Speaker: Janos Szabadics (KOKI: Institute of Experimental Medicine, Hungary)

Title: Compensating potassium conductance maintains uniform action potential shape along individual axons with variable calibre in hippocampus

Abstract: The axonal diameter varies within individual axons. There are smaller and larger boutons along the thin axonal trunk. This morphological diversity is also reflected by the biophysical environment, as the smaller diameter means smaller capacitance and typically larger input resistance. The local biophysical environment influences spike shapes, which is the most important neuronal output signal. For example, wider action potentials usually result in more reliable and larger synaptic responses. Therefore, the variability of axonal size can make axonal signalling quite complex because each synapse would see a different dynamic signal. To address how axons handle this issue we used direct patch clamp recording and voltage imaging from small and large mossy fibres and axons originating from the supramammillary nucleus in the hippocampus. The results revealed that the amplitudes and shapes of the APs were surprisingly similar within the same type of axons, regardless of the axonal thickness. Thus, despite the different local biophysical environments, variable diameter axons actively maintain uniform action potential shapes. Outside out patch recordings of the isolated currents and pharmacological evidence suggest that smaller axons utilize more potassium currents to accelerate action potentials relative to larger axon segments. Specifically, the contribution of Kv1 channels is more prominent in smaller diameter axons than in larger boutons. Thus, we conclude that uniform AP shape is actively maintained within the same type of axons and axons provide similar digital signals to each of their synapses for maintaining output.

An informal social will follow with drinks offered by the society!