A Study On The Correlation Between Depression And Cerebrovascular Factors In Rat Models

PartⅠBehavioral and brain glucose metabolism study in rat depression model induced by Chronic Unpredicatable Mild Stress[Objectives] To investigate behavioral features of depression rats and explore the relationships between depression and brain glucose metabolism by establishing rat depression model induced by Chronic Unpredicatable Mild Stress.[Methods] The study was carried out using twenty healthy male Sprague-Dawley (SD) rats:normal control group (CON, n=10), depression model group (CUMS, n=10). To establish rat depression model, it was designed to meet the procedures of Chronic Unpredictable Mild Stress, which were internationally recognized and were carried out continuously for a total of 4 weeks, including water deprivation, empty water bottle, continuous lighting, cage tilt, paired housing, damp bedding, white noise and strobe light. For all of rats, sucrose test and body weight were measured before beginning the CUMS procedures, and then conducted weekly throughout the CUMS periods under similar conditions. All parameters in sucrose test were recorded, including total fluid intake, sucrose intake and water intake, and then sucrose relative intake, water relative intake and sucrose preference=[sucrose solution intake (ml)/ total fluid intake (ml)]×100 were calculated. Sucrose preference tests were employed to operationally define anhedonia. Besides these, all rats were tested one by one in an open field test at baseline and week 4 to investigate behavioral characters. All rats' behaviors were recorded using a video camera and were scored manually from a TV screen. Behavioral parameters were as follows:the number of total activity, peripheral activity, central activity in five minutes; the number of first minute activity, the number of grooming and defecation. Ten rats (CUMS, n=10) were given 18F-FDG micro PET scan at baseline and week 4, respectively. Statistical analysis:sucrose test and body weight were analyzed using a repeated measurement ANOVA. Open-field test was analyzed using a non-parametric Friedman ANOVA. We used voxel-based statistical analyses by SPM5 software and used paired t-tests for the comparison between pre-CUMS and CUMS groups. Spearman rank correlation coefficients were calculated.[Results]①Body weight:the body weight gain of the CUMS rats was slightly lower than the CON rats during the last two weeks of the CUMS periods (p<0.05).②Sucrose test:CUMS gradually reduced the relative intake of the sucrose solution. Tests of the main effects for the periods of CUMS (weeks 1-4) showed a difference between the two groups of sucrose relative intake [F(1,18)=40.72, p<0.001]. There was a strong tendency for interaction between group and week [F (4,72)=7.49, p<0.001]. However, no significant differences in water relative intake were found at any point at baseline and during the CUMS periods between two groups. Compared with the CON rats, CUMS rats show no difference at the baseline, but a significantly reduced sucrose preference, especially at week 3 and 4 (all p<0.001).③Open-field test:The CUMS rats exhibited enhanced locomotor activity during the first minute [χ2 (10, 1)=6.4,p=0.011] compared with CON animals. Furthermore, there was a tendency to lower activity in the center squares and reduced rearing for the CUMS rats than the CON rats at week 4[χ2 (10, 1)=9.0,p=0.003;χ2 (10,1)=5.4,p=0.02, respectively]. In comparison to the CON rats, a significant increase in grooming and defecation was observed in CUMS rats[χ2(10, 1)=6.4,p=0.011;χ2(10, 1)=5.4,p=0.02, respectively).④18F-FDG micro PET:using 18F-FDG micro PET, we found that piriform cortex, septal nuclei, inferior colliculus and periaqueductal gray were deactivated while only auditory cortex was activated after 4 weeks of Chronic Unpredictable Mild Stress (all p<0.01). These significant brain region changes were predominantly found in the left hemisphere, and the change of glucose metabolism in auditory cortex has negative correlation with the change value of inferior colliculus (R=-0.785,p=0.007).