Effect of XingPiJieYu decoction on spatial learning and memory and cAMP-PKA-CREB-BDNF pathway in rat model of depression through chronic unpredictable stress

Combined corticosterone treatment and chronic restraint stress lead to depression associated with early cognitive deficits in mice

Many models, such as chronic mild stress, chronic stress or chronic corticosterone injections are used to induce depression associated with cognitive deficits. However, the induction period in these different models is still long and face constraints when it is short such as in the chronic mild stress done in a minimum period of 21 days. This study aimed to characterize a model of depression with early onset cognitive deficit. 14 days combined chronic injection of corticosterone followed by 2 h restraint stress using a restrainer was used to induce depression with early cognitive deficit onset. The forced swim test, sucrose test and plasma corticosterone concentration were used to assess depression-like characteristics. The Morris water maze, novel object recognition task, as well as hippocampal acetylcholinesterase activity were used to assess cognitive deficit. The combined corticosterone injection + chronic restraint stress group presented with marked depression-like behaviour and a higher plasma corticosterone concentration compared to corticosterone injection alone and restraint stress alone. It also showed an alteration in the learning process, memory deficit as well as increased acetylcholinesterase activity compared to corticosterone injection and restraint stress alone groups. These findings suggest that the combined corticosterone administration and chronic restraint stress can be used not only as an animal model for severe depression, but also for depression with early onset cognitive deficit.

Treatment with Shuyu capsule increases 5-HT1AR level and activation of cAMP-PKA-CREB pathway in hippocampal neurons treated with serum from a rat model of depression

Depressive disorder (DD) is one of the typical affective disorders with a high morbidity, high suicide rate and high recurrence rate. Dysfunction of the 5-hydroxytryptamine 1A receptor (5-HT1AR) in the brain may serve an important role in the pathogenesis of DD. Currently, selective serotonin reuptake inhibitors are the first line antidepressants with 60–70% efficacy and severe adverse effects. Previous studies have demonstrated that Chinese herbal medicines, including the Shuyu capsule (SYC), are effective antidepressants with few side effects. However, the mechanism remains unclear. In the present study, the effects of the SYC on the 5-HT1AR level and the activation of adenylyl cyclase-cyclic adenosine monophosphate (cAMP)-protein kinase A (PKA)-cAMP response element-binding (CREB) signaling pathway that 5-HT1AR mediates in the cells of hippocampal neurons were investigated in vitro. The SYC demonstrated an antidepressant effect similar to that of fluoxetine in a rat depression model. Treatment of hippocampal neurons with the serum of depressive rats resulted in a decrease in the 5-HT1AR protein level and the activation of the cAMP-PKA-CREB signaling pathway in hippocampal neurons. Exposure to the serum of rats that received chronic mild stress plus SYC treatment led to no alterations in the 5-HT1AR level or the activation of the cAMP-PKA-CREB signaling pathway compared with those of cells exposed to normal rat serum. This effect is similar to the effects of 5-HT1AR antagonist WAY-100635. In addition, the 5-HT1A agonist 8-hydroxy-(dipropylamino) tetralin did not antagonize the effects of the SYC. Furthermore, the SYC exhibited an increased effect compared with fluoxetine on 5-HT1AR levels and CREB activation. The present study suggested that the SYC functions by increasing 5-HT1AR protein levels and the activation of the 5-HT1AR-mediated cAMP-PKA-CREB signaling pathway in hippocampal neurons.

Neuroplasticity-related mechanisms underlying the antidepressant-like effects of traditional herbal medicines

Traditional herbal medicine can offer efficacious and safe alternative pharmacotherapies for depression. The ability of an herbal medicine to produce neuroadaptive processes, that enhance neuroplasticity and cellular resilience in response to chronic stress, may point to its antidepressant potential. We suggest that among many investigated herbal medicines, those that can enhance neuroplasticity may have stronger therapeutic potential. The current article presents a summary of traditional herbal medicines, which are thought to exert antidepressant-like effects in chronic stress models via neuroplasticity enhancement. Brain-derived neurotrophic factor (BDNF) is a biomarker for neuroplasticity-related mechanisms compromised in depression and recovered by conventional antidepressants, including synaptic plasticity, cell survival, neurogenesis and spine formation. We therefore presumed that if an herbal medicine up-regulates BDNF in the hippocampus and/or prefrontal cortex (PFC), its antidepressant-like effect is mediated, at least partially, via neuroplasticity-related mechanisms. Literature search was performed using the general terms depression, stress, neuroplasticity and herbal medicines. Screening of retrieved preclinical studies revealed 30 traditional herbal medicines: 8 single herbs, 15 bioactive constituents, and 7 herbal formulas. The antidepressant-like effects of these medicines were associated with reversal of chronic stress-induced impairment in neuroplasticity, most notably by BDNF up-regulation, activation of BDNF downstream signaling pathways and increase in neurogenesis in the hippocampus and/or PFC/frontal cortex. In light of the ability of these medicines to enhance neuroplasticity, we suggest that they may be suitable candidates for clinical investigation in depressed individuals. Once their efficacy, tolerability and safety will be substantiated, they may serve as natural alternatives to conventional antidepressants.