Characterizing the endocrine, digestive and morphological adjustments of the intestine in response to food deprivation and torpor

Hayes, James (2014) Characterizing the endocrine, digestive and morphological adjustments of the intestine in response to food deprivation and torpor. Masters thesis, Memorial University of Newfoundland.

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Abstract

The cunner, Tautogolabrus adspersus, is a marine teleost endemic to the cold waters of the Northwest Atlantic Ocean. The cunner is non-migratory and is known for its remarkable ability to endure the freezing winter months with little to no food. During this period, the cunner seeks refuge in the same rocky shelters it inhabits during the summer months and enters a torpid/dormant state. This response is characterized by a cessation of feeding, sluggish movements and a lowering of metabolic rate. Such a response calls for strict control of energy balance, and might use in part regulatory mechanisms present within the gut. To evaluate the physiological strategies employed by the cunner’s intestinal tract to withstand food deprivation, experimental fasting trials were conducted. Cunner were sampled for their stomachless digestive tract after a four-week period of acute food deprivation in July and August during their summer (active/feeding) state, and during their natural overwinter fasting in March. Digestive enzyme activities were assessed by biochemical assay. Specific activities for trypsin, alkaline phosphatase and lipase were all reduced in both 4-week fasted and torpid fish, whereas aminopeptidase-N was only lowered in 4-week fasted fish. Neither summer nor winter fasting caused significant changes in the intestinal mRNA expressions of digestive enzymes, with the exception of a decrease in aminopeptidase-N expression during torpor. Transcript expression in the gastrointestinal tract was also quantified for four putative appetite regulators. Orexin, the mechanistic target of rapamycin and cholecystokinin expressions were all reduced in torpid cunner, but not in summer fasting whereas apelin expression was reduced in summer fasting, but not in torpid fish. This work contributes to the overall understanding of energy balance in fish and provides novel insights into the intestine’s endocrine contribution to appetite regulation and digestive function in cunner during natural fasting and acute food deprivation.

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