Abstract
The descending contralateral movement detector (DCMD) is a high‐performance interneuron in locusts with an axon capable of transmitting action potentials (AP) at more than 500 Hz. We investigated biophysical mechanisms for fidelity of high‐frequency transmission in this axon. We measured conduction velocities (CVs) at room temperature during exposure to 10 mmol/L cadmium, a calcium current antagonist, and found significant reduction in CV with reduction at frequencies >200 Hz of ~10%. Higher temperatures induced greater CV reductions during exposure to cadmium across all frequencies of ~20–30%. Intracellular recordings during 15 min of exposure to cadmium or nickel, also a calcium current antagonist, revealed an increase in the magnitude of the afterhyperpolarization potential (AHP) and the time to recover to baseline after the AHP (Medians for Control: −19.8%; Nickel: 167.2%; Cadmium: 387.2%), that could be due to a T‐type calcium current. However, the removal of extracellular calcium did not mimic divalent cation exposure suggesting calcium currents are not the cause of the AHP increase. Computational modeling showed that the effects of the divalent cations could be modeled with a persistent sodium current which could be blocked by high concentrations of divalent cations. Persistent sodium current shortened the AHP duration in our models and increased CV for high‐frequency APs. We suggest that faithful, high‐frequency axonal conduction in the DCMD is enabled by a mechanism that shortens the AHP duration like a persistent or resurgent sodium current.
Highlights
In axons, supernormal and subnormal conduction occur when action potential (AP) propagation velocity is increased or decreased relative to an initial AP in previously inactive membrane (Bucher and Goaillard 2011)
Subnormal conduction commonly occurs during bursts of high-frequency APs as the relative refractory period of the preceding AP decreases the number of active sodium channels available for the subsequent AP and can compromise transmission by high-frequency firing neurons
Physiological Reports published by Wiley Periodicals, Inc. on behalf of the American Physiological Society and The Physiological Society
Summary
Supernormal and subnormal conduction occur when action potential (AP) propagation velocity is increased or decreased relative to an initial AP in previously inactive membrane (Bucher and Goaillard 2011). Subnormal conduction commonly occurs during bursts of high-frequency APs as the relative refractory period of the preceding AP decreases the number of active sodium channels available for the subsequent AP and can compromise transmission by high-frequency firing neurons. The descending contralateral movement detector (DCMD) neuron in the locust provides a model axon for studies of high-frequency transmission. Divalent cations significantly reduced conduction velocity (CV), at high frequencies in the DCMD axon, and increased the afterhyperpolarization (AHP) magnitude. Computational models confirm that currents that shorten the AHP magnitude and duration, like the persistent and resurgent sodium currents, can improve high-frequency conduction by the axon. Physiological Reports published by Wiley Periodicals, Inc. on behalf of the American Physiological Society and The Physiological Society
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
