|
| |
|
|
|
|
||||
| Home Help Feedback Subscriptions Archive Search Table of Contents | ||||
First published online June 29, 2006
Journal of Experimental Biology 209, 2794-2803 (2006)
Published by The Company of Biologists 2006
doi: 10.1242/jeb.02307
Evidence for a role of orcokinin-related peptides in the circadian clock controlling locomotor activity of the cockroach Leucophaea maderae
Fachbereich Biologie, Tierphysiologie, Philipps Universität Marburg, D-35032 Marburg, Germany
* Author for correspondence (e-mail: homberg{at}staff.uni-marburg.de)
Accepted 3 May 2006
 |
Summary |
|---|
 TOP Summary IntroductionMaterials and methodsResultsDiscussionReferences |
|---|
Key words: orcokinin, insect brain, circadian rhythms, accessory medulla, phase-response curve, light entrainment, cockroach, Leucophaea maderae
|
Introduction |
|---|
|
TOPSummaryIntroductionMaterials and methodsResultsDiscussionReferences |
|---|
; Bungart et al.,
1995; Huybrechts et al.,
2003; Pascual et al.,
2004; Hofer et al.,
2005). All orcokinins are highly conserved between species and, in
the investigated crustaceans, occur in multiple isoforms within a given
species (Bungart et al., 1995;
Yasuda-Kamatani and Yasuda,
2000; Skiebe et al.,
2002; Huybrechts et al.,
2003; Fu et al.,
2005). The insect orcokinins identified to date, the
tetradecapeptide Scg-OK1 from the locust Schistocerca gregaria and
the dodecapeptide Blatella-OKL from the cockroach Blatella germanica,
are closely related to crustacean orcokinins by identical N-terminal
NFDEIDRSGF-sequence with crustacean Asn13-, Val13- and
Ala13-orcokinins. Immunocytochemistry with an antiserum against
Asn13-orcokinin revealed widespread distribution of orcokinins in
the brain of polyneopteran insects, such as the cockroach Leucophaea
maderae and the locust Schistocerca gregaria, but complete lack
of immunostaining in the brain of endopterygote insects
(Hofer et al., 2005). Labeling
of brain interneurons and processes in the neurohemal retrocerebral complex in
the cockroach and locust suggests that orcokinin-related peptides function
both as hormones and as neuromodulators in these insects, as described for
crustaceans.
In the present study, we have analyzed the role of orcokinin-related
peptides in the circadian system of the cockroach Leucophaea maderae.
As in the fruitfly Drosophila melanogaster, neurons with
arborizations in the accessory medulla (AMe), a small neuropil at the anterior
base of the medulla, constitute the master circadian clock in the brain of the
cockroach (Reischig and Stengl,
2003a) (reviewed by Homberg et
al., 2003;
Helfrich-Förster, 2005).
The cockroach AMe consists of a core of dense nodular neuropil, embedded in
and surrounded by coarse neuropil (Petri
et al., 1995; Reischig and
Stengl, 1996; Reischig and
Stengl, 2003b). Six groups of somata near the AMe send neurites
into the AMe neuropil (Reischig and
Stengl, 2003b). Neurons of the distal tract connect the medulla to
the AMe (Reischig and Stengl,
1996; Reischig and Stengl,
2003b; Petri et al.,
2002) and are candidates for mediating light entrainment of the
clock through photoreceptors of the compound eye
(Roberts, 1965;
Nishiitsutsuji-Uwo and Pittendrigh,
1968). Neural connections between both brain hemispheres of L.
maderae serve for bilateral coupling of the clocks and, in addition, for
light entrainment of the clock through the contralateral compound eye
(Page, 1978;
Page, 1981;
Page, 1983a). Commissural
neurons between both AMae, which might mediate these functions, have been
identified (Loesel and Homberg,
2001; Reischig and Stengl,
2002; Reischig et al.,
2004). Immunocytochemical studies and injections of neuroactive
substances suggest that several neuropeptides and 
-aminobutyric acid
(GABA) play roles as neuromediators in the circadian system of the cockroach
(Petri et al., 1995;
Petri et al., 2002;
Petri and Stengl, 1997;
Schneider and Stengl, 2005).
