Meeting Abstract

40.2  Friday, Jan. 4  Rewriting the Motor Code to a Muscle in a Running Insect Alters Function from Energy Absorption to Production SPONBERG, S*; LIBBY, T; FULL, RJ; Univ. of CA, Berkeley sponberg@berkeley.edu

A mechanistic understanding of neural feedback in a locomoting organism requires linking the functional response of individual muscles to changes in body dynamics. To determine the control potential of individual muscles on body dynamics in freely running cockroaches (Blaberus discoidalis), we added direct, phase-locked muscle stimulation (muscle action potentials, MAPs) in a manner simulating known patterns of neural feedback. We targeted muscle 137, a middle leg femoral extensor, which in situ work loops have shown absorbs energy during simulated running. Adding 1-3 additional MAPs in our in vivo experiments to the 2-3 produced naturally did not alter the animal�s center of mass or individual leg dynamics as measured by a 3-axis microaccelerometer backpack and videography. Adding 5 or more additional MAPs did change the animal�s center of mass dynamics and resulted in a prolonged stance phase and leg extension (P < 0.001). To understand the mechanism affecting the center of mass, we measured the work loop of muscle 137 in intact legs under conditions mimicking the effects of neural feedback in the behaving animal. Adding 1-3 MAPs in the intact leg, work loop experiments did not result in a change in function. Muscle 137 with this moderate additional stimulation still absorbed energy. However, adding 5 or more MAPs with the longer stance period resulted in a dynamic shift to producing positive net work. Sufficient levels of feedback activation result in prolonged extension and a longer period of muscle shortening with significant force production. The functional shift is non-linear, matching the changes in both this muscle�s control potential and its control sensitivity during locomotion. NSF FIBR grant and the Fannie and John Hertz Foundation.