Cellular composition of primary cultures from cerebral cortex, striatum, hippocampus, brainstem and cerebellum

Effects of Budesonide and Dexamethasone on Cell Morphology, Thymidine Incorporation and Glutamine Synthetase Activity in Rat Primary Astroglial Culture

Glucocorticoids are widely used in medical practice. Since astrocytes are target cells for glucocorticoids, the effects of two glucocorticoids, budesonide and dexamethasone, on cell morphology, thymidine incorporation into DNA and glutamine synthetase (GS) activity, were evaluated in primary astroglial cultures. Both budesonide and dexamethasone caused a threefold increase in GS activity over a dose range of 10-6–10-9M. There were no differences between the effects of the two glucocorticoids. No morphological changes were obtained with the glucocorticoids with the same concentration range as above and with incubation periods of up to 48 hours. Nor were any effects on [3H]-thymidine incorporation observed. It is concluded that glucocorticoids can regulate intracellular amino acid metabolism in astrocytes by an activation of GS, while cell morphology and cell replication appear not to be affected.

DNA methylation analysis on purified neurons and glia dissects age and Alzheimer's disease-specific changes in the human cortex

Background

Epigenome-wide association studies (EWAS) based on human brain samples allow a deep and direct understanding of epigenetic dysregulation in Alzheimer’s disease (AD). However, strong variation of cell-type proportions across brain tissue samples represents a significant source of data noise. Here, we report the first EWAS based on sorted neuronal and non-neuronal (mostly glia) nuclei from postmortem human brain tissues.

Results

We show that cell sorting strongly enhances the robust detection of disease-related DNA methylation changes even in a relatively small cohort. We identify numerous genes with cell-type-specific methylation signatures and document differential methylation dynamics associated with aging specifically in neurons such as CLU, SYNJ2 and NCOR2 or in glia RAI1,CXXC5 and INPP5A. Further, we found neuron or glia-specific associations with AD Braak stage progression at genes such as MCF2L, ANK1, MAP2, LRRC8B, STK32C and S100B. A comparison of our study with previous tissue-based EWAS validates multiple AD-associated DNA methylation signals and additionally specifies their origin to neuron, e.g., HOXA3 or glia (ANK1). In a meta-analysis, we reveal two novel previously unrecognized methylation changes at the key AD risk genes APP and ADAM17.

Conclusions

Our data highlight the complex interplay between disease, age and cell-type-specific methylation changes in AD risk genes thus offering new perspectives for the validation and interpretation of large EWAS results.

Electronic supplementary material

The online version of this article (10.1186/s13072-018-0211-3) contains supplementary material, which is available to authorized users.

Therapeutic innovation: Inflammatory-reactive astrocytes as targets of inflammation

This study aimed to test pharmaceutical compounds targeting astrocytes showing inflammatory dysregulation. The primary rat brain cultures were treated with different batches of serum with or without microglia added to make the cells inflammatory-reactive. Lipopolysaccharide (LPS) and tryptase were used as inflammatory inducers. Expression levels of Toll-like receptor 4 (TLR4), Na⁺/K⁺-ATPase, and matrix metalloprotease-13 (MMP-13), as well as actin filament organization, pro-inflammatory cytokines, and intracellular Ca²⁺ release, were evaluated. LPS combined with tryptase upregulated TLR4 expression, whereas Na⁺/K⁺-ATPase expression was downregulated, ATP-evoked Ca²⁺ transients were increased, actin filaments were reorganized and ring structures instead of stress fibers were observed. Other aims of the study were to prevent astrocytes from becoming inflammatory-reactive and to restore inflammatory dysregulated cellular changes. A combination of the μ-opioid antagonist (-)-naloxone in ultra-low concentrations, the non-addictive μ-opioid agonist (-)-linalool, and the anti-epileptic agent levetiracetam was examined. The results indicated that this drug cocktail prevented the LPS- and tryptase-induced inflammatory dysregulation. The drug cocktail could also restore the LPS- and tryptase-treated cells back to a normal physiological level in terms of the analyzed parameters.

Axo-glial communication through neurexin-neuroligin signaling regulates myelination and oligodendrocyte differentiation

Axonal transsynaptic signaling between presynaptic neurexin (NX) and postsynaptic neuroligin (NL) is essential for many properties of synaptic connectivity. Here, we demonstrate the existence of a parallel axo-glial signaling pathway between axonal NX and oligodendritic (OL) NL3. We show that this pathway contributes to the regulation of myelinogenesis, the maintenance of established myelination, and the differentiation state of the OL using in vitro models. We first confirm that NL3 mRNA and protein are expressed in OLs and in OL precursors. We then show that OLs in culture form contacts with non-neuronal cells exogenously expressing NL3's binding partners NX1α or NX1β. Conversely, blocking axo-glial NX-NL3 signaling by saturating NX with exogenous soluble NL protein (NL-ECD) disrupts interactions between OLs and axons in both in vitro and ex vivo assays. Myelination by OLs is tied to their differentiation state, and we find that blocking NX-NL signaling with soluble NL protein also caused OL differentiation to stall at an immature stage. Moreover, in vitro knockdown of NL3 in OLs with siRNAs stalls their development and reduces branching complexity. Interestingly, inclusion of an autism related mutation in the NL blocking protein attenuates these effects; OLs differentiate and the dynamics of OL-axon signaling occur normally as this peptide does not disrupt NX-NL3 axo-glial interactions. Our findings provide evidence not only for a new pathway in axo-glial communication, they also potentially explain the correlation between altered white matter and autism. GLIA 2015;63:2023-2039.

Species-Specific Regulation of t-PA and PAI-1 Gene Expression in Human and Rat Astrocytes

In recent years, the role and physiological regulation of the serine protease tissue-type plasminogen activator (t-PA) and its inhibitors, including plasminogen activator inhibitor type-1 (PAI-1), in the brain have received much attention. However, as studies focusing these issues are difficult to perform in humans, a great majority of the studies conducted to date have utilized rodent in vivo and/or in vitro models. In view of the species-specific structural differences present in both the t-PA and the PAI-1 promoters, we have compared the response of these genes in astrocytes of rat and human origin. We reveal marked quantitative and qualitative species-specific differences in gene induction following treatment with various physiological and pathological stimuli. Thus, our findings are of importance for the interpretation of previous and future results related to t-PA and PAI-1 expression.

Morphological effects of excitatory amino acid analogs on primary astroglial cultures

In vivo administration of excitatory amino acids (excitotoxins) causes gliotoxicity in addition to neurotoxicity. The astrocyte reaction has been proposed to be secondary to neurotoxic effects, but this suggestion is based on circumstantial evidence. In the present study, this issue was addressed by examination of morphological alterations of astrocytes in primary culture to exposure of different excitotoxins. Two-week-old rat hippocampal cultures were exposed to the type agonists N-methyl-d-aspartate (NMDA), kainic acid (KA), quisqualate (QA) and to the mixed agonist glutamate (GLU). Agonists were included at 1 mM and exposure was continued for 22 h. NMDA-treated cultures did not differ from controls. However, KA induced a complex pattern of morphological reactions. Further, GLU and QA caused astrocyte swelling which was spontaneously reversed after GLU addition while QA killed astrocytes after 22 h of incubation. Excitotoxins induce astrocyte edema in vivo regardless of their receptor preference. The present study failed to disclose a similar stereotyped response, suggesting that in vivo gliotoxicity of excitotoxins is unrelated to direct effects on astroglia.

