Selective killing of cholinergic neurons by microglial activation in basal forebrain mixed neuronal/glial cultures

DE-71 affected the cholinergic system and locomotor activity via disrupting calcium homeostasis in zebrafish larvae

Polybrominated diphenyl ethers (PBDEs) can induce neurotoxicity, but the mechanism of their toxicity on the cholinergic system and locomotion behavior remains unclear. In this paper, zebrafish embryos were exposed to DE-71 (0, 1, 3, 10, 30, and 100 µg/L) until 120 h post fertilization, and its effects on the behavior and cholinergic system of zebrafish larvae and its possible mechanism were investigated. Results indicated a general locomotor activity impairment in the light-dark transition stimulation without affecting the secondary motoneurons. However, with the extension of test time in the dark or light, the decreased locomotor activity was diminished, a significant decrease only observed in the 100 µg/L DE-71 exposure groups in the last 10 min. Furthermore, whole-body acetylcholine (ACh) contents decreased after DE-71 exposure, whereas no changes in NO contents and inducible nitric oxide synthase activity were found. The expression of certain genes encoding calcium homeostasis proteins (e.g., grin1a, camk2a, and crebbpb) and the concentrations of calcium in zebrafish larvae were significantly decreased after DE-71 exposure. After co-exposure with calcium channel agonist (±)-BAY K8644, calcium concentrations, ACh contents, and locomotor activity in the light-dark transition stimulation was significantly increased compared with the same concentrations of DE-71 exposure alone, whereas no significant difference was observed compared with the control, indicating that calcium homeostasis is involved in the impairment of cholinergic neurotransmission and locomotor activity. Overall, our results suggested that DE-71 can impair the cholinergic system and locomotor activity by impairing calcium homeostasis. Our paper provides a better understanding of the neurotoxicity of PBDEs.

Lipopolysaccharide-Induced Neuroinflammation as a Bridge to Understand Neurodegeneration

A large body of experimental evidence suggests that neuroinflammation is a key pathological event triggering and perpetuating the neurodegenerative process associated with many neurological diseases. Therefore, different stimuli, such as lipopolysaccharide (LPS), are used to model neuroinflammation associated with neurodegeneration. By acting at its receptors, LPS activates various intracellular molecules, which alter the expression of a plethora of inflammatory mediators. These factors, in turn, initiate or contribute to the development of neurodegenerative processes. Therefore, LPS is an important tool for the study of neuroinflammation associated with neurodegenerative diseases. However, the serotype, route of administration, and number of injections of this toxin induce varied pathological responses. Thus, here, we review the use of LPS in various models of neurodegeneration as well as discuss the neuroinflammatory mechanisms induced by this toxin that could underpin the pathological events linked to the neurodegenerative process.

Adolescent binge ethanol-induced loss of basal forebrain cholinergic neurons and neuroimmune activation are prevented by exercise and indomethacin

Basal forebrain cholinergic neurons mature in adolescence coinciding with development of adult cognitive function. Preclinical studies using the rodent model of adolescent intermittent ethanol (AIE; 5.0 g/kg, i.g., 2-days on/2-days off from postnatal day [P]25 to P55) reveal persistent increases of brain neuroimmune genes that are associated with cognitive dysfunction. Adolescent intermittent ethanol exposure also reduces basal forebrain expression of choline acetyltransferase (ChAT), an enzyme critical for acetylcholine synthesis in cholinergic neurons similar to findings in the post-mortem human alcoholic basal forebrain. We report here that AIE decreases basal forebrain ChAT+IR neurons in both adult female and male Wistar rats following early or late adolescent ethanol exposure. In addition, we find reductions in ChAT+IR somal size as well as the expression of the high-affinity nerve growth factor (NGF) receptor tropomyosin receptor kinase A (TrkA) and the low-affinity NGF receptor p75NTR, both of which are expressed on cholinergic neurons. The decrease in cholinergic neuron marker expression was accompanied by increased phosphorylation of NF-κB p65 (pNF-κB p65) consistent with increased neuroimmune signaling. Voluntary wheel running from P24 to P80 prevented AIE-induced cholinergic neuron shrinkage and loss of cholinergic neuron markers (i.e., ChAT, TrkA, and p75NTR) as well as the increase of pNF-κB p65 in the adult basal forebrain. Administration of the anti-inflammatory drug indomethacin (4.0 mg/kg, i.p prior to each ethanol exposure) during AIE also prevented the loss of basal forebrain cholinergic markers and the concomitant increase of pNF-κB p65. In contrast, treatment with the proinflammatory immune activator lipopolysaccharide (1.0 mg/kg, i.p. on P70) caused a loss of cholinergic neuron markers that was paralleled by increased pNF-κB p65 in the basal forebrain. These novel findings are consistent with AIE causing lasting activation of the neuroimmune system that contributes to the persistent loss of basal forebrain cholinergic neurons in adulthood.

Adolescent, but not adult, binge ethanol exposure leads to persistent global reductions of choline acetyltransferase expressing neurons in brain

During the adolescent transition from childhood to adulthood, notable maturational changes occur in brain neurotransmitter systems. The cholinergic system is composed of several distinct nuclei that exert neuromodulatory control over cognition, arousal, and reward. Binge drinking and alcohol abuse are common during this stage, which might alter the developmental trajectory of this system leading to long-term changes in adult neurobiology. In Experiment 1, adolescent intermittent ethanol (AIE; 5.0 g/kg, i.g., 2-day on/2-day off from postnatal day [P] 25 to P55) treatment led to persistent, global reductions of choline acetyltransferase (ChAT) expression. Administration of the Toll-like receptor 4 agonist lipopolysaccharide to young adult rats (P70) produced a reduction in ChAT+IR that mimicked AIE. To determine if the binge ethanol-induced ChAT decline was unique to the adolescent, Experiment 2 examined ChAT+IR in the basal forebrain following adolescent (P28-P48) and adult (P70-P90) binge ethanol exposure. Twenty-five days later, ChAT expression was reduced in adolescent, but not adult, binge ethanol-exposed animals. In Experiment 3, expression of ChAT and vesicular acetylcholine transporter expression was found to be significantly reduced in the alcoholic basal forebrain relative to moderate drinking controls. Together, these data suggest that adolescent binge ethanol decreases adult ChAT expression, possibly through neuroimmune mechanisms, which might impact adult cognition, arousal, or reward sensitivity.

Inflammation and the pathophysiology of Alzheimer's disease

There is increasing evidence that a chronic inflammatory response in the brain in Alzheimer's disease (AD) ultimately leads to neuronal injury and cognitive decline. Microglia, the primary immune effector cells of the brain, are thought to be key to this process. This paper discusses the evidence for inflammation in AD, and describes the mechanism whereby microglia generate neurotoxic cytokines, reactive oxygen species, and nitric oxide. Evidence that the cytokine macrophage colony-stimulating factor (M-CSF) is an important cofactor in microglial activation in AD is presented. Ongoing work using organotypic hippocampal expiant cultures to model the inflammatory process in the AD brain is also discussed. Potential avenues for therapeutic intervention are outlined.

Microglia-inhibiting activity of Parkinson's disease drug amantadine

Amantadine is currently used as an antiviral and an antiparkinsonian drug. Although the drug is known to bind a viral proton channel protein, the mechanism of action in Parkinson's disease (PD) remains to be determined. This study investigated whether the drug has an inhibitory effect on microglial activation and neuroinflammation, which have been implicated in the progression of neurodegenerative processes. Using cultured microglial cells, it was demonstrated that the drug inhibited inflammatory activation of microglia and a signaling pathway that governs the microglial activation. The drug reduced the expression and production of proinflammatory mediators in bacterial lipopolysaccharide-stimulated microglia cells. The microglia-inhibiting activity of amantadine was also demonstrated in a microglia/neuron coculture and animal models of neuroinflammation and Parkinson's disease. Collectively, our results suggest that amantadine may act on microglia in the central nervous system to inhibit their inflammatory activation, thereby attenuating neuroinflammation. These results provide a molecular basis of the glia-targeted mechanism of action for amantadine.

