Evaluation of the Effects of Eye Drops for Dry Eyes on Neuronal Pain Receptors in a Primary Culture Model of Trigeminal Ganglion Cells

<b>Background:</b> Dry eye disease is a multifactorial ocular surface disorder characterized by tear film instability, inflammation, and neurosensory abnormalities that can lead to corneal pain and discomfort. In this study, we evaluated the effects of specific eye drops for dry eyes on neuronal pain receptors to gain insight into the mechanisms underlying corneal nerve pain in patients with dry eyes using a primary cell culture model of murine trigeminal ganglion cells. <b>Methods:</b> Trigeminal ganglia were obtained from wild-type postnatal day 7-10 mice. Primary cultures were prepared using the cell suspension method. After culturing for one week, the cells were stained with neuron-specific anti-neuronal nuclei, polymodal nociceptor, and transient receptor potential vanilloid 1 (TRPV1) antibodies. The calcium ion probe Fura2-AM^® was added to cultured cells after 2 weeks of incubation. The effects of capsaicin alone, in combination with the TRPV1 antagonist AMG9810, and in the presence of components of commercially available eye drops (cyclosporine, diquafosol tetrasodium, or rebamipide) were evaluated by monitoring calcium signals. <b>Results:</b> Neural excitation and capsaicin-induced increase in fluorescence intensity ratio were suppressed by AMG9810, cyclosporine, and diquafosol tetrasodium, but not by rebamipide. <b>Conclusions:</b> Inhibition of cellular excitation by cyclosporine and diquafosol tetrasodium may underlie their clinical pain suppressive effects. The primary culture model described here may serve as a useful tool for future studies on corneal perception.