Some cells co-release neuromodulator with neurotransmitter. Propagation down axon. There is some mechanism for removing them from synaptic cleft. Measure synthesis and metabolism. Inject probe to neuron.
Purpose is for studying release.
Freeze dried tissue exposed to formaldehyde gas. Highlights NT as fluorescent under ultraviolet light. Absorbed by neurons. Metabolized to a toxic state in the neuron to cause cell death. Lose one NT system.