Biology subjects

Gottschalk, A.

Publications and source records attributed to Gottschalk, A..

At least 19 recordsLinked to original sources

bioRxiv2026

The copine protein NRA-1 regulates activity-dependent cholinergic signalling and sensory integration in C. elegans

Membrane-associated proteins regulate the localisation and function of ligand-gated ion channels, yet how they shape synaptic efficacy and behaviour remains poorly understood. Here, we identify the copine family protein NRA-1 as an activity-dependent regulator of cholinergic signalling and sensory circuit function. Electrophysiological recordings at the neuromuscular junction of C. elegans revealed that loss of nra-1 does not alter responses to acute agonist application or the initial response to synaptic stimulation but selectively impairs sustained and repetitive cholinergic transmission during ongoing activity. Single-channel recordings further demonstrated that NRA-1 does not affect the unitary conductance of levamisole-sensitive acetylcholine receptors (L-AChRs) but instead regulates receptor gating by increasing channel closed times and reducing opening frequency, resulting in an overall decrease in receptor activity. Despite these synaptic defects, nra-1 mutants displayed normal baseline locomotion but exhibited impaired chemotaxis, abnormal food localisation and defective egg-laying behaviour. Together, our findings identify NRA-1 as an activity-dependent regulator of postsynaptic receptor function that sustains cholinergic signalling during repeated activity and links receptor dynamics to sensory behaviour. These results establish copine proteins as important modulators of synaptic efficacy and suggest that activity-dependent control of receptor function represents a conserved mechanism for tuning neural circuit performance.

neuroscience↗

bioRxiv2026

All-optical analysis of electrical coupling in muscle ensembles reveals contributions of individual innexins to cell synchronizationand locomotion

Gap junctions (GJs), formed by connexins in vertebrates and innexins in invertebrates, enable direct ion flow between adjacent cells. GJ coupling is typically analyzed by electrophysiological methods, which, however, are invasive and cannot be conducted in intact animals. Here, we used all-optical methods to non-invasively investigate electrical coupling in body wall muscle (BWM) cells of intact Caenorhabditis elegans. We analyzed the roles of specific innexins (unc-9, inx-11, inx-16) in BWMs, using the genetically encoded fluorescent voltage indicator QuasAr2 to assess spontaneous muscle activity. unc-9 mutants showed strongly reduced coupling and asynchronous activity, and this was accompanied by severe locomotion defects. Overexpression of the murine connexin Cx36 increased synchronization but disrupted locomotion. inx-16 mutants exhibited increased excitability of individual muscle cells, likely due to reduced leak currents, while inx-11 mutants displayed only moderate defects. Patch-clamp recordings confirmed altered action potentials and increased input resistance in inx-16 mutants. Additionally, we established a cell-specific optogenetic voltage clamp (cOVC) method, directly revealing changes in junctional conductance in live, non-dissected animals. In sum, our findings demonstrate that a balanced level of GJ coupling is essential for coordinated muscle activity and proper motor behavior. Significance statementCoordination of cells in muscular organs requires electrical coupling via intercellular channels termed gap junctions (GJs). How this coupling contributes to coordinated activity like locomotion in an intact animal is difficult to assess, since commonly used electrophysiological methods require dissection, and are incompatible with behavior. Here, we developed all-optical electrophysiology methods to study GJ coupling in live C. elegans. Different innexin mutants, as well as overexpression of mammalian connexin Cx36, induced different locomotion defects and, compared to wild type, were accompanied by more or less electrical coupling and synchronicity of individual muscle cells. Loss of some innexins caused the insulated muscle cells to be more excitable. Thus, GJ coupling is required for fine-tuning locomotion, and can be studied by voltage imaging.

