GLIA

Retinal gliosis is characterized by biochemical and physiological changes that often lead to Müller glia proliferation and hypertrophy and is a feature of many neuro‐degenerative and inflammatory diseases such as proliferative vitreoretinopathy (PVR). Although Müller glia are known to release inflammatory factors and cytokines, it is not clear whether cytokine production by these cells mirrors the pattern of factors present in the gliotic retina. Lysates from normal cadaveric retina and gliotic retinal specimens from patients undergoing retinectomy for treatment of PVR, the Müller cell line MIO‐M1 and four human Müller glial cell preparations isolated from normal retina were examined for their expression of cytokines and inflammatory factors using semi‐quantitative dot blot antibody arrays and quantitative arrays. Comparative analysis of the expression of inflammatory factors showed that in comparison with normal retina, gliotic retina exhibited greater than twofold increase in 24/102 factors examined by semiquantitative arrays, and a significant increase in 19 out of 27 factors assessed by quantitative methods (P < 0.05 to P < 0.001). It was observed that with the exception of some chemotactic factors, the majority of cytokines and inflammatory factors were produced by Müller glia in vitro and included G‐CSF, MCP‐1, PDGF‐bb, RANTES, VEGF, and TGFβ2. These results showed that a large number of inflammatory factors expressed by Müller glia in vitro are upregulated in the gliotic retina, suggesting that targeting the production of inflammatory factors by Müller glia may constitute a valid approach to prevent neural damage during retinal gliosis and this merits further investigations. GLIA 2016;64:495–506

We studied the effects of olfactory ensheathing cells (OECs) transplanted in a photochemical spinal cord injury in adult rats. After dorsal laminectomy at T8 vertebra, subjacent spinal cord was bathed with rose Bengal for 10 min and illuminated with visible light by means of an optic fiber connected to a halogen lamp for 2.5 min at maximal intensity of 8 kLux. Eight injured rats received a suspension of OECs in DMEM, and another eight rats received DMEM alone. Locomotor ability scored by the BBB scale, pain sensibility by the plantar algesimetry test, and motor‐ and somatosensory‐evoked potentials by electrophysiological techniques were evaluated for 3 months postsurgery. Finally, all rats were perfused with paraformaldehyde and transverse sections from the spinal cord segment at the lesion site were immunostained against GFAP. Area of the preserved spinal cord parenchyma was measured from the GFAP‐immunolabeled cord sections. The BBB score and the amplitude of motor‐ and somatosensory‐evoked potentials were higher in OECs‐transplanted rats than in DMEM‐injected animals throughout follow‐up, whereas the withdrawal response to heat noxious stimulus was lower in OEC‐ than in DMEM‐injected rats. The area of preserved spinal cord was significantly larger in OECs‐transplanted rats than in DMEM‐injected animals. These results indicate that OECs promote functional and morphological preservation of the spinal cord after photochemical injury. GLIA 42:275–286, 2003. © 2003 Wiley‐Liss, Inc.

Olfactory ensheathing cells (OECs) may support axonal regrowth, and thus might be a viable treatment for spinal cord injury (SCI); however, peripherally– derived OECs remain untested in most animal models of SCI. We have transplanted OECs from the lamina propria (LP) of mice expressing green fluorescent protein (GFP) in all cell types into immunosuppressed rats with cervical or lumbar dorsal root injuries. LP‐OECs were deposited into either the dorsal root ganglion (DRG), intact or injured dorsal roots, or the dorsal columns via the dorsal root entry zone (DREZ). LP‐OECs injected into the DRG or dorsal root migrated centripetally, and migration was more extensive in the injured root than in the intact root. These peripherally deposited OECs migrated within the PNS but did not cross the DREZ; similarly, large‐ or small‐caliber primary afferents were not seen to regenerate across the DREZ. LP‐OEC deposition into the dorsal columns via the DREZ resulted in a laminin‐rich injection track: due to the pipette trajectory, this track pierced the glia limitans at the DREZ. OECs migrated centrifugally through this track, but did not traverse the DREZ; axons entered the spinal cord via this track, but were not seen to reenter CNS tissue. We found a preferential association between CGRP‐positive small‐ to medium‐diameter afferents and OEC deposits in injured dorsal roots as well as within the spinal cord. In the cord, OEC deposition resulted in increased angiogenesis and altered astrocyte alignment. These data are the first to demonstrate interactions between sensory axons and peripherally– derived OECs following dorsal root injury. © 2004 Wiley‐Liss, Inc.

