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Inconsistency in the expression of locomotor and ERG circadian rhythms in the German cockroach Blattella germanica (L.)

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Archives of Insect Biochemistry and Physiology 48:155–166 (2001)
Inconsistency in the Expression of Locomotor and
ERG Circadian Rhythms in the German Cockroach,
Blattella germanica (L.)
Huan-Wen Chang and How-Jing Lee
Department of Entomology, National Taiwan University, Taipei, Taiwan
ERG recordings from German cockroaches showed that the amplitude of light-evoked responses have a circadian rhythmicity
in adult males that coincided with the locomotor circadian
rhythm. The peak of the response occurred during the subjective night, and the circadian period was less than 24 h under DD
condition. In contrast, although the locomotor circadian rhythm
was masked by the development of ovaries and pregnancy in females, their visual responses displayed circadian rhythmicity.
This inconsistency in expression of locomotor and visual sensitivity circadian rhythms in females implied separate pacemakers for these two overt rhythms. After severing the optic nerves,
changes in ERG amplitude of the operated cockroaches still displayed a circadian rhythm under DD condition, demonstrating
that the visual sensitive pacemaker was located in the eye and
independent from the locomotor pacemaker. Arch. Insect
Biochem. Physiol. 48:155–166, 2001. © 2001 Wiley-Liss, Inc.
Key words: electroretinogram; circadian rhythm; masking effect; pacemaker;
ovarian factors
INTRODUCTION
Male adults of the German cockroach, Blattella germanica (L.), express robust circadian
rhythmicity in their locomotor activity (Dreisig
and Nielsen, 1971; Sommer, 1975; Leppla et al.,
1989; Lin and Lee, 1996). In contrast, female
adults do not display a locomotor circadian
rhythm. Rather their cyclic changes of daily locomotor activity are masked by the effects of their
ovarian development (Lee and Wu, 1994; Lin and
Lee, 1996). Based on the finding that ovariectomized females express a locomotor circadian
rhythm that has the same circadian period as
male adults, the endogenous circadian clock for
locomotor activity is present in adult females.
However, it is normally masked by ovarian factors (Lin and Lee, 1996; Tsai and Lee, 2000).
© 2001 Wiley-Liss, Inc.
The locomotor pacemaker is located in optic
lobes of the German cockroach (Wen and Lee,
2000) as well as in other cockroach species
(Helfrich-Forster et al., 1998). Since the internal
masking effect of the locomotor circadian rhythm
is a unique characteristic of the German cockroach, identification of the site at which masking
factors interact with the circadian system is an
interesting project to pursue, assuming that the
locomotor pacemaker is the master clock that conContract grant sponsor: National Science Council, ROC; Contract grant number: NSC 89-2313-B-002-030.
*Correspondence to: Dr. How-Jing Lee, Dept. Entomology,
National Taiwan University, Taipei 106, Taiwan.
E-mail: m480@ccms.ntu.edu.tw
Received 3 November 2000; Accepted 11 June 2001
156
Chang and Lee
trols other overt circadian rhythms. However, if
another circadian rhythm can be identified in female adults expressing arrhythmic locomotion, we
would have eliminated the possibility of the master pacemaker itself serving as an interaction site
for the masking factors.
The ERG (electroretinogram) has been proven
to be particularly useful as an easy method for
quantifying of visual responses. Using this technique, circadian rhythms of visual responses in a
variety of arthropods including several species of
insect have been documented (Koehler and Fleissner, 1978). Wills et al. (1985) suggested that
the pacemaker that controls circadian rhythmicity of the ERG resides in the optic lobes and is
anatomically close to, or identical with, the pacemaker that regulates the locomotor activity
rhythm in the cockroach, Leucophaea maderae.
The ERG in the German cockroach, therefore, was
chosen for investigating the relationship between
the locomotor activity and visual response circadian rhythms and between pacemakers of these
rhythms.
MATERIALS AND METHODS
Insects
All experiments were performed with adult
German cockroaches, Blattella germanica (L.), collected from households in Taipei, Taiwan, and
reared in an environmental chamber at 28°C and
LD 16:8 h for several generations. Dog chow and
water were provided ad libitum. Last-instar
nymphs were separated daily and kept under
identical rearing conditions. The adults that
emerged within 24 h were defined as 0-day-old.
Detailed rearing procedures were described in a
previous report (Lee and Wu, 1994).
