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 Table of Contents  
ORIGINAL ARTICLE
Year : 2021  |  Volume : 5  |  Issue : 4  |  Page : 119-131

Unpredictable chronic mild stress-induced depressive-like behaviors in spontaneously hypertensive rats


Department of Cardiology, Beijing Anzhen Hospital Affiliated to Capital Medical University, Beijing, China

Date of Submission09-Aug-2021
Date of Acceptance05-Nov-2021
Date of Web Publication30-Nov-2021

Correspondence Address:
Prof. Meiyan Liu
Department of Cardiology, Beijing Anzhen Hospital Affiliated to Capital Medical University, No. 2 Anzhen Road, Chaoyang District, Beijing 100 029
China
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/hm.hm_49_21

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  Abstract 

Objective: The objective is to explore whether hypertension influences unpredictable chronic mild stress (UCMS)-induced depressive-like behaviors and the potential therapeutic effect of Guan-Xin-Shu-Tong capsules (GXST) in controlling hypertension and depressive-like behaviors. Materials and Methods: Fifteen spontaneously hypertensive rats (SHR) and 15 wistar rats were divided into three groups respectively (n = 5, in each group), including control, UCMS, and UCMS + GXST groups. The systolic blood pressure (SBP), diastolic blood pressure (DBP), mean arterial pressure (MAP), and heart rate (HR) were recorded at baseline and at the end of the experiment. Rats were subjected to seven kinds of UCMS over 4 weeks. GXST treatments were administrated (2.8 g/kg) by intragastric gavage once a day over 4 consecutive weeks during UCMS treatment. Sucrose-preference and open-field tests were used to detect depressive-like behaviors. Results: SHR exposed to 4-week UCMS treatment had lower HR when compared with control and UCMS + GXST groups (P < 0.05); Wister rats receiving UCMS or UCMS + GXST had lower SBP (P < 0.05), lower DBP (P < 0.05) and lower MAP (P < 0.05) than controls. Compared with the controls, UCMS reduced the sucrose preference of Wistar rats, UCMS and UCMS + GXST decreased both grid-crossings and the number of upright postures measured in Wistar rats (P < 0.05). SHR showed lower sucrose consumption, less sucrose preference, and fewer grid-crossings after UCMS than control SHR. However, the lower incidence of upright postures in SHR was prevented by GXST treatment (P < 0.05). Linear correlation showed that grid-crossings or upright postures were negatively related to the values of SBP, DBP, or MAP, presenting the positive relationship between depressive-like behaviors and SBP, DBP, or MAP reduction in Wistar rats; there was a negative correlation between grid-crossings and DBP responses, and MAP responses in SHR, and a positive correlation between depressive-like behaviors and DBP and MAP response elevation in SHR. Conclusions: UCMS-induced depressive-like behaviors in Wistar and SHR, accompanied by a blood pressure decrease in Wistar rats but not in SHR. While GXST exhibited effective relief of depressive-like behaviors in SHR without influencing their blood pressure.

Keywords: Depressive-like behaviors, hypertension, stress


How to cite this article:
Zhang L, Liu M. Unpredictable chronic mild stress-induced depressive-like behaviors in spontaneously hypertensive rats. Heart Mind 2021;5:119-31

How to cite this URL:
Zhang L, Liu M. Unpredictable chronic mild stress-induced depressive-like behaviors in spontaneously hypertensive rats. Heart Mind [serial online] 2021 [cited 2022 Sep 28];5:119-31. Available from: http://www.heartmindjournal.org/text.asp?2021/5/4/119/331565


  Introduction Top


Emerging evidence suggests a strong association between hypertension and psychological stress. A meta-analysis has demonstrated that patients with hypertension are particularly vulnerable to psychological stress (odds ratio [OR] = 2.69, 95% confidence interval [CI] = 2.32–3.11), and patients with depression, anxiety, or other acute/chronic psychological stress are at higher risk of hypertension (OR = 2.40, 95% CI = 1.65–3.49).[1] Further, depression has been recognized as an independent risk factor in hypertension, 33% of patients combine hypertension with depression.[2] In addition, anxiety is regarded as a contributory factor to hypertension, and increases the risk of developing hypertension.[3] Acute stress can lead to sudden elevation of blood pressure, and Matthews demonstrated that after a 5-min mental arithmetic stress, patients' blood pressures increased rapidly.[4] While, job strain, low social support, high economic stress all increase the risk of hypertension.[5],[6] Moreover, we need to pay attention to the adverse prognosis of mental stress-induced hypertension with respect to its adverse cardiovascular outcomes, including coronary artery disease, ischemic heart disease, arrhythmia, and stroke.[7]

