Biology subjects

Cheng, R.-K.

Publications and source records attributed to Cheng, R.-K..

9 recordsLinked to original sources

bioRxiv2026

Relaxin-3 neurons of the zebrafish periaqueductal gray mediate behavioral responses evoked by darkness

Ambient illumination influences many aspects of brain function, including responses to threats. One brain region proposed to mediate these effects is the periaqueductal gray (PAG), an evolutionarily conserved midbrain structure that contains multiple subpopulations of peptidergic neurons. Here we ask which cell types in the larval zebrafish PAG respond to changes in ambient illumination. By registering post hoc gene expression to neurons recorded during exposure to sensory stimuli, we show that GABAergic PAG neurons expressing the neuropeptide Relaxin-3 (rln3a+) are persistently activated by darkness, while a neighboring subpopulation of GABAergic PAG neurons expressing penka is not. Zebrafish lacking rln3a show a reduction in locomotion during darkness. We propose that darkness recruits Relaxin-3-releasing PAG neurons to promote vigilance and potentiate defense circuits. These results identify a specific peptidergic population of PAG neurons that are potentially relevant to behavioral state dysregulation associated with excessive darkness.

neuroscience↗

bioRxiv2025

Comparative transcriptomics of lateral hypothalamic cell types reveals conserved growth hormone-tachykinin dynamics in feeding

The lateral hypothalamus (LH) is a highly heterogeneous brain region regulating hunger and motivated behaviors. In zebrafish, the LH shows distinct neural activity across hunger, feeding, and satiety states. However, the functional and evolutionary conservation of relevant neural circuits remain unclear. Using integrative transcriptomics of zebrafish and mouse LH, we identify conserved cellular clusters with shared molecular markers, particularly within GABAergic neurons. We highlight a conserved GABAergic population expressing tachykinin and growth hormone receptors, which is responsive to food cues and modulated by hunger and feeding states. This cluster may mediate acute appetite-enhancing effects of growth hormone. In both species, feeding elevates growth hormone receptor and tachykinin expression and activates these neurons, while human growth hormone increases their activity and food intake in zebrafish. These findings suggest a conserved neural mechanism by which metabolic hormones influence feeding behavior. Our comparative LH atlas highlights the evolutionary biology of appetite regulation and the integration of hormonal and neural signals driving energy homeostasis.

neuroscience↗

bioRxiv2020

The habenula clock regulates response to a stressor

The response of an animal to a sensory stimulus depends on the nature of the stimulus and on predictions mediated by spontaneous activity in neurons. Here, we ask how circadian variation in the prediction of danger, and thus the response to a potential threat, is controlled. We focus on the habenula, a mediator of threat response that functions by regulating neuromodulator release, and use zebrafish as the experimental system. Single cell transcriptomics indicates that multiple clock genes are expressed throughout the habenula, while quantitative in situ hybridization confirms that the clock oscillates. Two-photon calcium imaging indicates a circadian change in spontaneous activity of habenula neurons. To assess the role of this clock, a truncated clocka gene was specifically expressed in the habenula. This partially inhibited the clock, as shown by changes in per3 expression as well as altered day-night variation in dopamine, serotonin and acetylcholine levels. Behaviourally, anxiety-like responses evoked by an alarm pheromone were reduced. Circadian effects of the pheromone were disrupted, such that responses in the day resembled those at night. Behaviours that are regulated by the pineal clock and not triggered by stressors were unaffected. These findings establish that the habenula clock regulates the expectation of danger, thus identifying one mechanism for circadian change in the response to a stressor.

neuroscience↗

bioRxiv2020

Larval zebrafish respond to the alarm pheromone Schreckstoff by immobility and a change in brain state