ERG
For recording the ERG (Electroretinogram),
a cockroach that had been maintained in a lightdark cycle (16:8h) was immobilized by waxing the
head capsule to the lucite stage. The cockroach’s
legs were restrained with wax, and its antennae
were removed. An active electrode was made of a
glass micropipette filled with three M KCl. A
small hole in the compound eyes was made with
a sharp needle to allow access for the active electrode that penetrated just below the surface of
the cornea of the eye. An indifferent electrode was
made of silver wire and placed in the haemocoele
through a small hole in the tergum of the thorax.
The laceration was sealed with petroleum jelly.
After the electrodes were in place, the cockroach
was placed in a light-tight box, and kept in constant darkness throughout the recording period.
During the recording period, the cockroach was
given access to water.
To stimulate the retina, a fiber-optic solidstate color wheel (WPI, Sarasota, FL) was used
to generate a blue light stimulus (spectral maximum at 470 nm). Based on the spectral sensitivity of the German cockroach (Koehler et al., 1987),
blue light stimulation produces maximal visual
responses. Stimulation was controlled by a digital stimulator (Grass, Inc., Quincy, MA) that triggered a train of light pulses that consisted of a
burst of 23 to 150 ms pulses presented at 5-s intervals for 2 min every 2 h. The light pulses were
delivered through fiber optics to the vicinity of a
compound eye where maximum responses of ERG
amplitude could be recorded. The distance between the eye and light source was 5 mm.
The differences in voltage recorded by the
active and indifference electrodes were amplified
by a preamplifier (S-7071A, WPI, Sarasota, FL)
and digitized with an A/D converters (digidata
1200A , Axon, Foster City, CA), and filtered (gain
8×, bandpass 0.5–10 Hz). A computer program,
Axoscope 1.1 (Axon, Foster City, CA), was used
to analyze the data and transfer them to Origin
4.1 (Microcal Software, Inc., Northampton, MA)
for graphic presentation. Changes of retinal sensitivity were indicated by changes in ERG amplitude based on an averaging 15 responses to light
pulses every 2 h.
The cyclic pattern of ERG was determined
by eye-fitting sine wave course and the free-running period was calculated as the mean value of
successive time laps between two amplitude peaks
(Colwell and Page, 1989).
Optic Nerve Severance
Newly emerged male adults were anesthetized on crushed ice and their optic nerves were
exposed by cutting the cuticle across the inner
margin of the compound eye at the postgena with
a microscalpel. The optic nerves between retina
and lamina of optic lobes were cut by inserting
Inconsistent Expression of Two Circadian Rhythms
fine iridectomy scissors. The operated insects
were placed in a humid environment without food
for one day to recover from the surgery, after
which they were examined individually for ERG
responses from the operated compound eyes.
Locomotor Activity
Locomotion of individual German cockroaches
was automatically recorded with an infrared motion detector system described in a previous report (Lin and Lee, 1998). All insects were tested
at 28°C in constant darkness (DD). Although they
were fed beforehand, adults being tested were
kept in the motion detector boxes with water only.
Locomotor activity was measured as the number
of times in an hour that the infrared sensor was
triggered by movement of the cockroach. The
rhythmicity of daily locomotion and the circadian
period (τ) were calculated and for data recorded
during 10 consecutive days using a chi-square
periodogram (Sokolove and Bushell, 1978) at 0.05
significant level.
RESULTS
ERG Waveform
An ERG is an extracellular recording of a
light-induced electrical activity in the retina of
157
compound eyes. A typical response of the ERG
elicited by a moderate intensity (0.0317 Lum/sf)
of blue light for 150 ms, showed a slow monophasic negative potential after 10–30 ms of illumination, then maintained itself at a steady level
and returned to base line slowly when the light
was extinguished (Fig. 1). The negative potential
typically peaked at 150 ms after the beginning of
the light stimulation. Although the retina immediately responded to the light pulse, the negative
potential of ERG did not return to base line right
after the light off. ERG waveforms from male and
female adults were the same.
The kinetics of the ERG at the most sensitive time (Zeitgeber time = 19 h) under constant
darkness condition were analyzed using the following parameters: (1) The time required to initiate the ERG (latency): defined as time elapsed
between the stimulation of light on and the initiation of the ERG; (2) The rate of rise of the ERG
(initial slope): defined as the rate to reach 50% of
the maximal response following the initiation of
the response; (3) The recovery of the ERG (time
to repolarization): defined as the time to return
halfway to the resting potential before the stimulation following the termination of the stimulation (Fig. 2). The high light intensity caused not
only a high amplitude response (Fig. 2A), but also
Fig. 1. An example of electroretinal response to a light pulse
recorded from the compound eyes
of the German cockroach, B. germanica (L.) under constant darkness condition. The response was
elicited with a 150 ms of light
pulse (λmax 470 nm).