Inflammatory activation enhances NMDA-triggered Ca2+ signalling and IL-1β secretion in primary cultures of rat astrocytes

The aim of the present study was to measure the effects of NMDA receptor antagonists on rat astroglial-enriched primary cultures after incubation with lipopolysaccharide (LPS), with a view to explaining the role of NMDA receptors in the inflammatory activation of astrocytes. First, the presence of NMDA receptor subunits was confirmed at the protein level by immunocytochemical methods. The presence of functional NMDA receptors containing GluN2B subunits was then established by ratiometric fluorescent Ca(2+) imaging which revealed transient NMDA-triggered Ca(2+) responses. These responses could be blocked by the competitive antagonist 2-amino-5-phosphonopentoate (APV) and the non-competitive GluN2B subunit-selective antagonist ifenprodil. The NMDA-evoked Ca(2+) transients were dependent on Ca(2+) release from intracellular stores via interaction with InsP3-sensitive receptors as they were blocked by thapsigargin or xestospongin C. Following 24h incubation with LPS, astroglial inflammatory activation increased IL-1β secretion and NMDA-triggered Ca(2+) transients. The addition of APV or ifenprodil inhibited these enhanced responses, suggesting that LPS exposure stimulates IL-1β release from astrocytes through a mechanism that requires NMDA receptor stimulation.

Decreased oxidative stress during glycolytic inhibition enables maintenance of ATP production and astrocytic survival

Depressed energy metabolism and oxidative stress are common features in many pathological situations in the brain, including stroke. In order to investigate astrocytic responses to such stress, we induced metabolic depression in cultured rat astrocytes. Iodoacetate (IA), an inhibitor of the glycolytic enzyme glyceraldehyde-3-phosphate dehydrogenase (GAPDH) was used and resulted in a rapid inhibition of GAPDH activity. After 1h of GAPDH inhibition the ATP levels started to decrease and were completely abolished at 4h. In parallel, the activity of reactive oxygen species (ROS) was significantly increased, followed by extensive cell death involving flipping of phosphatidylserine and translocation of apoptosis-inducing factor, but not caspase-3 activation. When IA was combined with azide, a respiratory chain complex IV inhibitor, the ATP levels decreased immediately. Interestingly, with azide present, the ROS activity remained low and the astrocytes remained viable even at very low ATP levels. Addition of exogenous ROS-scavengers prevented the IA-induced ROS activity, the ATP levels were maintained and cell death was prevented. Similar protection could be obtained when astrocytes, prior to addition of IA, were incubated with substances known to activate the nuclear factor erythroid 2-related factor 2 (Nrf2)-regulated endogenous antioxidant system. When IA was washed out, after a relatively moderate ATP depression, massive cell death occurred. This was efficiently prevented by addition of azide or ROS scavengers during the IA treatment or by pre-activation of the Nrf2 system. Our results demonstrate that astrocytes in culture can endure and recover from glycolytic inhibition if the ROS activity remained at a low level and suggest that oxidative stress can be an important component for astrocytic cell death following metabolic stress.

Naloxone in ultralow concentration restores endomorphin-1-evoked Ca²⁺ signaling in lipopolysaccharide pretreated astrocytes

Long-term pain is a disabling condition that affects thousands of people. Pain may be sustained for a long time even after the physiological trigger has resolved. Possible mechanisms for this phenomenon include low-grade inflammation in the CNS. Astrocytes respond to inflammatory stimuli and may play an important role as modulators of the inflammatory response in the nervous system. This study aimed first to assess how astrocytes in a primary culture behave when exposed to the endogenous μ-opioid receptor agonist endomorphin-1 (EM-1), in a concentration-dependent manner, concerning intracellular Ca²⁺ responses. EM-1 stimulated the μ-opioid receptor from 10⁻¹⁵ M up to 10⁻⁴ M with increasing intensity, usually reflected as one peak at low concentrations and two peaks at higher concentrations. Naloxone, pertussis toxin (PTX), or the μ-opioid receptor antagonists CTOP did not totally block the EM-1-evoked Ca²⁺ responses. However, a combination of ultralow concentration naloxone (10⁻¹² M) and PTX (100 ng/ml) totally blocked the EM-1-evoked Ca²⁺ responses. This suggests that ultralow (picomolar) concentrations of naloxone should block the μ-opioid receptor coupled G(s) protein, and that PTX should block the μ-opioid receptor coupled G(i/o) protein. The second aim was to investigate exposure of astrocytes with the inflammatory agent lipopolysaccharide (LPS). After 4 h of LPS incubation, the EM-1-evoked Ca²⁺ transients were attenuated, and after 24 h of LPS incubation, the EM-1-evoked Ca²⁺ transients were oscillated. To restore the EM-1-evoked Ca²⁺ transients, naloxone was assessed as a proposed anti-inflammatory substance. In ultralow picomolar concentration, naloxone demonstrated the ability to restore the Ca²⁺ transients.

Ifenprodil restores GDNF-evoked Ca(2+) signalling and Na(+)/K(+) -ATPase expression in inflammation-pretreated astrocytes

Glial cell line-derived neurotrophic factor (GDNF) plays an important role in neuroinflammatory and neuropathic pain conditions. Astrocytes produce and secrete GDNF, which interacts with its receptors to induce Ca(2+) transients. This study aimed first to assess intracellular Ca(2+) responses of astrocytes in primary culture when exposed to the neuroprotective and anti-inflammatory peptide GDNF. Furthermore, incubation with the inflammatory inducers lipopolysaccharide (LPS), NMDA, or interleukin 1-β (IL-1β) attenuated the GDNF-induced Ca(2+) transients. The next aim was to try to restore the suppressed GDNF responses induced by inflammatory changes in the astrocytes with an anti-inflammatory substance. Ifenprodil, an NMDA receptor antagonist at the NR2B subunit, was tested. It was shown to restore the GDNF-evoked Ca(2+) transients and increased the Na(+)/K(+) -ATPase expression. Ifenprodil seems to be a potent anti-inflammatory substance for astrocytes which have been pre-activated by inflammatory stimuli.

Naloxone and ouabain in ultralow concentrations restore Na+/K+-ATPase and cytoskeleton in lipopolysaccharide-treated astrocytes

Astrocytes respond to inflammatory stimuli and may be important modulators of the inflammatory response in the nervous system. This study aimed first to assess how astrocytes in primary culture behave in response to inflammatory stimuli concerning intracellular Ca(2+) responses, expression of Toll-like receptor 4 (TLR4), Na(+)/K(+)-ATPase, actin filament organization, and expression of cytokines. In a cell culture model with lipopolysaccharide (LPS), astrocyte response was assessed first in the acute phase and then after incubation with LPS for 1-48 h. The concentration curve for LPS-stimulated Ca(2+) responses was bell-shaped, and the astrocytes expressed TLR4, which detects LPS and evokes intracellular Ca(2+) transients. After a long incubation with LPS, TLR4 was up-regulated, LPS-evoked Ca(2+) transients were expressed as oscillations, Na(+)/K(+)-ATPase was down-regulated, and the actin filaments were disorganized. Interleukin-1β (IL-1β) release was increased after 24 h in LPS. A second aim was to try to restore the LPS-induced changes in astrocytes with substances that may have dose-dependent anti-inflammatory properties. Naloxone and ouabain were tested separately in ultralow or high concentrations. Both substances evoked intracellular Ca(2+) transients for all of the concentrations from 10(-15) up to 10(-4) M. Neither substance blocked the TLR4-evoked Ca(2+) responses. Naloxone and ouabain prevented the LPS-induced down-regulation of Na(+)/K(+)-ATPase and restored the actin filaments. Ouabain, in addition, reduced the IL-1β release from reactive astrocytes. Notably, ultralow concentrations (10(-12) M) of naloxone and ouabain showed these qualities. Ouabain seems to be more potent in these effects of the two tested substances.

