bioRxiv Subject Collection: Neuroscience's Journal
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Tuesday, April 15th, 2025
| Time |
Event |
| 4:42a |
Glia phagocytose neuronal sphingolipids to infiltrate developing synapses
The complex morphologies of mature neurons and glia emerge through profound rearrangements of cell membranes during development. Despite being integral components of these membranes, it is unclear whether lipids might actively sculpt these morphogenic processes. By analyzing lipid levels in the developing fruit fly brain, we discover dramatic increases in specific sphingolipids coinciding with neural circuit establishment. Disrupting this sphingolipid bolus via genetic perturbations of sphingolipid biosynthesis and catabolism leads to impaired glial autophagy. Remarkably, glia can obtain sphingolipid precursors needed for autophagy by phagocytosing neurons. These precursors are then converted into specific long-chain ceramide phosphoethanolamines (CPEs), invertebrate analogs of sphingomyelin. These lipids are essential for glia to arborize and infiltrate the brain, a critical step in circuit maturation that when disrupted leads to reduced synapse numbers. Taken together, our results demonstrate how spatiotemporal tuning of sphingolipid metabolism during development plays an instructive role in programming brain architecture.
HighlightsO_LIBrain sphingolipids (SLs) remodel during circuit maturation
C_LIO_LIGlial autophagy requires de novo SL biosynthesis coordinated across neurons and glia
C_LIO_LIGlia evade a biosynthetic blockade by phagolysosomal salvage of neuronal SLs
C_LIO_LICeramide Phosphoethanolamine is critical for glial infiltration and synapse density
C_LI | | 4:42a |
Modeling AP2M1 Developmental and Epileptic Encephalopathy in Drosophila
Genetic defects in AP2M1, which encodes the -subunit of the adaptor protein complex 2 (AP-2) essential for clathrin-mediated endocytosis (CME), cause a rare form of developmental and epileptic encephalopathy (DEE). In this study, we modeled AP2M1-DEE in Drosophila melanogaster to gain deeper insights into the underlying disease mechanisms. Pan-neuronal knock-down of the Drosophila AP2M1 ortholog, AP-2, resulted in a consistent heat-sensitive paralysis phenotype and altered morphology in class IV dendritic arborization (c4da) neurons. Unexpectedly, affected flies were resistant to antiseizure medications and exhibited increased resistance to electrically induced seizures. A CRISPR-engineered fly line carrying the recurrent human disease variant p.Arg170Trp displayed a milder seizure resistance phenotype. While these findings contrast with the human phenotype, they align with previous studies on other CME-related genes in Drosophila. Our results suggest that hyperexcitability and seizures in AP2M1-DEE may stem from broader defects in neuronal development rather than direct synaptic dysfunction. | | 4:42a |
CO2 sensitive connexin channel synapses in the VTA release 5HT to regulate dopaminergic neurons
It is now well established that the major mid-brain dopaminergic center, the ventral tegmental area (VTA), plays an important role in the control of sleep-wake state transitions, producing arousal from sleep states upon activation. We recently showed that the VTA may also be involved in producing arousal in response to hypercapnia, a key survival response. We found that connexin 26 (Cx26) CO2-sensitive hemichannels are expressed by VTA GABAergic neurons and modulate their excitability. Here we have extended our investigation of VTA chemosensing and have discovered additional novel mechanisms of CO2 neural signalling: connexin co-synapses. CO2-sensitive hemichannels are expressed on the cell bodies and the terminals of dorsal raphe (DR) serotonergic neurons that cluster around VTA TH+ dopaminergic neurons colocalizing both with the 5HT transporter SERT and with VGLUT3. Using pharmacological dissection and GRAB5-HT sensors, we showed that 5HT can permeate through open Cx26 hemichannels to modulate the excitability of VTA dopamine neurons. Brief elevations of pCO2 regulate dopaminergic neuron excitability via 5HT3 and 5HT2A/C receptors activation. Longer applications of raised pCO2 modulates HCN channel opening in response to hyperpolarizing current steps, an effect blocked by 5HT2 receptor antagonists. These effects of pCO2 can be blocked with the connexin inhibitor lanthanum. In vivo, CO2 challenge (hypercapnia) activates VTA neurons (including dopaminergic neurons), with the activation greatly reduced by the conditional knockdown of Cx26 expression in the VTA. We therefore propose that the VTA could play an important role in hypercapnic arousal with at least two distinct mechanisms of CO2 signalling: modulation of GABAergic neuron excitability via soma Cx26 hemichannels and channel-mediated release of 5HT via CO2 sensitive Cx26 co-synapses on DR nerve terminals that regulate the excitability of dopaminergic neurons. | | 6:19a |
Experience reorganizes content-specific memory traces in macaques
Memory formation requires neural activity reorganization during experience that persists in sleep. How these processes promote learning while preserving established memories remains unclear. We recorded neural ensemble activity from hippocampal and associated regions in freely moving macaques as they recalled item sequences presented that day ("new"), one day prior ("recent"), or over two weeks prior ("old"). Cell assemblies biased for old sequences showed less drift, greater network connectivity, and stronger sleep reactivation than new-biased assemblies. Pairs of old and recent assemblies formed persistent task-to-sleep coupling ("metassemblies"), unlike new assembly pairs. In the hippocampus, the propensity for superficial and deep CA1 pyramidal cells to form integrated assemblies increased with memory age. These findings reveal rapid organization and stabilization of neural activity in the primate brain, suggesting potential mechanisms for balancing learning with memory linking and durability. | | 9:45a |
Brain Diffusion Transformer for Personalized Neuroscience and Psychiatry