The endotoxin-induced neuroinflammation model of Parkinson's disease

Parkinson's disease (PD) is a common neurodegenerative disorder characterized by the progressive loss of dopaminergic (DA) neurons in the substantia nigra. Although the exact cause of the dopaminergic neurodegeneration remains elusive, recent postmortem and experimental studies have revealed an essential role for neuroinflammation that is initiated and driven by activated microglial and infiltrated peripheral immune cells and their neurotoxic products (such as proinflammatory cytokines, reactive oxygen species, and nitric oxide) in the pathogenesis of PD. A bacterial endotoxin-based experimental model of PD has been established, representing a purely inflammation-driven animal model for the induction of nigrostriatal dopaminergic neurodegeneration. This model, by itself or together with genetic and toxin-based animal models, provides an important tool to delineate the precise mechanisms of neuroinflammation-mediated dopaminergic neuron loss. Here, we review the characteristics of this model and the contribution of neuroinflammatory processes, induced by the in vivo administration of bacterial endotoxin, to neurodegeneration. Furthermore, we summarize the recent experimental therapeutic strategies targeting endotoxin-induced neuroinflammation to elicit neuroprotection in the nigrostriatal dopaminergic system. The potential of the endotoxin-based PD model in the development of an early-stage specific diagnostic biomarker is also emphasized.

Neuroinflammation not associated with cholinergic degeneration in aged-impaired brain

Degeneration of the cholinergic neurons in the basal forebrain and elevation of inflammatory markers are well-established hallmarks of Alzheimer's disease; however, the interplay of these processes in normal aging is not extensively studied. Consequently, we conducted a neuroanatomical investigation to quantify cholinergic neurons and activated microglia in the medial septum/vertical diagonal band (MS/VDB) of young (6 months) and aged (28 months) Fisher 344 × Brown Norway F(1) rats. Aged rats in this study were impaired relative to the young animals in spatial learning ability as assessed in the Morris water maze. Stereological analysis revealed no difference between aged and young rats in the total numbers of cholinergic neurons, demonstrating that loss of cholinergic neurons is not a necessary condition to observe impaired spatial learning in aged rats. In this same region, the total number of activated microglia was substantially greater in aged rats relative to young rats. Jointly, these data demonstrate that aging is characterized by an increase in the basal inflammatory state within the MS/VDB, but this inflammation is not associated with cholinergic neuron death.

Benzamide protects delayed neuronal death and behavioural impairment in a mouse model of global cerebral ischemia

The present study is aimed at evaluating the functional and neuroprotective effect of benzamide, a poly-(ADP-ribose) polymerase (PARP) inhibitor on delayed neuronal death (DND) in hippocampus CA1 region and memory impairment following global cerebral ischemia (GCI) in a mouse model. GCI was induced by bilateral common carotid artery occlusion (BCAo) for 20 min followed by reperfusion for 9 days. Postischemic continuous treatment with benzamide (160 mg/kg b w i.p. for 9 days) significantly reversed the GCI-induced anterograde memory impairment in passive avoidance step through and elevated plus maze tasks. The observed memory impairment in vehicle treated ischemia group was found to be well correlated with DND and downregulation of cholinergic muscarinic receptor-1 expression, which was possibly mediated by inflammation and apoptosis, as revealed from inducible nitric oxide synthase (iNOS) expression and number of TUNEL positive neurons in hippocampus CA1 region. It is clear from the present experiment that benzamide treatment significantly decreases the iNOS expression and number of apoptotic neurons and thereby improves the neuronal survival and memory during GCI. Our present findings provide compelling evidence that multiple doses of benzamide treatment is a promising therapeutic approach for cerebrovascular and neurodegenerative diseases, which deserves further clinical evaluation.

PMS777, A Bis-interacting Ligand for PAF Receptor Antagonism and AChE Inhibition, Attenuates PAF-induced Neurocytotoxicity in SH-SY5Y Cells

(1) HIV-1 and viral proteins-evoked chronic brain inflammation, which is characterized by microglial activation, is the pivotal neuropathogenesis of HIV-1-associated dementia (HAD). Platelet-activating factor (PAF), mainly released from activated microglia and acts as a high potent inflammatory mediator and a neurotoxin, is indicated to be a principle initiator of neuroinflammation, neuronal dysfunction, and apoptosis related to HAD. Thus, bis-interacting ligands of acetylcholinesterase (AChE) inhibition and PAF receptor antagonism would be of great interest in the therapeutic potential of HAD not only for improvement of cognitive performance, but also for disease-modifying. (2). We have previously reported that a novel tetrahydrofuran-derived bis-interacting ligand PMS777 had satisfying potencies for PAF receptor blockade and AChE inhibition, and markedly improved cholinergic dysfunction-induced cognitive impairment in mice. Continuing with our research, we further investigated the neuroprotective activities of PMS777 on PAF-triggered neuronal injury in human neuroblastoma SH-SY5Y cells. (3) The bis-interacting ligand PMS777 (10 muM) obviously alleviated PAF-induced cell apoptosis in SH-SY5Y cells. Pretreatment with PMS777 also markedly inhibited intracellular Ca(2+) overload, down-regulation of anti-apoptotic bcl-2 mRNA, stimulation of pro-apoptotic bax mRNA expression and activation of caspase-3 pathway. Also, PMS777 could fine-tune pro-inflammatory cyclooxygenase-2 (cox-2) mRNA expression in PAF-treated cells. (4) These results suggest that PMS777 possesses a neuroprotective profile via anti-apoptotic/inflammatory signaling and warrant further investigations in connection with the potential value of this compound in HAD treatment.

Effect of anti-dementia drugs on LPS induced neuroinflammation in mice

Inflammation has been recently implicated in pathogenesis of dementia disorders. Effect of anti-dementia (Acetylcholinesterase inhibitor) drugs tacrine, rivastigmine and donepezil were studied on neuroinflammation induced by intraperitoneal administration of lipopolysaccharide (LPS) in mice. Interleukin-2 (IL-2) and isoforms of acetylcholinesterase (AChE) were estimated in different brain areas as marker for neuroinflammation and cholinergic activity respectively. LPS significantly increased the level of IL-2 in all the brain areas while enhancement of AChE activity varied in brain areas. It was found that administration of tacrine, rivastigmine and donepezil in mice significantly attenuated the LPS induced increased levels of IL-2 along with the significant reduction of AChE activity predominantly in salt soluble (SS) fraction as compared to the detergent soluble (DS) fraction in a dose dependent manner. In vitro effect of LPS was also studied in different brain areas. LPS significantly increased the AChE activity in SS fractions but the significant increase was not found in DS fractions. The present study indicate that cholinesterase inhibitor anti-dementia drugs are effective against LPS induced neuroinflammation that may be linked to enhanced cholinergic activity.

