Extracellular long-term recordings of the isolated accessory medulla,the circadian pacemaker center of the cockroach <Emphasis Type="Italic">Leucophaea maderae</Emphasis>, reveal ultradian and hint circadian rhythms |
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Authors: | Nils-Lasse Schneider Monika Stengl |
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Institution: | (1) Biology, Animal Physiology, Philipps-University of Marburg, Karl von Frisch Str., 35032 Marburg, Germany |
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Abstract: | In the cockroach Leucophaea maderae transplantation studies located the circadian pacemaker center, which controls locomotor activity rhythms, to the accessory
medulla (AMe), ventromedially to the medulla of the brain’s optic lobes. The AMe is densely innervated via GABA- and manyfold
peptide-immunoreactive neurons. They express ultradian action potential oscillations in the gamma frequency range and form
phase-locked assemblies of synchronously spiking cells. Peptide application resulted in transient rises of extracellularly
recorded activity. It remained unknown whether transient rises in spontaneous electrical activity as a possible indication
of peptide release occur in the isolated circadian clock in a rhythmic manner. In extracellular glass electrode recordings
of the isolated AMe in constant darkness, which lasted at least 12 h, the distribution of daytime-dependent changes in activity
independently of the absolute action potential frequency was examined. Rapid, transient changes in activity preferentially
occurred at the mid-subjective night, with a minimum at the middle of the subjective day, hinting the presence of circadian
rhythms in the isolated circadian clock. Additionally, ultradian rhythms in activity change that are multiples of a fundamental
2 h period were observed. We hypothesize that circadian rhythms might originate from coupled ultradian oscillations, possibly
already at the single cell level. |
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Keywords: | Circadian clock Neuropeptides Action potential rhythms Synchronization Oscillations |
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