cell biology↗

bioRxiv2025

Stabilized ion selectivity corrects activation drift in kalium channelrhodopsins

Effective optogenetic inhibition of neuronal activity requires tools that can reliably silence neurons across diverse conditions and cell types. Potassium-selective channelrhodopsins (KCRs) have emerged as promising alternatives to chloride-conducting channels for optogenetic inhibition of cellular excitability, but they exhibit dynamic ion selectivity shift under prolonged or intense illumination, causing activation. This inhibition to activation transition limits their utility for silencing circuits. Through behavioral and electrophysiological analyses in Drosophila, and C. elegans, we found that the C29D variant of KCR1 maintains the most stable potassium selectivity among tested variants. While other KCR variants showed excitation defects, KCR1-C29D consistently provided robust in vivo inhibition across cell types, illumination conditions, and species. Electrophysiological recordings revealed that while most KCRs show declining PK/PNa ratios during illumination, KCR1-C29D maintains stable ion selectivity, consistent with its robust silencing capability. This work resolves a key limitation of KCR optogenetics and shows that KCR1-C29D is a superior tool for reliable inhibition. Our findings offer valuable mechanistic and practical insights for the design of next generation optogenetic inhibitors.

neuroscience↗

bioRxiv2025

In situ structure of a gap junction - stomatin complex

Gap junctions (GJ) are intercellular channels that mediate electrical signals and the transfer of small molecules. GJs are crucial for the functions of the brain, heart and other organs. While structures of purified homomeric GJs are available, we lack in situ structures. In vivo, GJs can form heteromers with different functionalities, and may associate with other proteins. Here, we analyzed Caenorhabditis elegans GJs by cryo-electron tomography and sub-tomogram averaging. We observed hexagonal arrays of GJs at cellular junctions in primary embryonal cell culture that displayed distinct wide and narrow conformations. Moreover, in about 20% of the observed channels, we found a cap-like, cytosolic protein assembly enclosing the channel pore. We propose that the cap-structure is formed by the stomatin UNC-1, which is known to interact with C. elegans GJs, and strengthen this hypothesis by matching AlphaFold3 models of UNC-1 multimers with our GJ average. Furthermore, expressing UNC-1 and the C. elegans innexin UNC-9 in HEK cells resulted in similar structures at cell-cell contacts. UNC-1/stomatin ring assemblies may affect GJ formation or functions like rectification, that might be evolutionarily conserved. Significance StatementGap junction (GJ) channels connect neighboring cells. Structures of (purified) GJs have been studied in vitro, but not in situ. We identified GJ channels in primary Caenorhabditis elegans cells by cryo-electron tomography, and analyzed their structure by sub-tomogram averaging. The channels transverse the membranes of connected cells, and AlphaFold3 (AF3) models of the GJ subunit UNC-9, assuming dodecamers, fit the experimentally obtained surface map well. We observed a cytosolic cap structure on the GJ channels. The stomatin protein UNC-1 is known to physically interact with UNC-9 GJs. AF3 models of UNC-1 hexadecamers fit the cap structure, indicating that it may be formed by UNC-1, providing a first idea how UNC-1 interacts with, and may functionally influence, GJ channels.

neuroscience↗

bioRxiv2025

Multimodal characterization and optogenetic potential of the bistable Gi/o-coupled vertebrate ancient opsin from the flashlight fish Anomalops katoptron

Vertebrate ancient long opsin, or VAL opsin, is a light-sensitive protein that is found within and outside the visual system in vertebrates. In accordance with its wide distribution in the retina, brain, testis and skin, VAL is suggested to play a role in light-dependent physiological processes that are beyond vision. However, many aspects of the physiological properties and specific functions of VAL remain unclear. Here we identified and characterized the VAL opsin from the flashlight fish Anomalops katoptron (AkVAL) and show that this opsin is bistable and reversibly converts between active and inactive states by responding to cycles of green and blue/UV lights. We further show that AkVAL couples to the Gi/o pathway and controls the activity of GIRK channels in a bistable manner. In line with this, we demonstrated that AkVAL modulates neuronal activity in cerebellar Purkinje cells, where neuronal activity is reduced by UV/blue light and increased by green/red light illumination. In addition, upon the in vivo expression of AkVAL in neurons innervating body muscles of Caenorhabditis elegans the worms body movement can be bidirectionally controlled altering blue/UV and green illuminations. These data highlight the potential of AkVAL as an optogenetic tool to control cells in vitro and in vivo, in a bistable manner.

