Changes in rat soleus muscle phenotype consecutive to a growth in hypergravity followed by normogravity

Abstract

Picquet, F., V. Bouet, L. Cochon, M. Lacour, and M. Falempin. Changes in rat soleus muscle phenotype consecutive to a growth in hypergravity followed by normogravity. Am J Physiol Regul Integr Comp Physiol 289: R217-R224, 2005. First published March 17, 2005; doi:10.1152/ajpregu.00596.2004.-It has been demonstrated that a long-term stay in hypergravity (HG: 2G) modified the phenotype and the contractile properties of rat soleus muscle. The ability of this muscle to contract was drastically reduced, which is a sign of anticipated aging. Consequently, our aim was to determine whether rats conceived, born, and reared in hypergravity showed adaptative capacities in normogravity (NG: 1G). This study was performed on rats divided into two series: the first was reared in HG until 100 days and was submitted to normogravity until 115 to 220 postnatal days (HG-NG rats); the second was made up of age paired groups reared in normogravity (NG rats). The contractile, morphological, and phenotypical properties of soleus muscle were studied. Our results showed that the NG rats were characterized by coexpressions of slow and fast myosin, respectively, 76.5 and 23.5% at 115 days. During their postnatal maturation, the fast isoform was gradually replaced by slow myosin. At 220 days, the relative proportions were respectively 91.05% and 8.95%. From 115 to 220 days, the HG-NG rats expressed 100% of slow myosin isoform and they presented a slower contractile behavior compared with their age-matched groups; at 115 days, the whole muscle contraction time was increased by 35%, and by 15%, at 220 days. Our study underlined the importance of gravity in the muscular development and suggested the existence of critical periods in muscle phenotype installation. muscular properties; myosin transition; gravity change; hindlimb muscle ALL LIVING ORGANISMS ARE DIRECTLY under the influence of a common and constant factor, gravity. It is well known that the development and the maturation of numerous life systems such as cell division, axonal growth, posture, and body movements are directly regulated by this factor (6,14,15,16).The effects of real (spaceflight) and simulated (hypodynamia-hypokinesia model, HH) microgravity on the neuromuscular system are well documented. In hindlimb muscles, an exposure to a HH period induces more marked effects in slow extensor muscles such as the soleus than in fast muscles (for a review, see Refs. 23 and 24). Most studies have been carried out in adult rats. Indeed, in soleus muscle from rats submitted to real and simulated microgravity, a muscular atrophy correlated to a decrease both in fiber and muscle cross-sectional area and to a decrease in muscle strength, which has been commonly described (for review, see Ref. 13). A slow-to-fast phenotype transition, characterized by changes in contractile protein isoforms such as myosin heavy and light chains (3, 32) and regulatory proteins (2), has also been reported. Moreover, the proprioceptive information could be disturbed (9), and a cortical reorganization has b...

Vestibular-mediated increase in central serotonin plays an important role in hypergravity-induced hypophagia in rats

“…The effects of a hypergravity environment may be transduced by vestibular activation, bone and skeletal muscle load, body-fluid shift, and pressure changes, which then elicit physiological and pathophysiological responses (1,8,22,25). These putative afferent mechanisms could contribute to hypergravity-induced transient hypophagia.…”

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

“…Chronic centrifugation was expected to induce a shift to a slower type of fibre in the load‐bearing muscles, as has previously been reported in the soleus of rats conceived and reared in HG (Picquet et al ., ; Bozzo et al ., ); however, the proportion of fibres in the soleus did not change. The possibility that the animal's muscles adapted to earth gravity over the long period between training and testing is not consistent with previous reports of persistent change even after 120 days (Picquet et al ., ). We propose that the change in fibre typology was apparent in the rats in Picquet's study because they were centrifuged for a period of 100 days; in our study, the period of centrifugation was shorter (3 weeks), and was potentially not sufficient to induce a lasting change in fibre typology, because the adaptation of load‐bearing muscles to HG is known to be a slow process.…”

Hypergravity within a critical period impacts on the maturation of somatosensory cortical maps and their potential for use-dependent plasticity in the adult

“…As previously mentioned, Picquet et al (2002) showed that soleus antigravity muscle of rats conceived, born, and reared in HG until 100 days expressed 100% slow myosin phenotype. In a subsequent study, the same authors showed that in these animals, NG from 100 days to 115 or 220 days did not transform the muscle phenotype, suggesting the existence of a critical period in muscle phenotype determination (Picquet 2005). One may hypothesize that these persisting changes in descending pathways and muscle properties during subsequent exposure to NG were likely to lastingly influence the cortical integration of proprioceptive inputs, and thus the corresponding representations in the S1 map.…”