However, the potential underlying pathophysiological mechanisms remain to be further explored. The main mechanisms linked to mental stress-induced hypertension involve overactivity of the HPA and sympathetic nervous system (SNS),[8] endothelial dysfunction,[9] serotonin,[10] inflammation.[11] Mental stress activates the hypothalamus, stimulating corticotropin-releasing hormone, and cortisol release. The cortisol strengthens the vascular constriction response induced by noradrenaline and adrenaline, consequently contributing to the elevation of blood pressure. Furthermore, stress also activates the SNS, resulting in increases in noradrenalin and adrenalin. Moreover, increased blood flow and shear stress lead to endothelial dysregulation through release of more contraction factors and less diastolic factors.[9] In addition, 5-HT also plays a crucial role. Centrally, stress enhances the input/output transmission of the sympathetic ganglia, which results in increased 5-HT and activation of 5-HT3A receptors, inducing the elevation of blood pressure.[10] In the periphery, 5-HT functions as a kind of vasoconstrictor and may enhance vascular constriction. In addition, the immune system has been reported to participate,[11] as findings show unpredictable chronic mild stress (UCMS) may induce hypertension through tumor necrosis factor-α and p38/JNK pathways.[11]

To treat patients with mental stress-induced hypertension, despite antihypertensive drugs, physicians have used various therapies, such as contemplative meditation, yoga, or selective 5-HT reuptake inhibitors (SSRIs) and other antidepressant drugs.[12],[13] However, the side effects of antidepressants have limited their use. SSRIs could decrease DAergic neuronal activity, inhibit motivation and lead to motor dysfunction.[14] In addition, the side effects of SSRIs, such as sexual dysfunction, nausea, and sedation are associated with the does of SSRIs, which could lead to dropout of the antidepressant treatment.[15]

Guan-Xin-Shu-Tong capsules (GXST), are effective in clinical practice, but their mechanism is unclear. GXST is composed of five ingredients, Choerospondias axillaris, Salvia miltiorrhiza Bunge, Borneol, Syzygium aromaticum, Concretio silicea bambusae.[16] The chemical structure of proposed active components is shown in [Figure 1], including Gallic acid, Tanshinone IIA, Borneol, Eugenol, and Glycinebetaine. Clinical research has demonstrated that GXST exhibits a potent ability to decrease blood pressure in patients with hypertension[17] and to relieve depression and anxiety in patients with angina pectoris.[18] The antihypertensive and antidepressant effects of GXST may be a result of the activities of its main constituents. Gallic acid could reduce high blood pressure by suppressing Ca2+/calmodulin-dependent protein kinase II (CaMKII) induced apoptosis, and relieve depression via its antioxidant effect.[19] Borneol could pass through the blood-brain barrier to exert neuroprotective effect through inhibiting IκBα-NF-κB translocation signaling pathways.[20] Eugenol attenuates depressive-like behaviors by increasing levels of brain-derived neurotrophic factor (BDNF).[21] Eugenol has been implicated in lowering blood pressure by relaxing blood vessels.[22]
Figure 1: The chemical structures of different major GXST constituents. (a) The chemical structure of gallic acid. (b) The chemical structure of TanshinonIIA. (c) The chemical structure of borneol. (d) The chemical structure of eugenol. (e) The chemical structure of glycinebetaine

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However, to the best of our knowledge, no animal experiments have been conducted to explore the potential therapeutic effect of GXST in hypertension and UCMS induced depressive-like behaviors. Therefore, we conducted this study to understand the potential effects of GXST further. We suppose that this experiment could explain that whether UCMS could induce depressive-like behaviors in Wistar and spontaneously hypertensive rats (SHR), and whether GXST could exhibit effective relief of depressive-like behaviors in Wistar and SHR. We hope that this experiment could have clinical implications and expand the usage arrangement of GXST in clinical practice.


