ObjectiveTo investigate the effectiveness of compound Chai Jin Jie Yu Tablets (CJJYT) in ameliorating cognitive impairment associated with depression and its potential mechanism of action.

MethodsIn vitro experiments, the hippocampus was isolated from the whole brain of the fetal rat and cultured into hippocampal neuron cells. 50 μM corticosterone (CORT) was added to each group 18 h before the experiment for modeling depression, with the exception of the control group. After modeling, the blank serum group was added with 10% blank serum, the CJJYT group and the venlafaxine group were added with the corresponding 10% drug-containing serum, and the control group and the model group were added with equal volumes of culture medium. The intracellular Ca²⁺ mean fluorescence intensity, miniature excitatory postsynaptic current (mEPSC) current amplitude, and frequency of different hippocampal neurons were evaluated as indicators of synaptic function in the hippocampal neurons. In addition, the expression of synaptic plasticity related proteins, synaptophysin-α (SYN-α), N-methyl-D-aspartate receptor 2A (NR2A), N-methyl-D-aspartate receptor 2B (NR2B), post synaptic density 95 protein (PSD-95), calcium/calmodulin dependent protein kinaseⅡ (CaMKⅡ) and synaptic associated protein (SynGAP) were detected in the hippocampal neurons by immunofluorescence staining and high content analysis (HCA) system. Then, reverse transcription-polymerase chain reaction (RT-PCR) was used to detect the mRNA expression levels of SYN-α, NR2A, NR2B, PSD-95, CaMKⅡ and SynGAP. For in vivo experiments, except for those in the blank control group, all rats were treated within a single cage for chronic unpredictable stress-induced depression modeling and subjected to corresponding drug interventions. Behavioral tests were used to detect depressive behavior and determine learning, memory and other cognitive abilities, whereas enzyme-linked immunosorbent assay (ELISA) was used to detect the CORT levels. Golgi-Cox staining was used to observe changes in the synaptic morphology of parahippocampal gyrus CA1 area (CA1) and dentategyrus (DG).

ResultsIn vitro, CJJYT treatment reduced the intracellular Ca²⁺ mean flurorescence intensity in the hippocampal neurons (P < 0.05), causing a reduction in the frequency and current amplitude of mEPSC (P < 0.05), and thus inhibited the excessive activation of post-synaptic receptors. CJJYT treatment reduced the protein and mRNA expression of SYN-α, NR2A, NR2B and PSD-95 in the hippocampal neurons (P < 0.05), increased the mRNA and protein expression of CaMKⅡ and SynGAP (P < 0.05), and thereby improved the synaptic plasticity of the hippocampal neurons. In vivo, CJJYT intervention improved sucrose preference, voluntary activity , learning and memory ability of Morris water maze test, and suppressed appetite (P < 0.05), and increased the despair feeling of forced swimming test (P < 0.05). The CORT level was reduced (P < 0.05), leading to the repair of synaptic damage in the hippocampal neurons.

ConclusionsCJJYT can improve the synaptic function of hippocampal neurons and has obvious protective effects on neurons. It can repair the structural damage in the hippocampal neurons, improving the cognitive ability of the depressed model rats. The mechanism of CJJYT improving cognition in depressed rats may be related to the transmission and function of SYN-α/NR and its downstream neurotransmitters.