July 2019
Volume 60, Issue 9
Open Access
ARVO Annual Meeting Abstract  |   July 2019
Post injury mu-opioid receptor (mOR) expression in the oculo-trigeminal axis: Is Less mOR?
Author Affiliations & Notes
  • Nicholas Fowler
    University of Kentucky College of Medicine, Lexington, Kentucky, United States
  • Romulo Albuquerque
    University of Kentucky College of Medicine, Lexington, Kentucky, United States
  • Jooyoung Cho
    University of Kentucky College of Medicine, Lexington, Kentucky, United States
  • Footnotes
    Commercial Relationships   Nicholas Fowler, None; Romulo Albuquerque, None; Jooyoung Cho, None
  • Footnotes
    Support  None
Investigative Ophthalmology & Visual Science July 2019, Vol.60, 901. doi:
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      Nicholas Fowler, Romulo Albuquerque, Jooyoung Cho; Post injury mu-opioid receptor (mOR) expression in the oculo-trigeminal axis: Is Less mOR?. Invest. Ophthalmol. Vis. Sci. 2019;60(9):901.

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      © ARVO (1962-2015); The Authors (2016-present)

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Abstract

Purpose : Ocular surface injury results in ocular hypersensitivity behavior that peaks 10 days after corneal injury and returns to baseline thereafter. This apparent recovery is mediated the activation of mu-opioid receptors (mOR) in peripheral nerves also known as latent sensitization. Latent sensitization is therefore a positive adaptation to injury, but it also represents a state of pain susceptibility. Here, we aim at improving our understanding of peripheral latent sensitization by studying the changes in mOR expression along the cornea-trigeminal axis after ocular injury.

Methods : Confocal Microscopy
The cornea and TG of MOR-mCherry (Oprm1tm4Kff) male mice were optically cleared using the SeeDB protocol. mOR expression of an 8-wk status-post CSI mouse was compared to sham using Nikon NIS Elements v4.3.
Ex Vivo Quantification
6-8 week old C57BL/6 male mice (n=4 per group) were assigned to alkali burn or sham groups. Cornea and TG were harvested at differing points following CSI: 4d; 2; 4; 8w. Tissue samples were analyzed using western blot and qPCR. BCA and B III Tubulin loading control assays were performed. Quantification was performed using ImageStudioLite v5.2.

Results : Microscopy
MOR-mCherry mice expressed mOR in cornea and TG. In the cornea, the highest density of mOR were present in the terminal ends of the epithelial layer—compared to stromal and subbasal layers. In the TG, the majority of V1 neuron cell bodies expressed mOR. After CSI, a decrease in density of mOR in the ophthalmic division of the TG was seen.
Ex Vivo Quantification
WB analysis of 8wk post injury mice showed 1.6 fold decrease and 1.4 fold increase in ipsilateral cornea and TG, respectively.

Conclusions : Our results show that CSI paradoxically results in decreased levels of mOR in corneal nerves but increased levels in trigeminal ganglia. Confocal microscopy of mOR-mCherry mice unveils that mOR are primarily expressed in the corneal nerve terminal at the epithelial layer and corroborates our observation that the expression of mOR decreases in the cornea yet increases in the TG after corneal injury.

This abstract was presented at the 2019 ARVO Annual Meeting, held in Vancouver, Canada, April 28 - May 2, 2019.

 

Fig 1. mOR (RED) are expressed in (A) corneal nerves and (B) opthalmic distribution of the TG. mOR is more densely expressed in epithelial terminals compared to the subbasal and stromal nerves.

Fig 1. mOR (RED) are expressed in (A) corneal nerves and (B) opthalmic distribution of the TG. mOR is more densely expressed in epithelial terminals compared to the subbasal and stromal nerves.

 

Fig 2. mOR expression is decreased in cornea and increased in TG after corneal injury.

Fig 2. mOR expression is decreased in cornea and increased in TG after corneal injury.

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