Electrical coupling among Bergmann glial cells and its modulation by glutamate receptor activation

We studied the characteristics of electrical coupling between Bergmann glial cells in mouse cerebellar slices using Lucifer Yellow injection, patch-clamping cell pairs, and ultrastructural inspection. While early postnatal cells (days 5–7) were not coupled, coupling was abundant at postnatal days 20–24. Coupled cells were arranged perpendicular to the parallel fibers in a parasagittal section, forming a string, rather than a cluster of cells. Electron microscopy revealed that gap junctions were abundant in the distal parts of the processes. Gap junctions between cell bodies and processes were very rare, and no gap junctions were found between cell bodies of adjacent Bergmann glial cells. The junctional conductance was voltage and time independent and could be markedly reduced by halothane. Alkalization of cells (by applying NH₄⁺ increased the junctional conductance to 150%, while acidification of the cell interior (by removing NH₄⁺) led to a decrease to 70%. Activation of AMPA receptors induced a blockade of the junctional conductance to 30% of the control. This link is most likely mediated by the influx of Ca²⁺ via the receptor since this effect was not observed in Ca²⁺-free medium, suggesting that Ca²⁺ entry via the kainate receptor pore led to the closure of gap junctions. These studies indicate that electrical coupling between Bergmann glial cells is not only developmentally regulated but also controlled by physiological stimuli. © 1996 Wiley-Liss, Inc.     

ATP: an extracellular signaling molecule between neurons and glia

Recent studies on Schwann cells at the neuromuscular junction and non-synaptic regions of premyelinated axons indicate that extracellular ATP can act as an activity-dependent signaling molecule in communication between neurons and glia. Several mechanisms have been observed for the regulated release of ATP from synaptic and non-synaptic regions, and a diverse family of receptors for extracellular ATP has been characterized. The findings suggest functional consequences of neuron–glial communication beyond homeostasis of the extracellular environment surrounding neurons, including regulating synaptic strength, gene expression, mitotic rate, and differentiation of glia according to impulse activity in neural circuits.     

Cytoarchitectonics of substantia nigra grafts: a light and electron microscopic study of immunocytochemically identified dopaminergic neurons and fibrous astrocytes

Maturation of dopaminergic (DA) neurons and astroglia was studied in transplants of the substantia nigra grown for up to 7 months in the brain of rats. The investigation had three specific aims. The first was to observe effects of different transplant positions on the longevity of DA neurons. Second, the grafts were examined for changes of synaptic interactions and associations between DA neurons and astroglia. Third, an answer was sought to the question whether transplanted DA neurons migrate into the adjacent host brain. The grafts were taken from the ventral mesencephalon of rat embryos of different ages (day 14 to 18 of gestation) and placed into the cerebral cortex, tectum, cerebellum, or ventricles of newborn host animals. Following different times of survival the immunocytochemical localization of tyrosine hydroxylase (TH) and of glia filament protein (GFA) in the transplants were observed. In all of the transplantation sites, except for one, neurons of different morphologies that contained TH were found in the grafts. The cerebellar white matter of the host brain failed to support the long-term survival of DA neurons. The overall structure of mature substantia nigra grafts had some resemblance to intact substantia nigra (SN). On the ultrastructural level, it was found that morphological expression of some immature features of DA neurons, such as glial sheaths, somatic spines, and lack of oligodendroglia, persisted in mature grafts. Specific associations of DA neurons and astroglia in the grafts suggested that the cytoarchitectonic appearance of a given brain region may be related to the existence of particular neuron glia relationships. In contrast to intact SN, transplants revealed deficiencies in unlabeled pleomorphic boutons and contained some TH-immunoreactive terminals. Migration of DA neurons and their processes into the adjacent host brain was rarely observed.     

Glial ephrin-A3 regulates hippocampal dendritic spine morphology and glutamate transport

Increasing evidence indicates the importance of neuron-glia communication for synaptic function, but the mechanisms involved are not fully understood. We reported that the EphA4 receptor tyrosine kinase is in dendritic spines of pyramidal neurons of the adult hippocampus and regulates spine morphology. We now show that the ephrin-A3 ligand, which is located in the perisynaptic processes of astrocytes, is essential for maintaining EphA4 activation and normal spine morphology in vivo. Ephrin-A3-knockout mice have spine irregularities similar to those observed in EphA4-knockout mice. Remarkably, loss of ephrin-A3 or EphA4 increases the expression of glial glutamate transporters. Consistent with this, glutamate transport is elevated in ephrin-A3-null hippocampal slices whereas Eph-dependent stimulation of ephrin-A3 signaling inhibits glutamate transport. Furthermore, some forms of hippocampus-dependent learning are impaired in the ephrin-A3-knockout mice. Our results suggest that the interaction between neuronal EphA4 and glial ephrin-A3 bidirectionally controls synapse morphology and glial glutamate transport, ultimately regulating hippocampal function.     