Task-fMRI analyses typically focus on localized activation contrasts between stimuli, neglecting the brains dynamic hierarchy. We introduce Brain Diffusion Transformer (Brain-DiT), a deep generative model capturing recurrent processing underlying individualized neurocognitive state transitions via functional networks. Without prior assumptions, Brain-DiT identifies canonical cognitive regions in the brain and reveals replicable subgroups with distinct neural circuits in large cohorts, offering critical clinical insights overlooked by traditional methods: individuals exhibiting negative emotion bias, linked to language-related regions, had a 12-fold higher likelihood of major depression, and those with maladaptive inhibition strategies, associated with overactive medial frontal regions, showed a 9-fold increased risk of alcohol abuse. By bridging cognitive theory and psychiatric applications, Brain-DiT provides a unified analytical paradigm, paving the way for operational personalized medicine in psychiatry. | | 5:47p |
Depth-resolved fiber photometry of amyloid plaque signals in freely behaving Alzheimer's disease mice
Alzheimers disease pathology typically manifests itself across multiple brain regions yet assessment at this scale in mouse models remains a challenge. This hinders the development of novel therapeutic approaches. Here we introduce a novel fiber photometry approach to monitor amyloid pathology in freely behaving mice. We first demonstrated that flat fiber-based photometry can detect amyloid signals across multiple brain regions under anesthesia after injecting a blood-brain barrier permeable tracer, Methoxy-X04. The depth profile of in vivo fluorescent signals was correlated with postmortem histological plaque signals. After confirming its feasibility ex vivo, we chronically implanted a tapered fiber for depth-resolved fiber photometry in freely behaving mice. After injecting Methoxy-X04, fluorescent signals increased in a depth-specific manner in Alzheimers mice, but not in wild-type littermates. While fiber photometry has been widely adopted to monitor neuronal and non-neuronal activity, our approach expands the capabilities to monitor molecular pathologies such as amyloid plaques, even in a freely behaving condition. | | 8:32p |
Advection versus diffusion in brain ventricular transport
Cerebrospinal fluid (CSF) is integral to brain function. CSF provides mechanical support for the brain and helps distribute nutrients, neurotransmitters and metabolites throughout the central nervous system. CSF flow is driven by several processes, including the beating of motile cilia located on the walls of the brain ventricles. Despite the physiological importance of CSF, the underlying mechanisms of CSF flow and solute transport in the brain ventricles remain to be comprehensively resolved. This study analyzes and evaluates specifically the role of motile cilia in CSF flow and transport. We developed finite element methods for modeling flow and transport using the geometry of the zebrafish larval brain ventricles, for which we have detailed knowledge of cilia properties and CSF motion. The computational model is validated by in vivo experiments that monitor transport of a photoconvertible protein secreted in the brain ventricles. Our results show that while cilia contribute to advection of large particles, diffusion plays a significant role in the transport of small solutes. We also demonstrate how cilia location and the geometry of the ventricular system impact solute distribution. Altogether, this work presents a computational framework that can be applied to other ventricular systems, together with new concepts of how molecules are transported within the brain and its ventricles. | | 8:32p |
Nucleus raphe magnus serotonin neurons bidirectionally control spinal mechanical pain transmission
The perception of pain as an alarm signal is primarily processed by nociceptive transmission from the dorsal horn of the spinal cord (DHSC) to the brain. Descending pathways from the brainstem dynamically modulate this process, either facilitating or inhibiting nociceptive information based on physiological, emotional, genetic and environmental factors. Among these pathways, serotonergic neurons of the nucleus raphe magnus (NRM) play a critical role in nociceptive modulation, though their precise mechanisms of action remain elusive. Here we aimed to resolve this longstanding question. We investigated NRM serotonergic modulation of pain using imaging, behavioral, pharmacological, electrophysiological, chemogenetic and optogenetic approaches. We discovered that NRM serotonin neurons mediate bidirectional effects on nociception depending on the pattern of activation. Brief optogenetic stimulation induced analgesia, whereas prolonged stimulation paradoxically led to hyperalgesia. Mechanistically, we identified spinal inhibitory interneurons as the principal targets of NRM serotonergic inputs, with three distinct receptor subtypes underpinning bidirectional modulation. Furthermore, our model explains heightened pain perception via pathological NRM serotonin neuron hyperexcitability acting at 5-HT3 receptors. Targeting the activity of serotonin neurons within physiological ranges represents a promising therapeutic strategy for managing pain and preventing its chronic exacerbation; a finding of significance considering the opioid-based treatment crisis. | | 8:32p |
FL/FLT3 signaling enhances mechanical pain hypersensitivity through Interleukin-1 beta (IL-1β) in male mice
Fms-like tyrosine kinase 3 (FLT3) plays a critical role in chronic pain through its ligand FL, a cytokine that triggers mechanical pain hypersensitivity. However, the underlying molecular mechanisms remain unclear. Here, we investigate the potential interplay between FL and IL-1{beta} a key cytokine in DRG neurons sensitization and mechanical hyperalgesia through both in vitro and in vivo approaches. ELISA assays reveal that intrathecal FL administration significantly increases IL-1{beta} protein levels in both the DRG and dorsal spinal cord of mice, beginning four hours post-injection. Using video microscopy and [Ca2+]i fluorescence imaging in primary DRG neuron cultures, we demonstrate that FL potentiation of TRPV1 receptor responses to capsaicin is partially mediated by IL-1{beta} signalling, as evidenced by a significant reduction in this potentiation in the presence of the IL-1 receptor antagonist, IL-1Ra. Furthermore, FLT3-driven acute mechanical pain hypersensitivity in vivo is reduced both by prior administration of IL-1Ra and in IL-1 receptor knockout mice. Importantly, IL-1{beta}-induced mechanical pain hypersensitivity remains independent of FLT3 signalling as shown in Flt3 knockout mice. Collectively our findings expand the understanding of neuro-immune interactions by demonstrating a potential functional link between FL/FLT3 and IL-1{beta}/IL-1R signalling in nociceptive processing.
