Astrocytes from forebrain, cerebellum, and spinal cord differ in their responses to vasoactive intestinal peptide

Kir 5.1-dependent CO2 /H+ -sensitive currents contribute to astrocyte heterogeneity across brain regions

Astrocyte heterogeneity is an emerging concept in which astrocytes within or between brain regions show variable morphological and/or gene expression profiles that presumably reflect different functional roles. Recent evidence indicates that retrotrapezoid nucleus (RTN) astrocytes sense changes in tissue CO2/ H+ to regulate respiratory activity; however, mechanism(s) by which they do so remain unclear. Alterations in inward K+ currents represent a potential mechanism by which CO2 /H+ signals may be conveyed to neurons. Here, we use slice electrophysiology in rats of either sex to show that RTN astrocytes intrinsically respond to CO2 /H+ by inhibition of an inward rectifying potassium (Kir ) conductance and depolarization of the membrane, while cortical astrocytes do not exhibit such CO2 /H+ -sensitive properties. Application of Ba2+ mimics the effect of CO2 /H+ on RTN astrocytes as measured by reductions in astrocyte Kir -like currents and increased RTN neuronal firing. These CO2 /H+ -sensitive currents increase developmentally, in parallel to an increased expression in Kir 4.1 and Kir 5.1 in the brainstem. Finally, the involvement of Kir 5.1 in the CO2 /H+ -sensitive current was verified using a Kir5.1 KO rat. These data suggest that Kir inhibition by CO2 /H+ may govern the degree to which astrocytes mediate downstream chemoreceptive signaling events through cell-autonomous mechanisms. These results identify Kir channels as potentially important regional CO2 /H+ sensors early in development, thus expanding our understanding of how astrocyte heterogeneity may uniquely support specific neural circuits and behaviors.

TGF beta 1 and TNF alpha potentiate nitric oxide production in astrocyte cultures by recruiting distinct subpopulations of cells to express NOS-2

Nitric oxide (NO) synthase-2 (NOS-2), a key source of NO at sites of neuroinflammation, is induced in astrocyte cultures treated with lipopolysaccharide (LPS) plus interferon-gamma (IFN gamma). A recent study examining the regulation of astrocytic NOS-2 expression demonstrated that transforming growth factor-beta1 (TGF beta 1) potentiated LPS plus IFN gamma-induced NOS-2 expression via expansion of the pool of astrocytes that express NOS-2. Results in the current report indicate that this population-based mechanism of increasing NOS-2 expression is not restricted to TGF beta 1, since it also accounts for the potentiation of NO production in astrocyte cultures by tumor necrosis factor-alpha (TNFalpha). In contrast to TGF beta 1, which required 24h preincubation for optimal potentiation of NO production, TNF alpha was maximally effective when added concurrently with LPS plus IFN gamma. Nevertheless, under conditions that optimally potentiated NO production, both cytokines recruited similar numbers of astrocytes to express NOS-2 (% NOS-2-positive cells after LPS plus IFN gamma alone or with TNFalpha or TGF beta 1 was 9.5+/-1.2, 25.3+/-2.9, and 32.4+/-3.0, respectively). Interestingly, stimulation of astrocytes in the presence of both TGF beta 1 and TNFalpha additively increased the number of astrocytes that expressed NOS-2 protein (% NOS-2-positive cells was 61.0+/-4.2) relative to each cytokine alone. Potentiation of NO production by either TNF alpha or TGF beta 1 was not ablated by neutralizing antibodies to TGF beta 1 or TNFalpha, respectively. Thus, the two cytokines act independently to recruit separate pools of astrocytes to express NOS-2. These results are consistent with the notion that astrocytes possess an innate heterogeneity with respect to responsiveness to these cytokines.

Evidence for astrocyte heterogeneity: a distinct subpopulation of protoplasmic-like glial cells is detected in transgenic mice expressing Lmo1-lacZ

The adult mammalian central nervous system (CNS) contains a large number of different cell types, which arise from the ventricular (VZ) and subventricular zones during embryonic development. In this study, we used a transgenic mouse expressing Lmo1-LacZ from a randomly inserted promoter/reporter gene construct to identify a glial subpopulation. LMO1 is an LIM domain-containing protein, thought to act in protein-protein interactions. We found first that in the adult transgenic CNS, beta-galactosidase (beta-gal) was expressed in a specific subpopulation of protoplasmic-like cells, which did not express detectable levels of glial fibrilary acidic protein unless a lesion was produced. Secondly, during development, beta-gal(+) cells were found arising from discrete regions of the VZ. Taken together, these results identify a subpopulation of protoplasmic glial cells in the adult CNS and suggest that they arise from a restricted VZ region during CNS development.

Mouse models of neurofibromatosis 1 and 2

The neurofibromatoses represent two of the most common inherited tumor predisposition syndromes affecting the nervous system. Individuals with neurofibromatosis 1 (NF1) are prone to the development of astrocytomas and peripheral nerve sheath tumors whereas those affected with neurofibromatosis 2 (NF2) develop schwannomas and meningiomas. The development of traditional homozygous knockout mice has provided insights into the roles of the NF1 and NF2 genes during development and in differentiation, but has been less instructive regarding the contribution of NF1 and NF2 dysfunction to the pathogenesis of specific benign and malignant tumors. Recent progress employing novel mouse targeting strategies has begun to illuminate the roles of the NF1 and NF2 gene products in the molecular pathogenesis of NF-associated tumors.

Neuronal release of vasoactive intestinal peptide is important to astrocytic protection of neurons from glutamate toxicity

Astrocytes regulate clearance of glutamate from the vicinity of neurons. This helps to protect neurons directly from glutamate toxicity. Recent findings have indicated that a complex molecular interaction between neurons and astrocytes that is necessary for this protection occurs. In the present investigation the role of vasoactive intestinal peptide (VIP) in signaling between neurons and astrocytes was investigated. VIP was found to be necessary for the protective effects of astrocytes in a coculture system. VIP in combination with neuronal-conditioned medium enhanced glutamate uptake by astrocytes. Also, VIP enhanced the expression of the high-affinity VIP receptor, increased astrocytic release of interleukin-6, and indirectly reduced the toxicity of glutamate in neuronal-conditioned astrocyte medium. These results indicate that VIP is essential to the molecular interaction of neurons and astrocytes and is involved in the regulation of the protective effects of astrocytes for neurons.

Differential expression of inflammatory mediators in rat microglia cultured from different brain regions

Microglial cells show a rather uniform distribution of cell numbers throughout the brain with only minor prevalences in some brain regions. Their in situ morphologies, however, may vary markedly from elongated forms observed in apposition with neuronal fibers to spherical cell bodies with sometimes extremely elaborated branching. This heterogeneity gave rise to the hypothesis that these cells are differentially conditioned by their microenvironment and, therefore, also display specific patterns of differential gene expression. In this study, microglia were isolated from 2-4 week-old mixed CNS cultures that had been prepared from neonatal rat diencephalon, tegmentum, hippocampus, cerebellum and cerebral cortex, and were investigated 24 h later. Messenger RNA levels of proteins involved in crucial immune functions of this cell type (TNF-alpha, CD4, Fcgamma receptor II, and IL-3 receptor beta-subunit) have been determined by semi-quantitative RT-PCR. The results clearly show, that three of these mRNAs (TNF-alpha, CD4, Fcgamma receptor II) are differentially expressed in microglia with hippocampal microglia displaying the highest levels of these mRNAs. The data strongly support the notion that the status of microglial gene expression depends on their localization in brain and on specific interactions with other neural cell types. Consequently, it is hypothesized that their responsiveness to signals arising in injury or disease may vary from one brain region to another.

