A comparison of the effects of days 1 and 10 unilateral lesions of medial prefrontal cortex on cerebral morphogenesis and behavior.

The purpose of this study was to compare the behavioral and anatomical effects of unilateral medial prefrontal cortex (mPFC) ablation on newborn (day of birth, P1), neonatal (10 days old, P10), and sham-operated rats. The infant operates were impaired bilaterally at skilled reaching and forelimb inhibition in swimming, and contralaterally at traversing a rung ladder. There was no effect of age-at-injury. They also had mild deficits on spatial navigation tasks. Anatomically, the cortex of the injured hemisphere was generally thinner throughout, with the effect being larger in the rostral half of the hemisphere. In contrast, the medial prefrontal cortex in the intact hemisphere was significantly thicker than in sham controls. There were no effects on cortical thickness elsewhere in the intact hemisphere. Analysis of golgi-stained layer III pyramidal cells in the intact mPFC found the cells to have less extensive dendritic arborization than in the shams. These results contrast with the effect of unilateral motor cortex injuries at the same ages.