[Conclusions]①CUMS rats can mimic the core symptoms of depression, an anhedonia to sucrose preference, and anxiety-, fear-like behaviours, which support the face validity of CUMS as an animal model for human depression.②The changes of brain activity are associated with depression and left hemisphere is dominated, especially in many brain regions, such as piriform cortex, septal nuclei, inferior colliculus, periaqueductal gray and auditory cortex, whose glucose metabolism changes are most notable.Part II Behavioral and brain glucose metabolism study in rat cerebrovascular factor model induced by high lipid feed[Objectives] To investigate behavioral features of hyperlipidemia rats and explore the relationships between depression and hyperlipidemia by establishing rat cerebrovascular factor model induced by high lipid feed.[Methods] The study was carried out using twenty healthy male Sprague-Dawley (SD) rats:normal control* group (CON*, n=10), cerebrovascular factor model group (CVF, n=10). To establish rat cerebrovascular factor model, it was designed to high lipid feed for a total of 9 weeks (feed formulation:custard powder 10%, lard 20%, cholesterol 2.5%, sodium cholate 0.2%, thiamazole 0.1%, sucrose 2% and common feed 65.2%). For all of rats, sucrose test, body weight and open-field test were measured before beginning high lipid feed, and then conducted at week 9 under similar conditions. All observed parameters in above tests have been given detailed descriptions in the partⅠ. Besides these, all rats were taken blood 5ml via caudal vein at week 9. Triglycerides (TG) and total cholesterol (TC) were measured using the method of enzyme linked immunosorbent assay, and high density lipoprotein cholesferol (HDLC) and low density lipoprotein cholesferol (LDLC) were measured using the method of phosphotungstic acid-magnesium sedimentation. Twenty rats (CON*, n=10; CVF, n=10) were given 18F-FDG micro PET scan at week 9. Statistical analysis:sucrose test and body weight were analyzed using a repeated measurement ANOVA. Open-field test was analyzed using a non-parametric Friedman ANOVA. Comparison of serum lipids was analyzed using student's t-test. We used voxel-based statistical analyses by SPM5 software and used student's t-test for the comparison between CON* and CVF groups. Spearman rank correlation coefficients were calculated.[Results]①Body weight and serum lipids:the body weight gain of the CVF rats was significantly higher than the CON* rats (t=18.824,p<0.001); TC (t=11.76, p<0.001) and LDL (t=6.96, p<0.001) were both significantly increased, however, HDL (t=-3.43,p<0.001) was significantly decreased at week 9.②Sucrose test:no significant differences in sucrose relative intake were found at baseline and week 9 between two groups [F(1,18)=0.896,p=0.356]. Compared with water relative intake at baseline, CVF rats increased water relative intake at week 9 (t=5.747,p<0.001) and significantly decreased sucrose preference (t=-5.565,p<0.001).③Open-field test:no significant differences were found at baseline and week 9 between two groups (all p>0.05).④18F-FDG micro PET:using 18F-FDG micro PET, we found that thalamus and striatum were deactivated of CVF rats, compared with CON* rats at week 9 (all p<0.01). On the other hand, the correlation between the changes of sucrose preference and the changes of brain glucose metabolism in thalamus and striatum was positive (R=0.782,p<0.01, R=0.806, p<0.01, respectively).[Conclusions]①CVF rats present the core symptom of depression, and severity of this symptom has positive correlation with the changes of brain glucose metabolism in thalamus and striatum.②The changes of brain activity in "limbic system-striatum-thalamus" circuit induced by hyperlipidemia are associated with depression and right hemisphere is dominated.