Computational modelling of functional maturation of primary motoneuron firing properties in developing zebrafish

Several ion currents of zebrafish primary motoneurons undergo changes in expression level during early development. Similarly, the firing properties of primary motoneurons and their involvement during locomotor activity change during early development as locomotor control of developing zebrafish matures. To test whether the experimentally observed changes in ion currents during development could underlie changes in firing properties and in participation during locomotor activity, we created models of primary motoneurons at developmental stages. Changes in the expression levels of a persistent outward potassium current, persistent inward potassium current, and several high-voltage activated calcium currents were modelled based on experimental observations. Simulations of our computational models replicated shifts in primary motoneuron firing properties and involvement during light-evoked swimming observed at 3 and 5 days post-fertilization. Our results suggest that developmental changes in specific ion currents of primary motoneurons could be sufficient to foster changes in firing properties of primary motoneurons that shape their activity level during maturation of motor control in developing zebrafish. Key pointsO_LIDevelopmental changes in persistent inward and outward currents could explain changes in firing properties of primary motoneurons in larval zebrafish C_LIO_LIModelling suggests these currents are sufficient to explain differences in primary motoneuron firing during light-evoked swimming responses at two developmental stages C_LIO_LIDevelopmental changes in high-voltage activated calcium currents explain differences in appearance of persistent inward currents during voltage-clamp ramp C_LIO_LIInteraction between high-voltage activated calcium currents and calcium-dependent potassium currents could explain why blocking calcium currents increases primary motoneuron firing C_LI