  Materials and Methods Top


Animals

A total of 30 rats were included in this study, including 15 SHR (190–210 g) and 15 Wistar Kyoto rats (190–210 g). In order to avoid the effect of the steroid hormone estrogen in females, male rats were chosen. SHR and Wistar rats were divided into three groups respectively (n = 5, in each group), including control, UCMS, and UCMS + GXST groups. All the rats were purchased from Beijing Vital River Laboratory Animal Technology Co., Ltd.(SHR No. 1100111911010620; Wistar No. 1100111911010621). After arriving in the animal laboratory, the rats were fed normally for 5 days to adapt to the habitation (humidity: 45%, room temperature 23 ± 2°C, 12 h/12 h light-dark cycle).

Blood pressure

The systolic blood pressure (SBP), diastolic blood pressure (DBP), mean arterial pressure (MAP), and heart rate (HR) of the rats were detected using the noninvasive tail-cuff method (Intelligent noninvasive sphygmomanometer, Softron Biotechnology Ltd.). The rat was restricted in a special bag exposing its tail. Then the tail was inserted in the tail-cuff to enable the sphygmomanometer to detect the blood pressure and other parameters. The results could be read from the computer automatically. The procedure was conducted at baseline and again at the end of the experiment [Figure 2].
Figure 2: Equipment used for detecting blood pressure of subject rats

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Unpredictable chronic mild stress

Seven kinds of UCMS were chosen in this study, which were commonly used in animal experiments.[23],[24] including physical restraint (2 h), cold water swimming (4°C, 5 min), tail clipping (1 min), inversion of the light/dark cycle (24 h), foot shock (30V, 5s), level shaking (160HZ, 5 min), and hot environment (40°C, 5 min). The UCMS treatment lasted 4 weeks. To avoid adaptation, no method appeared twice in the same week. UCMS was arranged in the sequence as shown in [Table 1].
Table 1: Unpredictable chronic mild stress

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Drug administration GXST capsules (Buchang Pharma) were administrated 2.8 g/kg by intragastric gavage once a day over 4 consecutive weeks. For a human, the regular dose of GXST is 2.7 g/day/60 kg (0.3 g/one capsule, 3 capsules/once, three times a day). Therefore, we chose the dose of 2.8 g/kg/day for a rat whose drug dose is 10–20 times higher when compared with a human.

Sucrose preference testing

Forty-eight hours before the sucrose preference test, one bottle of 1% sucrose solution and one bottle of tap water of the same weight were presented to the rats for adaptation. After fasting for 20 h, the rats were given a choice of either 1% sucrose solution or tap water positioned as before for 1 h, and the position was switched in the middle of this time to avoid adaptation. Then, the sucrose consumption and tap water consumption were recorded. Sucrose preference was calculated as: Sucrose preference (%) = sucrose consumption (g)/[sucrose consumption (g) + tap water consumption (g)] ×100%.[25]

Open field testing

The open-field test was conducted in a gray box (100 cm length × 100 cm width × 40 cm height). and the floor was divided into 25 equal grids. Before the day of the test, the rats were placed in the open field for adaptation for 5 min. The next day, the rats were placed in the center of the floor, and then their activities were recorded by an automatic camera for 5 min. The horizontal activity was calculated by counting the number of blocks crosssed, and the vertical activity was calculated by taking the times of the upright postures. The total scores were calculated as the sum of horizontal and vertical activities.[24],[26]

Statistical analysis

A Shapiro–Wilk test was conducted to determine the normal distribution of data, and the data were presented as mean ± standard deviation. One-way analysis of variance was used to compare UCMS, and UCMS + GXST groups in HR, SBP, DBP, MAP, and the value of behavior tests. The Student's t-test was applied to compare Wistar rats and SHR across all related factors. Linear correlation was used to calculate the relationship between hemodynamic factors and depressive-like behaviors. When the linear correlation was significant, linear regression was used to calculate the regression squares. Two-tail P < 0.05 was considered to be significant. All statistical analyses were carried out by IBM SPSS 24.0 software (IBM Corp., Armonk, NY, USA) and Prism 6.0 software (GraphPad Software, Inc., San Diego, CA, USA).

Ethic statements

The study obeyed Animal Welfare and Rights requirements and was approved by the Animal Ethical and Welfare Committee of Beijing Anzhen Hospital affiliated to the Capital Medical University.


