Regulation of astroglial-derived dopaminergic neurotrophic factors by interleukin-1 beta in the striatum of young and middle-aged mice

Neonatal 6-OHDA lesion of the SNc induces striatal compensatory sprouting from surviving SNc dopaminergic neurons without VTA contribution

Dopamine (DA) neurons of the substantia nigra pars compacta (SNc) are uniquely vulnerable to neurodegeneration in Parkinson's disease (PD). We hypothesize that their large axonal arbor is a key factor underlying their vulnerability, due to increased bioenergetic, proteostatic and oxidative stress. In keeping with this model, other DAergic populations with smaller axonal arbors are mostly spared during the course of PD and are more resistant to experimental lesions in animal models. Aiming to improve mouse PD models, we examined if neonatal partial SNc lesions could lead to adult mice with fewer SNc DA neurons that are endowed with larger axonal arbors because of compensatory mechanisms. We injected 6-hydroxydopamine (6-OHDA) unilaterally in the SNc at an early postnatal stage at a dose selected to induce loss of approximately 50% of SNc DA neurons. We find that at 10 and 90 days after the lesion, the axons of SNc DA neurons show massive compensatory sprouting, as revealed by the proportionally smaller decrease in tyrosine hydroxylase (TH) in the striatum compared with the loss of SNc DA neuron cell bodies. The extent and origin of this axonal sprouting was further investigated by AAV-mediated expression of eYFP in SNc or ventral tegmental area (VTA) DA neurons of adult mice. Our results reveal that SNc DA neurons have the capacity to substantially increase their axonal arbor size and suggest that mice designed to have reduced numbers of SNc DA neurons could potentially be used to develop better mouse models of PD, with elevated neuronal vulnerability.

Corneal Cells: Fine-tuning Nerve Regeneration

The cornea is a transparent outermost structure of the eye anterior segment comprising the highest density of innervated tissue. In the process of corneal innervation, trigeminal ganglion originated corneal nerves diligently traverse different corneal cell types in different corneal layers including the corneal stroma and epithelium. While crossing the stromal and epithelial cell layers during innervation, due to the existing physical contacts, close interactions occur between stromal keratocytes, epithelial cells, resident immune cells and corneal nerves. Furthermore, by producing various trophic and growth factors corneal cells assist in maintaining the growth and function of corneal nerves. Similarly, corneal nerve generated growth factors critically modify the corneal cell function in all the corneal layers. Due to their close association and contacts, on-going cross-communication between these cell types and corneal nerves play a vital role in the modulation of corneal nerve function, regeneration during wound healing. The present review highlights the influence of different corneal cell types and growth factors released from these cells on corneal nerve regeneration and function.

Ischemic stroke in neonatal and adult astrocytes

The objective of this paper is to review current information regarding astrocytes function after a stroke in neonatal and adult brain. Based on the current literature, there are some molecular differences related to blood brain barrier (BBB) homeostasis disruption, inflammation and reactive oxygen species (ROS) mediated injury between the immature and mature brain after an ischemic event. In particular, astrocytes, the main glial cells in brain, play a different role in neonatal and adult brain after stroke, as time course of glial activation is strongly age dependent. Moreover, the present review provides further insight into the therapeutic approaches of using neonatal and adult astrocytes after stroke. More research will be needed in order to translate them into an effective treatment against stroke, the second main cause of death and disability worldwide.

Estrogen protects against dopamine neuron toxicity in primary mesencephalic cultures through an indirect P13K/Akt mediated astrocyte pathway

Astrocytes regulate neuronal homeostasis and have been implicated in affecting the viability and functioning of surrounding neurons under stressed and injured conditions. Previous data from our lab suggests indirect actions of estrogen through ERα in neighboring astroglia to protect dopamine neurons against 1-methyl-4-phenylpyridinium (MPP(+)) toxicity in mouse mesencephalic cultures. We further evaluate estrogen signaling in astrocytes and the mechanism of estrogen's indirect neuroprotective effects on dopamine neurons. Primary mesencephalic cultures pre-treated with 17β-estradiol and the membrane impermeable estrogen, E2-BSA, were both neuroprotective against MPP(+) -induced dopamine neuron toxicity, suggesting membrane-initiated neuroprotection. ERα was found in the plasma membrane of astrocyte cultures and colocalized with the lipid raft marker, flotillin-1. A 17β-estradiol time course revealed a significant increase in Akt, which was inhibited by the PI3 kinase inhibitor, LY294004. Estrogen conditioned media collected from pure astrocyte cultures rescued glial deficient mesencephalic cultures from MPP(+). This indirect estrogen-mediated neuroprotective effect in mesencephalic cultures was significantly reduced when PI3 kinase signaling in astrocytes was blocked prior to collecting estrogen-conditioned media using the irreversible PI3 kinase inhibitor, Wortmannin. Estrogen signaling via astrocytes is rapidly initiated at the membrane level and requires PI3 kinase signaling in order to protect primary mesencephalic dopamine neurons from MPP(+) neurotoxicity.

Astrocytes, therapeutic targets for neuroprotection and neurorestoration in ischemic stroke

Astrocytes are the most abundant cell type within the central nervous system. They play essential roles in maintaining normal brain function, as they are a critical structural and functional part of the tripartite synapses and the neurovascular unit, and communicate with neurons, oligodendrocytes and endothelial cells. After an ischemic stroke, astrocytes perform multiple functions both detrimental and beneficial, for neuronal survival during the acute phase. Aspects of the astrocytic inflammatory response to stroke may aggravate the ischemic lesion, but astrocytes also provide benefit for neuroprotection, by limiting lesion extension via anti-excitotoxicity effects and releasing neurotrophins. Similarly, during the late recovery phase after stroke, the glial scar may obstruct axonal regeneration and subsequently reduce the functional outcome; however, astrocytes also contribute to angiogenesis, neurogenesis, synaptogenesis, and axonal remodeling, and thereby promote neurological recovery. Thus, the pivotal involvement of astrocytes in normal brain function and responses to an ischemic lesion designates them as excellent therapeutic targets to improve functional outcome following stroke. In this review, we will focus on functions of astrocytes and astrocyte-mediated events during stroke and recovery. We will provide an overview of approaches on how to reduce the detrimental effects and amplify the beneficial effects of astrocytes on neuroprotection and on neurorestoration post stroke, which may lead to novel and clinically relevant therapies for stroke.

Novel targets for Spinal Cord Injury related neuropathic pain

Millions of people suffer from spinal cord injury (SCI) with little known effective clinical therapy. Neuropathic pain (NP) is often accompanied with SCI, making clinical treatment challenging. Even though the key mediators in the development of NP have been discovered, the pathogenesis is still unclear. Some of the key mediators in the sustenance of NP include the inflammatory processes, cannabinoid receptors, matrix metalloproteases, and their tissue inhibitors. Animal models have shown promising results with modulation of these mediators, yet the clinical models have been unsuccessful. One such study with matrix metalloproteases (MMPs) has yielded encouraging results. The relationship between MMPs and their tissue inhibitors (TIMPs) plays a significant role in the pathogenesis and recovery of SCI and the CNS. Key factors that lead to the functional consequences of MMP activity are cellular localization, tissue distribution, and temporal pattern of MMP expression. Studies concluding that MMPs can be seen as contributors of tissue damage and as contributors in the repair mechanisms have provided a need to reexamine their roles after acute and chronic neuropathic pain

Neurotoxins released from interferon-gamma-stimulated human astrocytes

Astrocytes become activated in degenerative neurological diseases. In order to gain a greater understanding of the inflammatory factors released upon activation, we stimulated adult human astrocytes with interferon-gamma and examined the resultant conditioned medium (CM) for toxicity against differentiated human neuroblastoma SH-SY5Y cells. Cell death was measured by lactate dehydrogenase release assay. We then used various treatments of the media to determine the distribution and nature of the toxic components. Removal of interleukin-6 by a specific antibody reduced the toxicity by 22%. Blockade of proteases with an inhibitor cocktail reduced it by a further 22%. When oxygen-free radical production was blocked with NADPH oxidase inhibitors, the toxicity was reduced by 15.4%. When prostaglandin production was blocked by cyclooxygenase inhibitors, the toxicity of the CM was reduced by 14.5%. When glutamate was removed by treatment with glutamate decarboxylase, the toxicity was reduced by 10.3%. When the inhibitors were added together to the astrocyte culture, the total toxicity of the CM was reduced by 91%. This was in reasonable agreement with the 85.37% total obtained by adding the individual components. The data show that activated astrocytes release a specific combination of neurotoxic compounds. They suggest that effective anti-inflammatory treatment of such neurodegenerative diseases as Alzheimer's disease, Parkinson's disease and Amyotrophic lateral sclerosis could be improved by using an appropriate combination of anti-inflammatory agents instead of relying on any single agent.

