Gao-Zi-Yao Improves Learning And Memory Function in Old Spontaneous Hypertensive Rats Part 3

Effect of Gao‑Zi‑Yao on Morris water maze parameters in old SHR

Morris water maze data showed that both medium and high dosages of Gao-Zi-Yao treatment significantly reduced escape latency time on the first training day, from the second day, the difference did not exist (Fig.  8A). 

The relationship between escape latency and memory has always been a topic of great concern. We often feel that our memory is getting worse, but it is difficult to pinpoint the exact cause. Running away from lurking people often hurts memory. They tend to detach themselves from unpleasant experiences to get out of trouble, but this depletes a person's mental energy and therefore leads to memory loss.

Escape from lurking is a way for humans to cope with stress, and the short-term benefits it brings are obvious. By escaping unpleasant experiences, a person can temporarily feel relaxed. But this approach also misses critical learning opportunities. When we encounter difficulties or setbacks, we often try to forget these experiences, akin to hiding them deep inside. But in fact, the experiences and lessons brought by these experiences are far more valuable than we expected. Only by truly facing your problems can you gain strength and wisdom from them.

Therefore, facing difficulties positively is the key to improving memory. Some studies have found that human memory ability is interfered with by cognition. When we are in challenge mode, the brain will automatically find the optimal solution to enhance memory.

In modern society, we often encounter some challenges and difficulties, which must be faced and we cannot just escape. Only by actively facing these challenges can you open up ideas, explore solutions that suit you, and better utilize your memory and creativity. Therefore, only by daring to face your problems and actively seeking solutions can you better improve your memory and quality of life. It can be seen that we need to improve memory, and Cistanche deserticola can significantly improve memory, because Cistanche deserticola can also regulate the balance of neurotransmitters, such as increasing the levels of acetylcholine and growth factors. These substances are very important for memory and learning. In addition, Cistanche deserticola can also improve blood flow and promote oxygen delivery, which can ensure that the brain receives sufficient nutrients and energy, thereby improving brain vitality and endurance.

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Times of crossing the target quadrant were markedly increased in all dosage-treated groups on day 6 compared with the control group (Fig. 8B). 

Only a high dosage of Gao-Zi-Yao treatment markedly increased the percentage of time at the target platform quadrant and the percentage of path length in the quadrant (Fig. 8C, D). These results suggest that Gao-Zi-Yao could ameliorate the decline of learning and memory function in old SHR.

Effect of Gao‑Zi‑Yao on the number of neurons in the hippocampus in old SHR

Nissl staining was performed to demonstrate the number of neurons in the hippocampus (Fig.  9A). Results showed that treatment with Gao-Zi-Yao with all dosages had no marked effect on several neurons in the CA1 and CA2 areas in the hippocampus (Fig. 9B, C). 

However, the number of neurons in the DG area was markedly increased by medium and high dosages of Gao-Zi-Yao treatment, but not the low dosage of Gao-Zi-Yao (Fig.  9D). Tese data suggest Gao-Zi-Yao could protect aging-related neuron loss in old SHR.

Effect of Gao‑Zi‑Yao on expressions of learning and memory-related protein at hippocampus in old SHR

Western blot results showed that expression of GluR1 protein was increased by high dosage of Gao-Zi-Yao (Fig. 10A), NMDAR 2B protein expression was increased by all dosages of Gao-Zi-Yao (Fig. 10B), phosphorylatedCaMK II was increased by all dosages of Gao-Zi-Yao (Fig.  10C), and phosphorylated-CREB was increased by high dosage of Gao-Zi-Yao (Fig. 10D). 

These results suggest that Gao-Zi-Yao might be able to enhance synaptic plasticity by up-regulating synaptic plasticity-related protein expressions.

Discussion

In the present study, our observation reveals that Gao-ZiYao exerts anti-hypertensive and improves the learning and memory function of the old SHR, which may be by regulation of oxidative stress, inflammatory factors, neuron number in hippocampal DG area and the expression of the function of learning and memory-related proteins.

 Increasing evidence shows an important relationship between aging and hypertension and it was well-reviewed [40]. 

Aging increases oxidative stress, which is one of the central factors in the development of hypertension. Existing data showed that antioxidant treatment to reduce oxidative stress prevents the age-related development of high blood pressure in SHR [41, 42]. 