Adenosine stimulates stellation of cultured rat cortical astrocytes

We investigated the effect of adenosine on astrocyte morphology by using cell cultures prepared from the cerebral cortices of neonatal rats. Cultured rat cortical astrocytes exhibited flattened, polygonal morphology in the absence of stimulation, but differentiated into process-bearing stellate cells in response to adenosine (1-1000 microM). Adenosine-induced astrocyte stellation was abolished by treatment with microtubule inhibitors, colchicine and paclitaxel, indicating the involvement of cytoskeletal elements. The effect of adenosine was mimicked by other adenosine receptor agonists, and blocked by adenosine receptor antagonists and guanosine 5'-O-(2-thiodiphosphate), indicating that the effect of adenosine is mediated by G protein-coupled adenosine receptors. Although adenosine receptors are known to be linked to adenylate cyclase or phospholipase C, adenosine did not change intracellular cyclic AMP level nor intracellular Ca2+ concentration in astrocytes. Alternatively, adenosine-induced stellation was abolished by tyrosine phosphatase inhibitors, orthovanadate and phenylarsine oxide, suggesting that adenosine causes astrocyte stellation through tyrosine dephosphorylation. Adenosine may function as a factor regulating astrocyte differentiation.

Potentiation of adenosine 5'-triphosphate calcium responses by diadenosine pentaphosphate in individual rat cerebellar astrocytes

The calcium responses induced by adenosine 5'-triphosphate (ATP) were examined in single cerebellar type 1 astrocytes by fura-2 microfluorometry. ATP elicited fast and transient increases of intracellular calcium concentration ([Ca2+]i) even in the absence of extracellular calcium, indicating the involvement of metabotropic purinoceptors. The co-stimulation with P1P5-di(adenosine-5')pentaphosphate (Ap5A; 0.1 microM) potentiated ATP-metabotropic calcium responses. After this preincubation ineffective concentrations of ATP triggered 40% of maximal response. Co-stimulation with Ap5A and ATP was mandatory. The potentiated response to ATP was also independent of extracellular Ca2+ and was maintained for long periods of time (h). These results show a relevant interaction of purinoceptors that may imply a novel mechanism of action for diadenosine polyphosphates.

Peptide receptors on astrocytes

In recent years, it has become apparent that astrocytes (at least in vitro) harbor functional receptors to almost all possible neurotransmitters (with the potential noticeable exception of acetylcholine nicotinic receptors). Peptides are no exception, since receptors to all neuropeptides known to be produced in the CNS have been found on cultured astrocytes, and the presence of many of these has been confirmed on astrocytes in vivo. A variety of methodologies have been used to detect peptide receptors on astrocytes, as summarized in the current review. Special emphasis is also put on the possible roles that peptides may play in the regulation of astrocyte functions. These include proliferation, morphology, release of eicosanoids and arachidonic acid, induction of calcium transients and calcium waves, and control of internal pH, glucose uptake, glycogen metabolism, and gap junctional conductance. Recent data concerning the effects of natriuretic peptides on astrocytes are reviewed, and why these peptides may constitute priviledged tools to test the effects of peptides on astrocyte-neuron interactions is also discussed.

Mobilization of internal Ca2+ by vasoactive intestinal polypeptide in endothelial cells

The aims of the present study were to establish whether vasoactive intestinal polypeptide (VIP) could mobilize internally-stored Ca2+ and whether Ca2+ release could trigger Ca2+ influx from the extracellular space. Bovine pulmonary artery endothelial cells from an established cell line were loaded with fura-2/AM and cells were studied in suspension or were imaged in monolayers at 40-80% confluency. In Ca2+ imaging studies, VIP evoked Ca2+ transients in Ca2+-free medium containing 50 microM EGTA. This was observed in 33 out of 122 cells examined on 29 separate trials. With each cell, the spread of Ca2+ appeared to occur from the periphery of the cell to the central core. Cells which did not respond to VIP responded to other stimulants such as bradykinin, endoplasmic reticulum Ca2+ pump inhibitors, (cyclopiazonic acid and thapsigargin), and endoplasmic reticulum Ca2+ release channel opener, ryanodine. The reintroduction of Ca2+ following VIP-induced Ca2+ release did not evoke a Ca2+ response in 5 cells imaged. Cells in suspension showed typical biphasic responses to bradykinin, thapsigargin or cyclopiazonic acid in the presence of external Ca2+. Stimulation with VIP caused transient Ca2+ responses in Ca2+-free physiological saline containing 50 microM EGTA. However, only 1 out of 4 cells tested showed a response to Ca2+ when it was reintroduced to the bathing medium. This study provided direct evidence for the first time in these bovine endothelial cells for VIP-mediated elevation of cytosolic concentration of Ca2+. The results also suggested that other mechanisms might prevail preventing capacitative Ca2+ entry following the release of internally-stored Ca2+.

The interleukin-1beta-mediated regulation of proenkephalin and opioid receptor messenger RNA in primary astrocyte-enriched cultures

Opioids have been found to modulate the function of the immune system by regulating the biochemical and proliferative properties of its cellular components. The interaction of opioid and immune systems, however, is not unidirectional, but rather, bidirectional in nature. In the CNS, one cellular target of immune system activation is the astrocytes, glial cells known to synthesize proenkephalin. We have recently shown that these cells also express the messenger RNA transcripts for the opioid receptors mu, delta and kappa, raising the question of the functional significance of this opioid peptide and the related receptors in the astrocytes. That is, why do astrocytes express proenkephalin and opioid receptors, and are these molecules responsive to a factor to which the astrocytes could be exposed in vivo? Furthermore, do these molecules respond to this factor in a region-specific fashion? In the present study, in order to characterize the astrocytic opioid response to an immune factor, we examined the concomitant regulation of mu, delta, kappa and proenkephalin messenger RNAs by interleukin-1beta (1 ng/ml=60 pM, 24 h) in primary astrocyte-enriched cultures derived from the rat (post-natal day 1-2) cortex, striatum, cerebellum, hippocampus and hypothalamus. Interleukin-1beta treatment was found to increase by 55-75% the level of mu receptor messenger RNA in striatal, cerebellar and hippocampal cultures, but not in cultures derived from the cortex or hypothalamus. However, the cytokine had no effect on the level of delta receptor messenger RNA in any of the five cultures examined. In marked contrast to its stimulatory effects on mu receptor messenger RNA levels and its lack of an effect on 6 receptor messenger RNA expression, interleukin-1beta reduced to 10-30% of control levels the kappa receptor messenger RNA levels in all cultures. Interleukin-1beta had no effect on the level of proenkephalin messenger RNA in cortical, striatal, cerebellar and hypothalamic cultures, but did significantly decrease the expression of proenkephalin messenger RNA in hippocampal cultures to 40% of the control level. Therefore, interleukin-1beta differentially regulated opioid receptor messenger RNA in astrocyte-enriched cultures in a manner dependent upon both the receptor type and the brain region from which the culture was derived. The cytokine also differentially regulated proenkephalin messenger RNA in a region-dependent fashion. These findings suggest a capacity for astrocytes to differentially regulate opioid peptide and receptor messenger RNAs in response to an immune factor, supporting the potential existence of a novel immune-opioid system interaction in the CNS.