HighlightsCytokines are known to engage in complex interactions and regulate each other
FL increases IL-1{beta} in DRG and DSC within 4h, but IL-1{beta} does not affect FL levels
FL modulates capsaicin-induced Ca2+ influx via IL-1{beta}/IL-1R signalling in DRG neurons
IL-1R inhibition delays or abolishes FL-induced mechanical hypersensitivity in vivo
Graphical abstract
O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=92 SRC="FIGDIR/small/648037v1_ufig1.gif" ALT="Figure 1">
View larger version (20K):
org.highwire.dtl.DTLVardef@88f251org.highwire.dtl.DTLVardef@dcb9a8org.highwire.dtl.DTLVardef@120c716org.highwire.dtl.DTLVardef@ee91a0_HPS_FORMAT_FIGEXP M_FIG The timeline of the experimental design and the graphical abstract were created with BioRender.com
C_FIG | | 8:32p |
Zebrafish optic nerve injury results in systemic retinal ganglion cell dedifferentiation
Retinal ganglion cells (RGCs) are the sole projection neurons connecting the retina to the brain and therefore play a critical role in vision. Death of RGCs during glaucoma, optic neuropathies and after ocular trauma results in irreversible loss of vision as RGCs do not regenerate in the human eye. Moreover, there are no FDA approved therapies that prevent RGC death and/or promote RGC survival in the diseased or injured eye. There is a critical need to better understand the molecular underpinnings of neuroprotection to develop effective therapeutic approaches to preserve damaged RGCs. Unlike in mammals, RGCs in zebrafish are resilient to optic nerve injury, even after complete transection of the optic nerve. Here, we leveraged this unique model and utilized single-cell RNA sequencing to characterize RGC responses to injury and identify putative neuroprotective and regenerative pathways. RGCs are heterogeneous and studies in mice have shown that there is differential resiliency across RGC subtypes. Our results demonstrated that all RGC subtypes are resilient to injury in zebrafish. Quantifying changes in gene expression revealed the upregulation of progenitor and regenerative markers in all RGC subtypes after injury as well as distinct early and late phases to the injury response. This shift in gene expression causes injury-responsive RGCs to resemble RGC subtype 3, a low frequency population of endogenous immature RGCs that are normally maintained in the wild-type, uninjured adult retina. A similar but restricted transcriptomic injury response in RGCs of the uninjured contralateral eye was also detected, highlighting a systemic RGC response to unilateral optic nerve injury. Taken together, these results demonstrate that zebrafish RGCs dedifferentiate in response to injury, and this may be a novel mechanism mediating their unique cell survival and regenerative capabilities.
Author SummaryRetinal ganglion cells (RGCs) connect the eye to the brain and are essential for vision. Their death in conditions like glaucoma, affecting over 70 million people worldwide, leads to permanent blindness, with no FDA-approved treatments to prevent it. Unlike mammals, zebrafish RGCs are resilient to optic nerve injury. In this study, we used next-generation sequencing technologies to characterize the RGC response to optic nerve injury at the single-cell level. We discovered that all zebrafish RGCs survive damage by temporarily shifting into a less mature state, resembling a rare population of immature RGCs found in uninjured animals. We identified many genes whose expression changes early or late in the injury response as well as a similar but restricted transcriptomic injury response in the uninjured contralateral RGCs, highlighting the systemic RGC response to optic nerve injury. This work is significant because our detailed characterization of RGC responses to optic nerve injury identifies dedifferentiation as an injury response, possibly important for cell survival and axon regrowth. The genes and pathways we identify are potential therapeutic targets to enable RGC survival in the injured or diseased human eye. |
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