Abstract T P81: Long-Term Activity Levels Vary by Rat Strain Following Stroke: A Disruption of the Circadian Rhythm?

Abstract

Background: Assessment of long-term behavioral outcome after experimental cerebral ischemia is important for evaluating potential therapeutic interventions. In this study, we explored strain related differences in baseline behavior and in response to stroke. Methods: Spontaneous cage activity was monitored (cm moved per hr) and analyzed before and after 2 hour middle cerebral artery occlusion (MCAO) in male Lewis, Wistar, and Sprague Dawley (SD) rats using the Noldus PhenoTyper® cages and EthoVision® Software system. Stroke severity was assessed using the neuroscore, foot fault errors, and performance on the rotarod. Infarct volume at 24 hours was determined in a second cohort of animals. Animals were sacrificed 56 days after MCAO. Data are analyzed using non-parametric statistics. Results: Prior to stroke, the median distance moved per hour during the dark was similar among the 3 strains, but Lewis rats were more active during the light cycle (P=0.001). Neuroscores did not differ between strains at 3 hrs after MCAO nor did infarct volumes at 24 hours after MCAO. Lewis rats, however, performed worse on the rotarod in the month following MCAO (P<0.05 at each time point). Foot fault errors were similar throughout the study period. After stroke, Lewis rats became more active during the dark cycle while Wistar and SD rats became more active during the light cycle (Figure). Summary: The 3 strains of rats evaluated in this study had different patterns in the change in activity after MCAO. Lewis rats showed an increase in activity during the dark cycle while Wistar and SD rats showed an increase in activity during the light cycle. This observation suggests that there are genetic differences in the response to stroke that may alter the circadian rhythm after stroke.