A modeling study of spinal motoneuron recruitment regulated by ionic channels during fictive locomotion

AbstractDuring fictive locomotion cat lumbar motoneurons exhibit changes in membrane proprieties including a decrease in voltage threshold (Vth), afterhyperpolarization (AHP) and input resistance (Rin) and an increase in non-linear membrane property. The impact of these changes on the motoneuron recruitment remains unknown. Using modeling approach we investigated the channel mechanism regulating the motoneuron recruitment. Three types of motoneuron pools including slow (S), fatigue-resistant (FR) and fast-fatigable (FF) motoneurons were constructed based on the membrane proprieties of cat lumbar motoneurons. The transient sodium (NaT), persistent sodium (NaP), delayed-rectifier potassium [K(DR)], Ca2+-dependent K+ [K(AHP)] and L-type calcium (CaL) channels were included in the models. Simulation results showed that (1) Strengthening synaptic inputs increased the number of recruitments in all three types of motoneurons following the size principle. (2) IncreasingNaT or NaP or decreasingK(DR) orK(AHP) lowered rheobase of spike generation thus increased recruitment of motoneuron pools. (3) DecreasingRin reduced recruitment in all three types of motoneurons. (4) The FF-type motoneuron pool, followed by FR- and S-type, were the most sensitive to increase of synaptic inputs, reduction ofRin, upregulation ofNaT andNaP, and downregulation ofK(DR) andK(AHP). (5) IncreasingCaL enhanced overall discharge rate of motoneuron pools with little effect on the recruitment. Simulation results ...
Source: Journal of Computational Neuroscience - Category: Neuroscience Source Type: research