Abstract
Zebrafish is an excellent model that can be utilized as an adjunct to current rodent models for studies of eye diseases because the anatomy and ultrastructural characterization of its cornea show much similarity with the human cornea. Therefore, we developed a behavioral model of corneal nociception using the adult zebrafish (Danio rerio). We analyzed the nociceptive effect of hypertonic saline (0.15-5.0 M sodium chloride [NaCl]) applied to the surface of the right or left cornea, on the animals' gender and locomotor activity through the open-field test. The behavioral model of corneal nociception was characterized by the antinociceptive effect of morphine (8.0 or 16 mg/kg; intraperitoneally [i.p.]), an opioid analgesic, and capsazepine, an antagonist of transient receptor potential vanilloid type 1 channels. We also tested whether the corneal antinociceptive effect of morphine could be modulated by naloxone, an opioid antagonist. Finally, we used the light and dark test to assess the anxiolytic effect of hypertonic saline (5.0 M NaCl; 5 μL) applied to the right or left cornea of the animals. As a result, hypertonic saline significantly increased (p < 0.01 vs. control) the corneal nociceptive behavior of adult zebrafish (D. rerio). Morphine significantly inhibited (p < 0.01 vs. 5.0 M NaCl) the hypertonic saline-induced corneal nociception and this effect was blocked by naloxone. Capsazepine (20 mg/kg; i.p.) significantly inhibited (p < 0.05 vs. control) the corneal nociception induced by hypertonic saline. Hypertonic saline, applied to the surface of the right or left cornea of the animals, induced nociception and did not cause a presumptive anxiolytic effect. Gender and site of application did not affect the profile of response to hypertonic saline. The results suggest that the adult zebrafish can also be used as a behavioral model of corneal nociception, with the advantages of significant homology with the human genome and low cost.
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