Astrocytes Optimize the Synaptic Transmission of Information

Abstract

Chemical synapses transmit information via the release of neurotransmitter-filled vesicles from the presynaptic terminal. Using computational modeling, we predict that the limited availability of neurotransmitter resources in combination with the spontaneous release of vesicles limits the maximum degree of enhancement of synaptic transmission. This gives rise to an optimal tuning that depends on the number of active zones. There is strong experimental evidence that astrocytes that enwrap synapses can modulate the probabilities of vesicle release through bidirectional signaling and hence regulate synaptic transmission. For low-fidelity hippocampal synapses, which typically have only one or two active zones, the predicted optimal values lie close to those determined by experimentally measured astrocytic feedback, suggesting that astrocytes optimize synaptic transmission of information.

Spatiotemporal characteristics of calcium dynamics in astrocytes

“…1, 37,45,43,35,83,116,78,99 One example of the cross-talk is reflected in adenosine-5Ј-triphosphate ͑ATP͒-mediated calcium waves, which demonstrate the coupling between intracellular calcium dynamics and cell-cell communication via the extracellular space. 1, 37,56 Such waves, which typically decay in time and in space as they propagate, have a maximal propagation range of 200-350 m and a maximal velocity of 15-27 m 2 / s. 15,113,120,82,18 There is substantial evidence that Ca i 2+ waves in astrocytes are mediated by direct coupling between astrocytes via transport through gap junctions 49,105,114,94 and/or by paracrine ATP signaling via the extracellular space.…”

Dynamical patterns of calcium signaling in a functional model of neuron–astrocyte networks

“…The first model of a "dressed neuron" was introduced by Nadkarni and Jung [21,22]. They suggested a model of a neuron in contact with an astrocyte and studied how the release of glutamate during an action potential triggers the calcium dynamics of astrocytes and, in turn, changes the firing pattern of the same neuron Recently, this model was modified in order to describe the relevant details of synaptic neurotransmitter release [23,24].…”

Effects of the flavonoid casticin from Brazilian Croton betulaster in cerebral cortical progenitors in vitro: Direct and indirect action through astrocytes

“…Neuron-astroglia interactions play an important role in aspects of brain development, such as neurogenesis and the determination of the fate of stem cells (Lim and Alvarez-Buylla, 1999;Song et al, 2002;Lie et al, 2005;Ma et al, 2005;Martinez and Gomes, 2005;Johnson et al, 2007;Környei et al, 2007;de Sampaio e Spohr et al, 2008), neuronal migration (Hatten, 2002), axonal growth (Freire et al, 2004;Martinez and Gomes, 2002), synapse formation (Christopherson et al, 2005;Johnson et al, 2007;Nadkarni et al, 2008;Nishida and Okabe 2007;Santello and Volterra, 2009), and glial maturation (Gomes et al, 1999a;de Sampaio e Spohr et al, 2002;Schmid et al, 2003;Sousa et al, 2004;Barnabé-Heider et al, 2005;Patten et al, 2006;Stipursky and Gomes, 2007;Romão et al, 2008). In the mature mammal brain, astrocytes constitute nearly half of the total cells, providing structural, metabolic, and trophic support for neurons.…”