Biology subjects

Vaithianathan, T.

Publications and source records attributed to Vaithianathan, T..

5 recordsLinked to original sources

bioRxiv2026

Conspecific Presence Facilitates the Reliable Expression of Nicotine Reward in Juvenile Zebrafish

RationaleAdolescence is a period of heightened vulnerability to nicotine reinforcement. While zebrafish are a valuable model for investigating drug reward, standard conditioned place preference (CPP) assays typically test subjects in isolation. In this highly social species, solitary testing may act as an environmental stressor that confounds behavioral readouts. ObjectivesThis study examined how social context during testing (isolated vs. grouped) affects experimental attrition, behavioral stability, and nicotine CPP expression in late juvenile zebrafish. MethodsZebrafish housed in groups of four were tested either individually (isolated) or in their housing groups (grouped) during daily 20-minute sessions. Following baseline preference assessments, subjects underwent six days of conditioning pairing their initially non-preferred compartment with fish water or nicotine (0.5, 1.6, or 5.0 {micro}mol/L). Place preference, locomotion, and thigmotaxis were assessed on a drug-free test day. ResultsIsolated testing reduced distance traveled, decreased swimming speed, and increased time spent near tank walls, indicating heightened anxiety-like behavior. Experimental attrition was significantly higher in isolated (38.9%) than grouped (2.5%) subjects. Grouped subjects developed significant place preference at 1.6 and 5.0 {micro} mol/L nicotine, whereas preference was not detectable in isolated subjects. ConclusionsSolitary testing acts as a stressor that increases experimental attrition and masks place preference. Conversely, testing in the presence of conspecifics stabilizes behavior and facilitates the detection of nicotine reward in late juvenile zebrafish.

animal behavior and cognition↗

bioRxiv2025

Distinct Roles of CaMKII in Synaptic Vesicle Dynamics at Zebrafish Retinal Rod Bipolar Ribbon Synapses

Calcium (Ca{superscript 2}) not only serves as a fundamental trigger for neurotransmitter release but also participates in shaping neurotransmitter release (NTR) during prolonged presynaptic stimulation via multiple Ca2+-dependent processes. The Ca2+/calmodulin (CaM)-dependent protein kinase II (CaMKII) is enriched at various presynaptic terminals, including ribbon synapses, where it associates with synaptic ribbons and thus may contribute to the modulation of Ca2+-dependent NTR. This could arise via its ability to influence one or more steps that control either the Ca2+ signal, the release process, or synaptic vesicle dynamics affecting available pools. Yet, recent studies have yielded conflicting results regarding the ability of CaMKII to influence NTR at rod bipolar cell (RBC) ribbon synapses. To address this, we acutely manipulated CaMKII activity in synaptic terminals of zebrafish RBCs by infusion of either inhibitory peptides targeting CaMKII or CaM, or a constitutively active CaMKII, while using a combination of imaging and electrophysiological approaches. Neither inhibiting nor enhancing CaMKII activity affects presynaptic Ca2+ channel activity. However, capacitance measurements revealed that inhibition of either CaMKII or CaM reduces exocytosis. CaMKII inhibition also reduces synaptic vesicle replenishment. Surprisingly, elevation of CaMKII activity also diminished vesicle fusion, similar to the effect of CaMKII inhibition, suggesting that CaMKII activity naturally exists at optimal levels to support neurotransmitter release. In contrast to CaMKII inhibition, CaMKII activity elevation did not impair vesicle replenishment. Collectively, these data suggest that distinct synaptic vesicle populations are differentially reliant on the level of CaMKII activity. Significant StatementCaMKII is well-recognized for its postsynaptic participation in multiple forms of synaptic plasticity, yet it is well-documented to be prevalent in presynaptic compartments, where it may control NTR. The specific functions of CaMKII in synaptic vesicle dynamics remain poorly understood. While using a combination of imaging and electrophysiology approaches, we acutely manipulated CaMKII activity in presynaptic terminals by infusion of inhibitory peptides or constitutively active CaMKII. These manipulations revealed that deviations in CaMKII levels, in either direction, impair neurotransmitter release, suggesting that CaMKII is optimally present at these synapses. Yet CaMKII activity appears required for synaptic vesicle replenishment, suggesting that distinct aspects of synaptic vesicle dynamics are under differential control by CaMKII.

neuroscience↗

bioRxiv2024

Nanophysiology Approach Revealed Diversity in Calcium Microdomains in Zebrafish Retinal Bipolar Ribbon Synapses

