Investigating the control of gut motility in fish and how it is affected by temperature

Abstract

Efficient transport, breakdown and absorption of food in the gut is crucial for animals. This is achieved through coordinated movements of smooth muscle cells inside the gut wall. It is regulated by autonomous nerves (especially the enteric nervous system) and hormones. Interstitial cells of Cajal (ICC) play a role in initiating motility and modulating control. The aim of this study was to investigate how an acute temperature increase affects the control of gut motility in rainbow trout (Oncorhynchus mykiss) in vitro by analyzing cholinergic response and ICC. Muscle contractions were recorded at different temperatures (10 °C, 15 °C and 20 °C). Cholinergic activity was mimicked by adding increasing concentrations of carbachol and the mean force developed at each concentration as well as LogEC50 , i.e. the concentration where 50% response was attained, were calculated. I found that there was an effect of temperature in different aspects of both organs. In the intestines LogEC50 increased from -5.56±0.07 at 10 °C to -5.21±0.05 at 20 °C. But the controls also indicate a decrease in sensitivity and loss in developed force over time. ICC activity was studied by adding 50 µM benzbromarone which inhibited the activity of the stomach where only 63±9 % of the initial basal contractile force was retained, while no effect of benzbromarone was recorded for the intestine. We then examined the effects of ICC on cholinergic stimulation. The variation of results in both controls and treatments made it difficult to interpret if the decrease in response is caused by a change in temperature or due to time. Intestines at 10 °C decreased in sensitivity from LogEC50 (-5.76±0.10 to -5.25±0.09) for treatments and controls (-5.97±0.13 to -5.42±0.09). The extent of how temperature affects ICC remains unclear but could give implications for improvements of techniques.