Resumo

Evidence exists indicating that some aspects of human brain motor control are asymmetrically distributed in the population. Particularly, a series of studies in brain-damaged patients and in normal individuals have demonstrated that the left hemisphere plays a major role in controlling complex limb movements. No such asymmetries have been identified in rodents, in spite of the fact that these animals have been frequently used in studies assessing motor behavior. In this regard, here, we used unilateral hemispherectomy to study the relative importance of each hemisphere for the control of limb movement in mice. Adult male Swiss mice were submitted to one of the following three procedures: right unilateral hemispherectomy (RH, n = 27), left unilateral hemispherectomy (LH, n = 24) or sham (n = 25) surgery. Fifteen days after surgery, motor performance was evaluated in the accelerated rotarod test and in the foot fault test. In the first test, the latency to fall off the rotating bar (diameter: 3.2cm; acceleration rate: from 4 to 40 rpm/min over a period of 2 min) was measured in four trials. In the second test, mice were individually placed for 1 minute on a wired grid (grid area: 50x55x52cm, bars: 2mm in diameter spaced 1cm apart). Each successful foot placement onto the bar was recorded as a step and a foot fault was counted when a paw slipped through the grid hole. After the behavioral tests, the animals were anesthetized and perfused. The brains were examined macroscopically in order to evaluate the extension of hemisphere damage. In all hemispherectomized animals, most of the cerebral hemisphere was eliminated, with a variable midline residuum of medial thalamic, hypothalamic, ventral forebrain structures and medial remnants of the cortex. The surgical removal of the right hemisphere caused a more pronounced impairment in performance than the removal of the left hemisphere both in the rotarod [F (2,65) = 4.9; P = 0.01] and in the foot-fault [F (5.7,77.5) = 28.7; P < 0.001] tests. In the rotarod, while no differences were observed between the LH and sham groups, the RH group fell sooner than the sham one (p<0.05). In the foot-fault test, both the sham and the LH groups did not present differences between the performance of the left and right hindpaws. In contrast, the RH group presented a significant impairment in the contralateral hindpaw as compared to the ipsilateral one (p<0.05). Similarly to what has been observed in humans, our data suggest a major role of the right hemisphere in controlling skilled limb movements in mice.