  Results Top


The effects of unpredictable chronic mild stress on hemodynamic factors

Heart rate comparisons

Comparison of Wistar rat heart rate

There were no significant differences when comparing HR values at baseline and after 4-week treatment between control, UCMS, and UCMS + GXST groups of Wistar rats, respectively [P > 0.05: [Figure 3]a, [Figure 3]b, [Figure 3]c.
Figure 3: Comparisonsbetween both wistar rats and spontaneously hypertensive rats. (a) HR comparison between baseline and 4 weeks later in the wistar control group. (b) HR comparison between baseline and 4 weeks later in the Wistar UCMS group. (c) HR comparison between baseline and 4 weeks later in the wistar UCMS + GXST group. (d) HR comparison between control, UCMS, and UCMS + GXST groups of wistar rats. (e) HR response comparisons between control, UCMS, and UCMS + GXST groups of wistar rats. (f) HR comparison between baseline and 4 weeks later in the spontaneously hypertensive rats control group. (g) HR comparison between baseline and 4 weeks later in the spontaneously hypertensive rats UCMS group. (h) HR comparison between baseline and 4 weeks later in the spontaneously hypertensive rats UCMS + GXST group. (i) HR comparison between control, UCMS, and UCMS + GXST groups of spontaneously hypertensive rats. (j) HR responses comparison between control, UCMS, and UCMS + GXST groups in spontaneously hypertensive rats rats. (k) HR comparison between wistar rats and spontaneously hypertensive rats. (l) HR response comparison between wistar rats and spontaneously hypertensive rats

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Among the group comparisons, there was no significant difference in HR between the control, UCMS, or UCMS + GXST groups [P > 0.05: [Figure 3]d]. While the HR response was lower in the UCMS + GXST group when compared with the control and UCMS groups of Wistar rats [P < 0.05: [Figure 3]e].

Comparison of spontaneously hypertensive rats heart rate

There were no significant differences when comparing HR at baseline or after 4-week treatment between the control, UCMS, and UCMS + GXST SHR groups, respectively [P > 0.05: [Figure 3]f, [Figure 3]g, [Figure 3]h].

Comparing groups, HR was lower in the UCMS group relative to the control and UCMS + GXST groups [Figure 3]i. While there were no significant differences in HR response between the control, UCMS, and UCMS + GXST groups [P > 0.05: [Figure 3]j].

Heart rate comparisons between Wistar rats and spontaneously hypertensive rats

There were no significant differences seen in the comparisons of HR or the HR responses between Wistar rats and SHR [P < 0.05: [Figure 3]k and [Figure 3]l].

Systolic blood pressure comparisons between Wistar rat groups

Systolic blood pressure comparison in Wistar rats

UCMS decreased the SBP of Wistar rats significantly (P < 0.05). There was no significant difference when comparing SBP at baseline with that post-4-week treatment [P > 0.05: [Figure 4]a, [Figure 4]b, [Figure 4]c.
Figure 4: Systolic blood pressure comparisons between both wistar rats and spontaneously hypertensive rats. (a) systolic blood pressure comparison between baseline and 4 weeks later in the wistar control group. (b) systolic blood pressure comparison between baseline and 4 weeks later in the wistar UCMS group. (c) systolic blood pressure comparison between baseline and 4 weeks later in the wistar UCMS + GXST group. (d) systolic blood pressure compariso between control, UCMS, and UCMS + GXST groups in wistar rats. (e) systolic blood pressure responses comparison among control, UCMS, and UCMS + GXST groups in wistar. (f) systolic blood pressure comparison between baseline and 4 weeks later in the spontaneously hypertensive rats control group. (g) systolic blood pressure comparison between baseline and 4 weeks later in the spontaneously hypertensive rats UCMS group. (h) systolic blood pressure comparison between baseline and 4 weeks later in the spontaneously hypertensive rats UCMS + GXST group. (i) systolic blood pressure comparison between control, UCMS, and UCMS + GXST groups of spontaneously hypertensive rats. (j) systolic blood pressure responses comparison among control, UCMS, and UCMS + GXST groups in spontaneously hypertensive rats. (k) systolic blood pressure comparison between wistar rats and spontaneously hypertensive rats. (l) systolic blood pressure response comparison between wistar rats and spontaneously hypertensive rats

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The Wistar rat group comparisons showed that UCMS and UCMS + GXST decreased SBP significantly compared with the control group (P < 0.05). While there were no significant differences when comparing SBP between the three groups [P > 0.05: [Figure 4]d and [Figure 4]e].

