A qualitative and quantitative analysis of skilled forelimb reaching impairment following intracerebral hemorrhage in rats

The Montoya staircase test is commonly used to measure skilled forelimb reaching ability in a number of brain injury and disease models, but little has been done to characterize the precise nature of the impairments observed after stroke. The present study used slow motion video-recording to analyze staircase reaching performance both qualitatively and quantitatively, and to precisely determine the components of fine forelimb motor function that are disturbed in the collagenase model of hemorrhagic stroke. Male Sprague–Dawley rats were trained to reach for pellets in the staircase task, and subjected to either striatal hemorrhage induced by microinjections of bacterial collagenase or sham surgery. Reaching performance was recorded and examined before surgery, and 2 and 4 weeks later. Impaired animals made fewer attempts and retrieved less pellets than did shams, especially from the lower steps. Interestingly, impaired animals were less able to retrieve a pellet even when the forepaw made contact with it. Detailed qualitative analysis determined that significant disturbances were most prominent in components of skilled reaching that involved fine manipulation of the distal muscles, especially the wrist and digits. While some components of the reaching impairment were found to partially recover at 4 weeks post-surgery, the impairments in these distal motor movements persisted and there was no significant improvement in overall success. These results suggest that the collagenase model of intracerebral hemorrhage produces a functional impairment that most severely affects fine control of the distal forelimb and paw.