Basal and IL-1beta-stimulated cytokine and neuropeptide mRNA expression in brain regions of young and old Long-Evans rats

Role of cytokines and reactive oxygen species in brain aging

Aging is a complex process that produces profound effects on the brain. Although a number of external factors can promote the initiation and progression of brain aging, peripheral and central changes in the immune cells with time, also play an important role. Immunosenescence, which is an age-associated decline in immune function and Inflammaging, a low-grade inflammatory state in the aging brain contribute to an elevation in cytokine and reactive oxygen species production. In this review, we focus on the pro-inflammatory state that is established in the brain as a consequence of these two phenomena and the resulting detrimental changes in brain structure, function and repair that lead to a decline in central and neuroendocrine function.

The killifish visual system as an in vivo model to study brain aging and rejuvenation

Worldwide, people are getting older, and this prolonged lifespan unfortunately also results in an increased prevalence of age-related neurodegenerative diseases, contributing to a diminished life quality of elderly. Age-associated neuropathies typically include diseases leading to dementia (Alzheimer's and Parkinson's disease), as well as eye diseases such as glaucoma and age-related macular degeneration. Despite many research attempts aiming to unravel aging processes and their involvement in neurodegeneration and functional decline, achieving healthy brain aging remains a challenge. The African turquoise killifish (Nothobranchius furzeri) is the shortest-lived reported vertebrate that can be bred in captivity and displays many of the aging hallmarks that have been described for human aging, which makes it a very promising biogerontology model. As vision decline is an important hallmark of aging as well as a manifestation of many neurodegenerative diseases, we performed a comprehensive characterization of this fish's aging visual system. Our work reveals several aging hallmarks in the killifish retina and brain that eventually result in a diminished visual performance. Moreover, we found evidence for the occurrence of neurodegenerative events in the old killifish retina. Altogether, we introduce the visual system of the fast-aging killifish as a valuable model to understand the cellular and molecular mechanisms underlying aging in the vertebrate central nervous system. These findings put forward the killifish for target validation as well as drug discovery for rejuvenating or neuroprotective therapies ensuring healthy aging.

Ethanol and Cytokines in the Central Nervous System

The innate immune system plays a critical role in the ethanol-induced neuroimmune response in the brain. Ethanol initiates the innate immune response via activation of the innate immune receptors Toll-like receptors (TLRs, e.g., TLR4, TLR3, TLR7) and NOD-like receptors (inflammasome NLRs) leading to a release of a plethora of chemokines and cytokines and development of the innate immune response. Cytokines and chemokines can have pro- or anti-inflammatory properties through which they regulate the immune response. In this chapter, we will focus on key cytokines (e.g., IL-1, IL-6, TNF-α) and chemokines (e.g., MCP-1/CCL2) that mediate the ethanol-induced neuroimmune responses. In this regard, we will use IL-1β, as an example cytokine, to discuss the neuromodulatory properties of cytokines on cellular properties and synaptic transmission. We will discuss their involvement through a set of evidence: (1) changes in gene and protein expression following ethanol exposure, (2) association of gene polymorphisms (humans) and alterations in gene expression (animal models) with increased alcohol intake, and (3) modulation of alcohol-related behaviors by transgenic or pharmacological manipulations of chemokine and cytokine systems. Over the last years, our understanding of the molecular mechanisms mediating cytokine- and chemokine-dependent regulation of immune responses has advanced tremendously, and we review evidence pointing to cytokines and chemokines serving as neuromodulators and regulators of neurotransmission.

IL-1 interacts with ethanol effects on GABAergic transmission in the mouse central amygdala