Systolic blood pressure comparisons between spontaneously hypertensive rats groups

There were no significant differences seen on comparing SBP at baseline with post 4-week treatment for the control, UCMS, and UCMS + GXST groups of SHR respectively [P > 0.05: [Figure 4]f, [Figure 4]g, [Figure 4]h].

Among the group comparisons, there were no significant differences in SBP and SBP responses between the control, UCMS, and UCMS + GXST groups [P > 0.05: [Figure 4]i and [Figure 4]j].

Systolic blood pressure comparison between Wistar rats and spontaneously hypertensive rats

SHR had higher SBP than Wistar rats in all the three groups (P < 0.05), while no significant differences were seen when comparing the SBP responses between Wistar rats and SHR in any of the three groups [P > 0.05: [Figure 4]k and [Figure 4]l].

Diastolic blood pressure comparisons

Diastolic blood pressure comparisons between Wistar rat groups

Wistar rats had lower DBP after 4-week UCMS or UCMS + GXST treatments when compared with baseline values (P < 0.05), while no significant difference was seen in the control group between baseline and 4 weeks of treatment [P > 0.05: [Figure 5]a, [Figure 5]b, [Figure 5]c].
Figure 5: Diastolic blood pressure comparisons between wistar rats and spontaneously hypertensive rats. (a) diastolic blood pressure comparison between baseline and 4 weeks later in the wistar control group. (b) diastolic blood pressure comparison between baseline and 4 weeks later in the wistar UCMS group. (c) diastolic blood pressure comparison between baseline and 4 weeks later in the Wistar UCMS + GXST group. (d) diastolic blood pressure comparison among control, UCMS, and UCMS + GXST groups of wistar rats. (e) diastolic blood pressure responses comparison among control, UCMS, and UCMS + GXST groups of wistar rats. (f) diastolic blood pressure comparison between baseline and 4 weeks later in the spontaneously hypertensive rats control group. (g) diastolic blood pressure comparison between baseline and 4 weeks later in the spontaneously hypertensive rats UCMS group. (h) diastolic blood pressure comparison between baseline and 4 weeks later in the spontaneously hypertensive rats UCMS + GXST group. (i) diastolic blood pressure comparison between control, UCMS, and UCMS + GXST groups of spontaneously hypertensive rats. (j) diastolic blood pressure responses comparison among control, UCMS, and UCMS + GXST groups of spontaneously hypertensive rats. (k) diastolic blood pressure comparison between wistar rats and spontaneously hypertensive rats. (l) diastolic blood pressure response comparison between wistar rats and spontaneously hypertensive rats

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Comparing between groups, Wistar rats in the UCMS and UCMS + GXST groups had lower DBP and lower DBP responses than the control group [P < 0.05: [Figure 5]d and [Figure 5]e].

Diastolic blood pressure comparisons between spontaneously hypertensive rats groups

There were no significant differences found on comparing DBP at baseline and after 4-week treatment in the control, UCMS, and UCMS + GXST groups respectively [P > 0.05: [Figure 5]f, [Figure 5]g, [Figure 5]h].

Comparing between groups there were no significant differences in DBP and DBP responses between the control, UCMS, and UCMS + GXST groups [P > 0.05: [Figure 5]i and [Figure 5]j].

Diastolic blood pressure comparisons between Wistar rats and spontaneously hypertensive rats

SHR had higher DBP than Wistar rats in all three groups (P < 0.05). SHR had higher DBP responses than Wistar rats in the UCMS and UCMS + GXST groups [P < 0.05: [Figure 5]k and [Figure 5]l].

Mean arterial pressure comparisons

Mean arterial pressure comparisons between Wistar rat groups

Wistar rats had lower MAP after 4-week UCMS or UCMS + GXST treatments when compared with baseline values (P < 0.05), while no significant differences were seen in the control group between baseline and after 4-week treatment [P > 0.05; [Figure 6]a, [Figure 6]b, [Figure 6]c.
Figure 6: Mean arterial pressure comparisons between wistar rats and spontaneously hypertensive rats. (a) mean arterial pressure comparison between baseline and 4 weeks later in the wistar control group. (b) mean arterial pressure comparison between baseline and 4 weeks later in the wistar UCMS group. (c) mean arterial pressure comparison between baseline and 4 weeks later in the wistar UCMS + GXST group. (d) mean arterial pressure comparison among control, UCMS, and UCMS + GXST groups in wistar rats. (e) mean arterial pressure responses comparison among control, UCMS, and UCMS + GXST groups in wistar rats. (f) mean arterial pressure comparison between baseline and 4 weeks later in the spontaneously hypertensive rats control group. (g) mean arterial pressure comparison between baseline and 4 weeks later in the spontaneously hypertensive rats UCMS group. (h) mean arterial pressure comparison between baseline and 4 weeks later in the spontaneously hypertensive rats UCMS + GXST group. (i) mean arterial pressure comparison among control, UCMS, and UCMS + GXST groups in spontaneously hypertensive rats. (j) mean arterial pressure responses comparison among control, UCMS, and UCMS + GXST groups in spontaneously hypertensive rats. (k) mean arterial pressure comparison between wistar rats and spontaneously hypertensive rats. (l) mean arterial pressure response comparison between wistar rats and spontaneously hypertensive rats

