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
Serotonin modifies the sensitivity of the male silkmoth to pheromone
Laureline Gatellier1,
Takashi Nagao2 and
Ryohei Kanzaki3,*
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
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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.
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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).
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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).
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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).
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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.
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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.
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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).
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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).
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© The Company of Biologists Ltd 2004