neuroscience↗

bioRxiv2024

Neurons and molecules involved in noxious light sensation in Caenorhabditis elegans

Ultraviolet (UV) light is a danger to unpigmented organisms, inducing photodamage of cells and DNA. The transparent nematode Caenorhabditis elegans, despite having no eyes, detects light and exhibits negative phototaxis in order to evade sunlight. UV absorption is detected by the photosensor protein LITE-1, that also responds to reactive oxygen species. We investigated which neurons express LITE-1 and act as noxious photosensors and how they transmit this sensation to the nervous system to evoke escape behavior. We identified the interneuron AVG as a main focus of LITE-1 function in mediating the noxious light evoked escape behavior, with minor roles of the interneuron PVT, the sensory ASK neurons and touch receptor neurons. AVG is activated by blue light, and also its optogenetic stimulation causes escape behavior. Signaling from AVG involves chemical neurotransmission, likely directly to premotor interneurons, and to other cells, by extrasynaptic signaling through the neuropeptide NLP-10. NLP-10 signaling is not required for the acute response, but for maintaining responsiveness to repeated noxious stimuli. The source of NLP-10 in this context is largely AVG, however, also other cells contribute, possibly PVT. This work uncovers entry points of sensory information to the neuronal circuits mediating behavioral responses to noxious UV/blue light. Article SummaryC. elegans senses noxious light and induces escape behavior to avoid damage. The photosensor protein LITE-1 mediates this sensation but understanding responsible neural circuits is incomplete. We identified neurons expressing LITE-1 and identify AVG as the main site of action. The neurotransmitter GABA plays a role in acuteness of the response. AVG, and other cells, need to release the neuropeptide NLP-10 to maintain responsiveness to repeated noxious stimuli. These findings help understanding the C. elegans photophobic response and will guide future work delineating the precise circuit pathways, as an example of how similar photosensation can evoke protective behavior in invertebrates.

neuroscience↗

bioRxiv2024

Wideband ratiometric measurement of tonic and phasic dopamine release in the striatum

Reward learning, cognition, and motivation are supported by changes in neurotransmitter levels across multiple timescales. Current measurement technologies for various neuromodulators (such as dopamine and serotonin) do not bridge timescales of fluctuations, limiting the ability to define the behavioral significance, regulation, and relationship between fast (phasic) and slow (tonic) dynamics. To help resolve longstanding debates about the behavioral significance of dopamine across timescales, we developed a novel quantification strategy, augmenting extensively used carbon-fiber Fast Scan Cyclic Voltammetry (FSCV). We iteratively engineered the FSCV scan sequence to rapidly modify electrode sensitivity within a sampling window and applied ratiometric analysis for wideband dopamine measurement. This allowed us to selectively eliminate artifacts unrelated to electrochemical detection (i.e., baseline drift), overcoming previous limitations that precluded wideband dopamine detection from milliseconds to hours. We extensively characterize this approach in vitro, validate performance in vivo with simultaneous microdialysis, and deploy this technique to measure wideband dopamine changes across striatal regions under pharmacological, optogenetic, and behavioral manipulations. We demonstrate that our approach can extend to additional analytes, including serotonin and pH, providing a robust platform to assess the contributions of multi-timescale neuromodulator fluctuations to cognition, learning, and motivation.

neuroscience↗

bioRxiv2024

Loss of Flower/FLWR-1 induces an increase in neuronal excitability and causes defective recycling of synaptic vesicles

The Flower protein was suggested to couple the fusion of synaptic vesicles (SVs) to their recycling in different model organisms. It is supposed to trigger activity-dependent bulk endocytosis by conducting Ca2+ at endocytic sites. However, this mode of action is debated. Here, we investigated the role of the Caenorhabditis elegans homolog FLWR-1 in neurotransmission. Our results confirm that FLWR-1 facilitates the recycling of SVs at the neuromuscular junction (NMJ). Ultrastructural analysis of synaptic boutons after hyperstimulation revealed an accumulation of large endocytic structures in flwr-1 mutants. These findings do not support a role of FLWR-1 in the formation of bulk endosomes but rather a function in their breakdown. Unexpectedly, loss of FLWR-1 led to increased neuronal Ca2+ levels in axon terminals during stimulation, particularly in GABAergic motor neurons, causing excitation-inhibition imbalance. We found that this increased NMJ transmission might be caused by deregulation of MCA-3, the nematode orthologue of the plasma membrane Ca2+ ATPase (PMCA). In vivo molecular interactions indicated that FLWR-1 may be a positive regulator of the PMCA and might influence its recycling through modification of plasma membrane levels of PI(4,5)P2.

