Motor skill learning enhances the expression of activity-regulated cytoskeleton-associated protein in the rat cerebellum

Neuroplasticity induced by the retention period of a complex motor skill learning in rats

Learning complex motor skills is an essential process in our daily lives. Moreover, it is an important aspect for the development of therapeutic strategies that refer to rehabilitation processes since motor skills previously acquired can be transferred to similar tasks (motor skill transfer) or recovered without further practice after longer delays (motor skill retention). Different acrobatic exercise training (AE) protocols induce plastic changes in areas involved in motor control and improvement in motor performance. However, the plastic mechanisms involved in the retention of a complex motor skill, essential for motor learning, are not well described. Thus, our objective was to analyze the brain plasticity mechanisms involved in motor skill retention in AE . Motor behavior tests, and the expression of synaptophysin (SYP), synapsin-I (SYS), and early growth response protein 1 (Egr-1) in brain areas involved in motor learning were evaluated. Young male Wistar rats were randomly divided into 3 groups: sedentary (SED), AE, and AE with retention period (AER). AE was performed three times a week for 8 weeks, with 5 rounds in the circuit. After a fifteen-day retention interval, the AER animals was again exposed to the acrobatic circuit. Our results revealed motor performance improvement in the AE and AER groups. In the elevated beam test, the AER group presented a lower time and greater distance, suggesting retention period is important for optimizing motor learning consolidation. Moreover, AE promoted significant plastic changes in the expression of proteins in important areas involved in control and motor learning, some of which were maintained in the AER group. In summary, these data contribute to the understanding of neural mechanisms involved in motor learning in an animal model, and can be useful to the construction of therapeutics strategies that optimize motor learning in a rehabilitative context.

Motor Skill Learning Is Associated with Phase-Dependent Modifications in the Striatal cAMP/PKA/DARPP-32 Signaling Pathway in Rodents

Abundant evidence points to a key role of dopamine in motor skill learning, although the underlying cellular and molecular mechanisms are still poorly understood. Here, we used a skilled-reaching paradigm to first examine changes in the expression of the plasticity-related gene Arc to map activity in cortico-striatal circuitry during different phases of motor skill learning in young animals. In the early phase, Arc mRNA was significantly induced in the medial prefrontal cortex (mPFC), cingulate cortex, primary motor cortex, and striatum. In the late phase, expression of Arc did not change in most regions, except in the mPFC and dorsal striatum. In the second series of experiments, we studied the learning-induced changes in the phosphorylation state of dopamine and cAMP-regulated phosphoprotein, 32k Da (DARPP-32). Western blot analysis of the phosphorylation state of DARPP-32 and its downstream target cAMP response element-binding protein (CREB) in the striatum revealed that the early, but not late, phase of motor skill learning was associated with increased levels of phospho-Thr34-DARPP-32 and phospho-Ser133-CREB. Finally, we used the DARPP-32 knock-in mice with a point mutation in the Thr34 regulatory site (i.e., protein kinase A site) to test the significance of this pathway in motor skill learning. In accordance with our hypothesis, inhibition of DARPP-32 activity at the Thr34 regulatory site strongly attenuated the motor learning rate and skilled reaching performance of mice. These findings suggest that the cAMP/PKA/DARPP-32 signaling pathway is critically involved in the acquisition of novel motor skills, and also demonstrate a dynamic shift in the contribution of cortico-striatal circuitry during different phases of motor skill learning.