Genetically encoded sensors for analysing neurotransmission among synaptically-connected neurons
Anatomical connectome mapping in small areas of the nervous system as well as large-scale detection of neuronal activity patterns have been respectively achieved; however, it is still challenging to evaluate the functional connections among anatomically-connected neurons in a large-scale nervous system. We have developed a novel method to visualize neurotransmission named Split Protein HEmispheres for REconstitution (Sphere). By splitting a sensor into two fragments and expressing them in pre- and postsynaptic neurons separately, functional neurotransmitter sensors can be reconstituted only at the synapses between those neurons. We developed a Sphere-SF-iGluSnFR to measure glutamate levels, and further demonstrated that this system is functional in cultured cells, worms, and mouse brains. Moreover, this system is applicable to sensors other than glutamate, and colour variants have also been developed. This could allow for brain-wide imaging of functional synaptic transmission among particular neurons and identification of important neuronal circuits in the nervous system.