Metabotropic glutamate receptor 5 mediates phosphorylation of vascular endothelial cadherin and nuclear localization of β-catenin in response to homocysteine

Brain microvascular endothelial cell metabolism and its ties to barrier function

Brain microvascular endothelial cells, which lie at the interface between blood and brain, are critical to brain energetics. These cells must precisely balance metabolizing nutrients for their own demands with transporting nutrients into the brain to sustain parenchymal cells. It is essential to understand this integrated metabolism and transport so that we can develop better diagnostics and therapeutics for neurodegenerative diseases such as Alzheimer's disease, multiple sclerosis, and traumatic brain injury. In this chapter, we first describe brain microvascular endothelial cell metabolism and how these cells regulate both blood flow and nutrient transport. We then explain the impact of brain microvascular endothelial cell metabolism on the integrity of the blood-brain barrier, as well as how metabolites produced by the endothelial cells impact other brain cells. We detail some ways that cell metabolism is typically measured experimentally and modeled computationally. Finally, we describe changes in brain microvascular endothelial cell metabolism in aging and neurodegenerative diseases. At the end of the chapter, we highlight areas for future research in brain microvascular endothelial cell metabolism. The goal of this chapter is to underscore the importance of nutrient metabolism and transport at the brain endothelium for cerebral health and neurovascular disease treatment.

Homocysteine-potentiated Kelch-like ECH-associated protein 1 promotes senescence of neuroblastoma 2a cells via inhibiting ubiquitination of β-catenin

Elevated serum homocysteine (Hcy) level is a risk factor for Alzheimer's disease (AD) and accelerates cell aging. However, the mechanism by which Hcy induces neuronal senescence remains largely unknown. In this study, we observed that Hcy significantly promoted senescence in neuroblastoma 2a (N2a) cells with elevated β-catenin and Kelch-like ECH-associated protein 1 (KEAP1) levels. Intriguingly, Hcy promoted the interaction between KEAP1 and the Wilms tumor gene on the X chromosome (WTX) while hampering the β-catenin-WTX interaction. Mechanistically, Hcy attenuated the methylation level of the KEAP1 promoter CpG island and activated KEAP1 transcription. However, a slow degradation rate rather than transcriptional activation contributed to the high level of β-catenin. Hcy-upregulated KEAP1 competed with β-catenin to bind to WTX. Knockdown of both β-catenin and KEAP1 attenuated Hcy-induced senescence in N2a cells. Our data highlight a crucial role of the KEAP1-β-catenin pathway in Hcy-induced neuronal-like senescence and uncover a promising target for AD treatment.

NMDA mediates disruption of blood-brain barrier permeability via Rho/ROCK signaling pathway

Glutamate can activate the N-methyl-D-aspartatic acid (NMDA) receptor (NMDAR), damage brain microvascular endothelial cells, and disturb the intercellular tight junctions (TJs). These result in changes in the permeability of the blood brain barrier (BBB). In neurons, the activation of Rho/ROCK signaling pathway is related to the activation of NMDAR，however, whether human brain vascular endothelial cells NMDAR mediates the Rho/ROCK pathway is not fully understood. The present study evaluates the effects of excessive NMDAR activation induced by NMDA (a glutamate analog) on the Rho/ROCK signaling pathway and the permeability of BBB by using a primary human brain microvascular endothelial cell (HBMEC) model. NMDAR subunit GluN1 was expressed in HBMECs and promoted by NMDA detected by Western blot and qRT-PCR. Furthermore, NMDA exposure decreased HBMEC viability, promoted HBMEC apoptosis, increased intracellular reactive oxygen species (ROS) levels, and destroyed the endothelial cytoskeleton. Additionally, NMDA exposure suppressed transendothelial electrical resistance (TEER) values and the expression of TJ proteins occludin and claudin5; it also promoted ROCK activated substrate myosin phosphatase target subunit-1 (MYPT)-1 phosphorylation and the transmittance of sodium fluorescein. In contrast, these effects were attenuated by ROCK inhibitor hydroxyfasudil (HF) and NMDAR antagonist MK801, respectively. Therefore, these results indicate that excessive endothelial NMDAR activation induced by NMDA may induce TJs and cytoskeleton damage, while HF attenuated NMDA-induced cytotoxicity in HBMECs by inhibiting the Rho/ROCK signaling pathway.