The Nrf2-inducible antioxidant defense in astrocytes can be both up- and down-regulated by activated microglia:Involvement of p38 MAPK

The effects of microglia-conditioned medium (MCM) on the inducible Nrf2 system in astrocyte-rich cultures were investigated by determination of glutathione (GSH) levels, γglutamylcysteine ligase (γGCL) activity, the protein levels of Nrf2, Keap1, the modulatory subunit of γGCL (γGCL-M) and activated MAP kinases (ERK1/2, JNK and p38). Microglia were either cultured for 24 h in serum-free culture medium to achieve microglia-conditioned medium from non-activated cells (MCM(0) ), used as control condition, or activated with different concentrations (0.1-1,000 ng mL(-1) ) of lipopolysaccharide (LPS) to produce MCM(0.1-1,000) . Acute exposure (24 h) to MCM(100) increased GSH, γGCL activity, the protein levels of γGCL-M, Nrf2, and activated JNK and ERK1/2 in astrocyte-rich cultures. In contrast, treatment with MCM(10) for 24 h decreased components of the Nrf2 system in parallel with activation of p38 MAPK. Stimulation of the Nrf2 system by tBHQ was partly intact after 24 h but blocked after 72 h treatment with MCM(10) and MCM(100) . This down-regulation after 72 h correlated with activation of p38 MAPK and lack of ERK1/2 and JNK activation. The negative effects were partly reversed by an inhibitor of p38 which restored tBHQ mediated protection against oxidative stress. In conclusion, the study showed a negative effect of MCM(10) on the inducible anti-oxidant defense in astrocyte-rich cultures at both 24 and 72 h that correlated with activation of p38 and was partly reversed by a p38 inhibitor. A transient protective effect of MCM(100) on astrocyte-rich cultures against H(2)O(2) toxicity was observed at 24 h which coincided with activation of JNK and ERK1/2.

Implications for glycine receptors and astrocytes in ethanol-induced elevation of dopamine levels in the nucleus accumbens

Elevated dopamine levels are believed to contribute to the rewarding sensation of ethanol (EtOH), and previous research has shown that strychnine-sensitive glycine receptors in the nucleus accumbens (nAc) are involved in regulating dopamine release and in mediating the reinforcing effects of EtOH. Furthermore, the osmoregulator taurine, which is released from astrocytes treated with EtOH, can act as an endogenous ligand for the glycine receptor, and increase extracellular dopamine levels. The aim of this study was to address if EtOH-induced swelling of astrocytes could contribute to elevated dopamine levels by increasing the extracellular concentration of taurine. Cell swelling was estimated by optical sectioning of fluorescently labeled astrocytes in primary cultures from rat, and showed that EtOH (25-150 mM) increased astrocyte cell volumes in a concentration- and ion-dependent manner. The EtOH-induced cell swelling was inhibited in cultures treated with the Na(+) /K(+) /2Cl⁻ cotransporter blocker furosemide (1 mM), Na(+) /K(+) -ATPase inhibitor ouabain (0.1 mM), potassium channel inhibitor BaCl₂ (50 µM) and in cultures containing low extracellular sodium concentration (3 mM). In vivo microdialysis performed in the nAc of awake and freely moving rats showed that local treatment with EtOH enhanced the concentrations of dopamine and taurine in the microdialysate, while glycine and β-alanine levels were not significantly modulated. EtOH-induced dopamine release was antagonized by local treatment with the glycine receptor antagonist strychnine (20 µM) or furosemide (100 µM or 1 mM). Furosemide also prevented EtOH-induced taurine release in the nAc. In conclusion, our data suggest that extracellular concentrations of dopamine and taurine are interconnected and that swelling of astrocytes contributes to the acute rewarding sensation of EtOH.

PACAP attenuates 5-HT, histamine, and ATP-evoked Ca2+ transients in astrocytes

Pituitary adenylate cyclase-activating polypeptide (PACAP) has neuroprotective properties and plays an important role in neuroinflammation. PACAP38 interacts with its receptors, PAC1, and VPAC, on astrocytes at 10(-8) M to induce biphasic Ca2+ transients, which were reduced to a single transient by the PAC1-blocking PACAP antagonist PACAP6-38. At 10(-12) M even the single transient, corresponding to PAC1 was blocked. PACAP-induced Ca2+ transients were more pronounced in astrocytes cocultured with brain endothelial cells than in monocultured astrocytes, indicating that astrocytes that receive signals from microvessels develop more sensitive signal transduction systems for Ca. In this sensitive system, PACAP38 attenuated 5-HT, histamine, and ATP-evoked Ca2+ transients, showing the anti-inflammatory properties of PACAP.

In inflammatory reactive astrocytes co-cultured with brain endothelial cells nicotine-evoked Ca(2+) transients are attenuated due to interleukin-1beta release and rearrangement of actin filaments

The aim of this study was to investigate whether nicotine acetylcholine receptors (nAChRs) are expressed in a more pronounced way in astrocytes co-cultured with microvascular endothelial cells from adult rat brain, compared with monocultured astrocytes, as a sign of a more developed signal transduction system. Also investigated was whether nicotine plays a role in the control of neuroinflammatory reactivity in astrocytes. Ca(2+) imaging experiments were performed using cells loaded with the Ca(2+) indicator Fura-2/AM. Co-cultured astrocytes responded to lower concentrations of nicotine than did monocultured astrocytes, indicating that they are more sensitive to nicotine. Co-cultured astrocytes also expressed a higher selectivity for alpha7nAChR and alpha4/beta2 subunits and evoked higher Ca(2+) transients compared with monocultured astrocytes. The Ca(2+) transients referred to are activators of Ca(2+)-induced Ca(2+) release from intracellular stores, both IP(3) and ryanodine, triggered by influx through receptor channels. The nicotine-induced Ca(2+) transients were attenuated after incubation with the inflammatory mediator lipopolysaccharide (LPS), but were not attenuated after incubation with the pain-transmitting peptides substance P and calcitonin-gene-related peptide, nor with the infection and inflammation stress mediator, leptin. Furthermore, LPS-induced release of interleukin-1beta (IL-1beta) measured by enzyme-linked immunosorbent assay (ELISA) was more pronounced in co-cultured versus monocultured astrocytes. Incubation with both LPS and IL-1beta further attenuated nicotine-induced Ca(2+) response. We also found that LPS and IL-1beta induced rearrangement of the F-actin filaments, as measured with an Alexa488-conjugated phalloidin probe. The rearrangements consisted of increases in ring formations and a more dispersed appearance of the filaments. These results indicate that there is a connection between a dysfunction of nicotine Ca(2+) signaling in inflammatory reactive astrocytes and upregulation of IL-1beta and the rearrangements of actin filaments in the cells.

mu-Opioid agonists inhibit the enhanced intracellular Ca(2+) responses in inflammatory activated astrocytes co-cultured with brain endothelial cells

In order to imitate the in vivo situation with constituents from the blood-brain barrier, astrocytes from newborn rat cerebral cortex were co-cultured with adult rat brain microvascular endothelial cells. These astrocytes exhibited a morphologically differentiated appearance with long processes. 5-HT, synthetic mu-, delta- or kappa-opioid agonists, and the endogenous opioids endomorphin-1, beta-endorphin, and dynorphin induced higher Ca(2+) amplitudes and/or more Ca(2+) transients in these cells than in astrocytes in monoculture, as a sign of more developed signal transduction systems. Furthermore, stimulation of the co-cultured astrocytes with 5-HT generated a pronounced increase in intracellular Ca(2+) release in the presence of the inflammatory or pain mediating activators substance P, calcitonin gene-related peptide (CGRP), lipopolysaccharide (LPS), or leptin. These Ca(2+) responses were restored by opioids so that the delta- and kappa-opioid receptor agonists reduced the number of Ca(2+) transients elicited after incubation in substance P+CGRP or leptin, while the mu- and delta-opioid receptor agonists attenuated the Ca(2+) amplitudes elicited in the presence of LPS or leptin. In LPS treated co-cultured astrocytes the mu-opioid receptor antagonist naloxone attenuated not only the endomorphin-1, but also the 5-HT evoked Ca(2+) transients. These results suggest that opioids, especially mu-opioid agonists, play a role in the control of neuroinflammatory activity in astrocytes and that naloxone, in addition to its interaction with mu-opioid receptors, also may act through some binding site on astrocytes, other than the classical opioid receptor.

