Caffeine and Nicotine of Different Concentrations Result in Varying Heart Rates of Daphnia magna

Abstract

In cardiac muscle cells of most vertebrates, the sympathetic nervous system is stimulated when agonists bind to adrenergic receptors (Shaw & French, 2018). The Daphnia magna heart and the autonomic nervous system of many vertebrates have similar properties; therefore, using Daphnia magna as a model organism is justifiable way to determine the effects of stimulants on heart rate. In this investigation, we studied the effects of two central nervous system stimulants, caffeine and nicotine, on Daphnia magna. For four trials each, we manipulated concentrations of 0.5% caffeine, 1% caffeine, 1 mM nicotine, and 10 mM nicotine in order to measure the effects on Daphnia magna heart rate. In the end, we found varying trends in our data. The 0.5% caffeine and 10 mM nicotine showed a positive slope in percent change; on the other hand, the 1% caffeine and 1 mM nicotine showed a negative slope. This is significant because it shows that Daphnia magna have inconsistent responses to common stimulants. We expect this experiment to be of interest to researchers and future experimenters who study the excitatory effects of these common stimulants on other organisms.