It is becoming increasingly clear that astrocytes play very dynamic and interactive roles that are important for the normal functioning of the central nervous system. In culture, astrocytes express many receptors coupled to increases in intracellular calcium ([Ca²⁺]_i). In vivo, it is likely that these receptors are important for the modulation of astrocytic functions such as the uptake of neurotransmitters and ions. Currently, however, very little is known about the expression or stimulation of such astrocytic receptors in vivo. To address this issue, confocal microscopy and calcium sensitive fluorescent dyes were used to examine the dynamic changes in astrocytic [Ca²⁺]_i, within acutely isolated hippocampal slices. Astrocytes were subsequently identified by immunocytochemistry for glial fibrillary acidic protein. In this paper, we present data indicating that hippocampal astrocytes in situ respond to glutamate, kainate, α‐amino‐3‐hydroxy‐5‐methylisoxazole‐4‐propionic acid (AMPA), 1‐aminocyclopentane‐trans‐1,3‐dicarboxylic acid (t‐ACPD), N‐methyl‐D‐aspartate (NMDA), and depolarization with increases in [Ca²⁺]_i. The increases in [Ca²⁺]_i occurred in both the astrocytic cell bodies and the processes. Temporally the changes in [Ca²⁺]_i were very dynamic, and various patterns ranging from sustained elevations to oscillations of [Ca²⁺]_i were observed. Individual astrocytes responded to neuroligands selective for both ionotropic and metabotropic glutamate receptors with increases in [Ca²⁺]_i. These findings indicate that astrocytes in vivo contain glutamatergic receptors coupled to increases in [C²⁺]_i and are able to respond to neuronally released neurotransmitters. (c) 1995 Wiley‐Liss, Inc.

Astrocytes are found throughout the central nervous system. They interact closely with surrounding structures, their processes contributing to the glia limitans of the neural tube, and to the glial investment of blood vessels, and of the somas, axons, and synaptic structures of neurones. This paper presents evidence that astrocytes in the central nervous system also interact with each other in a dual way, adhering to their neighbours via their processes, and repelling the somas of those neighbours. We suggest that this interaction, which has been termed contact spacing, distributes astrocytes through the central nervous system, and forms the basis of their structural role.

Stimulation‐evoked transient changes in extracellular potassium ([K⁺]_e) and pH (pH_e) were studied in the neonatal rat spinal cords isolated from 3–13‐day‐old pups. In unstimulated pups the [K⁺]_e baseline was elevated and pH_e was more acid than that in Ringer's solution (3.5 mM K⁺, pH 7.3–7.35). The [K⁺]_e and pH_e in 3–6‐day‐old pups was 3.91 ± 0.12 mM and pH_e 7.19 ± 0.01, respectively, while in 10–13‐day‐old pups it was 4.35 ± 0.15 mM and 7.11 ± 0.01, respectively. The [K⁺]_e changes evoked in the dorsal horn by a single electrical stimulus were as large as 1.5–2.5 mM. Such changes in [K⁺]_e are evoked in the adult rat spinal cord with stimulation at a frequency of 10–30 Hz. The maximal changes of 2.1–6.5 mM were found at a stimulation frequency of 10 Hz in 3–6‐day‐old animals. In older animals the [K⁺]_e changes progressively decreased. The poststimulation K⁺‐undershoot was found after a single stimulus as well as after repetitive stimulation.

