Molecular approaches for manipulating astrocytic signaling in vivo

Astrocytes are the predominant glial type in the central nervous system and play important roles in assisting neuronal function and network activity. Astrocytes exhibit complex signaling systems that are essential for their normal function and the homeostasis of the neural network. Altered signaling in astrocytes is closely associated with neurological and psychiatric diseases, suggesting tremendous therapeutic potential of these cells. To further understand astrocyte function in health and disease, it is important to study astrocytic signaling in vivo. In this review, we discuss molecular tools that enable the selective manipulation of astrocytic signaling, including the tools to selectively activate and inactivate astrocyte signaling in vivo. Lastly, we highlight a few tools in development that present strong potential for advancing our understanding of the role of astrocytes in physiology, behavior, and pathology

Intracellular Astrocyte Calcium Waves In Situ Increase the Frequency of Spontaneous AMPA Receptor Currents in CA1 Pyramidal Neurons

Spontaneous neurotransmitter release and activation of group I metabotropic glutamate receptors (mGluRs) each play a role in the plasticity of neuronal synapses. Astrocytes may contribute to short- and long-term synaptic changes by signaling to neurons via these processes. Spontaneous whole-cell AMPA receptor (AMPAR) currents were recorded in CA1 pyramidal cell

Astrocyte Calcium Signaling: From Observations to Functions and the Challenges Therein

We provide an overview of recent progress on the study of astrocyte intracellular Ca2+ signaling. We consider the methods that have been used to monitor astrocyte Ca2+ signals, the various types of Ca2+ signals that have been discovered (waves, microdomains, and intrinsic fluctuations), the approaches used to broadly trigger and block Ca2+ signals, and, where possible, the proposed and demonstrated physiological roles for astrocyte Ca2+ signals within neuronal microcircuits. Although important progress has been made, we suggest that further detailed work is needed to explore the biophysics and molecular mechanisms of Ca2+ signaling within entire astrocytes, including their fine distal extensions, such as processes that interact spatially with neurons and blood vessels. Improved methods are also needed to mimic and block molecularly defined types of Ca2+ signals within genetically specified populations of astrocytes. Moreover, it will be essential to study astrocyte Ca2+ activity in vivo to distinguish between pharmacological and physiological activity, and to study Ca2+ activity in situ to rigorously explore mechanisms. Once methods to reliably measure, mimic, and block specific astrocyte Ca2+ signals with high temporal and spatial precision are available, researchers will be able to carefully explore the correlative and causative roles that Ca2+ signals may play in the functions of astrocytes, blood vessels, neurons, and microcircuits in the healthy and diseased brain

Hippocampal Astrocytes In Situ Respond to Glutamate Released from Synaptic Terminals

A long-standing question in neurobiology is whether astrocytes respond to the neuronal release of neurotransmitter

Retroviral Inhibition of cAMP-Dependent Protein Kinase Inhibits Myelination But Not Schwann Cell Mitosis Stimulated by Interaction with Neurons

Schwann cells are the myelinating glia of the peripheral nervous system. Neuron-Schwann cell contact profoundly affects several aspects of Schwann cell phenotype, including stimulation of mitosis and myelin formation. Many reports suggest that neuronal contact exerts this influence on Schwann cells by elevating Schwann cell cAMP and activating cAMP-dependent protein kinase A (PKA). To elucidate the importance of Schwann cell PKA in neuronal stimulation of Schwann cell mitosis and myelination, the gene encoding the PKA inhibitory protein RIalphaAB or PKIEGFP was delivered to Schwann cells using retroviral vectors. PKA inhibitory retroviral vectors effectively blocked forskolin-stimulated Schwann cell mitosis and morphological change, demonstrating the ability of the vectors to inhibit PKA in infected Schwann cells. Treatment of dorsal root ganglia neuron-Schwann cell cocultures with H-89 (10 microm) or KT5720 (1-10 microm), chemical inhibitors selective for PKA, significantly inhibited neuronal stimulation of Schwann cell mitosis. In contrast, retrovirus-mediated inhibition of Schwann cell PKA had no effect on the ability of neurons to stimulate Schwann cell mitosis. However, markedly fewer myelin segments were formed by Schwann cells expressing PKA inhibitory proteins compared with controls. These results suggest that activation of Schwann cell PKA is required for myelin formation but not for Schwann cell mitosis stimulated by interaction with neurons

Astrocyte IP3R2-dependent Ca2+ signaling is not a major modulator of neuronal pathways governing behavior