Neuroinflammation is hypothesized to enhance alcohol consumption and contribute to the development of alcoholism. GABAergic transmission in the central amygdala (CeA) plays an important role in the transition to alcohol dependence. Therefore, we studied the effects of interleukin-1β (IL-1β), a proinflammatory cytokine mediating ethanol-induced neuroinflammation, and its interaction with ethanol on CeA GABAegic transmission in B6129SF2/J mice. We also assessed ethanol intake in B6129SF2/J mice. Intake with unlimited (24 h) ethanol access was 9.2–12.7 g/kg (3–15% ethanol), while limited (2 h) access produced an intake of 4.1 ± 0.5 g/kg (15% ethanol). In our electrophysiology experiments, we found that recombinant IL-1β (50 and 100 ng/ml) significantly decreased the amplitude of evoked inhibitory postsynaptic potentials (eIPSPs), with no significant effects on paired-pulse facilitation (PPF). IL-1β (50 ng/ml) had dual effects on spontaneous miniature inhibitory postsynaptic currents (mIPSCs): increasing mIPSC frequencies in most CeA neurons, but decreasing both mIPSC frequencies and amplitudes in a few cells. The IL-1β receptor antagonist (IL-1ra; 100 ng/ml) also had dual effects on mIPSCs and prevented the actions of IL-1β on mIPSC frequencies. These results suggest that IL-1β can alter CeA GABAergic transmission at pre- and postsynaptic sites. Ethanol (44 mM) significantly increased eIPSP amplitudes, decreased PPFs, and increased mIPSC frequencies. IL-1β did not alter ethanol’s enhancement of the eIPSP amplitude, but, in IL-1β-responsive neurons, the ethanol effects on mIPSC frequencies were lost. Overall, our data suggest that the IL-1 system is involved in basal GABAergic transmission and that IL-1β interacts with the ethanol-induced facilitation of CeA GABAergic transmission.

Differential rescue of spatial memory deficits in aged rats by L-type voltage-dependent calcium channel and ryanodine receptor antagonism

Age-associated memory impairments may result as a consequence of neuroinflammatory induction of intracellular calcium (Ca(+2)) dysregulation. Altered L-type voltage-dependent calcium channel (L-VDCC) and ryanodine receptor (RyR) activity may underlie age-associated learning and memory impairments. Various neuroinflammatory markers are associated with increased activity of both L-VDCCs and RyRs, and increased neuroinflammation is associated with normal aging. In vitro, pharmacological blockade of L-VDCCs and RyRs has been shown to be anti-inflammatory. Here, we examined whether pharmacological blockade of L-VDCCs or RyRs with the drugs nimodipine and dantrolene, respectively, could improve spatial memory and reduce age-associated increases in microglia activation. Dantrolene and nimodipine differentially attenuated age-associated spatial memory deficits but were not anti-inflammatory in vivo. Furthermore, RyR gene expression was inversely correlated with spatial memory, highlighting the central role of Ca(+2) dysregulation in age-associated memory deficits.

Hypothalamic inflammation and energy homeostasis: resolving the paradox

Determining the effect of hypothalamic inflammatory signals on energy balance presents a paradox. On the one hand, a large body of work has identified inflammatory signaling in the hypothalamus as an essential mediator of the sickness response--the anorexia, cachexia, fever, inactivity, lethargy, anhedonia and adipsia that are triggered by systemic inflammatory stimuli and promote negative energy balance. On the other hand, numerous recent studies implicate inflammatory activation within the hypothalamus as a key factor whereby high-fat diets--and saturated fats in particular--cause central leptin and insulin resistance and thereby promote the defense of elevated body weight. This paradox will likely remain unresolved until several issues have been addressed. Firstly, the hypothalamus--unlike many peripheral inflamed tissues--is an extremely heterogeneous tissue comprised of astrocytes, oligodendrocytes, microglia, endothelial cells, ependymal cells as well as numerous neuronal subgroups. Determining exactly which cells activate defined inflammatory signals in response to a particular stimulus--i.e. sepsis vs. nutrient excess--may yield critical clues. Secondly, for the sake of simplicity many studies evaluate inflammation as an on/off phenomenon. More realistically, inflammatory signaling occurs as a cascade or cycle that changes and progresses over time. Accordingly, even within the same cell type, the low-grade, chronic signal induced by nutrient excess may invoke a different cascade of signals than a strong, acute signal such as sepsis. In addition, because tolerance can develop to certain inflammatory mediators, physiological outcomes may not correlate with early biochemical markers. Lastly, the neuroanatomical location, magnitude, and duration of the inflammatory stimulus can undoubtedly influence the net CNS response. Rigorously evaluating the progression of the inflammatory signaling cascade within specific hypothalamic cell types is a key next step towards resolving the paradox surrounding the effect of inflammatory signaling on energy homeostasis.

