Fig 1.
Increase then depression of locomotor activity after high temperature experience.
(A-D) Walking distance of flies was recorded over 3 min using the heat-box apparatus. After two initial 30 s periods at 24°C the chambers were heated to 29°, 33°, 37° or 41°C for 30 s (A-D; dark gray columns). After high temperature exposure chambers were cooled down to 24°C. Control flies were kept at constant 24°C (light gray columns). Walking distance increased with high temperature exposure (F = 17.12, P< 0.00001. Newman-Keuls post-hoc tests = p ≤ 0.001 = *** comparing with and without high temperature exposure). (E-F) Normalized walking distance during (E) and after (F) high temperature exposure. During high temperature exposure, fly’s locomotor activity increases. In the range of 29° to 41°C the relationship between temperature and walking distance shows a strong linear correlation (p = 0.0059 = **). After high temperature exposure of 37° and 41°C locomotion is significantly reduced compared to control flies (Newman-Keuls post-hoc tests = p ≤ 0.001 = *** comparing with and without high temperature exposure). The bars represent mean values and the error bars are standard errors of the mean.
Fig 2.
Depressed locomotor activity is not due to fatigue and is a general phenomenon.
(A-B) To examine whether or not depressed walking distance is due to fatigue, flies were exposed to high temperature five times. During high temperature exposures walking distance remains high for both 37° (A) and 41°C (B), indicating that flies are still able to maintain a high level of walking (F = 83.8, P < 0.00001, Newman-Keuls post-hoc test between exposed and non-exposed flies p < 0.001 = ***). No statistical difference was detected for walking distance during the five different high temperature exposures (p37°C = 0.68; p41°C = 0.92). (C) Depressed walking distance is context independent and not due to fatigue. Flies were exposed to either high temperatures outside the heat-box (‘tube’) or outside the heat-box with almost no ability to walk (‘immobil’). For both experimental groups and at 37 and 41°C, walking distance decreased similar to flies exposed within the heat-box apparatus (‘HB’ F = 90.1 and 650.7, pHB < 0.001 = ***; ‘tube’ F = 14.6 and 61.9, ptube < 0.01 and < 0.001 = ** and ***, ‘immobil’ F = 20.9 and 40.1, pimmobil < 0.01 and < 0.001 = ** and ***). (D) Depressed walking distance was also seen after giving the flies electric shocks as a different aversive stimulus (F = 16.9, P < 0.00001; Newman-Keuls post-hoc comparison for flies with and without shock: p10V = 0.551; p40V = 0.003 = **; p70V < 0.001 = ***; p100V < 0.001 = ***). The bars represent mean values and the error bars are standard errors of the mean.
Fig 3.
Locomotor depression after high temperature and electric shock exposure is a long lasting change in behavior.
(A-D) Extended recording of walking activity after high temperature exposure (37° and 41°C) revealed a steady change in locomotion. Activity increased with high temperature exposure (F = 22.14, P < 0.00001, Newman-Keuls post-hoc test p < 0.001 = ***). Moreover, (B, D) walking activity is strongly reduced 30 s after the 37°C stimulus but largely normal 8 min later (B) and is still highly significantly different for flies exposed to 41°C at both time points (D) when compared to control animals kept at 24°C (F = 33.27 and 81.78, P’s < 0.0001; Newman-Keuls post-hoc test p37°C 30s < 0.001 = ***; p37°C 8 min = 0.47; p41°C 30s <0.001 = ***; p41°C 8 min < 0.0001 = ***). (E,F) Walking distance was depressed after exposure to high temperatures and electric shock. A significant reduction in locomotor activity was evident up to 5 hours after exposure to 41°C, and up to 8 hours after exposure to electric shocks (temperature: Fs’ = 0.007, 15.3, 20.9, 13.6, 7.4, 5.7, 1.5, 1.2. shock: F’s = 0.16, 48.7, 23.8, 12.1, 5.7, 7.9, 6.6, and 1.3. P’s < 0.001 = ***, P’s < 0.01 = **; P < 0.05 = *). The bars represent mean values and the error bars are standard errors of the mean.
Fig 4.
The role of octopamine / Tyramine and serotonin in changes of locomotor activity following high temperature exposure.
(A-B) Genetically modified flies that lack the expression of octopamine and increases in tyramine ((A), TbH[M18])) or reduced serotonin function ((B) Trh-GAL4 / UAS-TeTxLC)) were exposed to a single high temperature stimulus (41°C, 30 s) and locomotion was recorded for 8 minutes. (A) The TbH[M18] flies had a strongly reduced response to the 41°C pulse but a similar reduction in walking distance after the exposure (F = 31.01, P < 0.001, Newman-Keuls post-hoc test p < 0.001 = ***). (B) Moreover, Trh-GAL4 / UAS-TeTxLC flies had a reduced initial response to 41°C, but showed a similar reduction in walking distance compared to genetic control flies (F = 2.1, P < 0.02, Newman-Keuls post-hoc comparison p < 0.001 = ***). The bars represent mean values and the error bars are standard errors of the mean.