Neuroplastic changes in depression: a role for the immune system

Accumulating evidence suggests that there is a rich cross-talk between the neuroimmune system and neuroplasticity mechanisms under both physiological conditions and pathophysiological conditions in depression. Anti-neuroplastic changes which occur in depression include a decrease in proliferation of neural stem cells (NSCs), decreased survival of neuroblasts and immature neurons, impaired neurocircuitry (cortical-striatal-limbic circuits), reduced levels of neurotrophins, reduced spine density and dendritic retraction. Since both humoral and cellular immune factors have been implicated in neuroplastic processes, in this review we present a model suggesting that neuroplastic processes in depression are mediated through various neuroimmune mechanisms. The review puts forward a model in that both humoral and cellular neuroimmune factors are involved with impairing neuroplasticity under pathophysiological conditions such as depression. Specifically, neuroimmune factors including interleukin (IL)-1, IL-6, tumour necrosis factor (TNF)-α, CD4⁺CD25⁺T regulatory cells (T reg), self-specific CD4⁺T cells, monocyte-derived macrophages, microglia and astrocytes are shown to be vital to processes of neuroplasticity such as long-term potentiation (LTP), NSC survival, synaptic branching, neurotrophin regulation and neurogenesis. In rodent models of depression, IL-1, IL-6 and TNF are associated with reduced hippocampal neurogenesis; mechanisms which are associated with this include the stress-activated protein kinase (SAPK)/Janus Kinase (JNK) pathway, hypoxia-inducible factors (HIF)-1α, JAK-Signal Transducer and Activator of Transcription (STAT) pathway, mitogen-activated protein kinase (MAPK)/cAMP responsive element binding protein (CREB) pathway, Ras-MAPK, PI-3 kinase, IKK/nuclear factor (NF)-κB and TGFβ activated kinase-1 (TAK-1). Neuroimmunological mechanisms have an active role in the neuroplastic changes associated with depression. Since therapies in depression, including antidepressants (AD), omega-3 polyunsaturated fatty acids (PUFAs) and physical activity exert neuroplasticity-enhancing effects potentially mediated by neuroimmune mechanisms, the immune system might serve as a promising target for interventions in depression.

Interleukin-1 beta and neurotrophin-3 synergistically promote neurite growth in vitro

Pro-inflammatory cytokines such as interleukin-1 beta (IL-1β) are considered to exert detrimental effects during brain trauma and in neurodegenerative disorders. Consistently, it has been demonstrated that IL-1β suppresses neurotrophin-mediated neuronal cell survival rendering neurons vulnerable to degeneration. Since neurotrophins are also well known to strongly influence axonal plasticity, we investigated here whether IL-1β has a similar negative impact on neurite growth. We analyzed neurite density and length of organotypic brain and spinal cord slice cultures under the influence of the neurotrophins NGF, BDNF, NT-3 and NT-4. In brain slices, only NT-3 significantly promoted neurite density and length. Surprisingly, a similar increase of neurite growth was induced by IL-1β. Additionally, both factors increased the number of brain slices displaying maximal neurite growth. Furthermore, the co-administration of IL-1β and NT-3 significantly increased the number of brain slices displaying maximal neurite growth compared to single treatments. These data indicate that these two factors synergistically stimulate two distinct aspects of neurite outgrowth, namely neurite density and neurite length from acute organotypic brain slices.

Dopamine-dependent ectodomain shedding and release of epidermal growth factor in developing striatum: target-derived neurotrophic signaling (Part 2)

Epidermal growth factor (EGF) and structurally related peptides promote neuronal survival and the development of midbrain dopaminergic neurons; however, the regulation of their production has not been fully elucidated. In this study, we found that the treatment of striatal cells with dopamine agonists enhances EGF release both in vivo and in vitro. We prepared neuron-enriched and non-neuronal cell-enriched cultures from the striatum of rat embryos and challenged those with various neurotransmitters or dopamine receptor agonists. Dopamine and a dopamine D(1) -like receptor agonist (SKF38393) triggered EGF release from neuron-enriched cultures in a dose-dependent manner. A D(2) -like agonist (quinpirole) increased EGF release only from non-neuronal cell-enriched cultures. The EGF release from striatal neurons and non-neuronal cells was concomitant with ErbB1 phosphorylation and/or with the activation of a disintegrin and metalloproteinase and matrix metalloproteinase. The EGF release from neurons was attenuated by an a disintegrin and metalloproteinase/matrix metalloproteinase inhibitor, GM6001, and a calcium ion chelator, BAPTA/AM. Transfection of cultured striatal neurons with alkaline phosphatase-tagged EGF precursor cDNA confirmed that dopamine D(1) -like receptor stimulation promoted both ectodomain shedding of the precursor and EGF release. Therefore, the activation of striatal dopamine receptors induces shedding and release of EGF to provide a retrograde neurotrophic signal to midbrain dopaminergic neurons.

Qualitative and quantitative re-evaluation of epidermal growth factor-ErbB1 action on developing midbrain dopaminergic neurons in vivo and in vitro: target-derived neurotrophic signaling (Part 1)

Although epidermal growth factor (EGF) receptor (ErbB1) is implicated in Parkinson's disease and schizophrenia, the neurotrophic action of ErbB1 ligands on nigral dopaminergic neurons remains controversial. Here, we ascertained colocalization of ErbB1 and tyrosine hydroxylase (TH) immunoreactivity and then characterized the neurotrophic effects of ErbB1 ligands on this cell population. In mesencephalic culture, EGF and glial-derived neurotrophic factor (GDNF) similarly promoted survival and neurite elongation of dopaminergic neurons and dopamine uptake. The EGF-promoted dopamine uptake was not inhibited by GDNF-neutralizing antibody or TrkB-Fc, whereas EGF-neutralizing antibody fully blocked the neurotrophic activity of the conditioned medium that was prepared from EGF-stimulated mesencephalic cultures. The neurotrophic action of EGF was abolished by ErbB1 inhibitors and genetic disruption of erbB1 in culture. In vivo administration of ErbB1 inhibitors to rat neonates diminished TH and dopamine transporter (DAT) levels in the striatum and globus pallidus but not in the frontal cortex. In parallel, there was a reduction in the density of dopaminergic varicosities exhibiting intense TH immunoreactivity. In agreement, postnatal erbB1-deficient mice exhibited similar decreases in TH levels. Although neurotrophic supports to dopaminergic neurons are redundant, these results confirm that ErbB1 ligands contribute to the phenotypic and functional development of nigral dopaminergic neurons.

Multitract microtransplantation increases the yield of DARPP-32-positive embryonic striatal cells in a rodent model of Huntington's disease

Embryonic striatal graft-mediated functional recovery in the rodent lesion model of Huntington's disease (HD) has been shown to correlate with the proportion of dopamine- and adenosine 3',5'-monophosphate-regulated phosphoprotein with a molecular weight of 32 kDa (DARPP-32)-positive neurons in the graft. The current study investigated the impact of graft distribution on the yield of DARPP-32-positive cells in the grafts following either single-tract or multitract cell delivery protocols using the microtransplantation approach. Cells derived from the whole ganglionic eminence of E15 rat embryos, ubiquitously expressing green fluorescent protein (GFP), were implanted into unilaterally QA-lesioned rat striatum either as 2 × 1.8 μl macrodeposits in a single tract, or as 18 × 0.2 μl microdeposits disseminated over six needle, multitract, penetrations. For both groups, an ultrathin glass capillary with an outer diameter of 50 μm was used. Histological assessment at 4 months after transplantation showed nearly twofold increase of DARRP-32-positive striatal-like neurons in the multitract compared to the single-tract group. However, the cellular make-up of the grafts did not translate into functional differences as tested in a basic spontaneous behavior test. Furthermore, the volumetric values for overall volume, DARPP-32-positive patches, and dopaminergic projection zones were similar between both groups. The results show that distribution of fetal striatal tissue in multiple submicroliter deposits provides for an increased yield of striatal-like neurons, potentially due to the enlargement of the graft-host border area intensifying the graft's exposure to host-derived factors. Furthermore, the use of embryonic tissue from GFP donors was validated in cell-based therapy studies in the HD model.

