You can see synaptic receptors (T-bars and post-synaptic densities) in EM, particularly if the staining is good. Neurotransmitter identification, not so much.

You can see synaptic receptors (T-bars and post-synaptic densities) in EM, particularly if the staining is good. Neurotransmitter identification, not so much. So you combine the EM connectomics with other studies like RNA sequencing or Fluorescent In-Situ Hybridization. In insects, you can have multiple transmitters with multiple receptors (possibly differing in sign) in the same cell, so there's that complication.