FIGURE 6.

Visualization of neurotransmitter transients in vivo. (A) Mapping glutamate transients in the mouse brain is performed through the chronic cranial window. One millisecond light visual stimulation induces an initial fast response followed by a clearly separated secondary response in awake Emx-CaMKII-iGluSnFR mouse (Xie et al., 2016). (B) Complex song learning in zebra finches is outlined. Left: juvenile zebra finch is exposed to the living adult male tutor. The song causes dopamine bursts in the high vocal center (HVC) of the juvenile bird, resulting in song learning. Right: juvenile zebra finch is exposed to the playback of the song. Dopamine bursts in the HVC of juvenile bird are not detected, and consequently, song learning does not occur (Tanaka et al., 2018). (C) Spectral multiplexing of green fluorescent dLight1.1 with either red fluorescent jRGECO1a biosensor or channelrhodopsin ChrimsonR activatable with red light. Left: both dopamine and calcium signals are detected in the mouse brain using multicolor fiber photometry. The sucrose application causes both dopamine transients and neuronal activity in the NAc (green and red squares), whereas the foot shock increases calcium but not dopamine transients (gray and red squares). Right: ChrimsonR channelrhodopsin is selectively expressed in the VTA of the mouse brain. Activation of ChrimsonR with red light causes the dopamine release in the NAc. The VTA neuron projections to NAc are shown with the arrow.