Mending the broken brain: neuroimmune interactions in neurogenesis

Neuroimmune networks and the brain endocannabinoid system contribute to the maintenance of neurogenesis. Cytokines and chemokines are important neuroinflammatory mediators that are involved in the pathological processes resulting from brain trauma, ischemia and chronic neurodegenerative diseases. However, they are also involved in brain repair and recovery. Compelling evidence obtained, in vivo and in vitro, establish a dynamic interplay between the endocannabinoid system, the immune system and neural stem/progenitor cells (NSC) in order to promote brain self-repair. Cross-talk between inflammatory mediators and NSC might have important consequences for neural development and brain repair. In addition, brain immune cells (microglia) support NSC renewal, migration and lineage specification. The proliferation and differentiation of multipotent NSC must be precisely controlled during the development of the CNS, as well as for adult brain repair. Although signalling through neuroimmune networks has been implicated in many aspects of neural development, how it affects NSC remains unclear. However, recent findings have clearly demonstrated that there is bi-directional cross-talk between NSC, and the neuroimmune network to control the signals involved in self-renewal and differentiation of NSC. Specifically, there is evidence emerging that neuroimmune interactions control the generation of new functional neurones from adult NSC. Here, we review the evidence that neuroimmune networks contribute to neurogenesis, focusing on the regulatory mechanisms that favour the immune system (immune cells and immune molecules) as a novel element in the coordination of the self-renewal, migration and differentiation of NSC in the CNS. In conjunction, these data suggest a novel mode of action for the immune system in neurogenesis that may be of therapeutic interest in the emerging field of brain repair.

The role of astroglia in neuroprotection

Astrocytes are the main neural cell type responsible for the maintenance of brain homeostasis. They form highly organized anatomical domains that are interconnected into extensive networks. These features, along with the expression of a wide array of receptors, transporters, and ion channels, ideally position them to sense and dynamically modulate neuronal activity. Astrocytes cooperate with neurons on several levels, including neurotransmitter trafficking and recycling, ion homeostasis, energy metabolism, and defense against oxidative stress. The critical dependence of neurons upon their constant support confers astrocytes with intrinsic neuroprotective properties which are discussed here. Conversely, pathogenic stimuli may disturb astrocytic function, thus compromising neuronal functionality and viability. Using neuroinflammation, Alzheimer's disease, and hepatic encephalopathy as examples, we discuss how astrocytic defense mechanisms may be overwhelmed in pathological conditions, contributing to disease progression.

Cell-specific and concentration-dependent actions of interleukin-1 in acute brain inflammation

Interleukin (IL)-1 is a pivotal pro-inflammatory cytokine and an important mediator of both acute and chronic central nervous system (CNS) injuries. Despite intense research in CNS IL-1 biology over the past two decades, its precise mechanism of action in inflammatory responses to acute brain disorders remains largely unknown. In particular, much effort has been focussed on using in vitro approaches to better understand the cellular and signalling mechanisms of actions of IL-1, yet some discrepancies in the literature regarding the effects produced by IL-1beta in in vitro paradigms of injury still exist, particularly as to whether IL-1 exerts neurotoxic or neuroprotective effects. Here we aim to review the cell-specific and concentration-dependent actions of IL-1 in brain cells, to depict the mechanism by which this cytokine induces neurotoxicity or neuroprotection in acute brain injury.

Driving GDNF expression: the green and the red traffic lights

Glial cell line-derived neurotrophic factor (GDNF) is widely recognized as a potent survival factor for dopaminergic neurons of the nigrostriatal pathway that degenerate in Parkinson's disease (PD). In animal models of PD, GDNF delivery to the striatum or the substantia nigra protects dopaminergic neurons against subsequent toxin-induced injury and rescues previously damaged neurons, promoting recovery of the motor function. Thus, GDNF was proposed as a potential therapy to PD aimed at slowing down, halting or reversing neurodegeneration, an issue addressed in previous reviews. However, the use of GDNF as a therapeutic agent for PD is hampered by the difficulty in delivering it to the brain. Another potential strategy is to stimulate the endogenous expression of GDNF, but in order to do that we need to understand how GDNF expression is regulated. The aim of this review is to do a comprehensive analysis of the state of the art on the control of endogenous GDNF expression in the nervous system, focusing mainly on the nigrostriatal pathway. We address the control of GDNF expression during development, in the adult brain and after injury, and how damaged neurons signal glial cells to up-regulate GDNF. Pharmacological agents or natural molecules that increase GDNF expression and show neuroprotective activity in animal models of PD are reviewed. We also provide an integrated overview of the signalling pathways linking receptors for these molecules to the induction of GDNF gene, which might also become targets for neuroprotective therapies in PD.

The role of mineralocorticoid receptor expression in brain remodeling after cerebral ischemia

Mineralocorticoid receptors (MRs) are classically known to be expressed in the distal collecting duct of the kidney. Recently it was reported that MR is identified in the heart and vasculature. Although MR expression is also found in the brain, it is restricted to the hippocampus and cerebral cortex under normal condition, and the role played by MRs in brain remodeling after cerebral ischemia remains unclear. In the present study, we used the mouse 20-min middle cerebral artery occlusion model to examine the time course of MR expression and activity in the ischemic brain. We found that MR-positive cells remarkably increased in the ischemic striatum, in which MR expression is not observed under normal conditions, during the acute and, especially, subacute phases after stroke and that the majority of MR-expressing cells were astrocytes that migrated to the ischemic core. Treatment with the MR antagonist spironolactone markedly suppressed superoxide production within the infarct area during this period. Quantitative real-time RT-PCR revealed that spironolactone stimulated the expression of neuroprotective or angiogenic factors, such as basic fibroblast growth factor (bFGF) and vascular endothelial growth factor (VEGF), whereas immunohistochemical analysis showed astrocytes to be cells expressing bFGF and VEGF. Thereby the incidence of apoptosis was reduced. The up-regulated bFGF and VEGF expression also appeared to promote endogenous angiogenesis and blood flow within the infarct area and to increase the number of neuroblasts migrating toward the ischemic striatum. By these beneficial effects, the infarct volume was significantly reduced in spironolactone-treated mice. Spironolactone may thus provide therapeutic neuroprotective effects in the ischemic brain after stroke.

Fetal striatum- and ventral mesencephalon-derived expanded neurospheres rescue dopaminergic neurons in vitro and the nigro-striatal system in vivo

The pathogenesis of Parkinson's disease (PD) involves ongoing apoptotic loss of dopaminergic neurons in the substantia nigra pars compacta. Local delivery of the trophic factors can rescue dopaminergic neurons and halt the progression of PD. In this study we show that fetal E11 striatum-derived neurospheres and E14.5 ventral mesencephalon (VM) -derived neurospheres (NS E11 and NSvm, respectively) are a source of factors that rescue dopaminergic neurons. First, long-term expanded NS E11 and NSvm rescued primary dopaminergic neurons from serum-deprivation induced apoptosis and promoted survival of dopaminergic neurons for 14 days in vitro and this effect was due to soluble contact-independent factor/s. Second, green fluorescent protein-expressing NS E11 and NSvm grafted into the midbrain of mice with unilateral 6-hydroxydopamine-induced Parkinsonism resulted in partial rescue of the nigro-striatal system and improvement of the hypo-dopaminergic behavioral deficit. Reverse transcription-polymerase chain reaction (RT-PCR) analysis demonstrated that intact NS E11 and NSvm expressed fibroblast growth factor-2, brain-derived neurotrophic factor (BDNF), pleiotrophin, neurotrophin-3, but not glial cell line-derived neurotrophic factor (GDNF). GDNF expression was also undetectable in vivo in grafted NS E11 and NSvm suggesting that NS-derived factor/s other than GDNF mediated the rescue of nigral dopaminergic neurons. Identification of NS-derived soluble factor(s) may lead to development of novel neuroprotective therapies for PD. An unexpected observation of the present study was the detection of the ectopic host-derived tyrosine hydroxylase (TH) -expressing cells in sham-grafted mice and NS E11- and NSvm -grafted mice. We speculate that injury-derived signals (such as inflammatory cytokines that are commonly released during transplantation) induce TH expression in susceptible cells.

