Neurofibrillary tangle-bearing neurons have reduced risk of cell death in mice with Alzheimer's pathology

A prevailing hypothesis is that neurofibrillary tangles play a causal role in driving cognitive decline in Alzheimer's disease (AD) because tangles correlate anatomically with areas that undergo neuronal loss. We used two-photon longitudinal imaging to directly test this hypothesis and observed the fate of individual neurons in two mouse models. At any time point, neurons without tangles died at >3 times the rate as neurons with tangles. Additionally, prior to dying, they became >20% more distant from neighboring neurons across imaging sessions. Similar microstructural changes were evident in a population of non-tangle-bearing neurons in Alzheimer's donor tissues. Together, these data suggest that nonfibrillar tau puts neurons at high risk of death, and surprisingly, the presence of a tangle reduces this risk. Moreover, cortical microstructure changes appear to be a better predictor of imminent cell death than tangle status is and a promising tool for identifying dying neurons in Alzheimer's.

The lateral habenula integrates age and experience to promote social transitions in developing rats

Early caregiving adversity (ECA) is associated with social behavior deficits and later development of psychopathology. However, the infant neural substrates of ECA are poorly understood. The lateral habenula (LHb), a highly conserved brain region with consistent links to adult psychopathology, is understudied in development, when the brain is most vulnerable to environmental impacts. Here, we describe the structural and functional ontogeny of the LHb and its behavioral role in infant and juvenile rat pups. We show that the LHb promotes a developmental transition in social approach behavior under threat as typically reared infants mature. By contrast, we show that ECA disrupts habenular ontogeny, including volume, protein expression, firing properties, and corticohabenular connectivity. Furthermore, inhibiting a specific corticohabenular projection rescues infant social approach deficits following ECA. Together, these results identify immediate biomarkers of ECA in the LHb and highlight this region as a site of early social processing and behavior control.

Developmentally stable representations of naturalistic image structure in macaque visual cortex

To determine whether post-natal improvements in form vision result from changes in mid-level visual cortex, we studied neuronal and behavioral responses to texture stimuli that were matched in local spectral content but varied in "naturalistic" structure. We made longitudinal measurements of visual behavior from 16 to 95 weeks of age, and of neural responses from 20 to 56 weeks. We also measured behavioral and neural responses in near-adult animals more than 3 years old. Behavioral sensitivity reached half-maximum around 25 weeks of age, but neural sensitivities remained stable through all ages tested. Neural sensitivity to naturalistic structure was highest in V4, lower in V2 and inferotemporal cortex (IT), and barely discernible in V1. Our results show a dissociation between stable neural performance and improving behavioral performance, which may reflect improved processing capacity in circuits downstream of visual cortex.

Movement-related increases in subthalamic activity optimize locomotion

The subthalamic nucleus (STN) is traditionally thought to restrict movement. Lesion or prolonged STN inhibition increases movement vigor and propensity, while optogenetic excitation has opposing effects. However, STN neurons often exhibit movement-related increases in firing. To address this paradox, STN activity was recorded and manipulated in head-fixed mice at rest and during self-initiated and self-paced treadmill locomotion. We found that (1) most STN neurons (type 1) exhibit locomotion-dependent increases in activity, with half firing preferentially during the propulsive phase of the contralateral locomotor cycle; (2) a minority of STN neurons exhibit dips in activity or are uncorrelated with movement; (3) brief optogenetic inhibition of the lateral STN (where type 1 neurons are concentrated) slows and prematurely terminates locomotion; and (4) in Q175 Huntington's disease mice, abnormally brief, low-velocity locomotion is associated with type 1 hypoactivity. Together, these data argue that movement-related increases in STN activity contribute to optimal locomotor performance.

Widespread receptive field remapping in early primate visual cortex

Predictive remapping of receptive fields (RFs) is thought to be one of the critical mechanisms for enforcing perceptual stability during eye movements. While RF remapping has been observed in several cortical areas, its role in early visual cortex and its consequences on the tuning properties of neurons have been poorly understood. Here, we track remapping RFs in hundreds of neurons from visual area V2 while subjects perform a cued saccade task. We find that remapping is widespread in area V2 across neurons from all recorded cortical layers and cell types. Furthermore, our results suggest that remapping RFs not only maintain but also transiently enhance their feature selectivity due to untuned suppression. Taken together, these findings shed light on the dynamics and prevalence of remapping in the early visual cortex, forcing us to revise current models of perceptual stability during saccadic eye movements.

