Bmal1 knockout results in behavioral and cerebrovascular defects in rats

Disruptions in circadian rhythms can increase the risk of cerebrovascular events and exacerbate anxiety, but the causative links are poorly understood. Previous work from our lab has shown an increase in brain water and blood brain barrier (BBB) permeability in Bmal1 knockout (Bmal1KO) rats and alterations of rhythms of genes involved in fluid homeostasis and cerebrovascular function. However, it is unknown if lack of Bmal1 impacts cerebrovascular physiology or anxiety-like behavior. We hypothesize that Bmal1KO rats have heightened anxiety and blunted reperfusion response to ischemia which are indicative of impaired cerebrovascular hemodynamics. We used male and female Bmal1KO and wildtype (WT) littermate controls and performed behavioral tests using open field, elevated plus maze, rotorod, and foot misplacement tests. We failed to observe any genotype differences in anxiety using the elevated plus maze. Bmal1KO rats had fewer entries into the center area during the open field test (10.25±2.5 vs 25.25±4.5, n=16-17/group; p=0.01). Bmal1KO rats showed poor coordination and motor learning ability compared to WT rats going a shorter average distance in the rotarod test (KO: 643.4±144.2 cm, n=11 vs. WT: 1257±226.5, n= 8; p=0.028). To measure cerebrovascular hemodynamics, we recorded left carotid blood flow via perivascular flow probe and simultaneously recorded mean arterial blood pressure via the right carotid artery. There were no genotype differences in baseline carotid blood flow, mean arterial pressure, or heart rate. Blood flow was suppressed for 40 seconds by occluding the left carotid artery, and peak flow (hyperemia) and time to return to baseline were evaluated following release. Peak blood flow (KO: 217.8±16.1 % of baseline, n=5 males, 5 females vs. WT: 164.4±6.1 %, n=7 males, 5 females; p=0.0035) and time to return to baseline (KO: 75.45±11.8 s time to baseline vs. WT: 37.48±9.1 s; p=0.006) following artery occlusion were both higher in Bmal1KO rats compared to WT. In the subset of animals that also had femoral artery occlusions, there was a similarly increased hyperemia response in Bmal1KO rats. Because both the carotid and femoral artery experiments had similar responses, this suggests that the increased reactive hyperemia response is a global phenomenon, not localized to the cerebrovascular system. The cerebrovascular hemodynamics were correlated to the results from the behavioral tests. There was a positive coloration between peak blood flow in response to ischemia and the average time it took for the rats to complete the foot misplacement test (n=13, p=0.02, slope=0.037). These results suggest that circadian rhythms are integral in maintaining proper cerebrovascular hemodynamics and that impaired cerebrovascular hemodynamics may contribute to impaired behavior in our model of circadian gene knockout. This research was supported in part by a pilot award from the Integrative Center for Aging Research to BKB and MTH. This abstract was presented at the American Physiology Summit 2025 and is only available in HTML format. There is no downloadable file or PDF version. The Physiology editorial board was not involved in the peer review process.