Region-specific tolerance criteria for the living brain

Computational models of traumatic brain injury (TBI) can predict injury-induced brain deformation. However, predicting the biological consequences (i.e. cell death or dysfunction) of induced brain deformation requires tolerance criteria. Here, we present a tolerance criterion for the cortex which exhibits important differences from that of the hippocampus. Organotypic slice cultures of the rat cortex, which maintain tissue architecture and cell content consistent with that in vivo, were mechanically injured with an in vitro model described previously. Cultures were stretched equibiaxially up to 0.35 Lagrangian strain at strain rates up to 50 s(-1). Cell death was quantified at 1, 2, 3, and 4 days following injury. Statistical analysis (repeated measures ANOVA) showed that all three factors (Strain, Strain Rate, and Time post-injury) significantly affected cell death. An equation describing cell death as a function of the significant parameters was then fit to the data. Compared to the hippocampus, the cortex was less vulnerable to stretch-induced injury and demonstrated a strain threshold below 0.20. Strain rate was also a significant factor for cortical but not hippocampal cell death. Cortical cell death began at an earlier time point than in the hippocampus, with cell death evident at 1 day post-injury versus 3 days in the hippocampus. In conclusion, different regions of the brain respond differently to identical mechanical stimuli, and this difference should be incorporated into finite element models of TBI if they are to more accurately predict in vivo consequences of TBI.

Microglial GLT-1 is upregulated in response to herpes simplex virus infection to provide an antiviral defence via glutathione

Herpes simplex virus (HSV) can enter the central nervous system and cause encephalitis (HSV-1) or meningitis (HSV-2). Microglia, the immunocompetent cells of the central nervous system, are potentially able to detect viral infections. Microglia have been shown to express the glutamate transporter GLT-1 during pathological events, leading to increased microglial glutamate uptake and glutathione synthesis. This study aims to address the role of GLT-1 and glutathione, a major antioxidant with antiviral properties, during HSV infections. Using neuron-enriched mixed primary cultures from rat, it was found that microglia have higher resistance to HSV infections than neurons or astrocytes after 24 h incubation with HSV. Purified microglia in culture were used to further address this. It was found that microglia were able to detect HSV and responded by releasing tumor necrosis factor-alpha (TNF-alpha) and upregulating GLT-1 after 24 h incubation with 1 PFU/cell HSV-1 or HSV-2. Furthermore, the microglial glutathione levels were not significantly diminished after 24 h. Inhibition of the microglial glutathione synthesis with 200 microM buthionine sulfoximide (BSO) led to significantly more infected cells after 24 h incubation with 1 PFU/cell HSV-1 or HSV-2. These data indicate that the higher resistance in microglia against HSV infections may be due to the expression of GLT-1, which can maintain the glutathione levels and provide a mechanism for microglial self-defense against HSV.

Microglial glutamate uptake is coupled to glutathione synthesis and glutamate release

The physiological function of microglial glutamate uptake has been debated as it is about 10% of that measured for astrocytes. This study addresses how glutamate, taken up from the extracellular space, is utilized by microglia. It was found that purified rat microglia incubated for 60 min with (3)H-glutamate had an increased intracellular accumulation of (3)H-glutamate after 12 h incubation with tumour necrosis factor alpha (TNF-alpha) but not after incubation with lipopolysaccharide (LPS). Furthermore, LPS- but not TNF-alpha-treated cells showed an increased efflux of (3)H-labelled compounds, presumably glutamate through the X(C) (-) system and treatment with LPS or TNF-alpha increased the microglial glutathione concentrations and led to an increased incorporation of (3)H-glutamate into glutathione. Depending on the stimuli, 3-6% of the total labelled contents were found in the form of glutathione and 25-35% in the form of glutamate. These results show that microglial glutamate uptake is directly coupled to glutathione synthesis and release of glutamate and/or glutamate metabolites. Additionally, the increased glutathione contents after LPS or TNF-alpha treatment were able to reduce microglial cell death after H(2)O(2) challenge, showing a potential (self)-protective function for microglial glutamate transporter expression and glutathione synthesis.

Exposure of Cultured Astroglial and Microglial Brain Cells to 900 MHz Microwave Radiation

The rapid rise in the use of mobile communications has raised concerns about health issues related to low-level microwave radiation. The head and brain are usually the most exposed targets in mobile phone users. In the brain, two types of glial cells, the astroglial and the microglial cells, are interesting in the context of biological effects from microwave exposure. These cells are widely distributed in the brain and are directly involved in the response to brain damage as well as in the development of brain cancer. The aim of the present study was to investigate whether 900 MHz radiation could affect these two different glial cell types in culture by studying markers for damage-related processes in the cells. Primary cultures enriched in astroglial cells were exposed to 900 MHz microwave radiation in a temperature-controlled exposure system at specific absorption rates (SARs) of 3 W/kg GSM modulated wave (mw) for 4, 8 and 24 h or 27 W/kg continuous wave (cw) for 24 h, and the release into the extracellular medium of the two pro-inflammatory cytokines interleukin 6 (Il6) and tumor necrosis factor-alpha (Tnfa) was analyzed. In addition, levels of the astroglial cell-specific reactive marker glial fibrillary acidic protein (Gfap), whose expression dynamics is different from that of cytokines, were measured in astroglial cultures and in astroglial cell-conditioned cell culture medium at SARs of 27 and 54 W/kg (cw) for 4 or 24 h. No significant differences could be detected for any of the parameters studied at any time and for any of the radiation characteristics. Total protein levels remained constant during the experiments. Microglial cell cultures were exposed to 900 MHz radiation at an SAR of 3 W/kg (mw) for 8 h, and I16, Tnfa, total protein and the microglial reactivity marker ED-1 (a macrophage activation antigen) were measured. No significant differences were found. The morphology of the cultured astroglial cells and microglia was studied and appeared to be unaffected by microwave irradiation. Thus this study does not provide evidence for any effect of the microwave radiation used on damage-related factors in glial cells in culture.

Sulfatide with short fatty acid dominates in astrocytes and neurons

Glycosphingolipids are located in cell membranes and the brain is especially enriched. We speculated that the subcellular location of glycosphingolipids depends on their fatty acid chain length because their sugar residues are constant, whereas fatty acid chain length can vary within the same molecule. To test this hypothesis we analysed the glycosphingolipid sulfatide, which is highly abundant in myelin and has mostly long fatty acids. We used a negative ion electrospray tandem mass spectrometry precursor ion scan to analyse the molecular species of sulfatide in cultured astrocytes and a mouse model of the human disease metachromatic leukodystrophy. In these arylsulfatase A (ASA)-deficient mice sulfatide accumulates intracellularly in neurons and astrocytes. Immunocytochemistry was also performed on cultured astrocytes and analysed using confocal laser scanning microscopy. Analyses of the molecular species showed that cultured astrocytes contained sulfatide with a predominance of stearic acid (C18), which was located in large intracellular vesicles throughout the cell body and along the processes. The same was seen in ASA-deficient mice, which accumulated a higher proportion (15 mol% compared with 8 mol% in control mice) of sulfatide with stearic acid. We conclude that the major fatty acid composition of sulfatide differs between white and grey matter, with neurons and astrocytes containing mostly short-chain fatty acids with an emphasis on stearic acid. Based on our results, we speculate that the fatty acid chain length of sulfatide might determine its intracellular (short chain) or extracellular (long chain) location and thereby its functions.

