Early postnatal motor experience shapes the motor properties of C57BL/6J adult mice

Abstract

This study aimed to evaluate the long-term consequences of early motor training on the muscle phenotype and motor output of middle-aged C57BL/6J mice. Neonatal mice were subjected to a variety of motor training procedures, for 3 weeks during the period of acquisition of locomotion. These procedures are widely used for motor training in adults; they include enriched environment, forced treadmill, chronic centrifugation, and hindlimb suspension. At 9 months, the mice reared in the enriched environment showed a slower type of fibre in slow muscles and a faster type in fast muscles, improved performance in motor tests, and a modified gait and body posture while walking. The proportion of fibres in the postural muscles of centrifuged mice did not change, but these mice showed improved resistance to fatigue. The suspended mice showed increased persistence of immature hybrid fibres in the tibialis, with a slower shift in the load-bearing soleus, without any behavioural changes. The forced treadmill was very stressful for the mice, but had limited effects on motor output, although a slower profile was observed in the tibialis. These results support the hypothesis that motor experience during a critical period of motor development shapes muscle phenotype and motor output. The different impacts of the various training procedures suggest that motor performance in adults can be optimized by appropriate training during a defined period of motor development.

Early movement restriction deteriorates motor function and soleus muscle physiology

“…However, despite the relevance of this topic, consequences of disuse during growth on the neuromuscular system and motor performance have been only poorly studied. In young rodents, hind limb unloading or restricted range of motion induces altered muscle physiology and phenotype (Huckstorf et al, 2000;Kawano et al, 2010;Picquet et al, 1998;Serradj et al, 2013), bone structure (Miranda et al, 2016) and changes in the locomotor pattern (Walton et al, 1992;Westerga and Gramsbergen, 1993). In these studies, rodents were immobilized by casting or hind limb unloading, from a few days to 2 months, at various periods of development, but the severity and duration of impairment is related to the age at which the animals were immobilized and the duration of immobilization (Walton et al, 1992).…”

“…In addition, muscle properties and motor function were rarely studied together, and whether they can recover is unclear. Interestingly, one study performed in mice suggests that motor performance in adults (9 months) is dependent on motor activity during a defined period of motor development (PND10 to PND30) (Serradj et al, 2013).…”

“…Thus, CSA recovered with a one month-period of normal sensorimotor activity. Serradj et al (Serradj et al, 2013) has also provided evidence for a recovery in mice submitted to unloading from birth to P21. On the other hand, the CSA for triceps surae myofibers was still reduced at P90 in SMR rats compared with controls (Coq et al, 2008;Delcour et al, 2018a;Marcuzzo et al, 2008) whereas quadriceps and hamstrings CSA were unchanged.…”