Ca2+-dependent phosphodiesterase 1 regulates the plasticity of striatal spiny projection neuron glutamatergic synapses

Long-term synaptic plasticity at glutamatergic synapses on striatal spiny projection neurons (SPNs) is central to learning goal-directed behaviors and habits. Our studies reveal that SPNs manifest a heterosynaptic, nitric oxide (NO)-dependent form of long-term postsynaptic depression of glutamatergic SPN synapses (NO-LTD) that is preferentially engaged at quiescent synapses. Plasticity is gated by Ca2+ entry through CaV1.3 Ca2+ channels and phosphodiesterase 1 (PDE1) activation, which blunts intracellular cyclic guanosine monophosphate (cGMP) and NO signaling. Both experimental and simulation studies suggest that this Ca2+-dependent regulation of PDE1 activity allows for local regulation of dendritic cGMP signaling. In a mouse model of Parkinson disease (PD), NO-LTD is absent because of impaired interneuronal NO release; re-balancing intrastriatal neuromodulatory signaling restores NO release and NO-LTD. Taken together, these studies provide important insights into the mechanisms governing NO-LTD in SPNs and its role in psychomotor disorders such as PD.

The chemokine Cxcl14 regulates interneuron differentiation in layer I of the somatosensory cortex

Spontaneous and sensory-evoked activity sculpts developing circuits. Yet, how these activity patterns intersect with cellular programs regulating the differentiation of neuronal subtypes is not well understood. Through electrophysiological and in vivo longitudinal analyses, we show that C-X-C motif chemokine ligand 14 (Cxcl14), a gene previously characterized for its association with tumor invasion, is expressed by single-bouquet cells (SBCs) in layer I (LI) of the somatosensory cortex during development. Sensory deprivation at neonatal stages markedly decreases Cxcl14 expression. Additionally, we report that loss of function of this gene leads to increased intrinsic excitability of SBCs-but not LI neurogliaform cells-and augments neuronal complexity. Furthermore, Cxcl14 loss impairs sensory map formation and compromises the in vivo recruitment of superficial interneurons by sensory inputs. These results indicate that Cxcl14 is required for LI differentiation and demonstrate the emergent role of chemokines as key players in cortical network development.

A hominoid-specific signaling axis regulating the tempo of synaptic maturation

Human cortical neurons (hCNs) exhibit high dendritic complexity and synaptic density, and the maturation process is greatly protracted. However, the molecular mechanism governing these specific features remains unclear. Here, we report that the hominoid-specific gene TBC1D3 promotes dendritic arborization and protracts the pace of synaptogenesis. Ablation of TBC1D3 in induced hCNs causes reduction of dendritic growth and precocious synaptic maturation. Forced expression of TBC1D3 in the mouse cortex protracts synaptic maturation while increasing dendritic growth. Mechanistically, TBC1D3 functions via interaction with MICAL1, a monooxygenase that mediates oxidation of actin filament. At the early stage of differentiation, the TBC1D3/MICAL1 interaction in the cytosol promotes dendritic growth via F-actin oxidation and enhanced actin dynamics. At late stages, TBC1D3 escorts MICAL1 into the nucleus and downregulates the expression of genes related with synaptic maturation through interaction with the chromatin remodeling factor ATRX. Thus, this study delineates the molecular mechanisms underlying human neuron development.

Pyruvate dehydrogenase complex E1 subunit α crotonylation modulates cocaine-associated memory through hippocampal neuron activation

Neuronal activation is required for the formation of drug-associated memory, which is critical for the development, persistence, and relapse of drug addiction. Nevertheless, the metabolic mechanisms underlying energy production for neuronal activation remain poorly understood. In the study, a large-scale proteomics analysis of lysine crotonylation (Kcr), a type of protein posttranslational modification (PTM), reveals that cocaine promoted protein Kcr in the hippocampal dorsal dentate gyrus (dDG). We find that Kcr is predominantly discovered in a few enzymes critical for mitochondrial energy metabolism; in particular, pyruvate dehydrogenase (PDH) complex E1 subunit α (PDHA1) is crotonylated at the lysine 39 (K39) residue through P300 catalysis. Crotonylated PDHA1 promotes pyruvate metabolism by activating PDH to increase ATP production, thus providing energy for hippocampal neuronal activation and promoting cocaine-associated memory recall. Our findings identify Kcr of PDHA1 as a PTM that promotes pyruvate metabolism to enhance neuronal activity for cocaine-associated memory.