③Hyperlipidemia is one of cerebrovascular risk factors, but it is more important to find that hyperlipidemia is also a risk factor in depression.PartⅢBehavioral and brain glucose metabolism study in rat cerebrovascular factor model combined with Chronic Unpredictable Mild Stress model of depression[Objectives] To establish successfully an animal model of cerebrovascular factor model induced by high lipid feed combined with Chronic Unpredictable Mild Stress (CUMS) model of depression, to investigate behavioral features and brain glucose metabolism changes of this model rats, and to explore what roles hyperlipidemia and CUMS played in depression.[Methods] The study was carried out using twenty healthy male Sprague-Dawley (SD) rats:normal control group (CON,n=10), double model factors group (DMY, n=10). To establish rat DMY model, it was designed to high lipid feed for a total of 9 weeks (see the PartⅡ), and then followed by CUMS for 4 weeks (see the PartⅠ). For all of rats, sucrose test and body weight were measured before beginning high lipid feed, at week 9, and then conducted weekly throughout the CUMS periods (week 10,11,12,13) under similar conditions. All rats were tested one by one in an open field test at baseline, week 9 and week 13. Besides these, all rats were taken blood 5ml via caudal vein at week 9 and then serum lipids were measured. All observed parameters in above tests have been given detailed descriptions in the partⅡ. Ten rats (DMY, n=10) were given 18F-FDG micro PET scan at week 9 and week13, respectively. Statistical analysis:for details, see the partⅠand partⅡ.[Results]①Serum lipids:TC (t=7.548,p<0.001) and LDL (t=6.175,p<0.001) were both significantly increased, however, HDL (t=-5.300,p<0.001) was significantly decreased at week 9 compared with the CON rats.②Body weight:the body weight gain of the DMY rats was significantly higher at week 9 (p<0.01) and slightly lower at week 13 (p<0.05) compared with CON rats.③Sucrose test:CUMS gradually reduced the relative intake of the sucrose solution at 4 time points during CUMS periods in DMY rats [F(1,18)=104.267, F(1,18)=55.986, F(1,18)=46.084, F(1, 18)=61.080, respectively; all p<0.001]. DMY rats increased water relative intake at week 9,11 and 13[F(1,18)=27.72,F(1,18)=16.13,F(1,18)=12.26, respectively; all p<0.001]. DMY rats gradually decreased sucrose preference at week 9 and 4 time points during CUMS periods [F(1,18)=28.891, F(1,18)=51.630, F(1,18)=103.794, F(1,18)=103.645, F(1,18)=119.104, respectively; all p<0.001].④Open-field test: compared with pre-CUMS, significant decrease activities in total squares in 5-min, central squares and peripheral squares were observed in DMY rats[χ2 (10, 1)=3.60, p=0.048;χ2 (10, 1)=10,p=0.002;χ2 (10, 1)=3.60,p=0.048, respectively]. Besides these, the number of rearing was reduced[χ2 (10, 1)=9.0, p=0.003], however, the number of grooming and defecation was significantly increased[χ2 (10, 1)=9.0, p=0.003;χ2 (10, 1)=9.0,p=0.03, respectively].⑤18F-FDG micro PET:using 18F-FDG micro PET, we found that hypothalamus and insular cortex were activated while hippocampus and entorhinal cortex were deactivated after 4 weeks of Chronic Unpredictable Mild Stress in DMY rats (all p<0.01). These significant brain region changes were predominantly found in the left hemisphere and the change of glucose metabolism in hypothalamus was negatively correlative with the change of hippocampus(R=-0.736, p=0.015).[Conclusions]①It is a method to mimic hyperlipidemia combined depression by establishing cerebrovascular factor model induced by high lipid feed for a total of 9 weeks, followed by depression model induced by Chronic Unpredictable Mild Stress (CUMS) for 4 weeks.②Under uncontrolled hyperlipidemia, severe depressive symptoms will present more early once exposure to a series of chronic stressors followed by significant autonomic nervous dysfunctional symptoms.③When hyperlipidemia combined with depression, it will significantly change in brain glucose metabolism of many brain regions related with emotion and neuroendocrine, especially in hippocampus. Furthermore, there are significant changes in entorhinal cortex and insular cortex, and left hemisphere is dominated.④CUMS and hyperlipidemia play a synergistic action in the changes of behavior and brain activity of depression.