Biology subjects

Jesuthasan, S. J.

Publications and source records attributed to Jesuthasan, S. J..

8 recordsLinked to original sources

bioRxiv2024

Kalium channelrhodopsins effectively inhibit neurons in the small model animals

The analysis of neural circuits has been revolutionized by optogenetic methods. Light-gated chloride-conducting anion channelrhodopsins (ACRs)--recently emerged as powerful neuron inhibitors. For cells or sub-neuronal compartments with high intracellular chloride concentrations, however, a chloride conductance can have instead an activating effect. The recently discovered light-gated, potassium-conducting, kalium channelrhodopsins (KCRs) might serve as an alternative in these situations, with potentially broad application. As yet, KCRs have not been shown to confer potent inhibitory effects in the small genetically tractable animals. Here, we evaluated the utility of KCRs to suppress behavior and inhibit neural activity in Drosophila, C. elegans, and zebrafish. In direct comparisons with ACR1, a KCR1 variant with enhanced plasma-membrane trafficking displayed comparable potency, but with improved properties that include reduced toxicity and superior efficacy in putative high-chloride cells. This comparative analysis of behavioral inhibition between chloride- and potassium-selective silencing tools establishes KCRs as next-generation optogenetic inhibitors for in vivo circuit analysis in behaving animals.

neuroscience↗

bioRxiv2021

Identification of potential astrocytes in the teleost brain

Astrocytes are abundant star-shaped glial cells in the mammalian brain, with essential roles in metabolism, development, homeostasis, response to injury, behavior, and learning. Surprisingly, most regions of the teleost brain are thought to lack astrocytes, based primarily on the use of GFAP (glial fibrillary acidic protein) as a marker1. Here, drawing on recent evidence that astrocytes are molecularly heterogeneous, we propose that astrocytes exist in the teleost brain, albeit of the olig2 subtype2. Highly branched cells are present throughout the zebrafish brain, as shown here in Tg(sox10:EGFP) fish and previously in Tg(olig2:GFP) fish. Transcriptome data indicates the presence of brain cells that are olig2 and sox10 positive, which also express the astrocyte markers sox9b, sparcl1 and slc1a2b but lack gfap and the oligodendrocyte marker mbp. In situ hybridization confirms that stellate sox10:EGFP cells express olig2 and sox9b, while immunofluorescence indicates that they lack HuC/D and GFAP. We suggest that these cells be classified as astrocytes as this may more accurately reflect their functions.

neuroscience↗

bioRxiv2020

Olfactory rod cells: a rare cell type in the larval zebrafish olfactory epithelium with an actin-rich apical projection

We report the presence of a rare cell type, the olfactory rod cell, in the developing zebrafish olfactory epithelium. These cells each bear a single actin-rich rod-like apical projection extending about 10 m from the epithelial surface. Live imaging with a ubiquitous Lifeact-RFP label indicates that the rods can oscillate. Olfactory rods arise within a few hours of the olfactory pit opening, increase in numbers and size during larval stages, and can develop in the absence of olfactory cilia. Olfactory rod cells differ in morphology from the known classes of olfactory sensory neuron, but express reporters driven by neuronal promoters. The cells also differ from secondary sensory cells such as hair cells of the inner ear or lateral line, or sensory cells in the taste bud, as they are not associated with established synaptic terminals. A sub-population of olfactory rod cells expresses a Lifeact-mRFPruby transgene driven by the sox10 promoter. Mosaic expression of this transgene reveals that olfactory rod cells have rounded cell bodies located apically in the olfactory epithelium.

developmental biology↗

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↗

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↗

bioRxiv2018

Features of criticality are asymmetric in the zebrafish habenula

The habenula is an evolutionarily conserved structure of the vertebrate brain that is essential for behavioural flexibility and mood control. It is spontaneously active and is able to access diverse states when the animal is exposed to sensory stimuli or reward. Here we analyze two-photon calcium imaging time-series of the habenula of larval zebrafish and find that percolation occurs, indicating the presence of long-range spatial correlations within each side of the habenula, with percolation occurring independently in each side. On the other hand, the analysis of neuronal avalanches suggests that the system is subcritical, implying that the flexibility in its dynamics may result from other dynamical processes.

neuroscience↗

bioRxiv2017

Masking of a circadian behavior in larval zebrafish involves the thalamo-habenula pathway

Light has the ability to disrupt or mask behavior that is normally controlled by the circadian clock. In mammals, masking requires melanopsin-expressing retinal ganglion cells that detect blue light and project to the thalamus. It is not known whether masking is wavelength-dependent in other vertebrates, nor is it clear what higher circuits are involved. Here, we address these questions in zebrafish. We find that diel vertical migration, a circadian behavior in larval zebrafish, is effectively masked by blue, but not by red light. Two-photon calcium imaging reveals that a retino-recipient thalamic nucleus and a downstream structure, the habenula, are tuned to blue light. Lesioning the habenula inhibits light-evoked climbing. These data suggest that a thalamo-habenula pathway may be involved in the ability of blue light to mask circadian behavior.

neuroscience↗