Characterization of transgenic mouse lines for selectively targeting satellite glial cells and macrophages in dorsal root ganglia.

The importance of glial cells in the modulation of neuronal processes is now generally accepted. In particular, enormous progress in our understanding of astrocytes and microglia physiology in the central nervous system (CNS) has been made in recent years, due to the development of genetic and molecular toolkits. However, the roles of satellite glial cells (SGCs) and macrophages-the peripheral counterparts of astrocytes and microglia-remain poorly studied despite their involvement in debilitating conditions, such as pain.

Control of aversion by glycine-gated GluN1/GluN3A NMDA receptors in the adult medial habenula.

The unconventional -methyl-d-aspartate (NMDA) receptor subunits GluN3A and GluN3B can, when associated with the other glycine-binding subunit GluN1, generate excitatory conductances purely activated by glycine. However, functional GluN1/GluN3 receptors have not been identified in native adult tissues. We discovered that GluN1/GluN3A receptors are operational in neurons of the mouse adult medial habenula (MHb), an epithalamic area controlling aversive physiological states.

AhR-deficiency as a cause of demyelinating disease and inflammation.

The Aryl hydrocarbon Receptor(AhR) is among the most important receptors which bind pollutants; however it also regulates signaling pathways independently of such exposure. We previously demonstrated that AhR is expressed during development of the central nervous system(CNS) and that its deletion leads to the occurrence of a congenital nystagmus. Objectives of the present study are to decipher the origin of these deficits, and to identify the role of the AhR in the development of the CNS.

Recent molecular approaches to understanding astrocyte function in vivo.

Astrocytes are a predominant glial cell type in the nervous systems, and are becoming recognized as important mediators of normal brain function as well as neurodevelopmental, neurological, and neurodegenerative brain diseases. Although numerous potential mechanisms have been proposed to explain the role of astrocytes in the normal and diseased brain, research into the physiological relevance of these mechanisms in vivo is just beginning. In this review, we will summarize recent developments in innovative and powerful molecular approaches, including knockout mouse models, transgenic mouse models, and astrocyte-targeted gene transfer/expression, which have led to advances in understanding astrocyte biology in vivo that were heretofore inaccessible to experimentation.

New tools for investigating astrocyte-to-neuron communication.

Gray matter protoplasmic astrocytes extend very thin processes and establish close contacts with synapses. It has been suggested that the release of neuroactive gliotransmitters at the tripartite synapse contributes to information processing. However, the concept of calcium (Ca(2+))-dependent gliotransmitter release from astrocytes, and the release mechanisms are being debated.

Modulation of the autonomic nervous system and behaviour by acute glial cell Gq protein-coupled receptor activation in vivo.

Glial fibrillary acidic protein (GFAP)-expressing cells (GFAP(+) glial cells) are the predominant cell type in the central and peripheral nervous systems. Our understanding of the role of GFAP(+) glial cells and their signalling systems in vivo is limited due to our inability to manipulate these cells and their receptors in a cell type-specific and non-invasive manner. To circumvent this limitation, we developed a transgenic mouse line (GFAP-hM3Dq mice) that expresses an engineered Gq protein-coupled receptor (Gq-GPCR) known as hM3Dq DREADD (designer receptor exclusively activated by designer drug) selectively in GFAP(+) glial cells.

Calcium Signaling and Gliotransmission in Normal vs. Reactive Astrocytes.

A prominent area of neuroscience research over the past 20 years has been the acute modulation of neuronal synaptic activity by Ca(2+)-dependent release of the transmitters ATP, D-serine, and glutamate (called gliotransmitters) by astrocytes. Although the physiological relevance of this mechanism is under debate, emerging evidence suggests that there are critical factors in addition to Ca(2+) that are required for gliotransmitters to be released from astrocytes. Interestingly, these factors include activated microglia and the proinflammatory cytokine Tumor Necrosis Factor α (TNFα), chemotactic cytokine Stromal cell-Derived Factor-1α (SDF-1α), and inflammatory mediator prostaglandin E2 (PGE(2)).

Hippocampal short- and long-term plasticity are not modulated by astrocyte Ca2+ signaling.

The concept that astrocytes release neuroactive molecules (gliotransmitters) to affect synaptic transmission has been a paradigm shift in neuroscience research over the past decade. This concept suggests that astrocytes, together with pre- and postsynaptic neuronal elements, make up a functional synapse. Astrocyte release of gliotransmitters (for example, glutamate and adenosine triphosphate) is generally accepted to be a Ca2+-dependent process.

Sorting out astrocyte physiology from pharmacology.

A number of exciting findings have been made in astrocytes during the past 15 years that have led many researchers to redefine how the brain works. Astrocytes are now widely regarded as cells that propagate Ca(2+) over long distances in response to stimulation, and, similar to neurons, release transmitters (called gliotransmitters) in a Ca(2+)-dependent manner to modulate a host of important brain functions. Although these discoveries have been very exciting, it is essential to place them in the proper context of the approaches used to obtain them to determine their relevance to brain physiology.

What is the role of astrocyte calcium in neurophysiology?

Astrocytes comprise approximately half of the volume of the adult mammalian brain and are the primary neuronal structural and trophic supportive elements. Astrocytes are organized into distinct nonoverlapping domains and extend elaborate and dense fine processes that interact intimately with synapses and cerebrovasculature. The recognition in the mid 1990s that astrocytes undergo elevations in intracellular calcium concentration following activation of G protein-coupled receptors by synaptically released neurotransmitters demonstrated not only that astrocytes display a form of excitability but also that astrocytes may be active participants in brain information processing.

