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Ionic dynamics and plasticity in developing neuronal networks

Periodic Report Summary 2 - IONDYNDEV (Ionic dynamics and plasticity in developing neuronal networks)

Ionic gradients are a fundamental feature of the nervous system and its development. They are established by the actions of ion pumps, transporters and channel proteins that reside in the membrane of cells. Maintaining these gradients is a prerequisite for generating fluxes of ions, which in turn drive cellular processes. Ion regulatory mechanisms can differ between cell types and changes in a cell’s intracellular ion composition have been implicated in multiple processes in the developing brain, from cell proliferation, to process outgrowth and the refinement of synaptic circuits. On a fast timescale for example, brief elevations in intracellular calcium have been shown to regulate dendritic growth and the stabilisation of synapses. Changes to other ions have received much less attention, but there is an emerging realisation that ion concentrations can exhibit a range of temporal and spatial dynamics, which would make them well-placed to drive a variety of developmental processes. This Project focuses upon two key ions: chloride ions (Cl-) and hydrogen ions (H+), which can exhibit intracellular changes over a range of timescales, from seconds to days. To advance our understanding of these ions during neuronal development, we are using approaches that enable us to dissect their behaviour and functions in intact neuronal circuits. At the mid-point of this Project, we have made significant progress towards the research objectives. A major achievement is that we have optimised new methods for measuring and manipulating intracellular chloride and hydrogen ions with excellent spatial and temporal control, and in a manner that is effective across different cell types. This is enabling us to address the central aims, which are to examine the nature and significance of intracellular ion dynamics in neural progenitor cells and different cell types in the nervous system. The work so far has resulted in the publication of a series of primary research articles in scientific journals. First, we have developed methods for optically monitoring and imaging neural progenitor cells in intact brain preparations. Second, we have shown that the two major cell types of the central nervous system, neurons and astrocytes, exhibit fundamentally different ion dynamics. Third, we have shown that developmental differences in intracellular ion homeostasis are critical for the proper emergence of synaptic connectivity. Fourth, we have published evidence of a novel molecular mechanism by which neurons are able to regulate their intracellular chloride. In the remainder of the Project, we will focus on whether our observations hold across different cell types and the molecular mechanisms that underpin the intracellular ion dynamics that we have observed. For example, we plan to investigate whether the chloride and hydrogen ion dynamics that we have observed in one type of progenitor cell, are also present in other types of neuronal progenitor cells. We are also dissecting the molecular mechanisms that underlie these ionic changes and are examining why neighbouring cells in the same region of the brain might exhibit distinct patterns of intracellular chloride dynamics.