  Chemical neurotransmission is central to neurotypical brain function but also
implicated in a variety of psychiatric and neurodegenerative diseases. The
release dynamics of neurotransmitters is correlated with but distinct from
electrical signal propagation. It is therefore necessary to track
neurotransmitter modulation separately from electrical activity. Here, we
present a new approach for imaging deuterated neurotransmitter molecules with
vibrational microscopy in the cell-silent window. Using stimulated Raman
scattering microscopy, we perform direct imaging of the neurotransmitters
dopamine and GABA in PC12 chromafin cells, and primary hippocampal neurons,
respectively, based on their C-D vibrational frequencies. We find that isotope
labelling does not perturb neurochemical activity. We further show that
stimulation of neurotransmitter release results in an overall 20-50% signal
reduction, with the ability to observe inter- and intracellular variation in
vesicular release potential. Taken together, our data suggest that
neurotransmitter isotopologues can serve as a generic, non-perturbative, method
to image neurotransmitters.
