White matter injury exacerbated anxiety-like behavior of db/db mice after distal middle cerebral artery occlusion / 中国医师进修杂志

ABSTRACT

Objective:To explore the possible mechanism of exacerbation of anxiety-like behavior in db/db mice after distal middle cerebral artery occlusion (dMCAO).Methods:The db/db mice was used to establish a type 2 diabetes mellitus model. Meanwhile, heterozygous db/+ mice and C57 wild-type (WT) mice were chosen as double control groups. Then a permanent distal middle cerebral artery occlusion model was employed as an acute ischemic stroke model. The blood glucose levels before and post-dMCAO surgery on day1, day3, and day5 were detected. The brain tissue loss at 35 days after stroke was measured by immunofluorescent staining of MAP2. The open-field test was performed to estimate anxiety-like behavior and general motor and exploring ability of the animals. Axons and myelin were immunostained with non-phosphorylated neurofilaments (SMI32) and myelin basic protein (MBP), respectively, to evaluate differences in white matter integrity in WT, db/+ and db/db mice 35 days after stroke. The correlation between SMI32/MBP and open field test parameters (time in center and corner) was analyzed. Flow cytometry was employed to detect the amount of T cells and B cells, including regulatory T cells (Tregs) in the brain tissue.Results:Blood glucose levels in db/db mice were significantly higher than db/+ mice and WT mice in both sham and dMCAO groups ( P<0.01). There was no significant difference in brain tissue loss 35 days post-stroke among db/db mice, db/+ mice, and WT mice. In the open field test, there were significant differences in the total distance of db/db mice, db/+ and WT mice in the sham and dMCAO groups. Db/db mice shorter than db/+ mice ( P<0.05), WT mice ( P<0.01), and db/+ mice shorter than WT mice ( P<0.05). There were significant time differences in the center among db/db, db/+, and WT mice in sham and dMCAO groups. In both the sham and dMCAO groups, db/db mice spent less time in the center area of the open field than WT mice ( P<0.01). In the sham group, db/+ mice spent less time in the center area than WT mice ( P<0.05). In dMCAO group, db/db mice spent less time in the center area than db/+mice ( P<0.05), and db/+ mice spent less time in the center area than WT mice ( P<0.01). For the time in the corner, in both the sham and dMCAO groups, db/db mice and db/+ mice consumed more time than WT mice ( P<0.01 or <0.05). In the dMCAO group, db/db mice spent more time in the corner than db/+ mice ( P<0.05). Referring to white matter injury, an increased SMI32/MBP ratio in EC area and CTX area (data was not shown in this article) after dMCAO in db/db, db/+ and WT mice were detected. In EC area, db/db mice have a higher SMI32 ratio than db/+ mice and WT mice 4.24 ± 0.37 vs. 1.96 ± 0.37, 1.80 ± 0.36, both have significant differences ( P<0.01). For db/db mice and WT mice, the SMI32/MBP ratio negatively correlates with time in center and positive correlation with time in the corner. Three days after dMCAO, the total cells of CD 3+ T cells, CD 8+ cells, Tregs, in db/db mice group have significantly decreased compared to WT group 4 079 ± 1 345 vs. 70 055 ± 3 374, 141.30 ± 28.36 vs. 2 714.00 ± 463.20, 148.00 ± 61.15 vs. 3 007.00 ± 639.90 ( P<0.01), while B cell has no change between two groups. Conclusions:By comparing the severity of anxiety-like behavior of db/db mice, the severity of white matter injury, and the number of T cells and B cells in brain tissue after dMCAO, immune-mediated brain white matter injury may aggravate db/db mice′s post-dMCAO anxiety-like behavior. Due to the gene dose effect, db/+ mice are not suitable as a control group for db/db mice in animal experiments involving anxiety-like behavior assessment.