Biology subjects

Reinhard, N.

Publications and source records attributed to Reinhard, N..

7 recordsLinked to original sources

bioRxiv2026

The neuronal clock network in the polar key species Antarctic krill (Euphausia superba)

Organisms are exposed to predictable daily and seasonal environmental oscillations. Biological clocks enable organisms to anticipate these changes and coordinate physiology and behaviour accordingly. While circadian mechanisms are well studied in terrestrial model organisms, little is known about the neuronal organisation of biological clocks in ecologically important species, especially in the marine environment. Antarctic krill (Euphausia superba) is central to the functioning of the Southern Ocean ecosystem and relies on precise timing to cope with the extreme, high-latitude fluctuations in photoperiod, food availability, and sea-ice cover in its habitat. Despite evidence for circadian and seasonal rhythms in krill behaviour and physiology, the neuronal architecture underlying these timing processes has remained unresolved. In this study, we use in situ hybridisation and antibody staining to characterise the circadian clock in the krill brain. Immunostaining with an antibody against crustacean {beta}-Pigment-dispersing hormone ({beta}-PDH) reveals distinct clusters of PDH-positive neurons in the optic lobes and dorsal central brain, along with an extensive PDH-positive fibre network. We further localise transcripts of the core clock genes cryptochrome-2 (cry2) and period (per) in cell clusters in the optic lobes, which also include the PDH-positive neurons. More specifically, PDH-positive neurons are a subgroup of the cry2 and per-positive cells. Together, these findings provide the first description of the neuronal architecture of the circadian clock in Antarctic krill and establish essential groundwork for future studies on biological timing, environmental adaptation, and the resilience of this key species in a rapidly changing Southern Ocean.

neuroscience↗

bioRxiv2026

THERM-D Uncovers Distinct Neural Mechanisms Separating Morning and Evening Body Temperature Rhythms in Drosophila

Animal body temperature rises throughout the day and peaks in the evening, a pattern conserved across diurnal endotherms and ectotherms. However, the mechanisms driving the robust body temperature rhythms (BTR) remain largely unclear. Here, we developed a machine learning-based platform, temperature homeostasis evaluation of rhythmicity in model Drosophila (THERM-D), enabling continuous, high-throughput analyses of BTR. Using THERM-D, we identified robust BTR patterns reflecting flies morning and evening behaviors and revealed the function of CRYPTOCHROME (CRY)-negative clock neurons. About half of all clock neurons lack CRY, yet their function was unclear. Newly developed Gal4 drivers targeting CRY-negative neurons demonstrated that these neurons control the morning temperature rise without affecting evening BTR. The data suggests that separate clock circuits regulate morning and evening BTR. Thus, THERM-D elucidated the role of CRY-negative clock neurons, which are specialized for BTR regulation and distinct from the circuits controlling sleep-wake cycles.

neuroscience↗

bioRxiv2025

RHODOPSIN 7: An ancient non-retinal photoreceptor for contrast vision, darkness detection, and circadian regulation

1Animals rely on light not only for vision but also to adapt behavior to their environment through non-image-forming pathways. In Drosophila, most rhodopsins mediate retinal image formation, but RHODOPSIN 7 (RH7) is widely expressed in the brain and optic lobe, acting as a non-canonical light sensor reminiscent of mammalian melanopsin. We combined expression mapping, behavioral assays, and phylogenetic comparisons to investigate its function. RH7 detects temporal changes in luminance, guiding rapid behavioral responses, and regulating daily activity patterns. Flies lacking RH7 are less active during the dark phase, while strains with constitutively active RH7 show increased activity. Phylogenetic analyses suggest that RH7 is an ancient rhodopsin present across panarthropods, representing an intermediate between G protein-coupled receptors and specialized rhodopsins, highlighting a key step in the evolution of non-visual light perception. These findings show that RH7 functions as a melanopsin-like sensor, shaping behavior, and illuminating the origins of light detection.

neuroscience↗

bioRxiv2024

Synaptic connectome of a neurosecretory network in the Drosophila brain

Hormones mediate inter-organ signaling which is crucial in orchestrating diverse behaviors and physiological processes including sleep and activity, feeding, growth, metabolism and reproduction. The pars intercerebralis and pars lateralis in insects represent major hubs which contain neurosecretory cells (NSC) that produce various peptide hormones. To obtain insight into how hormonal signaling is regulated, we have characterized the synaptic connectome of NSC in the adult Drosophila brain. Identification of neurons providing inputs to multiple NSC classes implicate diuretic hormone 44-expressing NSC as a major coordinator of physiology and behavior. Surprisingly, despite most NSC having dendrites in the subesophageal zone (primary taste processing center), inputs from peripheral gustatory neurons to NSC are largely indirect. We also deciphered pathways via which diverse olfactory inputs are relayed to NSC. Linear dynamical modeling of signal propagation through the connectome identifies enteric neurons as the strongest influencers of NSC activity compared to other sensory modalities. Further, our analyses revealed substantial inputs from brain descending neurons to NSC, suggesting that descending neurons regulate both endocrine and motor output to synchronize physiological changes with appropriate behaviors. In contrast to NSC inputs, synaptic output from NSC is sparse and mostly mediated by corazonin NSC. We show that both corazonin-expressing NSC and their downstream synaptic partner DNg27 influence egg-laying. We additionally explore putative paracrine interconnectivity between NSC classes and peptide hormone pathways from NSC to peripheral tissues by analyzing single-cell transcriptomic datasets. Our comprehensive characterization of the Drosophila neurosecretory network connectome provides a platform to understand complex hormonal networks and how they orchestrate animal behaviors and physiology.