Potential role of N-methyl-D-aspartate receptors as executors of neurodegeneration resulting from diverse insults: focus on memantine

Glutamatergic neurotransmission is critical to normal learning and memory and when the activity of glutamate neurons becomes excessive, or the normal function of its primary receptors becomes dysfunctional, this may lead to pathological changes associated with age-related neurodegenerative diseases. Anomalous glutamatergic activity associated with Alzheimer's disease may be due to a postsynaptic receptor and downstream defects that produce inappropriately timed or sustained glutamate activation of N-methyl-D-aspartate receptors, leading to neuronal injury and death and cognitive deficits associated with dementia. The mechanisms leading to the condition of chronically depolarized membranes on vulnerable neurons in the Alzheimer's disease brain are likely due to a complex interaction between oxidative stress, mitochondrial failure, chronic brain inflammation and the presence of amyloid-beta and hyperphosphorylated-tau; each of these factors are highly interrelated with each other and are discussed with an emphasis upon potential therapeutic mechanisms underlying the neuroprotective actions of memantine.

Interaction of interleukin-1beta with muscarinic acetylcholine receptor-mediated signaling cascade in cholinergically differentiated SH-SY5Y cells

Increased expression of interleukin (IL)-1beta has been found in Alzheimer brain, raising the question whether plaque-associated up-regulation of IL-1beta may contribute to neurodegeneration. IL-1beta is capable to induce a number of events that also occur in Alzheimer's disease such as stimulation of the amyloidogenic pathway of amyloid precursor protein processing. However, less is known on participation of IL-1beta in specific cholinergic cell loss. To reveal whether IL-1beta affects muscarinic acetylcholine receptor (mAChR)-mediated intracellular signaling, cholinergically differentiated SH-SY5Y cells were exposed to IL-1beta for various periods of time followed by stimulation of mAChR with carbachol for 1 h, and key molecules of cholinergic signaling cascades were determined including phosphoinositide hydrolysis, DNA-binding capacity of NFkappaB and AP-1, and activity of acetylcholinesterase (AChE). Carbachol stimulation of SH-SY5Y cells dose-dependently stimulated the activation of the transcription factors NFkappaB and AP-1 as revealed by electrophoretic mobility shift assay (EMSA), while pre-exposure of SH-SY5Y cells for 24 h with 1 ng/ml IL-1beta completely suppressed the carbachol response. mAChR-mediated enhancements of AChE activity by carbachol were impaired following pre-exposure of SH-SY5Y cells with IL-1beta, already detectable at a concentration of 1 ng/ml and 1 h of exposure time. The data indicate that IL-1beta may interfere with the cholinergic signal transduction cascade by inhibiting transcription factor activation, thus providing another mechanism by which IL-1beta may induce cholinergic dysfunction in Alzheimer's disease.

Basal forebrain cholinergic dysfunction in Alzheimer's disease--interrelationship with beta-amyloid, inflammation and neurotrophin signaling

Alzheimer's disease, the most common neurodegenerative disorder of senile dementia, is characterized by two major morpho-pathological hallmarks. Deposition of extracellular neuritic, beta-amyloid peptide-containing plaques (senile plaques) in cerebral cortical regions of Alzheimer patients is accompanied by the presence of intracellular neurofibrillary tangles in cerebral pyramidal neurons. Basal forebrain cholinergic dysfunction is also a consistent feature of Alzheimer's disease, which has been suggested to cause, at least partly, the cognitive deficits observed in patients with Alzheimer's disease. Impaired cortical cholinergic neurotransmission may also contribute to beta-amyloid plaque pathology in Alzheimer's disease by affecting expression and processing of the beta-amyloid precursor protein (APP). Vice versa, low level of soluble beta-amyloid has been observed to inhibit cholinergic synaptic function. Deposition of beta-amyloid plaques in Alzheimer's disease is also accompanied by a significant plaque-associated glial up-regulation of interleukin-1, which has been attributed to affect expression and metabolism of APP and to interfere with cholinergic transmission. Understanding the molecular mechanisms underlying the interrelationship between cortical cholinergic dysfunction, beta-amyloid formation and deposition, as well as local inflammatory upregulation, would allow to derive potential treatment strategies to pharmacologically intervene in the disease-causing signaling cascade.

Brain cholinergic vulnerability: Relevance to behavior and disease

The major populations of cholinergic neurons in the brain include two "projection" systems, located in the pontine reticular formation and in the basal forebrain. These two complexes comprise, in part, the anatomical substrates for the "ascending reticular activating system" (ARAS). The pontine cholinergic system relays its rostral influences mainly through thalamic intralaminar nuclei, but it also connects to the basal forebrain and provides a minor innervation of cortex. The basal forebrain cholinergic complex (BFCC) projects directly to cortex and hippocampus, and has a minor connection with the thalamus. Recent data reveal that a parallel system of basal forebrain GABAergic projection neurons innervates cortex/hippocampus in a way that seems to complement the BFCC. Generally, the picture developed from more than 50 years of research is consistent with a "global" influence of these two ascending cholinergic projections on cortical and hippocampal regions. Seemingly, the BFCC acts in tandem or in parallel with the pontine cholinergic projection to activate the electro-encephalogram, increase cerebral blood flow, regulate sleep-wake cycling, and modulate cognitive function. There are quite a number and variety of human brain conditions, notably including Alzheimer's disease, in which degeneration of basal forebrain cholinergic neurons has been documented. Whether the corticopetal GABA system is affected by disease has not been established. Studies of degeneration of the pontine projection are limited, but the available data suggest that it is relatively preserved in Alzheimer's disease. Hypotheses of BFCC degeneration include growth factor deprivation, intracellular calcium dysfunction, amyloid excess, inflammation, and mitochondrial abnormalities/oxidative stress. But, despite considerable research conducted over several decades, the exact mechanisms underlying brain cholinergic vulnerability in human disease remain unclear.

Modulation of human microglia and THP-1 cell toxicity by cytokines endogenous to the nervous system

Neuroinflammatory processes are thought to be a significant factor in the pathology of a number of degenerative neurological diseases. A variety of cytokines influence inflammatory levels. Here we show that a cooperative action of two or more cytokines is required to induce significantly human microglial and monocytic THP-1 cell toxicity towards SH-SY5Y neuroblastoma cells. Such toxicity was induced by the following combinations: interferon-gamma (IFN-gamma) with tumor necrosis factor-alpha (TNF-alpha); IFN-gamma with interleukin (IL) 1alpha or IL-1beta in the presence of TNF-alpha; and IL-6 with TNF-alpha. Toxicity induced by the various stimulatory combinations was not accompanied by an increased nitrite production. Of the potential inhibitors tested, IL-4 downregulated the toxic action of microglia when applied to THP-1 cells either before stimulation or 24 h after stimulation. Toxicity was not inhibited by IL-10, and was even enhanced by transforming growth factor-beta1 (TGF-beta1) and basic fibroblast growth factor (bFGF). These data suggest that antagonists of cytokine receptors, as well as inhibitors of their intracellular pathways may be effective anti-inflammatory agents.

Minocycline prevents cholinergic loss in a mouse model of Down's syndrome

Individuals with Down's syndrome develop Alzheimer's-like pathologies comparatively early in life, including progressive degeneration of basal forebrain cholinergic neurons (BFCNs). Cholinergic hypofunction contributes to dementia-related cognitive decline and remains a target of therapeutic intervention for Alzheimer's disease. In light of this, partial trisomy 16 (Ts65Dn) mice have been developed to provide an animal model of Down's syndrome that exhibits progressive loss of BFCNs and cognitive ability. Another feature common to both Down's syndrome and Alzheimer's disease is neuroinflammation, which may exacerbate neurodegeneration, including cholinergic loss. Minocycline is a semisynthetic tetracycline with antiinflammatory properties that has demonstrated neuroprotective properties in certain disease models. Consistent with a role for inflammatory processes in BFCN degeneration, we have shown previously that minocycline protects BFCNs and improves memory in mice with acute, immunotoxic BFCN lesions. We now report that minocycline treatment inhibits microglial activation, prevents progressive BFCN decline, and markedly improves performance of Ts65Dn mice on a working and reference memory task. Minocycline is an established antiinflammatory and neuroprotective drug and may provide a novel approach to treat specific AD-like pathologies.