Beta-adrenergic receptors regulate astrogliosis and cell proliferation in the central nervous system in vivo

Astrocytes express several cell surface receptors including the beta 2 -adrenergic receptor. To explore whether beta-adrenergic receptors (beta-ARs) directly regulate astrogliosis and glial scar formation, we evaluated the effects of beta-AR activation and blockade on astrocyte hypertrophy and cell proliferation in rabbit optic nerves in vivo. Artificial cerebrospinal fluid (CSF), isoproterenol (ISO; a beta-agonist), or propranolol (PROP; a beta-antagonist) were infused via osmotic minipumps into non-injured and crushed optic nerves for 14 days. Changes in nerve cell numbers and astroglial hypertrophy were monitored by ethidium bromide nuclear staining and glial fibrillary acidic protein (GFAP) immunohistochemistry, respectively. In non-injured nerves infused with CSF or PROP, there were no alterations in GFAP-immunoreactivity or cell numbers compared to normal optic nerves; however, in non-injured nerves infused with ISO, there was a significant increase in both GFAP-immunoreactivity and cell number. In crushed optic nerves, there was a significant increase in both GFAP-immunoreactivity and cell number compared to normal nerves, and this increase was not altered by infusion of either CSF or ISO. In contrast, PROP infusion significantly reduced the crush-induced increase in GFAP-immunofluorescence and cell number. These findings suggest that a) beta-AR activation, in the absence of injury, can promote astroglial hypertrophy and cell proliferation; b) after injury, beta-AR activation drives injury-induced astrogliosis and cell proliferation; c) astrocyte beta-ARs are maximally stimulated after neuronal injury; and d) neuronal regeneration may be influenced, both positively and negatively, through the pharmacological manipulation of glial receptors.

Primary astroglial cultures derived from several rat brain regions differentially express mu, delta and kappa opioid receptor mRNA

The existence of opioid receptors within glial cell membranes has been proposed by several laboratories based on biochemical and radioligand binding data. The recent cloning of the mu, delta and kappa receptors has enabled us to directly examine the issue of opioid receptor expression in rat brain astroglia by using solution hybridization/ribonuclease protection assays to analyze the total RNA obtained from primary cultures of cortical, striatal, cerebellar, hippocampal and hypothalamic astrocytes. The results indicate that all five glial cultures expressed mu, delta and kappa receptor mRNA. The rank order of receptor mRNA abundance, expressed collectively across all five cultures, was determined to be delta > or = kappa >> mu. An analysis of the glial distribution profile for each receptor type revealed that mu receptor mRNA levels were the most abundantly expressed in cortical cultures, while the greatest levels of delta receptor mRNA were found in the cortical and hypothalamic cultures, and significant kappa receptor mRNA levels were produced by the cortical, hypothalamic and cerebellar cultures. Furthermore, the five glial cultures each expressed different levels of total opioid receptor (mu + delta + kappa) mRNA. The rank order of total opioid receptor mRNA expression across different astroglial cultures was found to be cortex > hypothalamus > cerebellum = hippocampus > striatum. An analysis of the relative expression profiles for mu, delta and kappa receptor mRNA within each culture revealed that all cultures manifested relatively high levels of delta and kappa receptor mRNA, but relatively low levels of mu receptor mRNA. Generally, cortical, hippocampal and hypothalamic cultures were characterized by comparable levels of delta and kappa receptor mRNA, and little, if any, mu receptor mRNA. However, striatal cultures were characterized by a high level of delta receptor mRNA which was approximately twice and four times that of the kappa and mu receptor mRNA, respectively. In contrast, cerebellar cultures expressed predominantly kappa receptor mRNA at a level which was almost twice that of the delta receptor mRNA, and expressed very little mu receptor mRNA. These data show that primary astroglial cultures not only express mu, delta and kappa receptor mRNAs, but they do so in a manner dependent upon receptor type and brain region. This suggests a regional heterogeneity of astrocytes with respect to opioid receptor expression, a characteristic previously described only for neurons. Furthermore, it suggests the existence of an additional anatomical component in CNS opioid systems.

VIP as a cell-growth and differentiation neuromodulator role in neurodevelopment

In addition to its commonly recognized status as a neuromodulator of virtually all vital functions, including neurobiological, the neuropeptide VIP plays a role in the control of cell growth and differentiation and of neuronal survival. Through these actions, VIP, whose impact appears early in ontogeny, may possess developmental functions. VIP can be stimulatory or inhibitory on cell growth in function of the model considered. The growth regulatory actions of VIP, which are often independent of cAMP, are most likely significant when mitogenic or trophic factors, eventually released by nontarget cells, are simultaneously present in the extracellular medium. The intracellular mechanisms that mediate these actions of VIP may involve different transduction cascades triggered by subsets of VIP binding sites that may coexist in the same tissue.

Neurotrophic effects of conditioned media of astrocytes isolated from different brain regions on hippocampal and cortical neurons

The present study was designed to reveal whether astroglial cells from different brain regions produce diffusible factors that differentially support the survival of neurons and the establishment of neuronal morphology. For this purpose, astrocyte conditioned media (ACM) were prepared by conditioning chemically-defined medium with type I astrocyte culture dissociated from cerebral cortex, hippocampus and hypothalamus. Hippocampal and cortical neurons were cultured in ACM or in non-conditioned medium. ACM derived from three brain regions all supported the survival of hippocampal and cortical neurons better than non-conditioned control medium. Of these, hypothalamic ACM was the most effective in supporting the survival of cortical neurons. The ACM also potentiated the elongation of the longest neurite of hippocampal and cortical neurons. However, there were no significant differences in the promoting effects on neurite elongation among ACM from three brain regions.

Involvement of protein kinase C in the axonal growth-promoting effect on spinal cord neurons by target-derived astrocytes

Astroglial cells participate in a variety of developmental events during neuronal morphogenesis. We have shown that axonal, but not dendritic, outgrowth of spinal cord neurons can be promoted by a diffusible factor or factors secreted from target region-derived cerebellar astroglia in vitro in comparison with spinal astroglia. In the present study, we examined the involvement of protein kinase C (PKC) in the axon-promoting effect by astroglia. The inhibition of PKC by sphingosine or by the phorbol ester 12-O-tetradecanoylphorbol 13-acetate (TPA) at high concentration greatly reduced the mean axonal length of spinal neurons cultured in medium conditioned by cerebellar astroglia (SCn-CBg), while activation of PKC by TPA at low concentration, or by retinoic acid, was not additive to the glial effect. The activation of PKC by TPA or retinoic acid promoted axon growth of spinal neurons cultured in medium conditioned by spinal astroglia (SCn-SCg), which otherwise would not be as supportive for axon growth as cerebellar astroglia. Western blotting and PKC activity assays showed that there was a trend for increased PKC activity and protein levels (in particular, PKC beta) in SCn-CBg cultures, which correlated with enhanced axon growth. Inhibition of PKC by sphingosine appeared to decrease protein levels, especially PKC beta, which correlated with suppressed axon outgrowth. In SCn-SCg cultures, phorbol ester activation of PKC increased both activity and protein levels of both PKC alpha and PKC beta. This activation correlated with stimulated axonal outgrowth. These results suggest that the glial signaling that regulates specific axonal outgrowth by target astroglia is mediated in part by the PKC second messenger system.