Regulation of cytokine signaling and T-cell recruitment in the aging mouse brain in response to central inflammatory challenge

Aging is often accompanied by increased levels of inflammatory molecules in the organism, but age-related changes in the brain response to inflammatory challenges still require clarification. We here investigated in mice whether cytokine signaling and T-cell neuroinvasion undergo age-related changes. We first analyzed the expression of molecules involved in T-cell infiltration and cytokine signaling regulation in the septum and hippocampus of 2-3 months and 20- to 24-month-old mice at 4h after intracerebroventricular injections of tumor necrosis factor (TNF)-alpha or interferon-gammaversus saline injections. Transcripts of the chemokine CXCL9, intercellular adhesion molecule (ICAM)-1 and suppressor of cytokine signaling molecules (SOCS) 1 and 3 were increased in both age groups after cytokine injection; microglia-derived matrix metalloproteinase (MMP) 12 mRNA was induced in old mice also after control saline injections. Age-related changes in ICAM-1 protein expression and T-cell infiltration were then analyzed in mice of 3-4, 8-9 and 15-16 months at 48h after TNF-alpha injections. ICAM-1 immunoreactivity, and Western blotting in striatum, septum, hippocampus and hypothalamus showed progressive age-related enhancement of TNF-alpha-elicited ICAM-1 upregulation. Double immunofluorescence revealed ICAM-1 expression in microglia and astrocytic processes. CD3(+), CD4(+) and CD8(+) T-cells exhibited progressive age-related increases in brain parenchyma and choroid plexus after cytokine exposure. The findings indicate that the brain responses to inflammatory challenges are not only preserved with advancing age, but also include gradual amplification of ICAM-1 expression and T-cell recruitment. The data highlight molecular and cellular correlates of age-related increase of brain sensitivity to inflammatory stimuli, which could be involved in altered brain vulnerability during aging.

Time course of hippocampal IL-1 beta and memory consolidation impairments in aging rats following peripheral infection

We previously reported that aging F344XBN rats are more vulnerable to disruptions of memory consolidation processes following an injection of Escherichia coli than are young rats. Furthermore, this disruption was specific to hippocampal-dependent memory. In the present study we examined the time course of the proinflammatory cytokine IL-1 beta in young and old rats following a peripheral injection of E. coli. Compared to young rats, aging rats treated with E. coli showed an exaggerated and prolonged up-regulation of IL-1 beta protein in the hippocampus, but not in hypothalamus, parietal cortex, prefrontal cortex, serum or spleen. Aging rats showed greater hippocampal IL-1 beta protein levels than their young counterparts 4h after E. coli, and these levels remained significantly elevated for 8 but not 14 days after E. coli. In a second experiment, aging rats exhibited anterograde memory consolidation impairments 4 and 8 days after an E. coli injection, but not after 14 days. A third experiment revealed that following an E. coli injection, bacterial clearance from the spleen and peritoneum was not impaired in aged rats, suggesting that elevations in hippocampal IL-1 beta were not mediated by impaired clearance in the periphery in aging rats. These data suggest that the exaggerated and prolonged elevation of IL-1 beta, specifically in the hippocampus, may be responsible for hippocampal-dependent memory impairments observed in aging rats following a bacterial infection.

A central role for neuronal adenosine 5'-monophosphate-activated protein kinase in cancer-induced anorexia

The pathogenesis of cancer anorexia is multifactorial and associated with disturbances of the central physiological mechanisms controlling food intake. However, the neurochemical mechanisms responsible for cancer-induced anorexia are unclear. Here we show that chronic infusion of 5-amino-4imidazolecarboxamide-riboside into the third cerebral ventricle and a chronic peripheral injection of 2 deoxy-d-glucose promotes hypothalamic AMP-activated protein kinase (AMPK) activation, increases food intake, and prolongs the survival of anorexic tumor-bearing (TB) rats. In parallel, the pharmacological activation of hypothalamic AMPK in TB animals markedly reduced the hypothalamic production of inducible nitric oxide synthase, IL-1beta, and TNF-alpha and modulated the expression of proopiomelanocortin, a hypothalamic neuropeptide that is involved in the control of energy homeostasis. Furthermore, the daily oral and intracerebroventricular treatment with biguanide antidiabetic drug metformin also induced AMPK phosphorylation in the central nervous system and increased food intake and life span in anorexic TB rats. Collectively, the findings of this study suggest that hypothalamic AMPK activation reverses cancer anorexia by inhibiting the production of proinflammatory molecules and controlling the neuropeptide expression in the hypothalamus, reflecting in a prolonged life span in TB rats. Thus, our data indicate that hypothalamic AMPK activation presents an attractive opportunity for the treatment of cancer-induced anorexia.

