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In Homarus americanus, heartbeat frequency is controlled by the cardiac ganglion, a central pattern generator. Heart rate, along with the amplitude of the contraction force, determines volume flow rate, or cardiac output. Pressures in the system can also influence cardiac output. Thus, it should be able to influence heart rate and contraction force as well. The present study investigates responses in heart rate and contraction force to changes in a low versus a high afterload pressure imposed through the lobster’s dorsal abdominal artery. Our data show that contraction force decreased at high afterload pressures across all lobsters. Additionally, while changes in heart rate varied between lobsters at different afterload pressures, significant responses showed an inverse relationship with afterload pressure. These findings support the idea that pressure in the lobster cardiovascular system may be regulated in ways reminiscent of the baroreceptor reflex in vertebrates. Although we cannot conclude whether this is the specific stretch feedback pathway the lobster cardiovascular system utilizes, we can confirm that changes in afterload pressure have lobster-dependent effects on heartbeat frequency. Sensory input from the dorsal abdominal artery, such as stretch induced by changes in afterload pressure, communicate with the cardiac ganglion through mechanisms that remain unclear.
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