158
Chang and Lee
Fig. 2. The kinetic analysis of
ERG responses to various intensity of light pulses in the
German cockroach B. germanica (L.). A: The amplitude of
ERG. The amplitude was defined as the magnitude difference between the potentials
before lights on and the peak
of the ERG. B: The latency of
the ERG. It was defined as time
elapsed between the stimulation of light on and the initiation of the ERG. C: The rate of
rise of the ERG response. The
initial slope of the response was
defined as the rate to reach 50%
of the maximal response following the initiation of the response. D: The recovery of the
ERG response. The time to repolarization was defined as the
time to return half way to the
resting potential following the
termination of stimulation. The
different letters (a, b, c, d) on
the histogram indicates significant difference (Fisher PLSD, P
< 0.01). The error bars indicate
SEM. This typical kinetic analysis of ERG responses was a
representative of 12 male cockroaches.
rapid initiation of the ERG (Fig. 2B). On average, the retina responded to the light pulse within
10–30 ms. The initial slope of the ERG also increased as light intensity increased, producing a
more rapid ERG response (Fig. 2C). However, the
recovery of ERG following light off required 80 to
100 ms to reach halfway to the resting potential
(Fig. 2D). Within the range of light intensities
employed, there were no significant differences
in time for recovery. From the kinetic analysis of
ERG, latency and initial slope were the two key
parameters to contribute to the changes in ERG
regardless of circadian time.
When circadian activities were examined, the
amplitude changes of the ERG to the various tested
intensities showed a free-running rhythm (Fig. 3A).
The circadian pattern persisted throughout the recording period, and the rhythmic changes had a
period close to 24 h. From the analysis of kinetic
changes of the ERG, only one parameter, the rate
of rise of the ERG, displayed circadian rhythmicity (Fig. 3C). The rate to reach 50% of maximal
amplitude following the initiation of the response
increased in the subjective night, and decreased
in the subjective day. However, the other parameters, the latency and time for repolarization of
Inconsistent Expression of Two Circadian Rhythms
159
Fig. 3. Plots of the kinetic
changes for one out of five
testing males of B. germanica
(L.) in the ERG as the function of circadian time. The
daily changes of amplitude
(A), latency (B), speed (C), and
recovery (D) of the ERG for 3
consecutive days. The German
cockroach (B. germanica) was
maintained in constant darkness except when they were
stimulated every 4 h by a 150ms light pulse which triggered
an ERG response. The legend
is described in Figure 2.
the ERG, did not display clear circadian oscillation (Fig. 3B and D).
Intensity-response curves for the ERG measured during a free-running circadian cycle are presented in Figure 4. The amplitude changes of the
ERG in the adult male cockroach were measured
as the function of light intensity during one circadian cycle under constant darkness (Fig. 4A). In
responding to various light intensities, the amplitude of ERG increased as the light intensity increased and it peaked during the subjective night
(at zeitgeber time 15 and 19 h). Since the initial
slope was the only parameter that displayed cir-
cadian rhythmicity when we examined ERG kinetics, it also showed the same pattern of change
as that for change in ERG amplitude (Fig. 4B).
Circadian Rhythm of ERG
Male German cockroaches were maintained
in a light-dark cycle (LD 16:8 h) for one day before being placed in the ERG recording apparatus. The daily amplitude changes of the ERG of
adult male cockroach exhibited a distinctive temporal cycles (Fig. 5A). The amplitude of ERG
reached its maximum during the subjective night,
before gradually decreasing in the subjective day.
160
Chang and Lee
Fig. 4. Intensity-response curves
for the ERG measured during a
free-running circadian cycle of one
male B. germanica (L.). A: Amplitude changes during one circadian
cycle are plotted. B: Changes in
the initial slope of the ERG during one circadian cycle are plotted. Each response was evoked by
a 150-ms light pulse under darkness condition (re-plotted from the
first day data of Fig. 3).
This circadian cycle persisted for the entire recording period (at least 7 days). These rhythmic
changes were similar to the locomotor circadian
period in that the period was shorter than 24 h
(Table 1). After a few cycles, the rhythm had drifted
completely out of phase with the entrained lightdark cycle. In order to show the consistency of the
ERG and locomotor circadian rhythm, the locomotion of starving male adults was monitored (Fig.
