SynapShot Unveiled: Observing the Processes of Memory and Cognition in Real Time

SynapShot, developed by an international research team, marks a major advancement in neuroscience by enabling real-time, live observation of synaptic changes in the brain.

The human brain contains approximately 86 billion neurons and 600 trillion synapses that exchange signals between the neurons to help us control the various functions of the brain including cognition, emotion, and memory. Interestingly, the number of synapses decrease with age or as a result of diseases like Alzheimer’sAlzheimer's disease is a disease that attacks the brain, causing a decline in mental ability that worsens over time. It is the most common form of dementia and accounts for 60 to 80 percent of dementia cases. There is no current cure for Alzheimer's disease, but there are medications that can help ease the symptoms.” data-gt-translate-attributes=”[{“attribute”:”data-cmtooltip”, “format”:”html”}]” tabindex=”0″ role=”link”>Alzheimer’s, and research on synapses thus attracts a lot of attention. However, limitations have existed in observing the dynamics of synapseA synapse is a specialized junction between nerve cells that allows for the transfer of electrical or chemical signals, through the release of neurotransmitters by the presynaptic neuron and the binding of receptors on the postsynaptic neuron. It plays a key role in communication between neurons and in various physiological processes including perception, movement, and memory.” data-gt-translate-attributes=”[{“attribute”:”data-cmtooltip”, “format”:”html”}]” tabindex=”0″ role=”link”>synapse structures in real-time.

Figure 1. To observe dynamically changing synapses, dimerization-dependent fluorescent protein (ddFP) was expressed to observe flourescent signals upon synapse formation as ddFP enables fluorescence detection through reversible binding to pre- and postsynaptic terminals. Credit: KAIST Optogenetics & RNA therapeutics Lab

Breakthrough in Synapse Observation

On January 8, a joint research team led by Professor Won Do Heo from the KAISTEstablished in 1971, the Korea Advanced Institute of Science and Technology (KAIST) is a national research university located in Daedeok Innopolis, Daejeon, South Korea.” data-gt-translate-attributes=”[{“attribute”:”data-cmtooltip”, “format”:”html”}]” tabindex=”0″ role=”link”>KAIST Department of Biological Sciences, Professor Hyung-Bae Kwon from Johns Hopkins School of Medicine, and Professor Sangkyu Lee from the Institute for Basic Science (IBS) revealed that they have developed the world’s first technique to allow real-time observation of synapse formation, extinction, and alterations.

Professor Heo’s team conjugated dimerization-dependent fluorescent proteins (ddFP) to synapses in order to observe the process in which synapses create connections between neurons in real-time. The team named this technique SynapShot, by combining the words ‘synapse’ and snapshot’, and successfully tracked and observed the live formation and extinction processes of synapses as well as their dynamic changes.

Figure 2. Microscopic photos observed through changes of the flourescence of the synapse sensor (SynapShot) by cultivating the neurons of an experimental rat and expressing the SynapShot. The changes in the synapse that is created when the pre- and post-synaptic terminals come into contact and the synapse that disappears after a certain period of time are measured by the fluorescence of the SynapShot. Credit: KAIST Optogenetics & RNA therapeutics Lab

Enhancements and Applications of SynapShot

Through a joint research project, the teams led by Professor Heo and Professor Sangkyu Lee at IBS together designed a SynapShot with green and red fluorescence, and were able to easily distinguish the synapse connecting two different neurons. Additionally, by combining an optogenetic technique that can control the function of a molecule using light, the team was able to observe the changes in the synapses while simultaneously inducing certain functions of the neurons using light.

Figure 3. Simultaneous use of green-SynapShot and red-SynapShot to distinguish and observe synapses with one post-terminal and different pre-terminals. Credit: KAIST Optogenetics & RNA therapeutics Lab

Through more joint research with the team led by Professor Hyung-Bae Kwon at the Johns Hopkins School of Medicine, Professor Heo’s team induced several situations on live mice, including visual discrimination training, exercise, and anesthesia, and used SynapShot to observe the changes in the synapses during each situation in real-time. The observations revealed that each synapse could change fairly quickly and dynamically. This was the first-ever case in which the changes in synapses were observed in a live mammal.

Figure 4. Dimer-dependent fluorescent protein (ddFP) exists as a green fluorescent protein as well as a red fluorescent protein, and can be applied together with blue light-activated optogenetic technology. After activating Tropomyosin receptor kinase B (TrkB) by blue light using optogenetic technology, the strengthening of synaptic connections through signals of brain-derived neurotrophic factor is observed using red-SynapShot. Credit: KAIST Optogenetics & RNA therapeutics Lab

Conclusion and Future Prospects

Professor Heo said, “Our group developed SynapShot through a collaboration with domestic and international research teams, and have opened up the possibility for first-hand live observations of the quick and dynamic changes of synapses, which was previously difficult to do. We expect this technique to revolutionize research methodology in the neurological field, and play an important role in brightening the future of brain science.”

Figure 5. Micrographs showing real-time changing synapses in the visual cortex of mice trained through visual training using in vivo imaging techniques such as two-photon microscopy as well as at the cellular level. Credit: KAIST Optogenetics & RNA therapeutics Lab

This research, conducted by co-first authors Seungkyu Son (Ph.D. candidate), Jinsu Lee (Ph.D. candidate), and Dr. Kanghoon Jung from Johns Hopkins, was published in the online edition of Nature Methods on January 8 under the title “Real-time visualization of structural dynamics of synapses in live cells in vivo”, and will be printed in the February volume.

Reference: “Real-time visualization of structural dynamics of synapses in live cells in vivo” by Seungkyu Son, Kenichiro Nagahama, Jinsu Lee, Kanghoon Jung, Chuljung Kwak, Jihoon Kim, Young Woo Noh, Eunjoon Kim, Sangkyu Lee, Hyung-Bae Kwon and Won Do Heo, 8 January 2024, Nature Methods.
DOI: 10.1038/s41592-023-02122-4

This research was supported by Mid-Sized Research Funds and the Singularity Project from KAIST,  and by IBS.