Astroglial Wiring is Adding Complexity to Neuroglial Networking

Abstract

Astrocytes are organized as networks of communicating cells due to their high expression level of connexins, the molecular constituents of gap junction channels. Based on their permeability properties for ions and small signaling molecules such astroglial wiring interferes with neuronal activity and survival. In this paper, I identify and discuss which future technical and conceptual progress or advances should be achieved in order to better understand how neuroglial networking contributes to brain functions and dysfunctions.

Keywords: astrocytes; astroglial networks; connexins; gap junctions; glial cells.

Figure 1

Gap junction-mediated communication enlarges the loop of interaction between neurons (blue triangles) and astrocytes (green stars). Two situations are considered: a one-by-one relationship (A) and a networking that includes the propagation of intercellular signals between adjacent astrocytes (B). This later could occur thanks to calcium waves that involve GJCs, although other alternative pathways exist (see Scemes and Giaume, 2006). As a result, a signal triggered in the neuron on the left can affect the activity of a distant neuron on the right.

Figure 2

Diagram representing how the wiring of astrocytes adds more complexity to neuroglial networking. Several situations are considered: from a single one-by-one relationship (A), to a multiple relation with a single neuron that contacts several astrocytes (B) and the reverse situation where several neurons make synapses within an astrocytic domain (C). When considering the gap junction-mediated networking of astrocytes, the number of interactions is largely increased (D). Note that in (D), the interactions illustrated in (B) and those occurring between neurons themselves are not represented. Finally, the interaction between astrocytes and the vascular system are just suggested (gray arrows). The complex interactions illustrated in (D) (black arrows) are expected to affect the well-established role of astrocytic end-feet in the control of blood flow.