Heat-shock-induced thermoprotection of hindleg motor control in the locust

Abstract

Functional neuromuscular connections are critical for appropriate behavioural responses, but can be negatively affected by increases in temperature. We investigated the effects of heat shock on the thermosensitivity of a neuromuscular pathway to the hindleg tibial extensor muscle of Locusta migratoria. We found that exposure to heat shock induced thermoprotection of both neuromuscular transmission and extensor muscle contraction by (i) increasing the upper temperature limit for failure, (ii) improving recovery following heat-induced failure and (iii) stabilizing excitatory junction potential amplitude and duration and extensor muscle contraction force at high temperatures. Furthermore, the heat-shock-induced thermoprotection of extensor muscle contraction was not attributable to a protective effect on intrinsic components of muscle contraction. Finally, the use of jumping as a locomotor strategy to avoid capture, a behavioural response dependent upon functionally competent neuromuscular connections at the hindleg tibial extensor muscle, became less sensitive to temperature following heat shock. We conclude that the natural stress response of the locust stabilizes neuromuscular signalling during temperature stress, and that this can underlie a thermoprotection of muscle contraction force and thus alter the thermosensitivity of an escape behaviour critical for survival.