Corticosterone inhibits expression of the microglial glutamate transporter GLT-1 in vitro

The present study investigates the effect of the glucocorticoid corticosterone on microglial glutamate transporters in vitro. Microglial cultures obtained from rat cerebral cortex were found to express the excitatory amino acid transporter GLT-1, but not GLAST, and this expression was increased by 1 ng/ml lipopolysaccharide after 12 h of stimulation. This increase has previously been shown to be mediated by tumor necrosis factor-alpha, a cytokine released by microglia during pathological conditions. Furthermore, lipopolysaccharide increased the microglial release of tumor necrosis factor-alpha and 1 microM corticosterone inhibited this effect. Corticosterone also inhibited the lipopolysaccharide-induced increase of the GLT-1 expression as well as the expression in non-activated cells. The effect of corticosterone on the GLT-1 expression was dose dependent and accompanied by similar effects on the microglial glutamate uptake capacity. Additionally, exogenous tumor necrosis factor-alpha was found to counteract the effect of corticosterone on microglial GLT-1 expression. The effect of corticosterone appeared to be glucocorticoid receptor specific since 10 microM of the glucocorticoid receptor antagonist mifepristone inhibited the effect. Thus, corticosterone decreased the microglial uptake of glutamate by decreasing the expression of glutamate transporters, probably due to the inhibited microglial tumor necrosis factor-alpha release. These results provide insights into the mechanisms behind microglial glutamate transporter expression during pathological conditions, and contribute to the debate about the beneficial or harmful effects of glucocorticoids.

Glutathione peroxidase-1 contributes to the protection of glutamine synthetase in astrocytes during oxidative stress

Glutamine synthetase (GS) is an astrocytic enzyme that is essential for the glutamate-glutamine cycle between neurons and astrocytes. To measure the effects of oxidative stress on the activity of GS in astrocytes, astrocyte-rich primary cultures from the brains of wild-type and glutathione peroxidase-1 deficient mice (GPx1(-/-)) were exposed to a chronic hydrogen peroxide-generating system consisting of xanthine oxidase, hypoxanthine and superoxide dismutase. The specific activity of GS was strongly diminished by chronic exposure to hydrogen peroxide in astrocytes cultured from both mouse lines. After 60 min of oxidative stress in the presence of 5 mU/mL, 10 mU/mL and 20 mU/mL of xanthine oxidase, the specific GS activity of wild-type astrocytes was reduced to 47%, 22% and 13% of the initial activity, respectively. For all activities of xanthine oxidase applied, astrocytes from GPx1(-/-) mice experienced a significantly greater rate of GS inactivation compared to their wild-type counterparts. These results confirm that GS is sensitive to inactivation by chronic peroxide stress in viable astrocytes and show that glutathione peroxidase-1 helps to protect GS from inactivation by oxidative stress.

Kinetics of endothelin-induced inhibition and glucose permeability of astrocyte gap junctions

Gap junctions contribute to important functions of communicating glial cells in brain physiology and pathology. Endothelins (ETs), a vasoactive family of peptides present in the brain, have been described as potent inhibitors of astrocyte gap junctional communication. Through dye-coupling studies we demonstrate here that this inhibition occurs rapidly and then successively reverses and returns to control levels after 90 min of continuous ET1 or ET3 exposure. In addition, long-term exposure of cells to ET3, which acts mainly on ETB receptors, also desensitized the acute action of ET1, which was previously shown to act through either ETA or ETB receptor sites, or both. The gap junction blocker carbenoxolone did not show any time-dependent desensitization and was fully effective also in cultures treated with ETs for prolonged times. The ETs inhibitory effects were partially prevented when blocking pertussis toxin-sensitive G-proteins, chelating intracellular Ca2+, or omitting extracellular Ca2+. We further show that ETs modulate gap junction-mediated transfer of 2-[N-(7-nitrobenz-2-oxa-1,3-diazol-4-Y1)amino]-2-deoxyglucose (2-NBDG), a fluorescent glucose molecule, indicating a role of astrocyte gap junction coupling in metabolic trafficking and suggesting the importance of these peptides in the control of intercellular diffusion of energetic compounds. These findings might have particular relevance in early tissue reactions after various cerebral injuries, which commonly involve increased cerebral ET levels.

Topiramate reduces AMPA-induced Ca(2+) transients and inhibits GluR1 subunit phosphorylation in astrocytes from primary cultures

Topiramate (TPM) is a structurally novel broad spectrum anticonvulsant known to have a negative modulatory effect on the alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid (AMPA)/kainate subtypes of glutamate receptors and some types of voltage-gated Na(+) and Ca(2+) channels, and a positive modulatory effect on some types of gamma-aminobutyric acid(A) (GABA(A)) receptors and at least one type of K(+) channels in neurons. In an earlier work, we showed that the negative modulatory effect of TPM (100 mum) on AMPA/kainate receptors in neurons is dependent on TPM modulation of the phosphorylation state of these receptors. In this work, we investigated the effect of TPM on AMPA-induced intracellular calcium ([Ca(2+)](i)) responses in cultured rat cortical astrocytes, with special interest in intracellular mechanisms. Here, we report that the ability of TPM (1-100 mum) to inhibit AMPA-induced accumulation of Ca(2+) in astrocytes is inversely related to the level of protein kinase A (PKA) -mediated phosphorylation of channels activated by AMPA. The level of receptor phosphorylation was further determined with western blot using phosphorylation specific antibodies that recognize the glutamate receptor 1 (GluR1) subunit phosphorylated on Ser845. These results demonstrated that, even in cultured cortical astrocytes, TPM significantly reduced the phophorylation level of GluR1 subunits. Furthermore, it was shown that TPM binds to AMPA receptors in the dephosphorylated state and thereby exerts an allosteric modulatory effect on the ion channel.

Gap junction blockage limits intercellular spreading of astrocytic apoptosis induced by metabolic depression

Astrocytes are highly coupled by gap junction channels, which allow transfer of intracellular signalling molecules and metabolites between connected cells. Astrocytic gap junctions remain open during ischemic conditions as previously demonstrated in vitro and in situ. In this study, we investigated the effect of gap junction blockage on iodoacetate-induced ATP depression and cell death progression in astrocytes in primary rat hippocampal cultures. We demonstrated that blockage of gap junctions during iodoacetate-induced inhibition of the glycolysis induced an earlier onset of the ATP depression. Moreover, initiation of apoptotic processes, demonstrated by binding of Annexin V, was critically dependent on the ATP levels. The apoptotic event was also shown to spread and involve neighbouring cells, a process that was inhibited by blockage of gap junction communication. Chelating intracellular calcium using BAPTA-AM decelerated the iodoacetate-induced ATP depression. The chelation also decelerated the spreading of apoptotic processes. Inhibition of caspases did not alter the expansion of cell groups being Annexin V positive. However, the proportion of Annexin V positive cells also being propidium iodide positive was increased after caspase inhibition. The results show that inhibition of gap junctions during cellular metabolic depression interferes with the metabolic status and cell death progression in astrocytes.

Lactate induces tumour necrosis factor-alpha, interleukin-6 and interleukin-1beta release in microglial- and astroglial-enriched primary cultures

Hyperammonaemia has deleterious effects on the CNS in patients with liver dysfunction. Cellular mechanisms underlying the effects of hyperammonaemia are largely unknown, although astrocytes have been the main target of interest. This study investigated how treatment with NH4Cl and lactate, which increase in the brain as a consequence of hyperammonaemia, affects cells in primary rat cultures enriched in either astrocytes or microglia. Morphological changes were studied over time using light microscopy. Release of the proinflammatory cytokines tumour necrosis factor-alpha (TNF-alpha), interleukin (IL)-6 and IL-1beta was measured using ELISA. NH4Cl was found to induce vacuole formation in both culture systems. Lactate treatment altered astrocytic appearance, resulting in increased space between individual cells. Microglia adopted a round morphology with either NH4Cl or lactate treatment. Lactate, but not NH4Cl, induced release of TNF-alpha and IL-6 in both astroglial- and microglial-enriched cultures, while IL-1beta was released only in microglial cultures. Cytokine release was higher in the microglial- than in the astroglial-enriched cultures. Additionally, the astroglial-enriched cultures containing approximately 10% microglial cells released more cytokines than cultures containing about 5% microglial cells. Taken together, our data suggest that most TNF-alpha, IL-6 and IL-1beta release comes from microglia. Thus, microglia could play an important role in the pathological process of hyperammonaemia.

