Acid-induced ERK phosphorylation in Cortical Principle Neurons & Excitatory Synaptic Plasticity in RAIC in Mice?
Date Issued
2015
Date
2015
Author(s)
Hsieh, Pin-Nan
Abstract
In order to understand the mechanism of chronic muscle pain, the acid-induced muscle pain animal model (AIMP model) established by Sluka et al. (2001) was introduced. Bilateral widespread long-term hyperalgesia was reproduced by repeated acidic saline intramuscular injection into left gastrocnemius muscle. It was believed that central sensitization contributed the acid-induced muscle chronic pain and previous studies had discussed on the spinal cord or subcortical areas; however, the role of cortical areas was still unclear, including whether the nociceptive neurons was excitatory or inhibitory in the developing of chronic muscle pain. The study was interested in the cell-type of nociceptive neurons and synaptic plasticity within cortical areas, especially the rostral agranular insular cortex (RAIC). This study consisted of two main experiments, one was investigating the cell-type of nociceptive neurons in the cortical areas within AIMP model; the other was to examine whether a synaptic plasticity could be elicited in rostral granular insular cortex.
First, the phosphorylated extracellular signal-related kinase (pERK), a biological activity and nociceptive marker, had been examined after the second acid injection. The pERK-IR cells were elevated in the bilateral anterior cingulate cortex (ACC) and insular cortex (IC), and combined with double labeled pERK-NeuN immunostaining, showing that the pERK-IR cells were almost all (at least 96%) neurons. Next, calmodulin kinase II (CaMKII), a general marker for pyramidal cells, were used for labeling excitatory principle neurons; in the other way, GAD-GFP mice and VGAT-tdtomato mice were also used for labeling GABAergic neurons. Triple-labeled of pERK&CaMKII&GAD (or VGAT) showed that around 40% pERK-IR cells were CaMKII-IR principle neurons, and rarely pERK-IR cells were GABAergic interneurons in the ACC and IC.
Second, whole-cell patch clamp was done on the RAIC layer V pyramidal cell and evoking EPSPs by a local stimulation on RAIC layer II/III. Under high frequency stimulus with 100Hz in one second and repeated five or seven times (repeated times defined as train number ), a long-term potentiation of EPSP was elicited. The LTP on RAIC is train number-dependent and NMDA receptor-dependent. Furthermore, it was suggested that a threshold as train number of three within the RAIC for establishing LTP.
In conclusion, the excitatory pyramidal cells played the critical roles in the ERK activation and the synaptic plasticity, which helped us much understand the mechanism of chronic muscle pain, and might provide a hint on the research of fibromyalgia.
Subjects
Acid-induced chronic Muscle Pain model
pERK
Synaptic plasticity
Insular cortex
Type
thesis
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