Phorbol ester-stimulated stellation in primary cultures of astrocytes from different brain regions

Stellation is the process by which astrocytes change from epithelial-like to process-bearing cells. Stellation occurs following activation of either cyclic AMP-dependent protein kinase or protein kinase C. This process occurs through tubulin-dependent rearrangement of the cytoskeleton. We have evaluated the ability of phorbol, 12-myristate, 13-acetate (PMA) to induce astrocyte stellation. Astrocytes from five brain regions (cerebellum, cerebral cortex, hippocampus, diencephalon, and brain-stem) were examined to determine if all astrocytes would exhibit similar responses to this activator of protein kinase C. Stellation was evaluated following cell fixation by either phase optics using conventional light microscopy, or scanning laser confocal light microscopy of cultures prepared using immunocytochemistry for tubulin and glial fibrillary acidic protein. Both the number of cells responding to PMA and the sensitivity to PMA varied for astrocytes from each brain region. PMA-induced stellation was most robust in cerebellar and brainstem astrocytes, with greater than 70% responding. Less than 40% of hippocampal and diencephalic astrocytes responded to PMA at the maximum dose (10(-5) M). PMA also induced different numbers of processes or branching patterns of processes on astrocytes from different brain regions. The protein kinase C induced stellation response in astrocytes supports the hypothesis that astrocytes contribute to neural plasticity.

Regulation of interleukin 6 production by cAMP-protein kinase-A pathway in rat cortical astrocytes

In this study we analysed the involvement of the cAMP-protein kinase-A system in the regulation of interleukin 6 production by cultured cortical astrocytes. Vasoactive intestinal peptide strongly increased, in a dose-dependent manner, interleukin 6 production. This effect was reduced when protein kinase A was blocked by KT-5720; it was not affected by calphostin C, a protein kinase C inhibitor. Forskolin caused a concentration-dependent increase in interleukin 6 release, that was also inhibited by KT-5720. Since prostaglandins are believed to play a role in interleukin 6 production, we tried to determine whether the stimulatory effects of vasoactive intestinal peptide and forskolin on cytokine release might be mediated by stimulation of prostaglandin production in cortical astrocytes. Vasoactive intestinal peptide did not increase the production of either prostaglandin E2 or F2 alpha. Conversely, forskolin concentration-dependently stimulated the production of both prostaglandins, an effect that was blocked by indomethacin. Indomethacin did not affect either vasoactive intestinal peptide- or forskolin-stimulated interleukin 6 production. To exclude the possibility that prostaglandins participate in interleukin 6 production induced by forskolin, we tested the effect of prostaglandins E2 and F2 alpha on the cytokine production. The former was completely ineffective in eliciting the cytokine production, while prostaglandin F2 alpha slightly increase interleukin 6 only at the highest concentration. 8-Br-cAMP and (BU)2- cAMP stimulated interleukin 6 production to a lesser extent than vasoactive intestinal peptide and forskolin. In conclusion, we provide evidence that vasoactive intestinal peptide increases interleukin 6 production by astrocytes through the stimulation of the cAMP-protein kinase-A pathway, an effect that is reproduced by cAMP analogues. In addition, we point out that prostaglandins are not involved in vasoactive intestinal peptide- and forskolin-mediated induction of interleukin 6 production in cultured astrocytes.

Vasoactive intestinal peptide increases intracellular calcium in astroglia: synergism with alpha-adrenergic receptors

In type I astrocytes from rat cerebral cortex, vasoactive intestinal peptide (VIP) at concentrations below 1 nM evoked an increase in intracellular calcium ion concentration. This response, however, was observed in only 18% of the astrocytes examined. alpha-Adrenergic stimulation with phenylephrine or norepinephrine also resulted in an intracellular calcium response in these cells and the threshold sensitivity of astrocytes to phenylephrine was vastly different from cell to cell. Treatment of these astrocytes with VIP (0.1 nM) together with phenylephrine at subthreshold concentrations produced large increases in intracellular Ca2+ concentration ([Ca2+]i) and oscillations. The continued occupation of the alpha-adrenergic receptor was required for sustained synergism. Both alpha-receptor stimulation and stimulation with the mixture of agonists induced the cellular calcium response by triggering release of calcium from cellular stores, since the response persisted in the absence of extracellular calcium. Furthermore, thapsigargin pretreatment, which depletes intracellular stores, abolished the agonist-induced [Ca2+]i response. VIP (0.1 nM) and phenylephrine were found to increase cellular levels of inositol phosphates; however, there was no apparent additivity in this response when the agonists were added together. These observations suggest a calcium-mediated second messenger system for the high-affinity VIP receptor in astrocytes and that alpha-adrenergic receptors act synergistically with the VIP receptor to augment an intracellular calcium signal. The synergism between diverse receptor types may constitute an important mode of cellular signaling in astroglia.

Binding of atrial and brain natriuretic peptides to cultured mouse astrocytes from different brain regions and effect on cyclic GMP production

We prepared primary cultures of mouse astrocytes from the cerebral cortex, hypothalamus, and cerebellum to examine the possibility of regional disparity in binding of human atrial and porcine brain natriuretic peptides (hANP, pBNP) and their effect on cyclic guanosine monophosphate (cGMP) production. 125I-hANP and 125I-pBNP bound in a specific and saturable manner to all three regions. For both peptides, Scatchard analysis suggested a single population of binding sites on astrocytes from all three regions. No significant differences were observed in the maximal binding capacities (Bmax) or binding dissociation constants (KD) between the two peptides in the astrocyte preparations from different regions. ANP and BNP also evoked cGMP stimulation in a similar, dose-dependent fashion in astrocytes from all three regions, with maximal responses to both peptides reached at a concentration above 1 microM. While BNP elicited a greater maximal cGMP accumulation than ANP, no difference could be demonstrated in the cGMP responses to either peptide between brain regions. Thus we have been unable to demonstrate regional heterogeneity in the responsiveness of astrocytes to ANP and BNP.

AMPA-selective glutamate receptor subunits in astroglial cultures

We analysed AMPA ionotropic receptor subunits at the mRNA level (GluR-1 to -4) and at the protein level (GluR-1 and GluR-2/3/4c) in "primary astroglial cultures" (non-neuronal cell cultures highly enriched in glial fibrillary acidic protein [GFAP] positive cells) prepared from newborn rat cerebral hemispheres, cerebral cortex, hippocampus, and striatum and in "brain non-neuronal cell cultures" (low percentage of GFAP positive cells) prepared from cerebellum, brainstem, mesencephalon, and hypothalamus. For comparison, we also determined AMPA subunit mRNA and protein levels in different brain regions. By Northern blot analysis mRNAs for the AMPA receptor subunits (GluR-1,-2,-3,-4) were detected in primary rat cerebral hemispheres astroglial cultures. Immunoblotting analysis with anti-GluR-1 and anti-GluR-2/3/4c polyclonal antibodies confirmed the presence of low level of immunoreactive proteins of the same size of those identified in vivo as GluR subunits. Expression of GluR genes varied depending on the brain area used as starting material for the preparation of the cultures: GluR-1, -2, and -3 were mainly expressed in cortical cultures, while GluR-4 expression predominated in brainstem derived cultures. Interestingly this pattern of expression correlates with that observed in the intact brain, where high levels of GluR-4 mRNA and low levels of the other GluR subunits were found in the brainstem. In conclusion our results confirm the existence of glutamate ionotropic receptors of the AMPA type in primary astroglial cultures and suggest that GluR-4 is the main AMPA receptor subunit expressed in non-neuronal cells of the central nervous system.