Lipopolysaccharide increases microglial GLT-1 expression and glutamate uptake capacity in vitro by a mechanism dependent on TNF-α

This study investigates the effect of microglial activation on microglial glutamate transporters in vitro. Stimuli known to activate microglia and/or to be associated with pathological conditions with an impaired astroglial glutamate uptake were compared. Morphological changes and marked increases in ED1 antigen expression were found after 8-h incubation of rat microglia in 56 mM KCl, 1 ng/ml lipopolysaccharide (LPS), and 100 microM glutamate, as well as in acidic and basic conditions, showing that the cells were activated. Of the stimuli used, only LPS induced a significant release of the proinflammatory cytokines tumor necrosis factor-alpha (TNF-alpha) and interleukin-6 (IL-6), and was the only stimulus that increased microglial GLT-1 expression and glutamate uptake capacity after 12-h incubation. This effect was probably mediated by TNF-alpha, since this cytokine mimicked the effect of LPS. Furthermore, the effect of LPS was blocked by thalidomide, an inhibitor of TNF-alpha synthesis. Additionally, neutralizing antibodies against TNF-alpha also blocked the increase, indicating TNF-alpha as an inducer of GLT-1 expression in microglia. It was also found that preincubation with glutamate dose-dependently inhibited the microglial glutamate uptake. This could suggest different physiological functions for microglial and astroglial glutamate uptake and might indicate a reciprocal control of GLT-1 expression between microglia and astrocytes.

Ethanol acutely decreases astroglial gap junction permeability in primary cultures from defined brain regions

The acute effect of hyperosmotic ethanol on gap junction permeability was examined in astroglial cells in primary culture from five different brain regions. Gap junction permeability was analyzed by measuring dye spreading from cell to cell with the low molecular weight dye Lucifer Yellow. Ethanol concentrations 25-300 mM significantly decreased dye spreading in cultures from the cerebral cortex in a dose-dependent but time-independent manner for up to 60 min. Besides cerebral cortex, exposure to 150 mM ethanol decreased dye spreading in astroglial cultures from the hippocampus and from the brain stem, while cultures from the olfactory bulb and from the hypothalamus were not significantly affected. The ethanol-induced decrease in dye spreading in cultures from the cerebral cortex was not mediated through changes in cell volume, osmolarity, protein kinase C (PKC) phosphorylation, intracellular pH, or intracellular calcium concentration ([Ca(2+)](i)). The decrease in dye spreading was abolished upon incubation in sodium-reduced buffer, and after blockage of the Na(+)/K(+)/2Cl(-) cotransporter with furosemide. The results presented here indicate that ethanol-mediated decrease in dye spreading is directly or indirectly dependent on sodium.

Topiramate protects against glutamate- and kainate-induced neurotoxicity in primary neuronal-astroglial cultures

Potential neuroprotective effects of the antiepileptic drug (AED) topiramate (TPM) were evaluated using primary neuronal-astroglial cultures or astroglial-enriched cultures from newborn rats exposed to excitotoxic concentrations of glutamate (Glu) or kainate. Neurons expressed functional Glu receptors of the NMDA and AMPA/kainate types as evaluated by immunocytochemistry and Ca(2+) imaging. When Glu (10 mM) was added to 9-10-day cultures incubated with the fluorescent dye calcein/AM for 5h, there was a marked cell loss in both culture types, but was more pronounced in the neuronal-astroglial cultures. When TPM (5-10 microM) was included in the medium together with Glu, the amount of surviving cells was significantly higher in the neuronal-astroglial cultures, but not in the astroglial-enriched cultures. Immuno-labeling of the cultures revealed an enhanced survival of MAP positive neuronal cells when TPM was included in the Glu containing medium. As TPM has a proven negative modulatory effect on kainate activated receptors, neuronal-astroglial cultures were further exposed to excitotoxic concentrations of kainate (100 microM) and analyzed immunohistochemically. Significantly more MAP positive neurons survived in the TPM containing medium and showed a morphology similar to untreated cells. Valproate and phenytoin were used as reference AEDs. In conclusion, our results demonstrate a protective effect of TPM upon neuronal cells in primary culture, exposed to excitotoxic levels of Glu or kainate.

Endothelin-1 decreases glutamate uptake in primary cultured rat astrocytes

Endothelin-1 (ET-1) is a potent vasoconstrictor peptide that is also known to induce a wide spectrum of biological responses in nonvascular tissue. In this study, we found that ET-1 (100 nM) inhibited the glutamate uptake in cultured astrocytes expressing the glutamate/aspartate transporter (GLAST); astrocytes did not express the glutamate transporter-1 (GLT-1). The V(max) and the K(m) of the glutamate uptake were reduced by 57% and 47%, respectively. Application of the ET(A) and ET(B) receptor antagonists BQ-123 and BQ-788 partly inhibited the ET-1-evoked decrease in the glutamate uptake, whereas the nonspecific ET receptor antagonist bosentan completely inhibited this decrease. Incubation of the cultures with pertussis toxin abolished the effect of ET-1 on the uptake. The ET-1-induced decrease in the glutamate uptake was independent of extracellular free Ca(2+) concentration, whereas the intracellular Ca(2+) antagonists thapsigargin and 3,4,5-trimethoxybenzoic acid 8-(diethylamino)octyl ester abolished the effect of ET-1 on the glutamate uptake. Incubation with the protein kinase C (PKC) antagonist staurosporine, but not with the fatty acid-binding protein bovine serum albumin, prevented the ET-1-induced decrease in the glutamate uptake. These results suggest that ET-1 impairs the high-affinity glutamate uptake in cultured astrocytes through a G protein-coupled mechanism, involving PKC and changes in intracellular Ca(2+).

Stimulation of Na-K-2Cl cotransporter in neurons by activation of Non-NMDA ionotropic receptor and group-I mGluRs

In a previous study, we found that Na(+)-K(+)-2Cl(-) cotransporter in immature cortical neurons was stimulated by activation of the ionotropic N-methyl-D-aspartate (NMDA) glutamate receptor in a Ca(2+)-dependent manner. In this report, we investigated whether the Na(+)-K(+)-2Cl(-) cotransporter in immature cortical neurons is stimulated by non-NMDA glutamate receptor-mediated signaling pathways. Expression of the Na(+)-K(+)-2Cl(-) cotransporter and metabotropic glutamate receptors (mGluR1 and 5) was detected in cortical neurons via immunoblotting and immunofluorescence staining. Significant stimulation of cotransporter activity was observed in the presence of both trans-(+/-)-1-aminocyclopentane-trans-1,3-dicarboxylic acid (trans-ACPD) (10 microM), a metabotropic glutamate receptor (mGluR) agonist, and (RS)-3,5-dihydroxyphenylglycine (DHPG) (20 microM), a selective group-I mGluR agonist. Both trans-ACPD and DHPG-mediated effects on the cotransporter were eradicated by bis-(o-aminophenoxy)-N,N,N',N'-tetraacetic acid-AM, a Ca(2+) chelator. In addition, DHPG-induced stimulation of the cotransporter activity was inhibited in the presence of mGluRs antagonist (RS)-1-aminoindan-1,5-dicarboxylic acid (AIDA) (1 mM) and also with selective mGluR1 antagonist 7-(hydroxyimino)cyclopropa[b]chromen-1a-carboxylate ethyl ester (CPCCOEt) (100 microM). A DHPG-induced rise in intracellular Ca(2+) in cortical neurons was detected with Fura-2. Moreover, DHPG-mediated stimulation of the cotransporter was abolished by inhibition of Ca(2+)/CaM kinase II. Interestingly, the cotransporter activity was increased by activation of alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptor. These results suggest that the Na(+)-K(+)-2Cl(-) cotransporter in immature cortical neurons is stimulated by group-I mGluR- and AMPA-mediated signal transduction pathways. The effects are dependent on a rise of intracellular Ca(2+).

