Hysteresis in the production of force by larval Dipteran muscle

Abstract

SUMMARYWe describe neuromuscular hysteresis -the dependence of muscle force on recent motoneuron activity -in the body wall muscles of larval Sarcophaga bullata and Drosophila melanogaster. In semi-intact preparations, isometric force produced by a train of nerve impulses at a constant rate was significantly less than that produced by the same train of stimuli with a brief (200ms) high-frequency burst of impulses interspersed. Elevated force did not decay back to predicted values after the burst but instead remained high throughout the duration of the stimulus train. The increased force was not due to a change in excitatory junction potentials (EJPs); EJP voltage and time course before and after the high-frequency burst were not statistically different. Single muscle and semi-intact preparations exhibited hysteresis similarly, suggesting that connective tissues of the origin or insertion are not crucial to the mechanism of hysteresis. Hysteresis was greatest at low motoneuron rates -yielding a ~100% increase over predicted values based on constant-rate stimulation alone -and decreased as impulse rate increased. We modulated motoneuron frequency rhythmically across rates and cycle periods similar to those observed during kinematic analysis of larval crawling. Positive force hysteresis was also evident within these more physiological activation parameters.

Force–length relation of skeletal muscles: from sarcomeres to myofibril

“…This suggests the existence of three sarcomere F-L curves corresponding to the three contractile types, and hence implies a hysteretic nature of sarcomere F-L behaviours (Wilson et al 1970;Paterson et al 2010). As illustrated in Fig.…”

Cell-selective modulation of theDrosophilaneuromuscular system by a neuropeptide

“…7), force was detected using a custom force transducer composed of four silicon wafer strain gauges (Micron Instruments, Simi Valley, CA) in full Wheatstone bridge configuration and mounted about the narrowest part of a polycarbonate beam (Ormerod et al 2013;Paterson et al 2010). The transducer operates linearly between 1 N and 2 N and exhibited no temperature sensitivity between 10 and 30°C.…”

“…This stimulus protocol is within the range of motor output patterns underlying contractions recorded from tethered larvae (Paterson et al 2010). Muscle cells 6 and 7 contributed ϳ50% of the ventral longitudinal force generated by semi-intact preparations, and muscle cells 12 and 13 contributed ϳ30% (see representative traces in Fig.…”

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“…This preparation minimizes damage to dorsal-most 92 muscles on the recording side. Larvae dissected in this way generate spontaneous 93 crawling-related motor activity comparable to larvae dissected with the more common 94 dorsal-midline preparation, although at a faster rate [36]. 95 …”