mGluR5 regulates REST/NRSF signaling through N-cadherin/β-catenin complex in Huntington's disease

Repressor element 1-silencing transcription factor/neuron-restrictive silencer factor (REST/NRSF) is a transcription repressor and its expression is regulated by the Wnt pathway through β-catenin. Metabotropic glutamate receptor 5 (mGluR5) signaling plays a key role in controlling neuronal gene expression. Interestingly, REST/NRSF nuclear translocation and signaling, as well as mGluR5 signaling are altered in the presence of mutant huntingtin. It remains unclear whether mGluR5 can modulate Wnt and REST/NRSF signaling under physiological conditions and whether this modulation is altered in Huntington's disease (HD). Using primary corticostriatal neurons derived from wild type mouse embryos, we find that targeting mGluR5 using the agonist, DHPG, or the negative allosteric modulator, CTEP, modulates REST/NRSF expression by regulating the assembly of N-cadherin/ β-catenin complex in a Src kinase-dependent manner. We have validated our in vitro findings in vivo using two HD mouse models. Specifically, we show that pharmacological inhibition of mGluR5 in zQ175 mice and genetic ablation of mGluR5 in BACHD mice corrected the pathological activation of Src and rescued REST/NRSF-dependent signaling. Together, our data provide evidence that mGluR5 regulates REST/NRSF expression via the Wnt pathway and highlight the contribution of impaired REST/ NRSF signaling to HD pathology.

AKT2 maintains brain endothelial claudin-5 expression and selective activation of IR/AKT2/FOXO1-signaling reverses barrier dysfunction

Inflammation-induced blood-brain barrier (BBB) dysfunction and microvascular leakage are associated with a host of neurological disorders. The tight junction protein claudin-5 (CLDN5) is a crucial protein necessary for BBB integrity and maintenance. CLDN5 is negatively regulated by the transcriptional repressor FOXO1, whose activity increases during impaired insulin/AKT signaling. Owing to an incomplete understanding of the mechanisms that regulate CLDN5 expression in BBB maintenance and dysfunction, therapeutic interventions remain underdeveloped. Here, we show a novel isoform-specific function for AKT2 in maintenance of BBB integrity. We identified that AKT2 during homeostasis specifically regulates CLDN5-dependent barrier integrity in brain microvascular endothelial cells (BMVECs) and that intervention with a selective insulin-receptor (IR) agonist, demethylasterriquinone B1 (DMAQ-B1), rescued IL-1β-induced AKT2 inactivation, FOXO1 nuclear accumulation, and loss of CLDN5-dependent barrier integrity. Moreover, DMAQ-B1 attenuated preclinical CLDN5-dependent BBB dysfunction in mice subjected to experimental autoimmune encephalomyelitis. Taken together, the data suggest a regulatory role for IR/AKT2/FOXO1-signaling in CLDN5 expression and BBB integrity during neuroinflammation.

Putative Nox2 inhibitors worsen homocysteine-induced impaired acetylcholine-mediated relaxation

BACKGROUND AND AIM

Increased homocysteine (Hcy) is associated with coronary artery disease (CAD). Hcy increases reactive oxygen species (ROS) via NADPH oxidases (Nox), reducing acetylcholine-mediated vasorelaxation. We aimed to determine if putative Nox2 inhibitors prevent Hcy-impaired acetylcholine-mediated vasorelaxation.

METHODS AND RESULTS

New Zealand White rabbit and wild-type (C57BL/6) and Nox2^-/- (NOX) mice aortic rings were mounted in organ baths. Rabbit rings were incubated with either apocynin (10 μM), gp91ds-tat (GP, 1 μM) or PhoxI2 (1 μM) and mice rings GP (1 μM) only. Some rabbit rings were incubated with 3 mM Hcy, before pre-contraction, followed by dose-response relaxation to acetylcholine (ACh; 0.01μM-10μM). In rabbit rings treated with Hcy and GP, O₂‾ donor pyrogallol (1 μM) or Akt activator SC79 (1 μM) was added 5 min before ACh. Mice rings were used to compare Nox2 deletion to normal acetylcholine-mediated relaxation. In rabbits, Hcy reduced acetylcholine-mediated relaxation vs. control (p < 0.0001). Treatment + Hcy reduced relaxation compared with treatment alone (p < 0.0001). Pyrogallol and SC79 reversed the response of GP + Hcy (p = 0.0001). In mice, Nox2 deletion reduced acetylcholine-mediated vasorelaxation. Rabbit tissue analysis revealed that Hcy reduced eNOS phosphorylation at Thr⁴⁹⁵ and increased eNOS phosphorylation at Ser¹¹⁷⁷; no further alteration at Thr⁴⁹⁵ was observed with GP. In contrast, GP prevented increased phosphorylation at Ser¹¹⁷⁷.

