Spatiotemporal Ca dynamics in neuronal dendrites: Responses and support of travelling waves

Since the onset of intracellular voltage recording techniques, additional methods have been developed and improved upon, such as using voltage-activated dyes, sodium indicators, fluorescent proteins (namely Green fluorescent protein (GFP)), synthetic and genetically encoded indicators, in conjunction with calcium imaging. These techniques have shown that dendrites are not just simple transmission lines, but are sophisticated cellular systems with nonlinear multiscale dynamics that evolve over different timescales and are involved in neural signalling, information processing, along with any underlying computations. Calcium imaging has been important in this regard, having highlighted how reaction-diffusion processes between calcium, buffers and other proteins shape neuronal activity, through dynamical interaction and synaptic plasticity, over different timescales compared to the evolution of electrical signals. To this end, experiments have shown the involvement of calcium and calcium dependent buffers in the response dynamics of neurons. A novel participant during morphological studies, using electron microscopy, fluorescence and immunostaining have illustrated that the Endoplasmic Reticulum (ER) (present in the soma and extends into the distal dendrites) is also a calcium store that can release calcium as puffs through the activation ryanodine receptors into the cytosol of neuronal dendrites. This is called Ca2+ -induced Ca2+ release (CICR), which have been implicated in a number of processes, including the occurrence of calcium waves in the presence of a unsaturated buffer. In this situation, one can observe local changes to the Ca2+ and buffer concentrations in response to some stimuli, such as the presentation of orientated stationary or moving bars or gratings, in a selective fashion through the manifestation of a bias in the resulting calcium concentration in space along the dendrite, that underpins some computation. Studies have shown that Ca2+ plays many important roles in neuronal function and information processing. To better understand the role of Ca2+ , we constructed a computational model of a dendrite with a mechanism that describes CICR in the presence of an unsaturated buffer and study the conditions permitting the occurrence calcium waves and the underlying requirements of timed inputs from CICR. Modeling the heterogeneity of CICR from the endoplasmic reticulum by using a formulation that permits essential dynamics to be analyzed. Using a two-pool model calcium dynamics, we present an analysis of how CICR impacts calcium activity in space in the presence of a calcium buffer and study the potential conditions supporting the propagation of CICR induced Ca2+ waves.