| Our understanding of neurotransmission rests on our ability to comprehensively characterize synaptic inputs to the millions of neurons in our nervous system. Efficacy of synaptic input varies with the distribution of the synaptic sites along the various motoneuron compartments: soma, proximal and distal dendrites. Hence, systematic characterization of the distribution of synaptic input across different motoneuron compartments is vital for understanding their integrated physiological effect. Electron microscopy has been the method of choice to study synaptic distribution, but such studies are complex and involve intense manual analysis, thus limiting the scope to small sample sizes. The objective of this thesis was to develop and validate a robust technique that uses confocal imaging and semi-automated procedures to quantitatively analyze the distribution of synaptic inputs along different motoneuron compartments: soma, primary dendrites, and distal dendrites. The first specific aim was to develop the necessary techniques to quantitatively characterize synaptic inputs to motoneurons, specifically distribution and association with specific neurotransmitters. The second specific aim was to characterize the distribution of synaptic inputs, specifically glutamate, along the dendritic tree of phrenic motoneurons. The final specific aim was to characterize neuregulin, a new synaptic input, at phrenic motoneurons, describing its distribution and association with other synaptic inputs. The technique developed in this thesis was created to assess the synaptic distribution at individual motoneuron compartments and is a step forward in understanding the mechanisms that drive neurotransmission, enabling more robust understanding of neuroplastictity in injury and disease. |