Neurons immunoreactive for ß-pigment-dispersing factor (PDF) may serve as
pacemakers of the clock; some of these neurons with projections to the lamina
and selected parts of the midbrain might also serve as outputs of the clock
(Reischig et al., 2004), while
others with fibers in the anterior and posterior optic commissure transmit
coupling information into the contralateral clock
(Petri and Stengl, 1997;
Reischig et al., 2004).
GABA-immunoreactive neurons of the distal tract and allatotropin-related
peptides in local interneurons of the AMe are part of the ipsilateral light
entrainment pathway, as suggested by injection experiments
(Petri et al., 2002). Finally,
both GABA and PDF contribute to synchronize electrical activity among clusters
of neurons in the circadian clock of the cockroach
(Schneider and Stengl,
2005).
Orcokinin-related peptides were detected immunocytochemically in the AMe of
the cockroach (Hofer et al.,
2005; Hofer and Homberg,
2006). Detailed mapping showed that staining was present in about
30 neurons of the AMe (Hofer and Homberg,
2006). Staining in AMe neurons with axonal fibers in the posterior
optic commissure was particularly prominent, suggesting that orcokinin-ir
neurons participate in coupling of the bilateral clocks. The present study
shows that four pairs of orcokinin-ir neurons connect both AMae.
Microinjections of Asn13-orcokinin into the vicinity of the AMe
result in phase-dependent phase shifts in circadian wheel-running activity
resembling the phase-shifting effects of light. These experiments are the
first to demonstrate a physiological role of orcokinins in insects and suggest
that these peptide(s) plays a role in light entrainment of the clock
via the contralateral compound eye.
|
Materials and methods |
|---|
|
TOPSummaryIntroductionMaterials and methodsResultsDiscussionReferences |
|---|
Dextran injections
Animals (N=22) were anesthetized with CO2 and fixed in
a mounting device. A small window was cut into the head capsule above the left
optic lobe to expose the brain. An amount of 1-3 nl Texas Red-dextran solution
(TRed-D, dextran conjugated with Texas Red, 3000 kDa, lysine fixable,
Molecular Probes Inc., USA; 0.1 mg ml-1 in water) was
pressure-injected with a microinjector (Microinjector 5242, Eppendorf,
Germany) under stereomicroscopic control into one AMe with a glass capillary
(Clark, Pangbourne Reading, England). The capillary was pulled to a pipette as
used for patch clamp experiments, with a tip diameter of 1-3 µm. After the
injection, the head capsule was closed with wax to allow intracellular
transport of the dye in those insects that survived overnight.
Immunocytochemistry
The next day the injected brains of the cockroaches were removed and fixed
for 4 h or overnight in 4% paraformaldehyde/7.5% saturated picric acid in
sodium phosphate buffer (0.1 mol l-1, pH 7.4) at room temperature.
The brains were embedded in gelatine/albumin (4.8% gelatine and 12% ovalbumin
in demineralized water) and postfixed in 8% formalin in sodium phosphate
buffer (0.1 mol l-1, pH 7.4). The brains were sectioned in the
frontal plane at 40 µm thickness using a vibrating blade microtome (Leica,
Nussloch, Germany). The brain sections were washed in Tris-buffered saline
(TBS; 0.1 mol l-1 Tris-HCl/0.3 mol l-1 NaCl, pH 7.4)
containing 0.1% Triton X-100 (TrX). They were preincubated in TBS with 0.5%
TrX and 5% normal goat serum (NGS; Dako, Hamburg, Germany). Primary antiserum,
anti-Asn13-orcokinin (provided by Dr H. Dircksen, Department of
Zoology, Stockholm), was diluted at 1:4000 in TBS containing 0.5% TrX and 1%
NGS and was applied to the sections for 18-20 h at room temperature. The
sections were washed in TBS containing 0.1% TrX and incubated with
Cy2-conjugated goat anti-rabbit antiserum (GAR; Dianova Hamburg, Germany,
diluted 1:300) in TBS containing 0.5% TrX and 1% NGS for 1 h. Afterwards, the
sections were thoroughly washed, and mounted on chromalum/gelatine coated
microscope slides.
