Getting Graded: Teaching Principles of Chemical Synaptic Transmission Without Action Potentials.

The study of synaptic transmission is foundational for undergraduate neuroscience students. Chemical synaptic transmitter release is usually presented as evoked by action potentials, but it can also be caused by subthreshold, 'graded' changes in presynaptic membrane potential. In a 1980 publication in the , Graubard and colleagues measured synaptic activity in the crustacean stomatogastric ganglion; they found that postsynaptic voltage changes occur in response to both action potentials and to graded depolarizations in presynaptic neurons. This was one of the first papers to clearly demonstrate that both graded and spike-mediated chemical synaptic transmission could occur concurrently at an identified synapse. Discussion of this work in undergraduate classrooms can encourage students to think in greater depth about the diversity of transmission mechanisms available to neurons.