Our present GaoZi-Yao contains several herbs that possess antioxidant effects and could regulate tissue oxidative stress, such as Fructus Corni, Semen Cuscutae, Rhizoma Gastrodiae, Radix Cyathulae, Rhizoma Atractylodis Macrocephalae, Amomum villosum and Crocus sativus [16–21, 26]. 

Our present data clearly showed that Gao-Zi-Yao could increase serum level of NO, and reduce systolic blood pressure in old SHR, suggesting that the anti-hypertensive properties of GAOZi-Yao might be due to its antioxidant effect. 

Although recent clinical trials demonstrated that only two-thirds of Alzheimer's dementia cases are attributable to common age-related neuropathology [43], aging is generally accepted to be one of the main factors in the development of dementia [44, 45]. Age-dependent memory impairments in animal models were reported [46]. Numerous evidence showed that there is a cognitive behavior decline in dementia animal models [47]. 

Meanwhile, hypertension has more recently been linked to Alzheimer's disease major cause of dementia in older people, hypertension may also promote the neurodegenerative pathology underlying Alzheimer's disease [48]. Recent clinical trials have also indicated that improved hypertension control reduces the risk of cognitive impairment and dementia [49]. 

In the present study, we observed there is also a decline of learning and memory function in old SHR, which was consistent with previous observations reported that working memory and learning were found to be impaired by aging [50]. In addition, it was reported that significantly suppressed Morris water maze performance was found in 23-week SHR in comparison with age-matched SD rats [51]. 

Taking together, existing evidence strongly suggests that there is a decline in learning and memory function in old SHR. Aging combined with hypertension is a critical factor for the development of dementia. Gao-Zi-Yao exerts its function partially through its antihypertensive properties. 

In addition, oxidative damage is a key component of Alzheimer's disease etiology and pathogenesis [52], Gao-Zi-Yao increases systemic NO level, which may also contribute to ameliorating the dysfunction of the cerebral system. There is a growing body of evidence that both local and systemic inflammation is important in dementia [53], our present data also demonstrated that Gao-Zi-Yao exerts regulation effects on systemic inflammation by a decrease of IL-1β, IL-2, and. 

TNF-α, which may also play a role in the present animal model. Furthermore, a pronounced age-related decline in the number of neurons was observed in animals [54], aging caused a significant decrease of Nissl body amounts in hippocampal CA1 and CA3 regions in senescence-accelerated mice [55], in the present study, we also observed that is the decline of neuron number in the hippocampus in old SHR compared with young SHR, suggesting the impairment of learning and memory in old SHR might be due to the loss of neuron. There were significant impairments in long-term potential in middle-aged rat hippocampus slices compared with that of young rats, and a decrease of GluR1, and NMDAR protein expression, suggesting impaired synaptic plasticity by aging [56]. 

The other markers of synaptic plasticity, calmodulin-dependent protein kinase II (CaMKII) and phosphorylated CaMKII, CREB, and phosphorylated CREB, were also reported to be aging-related [57]. Our present study also demonstrated there is a lower level of synaptic plasticity-related protein expressions (GluR1, NMDAR 2B, phosphorylated CaMKII, phosphorylated CREB) in old SHR, suggesting there is also a decline of synaptic plasticity, which might contribute to the impairment of learning and memory function in old SHR. Increasing evidence demonstrated that TCM therapy has potential effects on the improvement of cognitive function [58]. Randomized controlled trial data supported the positive effects of TCM on age-associated memory impairment [59]. 

Several clinical trials also demonstrated the effective outcome of TCM on the enhancement of memory in aging patients or healthy persons [60, 61]. Several herbs included in the present prescription have been demonstrated to improve cognitive function. Loganin is a major iridoid glycoside obtained from Corni fructus that enhances long-term potentiation and recovers scopolamine-induced learning and memory impairments [62]. 

Semen Cuscutae attenuates scopolamine-induced memory deficit in mice [63]. Gastrodin, an active component isolated from the Rhizome Gastrodiae, significantly improved memory impairments in the Morris water maze test in mice [64]. 