5B). The male showed a free-running locomotor
rhythm with a period of 23.6 h under DD condition. Both the ERG and locomotor rhythms of male
adults expressed circadian rhythmicity with similar duration of circadian periods (Table 1).
Since male and female German cockroaches
differ in their circadian locomotor activity (Lin
and Lee, 1996), the ERG of starving females in
various stages of reproductive activity were also
monitored. ERG amplitude changes and locomotor patterns of 1-day-old starving adult females
are shown in Figure 6. Both the ERG (Fig. 6A)
and locomotor activities (Fig. 6B) displayed a freerunning rhythm under DD condition. Although
the ERG data were not monitored over a long
enough time period to calculate the circadian period by a statistical program, the cyclic pattern
did show a < 24-h circadian period (by measur-
ing the time between two peaks) that was similar to the circadian period of locomotion (Table
1). The peak amplitude of the ERG occurred during the subjective night at the same time as the
locomotion displayed the peak activity.
After 5 days of normal feeding, the ERG and
locomotor activities of female adults were monitored under conditions of starvation and DD. The
daily fluctuations of the ERG and locomotor activity of a 5-day-old female are shown in Figure
7. Although changes in ERG amplitude displayed
a free-running rhythm with a <24-h period (Fig.
7A), a locomotor circadian rhythm was not expressed (Fig. 7B). The peak amplitude of the ERG
occurred in the subjective night. The locomotor
pattern was similar to that monitored from normal fed virgin females, in that their locomotor
circadian rhythms were masked by the mature
development of their ovaries (Table 1).
Typical ERG fluctuations and locomotor activity patterns are shown in Figure 8 for starving pregnant females. Amplitude changes in the
daily ERG displayed a free-running rhythm with
a period of less than 24 h, and the peak amplitude occurring during the subjective night (Fig.
8A). However, the minimal locomotor activity of
the starving pregnant female prevented the de-
Inconsistent Expression of Two Circadian Rhythms
161
Fig. 5. A: Changes in the amplitude of the ERG as a function of circadian time. The 1-day-old male German cockroach
(B. germanica) was provided with water only and maintained
in constant darkness except every 2 h it was stimulated with
a 150-ms light pulse (light intensity = 0.0317 Lum/sf) to trigger an ERG response. The amplitude of the ERG fluctuated
cyclically and peaked during the subjective night. B: An
actogram of a starving 1-day-old male cockroach under 28°C,
constant darkness conditions. The bar on the top of the
actogram represents the photoperiod conditions. The horizontal lines show successive 24-h periods of locomotor activity. The superimposed line across the actogram represents
the predicted onset time for the locomotor activity based on
the length of the male’s circadian period (τDD= 23.6h). A and
B were the typical representative of 5 and 6 starving males,
respectively.
tection of circadian rhythmicity (Fig. 8B). Therefore, although the locomotor circadian rhythm was
masked by pregnancy, a circadian rhythm for visual sensitivity was clearly expressed (Table 1).
located in the optic lobes where the locomotor
pacemakers are located, and therefore pacemakers for visual sensitivity and locomotion of the
German cockroach are separated. The pacemaker
for visual responses is located in the eye while
the locomotor pacemaker is in the optic lobe.
Pacemaker of ERG
A classical way to demonstrate the possible
site of a pacemaker was to separate the neural
connection between the site and the brain. A freerunning ERG was produced by the compound eyes
in a male whose optic nerve was severed, disconnecting the eye from the optic lobe (Fig. 9). Therefore, the pacemaker of visual sensitivity was
demonstrated in the eye. This finding indicates
that the pacemaker for visual sensitivity was not
DISCUSSION
ERG Waveform
The responses of insect compound eyes to
light stimuli can be grouped on the basis of their
electrical activity and their visual behavior
(Autrum, 1958). One category of responses shows
a relatively simple negative potential when illu-
162
Chang and Lee
TABLE 1. Effects of Age on Circadian Period of ERG and Locomotion in the German Cockroach, B.
germanica, at 28°C and Constant Darkness Conditions
Y
X
a
1
X
a
5
X
a
10
Y
b
dn
ERG
N
Expression of circadian rhythm (%)
Circadian period (τDD)c
5
100
22.8 ± 1.89
5
100
23.5 ± 1.00
5
60
22.5 ± 0.1
5
100
22.38 ± 0.54
3
100
21.75 ± 0.35
Locomotion
N
Expression of circadian rhythm (%)
Circadian period (τDD)c
6
100
23.6 ± 0.23
10
100
23.7 ± 0.27
10
0
–
10
0
–
–
–
–
a
The initial age (days) of the testing is indicated in the subscript.
dn: the optic nerve of male was severed at the day of emergence.
c
The free-running period was calculated from measuring the time lapse between two amplitude peaks.
