Report

Glutamate-Dependent Neuroglial Calcium Signaling Differs Between Young and Adult Brain

Science  11 Jan 2013:
Vol. 339, Issue 6116, pp. 197-200
DOI: 10.1126/science.1226740

You are currently viewing the abstract.

View Full Text

The Adult Astrocyte Is Different

The concept of the tripartite synapse, whereby astrocytes actively modulate the communication between the pre- and postsynaptic site, is widely accepted. The release of gliotransmitters has been linked to release of Ca from intracellular stores via the activation of astrocytic metabotropic glutamate receptor 5 (mGluR5) by glutamate spillover from synapses. However, nearly all studies on the tripartite synapse have used brain tissue collected from young individuals. Many receptors undergo changes in expression level during development. Sun et al. (p. 197; see the Perspective by Grosche and Reichenbach) applied genomic analysis, electron microscopy, and calcium imaging in slices and in vivo to assess the presence and the functionality of mGluR5 and mGluR3 receptors during postnatal development in human and mouse astrocytes. Astrocytic expression of mGluR5 was lost by the third postnatal week in mice and was not present in human cortical astrocytes, which calls into question the viability of the tripartite synapse model for adult synapses.

Abstract

An extensive literature shows that astrocytes exhibit metabotropic glutamate receptor 5 (mGluR5)–dependent increases in cytosolic calcium ions (Ca2+) in response to glutamatergic transmission and, in turn, modulate neuronal activity by their Ca2+-dependent release of gliotransmitters. These findings, based on studies of young rodents, have led to the concept of the tripartite synapse, in which astrocytes actively participate in neurotransmission. Using genomic analysis, immunoelectron microscopy, and two-photon microscopy of astrocytic Ca2+ signaling in vivo, we found that astrocytic expression of mGluR5 is developmentally regulated and is undetectable after postnatal week 3. In contrast, mGluR3, whose activation inhibits adenylate cyclase but not calcium signaling, was expressed in astrocytes at all developmental stages. Neuroglial signaling in the adult brain may therefore occur in a manner fundamentally distinct from that exhibited during development.

View Full Text

Cited By...