糖皮质激素对成体海马神经祖细胞的影响

背景：体内研究显示,高浓度糖皮质激素可抑制大鼠内源性神经前体细胞增殖。而神经胶质抗原2蛋白聚糖阳性神经祖细胞(NG2细胞)是成熟中枢神经系统中最大的增殖细胞群体,具有多分化潜能。 目的：观察糖皮质激素对体外培养的成熟大鼠海马由来的NG2细胞生存和增殖的影响。 方法：原代及传代培养成年大鼠海马NG2细胞,以0,0.1,1,10,100 μmol浓度糖皮质激素类药物地塞米松干预48 h后,采用乳酸脱氢酶分析法测定细胞活性,原位缺口末端标记技术(即TUNEL法)观察细胞凋亡情况,5’-溴脱氧尿嘧啶核苷掺入法鉴定细胞增殖状况。 结果与结论：1,10,100 μmol浓度地塞米松干预明显减少NG2细胞数,并显著增加TUNEL阳性细胞率,明显减少BrdU阳性细胞率。结果可见高浓度糖皮质激素能抑制NG2细胞分裂增殖,并诱导细胞凋亡,从而明显减少NG2细胞数。     

Regionally specific properties of midbrain glia: I. Interactions with midbrain neurons

Regional astrocyte cultures were obtained by dissecting and dissociating medial and lateral sectors of the midbrain from 14-day Swiss mouse embryos. Once confluent, these cultures were tested by glial fibrillary acidic protein (GFAP) immunocytochemistry to confirm their astrocyte composition and for 2′-3′ cyclic nucleotide 3′-phosphohydrolase (CNPase) and microtubule-associated protein 2 (MAP₂) immunocytochemistry to rule out oligodendroglial and neuronal components, respectively. In confluent astrocyte cultures from either sector, virtually all cells were GFAP-positive elements, most of which were flat cells accompanied by smaller numbers of flat cells with processes. Confluent astrocyte cultures, derived from medial (M) or lateral (L) sectors, were used as substrata for culturing dissociated cells from medial (m) or lateral (1) sectors of 14-day embryonic midbrains. Fixed cocultures (LI, Lm, Mm, MI) were stained with an anti-MAP₂ antibody to verify neuronal aggregation and neuritic morphology. In spite of the morphological constancy of glia substrata at plating, MAP₂-positive cells in cocultures showed differences in the aggregation of somata and in the length, caliber, and branching of neurites. These differences, which depend mostly on the sector of origin of astrocytes, suggest that the substrata may differ in adhesiveness and/or growth-promoting vs. growth-interfering properties. Together with evidence for sectorial heterogeneity in brainstem radial glia, the present results raise the possibility that cultured astrocytes have properties that reflect the roles played by their parent radial glia in the developing brain. © 1995 Wiley-Liss, Inc.     

Glia cells in amyotrophic lateral sclerosis: New clues to understanding an old disease?

In classic neurodegenerative diseases such as amyotrophic lateral sclerosis (ALS), the pathogenic concept of a cell-autonomous disease of motor neurons has been challenged increasingly in recent years. Macro- and microglial cells have come to the forefront for their role in multistep degenerative processes in ALS and respective disease models. The activation of astroglial and microglial cells occurs early in the pathogenesis of the disease and seems to greatly influence disease onset and promotion. The role of oligodendrocytes and Schwann cells remains elusive. In this review we highlight the impact of nonneuronal cells in ALS pathology. We discuss diverse glial membrane proteins that are necessary to control neuronal activity and neuronal cell survival, and summarize the contribution of these proteins to motor neuron death in ALS. We also describe recently discovered glial mechanisms that promote motor neuron degeneration using state-of-the-art genetic mouse technology. Finally, we provide an outlook on the extent to which these new pathomechanistic insights may offer novel therapeutic approaches.