Rhizoma Atractylodis Macrocephalae contained prescription has a protective effect against ischemia-induced neuronal and cognitive impairments [65]. α-Isocubebenol and deoxyschisandrin are isolated from Fructus Schisandrae Chinensis and showed protective effects on cognitive impairment [66, 67]. Semen Ziziphi Spinosae ameliorates memory and learning performance in mice [23, 68]. MSS, a comprising mixture of mail (Prunus mume Sieb. et Zucc) concentrate, disodium succinate and Span80 (3.6:4.6:1 ratio) showed a significant improvement in memory in rats [69]. 

Crocus sativus L. extracts antagonize memory impairments in different behavioral tasks in the rat [70]. Panax notoginseng attenuates impairment of learning and memory in chronic stage ischemia–reperfusion injured rats [71] and in Aβ (1–42)-injected Rats [72]. Radix Ophiopogonis, a component of Shengmaisan, improves the learning and memory abilities of the rats [73]. Berberine, a natural isoquinoline alkaloid isolated from the Rhizoma coptidis, mitigates cognitive decline in an Alzheimer's Disease mouse model [74, 75]. 

All the above-mentioned literature supports that Gao-Zi-Yao might also improve learning and memory in old SHR. Our data demonstrated that Gao-Zi-Yao treatment decreases systolic blood pressure, regulates oxidative stress and inflammation, improves learning and memory, and up-regulates several neurons and synaptic plasticity-related protein expressions. These data strongly confirm that Gao-Zi-Yao could exert neuroprotective effects.

Limitation

It should be noted that whether a decrease in blood pressure contributes to the improvement of cognitive function was not included in the present observation. Since hypertension has been demonstrated to be an independent factor in the development of dementia, it is reasonable to speculate that a decrease in blood pressure might also play a role in the amelioration of cognitive function.

Conclusions

In conclusion, our present study demonstrates the antihypertensive and neuroprotective effects of Gao-Zi-Yao. Our data may provide basic evidence for the clinical application of Gao-Zi-Yao in the treatment of aged hypertension patients.

Abbreviations

SHR: Spontaneous hypertensive rats; AD: Alzheimer's disease; TCM: Traditional Chinese medicine; SBP: Systolic blood pressure; GluR1: Glutamate receptor A1; NMDAR: N-methyl-d-aspartate receptor; CaMKII: Calmodulin-dependent protein kinase II; p-CREB: Phosphorylated-cAMP responsive element-binding protein; DG: Dentate gyrus.

Acknowledgments

Not applicable

Authors' contributions

Meng-Xiao Han, Wen-Yi Jiang, Yan Jian, Lin-Hui Wang, and Rong Xue per‑ formed research. Guo-Xing Zhang analyzed data and wrote the paper. JingWei Chen designed the research. The author(s) read and approved the final manuscript.

Funding

This work was supported by the National Natural Science Foundation of China (81970422), Suzhou Municipal Science and Technology Bureau (SS201745, GSWS2019022), and the 5th 333 Project of Jiangsu Province.

Availability of data and materials

All data generated or analyzed during this study are included in this published article.

Declarations

Ethics approval and consent to participate

The experiments were performed according to the National Institutes of Health Guidelines for the Use of Laboratory Animals (NIH, publication number 85–23, revised 1996.), which were approved by and performed according to guidelines for the care and use of animals established by ethics licensing committee of Soochow University. All the herbs and other materials used in the preparation of Gao-Zi Yao were approved by the National Health Commission of the People's Republic of China. The present study is reported by ARRIVE guidelines.

Consent for publication

Not applicable.

Competing interests

Not applicable.

Author Details

1 Department of Physiology, Medical College of Soochow University, 199 Ren‑Ai Road, Dushu Lake Campus, Suzhou Industrial Park, 215123 Suzhou, People's Republic of China. 2 Suzhou Key Laboratory of Drug Research for Prevention and Treatment of Hyperlipidemic Diseases, Medical College of Soochow University, 199 Ren‑Ai Road, Dushu Lake Campus, Suzhou Industrial Park, Suzhou 215123, People's Republic of China. 3 Department of Internal Medicine, the Affiliated Suzhou Chinese Traditional Medicine Hospital, Nanjing University of Chinese Medicine, 18 Yang‑Su Road, Suzhou 215003, People's Republic of China.

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