Heterogeneity between hippocampal and septal astroglia as a contributing factor to differential in vivo AMPA excitotoxicity

Ginsenoside Re protects against kainate-induced neurotoxicity in mice by attenuating mitochondrial dysfunction through activation of the signal transducers and activators of transcription 3 signaling

It was demonstrated that ginsenosides exert anti-convulsive potentials and interleukin-6 (IL-6) is protective from excitotoxicity induced by kainate (KA), a model of temporal lobe epilepsy. Ginsenosides-mediated mitochondrial recovery is essential for attenuating KA-induced neurotoxicity, however, little is known about the effects of ginsenoside Re (GRe), one of the major ginsenosides. In this study, GRe significantly attenuated KA-induced seizures in mice. KA-induced redox changes were more evident in mitochondrial fraction than in cytosolic fraction in the hippocampus of mice. GRe significantly attenuated KA-induced mitochondrial oxidative stress (i.e. increases in reactive oxygen species, 4-hydroxynonenal, and protein carbonyl) and mitochondrial dysfunction (i.e. the increase in intra-mitochondrial Ca2+ and the decrease in mitochondrial membrane potential). GRe or mitochondrial protectant cyclosporin A restored phospho-signal transducers and activators of transcription 3 (STAT3) and IL-6 levels reduced by KA, and the effects of GRe were reversed by the JAK2 inhibitor AG490 and the mitochondrial toxin 3-nitropropionic acid (3-NP). Thus, we used IL-6 knockout (KO) mice to investigate whether the interaction between STAT3 and IL-6 is involved in the GRe effects. Importantly, KA-induced reduction of manganese superoxide dismutase (SOD-2) levels and neurodegeneration (i.e. astroglial inhibition, microglial activation, and neuronal loss) were more prominent in IL-6 KO than in wild-type (WT) mice. These KA-induced detrimental effects were attenuated by GRe in WT and, unexpectedly, IL-6 KO mice, which were counteracted by AG490 and 3-NP. Our results suggest that GRe attenuates KA-induced neurodegeneration via modulating mitochondrial oxidative burden, mitochondrial dysfunction, and STAT3 signaling in mice.

Combination Therapy of Mesenchymal Stem Cell Transplantation and Astrocyte Ablation Improve Remyelination in a Cuprizone-Induced Demyelination Mouse Model

Astrocytes display an active, dual, and controversial role in multiple sclerosis (MS), a chronic inflammatory demyelination disorder. However, mesenchymal stem cells (MSCs) can affect myelination in demyelinating disorders. This study aimed to investigate the effect of single and combination therapies of astrocyte ablation and MSC transplantation on remyelination in the cuprizone (CPZ) model of MS. C57BL/6 mice were fed 0.2% CPZ diet for 12 weeks. Astrocytes were ablated twice by L-a-aminoadipate (L-AAA) at the beginning of weeks 13 and 14 whereas MSCs were injected in the corpus callosum at the beginning of week 13. Motor coordination and balance were assessed through rotarod test whereas myelin content was evaluated by Luxol-fast blue (LFB) staining and transmission electron microscopy (TEM). Glial cells were assessed by immunofluorescence staining while mRNA expression was evaluated by quantitative real-time PCR. Combination treatment of ablation of astrocytes and MSC transplantation (CPZ + MSC + L-AAA) significantly decreased motor coordination deficits better than single treatments (CPZ + MSCs or CPZ + L-AAA), in comparison to CPZ mice. In addition, L-AAA and MSCs treatment significantly enhanced remyelination compared to CPZ group. Moreover, combination therapy caused a significant decrease in the number of GFAP⁺ and Iba-1⁺ cells, whereas oligodendrocytes were significantly increased in comparison to CPZ mice. Finally, MSC administration resulted in a significant upregulation of BDNF and NGF mRNA expression levels. Our data indicate that transient ablation of astrocytes along with MSCs treatment improve remyelination through enhancing oligodendrocytes and attenuating gliosis in a chronic demyelinating mouse model of MS.

