Journal article
Candidates for the light entrainment pathway to the circadian clock of the Madeira cockroach Rhyparobia maderae

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Schendzielorz, J.; Stengl, M.
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Cell and Tissue Research
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The circadian pacemaker controlling locomotor activity rhythms in the Madeira cockroach is located at the accessory medulla (AMe). The ipsi- and contralateral compound eyes provide light input to the AMe, possibly via the γ-aminobutyric acid (GABA)-immunoreactive (-ir) distal tract, which connects the glomeruli of the AMe to the ipsilateral medulla and lamina. To identify possible light-entrainment pathways, double-label immunocytochemistry was performed employing antibodies against GABA, myoinhibitory peptide (MIP), allatotropin (AT) and orcokinin (ORC). While all antisera tested, except the anti-ORC, prominently stained the glomeruli of the AMe, colocalization with anti-GABA was detected neither in the glomeruli nor in the distal tract. However, one median neuron that colocalized GABA-, AT- and MIP-immunoreactivity appeared to connect all glomeruli of the AMe to the medulla and lamina. Furthermore, one distal-frontoventral local neuron with arborizations in all glomeruli of the AMe colocalized anti-AT- and anti-MIP immunoreactivity. As candidates for contralateral light entrainment pathways, one ventromedian and one ventral neuron colocalized MIP- and ORC immunoreactivity, projecting via posterior and anterior commissures. Both branched in the interglomerular region of the AMe, where arborizations co-labeled with anti-ORC- and anti-MIP antisera. A possible role for MIP in light entrainment is supported also by injections of Rhyparobia maderae-specific MIP-2, which generated an all-advance phase-response curve late at night. Future experiments will challenge our hypothesis that GABA-, MIP- and AT-ir neurons provide ipsilateral light entrainment to all glomeruli, while MIP- and ORC-ir neurons carry contralateral light entrainment to the AMe's interglomerular region, either delaying or advancing AMe neurons light-dependently.


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Last updated on 2019-01-11 at 16:04