Organization and connectivity of spinal ascending pathways reporting to brainstem

Movement is the final output of neuronal activity in the spinal cord. In all vertebrates, motor neurons are grouped into motor neuron pools, the functional units innervating individual muscles. Spinal premotor interneurons are the last stage of integration of a variety of inputs from different brain regions and sensory afferents before directing them to motor neurons. For the generation of movement, precise activation of distinct motor neuron pools at the right moment in time is crucial and this precision is likley due to the cohorts of spinal premotor interneurons, connected with specificity to distinct motor neuron pools that regulate motor neuronal activity. However, for accurate generation of movement, motor pathways need to constantly compare action planning to action execution. To achieve this task, motor pathways establish efference copy collaterals at many level of the motor command stream. Spinal ascending signaling systems can be regarded as part of this reporting system and will represent the main focus of the here presented thesis.
I will present the result of my studies on the organization of spinal ascending pathways signaling information to the lateral reticular nucleus (LRN) in the brainstem using a newly-developed mouse genetic tool intersectionally with viruses. I will focus on : (1) the organization of forelimb premotors signaling information to the LRN, (2) their developmental origin and (3) the organization of spinal premotor and non-premotor input to the LRN. In the following chapters, I will also present preliminary behavioral data on the role of the LRN in reaching behavior before and after the learning of the motor task, as well as on the inhibitory inputs to spinocerebellar neurons in the lumbar spinal cord and differences among them.
The last part of my thesis concerns my contribution to the project of Cyrill Goetz. The aim is to elucidate the structural organization and composition of premotor neurons controlling muscles with distinct biomechanical functions, axial- versus limb muscles. I will show the results obtained in the premotor distribution of axial muscle innervating motor neurons and my contribution in corroborating these findings by means of an anterograde viral approach.