Abstract
Purpose :
Neurosensory abnormalities are a prominent feature in dry eye disease (DED), yet a cause for allodynia and hyperalgesia remains unclear. The trigeminal ganglion (TG) serves as a transitionary and modulatory site for sensation at the corneal interface and remains relatively uncharacterized in various experimental models of DED. Our study sought to explore the role of TG neurons in a chronic, genetic experimental mouse model of DED.
Methods :
Primary neuron cell cultures were derived from TG of 8-12-week-old RHJ/LeJ+/- (control) and RHJ/LeJ-/- (DED) mice (N=8 mice, n= 1036 neurons). After 24 hours, cultures were incubated with Fura2-AM (1 µg/mL) prior to calcium imaging. Baseline neural activity was established over 5 minutes of exposure to a 5 mM external solution. Nociceptive response was evaluated in a concentration dependent manner to 10, 30, 300 and 1000 nM capsaicin over 3 minutes. As a positive control, neurons were exposed to a 70 mM K+ solution for 30 seconds. Neural responses less than 40% of the established baseline were excluded from the data set. Mann-Whitney and multiple unpaired t-tests were used for statistical analysis.
Results :
Baseline TG activity was significantly elevated (P<0.001) in the DED mice. Inversely, the K+ elicited depolarization response was diminished in DED animals (P<0.001). A greater dose was required to reach the EC50 in the DED animals (68.79 nM RHJ/LeJ-/-, 18.72 nM RHJ/LeJ+/-) suggesting an elevated threshold for neural activation. The response of TG neurons to capsaicin was significantly lower in DED mice compared to controls at 10, 30 and 300 nM (P=0.0045, P<0.00001, P=0.000008, respectively). No difference was observed at 1000 nM indicating a maximal capsaicin response was achieved from both experimental groups. The proportion of neurons that elicited a response to capsaicin was diminished in DED mice at all doses.
Conclusions :
Neurons isolated from the TG of a chronic, genetic model of DED did not elicit greater responses to noxious stimulus. However, an elevated baseline activity and higher EC50 in the DED animals suggests an initial hyperexcitable state, possibly relating to spontaneous neural activity followed by capsaicin-induced desensitization or defunctionalization. Further studies are required to understand the receptor expression and morphological changes that account for neurosensory abnormalities in the TG of this model of DED.
This abstract was presented at the 2023 ARVO Annual Meeting, held in New Orleans, LA, April 23-27, 2023.