Influence of chronic intracerebroventricular infusion of vasoactive intestinal peptide (VIP) on memory processes in Morris water pool test in the rat

In our previous study, bolus injection of VIP into the lateral cerebral ventricle, at nonphysiological high doses, has been shown to produce amnesia. Accordingly, in the present study, VIP was infused chronically into the cerebral ventricle of the rat at a rate of 10 ng per day for 2 weeks. During the infusion period, the animals were subjected to the Morris water pool test. The VIP infusion caused an apparent impairment of memory, particularly in the acquisition of new information; VIP(1-12) also caused similar impairment, but to a lesser extent. The VIP antagonists did not affect the performance of learned tasks. However, cerulein treatment prevented the VIP-induced memory impairment.

Morphine suppresses DNA synthesis in cultured murine astrocytes from cortex, hippocampus and striatum

To determine whether there are regional differences in the ability of opiates to affect astrocyte proliferation, the effects of morphine were examined in astrocyte-enriched cultures from striatum, hippocampus and cerebral cortex derived from newborn mouse brains. Cultures from each region were continuously incubated in media alone (controls), or in media treated with 1 microM morphine, 1 microM morphine plus 3 microM naloxone, or 3 microM naloxone alone. Before harvesting at 6 days in vitro, cultures were exposed to [3H]thymidine (0.24 mu CI/ml for 16 h). Thymidine-labeling index was determined autoradiographically in flat, polyhedral (type 1) glial fibrillary acidic protein (GFAP)-immunoreactive astrocytes. Morphine significantly inhibited [3H]thymidine incorporation in astrocytes from all three brain regions, although regional differences in labeling indices were noted. The results show that opiates can intrinsically affect the proliferative rate of astrocytes from diverse brain regions.

Chronic treatment of newborn rats with naltrexone alters astrocyte production of nerve growth factor

Newborn rats were treated with the opiate antagonist naltrexone daily for 1-2 wk in order to examine the effects of endogenous opioid peptides on astrocytes during CNS development. Nerve growth factor (NGF) and cyclic AMP were measured in astrocytes cultured from cerebellum, striatum, and hippocampus of 1 d, 1 wk, and 2 wk postnatal rats. Cerebellar and striatal, but not hippocampal, astrocytes prepared from naltrexone-treated animals produced higher levels of NGF than those from controls. The turnover rate of cyclic AMP, measured following treatment of the cells with forskolin in the presence of the phosphodiesterase inhibitor IBMX, was increased in naltrexone-derived cerebellar and striatal astrocytes. Opiate receptors could not be detected on the cultured astrocytes, either by direct binding of 3H-etorphine or by modulation of cyclic AMP content. These results suggest that endogenous opioid peptides may function indirectly to alter trophic factor synthesis in astrocytes.

Astrocyte subtypes in the rat olfactory bulb: morphological heterogeneity and differential laminar distribution

Despite increased recognition of the importance and heterogeneity of astrocyte functions throughout the central nervous system (CNS) relatively little attention has been paid to morphological diversity among astrocytes. Recent studies have indicated that subsets of astrocytes are involved in glial-axonal interactions critical to both development and reinnervation of the rat olfactory bulb. Here, we have characterized the morphologies and distribution of astrocytes within anatomically and functionally distinct layers of the adult main olfactory bulb (MOB). Using a known immunohistochemical marker for astrocytes, glial fibrillary acidic protein (GFAP), and the classic gold sublimate method, we identified six astrocyte subtypes based on their morphology and distribution: (1) unipolar, (2) irregular, (3) wedge-shape, (4) circular, (5) semicircular, and (6) elongate. Unipolar, irregular and wedge-shape astrocytes have not been previously described in the CNS. The unipolar and irregular types are located exclusively in the olfactory nerve layer. Wedge-shape astrocytes are unique to, and are the major subtype in, the glomerular layer. These three morphologically unique astrocyte subtypes may correspond to olfactory nerve layer (ONL) and glomerular layer (GL) astrocytes, which express molecules that regulate axonal growth or synaptogenesis during development and/or regeneration of the olfactory nerve. In the glomerular layer, astrocytes are highly organized with respect to the glomeruli. Individual astrocytes are loyal to a single glomerulus. In the external plexiform layer, astrocytes are spaced relatively uniformly. In the granule cell layer, astrocytes appear to compartmentalize granule cell aggregates, recently shown to be coupled by tight junctions. The distribution and patterns of astrocyte processes and the density of GFAP immunoreactivity are distinctive for each of the layers of the olfactory bulb. The spacing of astrocytes and the organization of their processes may be important to compartmentalization of neuronal functions. High levels of GFAP immunoreactivity correlated with layers of high neuronal plasticity. The morphological diversity and differential distribution of astrocytes in the olfactory bulb reported here support growing evidence for functional diversity of astrocytes and important interactions among specific astrocyte and neuron subtypes. It is reasonable to hypothesize, therefore, that as for neurons, morphologically distinctive astrocyte subtypes may correspond to functionally specific classes.

Regulation of bradykinin-induced phosphoinositide turnover in cultured cerebellar astrocytes: possible role of protein kinase C

Phosphoinositide hydrolysis was studied in primary cultures of rat cerebellar astrocytes prelabeled with [3H]myo-inositol. Among the agonists examined, the rank order of efficacies in causing phosphoinositide hydrolysis was bradykinin > endothelin-1 > ATP > norepinephrine. The bradykinin response was robust (24-fold increase) with EC50 value of 30 nM and saturating concentration of 1 microM. Preincubation of cells with pertussis toxin did not affect the activation of phosphoinositide turnover by bradykinin. Although short-term (within 90 min) treatment of cells with phorbol dibutyrate attenuated bradykinin-induced phosphoinositide breakdown, the inhibitory effect was lost after 3-6 h of phorbol dibutyrate treatment. Extended (24 h) preincubation resulted in a potentiation of bradykinin response. Homologous desensitization of bradykinin response was observed in cells prestimulated with bradykinin for up to 6 h. However, similar to the effect of phorbol dibutyrate, 24-h pretreatment with bradykinin selectively sensitized the response to bradykinin. Up-regulation of the bradykinin response was also observed in cells prestimulated with endothelin-1 or norepinephrine for 24 h, although these treatments resulted in only homologous desensitization to their own response. Our results suggest that cultured cerebellar astrocytes express bradykinin receptors coupled to phospholipase C and in these cells protein kinase C plays a more prominent role in the negative-feedback regulation of bradykinin-evoked phosphoinositide response.

Transforming growth factor-beta 1 differentially regulates proliferation and MHC class-II antigen expression in forebrain and brainstem astrocyte primary cultures

To facilitate investigation of cytokine regulation of reactive astrogliosis, primary astrocyte cultures from neonatal murine forebrain and brainstem were established. Forebrain and brainstem astrocytes proliferated at a similar rate under basal culture conditions, and both were growth-inhibited by treatment with recombinant murine interferon-gamma. The growth of cultured brainstem astrocytes was significantly enhanced by exposure to recombinant human transforming growth factor-beta 1. In contrast, proliferation of forebrain astrocytes was not significantly affected by transforming growth factor-beta 1. The disparate responses of brainstem and forebrain astrocytes to transforming growth factor-beta 1 treatment were not limited to effects on cell growth, since transforming growth factor-beta 1 could block interferon-gamma-induced MHC class-II antigen expression on cultured brainstem astrocytes but not on forebrain cells. Results could not be attributed to use of an heterologous cytokine/cellular target system, since similar variability in transforming growth factor-beta 1 modulation of major histocompatibility complex antigen expression could be demonstrated using two human astrocytoma cell lines. This report is the first to document mitogenic response to transforming growth factor-beta 1 for neuroepithelial cells. The role of transforming growth factor-beta 1 in regulating aspects of reactive astrogliosis, particularly in the context of inflammatory demyelination, requires further investigation. Furthermore, these studies may provide insight into regional variability in the sequelae of inflammation within the central nervous system.