Bioluminescent imaging of Ca2+ activity reveals spatiotemporal dynamics in glial networks of dark-adapted mouse retina.

Glial Ca(2+) excitability plays a key role in reciprocal neuron-glia communication. In the retina, neuron-glia signalling is expected to be maximal in the dark, but the glial Ca(2+) signal characteristics under such conditions have not been evaluated. To address this question, we used bioluminescence imaging to monitor spontaneous Ca(2+) changes under dark conditions selectively in Müller cells, the principal retinal glial cells.

Selective stimulation of astrocyte calcium in situ does not affect neuronal excitatory synaptic activity.

Astrocytes are considered the third component of the synapse, responding to neurotransmitter release from synaptic terminals and releasing gliotransmitters--including glutamate--in a Ca(2+)-dependent manner to affect neuronal synaptic activity. Many studies reporting astrocyte-driven neuronal activity have evoked astrocyte Ca(2+) increases by application of endogenous ligands that directly activate neuronal receptors, making astrocyte contribution to neuronal effect(s) difficult to determine. We have made transgenic mice that express a Gq-coupled receptor only in astrocytes to evoke astrocyte Ca(2+) increases using an agonist that does not bind endogenous receptors in brain.

Visualization of local Ca2+ dynamics with genetically encoded bioluminescent reporters.

Measurements of local Ca2+ signalling at different developmental stages and/or in specific cell types is important for understanding aspects of brain functioning. The use of light excitation in fluorescence imaging can cause phototoxicity, photobleaching and auto-fluorescence. In contrast, bioluminescence does not require the input of radiative energy and can therefore be measured over long periods, with very high temporal resolution.

Magnetoencephalographic studies of two cases of diffuse subcortical laminar heterotopia or so-called double cortex.

Two cases (a young male and a girl, suffering intractable epilepsy) of diffuse subcortical laminar heterotopia, or so-called double cortex (DC) have been investigated using magnetoencephalography (MEG). MEG confirmed involvement of both cortices (hetero- and normocortex) in the genesis of interictal spikes, and, according to the heterogeneity of DC syndrome, some differences were observed: spike initiation in the normocortex and latter involvement of the heterotopic cortex in the man, and rather a cancellation in both cortices in the girl. In addition, participation of heterotopic cortex in physiological activities could be demonstrated in the man.

Lysosomal amino acid transporter LYAAT-1 in the rat central nervous system: an in situ hybridization and immunohistochemical study.

A first mammalian lysosomal transporter (LYAAT-1) was recently identified and functionally characterized. Preliminary immunocytochemical data revealed that LYAAT-1 localizes to lysosomes in some neurons. In order to determine whether it is expressed in specific neuron populations and other cell types, and to confirm whether it is localized at the membrane of lysosomes, we used in situ hybridization and immunohistochemistry methods in adult rat central nervous system (CNS).

Ion channel variation causes epilepsies.

The discovery of genetically transmissible form of epilepsy associated with a mutation in a gene that codes for a subunit of a ligand-gated channel shined a new light in this field of neurological diseases. Because this gene (CHRNA4) codes for a neuronal nicotinic acetylcholine receptor subunit, functional studies could be designed to evaluate the alterations caused by this mutation. Since this initial observation, five mutations were identified and determination of their functional properties initiated.

Identification and characterization of a lysosomal transporter for small neutral amino acids.

In eukaryotic cells, lysosomes represent a major site for macromolecule degradation. Hydrolysis products are eventually exported from this acidic organelle into the cytosol through specific transporters. Impairment of this process at either the hydrolysis or the efflux step is responsible of several lysosomal storage diseases.

Expression of FMR1, FXR1, and FXR2 genes in human prenatal tissues.

We analyzed the distribution of FMR1, FXR1, FXR2 mRNA, and FMRP in whole normal human embryos and in the brains of normal and fragile X fetuses. The distributions of mRNA for the 3 genes in normal whole embryos and in the brains of normal male and female carrier fetuses were similar, with large amounts of mRNA in the nervous system and in several non-nervous system tissues. No FMR1 (mRNA and protein) was detected and no evident neuropathologic abnormalities found in the brains of male carrier fetuses, suggesting that the FMR1 product (FMRP) may have no crucial function in early stages of nervous system development.

Localization of mRNA for CHRNA7 in human fetal brain.

The aim of this study was to determine the regional distribution in situ of the mRNA for the alpha 7 subunit of the neuronal nicotinic acetylcholine receptor in human fetal brain. We found high levels of alpha 7 gene expression in nuclei that receive sensory information, such as those of the neocortex and hippocampus, the thalamic nuclei, the reticular thalamic nucleus, the pontine nuclei and the superior olive complex. These data support a possible regulatory function for alpha 7-containing receptors in sensory processing, which may be involved in the pathological physiology of schizophrenia and autism.

Distribution of mRNA for the alpha4 subunit of the nicotinic acetylcholine receptor in the human fetal brain.

Neuronal nicotinic acetylcholine receptors (nAChRs) present in the central nervous system (CNS), are multimeric proteins constituted of two different subunits, alpha and beta, with different subtype arrangements and different pharmacological and functional properties. By in situ hybridization, we studied the distribution of the mRNA for the alpha4 subunit of nAChRs in brains of human 25-week old normal and fragile X fetuses. A strong hybridization signal was detected throughout the thalamus, cortex, pyramidal layer of the Ammon's horn, and the granular layer of the dentate gyrus.