Paw-reaching, sensorimotor, and rotational behavior after brain infarction in rats

Functional tests that are stable and consistent over time are an advantage for long-term evaluation of treatment in experimental stroke research. Because little information on this subject is available in rodents with focal cerebral ischemia, we investigated the outcome of three behavioral tests for a period of 3 months after the insult.

Spontaneously hypertensive rats were sham-operated (n = 27) or underwent an occlusion (n = 36) of the right middle cerebral artery. Before surgery all rats were tested for amphetamine-induced rotational behavior, and half of the rats were trained in a paw-reaching task. One, 2, and 3 months after surgery the tests were repeated, together with a test for sensorimotor function. Infarct size was measured morphometrically.

In the lesion group, total hemisphere area was reduced by 22%, caudate putamen by 47%, and the thalamus by 24%. Contralateral to the lesion, paw-reaching was highly impaired, regardless of whether or not the rats had been pretrained, and lesion size correlated significantly to paw-reach performance. Ipsilateral rotation increased and sensorimotor function recovered with time in infarcted rats.

In contrast to amphetamine-induced rotation and sensorimotor behavior, the paw-reaching test provides a stable behavioral parameter after a middle cerebral artery occlusion. Moreover, the lesion-induced deficit in paw-reaching is highly correlated to the extent of the infarct, suggesting that this test is useful in evaluating treatment effects for a longer period of time.