Effect of tetrahydrobiopterin on nitric oxide synthase-containing cells in the rat hippocampus

We have observed that tetrahydrobiopterin (BH4), a cofactor of nitric oxide synthase (NOS), acts as a self-protection factor against nitric oxide (NO) toxicity in PC12 cells. To further investigate the self-protection action of BH4 in vivo, the effect of deletion of endogenous BH4 on NO-producing cells was examined in the rat hippocampus. Following the peripheral infusion of 50 mM 2,4-diamino-6-hydroxypyrimidine (DAHP), an inhibitor of GTP cyclohydrolase I, using a miniosmotic pump for 14 days, BH4 content in the hippocampus decreased as compared with the control group administered with vehicle solution, which had no effect on brain BH4 content. When the rats were administered with 50 mM DAHP and 10 mM BH4, the DAHP-induced decrease in BH4 content was prevented. The extracellular concentration of NO metabolites remained unchanged following DAHP administration, suggesting that DAHP-induced decrease in BH4 content had no effect on NO production. The number of NOS-positive cells decreased following DAHP administration in the hippocampal regions, while the number of NOS-negative cells remained unchanged. The DAHP-induced decrease in the NOS-positive cell number was prevented by the administration of 10 mM BH4 and DAHP. These results suggest that endogenous BH4 may affect NOS-positive cell number in the rat hippocampus.

Effects of lipopolysaccharide on consolidation of partial learning in the Y-maze

Research on consolidation of long-term memory suggests that acute immune system activation induced by endotoxin lipopolysaccharide (LPS) may disrupt consolidation of newly acquired learning. Adult male Sprague-Dawley rats were trained to perform a simple Y-maze task and were immediately afterwards administered LPS (15 microg/kg) or saline. After a seven-day interval, subjects were returned to the Y-maze and were retrained to criterion. It was found that subjects treated with saline required significantly fewer trials to relearn the task relative to the LPS group and a no-partial-learning control group, which themselves did not differ. These results are most readily explained in terms of a disruptive effect of acute immune system activation on consolidation of newly induced acquired memories.

A polymorphism of the interleukin-1 beta gene at position +3953 influences progression and neuro-pathological hallmarks of Alzheimer’s disease

Interleukin-1 (IL-1) gene polymorphisms are associated with an increased risk of Alzheimer's disease (AD) and it has been suggested that altered immune responses of the brain may play a role in the pathogenesis of the disease. Here we investigated whether IL-1beta polymorphisms affected neuro-pathological features and clinical status of AD patients with autopsy confirmed diagnosis of the disease. AD patients (n=133) were genotyped for the polymorphic regions in the apolipoprotein E epsilon (APOE epsilon) and interleukin-1beta (IL-1beta) genes. APOE epsilon4 carriers showed increased neuritic amyloid plaques (NP) and neurofibrillary tangles (NFT). The IL-1beta +3953 polymorphism influenced survival in AD patients and those with the TT genotype and without the APOE epsilon4 allele showed the shortest cumulative survival. Patients with the +3953 IL-1beta T and without the APOE epsilon4 alleles had reduced NP and NFT, a delayed ages at onset and death, but a decreased duration of the disease. On the other hand a different polymorphism of the IL-1beta gene at position -511 did not influence any AD features. Our findings suggest that IL-1beta gene by affecting brain immune responses may influence the age at onset of the disease, survival and AD progression.

Lessons from the AN 1792 Alzheimer vaccine: lest we forget

Recent clinical and neuropathological data show that the AN 1792 vaccine enhanced the production of Abeta antibodies in the sera of Alzheimer's disease (AD) patients, but it appears to have been ineffective at stimulating the removal of Abeta deposits from the brain or at slowing the rate of cognitive decline. The 19 cases of meningoencephalitis were not linked in an obvious way to serum antibody titre, but they may have been linked to infiltration of the brain by antibodies and/or T-cells. Brain imaging indicated that oedema associated with the neuroinflammation did not reflect the typical distribution of neuritic plaques in AD. These outcomes were not anticipated by experiments on transgenic mice because compared to humans, these mice have less genetic variability, and their plaques have a different chemical composition, making them far more soluble and easier to remove. Furthermore, the consequences of vaccination are different. Vaccination of transgenic mice removes superfluous human Abeta while leaving endogenous mouse Abeta intact, whereas in humans the immune response is directed against an endogenous target that occurs naturally and is present in healthy brain tissue. The most important lesson to be learned from the AN 1792 trials is that new strategies for treating AD should not be tested on humans until they have been extensively tested on non-murine species.

Microglia release activators of neuronal proliferation mediated by activation of mitogen-activated protein kinase, phosphatidylinositol-3-kinase/Akt and delta-Notch signalling cascades

Microglia, the resident macrophage of the brain, can release substances that aid neuronal development, differentiation and survival. We have investigated the effects of non-activated microglia on the survival of cultured rat cerebellar granule neurones. Microglial-conditioned medium, collected from primary rat microglial cultures, was used to treat 7-day-in-vitro neurones, and neuronal viability and proliferation was assessed following a further 1 or 7 days in culture. Microglial-conditioned medium enhanced neuronal survival by up to 50% compared with untreated neurones and this effect was completely abated by pretreatment of the microglia with l-leucine methyl ester. The expression of the proliferation marker Ki-67 increased in neuronal cultures treated with microglial-conditioned medium suggesting enhanced proliferation of precursor neurones. Microglial-induced neuronal proliferation could be attenuated by specific inhibition of mitogen-activated protein kinase or phosphatidylinositol-3-kinase/Akt signalling pathways, and by selective fractionation and immunodepletion of the microglial-conditioned medium. Activation of the Notch pathway was enhanced as antibody against the Notch ligand, delta-1, prevented the microglial-induced neuronal proliferation. These results show that microglia release stable neurotrophic factors that can promote neuronal precursor cell proliferation.

Minocycline protects basal forebrain cholinergic neurons from mu p75-saporin immunotoxic lesioning

Two prominent characteristics of Alzheimer's disease are basal forebrain cholinergic degeneration and neuroinflammation characterized by glial activation and the release of pro-inflammatory cytokines. Mu p75- saporin (SAP) is a novel immunotoxin that mimics the selective loss of basal forebrain cholinergic neurons and induces cognitive impairment in mice. We report that cholinergic cell loss in the medial septal nucleus and ventral diagonal band after i.c.v. injection of mu p75-SAP is accompanied by simultaneous activation of microglia and astrocytes in the basal forebrain region as well as significant memory loss. Consistent with a role of glial cells in the pathology of Alzheimer's disease, minocycline, a second-generation tetracycline with known anti-inflammatory and neuroprotective properties, attenuated mu p75-SAP-induced cholinergic cell loss, glial activation and transcription of downstream pro-inflammatory mediators. In addition to neuroprotection, minocycline treatment mitigated the cognitive impairment that appears to be a functional consequence of mu p75-SAP lesioning. The current study demonstrates that glial-related inflammation plays a significant role in the selective neurotoxicity of mu p75-SAP, and suggests that minocycline may provide a viable therapeutic option for degenerating cholinergic systems.