Osteopontin mediates the formation of corpora amylacea-like structures from degenerating neurons in the CA1 region of the rat hippocampus after ischemia

We previously demonstrated that osteopontin (OPN) is closely associated with calcium precipitation in response to ischemic brain insults. The present study was designed to elucidate the possible association between deposition of OPN and progressive neurodegeneration in the ischemic hippocampus. To address this, we analyzed the OPN deposits in the rat hippocampus after global cerebral ischemia in the chronic phase (4 to 12 weeks) after reperfusion using immunoelectron microscopy and correlative light and electron microscopy. We identified three different types of OPN deposits based on their morphological characteristics, numbered according to the order in which they evolved. Dark degenerative cells that retained cellular morphology were frequently observed in the pyramidal cell layer, and type I OPN deposits were degenerative mitochondria that accumulated among these cells. Type II deposits evolved into more complex amorphous structures with prominent OPN deposits within their periphery and within degenerative mitochondria-like structures. Finally, type III had large concentric laminated structures with irregularly shaped bodies in the center of the deposits. In all types, OPN expression was closely correlated with calcification, as confirmed by calcium fixation and Alizarin Red staining. Notably, type II and III deposits were highly reminiscent of corpora amylacea, glycoprotein-rich aggregates found in aged brains, or neurodegenerative disease, which was further confirmed by ubiquitin expression and periodic acid-Schiff staining. Overall, our data provide a novel link between ongoing neurodegeneration and the formation of corpora amylacea-like structures and calcium deposits in the ischemic hippocampus, suggesting that OPN may play an important role in such processes.

Unraveling the Spatiotemporal Distribution of VPS13A in the Mouse Brain

Loss-of-function mutations in the human vacuolar protein sorting the 13 homolog A (VPS13A) gene cause Chorea-acanthocytosis (ChAc), with selective degeneration of the striatum as the main neuropathologic feature. Very little is known about the VPS13A expression in the brain. The main objective of this work was to assess, for the first time, the spatiotemporal distribution of VPS13A in the mouse brain. We found VPS13A expression present in neurons already in the embryonic stage, with stable levels until adulthood. VPS13A mRNA and protein distributions were similar in the adult mouse brain. We found a widespread VPS13A distribution, with the strongest expression profiles in the pons, hippocampus, and cerebellum. Interestingly, expression was weak in the basal ganglia. VPS13A staining was positive in glutamatergic, GABAergic, and cholinergic neurons, but rarely in glial cells. At the cellular level, VPS13A was mainly located in the soma and neurites, co-localizing with both the endoplasmic reticulum and mitochondria. However, it was not enriched in dendritic spines or the synaptosomal fraction of cortical neurons. In vivo pharmacological modulation of the glutamatergic, dopaminergic or cholinergic systems did not modulate VPS13A concentration in the hippocampus, cerebral cortex, or striatum. These results indicate that VPS13A has remarkable stability in neuronal cells. Understanding the distinct expression pattern of VPS13A can provide relevant information to unravel pathophysiological hallmarks of ChAc.

Diazoxide enhances excitotoxicity-induced neurogenesis and attenuates neurodegeneration in the rat non-neurogenic hippocampus

Diazoxide, a well-known mitochondrial KATP channel opener with neuroprotective effects, has been proposed for the effective and safe treatment of neuroinflammation. To test whether diazoxide affects the neurogenesis associated with excitotoxicity in brain injury, we induced lesions by injecting excitotoxic N-methyl-d-aspartate (NMDA) into the rat hippocampus and analyzed the effects of a daily oral administration of diazoxide on the induced lesion. Specific glial and neuronal staining showed that NMDA elicited a strong glial reaction associated with progressive neuronal loss in the whole hippocampal formation. Doublecortin immunohistochemistry and bromo-deoxyuridine (BrdU)-NeuN double immunohistochemistry revealed that NMDA also induced cell proliferation and neurogenesis in the lesioned non-neurogenic hippocampus. Furthermore, glial fibrillary acidic protein (GFAP)-positive cells in the injured hippocampus expressed transcription factor Sp8 indicating that the excitotoxic lesion elicited the migration of progenitors from the subventricular zone and/or the reprograming of reactive astrocytes. Diazoxide treatment attenuated the NMDA-induced hippocampal injury in rats, as demonstrated by decreases in the size of the lesion, neuronal loss and microglial reaction. Diazoxide also increased the number of BrdU/NeuN double-stained cells and elevated the number of Sp8-positive cells in the lesioned hippocampus. These results indicate a role for KATP channel activation in regulating excitotoxicity-induced neurogenesis in brain injury.

