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Open Access Highly Accessed Research

The mTOR signaling pathway regulates pain-related synaptic plasticity in rat entorhinal-hippocampal pathways

Dan Lyu13, Wenli Yu1, Ning Tang2, Ruirui Wang3, Zhenyu Zhao5, Fang Xie4, Yongjin He1, Hongyin Du1* and Jun Chen34*

Author Affiliations

1 Department of Anesthesiology, Tianjin First Center Hospital, TianJin 300192, China

2 Reproductive Medicine Center, General Hospital of Jinan Military Command, Jinan, Shandong 250031, China

3 Institute for Biomedical Sciences of Pain, Capital Medical University, Beijing 100069, China

4 Institute for Biomedical Sciences of Pain and Institute for Functional Brain Disorders, Tangdu Hospital, The Fourth Military Medical University, Xi’an 710038, China

5 Department of Neurosurgery, General Hospital of Jinan Military Command, Jinan, Shandong 250031, China

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Molecular Pain 2013, 9:64  doi:10.1186/1744-8069-9-64

Published: 9 December 2013

Abstract

Background

Our previous work demonstrated that persistent peripheral nociception (PPN) leads to synaptic plasticity and functional changes in the rat hippocampus. The protein kinase mTOR is a critical regulator of protein synthesis-dependent synaptic plasticity in the hippocampus as well as synaptic plasticity associated with central and peripheral pain sensitization. We examined the role of mTOR signaling in pain-associated entorhinal cortex (EC) - hippocampal synaptic plasticity to reveal possible cellular mechanisms underlying the effects of chronic pain on cognition and emotion.

Results

Subcutaneous injection of bee venom (BV) into one hind paw to induce PPN resulted in sustained (> 8 h) mTOR phospho-activation and enhanced phosphorylation of the mTOR target p70 S6 kinase (S6K) in the hippocampus. The magnitude and duration of long-term potentiation (LTP) in both EC - dentate gyrus (DG) and EC - CA1 synaptic pathways were elevated in BV-treated rats as measured by microelectrode array recording. Moreover, the number of potentiated synapses in the hippocampus was markedly upregulated by BV-induced PPN. Both elevated mTOR-S6K signaling and enhanced LTP induced by BV injection were reversed by systemic injection of the mTOR inhibitor rapamycin (RAPA). Rats injected with BV exhibited markedly reduced ambulation and exploratory activity in the open field (signs of depression and anxiety) compared to controls, and these effects were also reversed by RAPA.

Conclusion

We suggest that PPN-induced enhancement of synaptic plasticity in EC - hippocampal pathways and the behavioral effects of PPN are dependent on mTOR-S6K signaling.

Keywords:
Bee venom; Hippocampal formation; Synaptic plasticity; Rapamycin; mTOR signaling pathway