neuroscience↗

bioRxiv2024

Loss of neuropeptidergic regulation of cholinergic transmission induces CaV1-mediated homeostatic compensation in muscle cells

Chemical synaptic transmission at the neuromuscular junction (NMJ) is regulated by electrical activity of the motor circuit, but may also be affected by neuromodulation. Here, we assess the role of neuropeptide signaling in the plasticity of NMJ function in Caenorhabditis elegans. We show that the CAPS (Ca2+-dependent activator protein for secretion) ortholog UNC-31, which regulates the exocytosis of dense core vesicles (DCVs), affects both pre- and post-synaptic functional properties, as well as NMJ-mediated locomotion. Despite reduced evoked acetylcholine transmission, the loss of unc-31 results in a more vigorous response to presynaptic stimulation, i.e., enhanced muscle contraction and Ca2+ transients. Based on expression profiles, we identified neuropeptides involved in both cholinergic (FLP-6, NLP-9, NLP-21 and NLP-38) and GABAergic motor neurons (FLP-15, NLP-15), that mediate normal transmission at the NMJ. In the absence of these peptides, neurons fail to upregulate their transmitter output in response to increased cAMP signaling. We also identified proprotein convertases encoded by aex-5/kpc-3 and egl-3/kpc-2 that act synergistically to generate these neuropeptides. We propose that postsynaptic homeostatic scaling, mediated by increased muscle excitability, could compensate for the reduced cholinergic transmission in mutants affected for neuropeptide signaling, thus maintaining net synaptic strength. We show that in the absence of UNC-31 muscle excitability is modulated by upregulating the expression of the muscular L-type voltage gated Ca2+ channel EGL-19 (CaV1). Collectively, our results unveil a role for neuropeptidergic regulation in synaptic plasticity, linking changes in presynaptic transmission to compensatory changes in muscle excitability.

neuroscience↗

bioRxiv2024

Potassium-selective channelrhodopsins can exert hyper- or depolarizing effects in excitable cells of Caenorhabditis elegans, depending on experimental condition

One of the most frequent applications of optogenetic tools is for depolarization and stimulation of excitable cells such as neurons and muscles. Equally important, but less frequently used, are inhibitory tools that suppress activity through cellular hyperpolarization. These tools often rely on chloride conductance. Yet, in vivo, re- and hyperpolarization is typically mediated by potassium. In recent years, light-gated ion channels with a high preference for potassium were identified (Kalium channelrhodopsins, KCRs), and their inhibitory potential described in different organisms. Here, we characterized HcKCR1 and WiChR, in cholinergic neurons and muscles of Caenorhabditis elegans. Hyperpolarization of these cell types both induces muscle relaxation and, consequently, an elongation of the animals. Thus, we analyzed body length before, during, and after illumination, to assess KCR effectiveness, and to benchmark stimulation parameters like light intensity and duration. For HcKCR1 in cholinergic neurons, continuous illumination at high light intensities (1-4.5 mW/mm2) evoked only a transient elongation, while stimulation at 0.1 mW/mm2 could maintain inhibition for the duration of the stimulus in some transgenic strains. For animals expressing WiChR in body wall muscle cells or cholinergic neurons, we again observed brief hyperpolarization during continuous illumination, however, still during the stimulus, this changed to body contraction, corresponding to depolarization. This effect was long lasting, and required dozens of seconds for reversion, but could be reduced by pulsed illumination and fully avoided by less efficient channel activation using green or orange light. Hence, KCRs can be applied to hyperpolarize C. elegans cells, but require optimized illumination parameters. Article summaryTo inhibit excitable cells, light-gated, potassium-selective channels (KCRs) can be used. This study explores whether stimulation of KCRs HcKCR1 and WiChR in cholinergic neurons and muscle cells of Caenorhabditis elegans can induce inhibition during illumination. While inhibition could be achieved, depending on light conditions, the authors unexpectedly also observed excitation. These effects may occur due to a combination of high conductivity of KCRs, and partial conductance of other cations. These findings highlight the need for specific experimental conditions in future studies utilizing these tools. The authors also present conditions that can partially or fully avoid the unwanted depolarizing effects.