Melanocortins stimulate proliferation and induce morphological changes in cultured rat astrocytes by distinct transducing mechanisms

Melanocyte stimulating hormone (MSH), adrenocorticotropic hormone (ACTH), and several peptides derived from pro-opiomelanocortin, are present in the dorsolateral hypothalamus and arcuate nucleus of several vertebrate species. These peptides affect central nervous system (CNS) functions including behavior, memory, and foetal brain development. In this study we investigated the effects of ACTH1-24, ACTH1-17, ACTH4-10, alpha-MSH, beta-MSH, and a potent analog (Nle4,D-Phe7)-alpha-MSH (melanocortins) on immunocytochemically defined astroglial cells prepared from primary cultures of 1-2-day-old rat brains. A cyclic adenosine 3',5'-monophosphate (cAMP) response to the melanocortins was only detected in astrocytes and not in other cell types in the culture. The extent of the cAMP response was greatest on day 21, the latest time tested. On the other hand, (methyl3H)-thymidine incorporation in astrocytes was significantly stimulated (1.5-2-fold) by melanocortins only in 7 and not in 14 and 21 day cultures. This mitogenic activity of melanocortins was not mimicked by other agents such as forskolin or isoproterenol which efficiently stimulate cAMP production in astrocytes. ACTH1-17 as a melanocortin representative induced significant morphological changes in 7 and 14 day cultures which included rounding of the cell body and process extension. This response, however, resembled that induced by forskolin and hence appears to be cAMP mediated. These findings suggest that astrocytes in the CNS may serve as a target for melanocortins. These peptides appear to affect differentiation and proliferation of these cells during certain developmental periods. While the morphological effects of melanocortins seem to be cAMP mediated, induction of proliferation of the astrocytes by melanocortins appears to involve an alternative signal transduction pathway.

In situ transformation of striatal glia into cerebellar-like glia after brain transplantation

Transplants of striatum from rabbit embryo were implanted into the colliculus posterior of newborn mice. After 4 weeks, astroglial cells derived from the transplant had migrated into the cerebellum of the host. Whenever they had settled in the cerebellum they presented forms similar to local glia. Some migrated glial cells were found to transform into forms of glia, such as radial-like glia, which are not present in the striatum. This observation confirms that glial precursor cells are highly plastic. It is an in vivo demonstration that local conditions alone define the morphology of glial cells. After grafting in an heterotopic location they take on forms that they were not destined to express in the region of origin.

Target-derived astroglia regulate axonal outgrowth in a region-specific manner

The potential neuroanatomical specificity of astrocyte influence on neurite outgrowth was studied using an in vitro coculture system in which neurons from embryonic rat spinal cord or hippocampus were grown for 4 days in the presence of, but not in direct contact with, astrocytes derived either from the same region (homotopic coculture) or from different regions (heterotopic coculture) of the rat central nervous system. The results showed that axonal outgrowth was greatly enhanced in heterotopic cocultures in which spinal cord or hippocampal neurons were grown with astrocytes derived from their appropriate CNS target regions. This effect was remarkably specific, because the astroglia harvested from spinal or hippocampal target regions were not effective in promoting axon growth of nonafferent neuronal populations. Dendritic outgrowth was similar under all coculture conditions. These data suggest that diffusible signals, produced by astrocytes, can regulate neurite extension in vitro in a neuroanatomically specific manner and that axons are more sensitive than dendrites to the regional astrocyte environment.

Regulation of plasminogen activators and type-1 plasminogen activator inhibitor by cyclic AMP and phorbol ester in rat astrocytes

Two plasminogen activators (PAs): tissue-type plasminogen activator (t-PA) and urokinase-type plasminogen activator (u-PA), as well as the type-1 plasminogen activator inhibitor (PAI-1) are synthesized and secreted by rat astrocytes. Preliminary studies suggest that PA activity plays a role in astrocyte development and differentiation. We have examined the regulation of the PA system by the cAMP-dependent protein kinase (PKA) and protein kinase C (PKC) in purified rat astrocyte cultures. PKA activity was increased by exposing cultured astrocytes to forskolin or dibutyryl cyclic AMP, whereas PKC activity was stimulated with phorbol-12-myristate 13-acetate (PMA). Activation of both second-messenger pathways produced a time- and dose-dependent increase in the total PA activity. However, based on SDS-PAGE/zymography we found that forskolin increased t-PA activity and reduced u-PA activity, whereas PMA treatment caused a significant increase in u-PA activity without altering t-PA activity. Reverse zymography analysis revealed that astrocyte PAI-1 activity is decreased by forskolin and increased by PMA. Together, these results demonstrate that the components of the PA system in rat astrocytes are independently and reciprocally regulated by PKA and PKC. Our findings raise the possibility that the plasminogen activator system could be involved in some of the actions of growth factors and/or neuromodulators that modulate PKC or PKA in astrocytes.

Characterization of Gs alpha mRNA transcripts in primary cultures of rat brain astrocytes

A cDNA clone encoding a stimulatory G-protein alpha subunit (Gs alpha) was isolated from a cDNA library derived from cultured rat astrocytes. The nucleotide sequence of the cDNA indicated that it corresponds to the Gs alpha-2 form of Gs alpha mRNA, one of four Gs alpha mRNAs known to be derived by alternative splicing from the human Gs alpha gene. A ribonuclease protection assay using cRNA from this clone allowed distinction between the Gs alpha-1 and Gs alpha-2 mRNAs, which encode the 52-kDa (Gs-L) forms of Gs alpha. Astrocytes express relatively high amounts of Gs alpha-1 mRNA, much lower amounts of the Gs alpha-2 mRNA, and no detectable amounts of the mRNAs (Gs alpha-3 and Gs alpha-4) encoding the two 45-kDa forms of Gs alpha (Gs alpha-S). Similar results were obtained with RNA samples isolated from whole brain. The 45-kDa form of Gs alpha protein was not detectable by immunoblot analysis of a membrane preparation from rat cerebral cortex (the source of the astrocyte cultures). These results indicate that the expression of Gs alpha forms in astrocytes is similar to that found in whole brain.

