Pharmacological study of the one spike spherical neuron phenotype in Gymnotus omarorum

• Gymnotus shows one-spike neurons firing one-to-one after electric organ discharge.
• A low-threshold potassium channel supports such a profile, causing long refractoriness.
• These features subserve a dynamic sensory filter for streaming self-generated signals.
• Differences with wave fish suggest co-evolution of sensory and electromotor systems.
• Similarities with the auditory neurons suggest a convergent evolution.

The intrinsic properties of spherical neurons play a fundamental role in the sensory processing of self-generated signals along a fast electrosensory pathway in electric fish. Previous results indicate that the spherical neuron’s intrinsic properties depend mainly on the presence of two resonant currents that tend to clamp the voltage near the resting potential. Here we show that these are: a low-threshold potassium current blocked by 4-aminopyridine and a mixed cationic current blocked by cesium chloride. We also show that the low-threshold potassium current also causes the long refractory period, explaining the necessary properties that implement the dynamic filtering of the self-generated signals previously described. Comparative data from other fish and from the auditory system indicate that other single spiking onset neurons might differ in the channel repertoire observed in the spherical neurons of Gymnotus omarorum.