Confocal Imaging and k-Means Clustering of GABA and mGluR Mediated Modulation of Ca Spiking in Hippocampal Neurons.

Imaging cytosolic calcium in neurons is emerging as a new tool in neurological disease diagnosis, drug screening, and toxicity testing. Ca oscillation signatures show a significant variation depending on GPCR targeting agonists. Quantification of Ca spike trains in ligand induced Ca oscillations remains challenging due to their inherent heterogeneity in primary culture. Moreover, there is no framework available for identification of optimal number of clusters and distance metric to cluster Ca spike trains. Using quantitative confocal imaging and clustering analysis, we show the characterization of Ca spiking in GPCR targeting drug-treated primary culture of hippocampal neurons. A systematic framework for selection of the clustering method instead of an intuition-based method was used to optimize the cluster number and distance metric. The results discern neurons with diverse Ca response patterns, including higher amplitude fast spiking and lower spiking responses, and their relative percentage in a neuron population in absence and presence of GPCR-targeted drugs. The proposed framework was employed to show that the  clustering pattern of Ca spiking can be controlled using GABA and mGluR targeting drugs. This approach can be used for unbiased measurement of neural activity and identification of spiking population with varying amplitude and frequencies, providing a platform for high-content drug screening.