This is a resubmission (A1) of application 1R15 NS120154-01, “The neuropathology of cerebellum in spinal muscular atrophy”, which was reviewed in June 2020 at the ZRG1 MDCN-R (86) section. Spinal muscular atrophy (SMA) is the leading genetic cause of infant mortality. It arises from the mutation of the survival motor neuron one (SMN1) gene. Despite decades of research, its mechanisms of neuropathology are far from clear. The recent US FDA approved SMN restoration therapies (Nusinersen, Zolgensma, and Risdiplam) are effective in rescuing the motor dysfunction but not cure for SMA. It is not clear how long the effect will last, nor whether patients will suffer problems due to dysfunction of SMN deficient neurons in other parts of the nervous system. Accumulating evidence suggests that low levels of SMN not only alter the function of spinal motor neurons, but also of neurons and neural circuits in other parts of the motor network. However, currently there is little understanding of neuronal pathology in SMA beyond the spinal cord motor neuron (MN) circuit. As new treatments allow patients to live longer, knowledge of the role of central motor network in the neuropathology of SMA will be key for developing long-term prognoses and treatment strategies for patients. The objective of this application is to investigate cerebellar pathology and neural circuit dysfunction in SMA mouse models using magnetic resonance imaging (MRI) and electrophysiological techniques. The rational for this project is based on the important role of cerebellum in motor control, the reports of cerebellar pathology in human SMA patients, as well as our preliminary data showing alterations in the structure and function of cerebellar neural network in mouse models of SMA. Our central hypothesis is that in SMA, alterations in the neurons and neural circuits of the cerebellum decrease cerebellar output and alter descending motor commands from the motor cortex and brainstem to the spinal cord, contributing to neuropathology and motor system dysfunction. This central hypothesis will be tested by three specific aims: 1) Identify changes in the morphology and fiber connections of the cerebellum in SMNΔ7 and MN rescue mice by magnetic resonance imaging techniques; 2) Elucidate the functional alteration of cerebellar neurons and neural circuits related to SMA pathophysiology using electrophysiological techniques; 3) Relate changes in cerebellar structure and neural circuit function to SMA disease progression in MN rescue mouse model. To determine the contribution of structural and functional pathology in the cerebellum to the phenotype of SMA, we will use MRI and electrophysiology to investigate the development of neuropathology in the cerebellum at pre-symptomatic (postnatal day 3–4, P3–P4), early- (P7–P8), and end-symptomatic (P12–P13) stage of SMA. The comparison studies between SMNΔ7 and motor neuron MN mouse models will confirm and elucidate the correlation of cerebellar neuropath...