Following focal brain lesions in the rat, usually substantial alterations, e.g. in neuronal excitability and receptor density, are observed in the surround of the lesion as well as in remote brain areas. In the present series of experiments we used a series of behavioral tests to examine whether a persistent functional deficit can be monitored following lesions in the sensorimotor cortex of the rat. Focal brain lesions with a diameter of about 2 mm were induced in the forelimb area and a more caudal brain area (Occ2/Par1) of male Wistar rats. The rats had to perform three behavioral tasks at different time points in the two months following surgery.

In the first test the rat was placed in a glass cylinder and the rearing behavior was observed. The movements of both forelimbs along the wall were counted. In the second task the rat had to walk over a grid; we counted false steps defined as slipping with the forelimb through the grid, and related this to the total number of steps. In the third test we analyzed the motion of the forelimb when the rat was swimming a straight distance in a water basin. In all tasks we distinguish between the limb affected by the lesion (impaired) and the healthy limb. The results were determined as scores for the impaired limb compared to controls.

Compared to control, animals with lesions in the forelimb representation area of the sensorimotor cortex (FL-SMC) showed functional deficits for the impaired forelimb in all three tests. In the first week after surgery the rats use either the healthy limb or both limbs together for motion along the wall in the cylinder. They have a high score of false steps by walking on the grid. Also the swim test showed a higher score for the impaired limb in the first week. After two weeks of recovery, the deficit has considerably recovered. With lesions in the parietal area, walking on a grid or swimming were not impaired. However, a small impairment of limb use developed within the first seven days.

The investigations show that (i) clear motor deficits can be demonstrated with focal brain lesions in the sensorimotor cortex; (ii) these show considerable recovery within the first two weeks following lesion induction; (iii) animals with lesions in parietal areas may show some change of limb preference indicating that the lesion has some remote behavioral effects. The present studies will allow us to study the recovery from brain lesions and their pharmacological modification.

Supported by Graduiertenkolleg and SFB 194.

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