IL-6 and tumor necrosis factor [TNF]-α) were significantly increased in the mouse hippocampus following TMT treatment. In BV-2 microglia, iNOS, IL-1β, TNF-α, and IL-6 expression increased significantly, whereas arginase-1 and CD206 expression decreased significantly after TMT treatment in a time- and concentration-dependent manner. In primary cultured astrocytes, iNOS, arginase-1, IL-1β, TNF-α, and IL-6 expression increased significantly, whereas IL-10 expression decreased significantly after TMT treatment in a time- and concentration-dependent manner. These results indicate that significant up-regulation of pro-inflammatory signals in TMT-induced neurotoxicity may be associated with pathological processing of TMT-induced neurodegeneration.

Possible role of the glycogen synthase kinase-3 signaling pathway in trimethyltin-induced hippocampal neurodegeneration in mice

Trimethyltin (TMT) is an organotin compound with potent neurotoxic effects characterized by neuronal destruction in selective regions, including the hippocampus. Glycogen synthase kinase-3 (GSK-3) regulates many cellular processes, and is implicated in several neurodegenerative disorders. In this study, we evaluated the therapeutic effect of lithium, a selective GSK-3 inhibitor, on the hippocampus of adult C57BL/6 mice with TMT treatment (2.6 mg/kg, intraperitoneal [i.p.]) and on cultured hippocampal neurons (12 days in vitro) with TMT treatment (5 µM). Lithium (50 mg/kg, i.p., 0 and 24 h after TMT injection) significantly attenuated TMT-induced hippocampal cell degeneration, seizure, and memory deficits in mice. In cultured hippocampal neurons, lithium treatment (0–10 mM; 1 h before TMT application) significantly reduced TMT-induced cytotoxicity in a dose-dependent manner. Additionally, the dynamic changes in GSK-3/β-catenin signaling were observed in the mouse hippocampus and cultured hippocampal neurons after TMT treatment with or without lithium. Therefore, lithium inhibited the detrimental effects of TMT on the hippocampal neurons in vivo and in vitro, suggesting involvement of the GSK-3/β-catenin signaling pathway in TMT-induced hippocampal cell degeneration and dysfunction.

Interleukin (IL)-1 and IL-6 regulation of neural progenitor cell proliferation with hippocampal injury: differential regulatory pathways in the subgranular zone (SGZ) of the adolescent and mature mouse brain

Current data suggests an association between elevations in interleukin 1 (IL-1)α, IL-1β, and IL-6 and the proliferation of neural progenitor cells (NPCs) following brain injury. A limited amount of work implicates changes in these pro-inflammatory responses with diminished NPC proliferation observed as a function of aging. In the current study, adolescent (21day-old) and 1year-old CD-1 male mice were injected with trimethyltin (TMT, 2.3mg/kg, i.p.) to produce acute apoptosis of hippocampal dentate granule cells. In this model, fewer 5-bromo-2'-deoxyuridine (BrdU)+ NPC were observed in both naive and injured adult hippocampus as compared to the corresponding number seen in adolescent mice. At 48h post-TMT, a similar level of neuronal death was observed across ages, yet activated ameboid microglia were observed in the adolescent and hypertrophic process-bearing microglia in the adult. IL-1α mRNA levels were elevated in the adolescent hippocampus; IL-6 mRNA levels were elevated in the adult. In subgranular zone (SGZ) isolated by laser-capture microdissection, IL-1β was detected but not elevated by TMT, IL-1a was elevated at both ages, while IL-6 was elevated only in the adult. Naïve NPCs isolated from the hippocampus expressed transcripts for IL-1R1, IL-6Rα, and gp130 with significantly higher levels of IL-6Rα mRNA in the adult. In vitro, IL-1α (150pg/ml) stimulated proliferation of adolescent NPCs; IL-6 (10ng/ml) inhibited proliferation of adolescent and adult NPCs. Microarray analysis of SGZ post-TMT indicated a prominence of IL-1a/IL-1R1 signaling in the adolescent and IL-6/gp130 signaling in the adult.