Dashes (–) indicate data not available.
b
Y
Fig. 6. A: The amplitude changes of ERG responses for an
adult female German cockroach (B. germanica) after emergence. The animal was provided with water only and maintained in constant darkness except every 2 h when it was
stimulated with a 150-ms light pulse (light intensity = 0.0317
Lum/sf) to trigger an ERG response. The amplitude of the
ERG fluctuated cyclically and peaked during the subjective
night. B: An actogram for a starving adult female German
cockroach under 28°C, constant darkness conditions. The legend is described in Figure 5. A and B were the typical representative of 5 and 10 starving females, respectively.
Inconsistent Expression of Two Circadian Rhythms
163
Fig. 7. A: The amplitude changes of ERG responses for an
adult female German cockroach (B. germanica) after 5 days
of normal feeding following eclosion. The animal was provided with water only and maintained in constant darkness
except every 2 h when it was stimulated with a 150-ms light
pulse (light intensity = 0.0317 Lum/sf) to trigger an ERG
response. The amplitude of the ERG fluctuated cyclically
and peaked during the subjective night. B: An actogram for
a starving adult female German cockroach under 28°C, constant darkness conditions. The legend is described in Figure 5. A and B were the typical representative of 5 and 10
starving females, respectively.
minated, while the other responses display a more
complex waveform (Armington, 1974). Based on
the waveform of its ERG (Fig.1), the German
cockroach expresses the first type of response. The
negative potential of the ERG will remain at a
steady level while the light is on and returns to
the base line when the light is extinguished. These
types of ERG responses can be found in relatively
slow jumping and crawling insects, such as most
cockroaches and crickets (Armington, 1974). In contrast, fast flying insects, such as blowflies and bees,
have more complex ERG waveforms. Although the
cockroach Leucophaea maderae is a slow-moving
insect, it is a strong flyer that is reflected in the
complex waveform of its ERG (Colwell and Page,
1989). In contrast, the minimal flight capability
of the German cockroach (Cornwell, 1968) is correlated with simpler waveform of its ERG.
Circadian Rhythms of ERG
An increase in the number of photons reaching the photoreceptors should increase the amplitude of the ERG response (Colwell and Page, 1989).
Kinetic analysis of the ERG in the German cockroach indicates that changes in ERG amplitude
are primarily due to the changes in the probability of photons captured, and that the rate of rise
of the ERG response is the reflection of the rate of
photons captured by the photoreceptors. Based on
these reasons, the daily changes in the ERG of
164
Chang and Lee
Fig. 8. A: The amplitude changes of ERG responses for a
pregnant female (carrying ootheca) German cockroach (B.
germanica) 10 days after emergence. The animal was provided with water only and maintained in constant darkness
except every 2 h when it was stimulated with a 150-ms light
pulse (light intensity = 0.0317 Lum/sf) to trigger an ERG
response. The amplitude of the ERG fluctuated cyclically
and peaked during the subjective nigh. B: An actogram for
a starving 10-day-old pregnant female German cockroach
under 28°C, constant darkness conditions. The legend is described in Figure 5. A and B were the typical representative
of 5 and 10 starving females, respectively.
the German cockroach may be caused by the movements of screening pigment in the photoreceptor
cells of retina, similar to that found in the housefly (Pyza and Meinertzhagen, 1997).
The ERG has proven to be a useful, easy
measurement of visual sensitivity in cockroach
(Colwell and Page, 1989). Based on the finding of
the current investigation, the high visual sensitivity of the German cockroach at night coincided
with high locomotor activity (Lin and Lee, 1996).
This matching of physiological function with a behavioral pattern is important for the German
cockroach since it is a nocturnal animal. In the
German cockroach, changes in ERG amplitude
that peak during the subjective night show circa-
dian rhythmicity (Fig. 5). From the analysis of
ERG kinetics, the speed of ERG response is the
main contributor of the three parameters to cause
circadian rhythm in the ERG amplitude changes.
