Exposure to Heat Shock Affects Thermosensitivity of the Locust Flight System R. M. Robertson, zyxwvuts * H. Xu, K. L. Shoemaker, and K. Dawson-Scully Department of Biology, Queen's University, Kingston, Ontario, Canada, K7L 3N6 SUMMARY zyxwvutsrq The natural habitat of the migratory locust, zyxwvutsr Locustu zyxwvu mi- grutoriu, zyxwvutsrqpon is likely to result in locusts being heat stressed during their normal adult life. It is known that locusts exhibit a heat-shock response: exposure to 45°C for 3 h induces thermotolerance and the expression of heat- shock proteins. We investigated the effects of exposure to heat-shock conditions on the thermosensitivity of flight rhythm generation in tethered, intact animals and in deafferented preparations. Heat shock had no effect on wingbeat frequency measured at the start of flight se- quences, nor did it affect the postimaginal maturation of this parameter. During sustained flight, heat shock slowed the characteristic asymptotic reduction of wing- beat frequency. Wingbeat frequency of heat-shocked an- imals was less sensitive to temperature in the range 24" to 47°C than that of control animals, and the upper tem- perature limit, above which flight rhythms could not be produced, was 6" to 7°C higher in heat-shocked animals. These results were mirrored in the response of deaffer- ented preparations, indicating that modifications in the properties of the flight neuromuscular system were in- volved in mediating the response of the intact animal. We propose that exposure to heat shock had the adaptive consequences of reducing thermosensitivity of the neural circuits in the flight system and allowing them to operate at higher temperatures. Keywords: insect, flight, temperature, heat shock, wing- beat frequency. zyxwv 0 1996 John Wiley & Sons, Inc. INTRODUCTION Neural operation within mammalian nervous sys- tems is to a large extent protected from variations in the physical characteristics of the environment. However, many other animal species lack homeo- static mechanisms that allow independence from environmental constraints. This is particularly true for poikilotherms whose internal temperatures are not physiologically regulated but are allowed to vary as ambient temperature fluctuates. Given the profound influence of temperature on neural pro- cesses (for reviews, see Montgomery and Macdon- ald, 1990; Janssen, 1992), this raises the problem of how the nervous system maintains adaptive function under different thermal regimens. The Received August 29, 1995; accepted November 2, 1995 Journal of Neurobiology, Vol. 29, No. 3, pp. 367-383 ( 1996) 0 1996 John Wiley &Sons, Inc. CCC 0022-3034/96/030367- I? * To whom correspondence should be addressed. problem is most pressing for animals that experi- ence large, rapid temperature changes as a conse- quence of their ecology. Behavioral adaptations for thermoregulation can mitigate, but usually not eradicate, the effects of experiencing extremes in ambient temperature. It is important to determine the neural adaptations that compensate for tem- perature variability, and those that permit opera- tion at extremely high temperatures. The migratory locust, zyxw Locusta zyx Pnigratoriu, is na- tive to semiarid regions of equatorial Africa and is thus normally exposed to a range of high environ- mental temperatures (Uvarov, 1966). Locusts of- ten fly when ambient temperature exceeds 30°C and the heat produced by working flight muscles significantly elevates thoracic temperature above ambient by between 6" and 10°C (Weis-Fogh, 1956, 1964). Under laboratory conditions the per- missive lower and upper limits of thoracic temper- ature for flight are around 24" and 42°C (Weis- Fogh, 1956; Neville and Weis-Fogh, 1963). As in other insects (May, 1981; Oertli, 1989), the wing- 367