Specificity controls
The anti-Asn13-orcokinin antiserum has been characterized
(Bungart et al., 1994) by
testing HPLC-fractions of different astacidean crustaceans with an
enzyme-linked immunosorbent assay (ELISA). On cockroach brain sections,
specificity of the antiserum was determined by liquid-phase preadsorption of
the diluted primary antiserum with various concentrations (10-4 mol
l-1 up to 10-11 mol l-1) of
Asn13-orcokinin [NFDEIDRSGFGFN-OH
(Stangier et al., 1992);
Bachem, Heidelberg, Germany], before adding the combined solution to the
preparation. Immunostaining was abolished after preadsorption with 1 nmol
l-1 Asn13-orcokinin for 18-20 h at room temperature.
Evaluation and visualization
Microscopic images were captured with a Zeiss microscope equipped with a
2-megapixel digital camera (Polaroid, Cambridge, MA, USA). A Leica TCS SP2
confocal laser scan microscope equipped with a spectrophotometric emission
light detection system was used to evaluate the double-staining experiments.
All scans were performed using a Leica HPX PL apochromate 40x/1.25 oil
immersion objective. To exclude crosstalk artifacts, the specimens were
scanned sequentially, and the detection ranges were separated as far as
possible. Cy2 fluorescence was excited with the 488 nm line of an argon laser
and detected between 505 and 525 nm. Texas Red fluorescence was excited with
the 543 nm line of a helium/neon laser and detected between 585 and 625
nm.
Operation and orcokinin injection in behavioral experiments
All manipulations were performed in dim red light using a microinjector
(see above). The experimental animals were removed at different circadian
times from their running wheels and mounted in metal tubes. The animals were
anesthetized with CO2. A small window was cut in the head capsule,
and one optic lobe was injected with 2 nl of Asn13-orcokinin
solution or saline in the vicinity of the AMe, following the procedure
described above for dextran injections. After the injection, the excised piece
of cuticle was waxed back and the animal was returned to the running wheel.
The time of injections did not take more than 15 min. The injection volume
(150 fmol in 2 nl saline with blue food dye [FD+C blue No. 1; McCormick,
Baltimore, MD, USA]) was controlled before and after injection with test
injections in mineral oil. The concentration of 10-4 mol
l-1 was chosen because similar doses had been effective in previous
peptide injection experiments (Petri and
Stengl, 1997; Petri et al.,
2002). Concentrations of 10-8 mol l-1 and
10-12 mol l-1 orcokinin were tested at circadian time
(CT) 13-15 of the circadian cycle, corresponding to the peak of the
phase-response curve, to investigate dose-dependency of the response. Control
injections consisted of 10% blue food dye in saline without orcokinin.
Behavioral assays and data analysis
Circadian behavior was analyzed from cockroaches kept in constant darkness
(DD) and constant temperature (28°C) and humidity (60%). Locomotor
activity was recorded with running wheels
(Wiedenmann, 1977) equipped
with a magnetic reed switch. One revolution of the running wheel resulted in
one impulse. Impulses were continuously counted by a computer over 1 min
intervals and condensed and processed by a custom-designed PC-compatible
software (developed by H. Fink, University of Konstanz). The data were plotted
in double plot activity histograms. The free-running period 
and the
induced phase shifts were estimated by converting the raw data into ASCII
format. They were then merged into 30 min intervals and analyzed with Chrono
II software (provided by Till Roenneberg)
(Roenneberg and Morse, 1993)
on a Macintosh computer. The 
2-periodograms were calculated
with Tempus 1.6 (Reischig,
2003), an add-in for Microsoft Excel, on an IBM-compatible PC.