Proteomics analysis of hypothalamic response to energy restriction in dairy cows

The hypothalamus is the central regulatory unit that balances a number of body functions including metabolic rate, hunger, and satiety signals. Hypothalamic neurons monitor and respond to alterations of circulating nutrients and hormones that reflect the peripheral energy status. These extracellular signals are integrated within the cell at the ATP:AMP ratio and at the level of ROS, triggering gene expression associated with glucose and lipid metabolism. In order to identify new molecular factors potentially associated with the control of energy homeostasis, metabolic adaptation, and regulation of feed intake, hypothalami from ad libitum fed and energy restricted cows were characterized using 2-DE and MALDI-TOF-MS. Among 189 different protein spots identified, nine proteins were found to be differentially expressed between groups. Beside the 5-aminoimidazole-4-carboxamide ribonucleotide formyltransferase/IMP cyclohydrolase, stress-induced phosphoprotein-1, heat shock protein 70 kDa-protein-5, dihydropyrimidinase-related protein-2, [Cu-Zn]-superoxide dismutase, ubiquitin carboxy-terminal hydrolase-L1, and inorganic pyrophosphatase were found to be up-regulated, whereas glyceraldehyde 3-phosphate dehydrogenase and aconitase-2 were down-regulated in the restricted group. In conclusion, differentially expressed proteins are related to energy and nucleotide metabolism and cellular stress under conditions of dietary energy deficiency. These proteins may be new candidate molecules that are potentially involved in signaling for maintaining energy homeostasis.

Age-related alterations of Apolipoprotein E and interleukin-1beta in the aging brain

With normal aging, the brain undergoes several alterations including reduced neuronal functioning and alterations in glia homeostasis. An increase in inflammatory signaling has also been reported in some studies of the aging brain, with inflammation potentially mediating age-related changes in the brain. Apolipoprotein E (ApoE) is produced in the brain and has been shown to possess anti-inflammatory properties in a variety of paradigms. In the present study, we correlated age-related alterations in ApoE expression with age-related changes in the cytokine interleukin-1 beta (IL-1beta), in the brain of rats of increasing age. No significant alteration in ApoE mRNA was found in any region examined. A significant increase in IL-1beta mRNA with age was observed only in the cortex. Neither ApoE nor IL-1beta protein expression was significantly altered with age in the brain. A significant linear correlation between ApoE and IL-1beta mRNA was found in the cortex but not in the striatum or hippocampus. No correlation was found between ApoE and IL-1beta protein in any region examined. Taken together, these studies demonstrate that ApoE expression is not altered during normal brain aging, but suggest that there may be a relationship between ApoE and IL-1beta transcription in the cerebral cortex.

Interleukin-1beta induces hyperpolarization and modulates synaptic inhibition in preoptic and anterior hypothalamic neurons

Most of the inflammatory effects of the cytokine interleukin 1beta (IL-1beta) are mediated by induction of cyclooxygenase (COX)2 and the subsequent synthesis and release of prostaglandin E2. This transcription-dependent process takes 45-60 min, but IL-1beta, a well-characterized endogenous pyrogen also exerts faster neuronal actions in the preoptic area/anterior hypothalamus. Here, we have studied the fast (1-3 min) signaling by IL-1beta using whole-cell patch clamp recordings in preoptic area/anterior hypothalamus neurons. Exposure to IL-1beta (0.1-1 nM) hyperpolarized a subset ( approximately 20%) of preoptic area/anterior hypothalamus neurons, decreased their input resistance and reduced their firing rate. These effects were associated with an increased frequency of bicuculline-sensitive spontaneous inhibitory postsynaptic currents and putative miniature inhibitory postsynaptic currents, strongly suggesting a presynaptic mechanism of action. These effects require the type 1 interleukin 1 receptor (IL-1R1), and the adapter protein myeloid differentiation primary response protein (MyD88), since they were not observed in cultures obtained from IL-1R1 (-/-) or from MyD88 (-/-) mice. Ceramide, a second messenger of the IL-1R1-dependent fast signaling cascade, is produced by IL-1R1-MyD88-mediated activation of the neutral sphingomyelinase. C2-ceramide, its cell penetrating analog, also increased the frequency of miniature inhibitory postsynaptic currents in a subset of cells. Both IL-1beta and ceramide reduced the delayed rectifier and the A-type K(+) currents in preoptic area/anterior hypothalamus neurons. The latter effect may account in part for the increased spontaneous inhibitory postsynaptic current frequency as suggested by experiments with the A-type K(+) channel blockers 4-aminopyridine. Taken together our data suggest that IL-1beta inhibits the activity of preoptic area/anterior hypothalamus neurons by increasing the presynaptic release of GABA.

