The EMG development of the longissimus and multifidus muscles after plugging the horizontal semicircular canals.

The effects of plugging both horizontal semicircular canals at the 5th postnatal day (P5) on the development of the EMG of two back muscles (the M. longissimus lateralis and the M. multifidus) were studied in rats between P5 and P46. The EMG was related to locomotion, grooming, and rearing of these rats. Special attention was paid to locomotor behavior. After this vestibular deprivation, the development of a consistent temporal relation between burst activity in the EMG of both Mm. longissimii laterales and the swing phase of one hind paw was retarded by about 3 days. The development of coupling of maximal activity in the M. longissimus lateralis to the swing phase of one of the hind paws was even more retarded. No differences were observed between normal and vestibularly deprived rats during the development of activity in the Mm. multifidi. Our results indicate that information from the horizontal semicircular canals is essential for dynamic postural development and probably, therefore, for motor development in general. Furthermore, lack of such information has effects on the fine tuning of back muscle activity during locomotion at least until P40.