Spatiotemporal Progression of Microcalcification in the Hippocampal CA1 Region following Transient Forebrain Ischemia in Rats: An Ultrastructural Study

Calcification in areas of neuronal degeneration is a common finding in several neuropathological disorders including ischemic insults. Here, we performed a detailed examination of the onset and spatiotemporal profile of calcification in the CA1 region of the hippocampus, where neuronal death has been observed after transient forebrain ischemia. Histopathological examinations showed very little alizarin red staining in the CA1 pyramidal cell layer until day 28 after reperfusion, while prominent alizarin red staining was detected in CA1 dendritic subfields, particularly in the stratum radiatum, by 14 days after reperfusion. Electron microscopy using the osmium/potassium dichromate method and electron probe microanalysis revealed selective calcium deposits within the mitochondria of degenerating dendrites at as early as 7 days after reperfusion, with subsequent complete mineralization occurring throughout the dendrites, which then coalesced to form larger mineral conglomerates with the adjacent calcifying neurites by 14 days after reperfusion. Large calcifying deposits were frequently observed at 28 days after reperfusion, when they were closely associated with or completely engulfed by astrocytes. In contrast, no prominent calcification was observed in the somata of CA1 pyramidal neurons showing the characteristic features of necrotic cell death after ischemia, although what appeared to be calcified mitochondria were noted in some degenerated neurons that became dark and condensed. Thus, our data indicate that intrahippocampal calcification after ischemic insults initially occurs within the mitochondria of degenerating dendrites, which leads to the extensive calcification that is associated with ischemic injuries. These findings suggest that in degenerating neurons, the calcified mitochondria in the dendrites, rather than in the somata, may serve as the nidus for further calcium precipitation in the ischemic hippocampus.

Spinal astrocytic activation contributes to both induction and maintenance of pituitary adenylate cyclase-activating polypeptide type 1 receptor-induced long-lasting mechanical allodynia in mice

Background

Pituitary adenylate cyclase-activating polypeptide (PACAP) and its receptors are present in the spinal dorsal horn and dorsal root ganglia, suggesting an important role of PACAP–PACAP receptors signaling system in the modulation of spinal nociceptive transmission. We have previously reported that a single intrathecal injection of PACAP or a PACAP specific (PAC1) receptor selective agonist, maxadilan, in mice induced dose-dependent aversive behaviors, which lasted more than 30 min, and suggested that the maintenance of the nociceptive behaviors was associated with the spinal astrocytic activation.

Results

We found that a single intrathecal administration of PACAP or maxadilan also produced long-lasting hind paw mechanical allodynia, which persisted at least 84 days without affecting thermal nociceptive threshold. In contrast, intrathecal application of vasoactive intestinal polypeptide did not change mechanical threshold, and substance P, calcitonin gene-related peptide, or N-methyl-D-aspartate induced only transient mechanical allodynia, which disappeared within 21 days. Western blot and immunohistochemical analyses with an astrocytic marker, glial fibrillary acidic protein, revealed that the spinal PAC1 receptor stimulation caused sustained astrocytic activation, which also lasted more than 84 days. Intrathecal co-administration of L-α-aminoadipate, an astroglial toxin, with PACAP or maxadilan almost completely prevented the induction of the mechanical allodynia. Furthermore, intrathecal treatment of L-α-aminoadipate at 84 days after the PAC1 stimulation transiently reversed the mechanical allodynia accompanied by the reduction of glial fibrillary acidic protein expression level.

Conclusion

Our data suggest that spinal astrocytic activation triggered by the PAC1 receptor stimulation contributes to both induction and maintenance of the long-term mechanical allodynia.