Rapid and high local calcium (Ca2+) signals are essential for triggering neurotransmitter release from presynaptic terminals. In specialized bipolar ribbon synapses of the retina, these local Ca2+ signals control multiple processes, including the priming, docking, and translocation of vesicles on the ribbon before exocytosis, endocytosis, and the replenishment of release-ready vesicles to the fusion sites for sustained neurotransmission. However, our knowledge about Ca2+ signals along the axis of the ribbon active zone is limited. Here, we used fast confocal quantitative dual-color ratiometric line-scan imaging of a fluorescently labeled ribbon binding peptide and Ca2+ indicators to monitor the spatial and temporal aspects of Ca2+ transients of individual ribbon active zones in zebrafish retinal rod bipolar cells (RBCs). We observed that a Ca2+ transient elicited a much greater fluorescence amplitude when the Ca2+ indicator was conjugated to a ribeye-binding peptide than when using a soluble Ca2+ indicator, and the estimated Ca2+ levels at the ribbon active zone exceeded 26 M in response to a 10-millisecond stimulus, as measured by a ribbon-bound low-affinity Ca2+ indicator. Our quantitative modeling of Ca2+ diffusion and buffering is consistent with this estimate and provides a detailed view of the spatiotemporal [Ca2+] dynamics near the ribbon. Importantly, our data demonstrates that the local Ca2+ levels may vary between ribbons of different RBCs and within the same cells. The variation in local Ca2+ signals is found to correlate with ribbon size and active zone extent. Our serial electron microscopy results provide new information about the heterogeneity in ribbon size, shape, and area of the ribbon in contact with the plasma membrane.

neuroscience↗

bioRxiv2023

The role of sphingosine-1-phosphate receptor 2 in mouse retina light responses

The bioactive sphingolipid sphingosine-1-phosphate (S1P) acts as a ligand for a family of G protein-coupled S1P receptors (S1PR1-5) to participate in a variety of signaling pathways. However, their specific roles in the neural retina remain unclear. We previously showed that S1P receptor subtype 2 (S1PR2) is expressed in murine retinas, primarily in photoreceptors and bipolar cells, and its expression is altered by retinal stress. This study aims to elucidate the role of S1PR2 in the mouse retina. We examined light responses by electroretinography (ERG), structural differences by optical coherence tomography (OCT), and protein levels by immunohistochemistry (IHC) in wild-type (WT) and S1PR2 knockout (KO) mice at various ages between 3 and 6 months. We found that a- and b-wave responses significantly increased at flash intensities between 400[~]2000 and 4[~]2,000 cd.s/m2 respectively, in S1PR2 KO mice relative to those of WT controls at baseline. S1PR2 KO mice also exhibited significantly increased retinal nerve fiber layer (RNFL) and outer plexiform layer (OPL) thickness by OCT relative to the WT. Finally, in S1PR2 KO mice, we observed differential labeling of synaptic markers by immunohistochemistry (IHC) and quantitative reverse transcription polymerase chain reaction (RT-qPCR). These results suggest a specific involvement of S1PR2 in the structure and synaptic organization of the retina and a potential role in light-mediated functioning of the retina.

physiology↗

bioRxiv2023

The Effects of Aging on Rod Bipolar Cell Ribbon Synapses

The global health concern posed by age-related visual impairment highlights the need for further research focused on the visual changes that occur during the process of aging. To date, multiple sensory alterations related to aging have been identified, including morphological and functional changes in inner hair cochlear cells, photoreceptors, and retinal ganglion cells. While some age-related morphological changes are known to occur in rod bipolar cells in the retina, their effect on these cells and on their connection to other cells via ribbon synapses remain elusive. To investigate the effects of aging on rod bipolar cells and their ribbon synapses, we compared synaptic calcium currents, calcium dynamics, and exocytosis in zebrafish (Danio rerio) that were middle-aged (MA,18 months) or old-aged (OA, 36 months). The bipolar cell terminal in OA zebrafish exhibited a decreased number of synaptic ribbons, an increased ribbon length, and a decrease in local Ca2+ signals at the tested ribbon location with little change in the overall magnitude of the calcium current or exocytosis in response to brief pulses. Staining of the synaptic ribbons with antibodies specific for PKC revealed shortening of the inner nuclear and plexiform layers (INL and IPL). These findings shed light on age-related changes in the retina that are related to synaptic ribbons and calcium signals.

neuroscience↗