Calcium-dependent release of gliotransmitters by astrocytes is reported to play a critical role in synaptic transmission and be necessary for long-term potentiation (LTP), long-term depression (LTD) and other forms of synaptic modulation that are correlates of learning and memory. Further, physiological processes reported to be dependent on Ca2+ fluxes in astrocytes include functional hyperemia, sleep, and regulation of breathing. The preponderance of findings indicate that most, if not all, receptor dependent Ca2+ fluxes within astrocytes are due to release of Ca2+ through IP3 receptor/channels in the endoplasmic reticulum. Findings from several laboratories indicate that astrocytes only express IP3 receptor type 2 (IP3R2) and that a knockout of IP3R2 obliterates the GPCR-dependent astrocytic Ca2+ responses. Assuming that astrocytic Ca2+ fluxes play a critical role in synaptic physiology, it would be predicted that elimination of astrocytic Ca2+ fluxes would lead to marked changes in behavioral tests. Here, we tested this hypothesis by conducting a broad series of behavioral tests that recruited multiple brain regions, on an IP3R2 conditional knockout mouse model. We present the novel finding that behavioral processes are unaffected by lack of astrocyte IP3R-mediated Ca2+ signals. IP3R2 cKO animals display no change in anxiety or depressive behaviors, and no alteration to motor and sensory function. Morris water maze testing, a behavioral correlate of learning and memory, was unaffected by lack of astrocyte IP3R2-mediated Ca2+-signaling. Therefore, in contrast to the prevailing literature, we find that neither receptor-driven astrocyte Ca2+ fluxes nor, by extension, gliotransmission is likely to be a major modulating force on the physiological processes underlying behavior

Implication of Kir4.1 Channel in Excess Potassium Clearance: An In Vivo Study on Anesthetized Glial-Conditional Kir4.1 Knock-Out Mice

The

Conditional Knock-Out of Kir4.1 Leads to Glial Membrane Depolarization, Inhibition of Potassium and Glutamate Uptake, and Enhanced Short-Term Synaptic Potentiation

During neuronal activity, extracellular potassium concentration ([

New onshore insights into the role of structural inheritance during Mesozoic opening of the Inner Moray Firth Basin, Scotland

The Inner Moray Firth Basin (IMFB) forms the western arm of the North Sea trilete rift system that initiated mainly during the Late Jurassic–Early Cretaceous with the widespread development of major NE–SW-trending dip-slip growth faults. The IMFB is superimposed over the southern part of the older Devonian Orcadian Basin. The potential influence of older rift-related faults on the kinematics of later Mesozoic basin opening has received little attention, partly owing to the poor resolution of offshore seismic reflection data at depth. New field observations augmented by drone photography and photogrammetry, coupled with U–Pb geochronology, have been used to explore the kinematic history of faulting in onshore exposures along the southern IMFB margin. Dip-slip north–south- to NNE–SSW-striking Devonian growth faults are recognized that have undergone later dextral reactivation during NNW–SSE extension. The U–Pb calcite dating of a sample from the synkinematic calcite veins associated with this later episode shows that the age of fault reactivation is 130.99  ±  4.60 Ma (Hauterivian). The recognition of dextral-oblique Early Cretaceous reactivation of faults related to the underlying and older Orcadian Basin highlights the importance of structural inheritance in controlling basin- to sub-basin-scale architectures and how this influences the kinematics of IMFB rifting

Combination of immunocytochemistry and radioligand receptor assay to identify beta-adrenergic receptor subtypes on astroglia in vitro

There is an increasing need to assess the distribution of receptors for neuroactive substances on specific neural cell types. This study describes the establishment of methodology that combines the quantification of beta-adrenergic receptor subtypes by radioligand binding assays with immunocytochemical analysis of the contribution of astroglia (identified by the presence of glial fibrillary acidic protein) and fibroblasts (identified by the presence of fibronectin) to cultures prepared from neonatal rat cerebral cortex. The effects of subtle changes in culture methodology on the cellular composition of cerebral cortical cultures and the distribution of beta-adrenergic receptor subtypes were examined. The data indicate that (1) a decrease in the density of the initial plating suspension, (2) an increase in the age of the animals, or (3) supplementation of the cortical cell suspension with meningeal fibroblasts all result in an increase in fibronectin staining and a decrease in glial fibrillary acidic protein antibody staining. This change in the cellular composition of the cortical cultures correlated with an increase in the number of beta 2- adrenergic receptors and a corresponding decrease in the number of beta 1-adrenergic receptors. These observations point out the care which must be exercised when preparing primary astroglial cultures of sufficient purity for large-scale biochemical and pharmacological studies