Early exclusive use of the affected forelimb after moderate transient focal ischemia in rats - Functional and anatomic outcome

Background and Purpose-Previous work by researchers in our laboratory has s hown that in the rat, the exclusive use of the affected forelimb during an early critical period exaggerates lesion volume and retards functional reco very after electrolytic lesions of the forelimb sensorimotor cortex. In the present study, we examined the effects of exclusive use of the affected fo relimb after middle cerebral artery occlusion (MCAO). Methods-Ischemia of moderate severity was produced in male Long-Evans rats through 45 minutes of occlusion of the left middle cerebral and both common carotid arteries. Exclusive use of either the affected or unaffected forel imb was forced through immobilization of either the ipsilateral (MCAO+ipsi) or contralateral (MCAO+contra) forelimb, respectively, for 10 days in a pl aster cast, or the animal was left uncasted (MCAO+nocast). Sham surgeries w ere performed, and animals were also casted for 10 days or left uncasted. S ensorimotor testing was performed during days 17 to 38. At the end of senso rimotor testing, cognitive performance was tested with use of the Morris wa ter maze. In a separate experiment, temperatures and corticosterone levels were measured during the 10-day period after 45-minute ischemia and casting . Results-The MCAO+ipsi group performed worse on sensorimotor tasks than the MCAO+contra, MCAO+nocast, and sham groups. Infarct volume was significantly larger in the MCAO+ipsi group than in the sham and MCAO+contra groups but not in the MCAO+nocast group. No group differences were found with the Morr is water maze, and no group differences were found in either temperature or plasma corticosterone level. Conclusion-The exclusive use of the affected forelimb immediately after foc al ischemia has detrimental effects on sensorimotor function that cannot be attributed to hyperthermia or stress.