Abstract The action potential and its all-or-none nature is fundamental to neural communication. Canonically the action potential is initiated once voltage-gated Na + channels are activated, and their rapid kinetics of activation and inactivation give rise to the action potential’s all-or-none nature. Here we show that cerebrospinal fluid contacting neurons (CSFcNs) surrounding the central canal of the mouse spinal cord employ a different strategy. Rather than using voltage-gated Na + channels to generate binary spikes, CSFcNs use two different types of voltage-gated Ca 2+ channel, enabling spikes of different amplitude. T-type Ca 2+ channels generate small amplitude spikes, whereas large amplitude spikes require high voltage-activated Cd 2+ sensitive Ca 2+ channels. We show that these different amplitude spikes signal input from different transmitter systems; purinergic inputs evoke smaller T-type dependent spikes while cholinergic inputs evoke large T-type independent spikes. Different synaptic inputs to CSFcNs can therefore be signalled by the spike amplitude.

Graded spikes differentially signal neurotransmitter input in cerebrospinal fluid contacting neurons of the mouse spinal cord