Similar behavior has been reported for recordings
of ERG amplitude from the cockroach L. maderae,
although only two (off-transient and sustain component) out of three components of ERG show circadian rhythmicity (Colwell and Page, 1989).
Inconsistency of Locomotor and Visual
Sensitivity Circadian Rhythm
A unique characteristic of the circadian system in the German cockroach is the existence of
a masking on the locomotor circadian rhythm as
Inconsistent Expression of Two Circadian Rhythms
165
Fig. 9. Daily changes of ERG response in the amplitude of
a male German cockroach whose optic nerve was severed
unilaterally. The animal was provided with water only and
maintained in constant darkness except every 2 h when it
was stimulated with a 150-ms light pulse (light intensity =
0.0317 Lum/sf) to trigger an ERG response. The amplitude
of the ERG fluctuated cyclically and peaked during the subjective night. This is a typical representative of three operated male cockroaches.
a result of the development of the ovaries (Lin
and Lee, 1996). This masking effect can be removed either by ovariectomy (Lin and Lee, 1996)
or by preventing ovarian development by starving the animal (Fig. 6). Once the females are
pregnant (carrying ootheca), their locomotor activity is very depressed, thereby masking the observation of a locomotor circadian rhythm (Tsai
and Lee, 2000). The only way to remove this
masking effect is to prevent the formation of
ootheca.
Female adults carrying ootheca express
circadian rhythmicity in their visual sensitivity even though their locomotor circadian
rhythm is masked (Table 1). This inconsistency
in the expression of locomotor and visual sensitivity circadian rhythms indicated the possibility that separate pacemakers exist in the
German cockroach. Some research findings suggest that the circadian pacemaking system in
the optic lobes of cockroach regulate locomotor
activity, modulate photoreceptor sensitivity, and
influence central processing of visual information (Wills et al., 1985). In the horseshoe crab
Limulus polyphemus, a circadian clock in the
brain has an important role in peripheral visual system (Kass and Barlow, 1992). The clock
can transmit neural activity to the eyes via efferent optic nerve fibers. Since the locomotor
pacemaker of the German cockroach is located
in the optic lobes (Wen and Lee, 2000), we severed the optic nerves to examine whether the
optic lobes control expression of the circadian
rhythm for visual responses. It is possible that
locomotor pacemaker can mediate ERG rhythm
through humoral signals, since we did not remove the pacemaker in the surgery. For the
regulation of visual sensitivity and locomotion
in the cockroach Leucophaea maderae, there
was a neural regulation between them (Colwell
and Page, 1989). In addition, when considering
the nature of ERG rhythm (it showed a rapid
amplitude change pattern), it implied neural
regulation. Therefore, our result may show the
existence of a visual sensitivity pacemaker in
the retina (Fig. 9). In cockroach L. maderae, the
pacemakers for locomotion and visual sensitivity are either identical or located close to each
other in the optic lobes (Wills et al., 1985;
Colwell and Page, 1989, 1990). Although the offtransient of the ERG disappeared when the
nerve connection between the lamina and the
medulla of the optic lobe was cut, the sustained
component still persisted (Colwell and Page,
1989). Since Colwell and Page (1989) did not
discuss the persistence of the circadian rhythm
for the sustained component, we doubt that the
visual response pacemaker of L. maderae is the
166
Chang and Lee
same one as the locomotor pacemaker. Based
on this reasoning, we conclude that the pacemaker for visual responses is located in the eye,
but not in the optic lobes.
This inconsistency in the expression of locomotor and visual response circadian rhythms is supported by our finding that the masking factors from
developing ovaries or pregnancy only acts on the
locomotor pacemaking system. However, we do suggest that the pacemakers for locomotion and visual
responses are strongly coupled or mutually interact (Wills et al., 1985). Since under some artificial
conditions that allow both locomotion and visual responses to display circadian rhythmicity, their circadian periods are the same (Table 1). In addition,
our results showed that the masking factors do not
act on the locomotor pacemaker itself, but on the
output pathway of the circadian system.
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brain transmits synchronous efferent signals to all
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ACKNOWLEDGMENTS
We thank Dr. En-Chang Yang for his technique
support and critical review on the original draft of
the manuscript. Thanks are also due to Dr. Charles
Page of the Rutgers University for his critical review and constructive suggestions. This study was
supported in part by a grant (NSC 89-2313-B-002030) from the National Science Council, R.O.C.
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expressions, cockroaches, german, circadian, locomotor, germanica, blattella, rhythms, erg, inconsistencies
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