Potential roles of Alzheimer precursor protein A4 and beta-amyloid in survival and function of aged spinal motor neurons after axonal injury

To study the potential role of Alzheimer precursor protein A4 (APP) and beta-amyloid (A/beta) on aging motor neuron survival, expression of APP, A/beta, and choline acetyltransferase (ChaT) were investigated in aged rats after either distal axotomy or root avulsion injury. Approximately 45% in number of total aged spinal motor neuron were normally APP-positive. A/beta-positive neurites were observed normally in the spinal ventral horn of aged rats. After distal axotomy, without apparent neurodegeneration such as cell loss and decreased ChaT-immunoreactivity, increased levels of APP expression were observed in the spinal cords of aged rats post-injury. In contrast, after avulsion, expression of APP and A/beta were downregulated in the spinal ventral horn of aged rats, and marked loss of spinal motor neurons and downregulated ChaT expression were observed. Our data indicate that APP and A/beta might play beneficial roles in neuronal survival of aged spinal motor neurons after axonal injury.

Inflammatory neurodegeneration mediated by nitric oxide, glutamate, and mitochondria

In inflammatory, infectious, ischemic, and neurodegenerative pathologies of the central nervous system (CNS) glia become "activated" by inflammatory mediators, and express new proteins such as the inducible isoform of nitric oxide synthase (iNOS). Although these activated glia have benefi- cial roles, in vitro they potently kill cocultured neurons, and there is increasing evidence that they contribute to pathology in vivo. Nitric oxide (NO) from iNOS appears to be a key mediator of such glial-induced neuronal death. The high sensitivity of neurons to NO is partly due to NO causing inhibition of respiration, rapid glutamate release from both astrocytes and neurons, and subsequent excitotoxic death of the neurons. NO is a potent inhibitor of mitochondrial respiration, due to reversible binding of NO to cytochrome oxidase in competition with oxygen, resulting in inhibition of energy production and sensitization to hypoxia. Activated astrocytes or microglia cause a potent inhibition of respiration in cocultured neurons due to glial NO inhibiting cytochrome oxidase within the neurons, resulting in ATP depletion and glutamate release. In some conditions, glutamate- induced neuronal death can itself be mediated by N-methyl-D-aspartate (NMDA)-receptor activation of the neuronal isoform of NO synthase (nNOS) causing mitochondrial damage. In addition NO can be converted to a number of reactive derivatives such as peroxynitrite, NO2, N2O3, and S-nitrosothiols that can kill cells in part by inhibiting mitochondrial respiration or activation of mitochondrial permeability transition, triggering neuronal apoptosis or necrosis.

Reduction of human monocytic cell neurotoxicity and cytokine secretion by ligands of the cannabinoid-type CB2 receptor

1 Two cannabinoid receptors, CB1 and CB2, have been identified. The CB1 receptor is preferentially expressed in brain, and the CB2 receptor in cells of leukocyte lineage. We identified the mRNA for the CB1 receptor in human neuroblastoma SH-SY5Y cells, and the mRNA and protein for the CB2 receptor in human microglia and THP-1 cells. 2 Delta(9)-and Delta(8)-tetrahydrocannabinol (THC) were toxic when added directly to SH-SY5Y neuroblastoma cells. The toxicity of Delta(9)- THC was inhibited by the CB1 receptor antagonist SR141716A but not by the CB2 receptor antagonist SR144528. The endogenous ligand anandamide was also toxic, and this toxicity was enhanced by inhibitors of its enzymatic hydrolysis. 3 The selective CB2 receptor ligands JWH-015 and indomethacin morpholinylamide (BML-190), when added to THP-1 cells before stimulation with lipopolysaccharide (LPS) and IFN-gamma, reduced the toxicity of their culture supernatants to SH-SY5Y cells. JWH-015 was more effective against neurotoxicity of human microglia than THP-1 cells. The antineurotoxic activity of JWH-015 was blocked by the selective CB2 receptor antagonist SR144528, but not by the CB1 receptor antagonist SR141716A. This activity of JWH-015 was synergistic with that of the 5-lipoxygenase (5-LOX) inhibitor REV 5901. 4 Cannabinoids inhibited secretion of IL-1beta and tumor necrosis factor-alpha (TNF-alpha) by stimulated THP-1 cells, but these effects could not be directly correlated with their antineurotoxic activity. 5 Specific CB2 receptor ligands could be useful anti-inflammatory agents, while avoiding the neurotoxic and psychoactive effects of CB1 receptor ligands such as Delta(9)-THC.

Soluble factors released by Toxoplasma gondii-infected astrocytes down-modulate nitric oxide production by gamma interferon-activated microglia and prevent neuronal degeneration

The maintenance of a benign chronic Toxoplasma gondii infection is mainly dependent on the persistent presence of gamma interferon (IFN-gamma) in the central nervous system (CNS). However, IFN-gamma-activated microglia are paradoxically involved in parasitism control and in tissue damage during a broad range of CNS pathologies. In this way, nitric oxide (NO), the main toxic metabolite produced by IFN-gamma-activated microglia, may cause neuronal injury during T. gondii infection. Despite the potential NO toxicity, neurodegeneration is not a common finding during chronic T. gondii infection. In this work, we describe a significant down-modulation of NO production by IFN-gamma-activated microglia in the presence of conditioned medium of T. gondii-infected astrocytes (CMi). The inhibition of NO production was paralleled with recovery of neurite outgrowth when neurons were cocultured with IFN-gamma-activated microglia in the presence of CMi. Moreover, the modulation of NO secretion and the neuroprotective effect were shown to be dependent on prostaglandin E(2) (PGE(2)) production by T. gondii-infected astrocytes and autocrine secretion of interleukin-10 (IL-10) by microglia. These events were partially eliminated when infected astrocytes were treated with aspirin and cocultures were treated with anti-IL-10 neutralizing antibodies and RP-8-Br cyclic AMP (cAMP), a protein kinase A inhibitor. Further, the modulatory effects of CMi were mimicked by the presence of exogenous PGE(2) and by forskolin, an adenylate cyclase activator. Altogether, these data point to a T. gondii-triggered regulatory mechanism involving PGE(2) secretion by astrocytes and cAMP-dependent IL-10 secretion by microglia. This may reduce host tissue inflammation, thus avoiding neuron damage during an established Th1 protective immune response.

Alzheimer vaccine: amyloid-beta on trial

A new therapeutic approach is being developed for the treatment of Alzheimer's disease (AD). This approach involves the deliberate induction of an autoimmune response to amyloid-beta (Abeta) peptide, the constituent of neuritic plaques that is thought to cause the neurodegeneration and dementia in AD. If this approach is to be effective, antibodies must be produced that can selectively target the toxic forms of Abeta, while leaving the functionally-relevant forms of Abeta and its precursor protein untouched. Furthermore, an approach needs to be found that avoids provoking an acute neuroinflammatory response. The situation is made even more challenging by uncertainty regarding which isoforms of Abeta contribute to the pathogenesis of AD.

Toxicity of human monocytic THP-1 cells and microglia toward SH-SY5Y neuroblastoma cells is reduced by inhibitors of 5-lipoxygenase and its activating protein FLAP

To explore whether the proinflammatory products of the 5-lipoxygenase (5-LOX) pathway are involved in microglia-mediated toxicity toward neuronal cells, we evaluated the effects of 5-LOX inhibitors using an in vitro assay system where human neuronal SH-SY5Y cells are exposed to toxic secretions from THP-1 monocytic cells or human microglia. The specific 5-LOX inhibitors, REV 5901, zileuton, and 5-hydroxyeicosatetraenoic acid lactone; the nonselective LOX inhibitors, phenidone and dapsone; the dual 5-LOX/cyclooxygenase inhibitor, tepoxalin; and the selective inhibitor of the 5-LOX-activating protein (FLAP), MK-886, inhibited such toxicity. The toxicity was enhanced by the 5-LOX product leukotriene (LT)D(4) and reduced by the selective cysteinyl LT receptor (CysLT(1)) antagonist MK-571. The mRNAs for 5-LOX and FLAP were detected in THP-1 cells and human microglia but not in SH-SY5Y cells. The data suggest that inhibition of proinflammatory LT production by 5-LOX inhibition could selectively reduce toxicity of microglial cells and thus be beneficial in neuroinflammatory diseases.

