Esketamine Improves Working Memory Impairment in Neuropathic Mice Through Hippocampal BDNF-TrkB Pathway

Objective To explore the effect of esketamine on working memory impairment in neuropathic mice and its underlying mechanism. Methods Fifty clean grade male C57BL/6J mice (2 months) were divided into 5 groups by random number table method: sham + saline (SN group), CCI + saline (CN group), CCI+(S)-ketamine(CE group), CCI + ANA-12 (CA group), CCI + ANA-12+(S)-ketamine (CAE group), with 10 mice in each group. Chronic constriction injury (CCI) was employed to establish a neuropathic pain model. On the 16th day after modeling, CE group and CAE group were administered ketamine (10 mg/kg), CAE group received ANA-12 (0.5 mg/kg) half an hour before ketamine injection, CA group was only given ANA-12, and SN group and CN group received an equivalent volume of saline. The administration was done through intraperitoneal injection for 5 consecutive days. The open-field test (OFT), paw withdrawal threshold (PWT), paw withdrawal latency (PWL) and Y-maze test were performed from day 21 after surgery. Bromo-2- deoxyUridine (BrdU) was dissolved in saline and intraperitoneally injected into the mice on days 21 to 23 after the surgery. Western blot was performed to determine the expression of Brain-derived neurotrophic factor(BDNF) in hippocampus, the immunofluorescence was performed to determine the number of bromodeoxyuridine nucleoside (BrdU) and doublecortxin (DCX) positive cells in the dentate gyrus (DG) area of hippocampal. Results Compared with SN group， the other four groups showed significant reductions in both PWT and PWL on day 21 after surgery (all P＜0.05); There was no significant difference in the total distance travelled by the 5 groups of mice (P=0.142) ; In the Y maze test, compared to SN group, the accurate percentage of spontaneous alternation in CN group showed significant reductions (P＜0.001), which was reversed by esketamine administration (P＜0.001); compared with CE group, there was a significant reduction of the accurate percentage of spontaneous alternation in CAE group (P=0.004). The expression of BDNF protein in CN group was lower than that in SN group(P=0.021) and CE group (P=0.03), and compared with CE group, the expression of BDNF was significant decreased in CEA group (P=0.043). The number of BrdU positive and DCX positive cells significantly reduced in the DG area of the hippocampus in CN group compared to SN group(P=0.025) and CE group (P=0.003). The number of BrdU positive and DCX positive cells in CAE group significantly reduced in the DG region of the hippocampus compared to CE group(P=0.014). Conclusion Esketamine improves working memory impairment in neuropathic mice and the neurogenesis in dentate gyrus area of hippocampal through the BDNF-TrkB pathway.