Meeting Abstract
The neurogenic heartbeat of crustaceans is controlled by a 9-neuron pattern generator, the cardiac ganglion (CG), which includes 5 motor neurons and 4 premotor neurons; these neurons are electrically and chemically coupled, so that they fire nearly synchronous driver potentials and bursts of action potentials. Dendritic processes of both motor and premotor neurons appear to provide direct stretch feedback to the CG. We characterized (1) natural stretches of the lobster heart in vivo and (2) responses of CG neurons to stretch in semi-isolated preparations that included the CG and the transverse muscle fibers that underlie the premotor neurons. In vivo we characterized natural deformations of the ventral heart surface at 3 locations and directions during ongoing heart contractions: anterior transverse, posterior transverse and longitudinal. Movements were determined from videos in which the ventral side of the lobster was removed to reveal the pericardial cavity, but supporting ligaments and arteries that suspend the heart remained intact. Strains along the posterior transverse direction were greater than those along either the anterior transverse or the longitudinal direction. Interestingly, the premotor neurons, richly associated with stretch-sensitive dendrites, are located in the posterior region. In isolated CG-muscle preparations, stretch over multiple heartbeats elicited increased frequency and decreased duration of driver potentials; these changes were highly dependent on force. Stretch also elicited an initial phase delay in the driver potentials, which was dependent not only on force but also on strain rate. NSF IOS-1353023, NIH 8P20GM103423-12, Doherty Fdn/Bowdoin College.
