Elevated body swing test after focal cerebral ischemia in rodents: methodological considerations

Abstract

Background: The elevated body swing test (EBST) is a behavioral test used to evaluate experimental stroke in rodents. The basic idea is that when the animal is suspended vertically by the tail, it will swing its head laterally to the left or right depending on lesion side. In a previous study from our lab using the EBST after middle cerebral artery occlusion (MCAo), rats swung contralateral to the infarct day 1 post-MCAo, but ipsilateral day 3 post-MCAo. This shift was unexpected and prompted us to perform the present study. First, the literature was systematically reviewed to elucidate whether a similar shift had been noticed before, and if consensus existed regarding swing direction. Secondly, an experiment was conducted to systematically investigate the suggested behavior. Eighty-three adult male and female Sprague-Dawley rats were subjected to MCAo or sham surgery and the EBST was performed up to 7 days after the lesion.

Results: Both experimentally and through systematic literature review, the present study shows that the direction of biased swing activity in the EBST for rodents after cerebral ischemia can differ and even shift over time in some situations. The EBST curve for females was significantly different from that of males after the same occlusion time (p = 0.023).

Conclusions: This study highlights the importance of adequate reporting of behavioral tests for lateralization and it is concluded that the EBST cannot be recommended as a test for motor asymmetry after MCAo in rats.

Fig. 1

EBST results in a previous study from our lab showing a shift phenomenon. Day 1 post-MCAo, the rats in two out of three stroke groups swung predominantly to the side contralateral to the ischemic hemisphere, but had day 3 post-MCAo developed an ipsilateral side bias. Adapted from Ström et al. [42].

Fig. 2

Flow chart of article inclusion for the systematic review. From the original Medline search and through reviewing the articles retrieved, together with the previous article from our lab [42], there were 33 articles. These were further analyzed with regard to main swing direction in the EBST after unilateral cerebral ischemia.

Fig. 3

Experimental outline. Fourteen days before MCAo the females were ovariectomized (day −14). On day 0 the animals were subjected to either MCAo or sham operation and on days 1, 2, 3 and 7 the EBST was performed. The animals were sacrificed on day 7.

Fig. 4

EBST performance (a, c, e) and infarct volumes including location of infarcts (b, d, f). There was a significant difference between the EBST curve for group Female 60 min (a) and Male 60 min (c) but not for the three male groups (Male 30 min, Male 60 min and Male 90 min). None of the MCAo groups (Male 30 min, Male 60 min, Male 90 min and Female 60 min) differed significantly in infarct volume of location of infarct (proportion of infarct in cortex). Asterisks indicate significant difference in proportion of right-side swings compared to baseline values of the group (p < 0.05). Mean ± SEM.

Fig. 5

EBST performance in males regrouped according to infarct size. Because of high variability in infarct sizes, the males were regrouped according to infarct size (Male small infarcts, Male medium infarcts and Male large infarcts) in an additional analysis to reflect actual severity of lesions produced rather than occlusion times. Asterisks indicate significant difference in proportion of right-side swings compared to baseline values of the group (p < 0.05).

Fig. 6

EBST performance of rats displaying a shift. EBST performance of rats from MCAo groups (Male 30 min, Male 60 min, Male 90 min and Female 60 min) displaying a shift in direction (proportion of right-side swings >0.8 on day 1 and <0.4 on days 2 or 3).