Functional recovery of cholinergic basal forebrain neurons under disease conditions: old problems, new solutions?

Recognition of the involvement of cholinergic neurons in the modulation of cognitive functions and their severe dysfunction in neurodegenerative disorders, such as Alzheimer's disease, initiated immense research efforts aimed at unveiling the anatomical organization and cellular characteristics of the basal forebrain (BFB) cholinergic system. Concomitant with our unfolding knowledge about the structural and functional complexity of the BFB cholinergic projection system, multiple pharmacological strategies were introduced to rescue cholinergic nerve cells from noxious attacks; however, a therapeutic breakthrough is still awaited. In this review, we collected recent findings that significantly contributed to our better understanding of cholinergic functions under disease conditions, and to the design of effective means to restore lost or damaged cholinergic functions. To this end, we first provide a brief survey of the neuroanatomical organization of BFB nuclei with emphasis on major evolutionary differences among mammalian species, in particular rodents and primates, and discuss limitations of the translation of experimental data to human therapeutic applications. Subsequently, we summarize the involvement of cholinergic dysfunction in the pathogenesis of severe neurological conditions, including stroke, traumatic brain injury, virus encephalitis and Alzheimer's disease, and emphasize the critical role of pro-inflammatory cytokines as common mediators of cholinergic neuronal damage. Moreover, we review leading functional concepts on the limited recovery of cholinergic neurons and their impaired plastic re-modeling, as well as on the hampered interplay of the ascending cholinergic and monoaminergic projection systems under neurodegenerative conditions. In addition, recent advances in the dynamic labeling of living cholinergic neurons by fluorochromated antibodies, referred to as in vivo labeling, and novel neuroimaging approaches as potential diagnostic tools of progressive cholinergic decline are surveyed. Finally, the potential of cell replacement strategies using embryonic and adult stem cells, and multipotent neural progenitors, as a means to recover damaged cholinergic functions, is discussed.

Scintigraphic visualization of inflammation in neurodegenerative disorders

In the past few decades, our understanding of the central nervous system has evolved from one of an immune-privileged site, to one where inflammation is pathognomonic for some of the most prevalent and tragic neurodegenerative diseases. Current research indicates that diseases as diverse as multiple sclerosis, stroke and Alzheimer's disease exhibit inflammatory processes that contribute to cellular dysfunction or loss. Inflammation, whether in the brain or periphery, is almost always a secondary response to a primary pathogen. In head trauma, for example, the blow to the head is the primary event. What typically concerns the neurologist and neurosurgeon more, however, is the secondary inflammatory response that will ensue and likely cause more neuron loss than the initial injury. This paper reviews the basic neuroinflammatory mechanisms, the potential neurotoxic mediators during activation of microglia, the brain resident macrophages, and their role in neurodegeneration. Alzheimer's disease is taken as a prototype for exploring these mechanisms, as it expresses more than 40 inflammatory mediators, it is the most extensively studied disorder in terms of immune-related pathogenesis, and because of its importance as the most prevalent type of dementia. Tools for the visualization of these neuroinflammatory processes, both structural and mainly functional, are critically reviewed and discussed.

The role of macrophage/microglia and astrocytes in the pathogenesis of three neurologic disorders: HIV-associated dementia, Alzheimer disease, and multiple sclerosis

Macrophage/microglia (M phi) are the principal immune cells in the central nervous system (CNS) concomitant with inflammatory brain disease and play a significant role in the host defense against invading microorganisms. Astrocytes, as a significant component of the blood-brain barrier, behave as one of the immune effector cells in the CNS as well. However, both cell types may play a dual role, amplifying the effects of inflammation and mediating cellular damage as well as protecting the CNS. Interactions of the immune system, M phi, and astrocytes result in altered production of neurotoxins and neurotrophins by these cells. These effects alter the neuronal structure and function during pathogenesis of HIV-1-associated dementia (HAD), Alzheimer disease (AD), and multiple sclerosis (MS). HAD primarily involves subcortical gray matter, and both HAD and MS affect sub-cortical white matter. AD is a cortical disease. The process of M phi and astrocytes activation leading to neurotoxicity share similarities among the three diseases. Human Immunodeficiency Virus (HIV)-1-infected M phi are involved in the pathogenesis of HAD and produce toxic molecules including cytokines, chemokines, and nitric oxide (NO). In AD, M phis produce these molecules and are activated by beta-amyloid proteins and related oligopeptides. Demyelination in MS involves M phi that become lipid laden, spurred by several possible antigens. In these three diseases, cytokine/chemokine communications between M phi and astrocytes occur and are involved in the balance of protective and destructive actions by these cells. This review describes the role of M phi and astrocytes in the pathogenesis of these three progressive neurological diseases, examining both beneficent and deleterious effects in each disease.

Different pathways for iNOS-mediated toxicity in vitro dependent on neuronal maturation and NMDA receptor expression

Co-localization of activated microglia and damaged neurones seen in brain injury suggests microglia-induced neurodegeneration. Activated microglia release two potential neurotoxins, excitatory amino acids and nitric oxide (NO), but their contribution to mechanisms of injury is poorly understood. Using co-cultures of rat microglia and embryonic cortical neurones, we show that inducible NO synthase (iNOS)-derived NO aloneis responsible for neuronal death from interferon gamma (IFNgamma) +lipopolysaccharide (LPS)-activated microglia. Neurones remain sensitive to NO irrespective of maturation state but, whereas blocking NMDA receptor activation with MK801 has no effect on NO-mediated toxicity to immature neurones, MK801 rescues 60-70% of neurones matured in culture for 12 days. Neuronal expression of NMDA receptors increases with maturation in culture, accounting for increased susceptibility to excitotoxins seen in more mature cultures. We show that MK801 delays the death of more mature neurones caused by the NO-donor DETA/NO indicating that NO elicits an excitotoxic mechanism, most likely through neuronal glutamate release. Thus, similar concentrations of nitric oxide cause neuronal death by two distinct mechanisms: NO acts directly upon immature neurones but indirectly, via NMDA receptors, on more mature neurones. Our results therefore extend existing evidence for NO-mediated toxicity and show a complex interaction between inflammatory and excitotoxic mechanisms of injury in mature neurones.

Evidence that toxicity of lipopolysaccharide upon cholinergic basal forebrain neurons requires the presence of glial cells in vitro

The cholinergic system of the basal forebrain is affected in brains of dementia patients and during neuroinflammation. The aim of this study was to establish a method to cultivate basal forebrain cholinergic neurons in dissociated, pure neuronal cultures and to apply this method to study the effect of acute and chronic experimentally-induced inflammation using lipopolysaccharide. Purity of the cultures, degrees of neuronal dissociation, connectivity and neuronal survival were investigated by immunocytochemistry for microtubule-associated protein-2 (neurons), glial fibrillary acidic protein (astroglia), complement receptor 3 (microglia), choline acetyltransferase and the neurotrophin receptor p75 (cholinergic neurons). Neuronal cultures only contained <7% astrocytes and <1% microglia when using a "sandwich-technique". Acute (1, 10 microg/ml) as well as chronic (0.1, 1 microg/ml) treatment with lipopolysaccharide did neither affect total number of neurons, nor number of p75-positive neurons or enhance expression of major histocompatibility complex I or II. Our results suggest that lipopolysaccharide-induced degeneration of both microtubule-associated protein-2-like immunoreactive as well as specific killing of cholinergic forebrain neurons in vitro are mediated by glial cells.

