Early Exclusive Use of the Affected Forelimb After Moderate Transient Focal Ischemia in Rats

Abstract

Background and Purpose-Previous work by researchers in our laboratory has shown that in the rat, the exclusive use of the affected forelimb during an early critical period exaggerates lesion volume and retards functional recovery after electrolytic lesions of the forelimb sensorimotor cortex. In the present study, we examined the effects of exclusive use of the affected forelimb 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 forelimb was forced through immobilization of either the ipsilateral (MCAOϩipsi) or contralateral (MCAOϩcontra) forelimb, respectively, for 10 days in a plaster cast, or the animal was left uncasted (MCAOϩnocast). Sham surgeries were performed, and animals were also casted for 10 days or left uncasted. Sensorimotor testing was performed during days 17 to 38. At the end of sensorimotor testing, cognitive performance was tested with use of the Morris water maze. In a separate experiment, temperatures and corticosterone levels were measured during the 10-day period after 45-minute ischemia and casting. Results-The MCAOϩipsi group performed worse on sensorimotor tasks than the MCAOϩcontra, MCAOϩnocast, and sham groups. Infarct volume was significantly larger in the MCAOϩipsi group than in the sham and MCAOϩcontra groups but not in the MCAOϩnocast group. No group differences were found with the Morris water maze, and no group differences were found in either temperature or plasma corticosterone level. Conclusions-The exclusive use of the affected forelimb immediately after focal ischemia has detrimental effects on sensorimotor function that cannot be attributed to hyperthermia or stress.

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