The cellular and behavioral consequences of interleukin-1 alpha penetration through the blood-brain barrier of neonatal rats: a critical period for efficacy

Proinflammatory cytokines circulating in the periphery of early postnatal animals exert marked influences on their subsequent cognitive and behavioral traits and are therefore implicated in developmental psychiatric diseases such as schizophrenia. Here we examined the relationship between the permeability of the blood-brain barrier to interleukin-1 alpha (IL-1 alpha) in neonatal and juvenile rats and their later behavioral performance. Following s.c. injection of IL-1 alpha into rat neonates, IL-1 alpha immunoreactivity was first detected in the choroid plexus, brain microvessels, and olfactory cortex, and later diffused to many brain regions such as neocortex and hippocampus. In agreement, IL-1 alpha administration to the periphery resulted in a marked increase in brain IL-1 alpha content of neonates. Repeatedly injecting IL-1 alpha to neonates triggered astrocyte proliferation and microglial activation, followed by behavioral abnormalities in startle response and putative prepulse inhibition at the adult stage. Analysis of covariance with a covariate of startle amplitude suggested that IL-1 alpha administration may influence prepulse inhibition. However, adult rats treated with IL-1 alpha as neonates exhibited normal learning ability as measured by contextual fear conditioning, two-way passive shock avoidance, and a radial maze task and had no apparent sign of structural abnormality in the brain. In comparison, when IL-1 alpha was administered to juveniles, the blood-brain barrier permeation was limited. The increases in brain IL-1 alpha content and immunoreactivity were less pronounced following IL-1 alpha administration and behavioral abnormalities were not manifested at the adult stage. During early development, therefore, circulating IL-1 alpha efficiently crosses the blood-brain barrier to induce inflammatory reactions in the brain and influences later behavioral traits.

Interleukin-1beta mediates proliferation and differentiation of multipotent neural precursor cells through the activation of SAPK/JNK pathway

Neural precursor cells (NPCs) have been experimentally used to repair the damaged nervous system either by exogenous transplantation or by endogenous activation. In post-injury inflammation, an array of cytokines including interleukin-1beta (IL-1beta) are released by host as well as invading immune cells and increased markedly. In the present study, we investigated the effects of IL-1beta on the survival, proliferation, differentiation and migration of NPCs as well as underlying intracellular signaling pathways. NPCs derived from the E16 rat brain were expanded in neurospheres that were found to express IL-1beta, IL-1RI and IL-1RII, but not IL-1alpha and IL-1ra. IL-1beta inhibited the proliferation of NPCs in a dose-dependent manner, an effect that can be reversed by IL-1ra, an antagonist for IL-1 receptor. This inhibitory effect of IL-1beta on NPCs proliferation resulted in part from its effect on increased apoptosis of NPCs. Moreover, IL-1ra did not affect NPCs lineage fate but rather inhibited GFAP expression in differentiated astrocytes. We also found that IL-1ra had no effect on the transmigration of NPCs in vitro. Finally, we showed that the effect of IL-1beta on NPCs proliferation and differentiation appeared to be mediated by SAPK/JNK, but not ERK, P38MAPK nor NF-kappaB pathways. These findings collectively suggest that the inflammatory environment following CNS injuries may influence the ability of NPCs to repair the damage.

Role of interleukin-1beta in the control of neuroepithelial proliferation and differentiation of the spinal cord during development

Interleukin-1beta (IL-1beta) is an important trophic factor in the nervous system (NS). IL-1beta is ubiquitously expressed from very early stages during the development of the amphibian NS and its action has been demonstrated in vitro on survival, proliferation and differentiation in mammalian embryos. In this report, we show that IL-1beta is immunocytochemically expressed in embryonic spinal cord from early stages, both in rat (embryonic day 12) and in chicken (stage 17-HH), in neuroepithelial cells and nerve fibres, dorsal root ganglia, anterior and posterior roots of the spinal nerves, and in the fibres of these nerves. Our in vivo experiments on chick embryos, with microbeads impregnated with IL-1beta implanted laterally to the spinal cord at the level of the wing anlage, demonstrate that this cytokine produces a statistically significant increase in nuclear incorporation of BrdU at the dorsal level and a reduction of this at the ventral level, whereas local immunoblocking with anti-IL-1beta antibodies causes a dorsal reduction of BrdU incorporation and alters ventral differentiation. These data demonstrate that IL-1beta plays a part in controlling proliferation and early differentiation during the development of the spinal cord in chick embryos.

Neuroprotection by estrogen against MPP+-induced dopamine neuron death is mediated by ERalpha in primary cultures of mouse mesencephalon

Estrogen involvement in neuroprotection is now widely accepted, although the specific molecular and cellular mechanisms of estrogen action in neuroprotection remain unclear. This study examines estrogenic effects in a mixed population of cells in attempts to identify the contributing cells that result in estrogen-mediated neuroprotection. Utilizing primary mesencephalic neurons, we found expression of both estrogen receptor alpha (ERalpha) and estrogen receptor beta (ERbeta) with a predominance of ERalpha on both dopamine neurons and astrocytes. We also found that 17beta-estradiol protects dopamine neurons from injury induced by the complex I inhibitor, 1-methyl-4-phenyl pyridinium (MPP(+)) in a time- and ER-dependent manner. At least 4 h of estrogen pre-treatment was required to elicit protection, an effect that was blocked by the ER antagonist, ICI 182,780. Moreover, ERalpha mediated the protection afforded by estrogen since only the ERalpha agonist, HPTE, but not the ERbeta agonist, DPN, protected against dopamine cell loss. Since glial cells were shown to express significant levels of ERalpha, we investigated a possible indirect mechanism of estrogen-mediated neuroprotection through glial cell interaction. Removal of glial cells from the cultures by application of the mitotic inhibitor, 5-fluoro-2'-deoxyuridine, significantly reduced the neuroprotective effects of estrogen. These data indicate that neuroprotection provided by estrogen against MPP(+) toxicity is mediated by ERalpha and involves an interplay among at least two cell types.

Glial degeneration and reactive gliosis in alpha-synucleinopathies: the emerging concept of primary gliodegeneration

The concept of gliodegenerative diseases has not been widely established although there is accumulating evidence that glial cells may represent a primary target of degenerative disease processes. In the central nervous system (CNS), examples that provide a "proof of concept" include at least one alpha-synucleinopathy, multiple system atrophy (MSA), but this disease is conventionally discussed under the heading of "neurodegeneration". Additional evidence in support of primary glial affection has been reported in neurodegenerative disorders such as Parkinson's disease, Alzheimer's disease and transmissible spongiform encephalopathies. Based on biochemical, genetic and transcriptomic studies it is also becoming increasingly clear that the molecular changes measured in whole tissue extracts, e.g. obtained from Parkinson's disease brain, are not based on a purely neuronal contribution. This important evidence has been missed in cell culture or laser capture work focusing on the neuronal cell population. Studies of animal and in vitro models of disease pathogenesis additionally suggest glial accountability for some CNS degenerative processes. This review provides a critical analysis of the evidence available to date in support of the concept of gliodegeneration, which we propose to represent an essential although largely disregarded component of the spectrum of classical "neurodegeneration". Examples from the spectrum of alpha-synucleinopathies are presented.

Selective glial cell line-derived neurotrophic factor production in adult dopaminergic carotid body cells in situ and after intrastriatal transplantation

Glial cell line-derived neurotrophic factor (GDNF) exerts a notable protective effect on dopaminergic neurons in rodent and primate models of Parkinson's disease (PD). The clinical applicability of this therapy is, however, hampered by the need of a durable and stable GDNF source allowing the safe and continuous delivery of the trophic factor into the brain parenchyma. Intrastriatal carotid body (CB) autografting is a neuroprotective therapy potentially useful in PD. It induces long-term recovery of parkinsonian animals through a trophic effect on nigrostriatal neurons and causes amelioration of symptoms in some PD patients. Moreover, the adult rodent CB has been shown to express GDNF. Here we show, using heterozygous GDNF/lacZ knock-out mice, that unexpectedly CB dopaminergic glomus, or type I, cells are the source of CB GDNF. Among the neural or paraneural cells tested, glomus cells are those that synthesize and release the highest amount of GDNF in the adult rodent (as measured by standard and in situ ELISA). Furthermore, GDNF expression by glomus cells is maintained after intrastriatal grafting and in CB of aged and parkinsonian 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine-treated animals. Thus, glomus cells appear to be prototypical abundant sources of GDNF, ideally suited to be used as biological pumps for the endogenous delivery of trophic factors in PD and other neurodegenerative diseases.