Ultrastructural investigation of microcalcification and the role of oxygen-glucose deprivation in cultured rat hippocampal slices

Intracellular calcium accumulation is associated with cell death in several neuropathological disorders including brain ischemia, but the exact mechanisms of calcification need to be clarified. We used organotypic hippocampal slice culture - cultures subjected to oxygen-glucose deprivation (OGD) mimicking the in vivo situation to investigate the events underlying ectopic calcification. Alizarin red staining indicating calcium deposition was observed in the cornu ammonis (CA)1 and dentate gyrus regions in control hippocampal slices despite no specific labeling for cell death markers. Electron microscopy using the osmium/potassium dichromate method revealed scattered degenerated cells throughout the normally appearing CA1 region. They contained electron-dense precipitates within mitochondria, and electron probe microanalysis confirmed that they were calcifying mitochondria. Selective calcium deposition was noted within, but not beyond, mitochondria in these mineralized cells. They showed ultrastructural features of non-necrotic, non-apoptotic cell death and retained their compact ultrastructure, even after the majority of mitochondria were calcified. Unexpectedly, no intracellular calcification was noted in necrotic CA1 pyramidal cells after OGD, and there was no progression of calcification in OGD-lesioned slices. In addition, mineralized cells in both control and OGD-lesioned slices were closely associated with or completely engulfed by astrocytes but not microglia. These astrocytes were laden with heterogeneous cytoplasmic inclusions that appeared to be related with their phagocytic activity. These data demonstrate that microcalcification specifically associated with mitochondria might lead to a novel type of cell death and suggest that astrocytes may be involved in the phagocytosis of these mineralized cells and possibly in the regulation of ectopic calcification.

Astroglia-Microglia Cross Talk during Neurodegeneration in the Rat Hippocampus

Brain injury triggers a progressive inflammatory response supported by a dynamic astroglia-microglia interplay. We investigated the progressive chronic features of the astroglia-microglia cross talk in the perspective of neuronal effects in a rat model of hippocampal excitotoxic injury. N-Methyl-D-aspartate (NMDA) injection triggered a process characterized within 38 days by atrophy, neuronal loss, and fast astroglia-mediated S100B increase. Microglia reaction varied with the lesion progression. It presented a peak of tumor necrosis factor-α (TNF-α) secretion at one day after the lesion, and a transient YM1 secretion within the first three days. Microglial glucocorticoid receptor expression increased up to day 5, before returning progressively to sham values. To further investigate the astroglia role in the microglia reaction, we performed concomitant transient astroglia ablation with L-α-aminoadipate and NMDA-induced lesion. We observed a striking maintenance of neuronal death associated with enhanced microglial reaction and proliferation, increased YM1 concentration, and decreased TNF-α secretion and glucocorticoid receptor expression. S100B reactivity only increased after astroglia recovery. Our results argue for an initial neuroprotective microglial reaction, with a direct astroglial control of the microglial cytotoxic response. We propose the recovery of the astroglia-microglia cross talk as a tissue priority conducted to ensure a proper cellular coordination that retails brain damage.

Phagocytic microglial phenotype induced by glibenclamide improves functional recovery but worsens hyperalgesia after spinal cord injury in adult rats

Microglial cell plays a crucial role in the development and establishment of chronic neuropathic pain after spinal cord injuries. As neuropathic pain is refractory to many treatments and some drugs only present partial efficacy, it is essential to study new targets and mechanisms to ameliorate pain signs. For this reason we have used glibenclamide (GB), a blocker of KATP channels that are over expressed in microglia under activation conditions. GB has already been used to trigger the early scavenger activity of microglia, so we administer it to promote a better removal of dead cells and myelin debris and support the microglia neuroprotective phenotype. Our results indicate that a single dose of GB (1 μg) injected after spinal cord injury is sufficient to promote long-lasting functional improvements in locomotion and coordination. Nevertheless, the Randall-Selitto test measurements indicate that these improvements are accompanied by enhanced mechanical hyperalgesia. In vitro results indicate that GB may influence microglial phagocytosis and therefore this action may be at the basis of the results obtained in vivo.

