EPFL scientists Aurélie Pala and Carl Petersen have observed and measured synaptic transmission in a live animal for the first time, using optogenetics* to stimulate single neurons in the mouse barrel cortex (which processes sensory information from the mouse’s whiskers).
They shined blue light on the neurons containing a gene-based light-sensitive protein, activating the neurons to fire. Then using microelectrodes, they measured resulting electrical signals in neighboring interneuron cells. They also used an advanced imaging technique (two-photon microscopy) that allowed them to look deep into the brain of the live mouse and identify the type of each interneuron they were studying.
The data showed that the neuronal transmissions from the light-sensitive neurons differed depending on the type of interneuron on the receiving end. Only a few studies have directly investigated synaptic transmission between specific neocortical neurons in vivo, presumably due to the technical difficulties in obtaining intracellular recordings from connected pairs of neurons in vivo, the authors say in their (open-access) paper in Neuron.
The research overcomes a limitation of in vitro (lab) studies, where associated biomolecules are different from those in a live animal, and where cutting neural tissue for lab work also introduces artifacts, the researchers suggest. “This is a proof-of-concept study,” says Pala, who received her PhD for this work. “Nonetheless, we think that we can use optogenetics to put together a larger picture of connectivity between other types of neurons in other areas of the brain.”