Neurons in lamina of mouse superior colliculus are selective for direction

An electrophysiology study led by researchers at Northwestern University has established that neurons in the most superficial lamina of the mouse superior colliculus (SC) are highly selective for stimulus direction. The original goal of the study was to characterize response properties of the neurons and define the receptive fields in the most superficial lamina of the mouse SC, which is not as commonly studied as other structures but is known to receive input from the retina for visual processing. With the results, the researchers hope that their discovery is one more step taken towards understanding signal transformation in the early visual system.

For all the experiments conducted during this study, in order to visualize the neural activity of the superficial layer of the SC, including the densely packed superficial lamina of the stratum griseum superficiale (sSGS), the researchers decided to employ in vivo two photon calcium imaging along with the calcium indicator Cal-520 as a fluorophobe. Before using Cal-520 for the extent of their project, the researchers had to design an initial experiment that could confirm that Cal-520 was compatible with their goal of detecting and characterizing neural activity. To address this matter, their first loading of Cal-520 was injected into the sSGS by glass pipette, and read simultaneously with imaging and cell-attached recordings while a visual stimulus of a flashing spot was applied. The resulting graphs were then compared for matching number of spikes and fluorescent signal changes to validate Cal-520's sufficient calcium response. Since both recordings had similar shape and size, the researchers could conclude that Cal-520 was a reliable indicator for measuring the response properties of neurons in the sSGS and surrounding SC.

This outcome is aligned with the knowledge that Cal-520 was optimized to exhibit high signal to noise ratio, which renders it ideal for use in two photon microscopy. Cal-520's improved intracellular retention enhances the sensitivity and stability of its signal, which is why it's a simple and time-saving fluorescent probe valuable for neural imaging and any other fluorescence application.

References

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1. Samsoon Inayat, Jad Barchini, Hui Chen, Liang Feng, Xiaorong Liu, and Jianhua Cang. Neurons in the Most Superficial Lamina of the Mouse Superior Colliculus Are Highly Selective for Stimulus Direction. The Journal of Neuroscience, 20 May 2015, 35(20): 7992-8003; doi: 10.1523/JNEUROSCI.0173-15.2015
2. Cal-520^®, AM. AAT Bioquest, n.d. Web. 29 June 2016