Targeting microglial K(ATP) channels to treat neurodegenerative diseases: a mitochondrial issue

Neurodegeneration is a complex process involving different cell types and neurotransmitters. A common characteristic of neurodegenerative disorders is the occurrence of a neuroinflammatory reaction in which cellular processes involving glial cells, mainly microglia and astrocytes, are activated in response to neuronal death. Microglia do not constitute a unique cell population but rather present a range of phenotypes closely related to the evolution of neurodegeneration. In a dynamic equilibrium with the lesion microenvironment, microglia phenotypes cover from a proinflammatory activation state to a neurotrophic one directly involved in cell repair and extracellular matrix remodeling. At each moment, the microglial phenotype is likely to depend on the diversity of signals from the environment and of its response capacity. As a consequence, microglia present a high energy demand, for which the mitochondria activity determines the microglia participation in the neurodegenerative process. As such, modulation of microglia activity by controlling microglia mitochondrial activity constitutes an innovative approach to interfere in the neurodegenerative process. In this review, we discuss the mitochondrial K_ATP channel as a new target to control microglia activity, avoid its toxic phenotype, and facilitate a positive disease outcome.

Possible role of spinal astrocytes in maintaining chronic pain sensitization: review of current evidence with focus on bFGF/JNK pathway

Although pain is regarded traditionally as neuronally mediated, recent progress shows an important role of spinal glial cells in persistent pain sensitization. Mounting evidence has implicated spinal microglia in the development of chronic pain (e.g. neuropathic pain after peripheral nerve injury). Less is known about the role of astrocytes in pain regulation. However, astrocytes have very close contact with synapses and maintain homeostasis in the extracellular environment. In this review, we provide evidence to support a role of spinal astrocytes in maintaining chronic pain. In particular, c-Jun N-terminal kinase (JNK) is activated persistently in spinal astrocytes in a neuropathic pain condition produced by spinal nerve ligation. This activation is required for the maintenance of neuropathic pain because spinal infusion of JNK inhibitors can reverse mechanical allodynia, a major symptom of neuropathic pain. Further study reveals that JNK is activated strongly in astrocytes by basic fibroblast growth factor (bFGF), an astroglial activator. Intrathecal infusion of bFGF also produces persistent mechanical allodynia. After peripheral nerve injury, bFGF might be produced by primary sensory neurons and spinal astrocytes because nerve injury produces robust bFGF upregulation in both cell types. Therefore, the bFGF/JNK pathway is an important signalling pathway in spinal astrocytes for chronic pain sensitization. Investigation of signaling mechanisms in spinal astrocytes will identify new molecular targets for the management of chronic pain.

Sustained expression of osteopontin is closely associated with calcium deposits in the rat hippocampus after transient forebrain ischemia

The present study was designed to evaluate the extent and topography of osteopontin (OPN) protein expression in the rat hippocampus 4 to 12 weeks following transient forebrain ischemia, and to compare OPN expression patterns with those of calcium deposits and astroglial and microglial reactions. Two patterns of OPN staining were recognized by light microscopy: 1) a diffuse pattern of tiny granular deposits throughout the CA1 region at 4 weeks after ischemia and 2) non-diffuse ovoid to round deposits, which formed conglomerates in the CA1 pyramidal cell layer over the chronic interval of 8 to 12 weeks. Immunogold-silver electron microscopy and electron probe microanalysis demonstrated that OPN deposits were indeed diverse types of calcium deposits, which were clearly delineated by profuse silver grains indicative of OPN expression. Intracellular OPN deposits were frequently observed within reactive astrocytes and neurons 4 weeks after ischemia but rarely at later times. By contrast, extracellular OPN deposits progressively increased in size and appeared to be gradually phagocytized by microglia or brain macrophages and some astrocytes over 8 to 12 weeks. These data indicate an interaction between OPN and calcium in the hippocampus in the chronic period after ischemia, suggesting that OPN binding to calcium deposits may be involved in scavenging mechanisms.