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Comparing between groups, Wistar rats in the UCMS and UCMS + GXST groups had lower MAP and MAP responses than the control group [P < 0.05: [Figure 6]d and [Figure 6]e].

Mean arterial pressure comparisons between spontaneously hypertensive rats groups

There were no significant differences seen on comparing MAP at baseline and post 4-week treatment in the control group, UCMS group, and UCMS + GXST groups respectively (P > 0.05) [Figure 6]f, [Figure 6]g, [Figure 6]h.

Comparing between groups, there were no significant differences in MAP or MAP responses between the control, UCMS, and UCMS + GXST groups [P > 0.05: [Figure 6]i and [Figure 6]j].

Mean arterial pressure comparisons between Wistar rats and spontaneously hypertensive rats

SHR had higher MAP than Wistar rats in all three groups (P < 0.05). SHR also had greater MAP responses than Wistar rats when comparing the UCMS groups [P < 0.05: [Figure 6]k and [Figure 6]l].

Unpredictable chronic mild stress-induced depressive-like behaviors

Sucrose preference tests and open field tests with Wistar rats

Neither UCMS nor UCMS + GXST treatments influenced total sucrose consumption by Wistar rats [Figure 7]a. However, UCMS treatment did reduce the sucrose preference shown by Wistar rats, and this was not significantly prevented by GXST [Figure 7]b.
Figure 7: Behavioral tests in wistar rats and spontaneously hypertensive rats. (a) Sucrose consumption comparison between control, UCMS, UCMS + GXST groups of wistar rats. (b) Sucrose preference comparison between control, UCMS, UCMS + GXST groups of wistar rats. (c) Grid-crossing comparison between control, UCMS, UCMS + GXST groups of wistar rats. (d) Upright postures comparison between control, UCMS, UCMS + GXST groups of wistar rats. (e) Sucrose consumption comparison between control, UCMS, UCMS + GXST group of spontaneously hypertensive rats. (f) Sucrose preference comparison between control, UCMS, UCMS + GXST groups of spontaneously hypertensive rats. (g) Grid-crossing comparison between control, UCMS, UCMS + GXST groups of spontaneously hypertensive rats. (h) Upright postures comparison between control, UCMS, UCMS + GXST groups of spontaneously hypertensive rats. (i) Sucrose consumption comparison between Wistar rats and spontaneously hypertensive rats. (j) Sucrose preference comparison between wistar rats and spontaneously hypertensive rats. (k) Grid-crossing comparison between wistar rats and spontaneously hypertensive rats. (l) Upright postures comparison between wistar rats and spontaneously hypertensive rats

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In the open field test, UCMS and UCMS + GXST treatments decreased both grid-crossing and occurrence of upright postures in treated Wistar rats compared with controls [Figure 7]c and [Figure 7]d.

The SPT and OFT results indicate that Wistar rats developed depressive-like behaviors when receiving UCMS, while GXST might have a small effect preventing Wistar rats from exhibiting depressive-like behaviors.

Sucrose preference tests and open field tests with spontaneously hypertensive rats

In the SPT, SHR showed lower sucrose consumption and less sucrose preference after UCMS treatment, while these effects were not found in SHR receiving UCMS + GXST treatment [Figure 7]e and [Figure 7]f. On the other hand, in the OFT, UCMS lowered grid crosing but not in those SHR also receiving GXST treatment. Similarly, UCMS decreased the occurrence of upright postures in SHR, and this effect could be prevented by GXST cotreatment [Figure 7]g and [Figure 7]h.

