Decifrar os circuitos neuronais subjacentes ao fenómeno de ‘cueing’ na doença de Parkinson

Despite the evidence that some patients with Parkinson’s disease (PD) show remarkable improvements in movement provided by external cues, our understanding of why this happens is scarce. This lack of knowledge undermines an effective and generalized use of external cues to help PD patients with treatment-resistant impairments that affect movement initiation, such as freezing of gait (1, 2). So far, clinical research on this subject has not provided a clear framework to understand this important question. We have shown in mice that SNc dopamine neurons are critical for the initiation and invigoration of self-paced movements(3), while other authors have shown that projections from the cerebellar Dentate and Interpositus nuclei (DN/IPN) and the midbrain Pedunculopontine and Midbrain Reticular Nuclei (PPN/MRN) have a critical role in cued movement initiation(4, 5). However, it has not been tested whether the activity of neurons in the motor thalamus that receive inputs from these distinct circuits (basal ganglia, cerebellum, and midbrain nuclei) is differentially affected in a mouse model of PD. In this project, we use an animal model of PD to propose a ground-breaking approach to understanding the beneficial effects of cueing. It starts with a novel and clear hypothesis: Self-paced movement initiations rely heavily on the dopamine-dependent basal ganglia outputs to engage the motor thalamus (mThalamus), while external cues recruit the mThalamus and initiate movements through cerebellar and midbrain pathways which are resilient to dopamine neuron loss. To adequately test this hypothesis, we have developed a new behavior task that trains mice to initiate locomotion in a self-paced or cued manner within the same session. Furthermore, we are combining this task with cutting-edge viral anterograde trans-synaptic tracing to record and manipulate the activity of different populations in the mThalamus, according to the different inputs they receive (basal ganglia, cerebellum, or midbrain PPN/MRN). This will allow us to test if the mThalamus activity that precedes self-paced movement initiation is higher in the population that receives inputs from the basal ganglia, whereas the activity preceding cued initiations is more notable in the mThalamus population of neurons that receives inputs from the cerebellum or midbrain. Finally, in the last set of experiments, we will induce a progressive loss of dopamine neurons using a viral vector to express a human mutated alpha-synuclein in the substantia nigra compacta of mice. With this inducible mouse PD model, we will measure the changes in the performance of self-paced vs cued initiations, predicting that self-paced movements will decline with neuron loss progression, and the corresponding activity of the different mThalamus populations will be significantly affected. Finally, we propose to rescue movement initiation impairments using optogenetic activation of specific thalamic neuron populations. In summary, our specific aims are: 1-To evaluate if the activity of neurons in the motor thalamus related to cued and self-paced movement initiation is different depending on the projections they receive 2 - To evaluate how movement initiation and the corresponding thalamic activity are changed by the progressive degeneration of dopamine neurons 3 - To test if optogenetic activation of specific thalamic neuron populations rescues movement initiation impairments induced by the loss of dopamine neurons