Data were evaluated from 110 of the 157 animals used. The remaining 47
cockroaches died after the operation. The free-running periods before and
after injection were calculated by linear regression through daily ctivity
onset. Changesa in
(
after=-before) were calculated,
with periods estimated by regression through activity onsets and by
2-periodogram analysis
(Enright, 1965;
Sokolove and Bushell, 1978).
Phase shifts were determined as time differences between the regression lines
before and after injection extrapolated to the day after treatment. Phase
delays were plotted as negative values and phase advances as positive values.
Time on the x-axis of the resulting phase-response curve is shown as
CT, with CT 12:00=activity onset= beginning of the subjective night. Daily
activity onsets were determined by using Chrono II
(Roenneberg and Morse,
1993).
The behavioral data were merged into 2 h time intervals and the means and standard deviations (s.d.) were calculated for each bin. Changes of phases and periods in a given time interval were considered to be significantly different from zero, if the calculated 95% confidence interval of phase shifts and periods in a respective time interval did not contain the value zero. The differences of phase and period changes were tested for each pair of orcokinin and control injections with a two-tailed Student's t-test. In addition, phase shifts caused by either orcokinin or control injections were tested separately aginst all other respective values applying ANOVA with Tukey's post-hoc test. Significant differences in all cases were assumed at P<0.05. The statistical analyses were performed with SPSS 11.0 (Superior Performing Software Systems; SPSS Inc.) and Excel XP (Microsoft). Smoothed phase-response curves were produced with Excel.
|
Results |
|---|
|
TOPSummaryIntroductionMaterials and methodsResultsDiscussionReferences |
|---|
|
|
|
Effects of Asn13-orcokinin injections on circadian locomotor activity rhythms
To investigate whether orcokinin plays a role as an input signal to the
circadian clock, we examined whether the peptide influences circadian
locomotor activity of the cockroach. Asn13-orcokinin was injected
into the vicinity of one AMe at different circadian times, and locomotor
activities of the free-running cockroaches were recorded before and after the
injections (Fig. 4). Control
injections with carrier solution alone (blue food dye in saline) did not cause
significant phase shifts in circadian locomotor rhythm, except for a small but
significant phase delay from CT21-23 (Table
1, Fig. 5B).
Injections of orcokinin resulted in large and significant phase-dependent
phase shifts in circadian activity at several circadian times. Maximal phase
delays (-3.8 hct) occurred when orcokinin was injected at CT13, and
maximal phase advances (2.2 hct) were observed at CT18
(Fig. 5A). As judged from the
95% confidence intervals, significant orcokinin-dependent phase delays
occurred from CT7-15 and significant phase advances from CT17-19
(Table 1,
Fig. 5). Phase shifts during
the rest of the cycle were not significantly different from zero.
Orcokinin-induced phase shifts from CT7-15 and from CT17-19 were also
significantly different from phase shifts induced by control injections.
Finally, orcokinin-induced phase shifts at CT21-23 were significantly
different from control injections, but not from zero
(Table 1,
Fig. 5C). Orcokinin-induced
phase shifts at CT13-15 were not significantly different from
orcokinin-induced phase shifts from CT7-13, but from all other
orcokinin-induced phase shifts. Similarly, orcokinin-induced phase shifts
between CT17 and CT19 were not significantly different from orcokinin-induced
phase shifts at CT19-7 and CT15-17.
|
|
|
Dose dependency of orcokinin-induced phase shifts
The orcokinin-dependent phase shifts at CT13-15 were positively correlated
with the dose of orcokinin-injections (Fig.
6). The phase delays decreased with decreasing amounts of injected
peptide. Significant phase delays were caused by injection of 150 fmol
[-2.92±0.81 h, mean ± s.d., CI=(-1.84, -4.00), N=5] and
1.5x10-2 fmol [-1.70±0.99 h, mean ± s.d.,
CI=(-2.73, -0.66), N=6] orcokinin. Phase shifts induced by injections
of 1.5x10-6 fmol orcokinin [-0.32±0.38 h, mean
± s.d., CI=(-0.64, 0.00), N=8] were neither significantly
different from zero nor from control injections
(Fig. 6).
|
|
Discussion |
|---|
|
TOPSummaryIntroductionMaterials and methodsResultsDiscussionReferences |
|---|
).