Altered cerebellar development in nuclear receptor TAK1/ TR4 null mice is associated with deficits in GLAST(+) glia, alterations in social behavior, motor learning, startle reactivity, and microglia

Previously, deficiency in the expression of the nuclear orphan receptor TAK1 was found to be associated with delayed cerebellar granule cell migration and Purkinje cell maturation with a permanent deficit in foliation of lobules VI–VII, suggesting a role for TAK1 in cerebellum development. In this study, we confirm that TAK1-deficient (TAK1(−/−)) mice have a smaller cerebellum and exhibit a disruption of lobules VI–VII. We extended these studies and show that at postnatal day 7, TAK1(−/−) mice exhibit a delay in monolayer maturation of dysmorphic calbindin 28K-positive Purkinje cells. The astrocyte-specific glutamate transporter (GLAST) was expressed within Bergmann fibers and internal granule cell layer at significantly lower levels in the cerebellum of TAK1(−/−) mice. At PND21, Golgi-positive Purkinje cells in TAK1(−/−) mice displayed a smaller soma (18%) and shorter distance to first branch point (35%). Neuronal death was not observed in TAK1(−/−) mice at PND21; however, activated microglia were present in the cerebellum, suggestive of earlier cell death. These structural deficits in the cerebellum were not sufficient to alter motor strength, coordination, or activity levels; however, deficits in acoustic startle response, prepulse startle inhibition, and social interactions were observed. Reactions to a novel environment were inhibited in a light/dark chamber, open-field, and home-cage running wheel. TAK1(−/−) mice displayed a plateau in performance on the running wheel, suggesting a deficit in learning to coordinate performance on a motor task. These data indicate that TAK1 is an important transcriptional modulator of cerebellar development and neurodevelopmentally regulated behavior.

Protease-activated receptor-1 expression in rat microglia after trimethyltin treatment

In the nervous system, protease-activated receptors (PARs), which are activated by thrombin and other extracellular proteases, are expressed widely at both neuronal and glial levels and have been shown to be involved in several brain pathologies. As far as the glial receptors are concerned, previous experiments performed in rat hippocampus showed that expression of PAR-1, the prototypic member of the PAR family, increased in astrocytes both in vivo and in vitro following treatment with trimethyltin (TMT). TMT is an organotin compound that induces severe hippocampal neurodegeneration associated with astrocyte and microglia activation. In the present experiments, the authors extended their investigation to microglial cells. In particular, by 7 days following TMT intoxication in vivo, confocal immunofluorescence revealed an evident PAR-1-related specific immunoreactivity in OX-42-positive microglial cells of the CA3 and hilus hippocampal regions. In line with the in vivo results, when primary rat microglial cells were treated in vitro with TMT, a strong upregulation of PAR-1 was observed by immunocytochemistry and Western blot analysis. These data provide further evidence that PAR-1 may be involved in microglial response to brain damage.

Injury-induced neurogenesis: consideration of resident microglia as supportive of neural progenitor cells

The induction of neurogenesis in the adult subgranular zone (SGZ) by injury is often accompanied by changes in the extracellular environment that can have significant impacts on neural progenitor cells (NPCs). We examined the induction of neurogenesis in the SGZ at 72 h following an injection of the hippocampal toxicant, trimethyltin (TMT; 2 mg/kg, ip) inducing apoptosis in dentate granule neurons. BrdU+ incorporation during the active period of neuronal death indicated NPC proliferation and migration of newly generated cells into the granule cell layer (GCL). BrdU+ cells were transiently in contact with process bearing microglia within the inner SGZ layer. Contact with GFAP+ astrocyte processes occurred once cells were within the GCL. A small percentage of the BrdU+ cells within the SGZ region showed immunoreactivity for tumor necrosis factor (TNF) p75 receptor (TNFp75R). In mice deficient for TNFp75R, TMT injection produced an equivalent level of dentate granule cell death however; BrdU+ cells were localized at the SGZ as compared to the presence of cells within the GCL in the WT mice dosed with TMT. These data suggest that cells generated by NPCs in the SGZ induced with a focal lesion to the dentate granule neurons of adolescent mice maintain the capacity to utilize the neuroinflammation and microglia responses within their environment for migration into the GCL.