Serum-dependence of LPS-induced neurotoxicity in rat cortical neurons

Previous studies have shown that the bacterial endotoxin, lipopolysaccharide (LPS), is neurotoxic both in vitro and in vivo. The rate of binding of LPS to a target cell is greatly enhanced by serum in general and by LPS binding protein (LBP) in particular. The purpose of the study described in this paper was to determine if microglia activation and LPS-induced neurotoxicity is serum or LBP dependent. A murine microglial cell line, BV2, was used to assess the serum dependence of nitric oxide production and tumor necrosis factor a release in microglia. Embryonic rat cortical neuron/glia mixed cultures were used to determine the serum dependence of LPS-induced neurotoxicity. Our results from both cell culture systems show that LPS-induced inflammatory responses are serum dependent at lower doses of LPS and progressively become serum independent above 10 ng/ml. Purified human recombinant LBP reconstitutes the lost LPS-induced inflammatory responses in primary and immortalized cell cultures treated with heat-denatured serum and appears to account for the serum dependence. These data suggest that the cell surface signaling receptor for LPS at the low and high concentrations are likely to differ, consistent with the existence of a variety of LPS receptors.

Neurogenic inflammation and particulate matter (PM) air pollutants

Exposure to a class of airborne pollutants known as particulate matter (PM) is an environmental health risk of global proportions. PM is thought to initiate and/or exacerbate respiratory disorders, such as asthma and airway hyper-responsiveness and is epidemiologically associated with causing death in the elderly and those with pre-existing respiratory, or cardiopulmonary disease. Plausible mechanisms of action to explain PM inflammation and its susceptible sub-population component are lacking. This review describes a series of published studies which indicate that PM initiates airway inflammation through sensory neural pathways, specifically by activation of capsaicin-sensitive vanilloid (e.g. VRI) irritant receptors. These acid-sensitive receptors are located on the sensory C nerve fibers that innervate the airways as well as on various immune and non-immune airway target cells. The activation of these receptors results in the release of neuropeptides from the sensory terminals that innervate the airways. Their interactions with airway target cells, result in signs of inflammation (e.g. bronchoconstriction, vasodilation, histamine release, mucous secretion etc.). Our data have linked the activation of the VR1 receptors to the surface charge carried on the colloidal particulates which constitute PM pollution. Related studies have examined how genetic and non-genetic factors modify the sensitivity of these irritant receptors and enhance the inflammatory responsiveness to PM. In summary, this review proposes a mechanism by which neurogenic elements initiate and sustain PM-mediated airway inflammation. Although neurogenic influences have been appreciated in normal airway homeostasis, they have not, until now, been associated with PM toxicity. The sensitivity of the sensory nervous system to irritants and its interactions with pulmonary target tissues, should encourage neuroscientists to explore the relevance of neurogenic influences to toxic disorders involving other peripheral target systems.

Advanced glycation endproducts co-localize with inducible nitric oxide synthase in Alzheimer's disease

Advanced glycation endproducts (AGEs), protein-bound oxidation products of sugars, have been shown to be involved in the pathophysiological processes of Alzheimer's disease (AD). AGEs induce the expression of various pro-inflammatory cytokines and the inducible nitric oxide synthase (iNOS) leading to a state of oxidative stress. AGE modification and resulting crosslinking of protein deposits such as amyloid plaques may contribute to the oxidative stress occurring in AD. The aim of this study was to immunohistochemically compare the localization of AGEs and beta-amyloid (Abeta) with iNOS in the temporal cortex (Area 22) of normal and AD brains. In aged normal individuals as well as early stage AD brains (i.e. no pathological findings in isocortical areas), a few astrocytes showed co-localization of AGE and iNOS in the upper neuronal layers, compared with no astrocytes detected in young controls. In late AD brains, there was a much denser accumulation of astrocytes co-localized with AGE and iNOS in the deeper and particularly upper neuronal layers. Also, numerous neurons with diffuse AGE but not iNOS reactivity and some AGE and iNOS-positive microglia were demonstrated, compared with only a few AGE-reactive neurons and no microglia in controls. Finally, astrocytes co-localized with AGE and iNOS as well as AGE and were found surrounding mature but not diffuse amyloid plaques in the AD brain. Our results show that AGE-positive astrocytes and microglia in the AD brain express iNOS and support the evidence of an AGE-induced oxidative stress occurring in the vicinity of the characteristic lesions of AD. Hence activation of microglia and astrocytes by AGEs with subsequent oxidative stress and cytokine release may be an important progression factor in AD.

Interferons: potential roles in affect

A review of the literature on interferons was conducted and possible roles in neuropsychiatric disorders with affective disturbances are assessed. Interferons and interferon receptors are present in the limbic system where they appear to exert physiological effects pertinent to affect, most potently when levels rise during CNS infections. Interferons interact closely with cytokines and nitric oxide, signaling molecules implicated in depression. Results from knock-out mice suggest a role for interferon-gamma in moderating fear and anxiety, while other lines of evidence point to a role in arousal and circadian rhythms. The interferon-alpha receptor deploys an arginine methyltransferase affecting RNA editing and splicing, which seem to be disrupted in schizophrenia and bipolar disorder. S-Adenosylmethionine (SAMe), an effective antidepressant, may owe its effects in the latter disorders in part to variations in the strength of interferon-alpha signaling impacting RNA processing. Antiviral effects of interferons are of interest in lieu of viral theories of affective disorders. Finally, the relative levels of interferons gamma and alpha might play important roles in neural, and glial, development, as well as the dialog between the CNS and the immune system.

Cytokine production consequent to T cell--microglia interaction: the PMA/IFN gamma-treated U937 cells display similarities to human microglia

Cognate interactions between human adult microglia and activated T lymphocytes induce the production of inflammatory cytokines. Since this interaction can occur in a non-antigen-dependent manner, it is relevant to a variety of CNS diseases where activated T cells, regardless of specificities, come into contact with microglia; these disorders include multiple sclerosis, trauma, stroke and Alzheimer's disease. A model cell line would facilitate studies of the engagement between T cells and human adult microglia, since the latter are difficult to obtain in substantial quantity or frequency. This study shows that the PMA/IFN gamma-treated U937 cell line shows similarities to microglia in its interaction with activated T lymphocytes, in that the production of tumor necrosis factor (TNF)-alpha, interleukin (IL)-4, IL-10 and IL-12 is induced. Morphological features and mechanisms of cytokine production resemble those observed in microglia--T cell co-cultures since CTLA-4 and CD40--CD40L blockades reduce TNF-alpha and IL-10 levels, while anti-CD23 inhibits IL-10 only in U937--T cell interactions. We propose that PMA/IFN gamma-treated U937 cells can serve as a model of human adult microglia to study cytokine generation in response to interactions with activated T cells.

Mechanisms to prevent the toxicity of chronic neuroinflammation on forebrain cholinergic neurons

Inflammatory processes may play an important role in the degeneration of basal forebrain cholinergic cells Alzheimer's disease. We infused the proinflammagen lipopolysaccharide into the basal forebrain of young rats and determined whether the chronic administration of two novel non-steroidal anti-inflammatory drugs or a pan-caspase synthesis inhibitor, z-Val-Ala-Asp(OMe)-fluoromethyl ketone (zVAD), could provide neuroprotection from the cytotoxic effects of the neuroinflammation. Chronic lipopolysaccharide infusions decreased choline acetyltransferase activity and increased the number of activated microglia within the basal forebrain region. The level of caspases 3, 8 and 9 was increased in ventral caudate/putamen. Non-steroidal anti-inflammatory drug therapy attenuated the toxicity of the inflammation upon cholinergic cells and reduced caspases 3, 8 and 9 activity in the caudate/putamen. zVAD treatment significantly decreased the levels of caspases 3, 8 and 9 but did not provide neuroprotection for the cholinergic neurons. These results suggest that prostaglandins contribute to the degeneration of forebrain cholinergic neurons in Alzheimer's disease.