These data suggest an involvement of orcokinin-related peptides in circuits
relaying photic information to the circadian pacemaker. In a previous study,
we showed that up to 30 neurons distributed in five cell groups of the AMe of
L. maderae are immunoreactive with an antiserum against
Asn13-orcokinin (Hofer and
Homberg, 2006). Dextran injections into one AMe combined with
orcokinin immunostaining revealed that four pairs of orcokinin-ir AMe neurons
provide direct connections between the bilateral pacemakers. The additional
arborizations of some of these neurons in the medulla proper suggest that
these neurons may be responsible for the light-like phase shifts seen in the
peptide injection experiments (see below).
Orcokinin-ir neurons form a direct coupling pathway between both AMae
For a well-synchronized circadian rhythm in behavior, the bilaterally
distributed pacemakers in the insect brain have to be mutually coupled. In
crickets, bilateral coupling of the clocks is relatively weak, but in the
cockroach L. maderae, bilateral coupling is strong
(Page et al., 1977;
Wiedenmann and Loher, 1984;
Ushirogawa et al., 1997), and
is assumed to be mediated by direct neuronal connections between the AMae in
the right and left brain hemisphere (Page,
1983a; Page,
1983b). Tracing studies showed that anterior neurons with cell
bodies in two clusters termed MC I (4 cells) and MC II (35 cells) near the AMe
connect both AMae directly (Reischig et
al., 2004). The MC I neurons correspond to four ventral neurons
(VNe), and the MC II cells are identical with the ventromedian neurons (VMNe)
of Reischig and Stengl (Reischig and
Stengl, 2003b). Three of the four VNe that connect both AMae
directly are PDF-ir (Reischig et al.,
2004). The neurons project via the anterior (two neurons)
and posterior (one neuron) optic commissures, innervate the internodular and
shell neuropils of the AMe, and send a fan of fibers along the distal surface
of the medulla toward the first optic chiasm and lamina. Neurons of this
morphological type were found to be unresponsive to light stimuli in
intracellular recordings (Loesel and
Homberg, 2001). Together with the non-photic phase-response curve
obtained by PDF injection, Petri and Stengl
(Petri and Stengl, 2002) and
Reischig et al. (Reischig et al.,
2004), therefore concluded that the three PDF-ir VNe transmit
phase information to the contralateral pacemaker. We show here that one
contralaterally projecting VNe is orcokinin-ir. Since colocalization of PDF
and orcokinin occurs neither in the anterior nor in the posterior optic
commissure (Hofer and Homberg,
2006), this neuron has to be the fourth non-PDF-ir VNe with
projections to the contralateral AMe.
Page (Page, 1978;
Page, 1983a;
Page, 1983b) proposed that the
bilateral optic lobe pacemakers of L. maderae not only exchange phase
information, but also receive entraining light signals from the contralateral
eye. The pathway for contralateral light entrainment is most likely provided
by the second group of commissural neurons, the VMNes. Neurons of this group
have contralaterally projecting fibers in the posterior optic tract; they
invade the internodular and shell neuropil of the AMe and, in contrast to
VNes, have tangential arborizations in a median layer of the medulla
(Reischig et al., 2004).
Interestingly, neurons of this type are highly sensitive to light stimuli
(Loesel and Homberg, 2001).
Ensemble reconstructions of orcokinin-ir VMNes
(Hofer and Homberg, 2006) and,
in this study, tracer injections combined with immunocytochemistry, clearly
show that three of the 35 contralaterally projecting VMNes are orcokinin-ir.
We, therefore, suggest that these neurons transmit light information to the
contralateral AMe, and that release of an orcokinin-like substance is the
output signal of these neurons. The neurotransmitter of the remaining 32 VMNes
is not known.