Heterogeneity of microglia and TNF signaling as determinants for neuronal death or survival

Microglia do not constitute a single, uniform cell population, but rather comprise cells with varied phenotypes, some which are beneficial and others that may require active regulatory control. Thus, gaining a better understanding of the heterogeneity of resident microglia responses will contribute to any interpretation regarding the impact of any such response in the brain. Microglia are the primary source of the pro-inflammatory cytokine, tumor necrosis factor (TNF) that can initiate various effects through the activation of membrane receptors. The TNF p55 receptor contains a death domain and activation normally leads to cellular apoptosis; however, under specific conditions, receptor activation can also lead to the activation of NF-kappaB and contribute to cell survival. These divergent outcomes have been linked to receptor localization with receptor internalization leading to cell death and membrane localization supporting cell survival. A second TNF receptor, TNF p75 receptor, is normally linked to cell growth and survival, however, it can cooperate with the p55 receptor and contribute to cell death. Thus, while an elevation in TNFalpha in the brain is often considered an indicator of microglia activation and neuroinflammation, a number of factors come into play to determine the final outcome. Data are reviewed demonstrating that heterogeneity in morphological response of microglia and the expression of TNFalpha and TNF receptors are critical in identifying and characterizing neurotoxic events as they relate to neuroinflammation, neuronal damage and in stimulating neuroprotection.

IGF-1 and pAKT signaling promote hippocampal CA1 neuronal survival following injury to dentate granule cells

Insulin-like growth factor-1 (IGF-1) protects neurons from apoptosis and in vivo offers neuroprotective support to hippocampal CA1 pyramidal neurons following ischemia or seizure. IGF-1 signals through IGF-1 receptors activating phosphytidylinositol 3-kinase (PI3K)/Akt or pMAPK pathways. IGF-1 can be induced with injury and microglia and astrocytes may serve as a source of this neurotrophic factor to promote neuronal survival. An acute systemic injection of trimethyltin (TMT; 2 mg/kg, ip) to mice induces apoptosis of dentate granule neurons within 24 h and a differential response of microglia with ramified microglia present in the CA-1 region. Using this model, we studied the role of IGF-1 in the survival of CA-1 pyramidal neurons under conditions of altered synaptic input due to changes in the dentate gyrus. Within 24 h of injection, IGF-1 mRNA levels were elevated in the hippocampus and IGF-1 protein detected in both astrocytes and microglia. IGF-1 was redistributed within the CA-1 neurons corresponding with an increase in cytoplasmic pAkt, elevated PKBalpha/Akt protein levels, and a decrease in the antagonist, Rho. pMAPK was not detected in CA-1 neurons and ERK2 showed a transient decrease followed by a significant increase, suggesting a lack of recruitment of the pMAPK signaling pathway for neuronal survival. In mice deficient for IGF-1, a similar level of apoptosis was observed in dentate granule neurons as compared to wildtype; however, TMT induced a significant level CA-1 neuronal death, further supporting a role for IGF-1 in the survival of CA-1 neurons.

Neuroinflammation and microglia: considerations and approaches for neurotoxicity assessment

BACKGROUND

The impact of an inflammatory response, as well as interactions between the immune and nervous systems, are rapidly assuming major roles in neurodegenerative disease and injury. However, it is now appreciated that the exact nature of such responses can differ with each type of insult and interaction. More recently, neuroinflammation and the associated cellular response of microglia are being considered for their contribution to neurotoxicity of environmental agents; yet, so far, the inclusion of inflammatory end points into neurotoxicity assessment have relied primarily on relatively limited measures or driven by in vitro models of neurotoxicity.

OBJECTIVE

To present background information on relevant biological considerations of neuroinflammation and the microglia response demonstrating the complex integrative nature of these biological processes and raising concern with regards to translation of effects demonstrated in vitro to the in vivo situation. Specific points are addressed that would influence the design and interpretation of neuroinflammation with regards to neurotoxicology assessment.

CONCLUSION

There is a complex and dynamic response in the brain to regulate inflammatory processes and maintain a normal homeostatic level. The classification of such responses as beneficial or detrimental is an oversimplification. Neuroinflammation should be considered as a balanced network of processes in which subtle modifications can shift the cells toward disparate outcomes. The tendency to overinterpret data obtained in an isolated culture system should be discouraged. Rather, the use of cross-disciplinary approaches to evaluate several end points should be incorporated into the assessment of inflammatory contributions to the neurotoxicity of environmental exposures.