The role of 6R-tetrahydrobiopterin in the nervous system

In addition to its cofactor activities for aromatic L-amino acid hydroxylases and nitric oxide synthase (NOS), 6R-tetrahydrobiopterin (6R-BH(4)) shows diverse actions on neurons. Dopamine release from the rat striatum or PC12 cells was stimulated by 6R-BH(4). The action of 6R-BH(4) was independent of its cofactor activities and stereospecific. Ca(2+) channels in rat brain and PC12 cells were activated by 6R-BH(4) via cAMP-protein kinase A pathway. Membrane potential of PC12 cells was deplorized by 6R-BH(4). Thus, it is assumed that 6R-BH(4) acts on its specific action site (possibly outside of the cell membrane) to stimulate dopamine release by activating Ca(2+) channels. Apoptosis induced by depletion of serum and nerve growth factor in PC12 cells was prevented by 6R-BH(4). The cell surviving effect of 6R-BH(4) was also mediated by activation of Ca(2+) channels and cAMP-protein kinase A pathway. However, since 6R-BH(4) did not activate mitogen activated protein kinase, it did not support neuronal differentiation. Nitric oxide (NO)-induced cell death was prevented by 6R-BH(4) in PC12 cells. NOS activity was not changed by exogenous 6R-BH(4), but NO metabolites in culture medium were decreased by 6R-BH(4). When endogenous 6R-BH(4) was reduced by inhibition of biosynthesis, cell death was induced in PC12 cells. Superoxide is observed to be generated during autoxidation of 6R-BH(4). Superoxide producing system mimicked the cell protective action of 6R-BH(4) against NO toxicity. Thus, it is considered that 6R-BH(4) protects PC12 cells against NO toxicity by generating superoxide during its autoxidation. These results raised the possibility that 6R-BH(4) is a self-protective factor against NO toxicity in NO producing neurons. Our findings indicate that 6R-BH(4) regulates neuronal activities in the brain and that 6R-BH(4) can be a promising drug for neurodegenerative disorders such as Parkinson's disease and Alzheimer's disease.

Reduction of lipopolysaccharide-induced neurotoxicity in mouse mixed cortical neuron/glia cultures by ultralow concentrations of dynorphins

Previously we reported that ultralow concentrations of dynorphins (10(-16) to 10(-12) M) inhibited lipopolysaccharide (LPS)-induced production of nitric oxide (NO) and proinflammatory cytokines in mouse glia without the participation of kappa-opioid receptors. In the current study using mouse cortical neuron-glia cocultures, we examined the possibility that inhibition of glia inflammatory response by dynorphins might be neuroprotective for neurons. LPS, in a concentration-dependent manner, markedly increased the release of lactate dehydrogenase (LDH), an indicator of cellular injury. Ultralow concentrations (10(-14) to 10(-12) M) of dynorphin (dyn) A-(1-8) significantly prevented the LPS-induced release of LDH, loss of neurons, and changes in cell morphology, in addition to inhibition of LPS-induced nitrite production. Meanwhile, ultralow concentrations (10(-15) to 10(-13) M) of des-[Tyr(1)]-dyn A-(2-17), a nonopioid peptide which does not bind to kappa-opioid receptors, exhibited the same inhibitory effect as dyn A-(1-17). These results suggest that dynorphins at ultralow concentrations are capable of reducing LPS-induced neuronal injury and these neuroprotective effects of dynorphins are not mediated by classical opioid receptors.

Reduction of lipopolysaccharide-induced neurotoxicity in mixed cortical neuron/glia cultures by femtomolar concentrations of pituitary adenylate cyclase-activating polypeptide

Stimulation of murine primary mixed cortical neuron/glia cultures with lipopolysaccharide, an endotoxin, was used as a model for inflammatory disorders of the central nervous system. Lipopolysaccharide (20 microg/ml) increased the secretion of lactate dehydrogenase, a marker for cell injury, and nitric oxide into the culture medium. The lipopolysaccharide-induced release of lactate dehydrogenase into the culture medium was reduced by pituitary adenylate cyclase-activating polypeptide (PACAP) at 10(-14)-10(-12) M. The 27- and 38-amino-acid forms of PACAP were equipotent and their dose-response curves were U-shaped. PACAP6-38, a specific type I PACAP receptor antagonist, blocked the reduction by PACAP38 of the lipopolysaccharide-induced release of lactate dehydrogenase. The lipopolysaccharide-induced secretion of nitric oxide into the culture medium was reduced by PACAP at 10(-14)-10(-12) M and 10(-8)-10(-6) M. The 27- and 38-amino-acid forms of PACAP were equipotent. PACAP6-38 blocked the reduction of the lipopolysaccharide-induced secretion of nitric oxide by PACAP38 at 10(-12) M, but not at 10(-8) M. Vasoactive intestinal polypeptide reduced the lipopolysaccharide-induced release of lactate dehydrogenase into the culture medium at 10(-14)-10(-12) M, but these concentrations of vasoactive intestinal polypeptide had no effect on the lipopolysaccharide-induced secretion of nitric oxide. PACAP6-38 did not effect the reduction of the lipopolysaccharide-induced release of lactate dehydrogenase into the culture medium by 10(-12) M vasoactive intestinal polypeptide. These results indicate that stimulation of type I PACAP receptors by femtomolar concentrations of PACAP can prevent neuron death in a model for inflammatory disorders of the CNS. These results suggest that PACAP is also an extraordinarily potent inhibitor of some microglial functions.

The effect of microglia on embryonic dopaminergic neuronal survival in vitro: diffusible signals from neurons and glia change microglia from neurotoxic to neuroprotective

When embryonic dopaminergic neurons are transplanted into the adult brain, approximately 95% die within a few days. To assess whether microglia activated during transplantation might be responsible for this rapid death, we examined the effect of microglia on rat embryonic dopaminergic neurons in vitro. Conditioned medium from 7-day-old microglia was found to decrease the number of dopamine neurons surviving in primary culture, but activation of the microglia with N-formyl-methionyl-leucyl-phenylalanine (FMLP) or Zymosan A did not increase the toxicity of the conditioned medium. We next tested the effect of coculturing microglia and dopaminergic neurons by placing microglia in semipermeable well inserts over the neuronal cultures. The presence of microglia now increased dopaminergic neuronal survival, microglial activation again having no effect. To increase yet further the possible interactions between microglia and neurons, the mesencephalic cells and microglia were mixed together and placed as a tissue in three-dimensional culture, and here again the presence of microglia increased dopaminergic neuronal survival with no effect of activation. Contact of microglia with the mesencephalic cells therefore converted them from being toxic to dopaminergic neurons to promoting their survival. The change in microglial effect from toxic to protective was caused by soluble molecules secreted by cells in the neuronal cultures, as conditioned medium derived from microglia-neuronal cocultures also had a dopaminergic neuron survival effect, indicating that microglia in cocultures behave differently from microglia removed from neuronal and glial influence. Microglia cocultured with either neurons or astrocytes downregulated inducible nitric oxide synthase (iNOS), indicating a decrease in the production of nitric oxide and possibly other toxic molecules. These findings indicate that in their natural environment, microglia are likely to be beneficial for the survival of embryonic dopaminergic grafts.