Age-related changes in glutathione and glutathione-related enzymes in rat brain

The most reliable and robust risk factor for some neurodegenerative diseases is aging. It has been proposed that processes of aging are associated with the generation of reactive oxygen species and a disturbance of glutathione homeostasis in the brain. Yet, aged animals have rarely been used to model the diseases that are considered to be age-related such as Parkinson's or Alzheimer's disease. This suggests that the results from these studies would be more valuable if aged animals were used. The present study was designed to provide insight into the glutathione redox state in young and aged rat siblings of both genders by studying the enzyme activities related to glutathione synthesis, cycling, and usage. The results suggested a significant age-related reduction of reduced glutathione (GSH) level in all brain regions examined, associated with an increase of GSH oxidation to glutathione disulfide (GSSG) and decrease of the GSH/GSSG ratio. These changes were accompanied by diminished gamma-glutamylcysteine synthetase activity in de novo glutathione synthesis and increased lipid peroxidation. In addition, these changes were associated with increased enzyme activities related to the GSH usage (glutathione peroxidase, gamma-glutamyl transpeptidase, and glutathione S-transferase). The results indicate that aged animals are likely more vulnerable to oxidative stress and insinuate the roles of aged animals in modeling age-related neurodegeneration diseases.

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

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

Age-dependent hypothalamic expression of neuropeptides in wild-type and melanocortin-4 receptor-deficient mice

In young (35- to 56-day-old) and middle-aged (9-mo-old) wild-type (+/+) and melanocortin-4 receptor (MC4R)-deficient (+/−, −/−) mice, expressions of neuropeptide Y (NPY), agouti-related protein (AGRP), pro-opiomelanocortin (POMC), and cocaine-and-amphetamine-regulated transcript (CART) were analyzed in the arcuate nucleus (ARC) and adjacent regions comprising the dorsomedial (DMN) and ventromedial (VMN) nucleus. In the ARC of young mice, NPY and AGRP expression increased and POMC and CART expression decreased with body fat content. Adjusting for the influence of body fat content by ANCOVA showed that the levels of NPY, POMC, and CART were highest and of AGRP lowest in young −/− mice. In the middle-aged mice, feedback from body fat content was weakened. For −/− mice ANCOVA revealed higher NPY and AGRP, lower POMC, and unchanged CART expression levels relative to young −/− mice. In the DMN and VMN, POMC and AGRP signals were absent at each age. CART was expressed in the DMN independent of age, fat content, and genotype. For NPY expression, an age-dependent induction was found in the DMN and VMN; it was absent in the young but present in the middle-aged mice, showing close positive correlations between body fat content and the numbers of NPY-labeled cells which were further enhanced in −/− mice. Thus MC4R deficiency augments age-induced NPY expression in the DMN and VMN with no feedback from body fat content. Negative feedback control by body fat content on ARC neuropeptide expression is present in young animals but vanishes with age and is modulated by MC4R deficiency.

