Motoneurons have an important role in translating the neural signal from supraspinal and reflex sources to a frequency code for the contraction of muscle. However, synaptic input alone cannot account for the signal that reaches the muscle fibers. Active dendritic conductances in the dendrites of motoneurons are essential for the generation of sufficient current to drive the motoneuron. The distribution and types of active dendritic conductances dictate the summation of input and resulting current that reaches the soma. Unlike cortical neurons, however, the spatial location of various dendritic conductances are still largely uncharacterized. Theoretically, the most reliable transfer of information would be through linear summation of synaptic inputs. The hypothesis is that ion channels are spatially distributed in the dendrites of motoneurons to allow for the linear summation of synaptic input current. The hypothesis will be tested using a combination of multiphoton fluorescence imaging and optimization of neuron models using a genetic algorithm. This research is important for the neurodegenerative disease ALS, which may be caused by excitotoxicity due to an immune reaction to calcium channels and is particularly marked in hypoglossal motoneurons. ? ?
