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First published online June 7, 2004
Journal of Experimental Biology 207, 2487-2496 (2004)
Published by The Company of Biologists 2004
doi: 10.1242/jeb.01035

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Serotonin modifies the sensitivity of the male silkmoth to pheromone

Laureline Gatellier¹, Takashi Nagao² and Ryohei Kanzaki^3,*

¹ Institute of Biological Sciences, University of Tsukuba, Tsukuba, Ibaraki 305-8572, Japan
² Human Information Systems, Kanazawa Institute of Technology, 3-1 Yakkaho, Matto, Ishikawa 924-0838, Japan
³ Department of Mechano-Informatics, Graduate School of Information Science and Technology, The University of Tokyo, Tokyo 113-8656, Japan

View larger version (18K): [in a new window]   Fig. 1. Experimental set-up. Four moths were placed in a closed box. Pheromone was applied through a 2 mm-diameter hole with a Pasteur pipette containing a piece of filter paper bearing pheromone. The pheromone stimulus was controlled by an electronic stimulator through a three-way solenoid valve, and an LED connected to the electronic stimulator flashed for the duration of the stimulus. The moths' response to pheromone and the LED flash were recorded with a CCD camera.

View larger version (18K): [in a new window]   Fig. 2. Effects of serotonin on the behavioral response of the male moth to different concentrations of artificial pheromone. 4 µl of 10-4 mol l-1 serotonin were applied to the desheathed brain 3 min before pheromone exposure. Sample size: control (N=76), serotonin (N=73), wash (N=75). Serotonin shifted the curve to the left; its effect was higher than the control and the wash (GLM, P<0.05).

View larger version (22K): [in a new window]   Fig. 5. Effects of serotonin antagonists on the behavioral response of the male moth to different concentrations of artificial pheromone. 4 µl of the drug were applied to the desheathed brain 3 min before pheromone exposure. Both drugs shifted the curve to the right (GLM, P<0.05), decreasing significantly the behavioral response in comparison with the control. (A) Mianserin at 10-4 mol l-1. Sample size: control (N=65), mianserin (N=64), wash (N=60). (B) Ketanserin at 10-3 mol l-1. Sample size: control (N=84), ketanserin (N=82), wash (N=34).

View larger version (25K): [in a new window]   Fig. 8. Daily variation of the male B. mori's behavior to different concentrations of artificial pheromone. Period during which the light was turned off is indicated by a gray bar along the x-axis. The N values for each group varied between 41 and 88. Around noon (10.00 h and 12.00 h),moths showed highest sensitivity to pheromone, significantly higher than during scotophase (GLM, P<0.05). The daily behavioral response to pheromone was strongly correlated to the daily variation of serotonin in the moth's brain (Fig. 7) (Pearson correlation coefficient: >0.90 for 0.1 ng, 0.5 ng and 1 ng).

View larger version (14K): [in a new window]   Fig. 3. Difference of means between the percentage of moths that responded to pheromone before and after three different concentrations of serotonin application. Values are means ± S.E.M. Sample size: 10-5 mol l-1 (N=129), 10-4 mol l-1 (N=73), 10-3 mol l-1 (N=60). The asterisk indicates significant difference (GLM, P<0.05); ns, non-significant.

View larger version (14K): [in a new window]   Fig. 6. Difference of means between the percentage of moths responding to pheromone before and after serotonin antagonist application. Values are means ± S.E.M. Sample size: 10-4 mol l-1 mianserin (N=64), 10-3 mol l-1 ketanserin (N=82), 10-4 mol l-1 ketanserin (N=84). Asterisks indicate significant difference (GLM, P<0.05); ns, non-significant.

View larger version (14K): [in a new window]   Fig. 4. Serotonin levels in the silkmoth's protocerebrum and antennal lobe (AL) after application of different concentrations of serotonin (10-5 mol l-1, 10-4 mol l-1 and 10-3 mol l-1). 4 µl of serotonin were applied to the desheathed brain 3 min before measurement with HPLC. Values are means ± S.E.M. Sample size: control (N=18), 10-5 mol l-1 serotonin (N=18), 10-4 mol l-1 serotonin (N=25), 10-3 mol l-1 serotonin (N=26), wash for 10-4 mol l-1 serotonin (N=9), wash for 10-3 mol l-1 serotonin (N=9). Differences between bars marked with the same letters were not significant (Kruskal–Wallis test, P<0.05).

View larger version (12K): [in a new window]   Fig. 7. Serotonin levels (+S.E.M.) in the brain (protocerebrum, antennal lobe and optic lobe) of B. mori exposed to a 16 h:8 hlight:dark cycle, at different time points over 24 h. The period during which the light was turned off is indicated by a gray bar along the x-axis. The N values for each group varied between 6 and 9. There was a circadian variation of serotonin in the brain (one-way ANOVA, P<0.05).