Lewis hypothalamic cells constitutively and upon stimulation express higher levels of mRNA for pro-inflammatory cytokines and related molecules: comparison with inflammatory resistant Fischer rat hypothalamic cells

Endogenous hypothalamic pro-inflammatory cytokines modulate the hypothalamic-pituitary-adrenal (HPA) axis responses. To investigate whether hypothalamic IL-1beta, IL-6, and tumor necrosis factor-alpha (TNF-alpha) are associated with differential inflammatory susceptibilities between Lewis (LEW/N) and Fischer (F344/N) rats, mRNA levels of pro-inflammatory cytokines and related molecules in hypothalamic cell cultures of both strains were quantified by real-time polymerase chain reaction (PCR). In addition to IL-1beta, IL-6, TNF-alpha, and their receptors, LEW/N hypothalamic cells also transcribed more anti-inflammatory molecules, IL-1RII, IL-1RA, and transforming growth factor (TGFbeta1), than F334/N cells. Our findings suggest that a balance exists between transcripts for endogenous pro- and anti-inflammatory molecules in LEW/N rats that may allow them, under basal conditions, to maintain hypothalamic homeostasis and health. However, under stimulated conditions, this balance may be more easily perturbed toward chronic inflammation.

Cytokines and cognition--the case for a head-to-toe inflammatory paradigm

The brain is not only immunologically active of its own accord, but also has complex peripheral immune interactions. Given the central role of cytokines in neuroimmmunoendocrine processes, it is hypothesized that these molecules influence cognition via diverse mechanisms. Peripheral cytokines penetrate the blood-brain barrier directly via active transport mechanisms or indirectly via vagal nerve stimulation. Peripheral administration of certain cytokines as biological response modifiers produces adverse cognitive effects in animals and humans. There is abundant evidence that inflammatory mechanisms within the central nervous system (CNS) contribute to cognitive impairment via cytokine-mediated interactions between neurons and glial cells. Cytokines mediate cellular mechanisms subserving cognition (e.g., cholinergic and dopaminergic pathways) and can modulate neuronal and glial cell function to facilitate neuronal regeneration or neurodegeneration. As such, there is a growing appreciation of the role of cytokine-mediated inflammatory processes in neurodegenerative diseases such as Alzheimer's disease and vascular dementia. Consistent with their involvement as mediators of bidirectional communication between the CNS and the peripheral immune system, cytokines play a key role in the hypothalamic-pituitary-adrenal axis activation seen in stress and depression. In addition, complex cognitive systems such as those that underlie religious beliefs, can modulate the effects of stress on the immune system. Indirect means by which peripheral or central cytokine dysregulation could affect cognition include impaired sleep regulation, micronutrient deficiency induced by appetite suppression, and an array of endocrine interactions. Given the multiple levels at which cytokines are capable of influencing cognition it is plausible that peripheral cytokine dysregulation with advancing age interacts with cognitive aging.

Neuropeptide Y-induced angiogenesis in aging

Age-related changes in NPY-driven angiogenesis were investigated using Matrigel and aortic sprouting assays in young (2 months.) and aged (18 months.) mice. In both assays, NPY-induced vessel growth decreased significantly with age. In parallel, aged mice showed reduced expression (RT-PCR) of Y2 receptors and the NPY converting enzyme, dipeptidyl peptidase IV (DPPIV), in spleens. Aging of human microvascular endothelial cells in vitro led to a loss of their mitogenic responses to NPY accompanied by a lack of NPY receptor mRNAs. Thus, NPY-dependent angiogenesis is impaired with age, which is associated with a decreased expression of endothelial NPY receptors (Y2) and DPPIV.

Selective increases in cytokine expression in the rat brain in response to striatal injection of alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionate and interleukin-1

A number of cytokines contribute to acute experimental neurodegeneration. The cytokine response can have detrimental or beneficial effects depending on the temporal profile and balance between pro- and anti-inflammatory molecules. Our recent data suggest that the pro-inflammatory cytokine interleukin-1beta (IL-1beta) acts at specific sites (e.g., the striatum) in the rat brain to cause distant cortical injury, when co-administered with the potent excitotoxin alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionate (S-AMPA). The objective of the present study was to investigate changes in the expression of several cytokines simultaneously in the rat striatum and cortex after intrastriatal administration of vehicle, S-AMPA or human recombinant (hr) IL-1beta alone or S-AMPA co-injected with hrIL-1beta using reverse transcription-polymerase chain reaction (RT-PCR; Taqman fluorogenic probes) and enzyme-linked immunosorbent assay (ELISA). Injection of S-AMPA alone increased IL-6 mRNA expression in the ipsilateral striatum after 8 h, whilst striatal injection of IL-1beta alone increased local IL-1beta and IL-1ra mRNAs. The levels of mRNA encoding IL-1alpha, IL-1beta, IL-1ra, IL-6, IL-10 and TNFalpha were markedly elevated in the ipsilateral cortex 8 h after co-injection of S-AMPA and hrIL-1beta. Cortical mRNA levels for IL-4, IL-18, TGFbeta and IFNgamma were not significantly different between treatment groups after 2 h or 8 h. A similar pattern of change in the levels of IL-1alpha and IL-6 protein was observed 8 h after treatment. These data demonstrate selective increases in the expression of cytokines in areas of remote cell death in response to administration of hrIL-1beta and S-AMPA. Such cytokines may be involved in the ensuing damage, and further clarification of their actions could aid future therapeutic strategies for several acute neurodegenerative disorders.