CONCLUSIONS

Apocynin, GP and PhoxI2 worsens acetylcholine-mediated vascular relaxation in rabbit aorta, which is supported by results from mouse Nox2 deletion data. These inhibitors worsen Hcy-induced vascular dysfunction, suggesting that current putative Nox2 inhibitors might not be useful in treating HHcy.

Ganoderma triterpenes Protect Against Hyperhomocysteinemia Induced Endothelial-Mesenchymal Transition via TGF-β Signaling Inhibition

Endothelial dysfunction is one of the most important pathological status in hyperhomocysteinemia (HHcy) related cardiovascular diseases. Whereas, the underlying mechanisms have not been fully elucidated yet, concomitant with the absence of effective treatment. The purpose of this study was to explore the main mechanisms involved in HHcy-induced endothelial injury and identify the protective effect of Ganoderma triterpenes (GT). Bovine aortic endothelial cells (BAECs) were applied as in vitro experimental model. The small molecular inhibitors were used to explore the signalings involved in HHcy-induced endothelial injury. The experimental results provided initial evidence that HHcy led to endothelial-mesenchymal transition (EndMT). Meanwhile, TGF-β/Smad, PI3K/AKT and MAPK pathways were activated in this process, which was demonstrated by pretreatment with TGF-β RI kinase inhibitor VI SB431542, PI3K inhibitor LY294002, p38 inhibitor SB203580, and ERK inhibitor PD98059. Furthermore, it was found that GT restrained the process of HHcy-induced EndMT via reducing oxidative stress and suppressing fore mentioned pathways with further inhibiting the activity of Snail. These results implicate that there is an untapped potential for GT as a novel therapeutic candidate for HHcy-induced EndMT through alleviating oxidative stress and canonical TGF-β/Smad and non-Smad dependent signaling pathways.

Glutamate triggers intracellular Ca2+ oscillations and nitric oxide release by inducing NAADP- and InsP3 -dependent Ca2+ release in mouse brain endothelial cells

The neurotransmitter glutamate increases cerebral blood flow by activating postsynaptic neurons and presynaptic glial cells within the neurovascular unit. Glutamate does so by causing an increase in intracellular Ca²⁺ concentration ([Ca²⁺ ]_i ) in the target cells, which activates the Ca²⁺ /Calmodulin-dependent nitric oxide (NO) synthase to release NO. It is unclear whether brain endothelial cells also sense glutamate through an elevation in [Ca²⁺ ]_i and NO production. The current study assessed whether and how glutamate drives Ca²⁺ -dependent NO release in bEND5 cells, an established model of brain endothelial cells. We found that glutamate induced a dose-dependent oscillatory increase in [Ca²⁺ ]_i , which was maximally activated at 200 μM and inhibited by α-methyl-4-carboxyphenylglycine, a selective blocker of Group 1 metabotropic glutamate receptors. Glutamate-induced intracellular Ca²⁺ oscillations were triggered by rhythmic endogenous Ca²⁺ mobilization and maintained over time by extracellular Ca²⁺ entry. Pharmacological manipulation revealed that glutamate-induced endogenous Ca²⁺ release was mediated by InsP₃ -sensitive receptors and nicotinic acid adenine dinucleotide phosphate (NAADP) gated two-pore channel 1. Constitutive store-operated Ca²⁺ entry mediated Ca²⁺ entry during ongoing Ca²⁺ oscillations. Finally, glutamate evoked a robust, although delayed increase in NO levels, which was blocked by pharmacologically inhibition of the accompanying intracellular Ca²⁺ signals. Of note, glutamate induced Ca²⁺ -dependent NO release also in hCMEC/D3 cells, an established model of human brain microvascular endothelial cells. This investigation demonstrates for the first time that metabotropic glutamate-induced intracellular Ca²⁺ oscillations and NO release have the potential to impact on neurovascular coupling in the brain.

