ABDOMINAL CARDIAC NERVES AND CARDIOREGULATION IN LIMULUS POLYPHEMUS

1. 1. A major response to stimulation of any of the abdominal cardiac nerves of Limulus polyphemus is an increased heart beat rate. 2. 2. Maximum increases in rate (6-8 beats/min) can be produced with stimulus frequencies as low as 5/sec. 3. 3. At all stimulus frequencies maximum increases in rate occur only after 30-40 sec of stimulation and the maximum rate of change in rate during this time (9 beats/min per min) is produced by stimulus frequencies between 5 and 10/sec. 4. 4. Recovery of heart rate after stimulation follows an exponential time course with a half-time of several minutes and is independent of temperature. 5. 5. In many cases the abdominal cardiac nerves also appear to carry cardio-inhibitory fibers with characteristics similar to the inhibitory fibers innervating the heart in the cephalothorax. © 1969.