Kindling modulates the IL-1beta system, TNF-alpha, TGF-beta1, and neuropeptide mRNAs in specific brain regions

Cytokines and neuropeptides may be involved in seizure-associated processes. Following amygdala kindling in rats, we determined alterations of IL-1beta, IL-1 receptor antagonist (IL-1Ra), IL-1 receptor type I (IL-1RI), IL-1 receptor accessory proteins (IL-1R AcPs) I and II, TNF-alpha, TGF-beta1, neuropeptide Y (NPY), glycoprotein 130 (gp 130) and pro-opiomelanocortin (POMC) mRNA levels in the parietal, prefrontal and piriform cortices, amygdala, hippocampus and hypothalamus. Messenger RNAs expression in all brain regions was determined 2 h or 3 weeks following the last generalized convulsive seizure triggered from the ipsilateral kindled amygdala. The same brain region sample was used to assay for changes of all mRNA components. The results show that the 2 h-kindled group exhibited a significant up-regulation of IL-1beta, IL-1RI, TNF-alpha and TGF-beta1 mRNAs in all three cortical brain regions, amygdala and hippocampus. The largest up-regulation occurred in the prefrontal cortex (about 30-fold induction for IL-1beta and TNF-alpha mRNAs). IL-1R AcP I and II mRNA levels were also up-regulated in the cortical regions. No changes in IL-1beta, IL-1RI or TNF-alpha mRNA levels occurred in the 3 week-kindled group. NPY mRNA levels increased in the hippocampus, prefrontal and piriform cortices in the 2 h-kindled group, while IL-1Ra, gp 130, or POMC mRNA levels did not change in any group. The overall profile of mRNA changes shows specificity of transcriptional modulation induced by amygdala kindling. The data support a role of cytokines and NPY in the adaptive mechanisms associated with generalized seizure activity, with implications for neuroprotection, neuronal dysfunction and vulnerability associated with epileptic activity.

Neither acute nor chronic exposure to a naturalistic (predator) stressor influences the interleukin-1beta system, tumor necrosis factor-alpha, transforming growth factor-beta1, and neuropeptide mRNAs in specific brain regions

Physical (neurogenic) stressors may influence immune functioning and interleukin-1beta (IL-1beta) mRNA levels within several brain regions. The present study assessed the effects of an acute or repeated naturalistic, psychogenic stressor (predator exposure) on brain cytokine and neuropeptide mRNAs. Acute predator (ferret) exposure induced stress-like behavioral effects, including elicitation of a startle response and reduced exploratory behaviors; these responses diminished after 30 sessions. Moreover, acute and repeated predator exposure, like acute restraint stress, increased plasma corticosterone levels measured 5 min later, but not 2 h after stressor exposure. In contrast, none of the stressors used influenced IL-1beta, IL-1 receptor antagonist, IL-1 receptor type I, IL-1 receptor accessory proteins I and II, or tumor necrosis factor-alpha mRNA levels in the prefrontal cortex, amygdala, hippocampus, or hypothalamus. Likewise, there were no stressor effects on transforming growth factor-beta1, neuropeptide Y, glycoprotein 130, or leptin receptor mRNAs in brain regions. Thus, the naturalistic/psychogenic stressor used does not affect any of the brain cytokine component mRNAs studied. It is suggested that this type of stressor activates homeostatic mechanisms (e.g., glucocorticoid release), which act to preclude brain cytokine alterations that would otherwise favor neuroinflammatory/neuroimmunological responses and the consequent increase of brain sensitivity to neurotoxic and neurodegenerative processes.