Serotonin promotes region-specific glial influences on cultured serotonin and dopamine neurons

To test the hypothesis that glia mediate interactions between embryonic serotonergic (5-HT) neurons and dopamine neurons, we studied the effects of 5-HT in co-cultures of E14 raphe neurons of mesencephalic dopamine neurons and radial glia/astrocytes derived from the same (homotypic) or opposite (heterotypic) brain region using a dose (10(-5) M) that would produce 5-HT uptake into glial cells as well as activate 5-HT receptors. Morphometric analysis of 5-HT and tyrosine hydroxylase (TH) immunoreactive neurons revealed regional differences in the effects of 5-HT (and nialamide) on survival, cell soma size, and dendrite-like neurite outgrowth in neuronal-glial co-cultures. In general, 5-HT had more significant effects on both types of monoamine neuron when they were cultured with mesencephalic glia (GSN). Stimulatory effects of 5-HT on growth of TH neurons in GSN cultures suggest that developing raphe axons, which reach the mesencephalon during the early differentiation of these neurons, may enhance the influence of local glial-derived trophic factors. Likewise, the promotion of 5-HT neuronal survival in these cultures suggests that glial factors in the mesencephalon may contribute to the support of 5-HT neurons in addition to the influences of raphe glia. The inhibitory effects of 5-HT on neurite outgrowth by raphe neurons in GSN co-cultures indicates enhanced sensitivity of these neurons to the inhibitory effects of 5-HT in the presence of mesencephalic glia. The region-specific effects of 5-HT and nialamide in glial co-cultures suggest that raphe and mesencephalic glia may express different capacities for 5-HT uptake, receptors, and/or monoamine oxidase (MAO) activities. These characteristics could be important for the specificity of growth-regulatory influences of glial cells on the development of brain monoamine neurons.

Different response of astrocytes and Bergmann glial cells to portacaval shunt: an immunohistochemical study in the rat cerebellum

The present study was performed in order to follow the response of rat cerebellum astroglial cells (Bergmann glial cells and astrocytes) to long-term portacaval shunt (PCS), by means of glial fibrillary acidic protein (GFAP) and vimentin immunoreactivities. Bergmann glia accumulated GFAP in response to PCS, whereas astrocytes decreased GFAP immunoreactivity when compared to control rats. The increase of GFAP occurs in cells located in the cerebellar layer where glutamate is mainly released. Since the vimentin content remained unaltered in response to PCS, when compared to control rats, it can be concluded that only the GFAP filaments are affected by PCS. Nevertheless, GFAP immunoreactivity presents regional differences in the cerebellar astroglial population, and the factors responsible for these variations are still unknown.

Migration patterns of donor astrocytes after reciprocal striatum-cerebellum transplantation into newborn hosts

Fragments of striatum or cerebellum from E 25 rabbit embryo were implanted into either the striatum or the mesencephalon of newborn mice. Implanted rabbit astrocytes were selectively identified by monoclonal antibodies to the GFAP which are unable to combine with mouse GFAP. Previous investigations had shown that xenogenic astrocytes have the capacity to migrate in host CNS. The purpose of this study was to compare the patterns of migration of transplant-derived astroglial cells according to the topographic origin of the transplant and location of the grafting site. We found that the migration pattern of the grafted cells from any of both selected sites of implantation was independent from the topographic origin of the transplant. The routes as well as the distances of migration were similar after homo- or heterotopic transplantation. We conclude that astroglial cells or their precursors do not express information which would direct them to move specifically toward a defined region in the host brain according to the region of origin in the donor.

Ca2+ waves in astrocytes

The glial cell is the most numerous cell type in the central nervous system and is believed to play an important role in guiding brain development and in supporting adult brain function. One type of glial cell, the astrocyte also may be an integral computational element in the brain since it undergoes neurotransmitter-triggered signalling. Here we review the role of the astrocyte in the central nervous system, emphasizing receptor-mediated Ca2+ physiology. One focus is the recent discovery that the neurotransmitter glutamate induces a variety of intracellular Ca2+ changes in astrocytes. Simple Ca2+ spikes or intracellular Ca2+ oscillations often appear spatially uniform. However, in many instances, the Ca2+ rise has a significant spatial dimension, beginning in one part of the cell it spreads through the rest of the cell in the form of a wave. With high enough agonist concentration an astrocyte syncitium supports intercellular waves which propagate from cell to cell over relatively long distances. We present results of experiments using more specific pharmacological glutamate receptor agonists. In addition to describing the intercellular Ca2+ wave we present evidence for another form of intercellular signalling. Some possible functions of a long-range glial signalling system are also discussed.

Cerebral type 2 astroglia are heterogeneous with respect to their ability to respond to neuroligands linked to calcium mobilization

Very little information is available concerning the pharmacology of type 2 astroglia. During the past decade it has become apparent that two distinct lineages of astroglial cells can be defined in vitro. These two lineages are commonly referred to as type 1 and type 2 and are distinguished from each other on the basis of their morphological features and antigenic phenotypes. In contrast to type 1 astroglia, very little is known about the pharmacology of type 2 astroglia. The lack of information concerning the responsiveness of these cells stems primarily from difficulties encountered in isolating large numbers of type 2 astroglia free of other cell types. In the present study video- and photometer-based imaging systems were used to monitor the influence of a series of neuroligands on the intracellular calcium levels of individual cerebral type 2 astroglia in order to assess their expression of calcium-mobilizing receptors. The responses of 85 immunocytochemically identified cerebral type 2 astroglia to bradykinin (BK), norepinephrine (NE), histamine (HIST), carbachol (CARB), 2-methyl-thio ATP (2MT-ATP), glutamate (GLUT), and serotonin (5-HT) were analyzed. Approximately 50% of cerebral type 2 astroglia responded to BK, NE, HIST, CARB, and 2MT-ATP whereas only 16% and 9% of the cells responded to GLUT and 5-HT, respectively. The number of neuroligands that increased calcium in individual cells ranged from 0 to 6. These responses are quite similar to those previously demonstrated in cultured cerebral type 1 astroglia. No pattern of receptor co-expression was observed for the different neuroligands tests.(ABSTRACT TRUNCATED AT 250 WORDS)

Substance P-induced release of prostaglandins from astrocytes: regional specialisation and correlation with phosphoinositol metabolism

Addition of substance P (SP) to astrocytes cultured from rat neonatal spinal cord evoked a time- and concentration-dependent increase in the accumulation of phosphoinositol and the release of prostaglandin (PG) D2 and PGE2. Both basal and stimulated releases were reduced to similar levels by indomethacin. In contrast, astrocytes cultured from cerebral cortex and cerebellum showed no SP-stimulated increase in phosphoinositol accumulation or release of PGs. Release of PGD2 and PGE2 was, however, stimulated by the calcium ionophore A23187, and both phosphoinositol accumulation and PG release were stimulated from cortical astrocytes incubated in the presence of serum. The results from this study suggest that SP-stimulated phosphoinositol accumulation and release of PGs from cultured rat neonatal astrocytes are regionally specialised in favour of cells derived from spinal cord.

Properties of kainate receptor/channels on cultured Bergmann glia

Following the localization, at the electron microscope level, of the immunoreactivity towards a putative kainate receptor on Bergmann glial cells in the chick cerebellar cortex, cultures of Bergmann glia were used to establish the presence of functional kainate receptor/channels and study their properties. Bergmann glia were identified by their fusiform morphology and their ability to bind an anti-kainate binding protein monoclonal antibody, a kainate receptor high affinity ligand--kainyl-bovine serum albumin--and a glial marker--anti-vimentin monoclonal antibody. Membranes prepared from the culture cells displayed, using 25 nM [3H]kainate, the binding of 4.1 pmol of [3H]kainate/mg protein and showed the presence in Western blots of the two polypeptides of 49 and 93 kDa attributed to the kainate binding protein. Kainate, at concentrations above 0.1 mM, was found to increase the influx into cultured Bergmann glia of 22Na+, 86Rb+, 45Ca2+ and 36Cl- ions. The traffic of 22Na+, induced by kainate and glutamate, observed only in the presence of 1 mM ouabain, was blocked by kainate receptor antagonists and by 0.01 mM quisqualate. Analysis of the kinetics of incorporation of 22Na+ and 45Ca2+ ions showed an initial accumulation of 22Na+ and 45Ca2+ ions followed by their total dissipation. The results indicate that the kainate-induced influx of Na+ ions through the kainate receptor/channel causes the reverse transport of Na+ ions, by activation of the Na+/Ca2+ and Na+/H+ exchangers which remove intracellular Na+ ions. Pre-exposure of the cells to 0.5 mM dibutyryl cAMP was found to greatly enhance the kainate-induced 22Na+ ion influx. We propose that the Bergmann glia kainate receptors modulate the efficacy of the glutamatergic synapses between the parallel fibers and Purkinje cell spines and form part of a glial machinery responsible for plastic changes in synaptic transmission.