Strain-dependent behavioral alterations induced by peripheral interleukin-1 challenge in neonatal mice

Interleukin-1 (IL-1) is implicated in the pathogenesis of various psychiatric diseases. Peripheral administration of IL-1alpha to neonatal rats induces cognitive and behavioral abnormalities and, therefore, the IL-1alpha-treated animals might serve as a schizophrenia model. The present study assessed genetic influences on IL-1alpha-triggered behavioral impairments, using four different strains of neonatal mice, C3H/He, DBA/2, C57BL/6, and ddY. Neonatal treatments with IL-1alpha differentially altered adult behavioral/cognitive traits in a strain-dependent manner. IL-1alpha treatment decreased prepulse inhibition in DBA/2 and C57BL/6 mice but not in C3H/He and ddY. The treatment increased locomotor activity and startle responses in DBA/2 mice and, conversely, decreased startle responses in C3H/He mice. Behavioral alterations were most remarkable in DBA/2 mice but undetectable in ddY mice. The magnitudes of IL-1alpha actions differed between the brain and periphery and were influenced by mouse genetic background. The IL-1-triggered acute signaling, Ikappa-B degradation, was significant in the frontal cortex of DBA/2 mice and in the hypothalamus of C3H/He mice. An increase in brain p38 MAP kinase phosphorylation was also most marked in the DBA/2 strain. In contrast, subchronic influences of IL-1alpha injections failed to illustrate the strain-dependent behavioral alterations. The peripheral effects of IL-1alpha did not match the strain-dependency of the behavioral alterations, either. Acceleration of tooth eruption and eyelid opening as well as attenuation of weight gain was most marked in C3H/He mice and the induction of serum amyloid protein was the largest in ddY mice. Thus, the peripheral effects of IL-1alpha in DBA/2 mice were relatively inferior to those in the other strains. The present animal study suggests that, in early postnatal development, circulating IL-1alpha trigger brain cytokine signaling and produce distinct influences on later neurobehavioral traits, both depending on genetic background.

Cellular distribution of interleukin-1α-immunoreactivity after MPTP intoxication in mice

In young rodents, peripheral injection of N-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) results in a dopaminergic nigrostriatal denervation (during the first week after injection), followed by a spontaneous dopaminergic reinnervation. Sprouting from residual neurons has been proposed to account for this event. It has been shown that an inflammatory process takes place during striatal dopaminergic denervation but its consequences remain controversial. Some clues notably indicate that interleukin (IL)-1alpha may participate in MPTP-induced inflammation and promote recovery. We therefore studied the immunohistochemical localization of IL-1alpha expression in the striatum and ventral mesencephalon at different times (1, 3, 6, 16, and 30 days) after MPTP injection in mice. IL-1alpha-immunoreactivity (ir) was observed in striatum, substantia nigra pars compacta, and ventral tegmental area. Apart from a few localization in mesencephalic activated microglia, IL-1alpha was almost exclusively found in activated astrocytes. However, in the striatal parenchyma, another component of IL-1alpha-ir colocalized with tyrosine hydroxylase (TH)-ir, a marker for dopaminergic neurons. Moreover, some parenchymal TH-positive axons were also found to express the growth cone-associated protein (GAP)-43, a marker for axonal growth cones. In the striatum, IL-1alpha-ir was also detected in a non-astrocytic perivascular component, with a distribution similar to GAP-43-ir. IL-1alpha could thus directly or indirectly influence striatal reorganization after MPTP.

Neuroprotective role of astrocytes in cerebral ischemia: focus on ischemic preconditioning

Following focal cerebral ischemia ("stroke") a complex and dynamic interaction of vascular cells, glial cells, and neurons determines the extent of the ensuing lesion. Traditionally, the focus has been on mechanisms of damage, while recently it has become clear that endogenous mechanisms of protection are equally important for the final outcome. Glial cells, in particular astrocytes, have always been viewed as supporters of neuronal function. Only recently a very active role for glial cells has been emerging in physiology and pathophysiology. Not surprisingly, then, specific protective pathways have been identified by which these cells can protect or even help to regenerate brain tissue after acute insults. However, as exemplified by the existence of the glial scar, which forms around lesioned brain tissue, is composed mainly of astrocytes and plays a key role in regeneration failure, it is an oversimplification to assign merely protective functions to astrocytes. The present review will discuss the role of astrocytes in ischemic brain injury with a focus on neuroprotection in general. In this context we will consider particularly the phenomenon of "ischemic tolerance," which is an experimental paradigm helpful in discriminating destructive from protective mechanisms after cerebral ischemia.

Influences of dopaminergic lesion on epidermal growth factor-ErbB signals in Parkinson's disease and its model: neurotrophic implication in nigrostriatal neurons

Epidermal growth factor (EGF) is a member of a structurally related family containing heparin-binding EGF-like growth factor (HB-EGF) and transforming growth factor alpha (TGFalpha) that exerts neurotrophic activity on midbrain dopaminergic neurons. To examine neurotrophic abnormality in Parkinson's disease (PD), we measured the protein content of EGF, TGFalpha, and HB-EGF in post-mortem brains of patients with Parkinson's disease and age-matched control subjects. Protein levels of EGF and tyrosine hydroxylase were decreased in the prefrontal cortex and the striatum of patients. In contrast, HB-EGF and TGFalpha levels were not significantly altered in either region. The expression of EGF receptors (ErbB1 and ErbB2, but not ErbB3 or ErbB4) was down-regulated significantly in the same forebrain regions. The same phenomenon was mimicked in rats by dopaminergic lesions induced by nigral 6-hydroxydopamine infusion. EGF and ErbB1 levels in the striatum of the PD model were markedly reduced on the lesioned side, compared with the control hemisphere. Subchronic supplement of EGF in the striatum of the PD model locally prevented the dopaminergic neurodegeration as measured by tyrosine hydroxylase immunoreactivity. These findings suggest that the neurotrophic activity of EGF is maintained by afferent signals of midbrain dopaminergic neurons and is impaired in patients with Parkinson's disease.

Interleukin-1: a master regulator of neuroinflammation

Interleukins 1alpha and 1beta (IL-1) are very potent signaling molecules that are expressed normally at low levels, but are induced rapidly in response to local or peripheral insults. IL-1 coordinates systemic host defense responses to pathogens and to injury and not surprisingly it has similar effects within the central nervous system (CNS). Numerous reports have correlated the presence of IL-1 in the injured or diseased brain, and its effects on neurons and nonneuronal cells in the CNS, but it is only recently that the importance of IL-1 signaling has been recognized. This article reviews studies that demonstrate that IL-1 is at or near the top of the hierarchical cytokine signaling cascade in the CNS that results in the activation of endogenous microglia and vascular endothelial cells to recruit peripheral leukocytes (i.e., neuroinflammation). The IL-1 system thus provides an attractive target for therapeutic intervention to ameliorate the destructive consequences of neuroinflammation.

The neuroprotective role of inflammation in nervous system Injuries

The contribution of inflammation to the pathogenesis of several nervous system disorders has long been established. Other observations, however, indicate that both inflammatory cells and mediators may also have beneficial functions, assisting in repair and recovery processes. There is compelling evidence to indicate that in the injured nervous system, as in other tissues, macrophages are needed at an early stage after injury in order for healing to take place. Likewise, activated T cells of a particular specificity can reduce the spread of damage. This neuroprotective effect of T cells may be caused, at least in part, by the production of neurotrophic factors such as neurotrophin-3 or brain-derived neurotrophic factor. Interestingly, recent findings indicate that immune cells are able to produce a variety of neurotrophic factors which promote neuronal survival and may also mediate anti-inflammatory effects. Numerous cytokines are induced after nervous system injuries. Some cytokines, such as TNF-alpha, IL-1 and IFN-gamma, are well known for their promotion of inflammatory responses. However, these cytokines also have immunosuppressive functions and their subsequent expression also assists in repair or recovery processes, suggesting a dual role for some pro-inflammatory cytokines. This should be clarified, as it may be crucial in the design of therapeutic strategies to target specific cytokine(s). Finally, there is a growing body of evidence to show that autoreactive IgM antibodies may constitute an endogenous system of tissue repair, and therefore prove of value as a therapeutic strategy. Available evidence would appear to indicate that the inflammatory response observed in several neurological conditions is more complex than previously thought. Therefore, the design of more effective therapies depends on a clear delineation of the beneficial and detrimental effects of inflammation.

