Neuroanatomical details of the lateral neurons of Drosophila melanogaster support their functional role in the circadian system

Abstract

Drosophila melanogaster is a long‐standing model organism in the circadian clock research. A major advantage is the relative small number of about 150 neurons, which built the circadian clock in Drosophila. In our recent work, we focused on the neuroanatomical properties of the lateral neurons of the clock network. By applying the multicolor‐labeling technique Flybow we were able to identify the anatomical similarity of the previously described E2 subunit of the evening oscillator of the clock, which is built by the 5th small ventrolateral neuron (5th s‐LNv) and one ITP positive dorsolateral neuron (LNd). These two clock neurons share the same spatial and functional properties. We found both neurons innervating the same brain areas with similar pre‐ and postsynaptic sites in the brain. Here the anatomical findings support their shared function as a main evening oscillator in the clock network like also found in previous studies. A second quite surprising finding addresses the large lateral ventral PDF‐neurons (l‐LNvs). We could show that the four hardly distinguishable l‐LNvs consist of two subgroups with different innervation patterns. While three of the neurons reflect the well‐known branching pattern reproduced by PDF immunohistochemistry, one neuron per brain hemisphere has a distinguished innervation profile and is restricted only to the proximal part of the medulla‐surface. We named this neuron “extra” l‐LNv (l‐LNvx). We suggest the anatomical findings reflect different functional properties of the two l‐LNv subgroups.

Shaw and Shal voltage‐gated potassium channels mediate circadian changes in Drosophila clock neuron excitability

“…Neurons were visualized by RFP fluorescence using a 555 nm LED light source on an upright Zeiss microscope (Examiner.Z1, Carl Zeiss Microscopy GmbH, Jena, Germany). LNv neurons were identified on the basis of their fluorescence, position and size as the l-LNvs have a cell soma diameter of approximately 10-11 µm and the s-LNvs have a diameter of approximately 7 µm (Schubert et al 2018). Whole-cell recordings were performed using glass electrodes with 8-18 M resistance filled with intracellular solution (in mM: 102 potassium gluconate, 17 NaCl, 0.94 EGTA, 8.5 HEPES, 0.085 CaCl 2 , 1.7 MgCl 2 or 4 Mg·ATP and 0.5 NaGTP, pH 7.2) and an Axon MultiClamp 700B amplifier, digitized with an Axon DigiData 1440A (sampling rate: 20 kHz; filter: Bessel 10 kHz) and recorded using pClamp 10 (Molecular Devices, Sunnyvale, CA, USA).…”

Light-mediated circuit switching in the Drosophila neuronal clock network

“…These neurons broadly innervate the dorsal part of the brain where they receive glutamatergic input (Guo et al, 2016). They also send fibers into the area of the accessory medulla of the fly brain, the location of the PDF cell bodies and an important pacemaker center in many other insect species (Helfrich-Förster et al, 2007; Schubert et al, 2018).…”

A circadian output circuit controls sleep-wake arousal threshold in Drosophila

“…Previous studies have reported that these PI-projecting CRY-negative DN1s connect to DH44+ PI neurons to regulate locomotor activity (Cavanaugh et al, 2014;Kunst et al, 2014). As wake-promoting E cells also direct target the PI region ( Figure 1b) (Schubert et al, 2018), the PI neurons may receive wake signals from two different circadian sources to promote different activities, e.g., mating, feeding, foraging etc.…”