Emergent dynamics in an astrocyte-neuronal network coupledvianitric oxide.

In the brain, both neurons and glial cells work in conjunction with each other during information processing. Stimulation of neurons can induce calcium oscillations in astrocytes which in turn can affect neuronal calcium dynamics. The 'glissandi' effect is one such phenomenon, associated with a decrease in infraslow fluctuations, in which synchronized calcium oscillations propagate as a wave in hundreds of astrocytes. Nitric oxide molecules released from the astrocytes contribute to synaptic functions based on the underlying astrocyte-neuron interaction network. In this study, by defining an astrocyte-neuronal (A-N) calcium unit as an integrated circuit of one neuron and one astrocyte, we developed a minimal model of neuronal stimulus-dependent and NO-mediated emergence of calcium waves in astrocytes. Incorporating inter-unit communicationviaNO molecules, a coupled network of 1000 such A-N calcium units is developed in which multiple stable regimes were found to emerge in astrocytes. We examined the ranges of neuronal stimulus strength and the coupling strength between A-N calcium units that give rise to such dynamical behaviors. We also report that there exists a range of coupling strength, wherein units not receiving stimulus also start showing oscillations and become synchronized. Our results support the hypothesis that glissandi-like phenomena exhibiting synchronized calcium oscillations in astrocytes help in efficient synaptic transmission by reducing the energy demand of the process.