Changes in FGF-2 expression in the distal spinal cord stump after complete cord transection: a comparison between infant and adult rats

STUDY DESIGN

Expression patterns of fibroblast growth factor-2 (FGF-2) in distal transected spinal cord in infant and adult rats were determined by reverse-transcription polymerase chain reaction (RT-PCR) and immunostaining.

OBJECTIVE

To reveal the expression pattern of FGF-2 in distal transected cord of infant and adult rats.

SUMMARY OF BACKGROUND DATA

Descending fibers in the spinal cord of infant and adult rats show different regenerative capacity. One explanation is that different levels of FGF-2, an important neurotrophic factor for promoting neurite outgrowth and repair, are expressed in the distal transected cords of the rats, providing different levels of support for severed axons.

MATERIALS AND METHODS

Spinal cords of infant and adult rats were completely transected. At 12, 24, and 72 hours and at 1 week, segments of distal spinal cord tissues were removed and expression of FGF-2 mRNA was evaluated by RT-PCR. The distribution of FGF-2 and the phenotype of FGF-2-positive cells were determined by immunostaining.

RESULTS

Expression of FGF-2 mRNA was shown to be up-regulated in the distal cord of infant rats but not adult rats. Immunohistochemical analysis showed that neurons in distal cord of infant rats were rich in FGF-2 immunoreactivity (IR), whereas in adult rat neurons FGF-2 IR was hardly observed at all, although a few FGF-2-positive astrocytes were observed in the white matter.

CONCLUSION

After complete spinal cord transection, the expression of FGF-2 in the distal cord of infant rats was high compared with that of adults. This may provide neurotrophic support for axonal extension and functional recovery.

Lipopolysaccharide and TNFalpha regulate the expression of GDNF, neurturin and their receptors

Inflammatory processes in the brain may trigger specific neuroprotective responses in glial cells. Here, we show that bacterial lipopolysaccharide strongly up-regulates glial derived neurotrophic factor (GDNF) mRNA while it down-regulates that of neurturin. Tumor necrosis factor alpha (TNFalpha) had different effects since it stimulated neurturin expression without enhancing GDNF mRNA. Interestingly, both lipopolysaccharide and TNFalpha triggered a significant decrease in the expression of the GDNF receptor, GFRalpha1, in glial cells. While the significance of such down-regulation during inflammatory processes remains to be characterised, the differential regulation of GDNF and neurturin following lipopolysaccharide and TNFalpha treatments suggest specific neuroprotective responses of glial cells in case of bacterial infection, trauma, transplantation or neurodegenerative diseases.

Intranigral infusion of interleukin-1beta activates astrocytes and protects from subsequent 6-hydroxydopamine neurotoxicity

Activation of glial cells is a prevalent response to neuronal damage in brain disease and ageing, with potential neuroprotective and neurotoxic consequences. We were interested in studying the role of glial activation on dopaminergic neurons of the substantia nigra in an animal model of Parkinson's disease. Thus, we evaluated the effect of a pre-existing glial activation on the dopaminergic neuronal death induced by striatal infusion of 6-hydroxydopamine. We established a model of local glial activation by stereotaxic infusion of interleukin-1beta in the substantia nigra of adult rats. Interleukin-1beta (20 ng) induced a marked activation of astrocytes at days 2, 5 and 10, revealed by heat-shock protein 27 and glial fibrillary acid protein immunohistochemistry, but did not affect the microglial markers OX-42 and heat-shock proteins 32 or 47. Intranigral infusion of interleukin-1beta 5 days before a striatal injection of 6-hydroxydopamine significantly protected nigral dopaminergic cell bodies, but not striatal terminals from the 6-hydroxydopamine lesion. Also, in the animals pre-treated with interleukin-1beta, a significant prevention of 6-hydroxydopamine-induced reduction of adjusting steps, but not of 6-hydroxydopamine-induced amphetamine rotations, were observed. These data show the characterization of a novel model of local astroglial activation in the substantia nigra and support the hypothesis of a neuroprotective role of activated astrocytes in Parkinson's disease.

D2 Dopamine receptor blockade results in sprouting of DA axons in the intact animal but prevents sprouting following nigral lesions

Recently it was demonstrated that sprouting of dopaminergic neurons and a microglial and astrocyte response follows both partial lesions of the substantia nigra pars compacta and blockade of the D2 dopamine receptor. We therefore studied the effects of the combination of these two treatments (lesioning and D2 dopamine receptor blockade). Haloperidol administration caused a 57% increase in dopaminergic terminal tree size (measured as terminal density per substantia nigra pars compacta neuron) and an increase of glia in the striatum. Following small to medium nigral lesions (less than 60%), terminal tree size increased by 51% on average and returned density of dopaminergic terminals to normal. In contrast, administration of haloperidol for 16 weeks following lesioning resulted in reduced dopaminergic terminal density and terminal tree size (13%), consistent with absent or impaired sprouting. Glial cell numbers increased but were less than with lesions alone. When haloperidol was administered after the striatum had been reinnervated through sprouting (16-32 weeks after lesioning), terminal tree size increased up to 150%, similar to the effect of haloperidol in normal animals. By examining the effect of administering haloperidol at varying times following a lesion, we concluded that a switch in the effect of D2 dopamine receptor blockade occurred after dopaminergic synapses began to form in the striatum. We postulate that when synapses are present, D2 dopamine receptor blockade results in increased terminal density, whereas prior to synapse formation D2 dopamine receptor blockade causes attenuation of a sprouting response. We speculate that D2 dopamine receptors located on growth cones 'push' neurites toward their targets, and blockade of these receptors could lead to attenuation of sprouting.

Sphingosine 1-phosphate induces the production of glial cell line-derived neurotrophic factor and cellular proliferation in astrocytes

Sphingosine 1-phosphate (S1P) is a platelet-derived bioactive sphingolipid that evokes a variety of biological responses. To understand the role of S1P in the central nervous system, we have examined the effect of S1P on the production of glial cell line-derived neurotrophic factor (GDNF) and growth regulation of cortical astrocytes from rat embryo. Moreover, we examined the possibility that the expression of GDNF is regulated differently in cultured astrocytes from the stroke-prone spontaneously hypertensive rat (SHRSP) than in those from Wistar kyoto rats (WKY). The mRNA expression was quantitated by RT-PCR based on the fluorescent TaqMan methodology. A new instrument capable of measuring fluorescence in real time was used to quantify gene amplification in astrocytes. GDNF protein was investigated by enzyme-linked immunosorbent assay. S1P induced the expression of GDNF mRNA and the production of GDNF protein in a dose-dependent manner in WKY astrocytes. Moreover, S1P increased cell numbers and induced the proliferation of astrocytes. In addition, the level of mRNA expression and protein production of GDNF was significantly lower in SHRSP than WKY astrocytes following exposure to S1P. These findings revealed that S1P augments GDNF protein production and cellular growth in astrocytes. Also, our results indicate that production in SHRSP astrocytes was attenuated in response to S1P compared with that observed in WKY. We conclude that S1P specifically triggers a cascade of events that regulate the production of GDNF and cell growth in astrocytes. Our results also suggest that the reduced expression of GDNF caused by S1P is a factor in the stroke proneness of SHRSP.

Targeting the host inflammatory response in traumatic spinal cord injury

Both acute and chronic inflammatory processes have been shown to influence outcome in experimental models of spinal cord injury. Although early inflammatory responses may participate in secondary injury processes, more delayed inflammatory events may be reparative. Therapeutic strategies that target these events are currently based on experimental findings that have clarified the cellular and molecular processes involved in the inflammatory response to injury. An increasing body of literature supports the hypothesis that acute inflammatory events are attenuated by therapeutic hypothermia and other anti-inflammatory strategies, whereas immune neuroprotection and axonal regeneration can be achieved by transfer of activated T cells or by treatment with therapeutic vaccines. These data are summarized in the present review.

