Amygdala dynorphin/κ opioid receptor system modulates depressive-like behavior in mice following chronic social defeat stress.

Major depression disorder is a severe and recurrent neuropsychological disorder characterized by lowered mood and social activity and cognitive impairment. Owing to unclear molecular mechanisms of depression, limited interventions are available in clinic. In this study we investigated the role of dynorphin/κ opioid receptor system in the development of depression. Mice were subjected to chronic social defeat stress for 14 days. Chronic social defeat stress induced significant social avoidance in mice characterized by decreased time duration in the interaction zone and increased time duration in the corner zone. Pre-administration of a κ opioid receptor antagonist norBNI (10 mg/kg, i.p.) could prevent the development of social avoidance induced by chronic social defeat stress. Social avoidance was not observed in κ opioid receptor knockout mice subjected to chronic social defeat stress. We further revealed that social defeat stress activated c-fos and ERK signaling in the amygdala without affecting the NAc, hippocampus and hypothalamus, and ERK activation was blocked by systemic injection of norBNI. Finally, the expression of dynorphin A, the endogenous ligand of κ opioid receptor, was significantly increased in the amygdala following social defeat stress; microinjection of norBNI into the amygdala prevented the development of depressive-like behaviors caused by social defeat stress. The present study demonstrates that upregulated dynorphin/κ opioid receptor system in the amygdala leads to the emergence of depression following chronic social defeat stress, and sheds light on κ opioid receptor antagonists as potential therapeutic agents for the prevention and treatment of depression following chronic stress.

Proteomic analysis of male rat nucleus accumbens, dorsal hippocampus and amygdala on conditioned place aversion induced by morphine withdrawal.

Addiction is characterized by compulsive drug seeking and taking behavior, which is thought to result from persistent neuroadaptations, encoded by changes of gene expression. We previously demonstrated that the changes in synaptic plasticity were required for the formation of aversive memories associated with morphine withdrawal. However, the proteins involved in synaptic plasticity and aversive memory formation have not been well explored. In the present study, we employed a two-dimensional gel electrophoresis (2-DE)-based proteomic technique to detect the changes of protein expression in the nucleus accumbens, amygdala and dorsal hippocampus of the rats that had developed conditioned morphine withdrawal. We found that twenty-three proteins were significantly altered in the amygdala and dorsal hippocampus after conditioned morphine withdrawal. These proteins can be classified into multiple categories, such as energy metabolism, signal transduction, synaptic transmission, cytoskeletal proteins, chaperones, and protein metabolism according to their biological functions. Eight proteins related to synaptic plasticity were further confirmed by western blot analysis. It is very likely that these identified proteins may contribute to conditioned morphine withdrawal-induced neural plasticity and aversive memory formation. Thus, our work will help understand the potential mechanism associated with generation of drug withdrawal memories.

Low-frequency repetitive transcranial magnetic stimulation inhibits the development of methamphetamine-induced conditioned place preference.

The abuse of amphetamine-type stimulants (ATS) has become a global public health issue in recent years, these new-type drugs can cause addiction and serious cognitive impairment. However, there are no effective methods for the prevention and treatment of ATS addiction at present. Repetitive transcranial magnetic stimulation (rTMS) is a painless and non-invasive new therapeutic approach that has been used for the treatment of depression and other neuropsychiatric disorders, but whether it can be used to treat drug addiction is unclear. In the present study, we investigated the possible effects of rTMS on methamphetamine(METH)-induced conditioned place preference (CPP). High-frequency (10 Hz) and low-frequency stimulation patterns (1 Hz) were applied to test the effect of rTMS on METH-induced CPP. The results showed that low-frequency but not high-frequency rTMS could block METH-CPP, accompanied with a downregulation of gamma-aminobutyric acid type B receptor subunit 1 (GABABR1) expression in rat dorsolateral striatum. These results suggested that low-frequency rTMS could effectively inhibit the development of METH addiction and shed light on the rTMS as a potential approach for the prevention of drug addiction.

KCC2 expression changes in Diazepam-treated neonatal rats with hypoxia-ischaemia brain damage.

Hypoxia-ischaemia brain damage (HIBD) is a major type of perinatal brain injury in newborns. In this study, we investigate the short- and long-term neuroprotective effects of Diazepam on neonatal rats with HIBD and the potential mechanisms underlying its protective effects. Seven-day-old Sprague-Dawley rats were subjected to left carotid artery ligation followed by a 2-h exposure to 8% oxygen and 92% nitrogen. Diazepam was administered immediately via intraperitoneal (i.p.) injection after inducing HIBD at a dose of 10 mg kg(-1)8h(-1) for three consecutive days. Three days after HIBD, rats were decapitated, and the extent of brain injury was evaluated using 2,3,5-triphenyltetrazolium chloride (TTC) staining. Additionally, the expression of Potassium-chloride cotransporter-2 (KCC2) was analysed using real-time PCR, Western blot analysis and immunohistochemistry. Three weeks after HIBD, rats were subjected to the Morris water maze (MWM) test and the locomotor activity test to determine the long-term therapeutic effects of Diazepam. We observed that the volume of infarction in the Diazepam group was significantly less (P<0.01) compared with the HIBD group. We also observed that the learning and memory abilities of the Diazepam rats improved significantly compared with the untreated rats (P<0.05) and that the decrease in KCC2 expression was prevented (P<0.01). Early treatment with Diazepam appears to attenuate HIBD and can efficiently improve the long-term learning and memory capabilities of the animal. A potential mechanism underlying these effects may involve preventing the decrease in KCC2 expression.

Establishment and characterization of a paclitaxel­resistant human esophageal carcinoma cell line.

The aim of this study was to establish a new paclitaxel (PTX)-resistant human esophageal squamous carcinoma (ESCC) cell line and investigate its biological characteristics. The resistant cell line (EC109/Taxol) was developed in vitro by intermittent exposure of the human ESCC cell line EC109 to a high concentration of PTX with time-stepwise increment over a period of 6 months. The MTT assay was performed to test the drug resistance of EC109 and EC109/Taxol cells. The morphological features were observed using inverted microscopy and apoptosis was measured by flow cytometry (FCM) and Hoechst 33258 fluorescence staining. Cell growth curves and colony formation of EC109 and EC109/Taxol cells were compared. FCM was also used to determine the distribution of the cell cycle. The protein levels of Bcl-2, Bax, Procaspase-3 and P-gp were detected by western blotting. P-gp activity was evaluated by Rh123 accumulation and efflux assay. In vivo resistance characterization was investigated. EC109/Taxol cells were 67.2-fold resistant to PTX in comparison with EC109 cells, and also exhibited cross-resistance to 5-fluorouracil (5-FU), cisplatin (CDDP) and epirubicin (EPI). FCM and Hoechst 33258 fluorescence staining confirmed that EC109 cells treated with PTX showed significantly higher percentage of apoptotic cells compared to EC109/Taxol cells. Simultaneously, EC109/Taxol cells exhibited changes in morphology, proliferation rate, doubling time, cell cycle distribution and colony formation rate were detected as compared with EC109 cells. The resistant cell line overexpressed Bcl-2, Procaspase-3 and P-gp protein, and showed decreased Bax expression. Further, EC109/Taxol cells did not change PTX resistance in vivo. This is the first report on the establishment of an EC109/Taxol cell line with higher resistance. Bcl-2, Bax, Procaspase-3 and P-gp are involved in the resistance of cell lines to PTX, which are invaluable tools to study the resistance of anticancer drugs and to identify the methods to overcome resistance.