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The Neurological Basis of Differential Anesthesia Tolerance in Cave-Adapted and Surface Conspecific Astyanax mexicanus

A recent hypothesis for the evolution of albinism in Astyanax cavefish has postulated the existence of a tradeoff between pigmentation and behavioral changes linked by catecholamine (CAT) levels. However, previous research did not identify any behavioral differences between surface and cave- dwelling Astyanax that occur during the critical period of larval pigment development. During a screen for behavioral or physiological differences linked to pigment development, I noted a difference in anesthesia tolerance. Anesthesia tolerance was tested by exposing fry to ice water or the chemical anesthetic tricaine methanesulfonate (MS- 222) and calculating the average time to unconsciousness, based on motion detection. The results suggest albino cavefish larvae treated with anesthesia remained conscious significantly longer than pigmented surface fish larvae. I discovered that the difference in anesthesia tolerance begins between 3 and 4 days post fertilization. Further testing showed that differences in anesthesia tolerance also persisted into adulthood: adult albino cavefish treated with anesthesia remained conscious significantly longer than pigmented adult surface fish. Pharmacological tests demonstrated a correlation between increased norepinephrine and increased anesthesia tolerance. Future testing will be done to elucidate the details of this relationship. Because cave- adapted and surface populations of Astyanax mexicanus are thus far the only natural model system for studying anesthesia tolerance, this research could help determine the general mechanism of anesthetic action.

Astyanax cavefish ; tradeoff ; melanin ; catecholamine ; anesthesia tolerance

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