neuroscience↗

bioRxiv2024

Neuropeptidergic regulation of neuromuscular signaling in larval zebrafish alters swimming behavior and synaptic transmission

The regulation of synaptic transmission is crucial for plasticity, homeostasis and learning. Chemical synaptic transmission is thus modulated to accommodate different activity levels, which also enables homeostatic scaling in pre- and postsynaptic compartments. In nematodes, cAMP signaling enhances cholinergic neuron output, and these neurons use neuropeptide signaling to modulate synaptic vesicle content. To explore if this mechanism is conserved in vertebrates, we studied the involvement of neuropeptides in cholinergic transmission at the neuromuscular junction of larval zebrafish. Optogenetic stimulation by photoactivated adenylyl cyclase (bPAC) resulted in elevated locomotion as measured in behavioural assays. Furthermore, post-synaptic patch-clamp recordings revealed that in bPAC transgenics, the frequency of miniature excitatory postsynaptic currents (mEPSCs) was increased after photostimulation. These results suggested that cAMP-mediated activation of ZF motor neurons leads to increased fusion of SVs, consequently resulting in enhanced neuromuscular activity. We generated mutants lacking the neuropeptide processing enzyme carboxypeptidase E (cpe), and the most abundant neuropeptide precursor in motor neurons, tachykinin (tac1). Both mutants showed exaggerated locomotion after photostimulation. cpe mutants exhibit lower mEPSC frequency during photostimulation and less large-amplitude mEPSCs. In tac1 mutants mEPSC frequency was not affected but amplitudes were significantly smaller. Exaggerated locomotion in the mutants thus reflected upscaling of postsynaptic excitability. cpe and tac1 mutant muscles expressed more nicotinic acetylcholine receptors (nAChR) on their surface. Thus, neuropeptide signaling regulates synaptic transmitter output in zebrafish motor neurons, and muscle cells homeostatically regulate nAChR surface expression, compensating reduced presynaptic input. This mechanism may be widely conserved in the animal kingdom.

neuroscience↗

bioRxiv2023

Hierarchical regulation of functionally antagonistic neuropeptides expressed in a single neuron pair

Neuronal communication involves small-molecule transmitters, gap junctions, and neuropeptides. While neurons often express multiple neuropeptides, our understanding of the coordination of their action and their mutual interactions remains limited. Here, we demonstrate that two neuropeptides, NLP-10 and FLP-1, released from the same interneuron pair, AVKL/R, exert antagonistic effects on locomotion speed in Caenorhabditis elegans. NLP-10 accelerates locomotion by activating the G protein-coupled receptor NPR- 35 on premotor interneurons that promote forward movement. Notably, we establish that NLP-10 is crucial for the aversive response to mechanical and noxious light stimuli. Conversely, AVK-derived FLP-1 slows down locomotion by suppressing the secretion of NLP-10 from AVK, through autocrine feedback via activation of its receptor DMSR-7 in AVK neurons. Our findings suggest that peptidergic autocrine motifs, exemplified by the interaction between NLP-10 and FLP-1, might represent a widespread mechanism in nervous systems across species. These mutual functional interactions among peptidergic co-transmitters could fine-tune brain activity. Highlights* A pair of neurons elicits opposing behaviors via two distinct neuropeptides * The neuropeptide NLP-10 accelerates locomotion by activating premotor interneurons * Release of the neuropeptide FLP-1 reduces NLP-10 release via autocrine feedback * NLP-10 is crucial for escaping aversive mechanical stimuli and noxious blue light eTOC blurbNeuropeptidergic communication is complex due to the hundreds of proteinaceous transmitters and receptors involved. Aoki and colleagues demonstrate a further layer of regulation, where one neuropeptide negatively influences release of an antagonistic neuropeptide by autocrine feedback, in a single neuron pair. This may represent a general principle in neuropeptidergic signaling.