ADP and AMP induce interleukin-1beta release from microglial cells through activation of ATP-primed P2X7 receptor channels

P2X(7) is a subtype of ATP-gated channels that is highly expressed in astrocytes, microglia, and other immune cells. Activation of P2X(7) purinoceptors by ATP or 3'-O-(4-benzoyl)-benzoyl ATP (BzATP) induces the formation of cytolytic pores and provokes release of interleukin-1beta from immune cells. We investigated the actions of other endogenous nucleotides on recombinant and microglial P2X(7) receptors using electrophysiology, fluorescence imaging, and interleukin-1beta release measurement. We found that initial application of ADP or AMP to Xenopus oocytes expressing P2X(7) receptors was ineffective. However, when ADP and AMP, but not UTP or adenosine, were applied after a brief exposure to ATP or BzATP, they activated P2X(7) receptors in a dose-dependent manner. Moreover, responses to ADP and AMP were also elicited after exposure to low concentrations of ATP and were recorded several minutes after removal of ATP from the extracellular medium. Whole-cell recordings from mouse microglial cells showed that significant responses to ADP and AMP were elicited only after ATP application. YO-PRO-1 dye uptake imaging revealed that, unlike ATP, prolonged application of ADP or AMP did not cause an opening of large cytolytic pores in mouse microglial cells. Finally, ADP and AMP stimulated the release of interleukin-1beta from ATP-primed mouse and human microglial cells. We conclude that selective sensitization of P2X(7) receptors to ADP and AMP requires priming with ATP. This novel property of P2X(7) leads to activation by ATP metabolites and proinflammatory cytokine release from microglia without cytotoxicity.

Guidance of dopaminergic neuritic growth by immature astrocytes in organotypic cultures of rat fetal ventral mesencephalon

Astrocytes, with their many functions in producing and controlling the environment in the brain, are of great interest when it comes to studying regeneration after injury and neurodegenerative diseases such as in grafting in Parkinson's disease. This study was performed to investigate astrocytic guidance of growth derived from dopaminergic neurons using organotypic cultures of rat fetal ventral mesencephalon. Primary cultures were studied at different time points starting from 3 days up to 28 days. Cultures were treated with either interleukin-1 beta (IL-1 beta), which has stimulating effects on astrocytic proliferation, or the astrocytic inhibitor cytosine arabinoside (Ara-C). Tyrosine hydroxylase (TH)-immunohistochemistry was used to visualize dopaminergic neurons, and antibodies against glial fibrillary acidic protein (GFAP) and S100 beta were used to label astrocytes. The results revealed that a robust TH-positive nerve fiber production was seen already at 3 days in vitro. These neurites had disappeared by 5 days. This early nerve fiber outgrowth was not guided by direct interactions with glial cells. Later, at 7 days in vitro, a second wave of TH-positive neuritic outgrowth was clearly observed. GFAP-positive astrocytic processes guided these neurites. TH-positive neurites arborized overlying S100 beta-positive astrocytes in an area distal to the GFAP-positive astrocytic processes. Treatment with IL-1 beta resulted in an increased area of TH-positive nerve fiber network. In cultures treated with Ara-C, neither astrocytes nor outgrowth of dopaminergic neurites were observed. In conclusion, this study shows that astrocytes play a major role in long-term dopaminergic outgrowth, both in axonal elongation and branching of neurites. The long-term nerve fiber growth is preceded by an early transient outgrowth of dopamine neurites.

Differential regulation of glial cell line-derived neurotrophic factor (GDNF) mRNA expression during hypoxia and reoxygenation in astrocytes isolated from stroke-prone spontaneously hypertensive rats

Glial cell line-derived neurotrophic factor (GDNF) plays several important roles in the survival and recovery of mature neurons during ischemia. We examined the possibility that the expression of GDNF mRNA and the release of GDNF protein are regulated differentially in cultured astrocytes from the stroke-prone spontaneously hypertensive rat (SHRSP) compared with those from Wistar Kyoto rats (WKY) during hypoxia and reoxygenation (H/R) and after exposure to glutamate and hydrogen peroxide (H(2)O(2)). The mRNA expression was quantitated by reverse transcription-polymerase chain reaction (RT-PCR) based on the fluorescent TaqMan methodology. A new instrument capable of measuring fluorescence in real-time was used to quantify gene amplification in astrocytes. GDNF protein was investigated by enzyme-linked immunosorbent assay (ELISA). GDNF mRNA expression and GDNF protein release at normoxia were greater in SHRSP than in WKY astrocytes. During H/R, however, the mRNA expression and protein release tended to be reduced in SHRSP compared with WKY. Glutamate and H(2)O(2) induced the expression of GDNF mRNA and the release of GDNF protein in both WKY and SHRSP in a dose-dependent manner. Levels of GDNF mRNA and protein in SHRSP were significantly lower than in WKY. These findings indicate that GDNF production in SHRSP astrocytes was low in response to H/R, glutamate, and H(2)O(2), compared with that observed in WKY. We conclude that the attenuated production of GDNF in astrocytes is involved in neuronal vulnerability in SHRSP during H/R, as GDNF production, which is stimulated by glutamate and H(2)O(2), is closely related to the protective effect against H/R-mediated neurotoxicity.

Novel alternative promoters of mouse glial cell line-derived neurotrophic factor gene

We previously isolated cDNA and genomic DNA of the mouse glial cell line-derived neurotrophic factor (GDNF) gene and found that the gene consists of three exons. Recently, it was suggested that an alternative promoter exists within intron 1 of the human GDNF gene, but this has not been confirmed. Novel cDNA clones of the mouse GDNF gene were isolated by 5'-rapid amplification of cDNA ends from postnatal day-14 striatum. A novel exon, containing 351 nucleotides, exists between exon 1 and exon 3 (referred to as exon 2 in our previous report). Luciferase reporter assay showed that a core promoter for the novel exon 2 requires its 5'-untranslated region. Primer extension analysis and reverse transcription-PCR identified another novel transcript that starts 39 bp upstream of exon 3, and the core promoter activity exists within a region containing putative Sp1 sites. Although the core promoters for the novel exons are different from those previously identified, transcripts derived from each promoter coincidentally increased with interleukin-1beta or tumor necrosis factor-alpha stimulation. Gel retardation assays suggested that the NF-kappaB binding site in intron 1 would be involved in the cytokine response of the mouse GDNF gene.

Inhibition of brain-derived neurotrophic factor and glial cell line-derived neurotrophic factor expression reduces dopaminergic sprouting in the injured striatum

After striatal injury, sprouting dopaminergic fibres grow towards and intimately surround wound macrophages which, together with microglia, express the dopaminergic neurotrophic factors glial cell line-derived neurotrophic factor (GDNF) and brain derived neurotrophic factor (BDNF). To evaluate the importance of these endogenously secreted neurotrophic factors in generating striatal peri-wound dopaminergic sprouting, the peri-wound expression of BDNF or GDNF was inhibited by intrastriatal infusion of antisense oligonucleotides for 2 weeks in mice. Knock-down of both BDNF and GDNF mRNA and protein levels in the wounded striatum were confirmed by in situ hybridization and enzyme-linked immunosorbent assay, respectively. Dopamine transporter immunohisto-chemistry revealed that inhibition of either BDNF or GDNF expression resulted in a marked decrease in the intensity of peri-wound sprouting. Quantification of this effect using [H3]-mazindol autoradiography confirmed that peri-wound sprouting was significantly reduced in mice receiving BDNF or GDNF antisense infusions whilst control infusions of buffered saline or sense oligonucleotides resulted in the pronounced peri-wound sprouting response normally associated with striatal injury. BDNF and GDNF thus appear to be important neurotrophic factors inducing dopaminergic sprouting after striatal injury.

