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Ian D. Meng, Masayuki Kurose; Corneal Dry-responsive Neurons in the Trigeminal Nucleus Respond to Innocuous Cooling in the Rat. Invest. Ophthalmol. Vis. Sci. 2012;53(14):5721.
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Corneal primary afferent neurons that respond to drying of the ocular surface have been previously characterized and found to respond to innocuous cooling, menthol, and hyperosmotic stimuli. The purpose of the present study was to examine the receptive field properties of second-order neurons in the trigeminal nucleus that respond to drying of the ocular surface.
Single-unit electrophysiological recordings were performed in anesthetized rats. Dry-responsive corneal units were isolated in the brainstem, at the transition zone between the spinal trigeminal subnucleus caudalis and subnucleus interpolaris. Corneal units were characterized according to their responses to changes in temperature (cooling and heating), hyperosmotic artificial tears, menthol, and low pH.
All dry-responsive corneal units responded to innocuous cooling of the ocular surface. In addition, these neurons responded to hyperosmotic stimuli and menthol application to the cornea. Approximately half of the neurons were also activated by noxious heat and low pH. Furthermore, neurons that were activated by noxious stimulation had a significantly lower response to cold and menthol stimulation.
Drying of the ocular surface activates primary afferent and second-order neurons involved in basal tearing. Many of the dry-responsive neurons recorded in the trigeminal nucleus receive input selectively from cold sensitive primary afferents. However, an additional subset of dry-responsive neurons receives convergent input from cold cells and polymodal nociceptive neurons. Alterations in the properties of dry-responsive neurons located in the trigeminal nucleus may contribute to dry eye syndrome.
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