The influence of betamethasone and dexamethasone on motor development in young rats.

Synthetic corticosteroids such as dexamethasone and betamethasone are widely used in clinical practice of the perinatal period to enhance lung maturation. However, indications emerged both on the basis of investigations in humans and in experimental animals that such treatment leads to abnormal brain development. In the present study, the neurologic development and the development of locomotion were studied in two groups of rats injected either with dexamethasone or with betamethasone on their 3rd and 4th d, and this was compared with development in a group of control rats injected with saline. Each group consisted of 12 rats. Neurologic reflexes were tested daily and the rat's physical development (body weight and age at eye opening) was noted from the 4th until the 21 st d. Locomotion was recorded on videotape and analyzed during playback runs. Results indicated a growth retardation in both groups of rats treated with corticosteroids, but remarkably, the opening of the eyes was advanced by about 1 d in the dexamethasone group compared with control rats and rats treated with betamethasone. Several reflexes showed normal development, but the negative geotaxis and free-fall righting responses developed retarded. Locomotion in both experimental groups was characterized by a postural tremor and an abnormal posture during walking from the 9th until the 15th d. Although the walking pattern after this age became fluent, the gait width remained abnormally increased until the 20th d. Our results indicate that both dexamethasone and betamethasone interfere with the development of vestibular and cerebellar functions involved in complex motor patterns.