Calcium and chloride dynamics in immature neurons and their role in dendritic growth

Thesis

Activity-dependent dendritic development is an important process in the maturation of neuronal circuits. The precise morphology of a neuron’s dendritic tree dictates which other cells it is able to interact with and how it will receive and process synaptic information. The aim of this Thesis was to investigate the mechanisms by which dendrites grow and, in particular, how changes in intracellular ion concentrations contribute to these mechanisms. One important activity-dependent signal is calcium as it can translate neuronal activity into morphological changes. Despite this, very little is known about calcium signalling during the period of dendritic development. Using single-cell electroporation of immature CA1 hippocampal pyramidal neurons, I characterised the spatial and temporal properties of local calcium transients in growing dendrites. This revealed a high frequency of transients at shaft filopodia and stable branchpoints, but an almost complete absence from the tips of dendritic branches. Another important factor during development is the intracellular chloride concentration because this regulates neuronal excitability. Prematurely lowering intracellular chloride by expressing the chloride co-transporter KCC2 led to less stable dendritic filopodia and stunted dendritic growth. These effects were independent of local calcium signalling and suggested that chloride regulation itself may be fundamental to normal dendritic growth. To examine this further I developed imaging techniques to measure the spatial and temporal dynamics of chloride in growing dendrites. This work revealed a somatodendritic gradient of increasing intracellular chloride, whereby the highest concentrations were found at sites of growth. Further analysis suggested a close link between local chloride regulation and morphological changes. The dendritic tips that exhibited high intracellular chloride levels and the potential to rapidly modulate these levels, also exhibited the greatest morphological dynamics. These findings have important implications for understanding the mechanisms of dendritic growth and establish the spatiotemporal regulation of chloride as a key parameter.

Authors: Wefelmeyer, W

• Publication date: 2010
• Type of award: DPhil
• Level of award: Doctoral
• Awarding institution: University of Oxford
• Language: English
• Keywords: calcium; dendrites; neuroscience; chloride; dendritic development
• Subjects: Neuroscience; Physiology and anatomy; Medical Sciences