The colabeling of dextran-injected and orcokinin-immunostained fibers in
the posterior but not in the anterior optic commissure suggests that the
orcokinin-immunolabeled VNe, like the VMNes, traverse the brain midline
via the posterior optic commissure. Since dextran transport through
the anterior optic commissure was often only of low intensity (see also
Reischig et al., 2004),
however, we cannot completely exclude the possibility, that the orcokinin-ir
VNe projects via the anterior optic commissure but was not detected
in the dextran injections.
Orcokinin injections into the AMe
Microinjections of orcokinin into the vicinity of the AMe resulted in phase
delays and phase advances of the circadian wheel running activity. The effects
of peptide injections were dose dependent and were significantly different
from control injections. The phase-response curve observed after orcokinin
injections is similar to the biphasic phase-response curve after light-pulses
(Page and Barrett, 1989)
(Fig. 7), as well as to
phase-response curves after GABA- and allatotropin injections
(Petri et al., 2002).
|
Our recent immunocytochemical study revealed widespread occurrence of
orcokinin-related peptides in different cell types, in addition to the
commissural neurons, in ventroposterior neurons (VPNe), in distal
frontoventral neurons (DFVNe), in ventral neurons (VNe), and in median neurons
(MNe) of the AMe (Hofer and Homberg,
2006) [for nomenclature see
(Reischig and Stengl, 2003b)].
Therefore, we suggest that orcokinin serves a multitude of functions in the
circadian system, possibly including a role in light entrainment, output
pathways and internal synchronization.
Interestingly, the maximal phase advance observed after orcokinin injection
was not as high as that observed for GABA- and allatotropin injections.
Furthermore, the peaks of the orcokinin-induced phase-response curve were
broader (with respect to the range of significant phase shifts) than the peak
phase shifts after light pulses, GABA, allatotropin and PDF injections
(Page and Barrett, 1989;
Petri and Stengl, 1997;
Petri et al., 2002). These
differences might be explained as follows. The AMae appear to be connected by
two types of orcokinin-ir neurons, which are part of functionally different
circadian coupling pathways: a pathway transmitting phase information (one
orcokinin-ir VNe) and a pathway transmitting light information (three
orcokinin-ir VMNe). Phase information appears to be carried by PDF-ir VNe, and
if the orcokinin-ir VNe plays a similar role, a mixture of light-like (three
neurons) and non-light-like (one neuron) phase responses should occur after
orcokinin injections, which would then lead to smaller and broader peaks in
the phase-response curve compared to those observed after light pulses, GABA
or allatotropin injections (Page and
Barrett, 1989; Petri et al.,
2002). This assumption is underlined by the fact that orcokinin
immunoreactivity occurs in five of the six morphologically distinguishable and
obviously also functionally divergent neuron groups associated with the AMe.
Nevertheless, after injection of orcokinin, the biphasic light-like
phase-response effects appear to dominate over an additionally expected
overlapping non-photic phase-response curve.
The role of orcokinin in the circadian pacemaker of the cockroach L. maderae
Combining the results of this work with previous immunocytochemical studies
(Hofer et al., 2005;
Hofer and Homberg, 2006), we
propose that orcokinin has the following functions in individual AMe neurons:
(1) Orcokinin-ir neurons (VMNe, VPNe and MNe) might play a role in the light
entrainment pathway; (2) orcokinin-ir neurons (VNe) might form output pathways
to different effectors of the clock; (3) one pair of orcokinin-ir neurons
(VNe) may transmit coupling information to the contralateral AMe. In summary,
our work supports earlier studies suggesting that orcokinin plays multiple
roles in the cockroach circadian system
(Hofer et al., 2005;
Hofer and Homberg, 2006), and
presents the first direct evidence for a physiological function of this
peptide in insects.
