Gap Junction-Mediated Astrocytic Networks in the Mouse Barrel Cortex

Abstract

The barrel field of the somatosensory cortex constitutes a well documented example of anatomofunctional compartmentalization and activity-dependent interaction between neurons and astrocytes. In astrocytes, intercellular communication through gap junction channels composed by connexin 43 and 30 underlies a network organization. Immunohistochemical and electrophysiological experiments were undertaken to determine the coupling properties of astrocyte networks in layer IV of the developing barrel cortex. The expression of both connexins was found to be enriched within barrels compared with septa and other cortical layers. Combination of dye-coupling experiments performed with biocytin and immunostaining with specific cell markers demonstrated that astrocytic networks do not involve neurons, oligodendrocytes or NG2 cells. The shape of dye coupling was oval in the barrel cortex whereas it was circular in layer IV outside the barrel field. Two-dimensional analysis of these coupling areas indicated that gap junctional communication was restricted from a barrel to its neighbor. Such enrichment of connexin expression and transversal restriction were not observed in a transgenic mouse lacking the barrel organization, whereas they were both observed in a double-transgenic mouse with restored barrels. Direct observation of sulforhodamine B spread indicated that astrocytes located between two barrels were either weakly or not coupled, whereas coupling within a barrel was oriented toward its center. These observations indicated a preferential orientation of coupling inside the barrels resulting from subpopulations of astrocytes with different coupling properties that contribute to shaping astrocytic networks. Such properties confine intercellular communication in astrocytes within a defined barrel as previously reported for excitatory neuronal circuits.

Astrocytic regulation of cortical UP states

“…Biocytin morphological processing revealed that astrocytes were highly connected, as demonstrated by the spread of biocytin across many astrocytes (51.2 ± 5.0 cells), covering a total area of 65.8 × 10 3 ± 5.6 × 10 3 μm 2 ( Fig. 1E) (n = 12 slices), similar to previous results (24,25).…”

Plasticity of astroglial networks in olfactory glomeruli

“…In the GL, GJC between astrocytes is preferentially confined within OG and thus overlaps neuronal organization. This feature results from at least two astroglial properties: (i) the oriented morphology of glomerular astrocytes processes toward the OG center (7)(8)(9) where most of the GL neuronal transmission occurs, and (ii) the enriched expression of the two astroglial Cxs within functional units, as already reported in the somatosensory cortex (25). In addition, the physical barrier formed by the somata of the juxtaglomerular neurons can also contribute to the gap in Cx expression observed around glomeruli (Fig.…”

Morphological plasticity of astroglia: Understanding synaptic microenvironment

“…Astrocytes are connected through the gap junction molecules connexin 43 (Cx43) and Cx30 (Anders et al, 2014; Chever et al, 2014; Pannasch and Rouach, 2013; Pannasch et al, 2011). Gap junctions might be involved directly or indirectly in synapse‐glia signaling (Houades et al, 2008). Recently, it has been reported that Cx43 mediates synaptic efficacy by setting the levels of synaptic glutamate in mice (Chever et al, 2014).…”