Cardioactive effects of diphenhydramine and curcumin in Daphnia magna

Although used as a model for examining the cardioactive effects of various compounds, the neuromuscular regulation of the heart of the crustacean Daphnia magna (D. magna) is not well understood. In the present study, we sought to determine how the heart rate of D. magna was affected by two previously untested compounds: curcumin and diphenhydramine (DPHM). DPHM produces a number of cardiotoxic side effects in vertebrates, particularly sinus tachycardia. Curcumin acts as a monoamine oxidase inhibitor (MAOI) and was expected toincrease the heart rate of D. magna. DPHM was found unexpectedly to lower the heart rate of D. magna with time. Curcumin increased heart rate when administered in higher concentrations. However, co-administration of curcumin with DPHM negated this effect. These findings may be explained by the potential role of histamine as a sympathetic cardiac neurotransmitter in D. magna.