ATP-dependent potassium channel blockade strengthens microglial neuroprotection after hypoxia-ischemia in rats

Stroke causes CNS injury associated with strong fast microglial activation as part of the inflammatory response. In rat models of stroke, sulphonylurea receptor blockade with glibenclamide reduced cerebral edema and infarct volume. We postulated that glibenclamide administered during the early stages of stroke might foster neuroprotective microglial activity through ATP-sensitive potassium (K(ATP)) channel blockade. We found in vitro that BV2 cell line showed upregulated expression of K(ATP) channel subunits in response to pro-inflammatory signals and that glibenclamide increases the reactive morphology of microglia, phagocytic capacity and TNFα release. Moreover, glibenclamide administered to rats 6, 12 and 24h after transient Middle Cerebral Artery occlusion improved neurological outcome and preserved neurons in the lesioned core three days after reperfusion. Immunohistochemistry with specific markers to neuron, astroglia, microglia and lymphocytes showed that resident amoeboid microglia are the main cell population in that necrotic zone. These reactive microglial cells express SUR1, SUR2B and Kir6.2 proteins that assemble in functional K(ATP) channels. These findings provide that evidence for the key role of K(ATP) channels in the control of microglial reactivity are consistent with a microglial effect of glibenclamide into the ischemic brain and suggest a neuroprotective role of microglia in the early stages of stroke.

Microarray analysis of rat hippocampus exposed to excitotoxicity: reversal Na(+)/Ca(2+) exchanger NCX3 is overexpressed in glial cells

Multiple factors are involved in the glutamate-induced excitotoxicity phenomenon, such as overload of ionotropic and metabotropic receptors, excess Ca(2+) influx, nitric oxide synthase activation, oxidative damage due to increase in free radicals, and release of endogenous polyamine, among others. In order to attempt a more integrated approach to address this issue, we established, by microarray analysis, the hippocampus gene expression profiles under glutamate-induced excitotoxicity conditions. Increased gene expression is mainly related to excitotoxicity (CaMKII, glypican 2, GFAP, NCX3, IL-2, and Gmeb2) or with cell damage response (dynactin and Ecel1). Several genes that augmented their expression are related to glutamatergic system modulation, in particular with NMDA receptor modulation and calcium homeostasis (IL-2, CaMKII, acrosin, Gmeb2, hAChE, Slc83a, and SP1 factor). Conversely, among genes that diminished their expression, we found the Syngap 1, which is downregulated by CaMKII, and the MHC II, which is downregulated by glutamate. Changes observed in gene expression induced by monosodium glutamate (MSG) neonatal treatment in the hippocampus are consistent with the activation of the mechanisms that modulate NMDA receptor function as well as with the implementation of plastic response to cell damage and intracellular calcium homeostasis. Regarding this aspect, we report here that NCX3/Slc8a3, a Na(+)/Ca(2+) membrane exchanger, is highly expressed in astrocytes, both in vitro and in vivo, in response to glutamate-induced excitotoxicity. Hence, the results of this analysis present a broad view of the expression profile elicited by MSG neonatal treatment, and lead us to suggest the possible molecular pathways of action and reaction involved under this experimental model of excitotoxicity.

Targeting astrocyte signaling for chronic pain

Clinical management of chronic pain after nerve injury (neuropathic pain) and tumor invasion (cancer pain) is a real challenge due to our limited understanding of the cellular mechanisms that initiate and maintain chronic pain. It has been increasingly recognized that glial cells, such as microglia and astrocytes in the CNS play an important role in the development and maintenance of chronic pain. Notably, astrocytes make very close contacts with synapses and astrocyte reaction after nerve injury, arthritis, and tumor growth is more persistent than microglial reaction, and displays a better correlation with chronic pain behaviors. Accumulating evidence indicates that activated astrocytes can release pro-inflammatory cytokines (e.g., interleukin [IL]-1β) and chemokines (e.g., monocyte chemoattractant protein-1 [MCP-1]/also called CCL2) in the spinal cord to enhance and prolong persistent pain states. IL-1β can powerfully modulate synaptic transmission in the spinal cord by enhancing excitatory synaptic transmission and suppressing inhibitory synaptic transmission. IL-1β activation (cleavage) in the spinal cord after nerve injury requires the matrix metalloprotease-2. In particular, nerve injury and inflammation activate the c-Jun N-terminal kinase in spinal astrocytes, leading to a substantial increase in the expression and release of MCP-1. The MCP-1 increases pain sensitivity via direct activation of NMDA receptors in dorsal horn neurons. Pharmacological inhibition of the IL-1β, c-Jun N-terminal kinase, MCP-1, or matrix metalloprotease-2 signaling via spinal administration has been shown to attenuate inflammatory, neuropathic, or cancer pain. Therefore, interventions in specific signaling pathways in astrocytes may offer new approaches for the management of chronic pain.