Gliotransmitters and cytokines in the control of blood-brain barrier permeability

The contribution of astrocytes and microglia to the regulation of neuroplasticity or neurovascular unit (NVU) is based on the coordinated secretion of gliotransmitters and cytokines and the release and uptake of metabolites. Blood-brain barrier (BBB) integrity and angiogenesis are influenced by perivascular cells contacting with the abluminal side of brain microvessel endothelial cells (pericytes, astrocytes) or by immune cells existing (microglia) or invading the NVU (macrophages) under pathologic conditions. The release of gliotransmitters or cytokines by activated astroglial and microglial cells is provided by distinct mechanisms, affects intercellular communication, and results in the establishment of microenvironment controlling BBB permeability and neuroinflammation. Glial glutamate transporters and connexin and pannexin hemichannels working in the tight functional coupling with the purinergic system serve as promising molecular targets for manipulating the intercellular communications that control BBB permeability in brain pathologies associated with excessive angiogenesis, cerebrovascular remodeling, and BBB-mediated neuroinflammation. Substantial progress in deciphering the molecular mechanisms underlying the (patho)physiology of perivascular glia provides promising approaches to novel clinically relevant therapies for brain disorders. The present review summarizes the current understandings on the secretory machinery expressed in glial cells (glutamate transporters, connexin and pannexin hemichannels, exocytosis mechanisms, membrane-derived microvesicles, and inflammasomes) and the role of secreted gliotransmitters and cytokines in the regulation of NVU and BBB permeability in (patho)physiologic conditions.

An In Vitro Model of the Blood-Brain Barrier: Naegleria fowleri Affects the Tight Junction Proteins and Activates the Microvascular Endothelial Cells

Naegleria fowleri causes a fatal disease known as primary amoebic meningoencephalitis. This condition is characterized by an acute inflammation that originates from the free passage of peripheral blood cells to the central nervous system through the alteration of the blood-brain barrier. In this work, we established models of the infection in rats and in a primary culture of endothelial cells from rat brains with the aim of evaluating the activation and the alterations of these cells by N. fowleri. We proved that the rat develops the infection similar to the mouse model. We also found that amoebic cysteine proteases produced by the trophozoites and the conditioned medium induced cytopathic effect in the endothelial cells. In addition, N. fowleri can decrease the transendothelial electrical resistance by triggering the destabilization of the tight junction proteins claudin-5, occludin, and ZO-1 in a time-dependent manner. Furthermore, N. fowleri induced the expression of VCAM-1 and ICAM-1 and the production of IL-8, IL-1β, TNF-α, and IL-6 as well as nitric oxide. We conclude that N. fowleri damaged the blood-brain barrier model by disrupting the intercellular junctions and induced the presence of inflammatory mediators by allowing the access of inflammatory cells to the olfactory bulbs.

The Role of Endothelial Ca2+ Signaling in Neurovascular Coupling: A View from the Lumen

BACKGROUND

Neurovascular coupling (NVC) is the mechanism whereby an increase in neuronal activity (NA) leads to local elevation in cerebral blood flow (CBF) to match the metabolic requirements of firing neurons. Following synaptic activity, an increase in neuronal and/or astrocyte Ca2+ concentration leads to the synthesis of multiple vasoactive messengers. Curiously, the role of endothelial Ca2+ signaling in NVC has been rather neglected, although endothelial cells are known to control the vascular tone in a Ca2+-dependent manner throughout peripheral vasculature.

METHODS

We analyzed the literature in search of the most recent updates on the potential role of endothelial Ca2+ signaling in NVC.

RESULTS

We found that several neurotransmitters (i.e., glutamate and acetylcholine) and neuromodulators (e.g., ATP) can induce dilation of cerebral vessels by inducing an increase in endothelial Ca2+ concentration. This, in turn, results in nitric oxide or prostaglandin E2 release or activate intermediate and small-conductance Ca2+-activated K⁺ channels, which are responsible for endothelial-dependent hyperpolarization (EDH). In addition, brain endothelial cells express multiple transient receptor potential (TRP) channels (i.e., TRPC3, TRPV3, TRPV4, TRPA1), which induce vasodilation by activating EDH.

CONCLUSIONS

It is possible to conclude that endothelial Ca2+ signaling is an emerging pathway in the control of NVC.