Somatostatin-binding sites on rat telencephalic astrocytes. Light- and electron-microscopic studies in vitro and in vivo

Using a somatostatin-gold conjugate as ligand, high-affinity binding sites for this neuropeptide were demonstrated at three levels: (i) cultured astrocytes from rat cortex, (ii) hippocampal slice cultures, and (iii) frozen tissue sections of rat telencephalon. The conjugate proved as active as the native peptide in competing for the binding sites. Light-microscopic visualization of bound ligand was achieved by silver intensification of the colloidal gold. This method is faster and yields superior resolution compared with autoradiography. Cultured astrocytes from cortex and hippocampus could be labeled by the ligand. At the light- and electron-microscopic level, astrocytes could be double-labeled by the somatostatin-gold conjugate and immunostaining for glial fibrillary acidic protein (GFAP). In hippocampal slice cultures, the conjugate did not penetrate into the neuropil because of a covering glial layer. However, a portion of this completely GFAP-positive covering glia reacted with the somatostatin ligand. In frozen brain sections, apart from delicate punctate structures, two types of labeled glia cells were seen: single stellate astrocytes and perivascular glia cells.

Delta and kappa opiate receptors in primary astroglial cultures from rat cerebral cortex

The effects of mu, delta, and kappa receptor-agonists on forskolin stimulated cyclic adenosine-3',5'-monophosphate (cAMP) formation were examined in astroglial enriched primary cultures from the cerebral cortex of newborn rats. Intracellular cAMP accumulation was quantified by radioimmunoassay. Morphine was used as a mu-receptor agonist, D-Ala-D-Leu-Enkephalin (DADLE) as a delta-receptor agonist and dynorphin 1-13 (Dyn) as a kappa-receptor agonist. Basal cAMP levels were unaffected by either the opiate agonists or the antagonists used. In the presence of the cAMP stimulator forskolin, morphine had no significant effect on the cytoplasmic cAMP levels. DADLE caused a dose related inhibition of the forskolin stimulated cAMP accumulation. The effects of this delta receptor stimulation was blocked with the selective antagonist ICI 174.864. In the presence of Dyn, the forskolin stimulated cAMP accumulation was inhibited in a dose related manner. This kappa receptor stimulation was blocked with the selective antagonist MR 2266. Co-administration of DADLE and Dyn resulted in a non additive inhibition of the forskolin stimulated accumulation of cAMP. These findings indicate that astroglial enriched cultures from the cerebral cortex of rats express delta and kappa-receptors co-localized on the same population of cells, and that these receptors are inhibitory coupled to adenylate cyclase.

Effect of isoproterenol on the uptake of [14C]glucose into glial cells

The effect of isoproterenol on the uptake of [14C]glucose into cultured glial cells was investigated in the present study. Isoproterenol markedly stimulated the uptake of [14C]glucose 30 min after incubation. This action was produced in a dose-dependent manner. A positive correlation between the increase of [14C]glucose uptake and the stimulation of adenylate cyclase induced by isoproterenol was obtained (r = 0.99). The effect of isoproterenol was reduced by the beta-adrenergic blockers but not by other blockers, indicating the selective action of isoproterenol. The results obtained suggest that isoproterenol stimulates the uptake of glucose into glial cells through the activation of beta-adrenoceptors which are linked to adenylate cyclase.

A rapid procedure for the preparation of oligodendrocyte-enriched cultures from rat spinal cord

Spinal cords and cerebra from 7-day-old rat pups were compared as tissue sources for the isolation of oligodendrocytes and for studies on the development of these cells in culture. After 1 day in culture the serum-containing medium was replaced by a chemically-defined medium, which contained a cocktail of hormones that stimulated oligodendrocyte development. The cultures were characterized with various immunocytochemical markers; monoclonal A2B5 for bipotential glial progenitor cells, anti-galactocerebroside (GC) serum for oligodendrocytes, and anti-glial fibrillary acidic protein (GFAP) serum for astrocytes. The number of positive cells was counted and expressed as a percentage of total cells. At 1 day in culture the cell cultures from spinal cord contained 30% GC+ cells, increasing to 90% after 7 days in culture. In cultures derived from cerebra the percentage of GC+ cells was always lower than in cultures from spinal cord. In cerebral cultures GFAP+ cells increased from 15% at 1 day in culture to 30% at 7 days in culture, whereas it remained low in spinal cord cultures. The activity of oligodendroglial marker enzyme 2',3'-cyclic-nucleotide 3'-phosphodiesterase was followed during development in culture. The specific activity increased rapidly in both types of culture but was more than threefold higher in cultures derived from spinal cord. This procedure yields, within one week and without subculture, primary glial cultures from rat spinal cord, that are highly enriched in oligodendrocytes (greater than or equal to 90%; 3.10(5) oligodendrocytes per rat pup).

Marked regional heterogeneity of 125I-Bolton Hunter substance P binding and substance P-induced activation of phospholipase C in astrocyte cultures from the embryonic or newborn rat

The specific binding of 125I-Bolton Hunter substance P (125I-BHSP) was estimated on 4- to 5-week-old primary cultures of astrocytes from several brain structures and the spinal cord of 16-day-old embryonic or newborn rats. In both cases, high levels of binding of 125I-BHSP were found on intact astrocytes from the brainstem, but this binding was low or negligible on cells from the cerebral cortex, striatum, hypothalamus, and mesencephalon. In addition, hippocampal astrocytes from newborn rats were also devoid of 125I-BHSP binding sites, while a binding of 125I-BHSP (half that of brainstem cells) was observed on astrocytes from the cerebellum and spinal cord. It was also shown that this regional heterogeneity in 125I-BHSP binding was not linked to differences in the inactivation of the ligand, cell plating density. or eventual cell contaminants. Five-day-old cultures from 16-day-old embryos were used to estimate 125I-BHSP binding on neuron-enriched cultures. Specific 125I-BHSP binding was found on cells from the brainstem, mesencephalon, and hypothalamus, but neurons from the cerebral cortex or the striatum contained low or negligible amounts of 125I-BHSP binding sites. Competition studies using tachykinins and SP analogues indicated that 125I-BHSP binding sites on brainstem astrocytes (16-day-old embryos) have the pharmacological profile expected for NK1 binding sites. SP (1 microM) stimulated phosphoinositide breakdown in cells rich in 125I-BHSP binding sites (brainstem) but not in those devoid of 125I-BHSP binding (striatum).(ABSTRACT TRUNCATED AT 250 WORDS)