Acute ethanol exposure induces [Ca2+]i transients, cell swelling and transformation of actin cytoskeleton in astroglial primary cultures

Acute exposure to 100 mM isotonic ethanol (EtOH) increased intracellular Ca2+ concentration ([Ca2+]i), induced cell swelling, and transformed actin cytoskeleton in astroglial primary cultures from rat cerebral cortex. Fluorometric recordings of fluo-3AM- or fura-2AM-incubated astroglial cells revealed that EtOH induced [Ca2+]i transients in a small population of the cells. Cell swelling was estimated using a new method based on three-dimensional fluorescence imaging in conjunction with image analysis and graphic visualization techniques. The method provides detailed results concerning the reformation of structural shape and specific volume alterations, as well as total proportions between the different states. Astroglial cell swelling was registered and quantified in 7 of 39 cells chosen from 12 different coverslips. EtOH also induced reversible conformational changes in filamentous actin, appearing as increases in ring formations and a more dispersed appearance of the filaments. Filamentous actin was stained with Alexa phalloidin after incubation with EtOH for varied periods. The results presented here suggest that EtOH affects astrocytes in a way that could be of physiological relevance.

Single-cell volume estimation by three-dimensional wide-field microscopy applied to astroglial primary cultures

Astrocytes, which constitute a prominent part of the number and volume of brain cells, have a high capacity for controlling their volume, and astrocytic swelling is associated with a number of pathological states affecting the CNS. In order to understand the mechanisms for regulating cell volume in astrocytes better, it is of utmost importance to develop technical instrumentation and analysis methods capable of detecting and characterizing dynamic cell shape changes in a quantitative and robust way. For this purpose, a new method was developed to quantify changes in cell volume at the single-cell level. This method is based on three-dimensional (3D) fluorescence imaging obtained by optical sectioning. An automated image acquisition system was developed for the collection of two-dimensional (2D) microscopic images. A deblurring algorithm was implemented in order to restore the originally unfocused image content. Advanced image analysis techniques were applied for accurate and automated determination of cell volume. The sensitivity and reproducibility of the method was evaluated by using fluorescent beads. The techniques were applied to fura-2-labeled astroglial cells in primary culture exposed to hypo- or hyperosmotic stress. The results show that this method is valuable for determining volume changes in cells or parts thereof.

Distinct pharmacological properties of ET-1 and ET-3 on astroglial gap junctions and Ca(2+) signaling

Astrocytes represent a major target for endothelins (ETs), a family of peptides that have potent and multiple effects on signal transduction pathways and can be released by several cell types in the brain. In the present study we have investigated the involvement of different ET receptor subtypes on intercellular dye diffusion, intracellular Ca(2+) homeostasis, and intercellular Ca(2+) signaling in cultured rat astrocytes from hippocampus and striatum. Depending on the ET concentration and the receptor involved, ET-1- and ET-3-induced intracellular Ca(2+) increases with different response patterns. Both ET-1 and ET-3 are powerful inhibitors of gap junctional permeability and intercellular Ca(2+) signaling. The nonselective ET receptor agonist sarafotoxin S6b and the ET(B) receptor-selective agonist IRL 1620 mimicked these inhibitions. The ET-3 effects were only marginally affected by an ET(A) receptor antagonist but completely blocked by an ET(B) receptor antagonist. However, the ET-1-induced inhibition of gap junctional dye transfer and intercellular Ca(2+) signaling was only marginally blocked by ET(A) or ET(B) receptor-selective antagonists but fully prevented when these antagonists were applied together. The ET-induced inhibition of gap junction permeability and intercellular Ca(2+) signaling indicates that important changes in the function of astroglial communication might occur when the level of ETs in the brain is increased.

Characterization of rat spinal cord neurons cultured in defined media on microelectrode arrays

Previous efforts to utilize mammalian spinal cord neurons as biosensor elements have relied on neuronal: glial co-cultures maintained in serum-containing media. We have examined the feasibility of culturing primary spinal cord neurons in serum-free medium, modified for neuronal longevity, on fabricated microelectrode arrays. Embryonic day 15 rat spinal cord cells were plated on trimethoxysilyl-propyldiethylenetriamine coated microelectrode arrays comprised of gold recording sites passivated with silicon nitride. Immunocytochemistry was performed to verify the presence of neurons and quantitatively assess astrocytes using antibodies against glial fibrillary acidic protein on the silicon nitride substrates. Modifications to culture media enabled viable neuronal culture to extend from approximately 14 days in vitro (DIV) to 40 DIV on the arrays containing only 1.1 +/- 0.5% (mean +/- SEM) astrocytes. Extracellular recording revealed tetrodotoxin-sensitive spontaneous electrical activity from the enriched neuronal culture. Threshold detection of extracellular potentials showed an increase in spike rate as a function of glutamate concentration with neurotoxicity at elevated levels. This approach suggests that functional measures related to biosensor applications, pharmacological screening, or the evaluation of neurological disease models can be implemented in a defined culture system.

Expression of the glutamate transporters in human temporal lobe epilepsy

Glutamate is the major excitatory neurotransmitter in the central nervous system and is implicated in the pathogenesis of neurodegenerative diseases. Five human glutamate transporters have been cloned and are responsible for the removal of potentially excitotoxic excess glutamate from the extracellular space. In this study we consider whether there are selective changes in the expression of the glutamate transporters in the medial temporal cortex and hippocampus from temporal lobe epilepsy patients, which might contribute to the development or maintenance of seizures. Since disruption of the glial transporter excitatory amino acid transporter 2 in mice results in lethal spontaneous seizures, we were interested primarily in studying changes in this transporter. Using in situ hybridization we show that there was no reduction in the level of excitatory amino acid transporter 2 encoding messenger RNA in the temporal lobe epilepsy cases compared to post mortem controls and indeed there was a relative increase in content of excitatory amino acid transporter 2 messenger RNA per cell in temporal lobe epilepsy cases. Western blotting showed that there was no change in the excitatory amino acid transporter 2 protein content in temporal lobe epilepsy cases as compared to post mortem controls. A small reduction in the level of the second astroglial transporter protein, excitatory amino acid transporter 1, was observed in temporal lobe epilepsy cases. Surprisingly, immunohistochemical experiments using a polyclonal antiexcitatory amino acid transporter 2 antibody, showed a different localization of this protein in epilepsy derived tissue as compared to post mortem controls although glial markers such as glial fibrillary acidic protein and glutamine synthase showed similar patterns of staining. However, repeating this experiment using control tissue from non-temporal lobe epilepsy biopsies demonstrated that this change in the excitatory amino acid transporter 2 transporter localization occurred post mortem. These data suggest that major changes in the level of expression of the glutamate transporters do not play an important role in the development of human temporal lobe epilepsy but may be implicated the aetiology of other types of epilepsy.

