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Backgrounds: Depression is among the most frequent psychiatric comorbid conditions in Alzheimer’s disease (AD). However, pharmacotherapy for depressive disorders in AD is still a big challenge；current antidepressants used clinically, such as monoamine antidepressants, have shown only modest or little clinical benefits. Here we investigated the mechanism of the interactions between depression and AD, which we believe would aid in the development of pharmacological therapeutics for the comorbidity of depression and AD. Methods: Female APP/PS1/Tau triple transgenic (3×Tg-AD) mice at 20 months of age and age- and gender-matched wild-type (WT) mice were used. The shuttle-box passive avoidance test (PAT), the open field test (OFT), and the tail suspension test (TST) were implemented to assess behavioral changes. High-performance liquid chromatography coupled to tandem mass spectrometry (HPLC-MS/MS) was used to detect the level of neurotransmitters related to depression in the hippocampus of mice. The data was identified by orthogonal projections to latent structures discriminant analysis (OPLS-DA). The expression of relative receptors was detected using Western blot. Results: Compared to WT, 3×Tg-AD mice displayed significant cognitive impairment in the PAT and depression-like behavior in the OFT and TST. They also showed significant decreases in the levels of L-tyrosine, norepinephrine, vanillylmandelic acid, 5-hydroxytryptamine, and acetylcholine, in contrast to significant increases in 5-hydroxyindoleacetic acid, L-histidine, L-glutamine, and L-arginine in the hippocampus. The expression of the alpha 1a adrenergic receptor (ADRA1A), serotonin 1A receptor (5HT1A), and γ-aminobutyric acid A receptor subunit alpha-2 (GABRA2) was significantly downregulated in the hippocampus of 3×Tg-AD mice, while histamine H3 receptor (H3R) expression was significantly upregulated. In addition, the ratio of phosphorylated cAMP-response element-binding protein (pCREB) and CREB was significantly decreased in the hippocampus relative to WT. Conclusions: We demonstrated in the present study that aged female 3×Tg-AD mice showed depression-like behavior accompanied with cognitive dysfunction. The complex and diverse mechanism appears not only relevant to the imbalance of multiple neurotransmitter pathways, including the transmitters and receptors of the monoaminergic, GABAergic, histaminergic, and cholinergic systems, but also related to the changes in L-arginine and CREB signaling molecules.

The detection method of characteristic spectrum for reference samples was established by preparing 15 batches of the reference samples of Huagan Decoction, and the peak attribution and the similarity range in the characteristic spectrum were clarified. The ranges of paste-forming rate, content, and transfer rate of the index components including geniposide, paeonol, and paeoniflorin were analyzed. The key quality attribute of the reference samples of Huagan Decoction was defined. The results showed that the 15 batches of the reference samples of Huagan Decoction had good similarities in the characteristic spectrum, which were all higher than 0.9. According to the information of characteristic peak, there were 18 characteristic peaks in the whole prescription, including seven common characteristic peaks from green tangerine peel and dried tangerine peel, four characteristic peaks from tree peony root bark(three of them were common characteristic peaks from tree peony root bark and red peony root), five characteristic peaks from cape jasmine fruit, one characteristic peak from paniculate bolbostemma, and one characteristic peak from oriental waterplantain rhizome.The paste-forming rate of the 15 batches of reference samples was 14.73%-18.83%. The content of geniposide was 1.68%-2.87%, with the average transfer rate of 70.05%±11.13%. The content of paeonol was 0.10%-0.16%, with the average transfer rate of 9.38%±1.78%. The content of paeoniflorin was 1.94%-2.74%, with the average transfer rate of 36.69%±4.63%. This study analyzed the quality value transfer of the reference samples of Huagan Decoction by the evaluation mode of combining the characteristic spectrum, the paste-forming rate, and the content of index components. The findings of this study initially established a stable and feasible standard decoction evaluation method and provided references for the quality control and the subsequent development of relevant preparations of Huagan Decoction.

One new alkaloid, 6, 7-dimethoxyisoquinoline