Alamandine reverses hyperhomocysteinemia-induced vascular dysfunction via PKA-dependent mechanisms

INTRODUCTION

Hyperhomocysteinemia (HHcy) impairs nitric oxide endothelium-dependent vasodilation, consequently leading to atherosclerosis, a risk factor for cardiovascular disease. Novel treatments for HHcy are necessary.

AIM

We tested the hypothesis that alamandine, a vasoactive peptide of the renin-angiotensin system (RAS), could reverse HHcy-induced vascular dysfunction through the MrgD receptor and that this is mediated by the protein kinase A (PKA) pathway. Furthermore, we sought to determine a putative binding model of alamandine to the MrgD receptor through docking and molecular dynamics simulations.

METHOD

The abdominal aorta was excised from New Zealand white rabbits (n = 15) and incubated with 3 mmol/L Hcy (to mimic HHcy) to induce vascular dysfunction in vitro. Vascular function was assessed by vasodilatory responses to cumulative doses of acetylcholine.

RESULT

Vasodilation was significantly impaired in HHcy-incubated aortic rings while alamandine reversed this effect (control, 74.2 ± 5.0%; Hcy, 30.3 ± 9.8%; alamandine + Hcy, 59.7 ± 4.8%, P < .0001). KT5720 (PKA inhibitor) significantly inhibited the ability of alamandine to attenuate the impaired vasodilation caused by HHcy (KT5720 + Hcy + alamandine, 27.1 ± 24.1, P < .01). Following immunohistochemistry analysis, the MrgD receptor was highly expressed within the media and endothelial layer of aortic rings in HHcy compared to control (media: 0.23 ± 0.003 vs control 0.16 ± 0.01, P < .05 and endothelium: 0.68 ± 0.07 vs control 0.13 ± 0.02, P < .01, in PA/I (A.U) units). Computational studies also propose certain interactions of alamandine within the MrgD transmembrane domain.

CONCLUSION

This study shows that alamandine is effective in reversing HHcy-induced vascular dysfunction, possibly through the PKA signaling pathway via MrgD. Our results indicate a therapeutic potential of alamandine in reversing the detrimental effects of HHcy.

Inducible nitric oxide synthase: Good or bad?

Nitric oxide synthases (NOS) are a family of isoforms responsible for the synthesis of the potent dilator nitric oxide (NO). Expression of inducible NOS (iNOS) occurs in conditions of inflammation, and produces large amounts of NO. In pathological conditions iNOS is regarded as a harmful enzyme and is proposed to be a major contributor to diseases of the cardiovascular system such as atherosclerosis. In this review, we address the notion that iNOS is a detrimental enzyme in disease and discuss its potentially beneficial roles. Additionally, we describe other molecules associated with iNOS in diseases such as atherosclerosis, and current research on therapeutic inhibitors tested to reduced pathology associated with cardiovascular diseases (CVD).

The connexin 43/ZO-1 complex regulates cerebral endothelial F-actin architecture and migration

Endothelial cell migration is a fundamental process during angiogenesis and, therefore, a point of intervention for therapeutic strategies aimed at controlling pathologies involving blood vessel growth. We sought to determine the role of the gap junction protein connexin 43 (Cx43) in key features of angiogenesis in the central nervous system. We used an in vitro model to test the hypothesis that a complex of interacting proteins, including Cx43 and zonula occludens-1 (ZO-1), regulates the migratory behavior of cerebral endothelium. With knockdown and overexpression experiments, we demonstrate that the rate of healing following scrape-wounding of endothelium is regulated by the level of Cx43 protein expression. The effects on cell motility and proliferation were independent of gap junction communication as cells were sensitive to altered Cx43 expression in single plated cells. Coupling of Cx43/ZO-1 critically regulates this process as demonstrated with the use of a Cx43 α-carboxy terminus 1 peptide mimetic (αCT1) and overexpression of a mutant ZO-1 with the Cx43-binding PDZ2 domain deleted. Disrupting the Cx43/ZO-1 complex with these treatments resulted in collapse of the organized F-actin cytoskeleton and the appearance of actin nodes. Preincubation with the myosin 2 inhibitors blebbistatin or Y-27632 disrupted the Cx43/ZO-1 complex and inhibited cell spreading at the leading edge of migration. Cells studied individually in time-lapse open field locomotion assays wandered less when Cx43/ZO-1 interaction was disrupted without significant change in speed, suggesting that faster wound healing is a product of linearized migration. In contrast to the breakdown of F-actin architecture, microtubule architecture was not obviously affected by treatments. This study provides new insight into the fundamental regulatory mechanisms of cerebral endothelial cell locomotion. Cx43 tethers the F-actin cytoskeleton through a ZO-1 linker and supports cell spreading and exploration during locomotion. Here, we demonstrate that releasing this actin-coupled tether shifts the balance of directional migration control to a more linear movement that enhances the rate of wound healing.

