USE-DEPENDENT EXACERBATION OF BRAIN-DAMAGE OCCURS DURING AN EARLY POSTLESION VULNERABLE PERIOD

For a period of time after unilateral brain injury, surviving neural t issue surrounding the lesion may be vulnerable to extremely high behav ioral demand. Previously, we found that lesions of the forelimb repres entation area of the sensorimotor cortex (FL-SMC) in rats increase in size substantially when the intact forelimb is immobilized with a plas ter of paris cast during the first 15 days after surgery, which forces overuse of the impaired forelimb. The present study was designed to d etermine whether the adult brain is more vulnerable to forced overuse of the impaired forelimb during the first 7 days post-lesion than duri ng the second 7 days post-lesion. Using behavioral tests of forelimb u se and stereological analysis of remaining tissue volume 40 days after FL-SMC lesions, we found that forced overuse of the impaired forelimb during the first 7 days after the initial damage caused expansion of neural injury and greatly interfered with restoration of function. In contrast, forced overuse of the impaired forelimb during the second 7 days had no significant effect on lesion size but nevertheless interfe red with restoration of function. Thus, surviving neural tissue in the damaged hemisphere and recovery of function appear to be vulnerable t o prolonged forced overuse of the impaired forelimb throughout the fir st 15 days, but tissue loss was detectable only when the animal was fo rced to use the impaired forelimb during the first 7 days after injury . (C) 1998 Elsevier Science B.V.