All the results of the SPT and OFT demonstrated that SHR receiving UCMS developed depressive-like behaviors, whilst GXST cotreatment could prevent this effect.

Behavioral tests comparisons between Wistar rats and spontaneously hypertensive rats

There were no significant differences in comparisons of SPT and OFT results between Wistar rats and SHR for any of the three groups. While we could see suggestions of lower sucrose consumption, and less grid-crossing in SHR than in Wistar rats receiving UCMS, this did not achieve significance [Figure 7]i, [Figure 7]j, [Figure 7]k, [Figure 7]l.

Linear correlations between hemodynamics and behavioral tests in Wistar rats

Linear correlation was used to analyze the relationship between hemodynamics (at baseline and after UCMS) and the results of the behavioral tests [Table 2]. When the linear correlation was significant, linear regression was used to analyze the regression equation. In Wistar rats, significant linear correlations were found between upright postures and SBP after UCMS (Y [upright postures] = −1.191 + 0.067 × [SBP after UCMS]), grid-crossings and DBP after UCMS (Y [grid-crossings] =25.314 + 0.220 X [DBP after UCMS]), upright postures and DBP after UCMS (Y [upright postures] =1.637 + 0.057 X [DBP after UCMS]), grid-crossings and MAP after UCMS (Y [grid-crossings] =20.670 + 0.249 X [MAP after UCMS]), upright postures and MAP after UCMS (Y [upright postures] =0.338 + 0.065 X [MAP after UCMS]). The results indicated that grid-crossing or upright posture behaviours are negatively related to the values of SBP, DBP or MAP, suggesting a positive relationship between depressive-like behaviors and SBP, DBP and/or MAP reductions in wistar rats.
Table 2: Linear correlation between hemodynamics and behavior tests

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Linear correlations between hemodynamics and behavioral tests in spontaneously hypertensive rats

Hemodynamic responses in SHR demonstrated differences after 4-week UCMS compared with those before UCMS. Linear correlation was used to analyze the relationship between hemodynamic responses and behavioral test results [Table 3]. When linear correlation was significant, linear regression was used to analyze the regression equation. There were significant linear correlations between grid-crossing and DBP responses in the SHR control group (Y [grid-crossings] = 41.801–0.331 X [DBP response]), grid-crossings and MAP responses in the SHR control group (Y [grid-crossings] = 38.586–0.517 X [MAP response]), and grid-crossing times and DBP responses in the SHR UCMS + GXST group (Y [grid-crossings] = 34.945–0.135 X [DBP response]). The results indicated a negative correlation between grid-crossing and DBP, and MAP responses in SHR, and a positive correlation between depressive-like behaviors and DBP responses, and MAP response elevation.
Table 3: Linear correlation between hemodynamic responses and behavioral tests

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  Discussion Top


We found that UCMS treatment decreased the HR of SHR significantly and decreased the SBP, DBP, and MAP of Wistar rats. Wistars and SHR also presented depressive-like behaviors after UCMS treatment.

We found differences between Wistar rats and SHR following linear correlation analysis of hemodynamic measurements and depressive-like behaviors. The hemodynamics at baseline didn't influence depressive-like behaviors. In contrast, we found that after UCMS treatment hemodynamics and hemodynamic responses show association with depressive-like behaviors. Moreover, linear correlation indicates that the lower SBP, DBP, and/or MAP, the more depressive the Wistar rats are, and that the higher the DBP and MAP responses, the more depressive SHR are.

It is well acknowledged that UCMS can be used to establish depressive-like behavioral models. In this study, depressive models of both Wistar rats and SHR resulting from 4-week consecutive UCMS treatments have been successfully established. In Lu's research, 16-week UCMS treatment-induced depressive-like behaviors as well as hypertension in rabbits.[11]

There have been inconsistent reports of a relationship between psychological stress and hypertension in both clinical studies and animal experiments.[27],[28],[29],[30] Despite many studies that have confirmed a strong positive link between mental stress[1] and hypertension, some produced opposing results. We found no relationship between blood pressure at baseline and depressive-like behaviors, similarly, in a 2-year follow-up study with 3914 participants, Delaney demonstrated that there was no association between baseline depressive symptoms and incident hypertension.[27] Our study shows a negative association between blood pressure, after UCMS treatment, and depressive-like behaviors. We suspect several reasons to explain this negative association: First, the period of UCMS is not long enough; secondly, the blood pressure detection is not after UCMS promptly; thirdly, the methods of mild stress are not suitable to stimulate the elevation of blood pressure. However, there are similar results from both clinic study and experiments. Licht reported that patients with depression had significantly lower SBP compared with healthy controls, which could be reversed by antidepressants.[28]