Homocysteine disrupts outgrowth of microvascular endothelium by an iNOS-dependent mechanism

OBJECTIVE

To test the hypothesis that Hcy impairs angiogenic outgrowth through an iNOS-dependent mechanism.

METHODS

Adult C57Bl/6 mouse choroid explants were used in angiogenic outgrowth assays. Mouse microvascular endothelial cells were studied in culture during scrape-induced migration and dispersed cell locomotion experiments. Activity of iNOS was manipulated with pharmacology (1400 W), siRNA, and by use of choroid explants from iNOS knockout mice (iNOS(-/-)).

RESULTS

Hcy (20 μM) significantly decreased the area of endothelial outgrowth without altering the number of cells in the choroid explant angiogenic assay, resulting in more densely packed outgrowth. Hcy prevented the outward orientation of actin filaments and decreased the number of actin projections along the leading edge of outgrowth. Hcy also slowed outgrowth from the edge of a scraped endothelial monolayer and in cultures of dispersed cells, Hcy impaired cell locomotion without affecting proliferation. Inhibition of iNOS activity rescued the effect of Hcy on area of explant outgrowth, cell density, number of projections, cell locomotion, and rate of outgrowth following scraping.

CONCLUSIONS

Hcy impairs microvascular endothelial outgrowth, but not proliferation, by disrupting cell locomotion through an iNOS-dependent mechanism.

Opening of the blood-brain barrier before cerebral pathology in mild hyperhomocysteinemia

Hyperhomocysteinemia (HHcy) is a risk factor for cognitive impairment. The purpose of this study was to determine the temporal pattern of cerebral pathology in a mouse model of mild HHcy, because understanding this time course provides the basis for understanding the mechanisms involved. C57Bl/6 mice with heterozygous deletion cystathionine β-synthase (cbs^+/−; Het) were used as a model of mild HHcy along with their wild-type littermates (cbs^+/+; WT). Mice were ‘young’ (5.3±0.2 months of age) and ‘old’ (16.6±0.9 months of age). Blood-brain barrier (BBB) permeability was quantified from Evans blue and sodium fluorescein extravasation. Microvascular architecture was assessed by z-stack confocal microscopy. Leukoaraiosis was measured from Luxol fast blue stained slides of paraffin brain sections. Inflammation was quantified using standard antibody-based immunohistochemical techniques. Cognitive function was assessed using the Morris water maze. BBB permeability was significantly greater in Het vs. WT mice at all ages (p<0.05). There were no differences in microvascular architecture among the groups. Compared with all other groups, old Het mice had significantly greater leukoaraiosis, inflammation in the fornix, and cognitive impairment (p<0.05). In mild HHcy, increased permeability of the BBB precedes the onset of cerebral pathology. This new paradigm may play a role in the progression of disease in HHcy.

Oxidant stress and signal transduction in the nervous system with the PI 3-K, Akt, and mTOR cascade

Oxidative stress impacts multiple systems of the body and can lead to some of the most devastating consequences in the nervous system especially during aging. Both acute and chronic neurodegenerative disorders such as diabetes mellitus, cerebral ischemia, trauma, Alzheimer’s disease, Parkinson’s disease, Huntington’s disease, and tuberous sclerosis through programmed cell death pathways of apoptosis and autophagy can be the result of oxidant stress. Novel therapeutic avenues that focus upon the phosphoinositide 3-kinase (PI 3-K), Akt (protein kinase B), and the mammalian target of rapamycin (mTOR) cascade and related pathways offer exciting prospects to address the onset and potential reversal of neurodegenerative disorders. Effective clinical translation of these pathways into robust therapeutic strategies requires intimate knowledge of the complexity of these pathways and the ability of this cascade to influence biological outcome that can vary among disorders of the nervous system.