Neurotrophic factors in Alzheimer's and Parkinson's disease brain

The biomedical literature on the subject of neurotrophic growth factors has expanded prodigiously. This essay reviews neurotrophic factors (NTF) and their receptors in Alzheimer's disease (AD) and Parkinson's disease (PD) brain and recent updates on receptor signaling. The hypotheses for specific NTF involvement in neurodegenerative diseases in human and as potential therapy are based mainly on experimental animal and in vitro models. There are wide gaps in information on regional synthesis and cell contents of NTFs and their receptors in human brain. Observations on AD brain indicate increases in NGF and decreases in BDNF in surviving neurons of hippocampus and certain neocortical regions and decreases in TrkA in cortex and nucleus basalis. In PD brain, the few data available indicate decreases in neuronal content of GDNF and bFGF in surviving substantia nigra dopaminergic neurons. There are very few data regarding age-dependent effects on NTFs and on their receptors in human brain. Since NTFs in neurons are subject to retrograde and, in at least some cases, to anterograde transport from and to target neurons, their effects may be related to synthesis in local or remote sites or to changes in axoplasmic transport. Also, certain NTFs and their receptors are found to be expressed in activated glia. Thus, comparative in situ data for transcription levels and protein contents for NTFs and their receptors in both sites of neuronal origin and termination in human brain are needed to understand their potential roles in treating human diseases.

Impact of a preceding striatal excitotoxic lesion and treatment with ciliary neurotrophic factor on striatal graft survival

The survival of grafted embryonic striatal tissue, dissected from the lateral ganglionic eminence, depends on the status of the host striatum. We found significantly larger volumes of surviving graft tissue and of striatal-like tissue (P-zone) within the graft, when the host striatum had been subjected to an excitotoxic lesion prior to transplantation surgery. Concomitantly the numbers of surviving grafted cells, assessed in both cresyl violet-stained sections and in sections stained with an immunohistochemical marker for striatal neurons, increased as compared to when graft tissue was placed in an intact unlesioned striatum. Finally, we examined the impact of treatment of the donor tissue with ciliary neurotrophic factor (CNTF) on graft survival. CNTF has previously been shown to protect striatal neurons against excitotoxic insults both in vitro and in vivo, but it did not improve striatal graft survival when added to the cell suspension prior to implantation.

Regulation of the heparan sulfate proteoglycan, perlecan, by injury and interleukin-1alpha

Perlecan is a specific proteoglycan that binds to amyloid precursor protein and beta-amyloid peptide, is present within amyloid deposits, and has been implicated in plaque formation. Because plaque formation is associated with local inflammation, we hypothesized that the mechanisms involved in brain inflammatory responses could influence perlecan biosynthesis. To test this hypothesis, we first studied perlecan regulation in mice after inflammation induced by a brain stab wound. Perlecan mRNA and immunoreactivity were both increased 3 days after injury. Interleukin-1alpha (IL-1alpha) is a cytokine induced after injury and plays an important role in inflammation. As such, IL-1alpha may be one of the factors participating in regulating perlecan synthesis. We thus studied perlecan regulation by IL-1alpha, in vivo. Regulation of perlecan mRNA by this cytokine was area-specific, showing up-regulation in hippocampus, whereas in striatum, perlecan mRNA was unchanged. To support this differential regulation of perlecan mRNA by IL-1alpha, basic fibroblast growth factor (bFGF), a growth factor also present in plaques, was studied in parallel. bFGF mRNA did not show any regional difference, being up-regulated in both hippocampus and striatum in vivo. In vitro, both astrocyte and microglia were immunoreactive for perlecan. Moreover, perlecan mRNA was increased in hippocampal glial cultures after IL-1alpha but not in striatal glia. These results show an increase in perlecan biosynthesis after injury and suggest a specific regulation of perlecan mRNA by IL-1alpha, which depends on brain area. Such regulation may have important implications in the understanding of regional brain variations in amyloid plaque formation.

Activated macrophages and microglia induce dopaminergic sprouting in the injured striatum and express brain-derived neurotrophic factor and glial cell line-derived neurotrophic factor

Nigrostriatal dopaminergic neurons undergo sprouting around the margins of a striatal wound. The mechanism of this periwound sprouting has been unclear. In this study, we have examined the role played by the macrophage and microglial response that follows striatal injury. Macrophages and activated microglia quickly accumulate after injury and reach their greatest numbers in the first week. Subsequently, the number of both cell types declines rapidly in the first month and thereafter more slowly. Macrophage numbers eventually cease to decline, and a sizable group of these cells remains at the wound site and forms a long-term, highly activated resident population. This population of macrophages expresses increasing amounts of glial cell line-derived neurotrophic factor mRNA with time. Brain-derived neurotrophic factor mRNA is also expressed in and around the wound site. Production of this factor is by both activated microglia and, to a lesser extent, macrophages. The production of these potent dopaminergic neurotrophic factors occurs in a similar spatial distribution to sprouting dopaminergic fibers. Moreover, dopamine transporter-positive dopaminergic neurites can be seen growing toward and embracing hemosiderin-filled wound macrophages. The dopaminergic sprouting that accompanies striatal injury thus appears to result from neurotrophic factor secretion by activated macrophages and microglia at the wound site.

Analysis of the human GDNF gene reveals an inducible promoter, three exons, a triplet repeat within the 3'-UTR and alternative splice products

Glial cell line-derived neurotrophic factor (GDNF), a distant member of the TGF-beta superfamily, is a survival factor for various neurons, making it a potential therapeutic agent for neurodegenerative disorders. Here we present the genomic structure and characterization of the promoter of the human GDNF (hGDNF) gene. It contains three exons coding for a cDNA of 4.6 kb including large 5'- and 3'-untranslated regions (UTRs). The 3'-UTR contains a polymorphic AGG repeat that appears not to be expanded in patients suffering from different neurodegenerative disorders. RT-PCR results in at least three different hGDNF transcripts including one that lacks exon 2. Transient expression experiments reveal that exon 2 is essential for proper cellular processing to yield a secreted form of hGDNF, whereas expression of exon 3 alone is sufficient to code for a mature form of hGDNF retained within the cell. Our data show that the hGDNF gene is driven by a TATA-containing promoter preceding exon 1. A second promoter element has been mapped to a region 5' of exon 2. Both promoters are in close proximity to CpG islands covering exons 1 and 2. Using luciferase as a reporter gene, the TATA-containing hGDNF promoter facilitates a 20- to 40-fold increase in transcription when compared with a corresponding promoterless construct, whereas the second promoter confers only weak activity. Furthermore, fibroblast growth factor 2, tetradecanoyl 12-phorbol acetate, an inflammatory agent, and cAMP increase promoter activity, suggesting that GDNF transcriptional regulation is a target of exogenous signals.

Induction of interleukin-1 associated with compensatory dopaminergic sprouting in the denervated striatum of young mice: model of aging and neurodegenerative disease

Young mice challenged with the neurotoxin 1-methyl-4-phenyl-1,2,3, 6-tetrahydropyridine (MPTP), which selectively destroys the substantia nigra dopaminergic neurons in the midbrain, exhibit spontaneous recovery of dopaminergic nerve terminals. However, such recovery becomes attenuated with age. Here we report that newly sprouted fibers originate from spared dopaminergic neurons in the ventral tegmental area. We found that interleukin-1 (IL-1), an immune response-generated cytokine that can enhance dopaminergic sprouting when exogenously applied, increased dramatically in the denervated striatum of young mice (2 months) compared with middle-aged mice (8 months) after MPTP treatment. Young mice displayed a maximal 500% induction of IL-1alpha synthesis that remained elevated for several weeks in the dorsal and ventral striatum, whereas middle-aged mice exhibited a modest 135% induction exclusively in the dorsal striatum for a week. IL-1alpha immunoreactivity was localized in GFAP-immunoreactive hypertrophied astrocytes and neurons within the denervated striatum of young mice. However, no induction of IL-1alpha mRNA was seen in the midbrain in either age group despite glial activation. Because we have reported that IL-1 can regulate astroglia-derived dopaminergic neurotrophic factors, it was surprising that no changes were observed in acidic and basic fibroblast growth factor or glial cell line-derived neurotrophic factor mRNA levels associated with MPTP-induced plasticity of dopaminergic neurons in the striatum of young mice. Interestingly, we found that dopaminergic neurons express IL-1 receptors, thus suggesting that IL-1alpha could directly act as a target-derived dopaminergic neurotrophic factor to initiate or enhance the sprouting of dopaminergic axonal terminals. These findings strongly suggest that IL-1alpha could play an important role in MPTP-induced plasticity of dopaminergic neurons.