Among the main authors of the study there are some young researchers at our University, such as Dr. Jacopo Lamanna – also teacher and coordinator of the Neurobiology of Learning and Memory course, Masters Degree in Psychology, Faculty of Psychology at UniSR – Drs. Maddalena Ripamonti, Gabriella Racchetti and Sara Spadini, and Dr. Mattia Ferro. Dr. Ferro states: “The contents of the Masters Degree in Psychology at San Raffaele University, strongly focused on the study of mind and brain from a psychological and neurobiological point of view, have given me the opportunity to develop and expand knowledge of physiology and biology concerning the nervous system: I believe it is a unique peculiarity offered by this course of study”.
The research, published by Nature Communications unveils for the first time, for now only in a mouse model, the activity of a synaptic circuit: “It’s as if you could finally photograph the activity of synaptic circuits within the brain of a living being, and this with a very high resolution” explains Professor Malgaroli. “The result of our “map” resembles a starry sky, where each star indicates a brain synapse and luminous intensity reflects the level of activity of this synapse”.
Communication between neuronal cells occurs at synaptic level, a microscopic contact point between the pre-synaptic and post-synaptic neurons. When the pre-synaptic neuron receives an electrical signal, it releases a packet of neurotransmitters who send a “message” to the post-synaptic neuron. These neurotransmitter packets are contained in the synaptic vesicles, small spherical organelles, whose fusion with the synapse membrane releases the neurotransmitter. This way, the electrical signal can propagate between neurons, letting the stimulus travel inside the circuit.
A map of activity of the visual cortex synapses activated by displaying the animal to a series of visual stimuli. The color gradation reflects the degree of activity of these synapses in the visual cortex (Area V1, Layer IV). Kind courtesy of the authors.
“The winning idea at the base of our study was to color the interior of the synaptic vesicles as they release the neurotransmitter. In this way the communicating circuits become visible with a color intensity that reflects the level of activity of the synaptic circuit” explains Professor Malgaroli.
To achieve this goal, the researchers artificially designed a molecule called SynaptoZip, by engineering a protein that is normally integrated in the membrane of synaptic vesicles. At the time of the electrical signal and the release of the neurotransmitter, if a fluorescent tracer (created by the researchers) is present outside the synapse, it is captured in an extremely effective way by SynaptoZip, thus “illuminating” the active synapse. “Although this powerful method is still not applicable to humans, we believe that its future applications are very important and will bring great progress in neuroscience”.