In addition, in Bayramgurler's study, UCMS did not give rise to systemic blood pressure change.[29] Puzserova and Bernatova also reported that 8-week crowding didn't cause blood pressure elevation in Wistar–Kyoto rats, an effect associated with increased no production and acetylcholine-induced relaxation.[30]

To speculate about the potential reasons for these results: First, the different basal hemodynamic status of the Wistars and the SHR could influence their blood pressure and behavioral reactions during exposure to UCMS; Second, 4-week UCMS treatment was not enough to induce blood pressure rise in either Wistar rats or SHR, adaptation to UCMS is unlikely because of the different sequences used to deliver the seven kinds of UCMS stimulation; Third, UCMS did increase parasympathetic system activity, rather than that of the sympathetic system, in Wistar rats, and the enhanced parasympathetic nervous system function leads to a blood pressure decrease.

From our study findings, GXST exerts no effect on blood pressure in either Wistars or SHR. While GXST could relieve the depressive-like behaviors of SHR. This experiment provided inconsistent results regarding the treatment of hypertension with GXST. A study of 6-month therapy combining GXST and valsartan revealed that GXST enhanced valsartan effects reducing blood pressure and improving left ventricular ischemia safely.[17] Another study also found that GXST was beneficial in hypertension and stable angina pectoris.[31] Moreover, as in our study, clinical practice has shown the beneficial effect of GXST in attenuating depression/anxiety. A clinical study including 90 patients with stable angina pectoris and anxiety/depression found that after a 4-week treatment with GXST, anxious/depressive symptoms were relieved significantly, and safely, compared with the control group.[18]

The antidepressant effect of GXST may rely on its major components Gallic acid, Borneol, and Eugenol. Gallic acid is the main constituent of Choerospondias axillaris. In an animal model of anxiety and depression induced by arsenic, the administration of Gallic acid increased the time spent in light and decreased the duration of immobility indicative of reduction in anxiety and depression. The antioxidant effect of Gallic acid plays a vital role in relieving depressive-like behaviors.[19] Nerve injury caused by neuronal apoptosis or by inflammation may lead to depression, which can be protected against by Borneol, through inhibition of the IκBα-NF-κB translocation signaling pathway.[20] Eugenol is the main constituent of Syzigium aromaticum, it exerts an antidepressant effect probably by increasing BDNF.[21] However, more efforts should be made to uncover potential mechanisms of GXST action to improve depressive-like behaviors.

However, there are some limitations in this experiment. First, in order to the animal protection ethics, we limit the sample size, which might affect the experiment exploration and statistical analysis of linear correlation between UCMS and blood pressure. We may further search the relationship between UCMS and blood pressure in our next experiment. Second, for this is the first step of our whole experiment in discovering the effectiveness of GXST in treating depressive behaviors of SHR, we have not designed pathophysiological mechanism detection. We will further explore the molecular mechanism and signaling pathway in the next experiment. Third, clinical research has not been done to prove the clinical effect of GXST, which will be conducted in the future.


  Conclusions Top


This is the first study to explore the therapeutic effect of GXST in treating depressive-like behaviors of Wistar rats and SHR. In this study, we found that UCMS could induce depressive-like behaviors in Wistar rats and SHR, whether accompanied by a decrease in blood pressure or not respectively. Whereas, GXST could exhibit a significant effect to relieve SHR's depressive-like behaviors without influencing their blood pressure. It presents that there is no positive association between depressive-like behaviors induced by UCMS and blood pressure. Moreover, it implicates that GXST could be used in clinical practice for relieving depression. In our opinion, GXST may, in future, show promise as an aid to antidepressant therapy owing to its demonstrated safety and efficiency in clinical practice.

Financial support and sponsorship

Nil.

Conflicts of interest

Prof. Meiyan Liu is the Executive Editor-in-Chief of the Heart and Mind journal. The article was subject to the journal's standard procedures, with peer review handled independently of Prof. Meiyan Liu and their research groups. There are no conflicts of interest.



 
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    Figures

  [Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5], [Figure 6], [Figure 7]
 
 
    Tables

  [Table 1], [Table 2], [Table 3]



 

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