Inflammatory Bowel Disease (IBD) affects more than one million Americans and is characterized by visceral hypersensitivity (VH), the mechanisms of which are not fully understood. The Central Nervous System immune cells, microglia, have been implicated in neuropathic pain and VH, with increased degrees of activation correlating with increased hypersensitivity; however, their role in visceral pain has been less studied.
This project is the first to investigate functional properties of microglia in the dorsal horn of rats with VH due to acute colon inflammation. We hypothesized that colon inflammation-induced microglial activation contributes to VH, which is diminished by reversion of microglia to a less reactive state.
This hypothesis was tested in two specific aims. In specific aim 1, we demonstrated a shift in microglial morphology from a surveillance state to a reactive state characterized by increased expression of CD11b and Iba1 proteins and membrane purinergic receptors (P2X4 and P2Y12). In specific aim 2, we showed that colon inflammation-induced VH is reversed by inhibiting microglia with minocycline, causing them to revert to a less reactive state.
Colon inflammation was induced in adult rats using intracolonic administration of 2,4,6-trinitrobenzenesulfonic acid. VH was evaluated in rats with colon inflammation and naïve rats using electromyography (EMG) recordings. Cellular markers and protein expression were evaluated in both groups using immunohistochemistry, Western blotting, and real-time PCR. Since neuronal hyperexcitability is associated with VH, extracellular action potentials from spinal cord neurons were recorded to determine whether there is a correlation between neuronal hyperexcitability and microglial activation.
We observed increased EMG responses in rats with TNBS-induced colon inflammation compared to naïve rats, which corresponded with increased expression of markers of microglial activation as well as changes in the expression of P2Y12R but not P2X4R In the dorsal horn of spinal cord segments L6-S1. Minocycline treatment, known to inhibit microglial activation, attenuated the EMG responses and resulted in a downregulation of markers of microglial activation. Furthermore, neuronal responses in L6-S1 of TNBS-treated rats were attenuated by minocycline, whereas naïve neuronal responses were not affected by minocycline. This further implicates microglia in the process of VH due to colon inflammation.
|Advisor:||Al-Chaer, Elie D.|
|Commitee:||Davies, David L., Drew, Paul D., Harik, Sami I., Hayar, Abdallah, Saab, Carl|
|School:||University of Arkansas for Medical Sciences|
|Department:||Neurobiology and Developmental Science|
|School Location:||United States -- Arkansas|
|Source:||DAI-B 72/12, Dissertation Abstracts International|
|Keywords:||Colon inflammation, Hypersensitivity, Inflammatory bowel disease, Microglia, Visceral pain|
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