Modulation of Cardiac Performance in the Blue Crab Callinectes sapidus

Many rhythmical behaviors such as walking, flying, breathing and chewing are generated by neural circuits. These neurons or “central pattern generators (CPGs)”, produce repetitive, rhythmical bursts of activity that are conveyed to the muscles or “effectors” that produce the behavior. Most behaviors are modified or modulated to adjust the behavior. The heart of the blue crab, Callinectes sapidus, is a simple central pattern generator-effector system. The 9 neuron cardiac ganglion (CG) is a simple CPG located within the cardiac musculature (see Figure 1A and 1B). 4 interneurons act as pacemakers that drive 5 motor neurons that trigger heart contractions. The basic rhythm of the blue crab CG can be modulated by both hormonal and neural signals. Pericardial organs (PO) are neurohaemal structures that flank the heart and release bioactive products into the circulation. The CG is also directly controlled by 3 cardioregulatory fibers that originate in the central nervous system. 1 of these fibers is inhibitory, while the other 2 are excitatory in nature. Blue crabs are poikilotherms that are exposed to a range of environmental temperatures due to their distribution (western Atlantic from Cape Cod to Argentina) and seasonal variations. Changes in environmental temperature pose physiological challenges to all poikilotherms. The long term aims of this study are (1) to examine the modulatory effects of two biogenic amines, Dopamine (DA) and Serotonin (5HT), that are released from the PO, on the crab heart, (2) to examine the effect of temperature on cardiac performance, and (3) to determine if the modulation of the crab heart by biogenic amines is altered by temperature