-aminobutyric acid
|
Acknowledgments |
|---|
|
References |
|---|
|
TOPSummaryIntroductionMaterials and methodsResultsDiscussionReferences |
|---|
Bungart, D., Dircksen, H. and Keller, R. (1994). Quantitative determination and distribution of the myotropic neuropeptide orcokinin in the nervous system of astacidean crustaceans. Peptides 15,393 -400.[CrossRef][Medline]
Bungart, D., Hilbich, C., Dircksen, H. and Keller, R. (1995). Occurrence of analogues of the myotropic neuropeptide orcokinin in the shore crab, Carcinus maenas: evidence for a novel neuropeptide family. Peptides 16, 67-72.[CrossRef][Medline]
Enright, J. T. (1965). The search for rhythmicity in biological time series. J. Theor. Biol. 8, 426-468.[CrossRef][Medline]
Fu, Q., Kutz, K. K., Schmidt, J. J., Hsu, Y.-W. A., Messinger, D. I., Cain, S. D., De La Iglesia, H. O., Christie, A. E. and Li, L. (2005). Hormone complement of the Cancer productus sinus gland and pericardial organ: an anatomical and mass spectrometric investigation. J. Comp. Neurol. 493,607 -626.[CrossRef][Medline]
Helfrich-Förster, C. (2005). Neurobiology of the fruit fly's cicadian clock. Genes Brain Behav. 4, 65-76.[Medline]
Hofer, S. and Homberg, U. (2006). Orcokinin immunoreactivity in the accessory medulla of the cockroach Leucophaea maderae. Cell Tissue Res. DOI:10.1007/s00441-00609155-y .
Hofer, S., Dircksen, H., Tollbäck, P. and Homberg, U. (2005). Novel insect orcokinins: characterization and neuronal distribution in the brains of selected dicondylian insects. J. Comp. Neurol. 490,57 -71.[CrossRef][Medline]
Homberg, U., Reischig, T. and Stengl, M. (2003). Neural organization of the circadian system of the cockroach Leucophaea maderae. Chronobiol. Int. 20,577 -591.
Huybrechts, J., Nusbaum, M. P., Bosch, L. V., Baggerman, G., De Loof, A. and Schoofs, L. (2003). Neuropeptidomic analysis of the brain and thoracic ganglion from the Jonah crab, Cancer borealis. Biochem. Biophys. Res. Commun. 308,535 -544.
Loesel, R. and Homberg, U. (2001). Anatomy and physiology of neurons with processes in the accessory medulla of the cockroach Leucophaea maderae. J. Comp. Neurol. 439,193 -207.
Nishiitsutsuji-Uwo, J. and Pittendrigh, C. S. (1968). Central nervous system control of circadian rhythmicity in the cockroach. III. The pathway of light signals that entrain the rhythm. Z. Vergl. Physiol. 58,1 -13.[CrossRef]
Page, T. L. (1978). Interactions between bilaterally paired components of the cockroach circadian system. J. Comp. Physiol. A 124,225 -236.[CrossRef]
Page, T. L. (1981). Effects of localized low-temperature pulses on the cockroach circadian pacemaker. Am. J. Physiol. 240,144 -150.
Page, T. L. (1983a). Regeneration of the optic tracts and circadian pacemaker activity in the cockroach Leucophaea maderae. J. Comp. Physiol. A 152,231 -240.
Page, T. L. (1983b). Effects of optic-tract regeneration on internal coupling in the circadian system of the cockroach. J. Comp. Physiol. A 153,353 -363.[CrossRef]
Page, T. L. and Barrett, R. K. (1989). Effects of lights on circadian pacemaker development. II. Responses to light. J. Comp. Physiol. A 165,41 -49.[CrossRef][Medline]
Page, T. L., Caldarola, P. C. and Pittendrigh, C. S.
(1977). Mutual entrainment of bilaterally distributed circadian
pacemakers. Proc. Natl. Acad. Sci. USA
74,1277
-1281.
Pascual, N., Castresana, J., Valero, M.-L., Andreu, D. and Bellés, X. (2004). Orcokinins in insects and other invertebrates. Insect Biochem. Mol. Biol. 34,1141 -1146.[CrossRef][Medline]
Petri, B. and Stengl, M. (1997). Pigment-dispersing hormone shifts the phase of the circadian pacemaker of the cockroach Leucophaea maderae. J. Neurosci. 17,4087 -4093.
Petri, B., Stengl, M., Würden, S. and Homberg, U. (1995). Immunocytochemical characterization of the accessory medulla in the cockroach Leucophaea maderae. Cell Tissue Res. 282,3 -19.