BackgroundDetection of predator cues changes the brain state in prey species and helps them avoid danger. Dysfunctionality in changing the central state appropriately in stressful situations is proposed to be an underlying cause of multiple psychiatric disorders in humans. MethodsHere, we investigate the dynamics of neural circuits mediating response to a threat, to characterize these states and to identify potential control networks. We use resonant scanning 2-photon microscopy for in vivo brain-wide imaging and custom designed behavioral assays for the study. ResultsWe first show that 5-7 day old zebrafish larvae react to an alarm pheromone (Schreckstoff) with reduced mobility. They subsequently display heightened vigilance, as evidenced by increased dark avoidance. Calcium imaging indicates that exposure to Schreckstoff elicits stimulus-locked activity in olfactory sensory neurons innervating a lateral glomerulus and in telencephalic regions including the putative medial amygdala and entopeduncular nucleus. Sustained activity outlasting the stimulus delivery was detected in regions regulating neuromodulator release, including the lateral habenula, posterior tuberculum, superior raphe, and locus coeruleus. ConclusionWe propose that these latter regions contribute to the network that defines the "threatened" state, while neurons with transient activity serve as the trigger. Our study highlights the utility of the zebrafish larval alarm response system to examine neural circuits during stress dependent brain state transitions and to discover potential therapeutic agents when such transitions are disrupted.

neuroscience↗

bioRxiv2020

BRAWNIN: A sORF-encoded Peptide Essential for Vertebrate Mitochondrial Complex III Assembly

The emergence of small open reading frame (sORF)-encoded peptides (SEPs) is rapidly expanding the known proteome at the lower end of the size distribution1,2. Here, we show that the mitochondria proteome is enriched for proteins smaller than 100 a.a. (defined as SEPs). Using a mitochondrial prediction and validation pipeline for small open-reading-frame (sORF)-encoded peptides (SEPs), we report the discovery of 16 endogenous mitochondrial SEPs (mito-SEPs) associated with oxidative phosphorylation (OXPHOS). Through functional prediction, proteomics, metabolomics and metabolic flux modeling, we demonstrate that BRAWNIN (BR), a 71 amino acid peptide encoded by the C12orf73 gene, is essential for respiratory chain complex III (CIII) assembly. In human cells, BR is induced by the energy-sensing AMPK pathway, and its depletion impairs mitochondrial ATP production. In vivo, BR is enriched in muscle tissues and its maternal zygotic deletion in zebrafish causes complete CIII loss, resulting in severe growth retardation, lactic acidosis and early death. Our findings demonstrate that BR is essential for oxidative phosphorylation across vertebrate species. We propose that mito-SEPs are an untapped resource for essential regulators of oxidative metabolism.

cell biology↗

bioRxiv2019

Identification of GABAergic neurons innervating the zebrafish lateral habenula

Habenula neurons are constantly active. The level of activity affects mood and behaviour, with increased activity in the lateral habenula reflecting exposure to punishment and a switch to passive coping and depression. Here, we identify GABAergic neurons that could reduce activity in the lateral habenula of larval zebrafish. GAD65/67 immunohistochemistry and imaging of gad1b:DsRed transgenic fish suggest the presence of GABAergic terminals in the neuropil and between cell bodies in the lateral habenula. Retrograde tracing with the lipophilic dye DiD suggests that the former derives from the thalamus, while the latter originates from a group of cells in the posterior hypothalamus that are located between the posterior tuberal nucleus and hypothalamic lobes. Two-photon calcium imaging indicates that blue light causes excitation of thalamic GABAergic neurons and terminals in the neuropil, while a subpopulation of lateral habenula neurons show reduced intracellular calcium levels. Whole-cell electrophysiological recording indicates that blue-light reduces membrane potential of lateral habenula neurons. These observations suggest that GABAergic input from the thalamus may mediate inhibition in the zebrafish lateral habenula. Mechanisms governing release of GABA from the neurons in the posterior hypothalamus, which are likely to be in the tuberomammillary nucleus, remain to be defined.

