Modeling presynapse-astrocyte interactions
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1
Tampere University of Technology, BioMediTech, Department of Electronics and Communications Engineering, Finland
Astrocytes have gained an increased interest in neuroscience due to their ability to influence synaptic transmission through gliotransmitters. Many studies and models concentrate on tripartite synapses formed by two neurons and an astrocyte. The effects of tripartite synapse on paired pulse facilitation and depression were suggested for example by De Pittá et al. (PLoS Comput. Biol. 2011). In the presented work we concentrated on the pathway from the presynapse to the astrocyte and back to the presynapse. We will investigate what effect the release amount of glutamate after a spike in the presynapse has on the release amount of IP3, calcium and glutamate in the astrocyte.
A version of Tsodyks-Markram presynaptic model is used as described by De Pittá et al. and astrocytic effects as described in the same paper. These effects are applied to spiking neuronal network INEX by Lenk (Lecture Notes in Comput. Sci. 2011). The simulators are combined by modifying values of synaptic strengths (W) in the INEX model according to neurotransmitters released in presynaptic models attached to each synapse. At an event of spike amount U calcium enters the presynaptic terminal and binds to vesicle sensors u. There is an amount of x neurotransmitter present in the presynapse at any given time. Amount of u*x resources are released (RR). Glutamate affects the value U by modifying parameter alpha. Alpha describes the effect of presynaptic glutamate receptors to release probability. U is changed towards alpha depending on glutamate amounts released by astrocyte. INEX parameter W is used for initial U for each synapse and resources released (RR) as weight for spiking synapse. The uptake of glutamate in the synaptic cleft triggers an IP3 increase in the astrocyte which in turn triggers a release of calcium from the endoplasmic reticulum. When the calcium concentration reaches a certain threshold glutamate is released from the astrocyte. The glutamate is detected by the presynapse and the effect decays over time. The glutamate level together with the frequency of occurring spikes affects the release amount RR in the presynapse. We simulated the interaction between one excitatory presynapse and an astrocyte and applied three different spike frequencies from low to high and three different initial excitatory synaptic strengths W.
Low input frequencies show no effect by the astrocytes. In the midrange spike frequencies the astrocyte gets activated and resources released become periodic. In too high frequencies the astrocyte is activated at the beginning. However, since the IP3 and calcium never fall below the threshold again, no more astrocyte effect is visible. To summarize, the results show that steady state input of spikes can lead to periodic output of the synapse. The periodical output is dependent of initial resources released level and frequency of spiking.
Acknowledgements
This research has been supported by the 3DNeuroN project in the European Union’s Seventh Framework Programme, Future and Emerging Technologies, grant agreement no296590.
References
Lenk, K. (2011). “A Simple Phenomenological Neuronal Model with Inhibitory and Excitatory Synapses,” in Advances in Nonlinear Speech Processing, ed. Travieso-González, C. M. and Alonso-Hernández, J. B. 232-238. doi: 10.1007/978-3-642-25020-0_30
De Pittà M., Volman V., Berry H., Ben-Jacob E. (2011). A tale of two stories: astrocyte regulation of synaptic depression and facilitation. PLoS Comput. Biol. 7:e1002293 10.1371/journal.pcbi.1002293
Keywords:
neuronal network model,
Astrocytes,
tripartite synapse,
Calcium,
Glutamate
Conference:
Neuroinformatics 2015, Cairns, Australia, 20 Aug - 22 Aug, 2015.
Presentation Type:
Poster, to be considered for oral presentation
Topic:
Computational neuroscience
Citation:
Räisänen
EA,
Hyttinen
JA and
Lenk
K
(2015). Modeling presynapse-astrocyte interactions.
Front. Neurosci.
Conference Abstract:
Neuroinformatics 2015.
doi: 10.3389/conf.fnins.2015.91.00036
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Received:
31 Mar 2015;
Published Online:
05 Aug 2015.
*
Correspondence:
Miss. Kerstin Lenk, Tampere University of Technology, BioMediTech, Department of Electronics and Communications Engineering, Tampere, Finland, lenk.kerstin@gmail.com