Effect of Ketamine on LTP and NMDAR EPSC in Hippocampus of the Chronic Social Defeat Stress Mice Model of Depression

Abstract

Depression is a common mental disorder that is associated with memory dysfunction. Ketamine has recently been demonstrated to be a rapid antidepressant. The mechanisms underlying how depression induces memory dysfunction and how ketamine relieves depressive symptoms remain poorly understood. This work compared three groups of male C57BL/6J mice: mice exposed to chronic social defeat stress (CSDS) to induce a depression-like phenotype, depression-like mice treated with ketamine, and control mice that were not exposed to CSDS or treated with ketamine. Spatial working memory and long term memory were assessed by spontaneous alternation Y-maze and fear conditioning tests, respectively. We used western blot to analyze the density of N-methyl-D-aspartate receptor (NMDAR) subunits in the hippocampus. We recorded long term potentiation (LTP) and NMDA receptor-mediated excitatory postsynaptic currents (EPSCs) in hippocampal slices. We observed that compared with control mice, depression-like mice had significant reductions in spatial working memory and contextual fear memory. The level of NR2B, LTP and NMDA receptor-mediated EPSCs of depression-like mice were decreased. Ketamine treatment attenuated the memory impairment, and increased the density of NR2B and the amplitude of LTP and NMDA receptor-mediated EPSCs in the hippocampus of depression-like mice. In conclusion, depression-like mice have deficits in working memory and contextual fear memory. The decrease of NR2B, LTP induction and NMDA receptor-mediated EPSCs in the hippocampus may be involved in this process. Ketamine can improve expression of NR2B, LTP induction and NMDA receptor-mediated EPSCs in the hippocampus of depression-like mice, which might be part of the reason why ketamine can alleviate the memory dysfunction induced by depression.

Keywords: EPSC; LTP; NMDAR; depression; ketamine.

Figure 1

Timetable of the experimental design.

Figure 2

Behavioral studies of mice. (A) Depression-like mice had least sucrose preference among the three groups, and ketamine improved sucrose preference performance of depression-like mice. (B) Working memory of depression-like mice was impaired, and ketamine treatment attenuated working memory impairment of depression-like mice. (C) Contextual fear conditioning memory of depression-like mice was impaired, and ketamine attenuated the memory impairment of depression-like mice. Means were showed, and SEM were represented by error bars, n = 12, per group. *P < 0.05, one-way ANOVA, post hoc Tukey-Kramer.

Figure 3

(A) Expression of NR2B subunit on the membrane of hippocampus neurons was tested by western blot. β-actin was selected as an internal standard and control for protein loading. (B,C) Expression of NR1 and NR2A on the membrane of hippocampus neurons was shown by western blot. β-actin was selected as an internal standard and control for protein loading. (D) NR2B/NR1 ratio. Means were showed, and SEM were shown by error bars, n = 12, per group. **P < 0.01, *P < 0.05, one-way ANOVA, post hoc Tukey-Kramer.

Figure 4

The long-term potentiation (LTP) in the hippocampal Schaffer collateral-CA1 in control mice, depression-like mice, and depression-like mice with ketamine. LTP of depression-like mice was blocked, and ketamine treatment attenuated the blockage of LTP in depression-like mice. (A) Control mice. (B) Depression-like mice. (C) Depression-like mice with ketamine. (D) Summarized data of average slope change (normalized to baseline value) from three groups of mice. Means were showed, and SEM were shown by error bars, n = 12, per group. **P < 0.01, one-way ANOVA, post hoc Tukey-Kramer.

Figure 5

Evoked N-methyl-D-aspartate receptor (NMDAR)-mediated excitatory postsynaptic currents (EPSCs) recorded from CA1 pyramidal cells in mice brain slices. (A) Evoke NMDA receptor-mediated EPSC of one mouse from each group. (B) EPSC after treatment with APV+NBQX. (C) Summarized amplitude of glutamate EPSC of three groups. (D) Summarized amplitude of NMDA EPSCs of three groups. (E) Summarized NMDA/AMPA ratio of three groups. Means were showed, and SEM were shown by error bars, n = 12 slices from 12 mice, per group. ***P < 0.001, **P < 0.01, *P < 0.05, one-way ANOVA, post hoc Tukey-Kramer.