neuroscience↗

bioRxiv2017

Optical inhibition of zebrafish behavior with anion channelrhodopsins

In behavioral analysis, optical electrical silencing provides a way to test neuronal necessity. Two light-gated anion channels, GtACR1 and GtACR2, have recently been shown--in neuronal culture and in Drosophila--to inhibit neurons potently. Here, we test the usefulness of these channels in zebrafish. When the GtACRs were expressed in motor neurons and actuated with blue or green light, fish spontaneous movement was inhibited. In GtACR1-expressing fish, only 3 {micro}W/mm2 of light was sufficient to have an effect; GtACR2, which is poorly trafficked, required stronger illumination. After light offset, GtACR-expressing fish movement increased; this suggested that termination of light-induced neural inhibition may lead to depolarization. Consistent with this, two-photon imaging of spinal neurons showed that intracellular calcium also increased following light offset. The activity elicited at light offset needs to be taken into consideration in experimental design, although this property may help provide insight into the effects of stimulating a circuit transiently. These results show that GtACR1 and GtACR2 can be used to optically inhibit neurons in zebrafish, and thus to test neural circuit necessity.

neuroscience↗

bioRxiv2017

Familiarity with companions aids recovery from fear inzebrafish

Interaction with social partners during or after a stressful episode aids recovery in humans and other mammals. We asked if a comparable phenomenon exists in zebrafish (Danio rerio) that live in shoals in the wild. In the first experiment, we observed that most quantifiable parameters of swimming behavior were similar when zerbafish swam alone or with companions. However, after exposure to an alarm substance (Schreckstoff), individuals recovering alone continued to display behaviors associated with fear after removal of the stimulus, while those recovering with companions did not. In the next two experiments, we examined the role of familiarity of companions. Subjects spent more time in the vicinity of familiar companions in a two-choice assay. While both familiar and unfamiliar companions reduced behavioral signs of distress, familiar companions additionally modulated cortisol and endogenous isotocin in subjects. Shortly after being united with familiar companions, isotocin spiked followed by a dampening of circulating cortisol levels. These results suggest that zebrafish experience fear attenuation in the presence of others and familiar companions are more effective at buffering the stress associated with escaping predation. Changes in behavior, circulating cortisol and isotocin levels due to social partners are reminiscent of changes due to amelioration of fear in some mammalian species in the presence of companions. The two phenomena may be related.

animal behavior and cognition↗

bioRxiv2016

Loss of the habenula neuromodulator Kisspeptin1 disrupts learning

Learning how to actively avoid a predictable aversive stimulus involves two steps: recognizing the cue that predicts upcoming punishment, and learning a behavioral response that will lead to avoidance. In zebrafish, ventral habenula (vHb) neurons have been proposed to participate in both steps by encoding the expected aversiveness of a stimulus. vHb neurons increase their firing rate as expectation of punishment grows, but reduce their activity as avoidance learning occurs. How the change in vHb activity occurs is not known. Here, we ask whether the neuromodulator kisspeptin1, which is expressed in the ventral habenula, could be involved. Kiss1 mutants were generated with Cas9 using guide RNAs targeted to the signal sequence. Mutants, which have a stop codon upstream of the kisspeptin1 peptide, have a deficiency in learning to avoid a shock that is predicted by light. Electrophysiology indicates that kisspeptin1 has a concentration-dependent effect on vHb neurons: depolarizing at low concentrations and hyperpolarizing at high concentrations. These data suggest that as the fish learns to cope with a threat, kisspeptin1 may differentially modulate vHb neurons. This implies that learning a behavioral strategy to overcome a stressor is accompanied by physiological change in habenula neurons.\n\nSignificance statementLearning to deal with adversity can positively affect ones ability to cope with challenges in the immediate future. Control thus causes short-term change in the brain. Here, we show that the neuromodulator kisspeptin1 is required to learn to avoid a punishment. Expression and electrophysiological recordings suggest that this molecule functions by controlling the ventral habenula, a region of the brain that mediates fear by regulating serotonin release. Kisspeptin1 may be a potential player in resilience developed as a result of control, extending previous findings that it can reduce fear.

animal behavior and cognition↗