Nonlinear gap junctions enable long-distance propagation of pulsating calcium waves in astrocyte networks.

A new paradigm has recently emerged in brain science whereby communications between glial cells and neuron-glia interactions should be considered together with neurons and their networks to understand higher brain functions. In particular, astrocytes, the main type of glial cells in the cortex, have been shown to communicate with neurons and with each other. They are thought to form a gap-junction-coupled syncytium supporting cell-cell communication via propagating Ca(2+) waves. An identified mode of propagation is based on cytoplasm-to-cytoplasm transport of inositol trisphosphate (IP(3)) through gap junctions that locally trigger Ca(2+) pulses via IP(3)-dependent Ca(2+)-induced Ca(2+) release. It is, however, currently unknown whether this intracellular route is able to support the propagation of long-distance regenerative Ca(2+) waves or is restricted to short-distance signaling. Furthermore, the influence of the intracellular signaling dynamics on intercellular propagation remains to be understood. In this work, we propose a model of the gap-junctional route for intercellular Ca(2+) wave propagation in astrocytes. Our model yields two major predictions. First, we show that long-distance regenerative signaling requires nonlinear coupling in the gap junctions. Second, we show that even with nonlinear gap junctions, long-distance regenerative signaling is favored when the internal Ca(2+) dynamics implements frequency modulation-encoding oscillations with pulsating dynamics, while amplitude modulation-encoding dynamics tends to restrict the propagation range. As a result, spatially heterogeneous molecular properties and/or weak couplings are shown to give rise to rich spatiotemporal dynamics that support complex propagation behaviors. These results shed new light on the mechanisms implicated in the propagation of Ca(2+) waves across astrocytes and the precise conditions under which glial cells may participate in information processing in the brain.

Erratum to: Glutamate regulation of calcium and IP(3) oscillating and pulsating dynamics in astrocytes.

[This corrects the article DOI: 10.1007/s10867-009-9155-y.].

Glutamate regulation of calcium and IP3 oscillating and pulsating dynamics in astrocytes.

Recent years have witnessed an increasing interest in neuron-glia communication. This interest stems from the realization that glia participate in cognitive functions and information processing and are involved in many brain disorders and neurodegenerative diseases. An important process in neuron-glia communications is astrocyte encoding of synaptic information transfer-the modulation of intracellular calcium (Ca(2+)) dynamics in astrocytes in response to synaptic activity. Here, we derive and investigate a concise mathematical model for glutamate-induced astrocytic intracellular Ca(2+) dynamics that captures the essential biochemical features of the regulatory pathway of inositol 1,4,5-trisphosphate (IP(3)). Starting from the well-known two-variable (intracellular Ca(2+) and inactive IP(3) receptors) Li-Rinzel model for calcium-induced calcium release, we incorporate the regulation of IP(3) production and phosphorylation. Doing so, we extend it to a three-variable model (which we refer to as the ChI model) that could account for Ca(2+) oscillations with endogenous IP(3) metabolism. This ChI model is then further extended into the G-ChI model to include regulation of IP(3) production by external glutamate signals. Compared with previous similar models, our three-variable models include a more realistic description of IP(3) production and degradation pathways, lumping together their essential nonlinearities within a concise formulation. Using bifurcation analysis and time simulations, we demonstrate the existence of new putative dynamical features. The cross-couplings between IP(3) and Ca(2+) pathways endow the system with self-consistent oscillatory properties and favor mixed frequency-amplitude encoding modes over pure amplitude-modulation ones. These and additional results of our model are in general agreement with available experimental data and may have important implications for the role of astrocytes in the synaptic transfer of information.

Silver halide photonic crystal fibers for the middle infrared.

Photonic crystal fibers are normally holey silica fibers, which are opaque in the mid- and far-infrared. We have fabricated novel fibers by multiple extrusions of silver halide crystalline materials, which are highly transparent in the mid-infrared. These fibers are composed of two solid materials; The core consists of pure AgBr, and the cladding includes AgCl fiberoptic elements arranged in two concentric hexagonal rings around the core. Flexible fibers of outer diameter 1 mm and length of approximately 1 m were fabricated, and their optical properties were measured. These fibers exhibited core-clad behavior and would be extremely useful for IR laser power transmission, IR radiometry, and IR spectroscopy.