neuroscience↗

bioRxiv2023

Synaptic and peptidergic connectomes of the Drosophila circadian clock

The circadian clock and its output pathways play a pivotal role in optimizing daily processes. To obtain novel insights into how diverse rhythmic physiology and behaviors are orchestrated, we have generated the first comprehensive connectivity map of an animal circadian clock using the Drosophila FlyWire brain connectome. Intriguingly, we identified additional dorsal clock neurons, thus showing that the Drosophila circadian network contains [~]240 instead of 150 neurons. We also revealed extensive contralateral synaptic connectivity within the network and discovered novel indirect light input pathways to the clock neurons. Interestingly, we observed sparse monosynaptic connectivity between clock neurons and down-stream higher-order brain centers and neurosecretory cells known to regulate behavior and physiology. Therefore, we integrated single-cell transcriptomics and receptor mapping to decipher putative paracrine peptidergic signaling by clock neurons. Our analyses identified additional novel neuropeptides expressed in clock neurons and suggest that peptidergic signaling significantly enriches interconnectivity within the clock network.

neuroscience↗

bioRxiv2023

PDF neuropeptide signals independently of Bruchpilot-labelled active zones in daily remodelled terminals of Drosophila clock neurons

The small ventrolateral neurons (sLNvs) are key components of the central clock in the Drosophila brain. They signal via the neuropeptide Pigment-dispersing factor (PDF) to align the molecular clockwork of different central clock neurons and to modulate downstream circuits. The dorsal terminals of the sLNvs undergo daily morphological changes that have been shown to affect presynaptic sites organised by the active zone protein Bruchpilot (BRP), a homolog of mammalian ELKS proteins. Although the circadian plasticity of the sLNv terminals is well established, whether and how it is related to the rhythmic release of PDF remains ill-defined. Here, we combined expansion microscopy with labelling of active zones by endogenously tagged BRP to examine the spatial correlation between PDF-containing dense-core vesicles and BRP-labelled active zones. We found that the number of BRP-labelled punctae in the sLNv terminals remained stable while their density changed during circadian plasticity. The relative distance between BRP- and PDF-labelled punctae was increased in the morning, around the reported time of PDF release. Spontaneous dense-core vesicle release profiles of the sLNvs in a publicly available ssTEM dataset (FAFB) consistently lacked spatial correlation to BRP-organised active zones. RNAi-mediated downregulation of brp and other active zone proteins expressed by the sLNvs did not affect PDF-dependent locomotor rhythmicity. In contrast, down-regulation of genes of the canonical vesicle release machinery, the dense-core vesicle-related protein CADPS, as well as PDF impaired locomotor rhythmicity. Taken together, our study suggests that PDF release from the sLNvs is independent of BRP-organised active zones which seem not to be circadianly destroyed and re-established.

neuroscience↗

bioRxiv2020

Dopamine signaling in wake promoting clock neurons is not required for the normal regulation of sleep in Drosophila

Dopamine is a wakefulness promoting neuromodulator in mammals and fruit flies. In D. melanogaster, the network of clock neurons that drives sleep/activity cycles comprises both wake and sleep promoting cell types, indicating that the sleep-wake circuitry is intimately linked to the circadian clock. The large and small ventrolateral neurons (l-LNvs and s-LNvs) have been identified as wake-promoting neurons within the clock neuron network. The l-LNvs are innervated by dopaminergic neurons, and earlier work proposed that dopamine signaling raises cAMP levels in the l-LNvs and thus induces excitatory electrical activity (action potential firing), which results in wakefulness and inhibits sleep. Here, we test this hypothesis by combining cAMP imaging and patch-clamp recordings in isolated brains. We find that dopamine application indeed increases cAMP levels and depolarizes the l-LNvs, but surprisingly, it does not result in increased firing rates. Down-regulation of the excitatory dopamine receptor, Dop1R1 in the l-and s-LNvs, but not of Dop1R2, abolished the depolarization of l-LNvs in response to dopamine. This indicates that dopamine signals via Dop1R1 to the l-LNvs. Down-regulation of Dop1R1 or Dop1R2 receptors in the l- and s-LNvs does not affect sleep. Unexpectedly, we find a moderate decrease of daytime sleep with down-regulation of Dop1R1 and of nighttime sleep with down-regulation of Dop1R2. Since the l-LNvs do not utilize Dop1R2 receptors and the s-LNvs respond also to dopamine, we conclude that the s-LNvs are responsible for the observed decrease in nighttime sleep. In summary, dopamine signaling in the wake-promoting LNvs is not required for daytime arousal, but likely promotes nighttime sleep via the s-LNvs. Significance statementIn insect and mammalian brains, sleep promoting networks are intimately linked to the circadian clock, and the mechanisms underlying sleep and circadian timekeeping are evolutionarily ancient and highly conserved. Here we show that dopamine, one important sleep modulator in flies and mammals, plays surprisingly complex roles in the regulation of sleep by clock containing neurons. Dopamine inhibits neurons in a central brain sleep center to promote sleep and excites wake-promoting circadian clock neurons. It is therefore predicted to promote wakefulness through both of these networks. Nevertheless, our results reveal that dopamine acting on wake promoting clock neurons promotes sleep, revealing a previously unappreciated complexity in the dopaminergic control of sleep.

neuroscience↗