Neuromodulation Changes the Biomechanics and Capabilities of the Aplysia Feeding

INTRODUCTION Neuromodulation is often used by the nervous system to change a muscle’s response to nervous system stimulation. Invertebrate preparations are well suited for study of neuromodulation because of their experimentally tractable nervous systems and biomechanics. The Aplysia smooth muscle I2 is a good model for neuromodulation because it is a muscle with known behavioral correlates [1], and it responds to serotonergic neuromodulation [2]. During two feeding behaviors, biting and swallowing, I2 moves the grasping structure toward the jaws [1]. During swallowing behaviors, the I2 muscle is sufficiently strong to move the grasper throughout the grasper’s full range of motion, but, during biting, an unmodulated I2 is insufficiently strong to generate the full motion of the grasper [3]. We used in vitro studies of I2’s response to serotonin to show that serotonergic neuromodulation can sufficiently strengthen I2 to allow the I2 to generate biting behaviors.