Petri, B., Homberg, U., Loesel, R. and Stengl, M. (2002). Evidence for a role of GABA and Mas-allatotropin in photic entrainment of the circadian clock of the cockroach Leucophaea maderae. J. Exp. Biol. 205,1459 -1469.
Reischig, T. (2003). Identification and characterisation of the circadian pacemaker of the cockroach Leucophaea maderae. PhD thesis, University of Marburg, Germany.
Reischig, T. and Stengl, M. (1996). Morphology and pigment-dispersing hormone immunocytochemistry of the accessory medulla, the presumptive circadian pacemaker of the cockroach Leucophaea maderae: a light- and electron-microscopic study. Cell Tissue Res. 285,305 -319.[CrossRef]
Reischig, T. and Stengl, M. (2002). Optic lobe commissures in a three-dimensional brain model of the cockroach Leucophaea maderae: a search for the circadian coupling pathways. J. Comp. Neurol. 443,388 -400.[Medline]
Reischig, T. and Stengl, M. (2003a). Ectopic
transplantation of the accessory medulla restores circadian locomotor rhythms
in arrhythmic cockroaches (Leucophaea maderae). J. Exp.
Biol. 206,1877
-1886.
Reischig, T. and Stengl, M. (2003b). Ultrastructure of pigment-dispersing hormone-immunoreactive neurons in a three-dimensional model of the accessory medulla of the cockroach (Leucophaea maderae). Cell Tissue Res. 314,421 -435.[CrossRef][Medline]
Reischig, T., Petri, B. and Stengl, M. (2004). Pigment-dispersing hormone (PDH)-immunoreactive neurons form a direct coupling pathway between the bilaterally symmetric circadian pacemakers of the cockroach Leucophaea maderae. Cell Tissue Res. 318,553 -564.[CrossRef]
Roberts, S. K. (1965). Photoreception and
entrainment of cockroach activity rhythms. Science
148,958
-959.
Roenneberg, T. and Morse, D. (1993). Two circadian oscillators in one cell. Nature 362,362 -364.[CrossRef]
Schneider, N.-L. and Stengl, M. (2005). Pigment-dispersing factor and GABA synchronize cells of the isolated circadian clock of the cockroach Leucophaea maderae. J. Neurosci. 25,5138 -5147.
Skiebe, P., Dreger, M., Meseke, M., Evers, J. F. and Hucho, F. (2002). Identification of orcokinins in single neurons in the stomatogastric nervous system of the crayfish, Cherax destructor. J. Comp. Neurol. 444,245 -259.
Sokolove, P. G. and Bushell, W. N. (1978). The chi square periodogram: its utility for analysis of circadian rhythms. J. Theor. Biol. 72,131 -160.[CrossRef][Medline]
Stangier, J., Hilbich, C., Burdzik, S. and Keller, R. (1992). Orcokinin: a novel myotropic peptide from the nervous system of the crayfish, Orconectes limosus. Peptides 13,859 -864.
Ushirogawa, H., Abe, Y. and Tomioka, K. (1997). Circadian locomotor rhythms in the cricket, Gryllodes sigillatus. II. Interactions between bilaterally paired circadian pacemakers. Zool. Sci. 14,729 -736.[Medline]
Wiedenmann, G. (1977). Two activity peaks in the circadian rhythm of the cockroach Leucophaea maderae. J. Interdiscipl. Cycle Res. 8,378 -383.
Wiedenmann, G. and Loher, W. (1984). Circadian control of singing in crickets: two different pacemakers for early-evening and before-dawn activity. J. Insect Physiol. 30,145 -151.[CrossRef]
Yasuda-Kamatani, Y. and Yasuda, A. (2000). Identification of orcokinin gene-related peptides in the brain of the crayfish Procambarus clarkii by the combination of MALDI-TOF and on-line capillary HPLC/Q-Tof mass spectrometries and molecular cloning. Gen. Comp. Endocrinol. 118,161 -172.[CrossRef][Medline]
| |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