Crosstalk between spinal astrocytes and neurons in nerve injury-induced neuropathic pain

Emerging research implicates the participation of spinal dorsal horn (SDH) neurons and astrocytes in nerve injury-induced neuropathic pain. However, the crosstalk between spinal astrocytes and neurons in neuropathic pain is not clear. Using a lumbar 5 (L5) spinal nerve ligation (SNL) pain model, we testified our hypothesis that SDH neurons and astrocytes reciprocally regulate each other to maintain the persistent neuropathic pain states. Glial fibrillary acidic protein (GFAP) was used as the astrocytic specific marker and Fos, protein of the protooncogene c-fos, was used as a marker for activated neurons. SNL induced a significant mechanical allodynia as well as activated SDH neurons indicated by the Fos expression at the early phase and activated astrocytes with the increased expression of GFAP during the late phase of pain, respectively. Intrathecal administration of c-fos antisense oligodeoxynucleotides (ASO) or astroglial toxin L-α-aminoadipate (L-AA) reversed the mechanical allodynia, respectively. Immunofluorescent histochemistry revealed that intrathecal administration of c-fos ASO significantly suppressed activation of not only neurons but also astrocytes induced by SNL. Meanwhile, L-AA shortened the duration of neuronal activation by SNL. Our data offers evidence that neuronal and astrocytic activations are closely related with the maintenance of neuropathic pain through a reciprocal “crosstalk”. The current study suggests that neuronal and non-neuronal elements should be taken integrally into consideration for nociceptive transmission, and that the intervention of such interaction may offer some novel pain therapeutic strategies.

A peptide c-Jun N-terminal kinase (JNK) inhibitor blocks mechanical allodynia after spinal nerve ligation: respective roles of JNK activation in primary sensory neurons and spinal astrocytes for neuropathic pain development and maintenance

Optimal management of neuropathic pain is a major clinical challenge. We investigated the involvement of c-Jun N-terminal kinase (JNK) in neuropathic pain produced by spinal nerve ligation (SNL) (L5). SNL induced a slow (>3 d) and persistent (>21 d) activation of JNK, in particular JNK1, in GFAP-expressing astrocytes in the spinal cord. In contrast, p38 mitogen-activated protein kinase activation was found in spinal microglia after SNL, which had fallen to near basal level by 21 d. Intrathecal infusion of a JNK peptide inhibitor, D-JNKI-1, did not affect normal pain responses but potently prevented and reversed SNL-induced mechanical allodynia, a major symptom of neuropathic pain. Intrathecal D-JNKI-1 also suppressed SNL-induced phosphorylation of the JNK substrate, c-Jun, in spinal astrocytes. However, SNL-induced upregulation of GFAP was not attenuated by spinal D-JNKI-1 infusion. Furthermore, SNL induced a rapid (<12 h) but transient activation of JNK in the L5 (injured) but not L4 (intact) DRG. JNK activation in the DRG was mainly found in small-sized C-fiber neurons. Infusion of D-JNKI-1 into the L5 DRG prevented but did not reverse SNL-induced mechanical allodynia. Finally, intrathecal administration of an astroglial toxin, l-alpha-aminoadipate, reversed mechanical allodynia. Our data suggest that JNK activation in the DRG and spinal cord play distinct roles in regulating the development and maintenance of neuropathic pain, respectively, and that spinal astrocytes contribute importantly to the persistence of mechanical allodynia. Targeting the JNK pathway in spinal astroglia may present a new and efficient way to treat neuropathic pain symptoms.

