Bilateral [¹⁴C]2-deoxyglucose uptake by motor pathways after unilateral neonatal cortex lesions in the rat

The left sensorimotor (SM) cortex was removed in 1-day-old and 30-day-old rats. At 90 days of age [¹⁴C]2-deoxyglucose (2DG) was injected and the right motor (MI) cortex was electrically stimulated to produce predominantly left vibrissae movements. Animals were sacrificed and their brains autoradiographed. Right motor cortex (MI) stimulation activated subcortical structures bilaterally in 3 of 5 neonatally lesioned rats. Right MI stimulation activated most subcortical structures unilaterally in 30-day lesioned rats. This implies that a critical period for SM cortex injury may occur between 1 and 30 days of age. We suggest that removal of left SM cortex at 1 day of age occurs before or during the critical period and this induces right MI cortex to form bilateral subcortical connections. The bilateral 2DG uptake increases imply the bilateral connections are functional. The unilateral subcortical activation in 2 of 5 neonatally lesioned animals may have been due to differences in size of the lesion, parameters of stimulation, or perhaps due to the time of the lesion being near the critical period. We also suggest that removal of left SM cortex at 30 days of age occurs after the critical period, but that this does not affect the predominantly ipsilateral subcortical connections from MI cortex which have previously formed during normal development.