Effects of artificial rearing on contractile properties of genioglossus muscle in Sprague–Dawley rat

Mammals suckle from a nipple during the early neonatal period to obtain nourishment. The genioglossus muscle helps position and move the tongue for efficient suckling. The purpose of this study was to examine the contractile properties and myosin heavy chain (MHC) phenotype of the genioglossus following an early period of artificial rearing, which reduced nutritive suckling. Beginning at 3 days of age, rats were fed via gastric cannula until postnatal day 14 (P14). At P14, artificially reared rat pups were either allowed to grow to postnatal day 42 (P42) or anaesthetised and prepared for experimentation. Comparisons were made between artificially reared and dam reared groups at P14 and P42. At P14 maximum tetanic tension and fatigue index were lower in the artificially reared group than the dam reared group. By P42, artificially reared rats had a higher fatigue index and lower percentage of MHCIIa than dam reared rats. The artificial rearing technique employed in this study was adequate to produce chronic changes in fatigue resistance and MHC distribution in genioglossus muscle of rat; the changes observed here may be similar to changes that occur in premature human infants requiring early artificial feedings.