Similar calcification process in acute and chronic human brain pathologies

Cellular microcalcification observed in a diversity of human pathologies, such as vascular dementia, Alzheimer's disease, Parkinson's disease, astrogliomas, and posttraumatic epilepsy, also develops in rodent experimental models of central nervous system (CNS) neurodegeneration. Central to the neurodegenerative process is the inability of neurons to regulate intracellular calcium levels properly, and this is extensible to fine regulation of the CNS. This study provides evidence of a common pattern of brain calcification taking place in several human pathologies, and in the rat with glutamate-derived CNS lesions, regarding the chemical composition, physical characteristics, and histological environment of the precipitates. Furthermore, a common physical mechanism of deposit formation through nucleation, lineal growth, and aggregation is presented, under the modulation of protein deposition and elemental composition factors. Insofar as calcium precipitation reduces activity signals at no energy expense, the presence in human and rodent cerebral brain lesions of a common pattern of calcification may reflect an imbalance between cellular signals of activity and energy availability for its execution. If this is true, this new step of calcium homeostasis can be viewed as a general cellular adaptative mechanism to reduce further brain damage.

In vivo co-ordinated interactions between inhibitory systems to control glutamate-mediated hippocampal excitability

We present an overview of the long-term adaptation of hippocampal neurotransmission to cholinergic and GABAergic deafferentation caused by excitotoxic lesion of the medial septum. Two months after septal microinjection of 2.7 nmol alpha-amino-3-hydroxy-5-methylisoxazole-4-propionate (AMPA), a 220% increase of GABA(A) receptor labelling in the hippocampal CA3 and the hilus was shown, and also changes in hippocampal neurotransmission characterised by in vivo microdialysis and HPLC. Basal amino acid and purine extracellular levels were studied in control and lesioned rats. In vivo effects of 100 mm KCl perfusion and adenosine A(1) receptor blockade with 1,3-dipropyl-8-cyclopentylxanthine (DPCPX) on their release were also investigated. In lesioned animals GABA, glutamate and glutamine basal levels were decreased and taurine, adenosine and uric acid levels increased. A similar response to KCl infusion occurred in both groups except for GABA and glutamate, which release decreased in lesioned rats. Only in lesioned rats, DPCPX increased GABA basal level and KCl-induced glutamate release, and decreased glutamate turnover. Our results evidence that an excitotoxic septal lesion leads to increased hippocampal GABA(A) receptors and decreased glutamate neurotransmission. In this situation, a co-ordinated response of hippocampal retaliatory systems takes place to control neuron excitability.

Constitutive expression of CCR2 chemokine receptor and inhibition by MCP-1/CCL2 of GABA-induced currents in spinal cord neurones

In the CNS, immune-like competent cells (microglia and astrocytes) were first described as potential sites of chemokine synthesis, but more recent evidence has indicated that neurones might also express chemokines and their receptors. The aim of the present work was to investigate further, both in vivo and in vitro, CC Chemokine Family Receptor 2 (CCR2) expression and functionality in rat spinal cord neurones. First, we demonstrated by RT-PCR and western blot analysis that CCR2 mRNA and protein were present in spinal extracts. Furthermore, we showed by immunolabelling that CCR2 was exclusively expressed by neurones in spinal sections of healthy rat. Finally, to test the functionality of CCR2, we used primary cultures of rat spinal neurones. In this model, similar to what was observed in vivo, CCR2 mRNA and protein were expressed by neurones. Cultured neurones stimulated with Monocyte Chemoattractant Protein-1 (MCP-1)/CCL2, the best characterized CCR2 agonist, showed activation of the Akt pathway. Finally, patch-clamp recording of cultured spinal neurones was used to investigate whether MCP-1/CCL2 could modulate their electrophysiological properties. MCP-1 alone did not affect the electrical properties of spinal neurones, but potently and efficiently inhibited GABA(A)-mediated GABAergic responses in these neurones. These data constitute the first demonstration of a modulatory role of MCP-1 on GABAergic neurotransmission and contribute to our understanding of the roles of CCR2 and MCP-1/CCL2 in spinal cord physiology, in particular with respect to nociceptive transmission, as well as the implication of this chemokine in neuronal adaptation or dysfunction during neuropathy.