neuroscience↗

bioRxiv2023

Coordinated electrical and chemical signaling between two neurons orchestrates switching of motor states

To survive in a complex environment, animals must respond to external cues, e.g., to escape threats or to navigate towards favorable locations. Navigating requires transition between motor states, e.g. switching from forward to backward movement. Here, we investigated how two classes of interneurons, RIS and RIM, fine-tune this transition in the nematode C. elegans. By Ca2+ imaging in freely moving animals, we found that RIS gets active slightly before RIM and likely biases decision-making towards a reversal. In animals lacking RIS, we observed lowered Ca2+-levels in RIM prior to a reversal. Combined photo-stimulation and voltage imaging revealed that FLP-11, a neuropeptide released by RIS, has an excitatory effect on RIM, while tyramine, released from RIM, inhibits RIS. Voltage imaging of intrinsic activity provided evidence for tight electrical coupling between RIS and RIM via gap junctions harboring UNC-7 innexins. Asymmetric junctional current flow was observed from RIS to RIM, and vice versa. We propose that the interplay of RIS and RIM is based on concerted electrical and chemical signaling, with a fast junctional current exchange early during the transition from forward to backward movement, followed by chemical signaling, likely during reversal execution.

neuroscience↗

bioRxiv2022

pOpsicle: An all-optical reporter system for synaptic vesicle recycling combining pH-sensitive fluorescent proteins with optogenetic manipulation of neuronal activity

pH-sensitive fluorescent proteins are widely used to study synaptic vesicle (SV) fusion and recycling. When targeted to the lumen of SVs, fluorescence of these proteins is quenched by the acidic pH. Following SV fusion, they are exposed to extracellular neutral pH, resulting in a fluorescence increase. SV fusion, recycling and acidification can thus be tracked by tagging integral SV proteins with pH-sensitive proteins. Neurotransmission is generally stimulated by electrophysiology, which is not feasible in small, intact animals, thus limiting the approach to cell culture regimes. Previous in vivo approaches depended on distinct (sensory) stimuli, thus limiting the addressable neuron types. To overcome these limitations, we established an all-optical approach to stimulate and visualize SV fusion and recycling. We combined distinct pH-sensitive fluorescent proteins (inserted into the SV protein synaptogyrin) and light-gated channelrhodopsins (ChRs) for optical stimulation, overcoming optical crosstalk and thus enabling an all-optical approach. We generated two different variants of the pH-sensitive optogenetic reporter of vesicle recycling (pOpsicle) and tested them in cholinergic neurons of intact Caenorhabditis elegans nematodes. First, we combined the red fluorescent protein pHuji with the blue-light gated ChR2(H134R), and second, the green fluorescent pHluorin combined with the novel red-shifted ChR ChrimsonSA. In both cases, fluorescence increases were observed after optical stimulation. Increase and subsequent decline of fluorescence was affected by mutations of proteins involved in SV fusion and endocytosis. These results establish pOpsicle as a non-invasive, all-optical approach to investigate different steps of the SV cycle.

neuroscience↗

bioRxiv2022

Rapid and reversible optogenetic silencing of synaptic transmission by clustering of synaptic vesicles

Silencing neurons acutely and specifically informs about their functional roles in circuits and behavior. Existing optogenetic silencers include ion pumps or channels, and tools that damage the neurotransmitter release machinery. While the former hyperpolarize the cell and can alter ionic gradients, the latter allow only slow recovery, requiring de novo synthesis. Thus, there is a need for other strategies combining fast activation and reversibility. Here, we use light-evoked homo-oligomerization of cryptochrome CRY2 to silence synaptic transmission, by clustering synaptic vesicles (SVs). We benchmark this tool, optoSynC, by electrophysiology and locomotion in Caenorhabditis elegans. optoSynC clusters SVs within 25 s, causing approximation, observable by electron microscopy. Locomotion silencing is rapid (tauon [~]15 s) and recovers quickly (tauoff [~]10 min) after light-off. Further, optoSynC can inhibit exocytosis for several hours, at very low light intensities. optoSynC is a highly efficient, non-ionic optogenetic silencer that may further allow to manipulate different SV pools.

