Cortisol Released Due to Experimental Handling and UVB Radiation in Xiphophorus Species
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Xiphophorus fish have been used as experimental models for UV-inducible melanoma for over 85 years. The aim of this study was to characterize the stress response (i.e., cortisol production) in Xiphophorus fish in skin after UV exposure. The primary stress response was characterized in X. maculatus Jp 163 B, X. couchianus, and F1 interspecies hybrids (Xm-Xh) produced from the cross X. maculatus Jp 163 B (x) X. couchianus. The stress response in treated fish suggests experimental handling of the animals was the primary stressor and that UVB exposure effectively suppressed cortisol production rates. In Xm-Xh hybrids cortisol production rates were intermediate between parental species, but more similar to X. maculatus Jp 163 B. Thus, the cortisol stress responses appeared to be more species specific than treatment specific.
To eliminate species specific effects, we tested albino and wild type X. hellerii that only differed in pigment expression (i.e. were tyrosinase deficient). Although wild type fish exhibited a primary stress response to experimental handling the albino fish did not. This may suggest a role for tyrosinase in synthesizing catecholamines that provide substrate for the overall stress response. Analysis of stress recovery showed the fish returned to baseline cortisol production by 6 h, except for the albinos. This suggests albino skin is still repairing UV induced damage whereas wild type have repaired it by 6 h. Understanding the effects of stress and cortisol are important for elucidating the genetic interactions that lead to reduced immune function and/or increased susceptibility to tumorigenesis.