5-Hydroxytryptamine and glutamate modulate velocity and extent of intercellular calcium signalling in hippocampal astroglial cells in primary cultures

The effects of 5-hydroxytryptamine or glutamate treatment on mechanically induced intercellular calcium waves were studied in gap junction-coupled astroglial cells using rat astroglial-neuronal primary cultures from hippocampus. Imaging software was developed to study amplitude, velocity and extent of wave propagation. Velocity software was designed to find the cell contours automatically and to calculate travelled distance and time-delay of the calcium wave as it propagates from the stimulated cell to all other cells. Propagation analyses were performed to calculate the area of wave propagation. Mechanical stimulation of a single astroglial cell induced an intercellular calcium wave spreading from cell to cell in the astroglial syncytium. When registering the appearances of calcium signals in individual cells along the wave path upon re-stimulation of the same cell, 44.7% of the cells responded with similar calcium signal appearances the second time as the first time. A second wave from the opposite direction resulted in similar calcium signal appearances in 27.3% of the studied cells. Both amplitude and velocity of the calcium signal decreased most prominently in the first part and showed a later flattening out. Treatment with 5-hydroxytryptamine or glutamate for 20-30 s before mechanical stimulation increased the velocity of the calcium waves. 5-Hydroxytryptamine treatment for varying times decreased the propagation area of the calcium waves. In contrast, glutamate treatment increased the propagation area.

Na+-K+-2Cl- cotransporter in immature cortical neurons: A role in intracellular Cl- regulation

Na+-K+-2Cl- cotransporter has been suggested to contribute to active intracellular Cl- accumulation in neurons at both early developmental and adult stages. In this report, we extensively characterized the Na+-K+-2Cl- cotransporter in primary culture of cortical neurons that were dissected from cerebral cortex of rat fetus at embryonic day 17. The Na+-K+-2Cl- cotransporter was expressed abundantly in soma and dendritic processes of cortical neurons evaluated by immunocytochemical staining. Western blot analysis revealed that an approximately 145-kDa cotransporter protein was present in cerebral cortex at the early postnatal (P0-P9) and adult stages. There was a time-dependent upregulation of the cotransporter activity in cortical neurons during the early postnatal development. A substantial level of bumetanide-sensitive K+ influx was detected in neurons cultured for 4-8 days in vitro (DIV 4-8). The cotransporter activity was increased significantly at DIV 12 and maintained at a steady level throughout DIV 12-14. Bumetanide-sensitive K+ influx was abolished completely in the absence of either extracellular Na+ or Cl-. Opening of gamma-aminobutyric acid (GABA)-activated Cl- channel or depletion of intracellular Cl- significantly stimulated the cotransporter activity. Moreover, the cotransporter activity was elevated significantly by activation of N-methyl-D-aspartate ionotropic glutamate receptor via a Ca2+-dependent mechanism. These results imply that the inwardly directed Na+-K+-2Cl- cotransporter is important in active accumulation of intracellular Cl- and may be responsible for GABA-mediated excitatory effect in immature cortical neurons.

Direct cloning of astrocytes from primary culture without previous immortalization

In primary cultures, much evidence shows the existence of different subtypes of astrocytes that are not all identified. One methodology for studying these subtypes can be their cloning. The present investigation shows a method for a direct cloning of astrocytes without previous immortalization. Astrocytes from the cerebral cortex of newborn rats were cultured, purified by shaking, and harvested by trypsinization. One single astrocyte was plated in a small volume of a homemade cloning medium. After getting a colony, successive platings were made using larger and larger vessels, up to 60-mm-diameter petri dishes. Then, subcultures were made. The yield of the cloning was similar to that of common eukaryotic cell clonings. All along the cloning procedure, the cells were positively immunostained with anti-glial fibrillary acidic protein antibodies. Cloned cells from some batches were spindle-shaped, looking like fibroblasts. Nevertheless, they were immunostained with anti-glial fibrillary acidic protein antibodies, unlike true fibroblasts. These spindle-shaped astrocytes were compared to cells from an astrocytoma cell line that had the same shape. The growth pattern of the astrocytoma cells was different from that of the astrocytes cloned from the primary cultures. All the types of studied cells contained glycogen. On the basis of the criteria of morphology, of glial fibrillary acidic protein immunolabeling, and of glycogen synthesis, the cloned cells kept the characteristics of astrocytes. This study shows that it is perfectly possible to get clones of astrocytes from one astrocyte without previous immortalization, giving thus a convenient material for the study of astrocyte biology.

Regulation of the glial glutamate transporter GLT-1 by glutamate and delta-opioid receptor stimulation

The excitatory effect of presynaptically released glutamate is tightly regulated and terminated by high affinity sodium-dependent glutamate transporters. The regulation of the glial glutamate transporter GLT-1 is potentially important in synaptic modulation. Using astroglial cultures prepared from the rat cerebral cortex, we found that the delta-opioid receptor agonist [D-pen2,D-pen5]-enkephalin decreases and glutamate increases the expression of the GLT-1 transporter mRNA. Corresponding changes in the uptake kinetics were found after incubation for 48 h with the respective agonists when glial glutamate uptake was measured in primary astroglial cultures. The data suggest that long-term receptor activation induces alterations in glial glutamate uptake properties.

Stimulation of 5-HT2A receptors on astrocytes in primary culture opens voltage-independent Ca2+ channels

Mechanisms underlying the 5-HT2A receptor induction of intracellular Ca2+ mobilization and Ca2+ influx in type I astroglial cells in primary culture from newborn rat cerebral cortex were evaluated. The 5-HT-evoked Ca(2+)-transients, inhibited by the 5-HT2A antagonists ketanserin or 4-(4-fluorobenzoyl)-1-(4-phenylbutyl) piperidine oxalate, consisted of an initial peak caused by inositol 1,4,5-trisphosphate (IP3)-mediated Ca2+ release from internal stores, and a second sustained part which was due to Ca2+ transport over the plasma membrane. The responses were pertussis toxin-insensitive, suppressed by the phospholipase C inhibitor neomycin and were inhibited by the Ca(2+)-ATPase inhibitor thapsigargin. Furthermore, the responses were inhibited by the IP3 receptor antagonist heparin. When the second sustained part of the 5-HT-evoked response was studied, it was concluded that Ca2+ influx was not a result of opening of voltage operated calcium channels of either L, N or T-type. Instead it appeared that Ca2+ entered the cells through specialized voltage independent Ca2+ channels which were dependent of the IP3 production and subsequent Ca2+ release from internal stores. From this, we conclude that 5-HT opens Ca2+ channels in astrocytes which closely resemble depletion-operated Ca2+ channels (DOCCs).

Adrenoceptor-induced changes of intracellular K+ and Ca2+ in astrocytes and neurons in rat cortical primary cultures

The calcium- and potassium sensitive fluorescent dyes fura-2 and K+-binding benzofuran isophtalate (PBFI) were used to detect changes in [Ca2+]i and [K+]i in type 1 astrocytes and neurons in mixed astroglial/neuronal rat cortical primary cultures after adrenoceptor stimulation. Noradrenalin (NA), phenylephrine (phe; alpha1-agonist), clonidine (clon; alpha2-agonist) and isoproterenol (iso; beta-agonist) were used. All agonists were able to increase [Ca2+]i and decrease [K+]i in the astrocytes with the exception of clon, which could not induce potassium responses. In the neurons, NA and phe evoked calcium transients while clon and iso did not. NA and clon were able to elicit reductions in [K+]i but no responses were seen after phe or iso stimulation. In neurons, the NA-evoked reductions in [K+]i always appeared immediately and gradually (after 30-50 s) returned to baseline even in the presence of the agonists. On the other hand, in the astrocytes, the NA-induced reductions in [K+]i appeared with some latency and always persisted at the lower level in the presence of the agonists. In addition, external tetraethylammonium (TEA) could severely reduce the NA-induced K+ responses in the astrocytes. The results indicate a clear heterogeneity regarding both adrenoceptor expression and response characteristics between astroglial cells and neurons.