Advances in two photon scanning and scanless microscopy technologies for functional neural circuit imaging

One of the great projects facing modern medicine and biology is to try and understand how the human brain functions. It is such a complex organ that despite all the knowledge that exists, it remains a mystery and continues to draw the focus of the academic community. Intrinsically involved in the understanding of the human brain is grasping the principles that are involved in the processing of information between neural circuits and this has been central to modern neuroscience research. Understanding this process completely would allow researchers to make significant breakthroughs in determining the pathology and potential treatment options of persistent neural diseases such as Alzheimer's Disease. Schultz et al. take a look at the different methods that are currently available for the dense recording of many neurons located within one tissue. The first method is the electrophysiological method.This can be effective in producing accurate images of the brain, but is invasive and can be damaging to the tissues by causing neural inflammation.

Because of the limitations presented by the electrophysiological method, much attention has been paid to the second method: the optical method. This has been lauded because it is non invasive and non-damaging and also because it allows for the spatial location of activity-related signals and can be used in conjunction with genetically targeted co-labelling to aid classification. The Cal-520^® AM calcium indicator is often used in this optical method specifically for this reason. It can be easily and accurately loaded into the cells being studied without damaging the environment around it. This allows it to emit accurate results that researchers know are not interfering with the overall functionality of the cells they are studying.

Within the optical method, the two-photon microscopy is the preferred and most promising method for observing neural activity. However, one of its limitations is the limited amplification of fluorescent signals which makes results less clear than in electrophysiology. Neural activity can be measured with fluorescent indicators that are sensitive to either calcium concentrations or membrane voltages. However, indicators that attempt to measure membrane voltages tend to produce very weak signals. The images produced by measuring calcium are much stronger, and are therefore the preferred method. Specific indicators like Cal-520 AM are making significant strides in increasing the effectiveness of the two photon microscopy method. It glows with an intensity that is almost 100 times stronger than any previous fluorescent indicators. This helps to make up for the fact that results obtained through the optical method tend to be weaker than the electrophysiological method. Because of effective indicators like Cal-520 AM, the optical method is gaining more prominence within the field of neuroscience and is allowing researchers to get a better look at neuronal activity. Further research has been made possible because of the accuracy and intensity of Cal-520 AM, the results of which have significant implications for the understanding of the brain and the potential treatments that can result from this understanding.

References

---

1. Simon R, Caroline Copeland, Amanda Foust, Peter Quicke, Renaud Schuck. Advances in two photon scanning and scanless microscopy technologies for functional neural circuit imaging BioRxiv (2016), doi: https://doi.org/10.1101/036632