In 3–8‐day‐old pups, the stimulation evoked an alkaline shift, which was followed by a smaller poststimulation acid shift when the stimulation was discontinued. In pups 3–4‐days‐old the stimulation evoked the greatest alkaline shifts, i.e., by as much as 0.05 pH units after a single pulse and by about 0.1 pH units during stimulation at a frequency of 10 Hz. In 5–8‐day‐old pups, the alkaline shift became smaller and the poststimulation acid shift increased. Stimulation in 10–13‐day‐old pups produced an acid shift of 0.03–0.07 pH units, which was preceded by a scarcely discernible alkaline shift. MgCl₂ (20 mM) reversibly reduced the alkaline but not the acid shifts by 50–60%. Bath application of the carbonic anhydrase inhibitor acetazolamide had no effect on the alkaline shift, while the acid shift decreased by 70–80%. The superfusion of the cord with 10 mM KCl resulted in acid shifts of 0.10–0.14 pH units.

We conclude that the [K⁺]_e ceiling level and the character of pH_e transients in the spinal cord are closely related to gliogenesis. Our results suggest that glial cells buffer the activity‐related [K⁺]_e increase and alkaline pH_e shifts in the extracellular space.

The morphology of glial cells in the intact rat optic nerve, a central nervous system (CNS) white matter tract, was analysed by filling over 500 macroglial cells intracellularly with horseradish peroxidase (HRP) or Lucifer yellow (LY). Two main cell types were distinguished: fibrous astrocytes and cells presumed to be oligodendrocytes. Intracellularly stained astrocytes were highly complex, with 50–60 long branching processes which passed radially from the cell body and terminated in end‐feet at the pial surface or on blood vessels; some processes ended freely in the nerve parenchyma. Astrocytes filled with LY were usually dye‐coupled to other astrocytes after the first week of life. Filled oligodendrocytes had a unique appearance that unmistakably distinguished them from astrocytes and were occasionally dye‐coupled to nearby oligodendrocytes. These cells had 20–30 longitudinally oriented processes 150–200 μm long, which passed exclusively along the long axis of the nerve parallel to axons; the longitudinal processes were connected to the cell body by thin branches 15–30 μm long. The longitudinal processes probably represent the tongue processes of the internodal myelin sheaths, and thus each oligodendrocyte appears to myelinate 20–30 axons with sheaths that are 150–200 μm in length.

It is becoming apparent that astrocytes carry out a large number of different functions in brain and are able to modify their characteristics throughout life, that is they exhibit a high degree of plasticity in their phenotype. For example, the morphology of astrocytes changes markedly during neuronal migration, maturation, and degeneration. It is conceivable that these cells must constantly adjust their abilities to meet changes in brain environment. Several examples of astrocytic plasticity are presented in this review. First, the ability of astrocytes to recognize neuronal signals can change qualitatively as well as quantitatively; evidence suggests that the expression of glial receptors may be developmentally regulated by both intrinsic and extrinsic signals. Second, the expression of adrenergic receptors by astrocytes in adult brain can change in response to neuronal degeneration. The up‐regulation of β‐adrenergic receptors in this case suggests that these receptors play a role in function of reactive astrocytes. Finally, glial morphology can be reciprocally regulated by neurotransmitters such as norepinephrine and glutamate. This reciprocal regulation may be significant since both ß‐adrenergic receptors and glutamate transporters are found predominantly in astrocytes in the brain. The change in glial morphology may also affect neuronal activity by changing the volume of the extracellular space. © 1994 Wiley‐Liss, Inc.

Accumulating evidence has demonstrated the existence of bidirectional communication between glial cells and neurons, indicating an important active role of glia in the physiology of the nervous system. Neurotransmitters released by presynaptic terminals during synaptic activity increase intracellular Ca²⁺ concentration in adjacent glial cells. In turn, activated glia may release different transmitters that can feed back to neuronal synaptic elements, regulating the postsynaptic neuronal excitability and modulating neurotransmitter release from presynaptic terminals. As a consequence of this evidence, a new concept of the synaptic physiology, the tripartite synapse, has been proposed, in which glial cells play an active role as dynamic regulatory elements in neurotransmission. In the present article we review evidence showing the ability of astrocytes to modulate synaptic transmission directly, with the focus on studies performed on cell culture preparations, which have been proved extremely useful in the characterization of molecular and cellular processes involved in astrocyte‐mediated neuromodulation. © 2004 Wiley‐Liss, Inc.