neuroscience↗

bioRxiv2022

All-optical closed-loop voltage clamp for precise control of muscles and neurons in live animals

Excitable cells can be stimulated or inhibited by optogenetics. Since optogenetic actuation regimes are often static, neurons and circuits can quickly adapt, allowing perturbation, but not true control. Hence, we established an optogenetic voltage-clamp (OVC). The voltage-indicator QuasAr2 provides information for fast, closed-loop optical feedback to the bidirectional optogenetic actuator BiPOLES. Voltage-dependent fluorescence is held within tight margins, thus clamping the cell to distinct potentials. We established the OVC in muscles and neurons of Caenorhabditis elegans, and transferred it to rat hippocampal neurons in slice culture. Fluorescence signals were calibrated to electrically measured potentials, and wavelengths to currents, enabling to determine optical I/V-relationships. The OVC reports on homeostatically altered cellular physiology in mutants and on Ca2+-channel properties, and can dynamically clamp spiking. Combining non-invasive imaging with control capabilities of electrophysiology, the OVC facilitates high-throughput, contact-less electrophysiology in individual cells and paves the way for true optogenetic control in behaving animals.

neuroscience↗

bioRxiv2021

Brain Water as a Function of Age and Weight in Normal Rats

Rats are frequently used to study water content of normal and injured brain, as well as changes in response to various osmotherapeutic regimens. Magnetic resonance imaging in humans has shown that brain water content declines with age as a result of progressive myelination. The purpose of this study was to quantify changes in brain water content during rat development and aging. Brain water content was measured by standard techniques in 129 normal male Sprague-Dawley rats that ranged in age (weight) from 13 to 149 days (18 to 759 g). Overall, the results demonstrated a decrease from 85.59% to 76.56% water content with increasing age (weight). Nonlinear allometric functions relating brain water to age and weight were determined. These findings provide age-related context for prior rat studies of brain water, emphasize the importance of using similarly aged controls in studies of brain water, and indicate that age-related changes in brain water content are not specific to humans.

physiology↗

bioRxiv2021

RIM and RIM-binding protein localize synaptic Cav2 channels in a differential manner to regulate transmission in neuronal circuits

At chemical synapses, voltage-gated Ca2+-channels (VGCCs) translate electrical signals into a trigger for synaptic vesicle (SV) fusion. VGCCs and the Ca2+ microdomains they elicit must be located precisely to primed SVs, to evoke rapid transmitter release. Localization is mediated by Rab3 interacting molecule (RIM) and RIM-binding proteins (RIM-BPs), which interact and bind to the C-terminus of the CaV2 VGCC -subunit. We studied this machinery at the mixed cholinergic/GABAergic neuromuscular junction (NMJ) of Caenorhabditis elegans. rimb-1 mutants had mild synaptic defects, through loosening the anchoring of UNC-2/CaV2 and delaying the onset of SV fusion. UNC-10/RIM deletion much more severely affected transmission. Even though postsynaptic depolarization was reduced, rimb-1 mutants had increased cholinergic (but reduced GABAergic) transmission, to compensate for the delayed release. This did not occur when the excitation-inhibition balance was altered by removing GABA transmission. RIMB-1 thus may differentially regulate transmission in mixed circuits. Untethering the UNC-2/CaV2 channel by removing its C-terminal PDZ ligand exacerbated the rimb-1 defects, and similar phenotypes resulted from acute degradation of the CaV2 {beta}-subunit CCB-1. Therefore, untethering of the CaV2 complex is as severe as its elimination, yet does not abolish transmission, likely due to compensation by CaV1. Thus, robustness and flexibility of synaptic transmission emerges from VGCC regulation.

neuroscience↗