Spontaneous and evoked synaptic vesicle release arises from a single releasable pool

The quantal content of an evoked postsynaptic response is typically determined by dividing it by the average spontaneous miniature response. However, this approach is challenged by the notion that different synaptic vesicle pools might drive spontaneous and evoked release. Here, we "silence" synaptic vesicles through pharmacological alkalinization and subsequently rescue them by optogenetic acidification. We find that such silenced synaptic vesicles, retrieved during evoked or spontaneous activity, cross-deplete the complementary release mode in a fully reversible manner. A fluorescently tagged version of the endosomal SNARE protein Vti1a, which has been suggested to identify a separate pool of spontaneously recycling synaptic vesicles, is trafficked to synaptic vesicles significantly only upon overexpression but not when endogenously tagged by CRISPR-Cas9. Thus, both release modes draw synaptic vesicles from the same readily releasable pool.

The versatile binding landscape of the TAAR1 pocket for LSD and other antipsychotic drug molecules

Increasing global concerns about psychoactive substance addiction and psychotic disorders highlight the need for comprehensive research into the structure-function relationship governing ligand recognition between these substances and their receptors in the brain. Recent studies indicate the significant involvement of trace amine-associated receptor 1 (TAAR1) in the signaling regulation of the hallucinogen lysergic acid diethylamide (LSD) and other antipsychotic drugs. This study presents structures of the TAAR1-Gs protein complex recognizing LSD, which exhibits a polypharmacological profile, and the partial agonist RO5263397, which is a drug candidate for schizophrenia and addiction. Moreover, we elucidate the cross-species recognition and partial activation mechanism for TAAR1, which holds promising implications from a drug discovery perspective. Through mutagenesis, functional studies, and molecular dynamics (MD) simulations, we provide a comprehensive understanding of a versatile TAAR1 pocket in recognizing various ligands as well as in the ligand-free state, underpinning the structural basis of its high adaptability. These findings offer valuable insights for the design of antipsychotic drugs.

Experience-dependent information routing through the basolateral amygdala shapes behavioral outcomes

It is well established that the basolateral amygdala (BLA) is an emotional processing hub that governs a diverse repertoire of behaviors. Selective engagement of a heterogeneous cell population in the BLA is thought to contribute to this flexibility in behavioral outcomes. However, whether this process is impacted by previous experiences that influence emotional processing remains unclear. Here we demonstrate that previous positive (enriched environment [EE]) or negative (chronic unpredictable stress [CUS]) experiences differentially influence the activity of populations of BLA principal neurons projecting to either the nucleus accumbens core or bed nucleus of the stria terminalis. Chemogenetic manipulation of these projection-specific neurons can mimic or occlude the effects of CUS and EE on behavioral outcomes to bidirectionally control avoidance behaviors and stress-induced helplessness. These data demonstrate that previous experiences influence the responsiveness of projection-specific BLA principal neurons, biasing information routing through the BLA, to drive divergent behavioral outcomes.

Comparative transcriptomic profiling reveals a role for Olig1 in promoting axon regeneration

The regenerative potential of injured axons displays considerable heterogeneity. However, the molecular mechanisms underlying the heterogeneity have not been fully elucidated. Here, we establish a method that can separate spinal motor neurons (spMNs) with low and high regenerative capacities and identify a set of transcripts revealing differential expression between two groups of neurons. Interestingly, oligodendrocyte transcription factor 1 (Olig1), which regulates the differentiation of various neuronal progenitors, exhibits recurrent expression in spMNs with enhanced regenerative capabilities. Furthermore, overexpression of Olig1 (Olig1 OE) facilitates axonal regeneration in various models, and down-regulation or deletion of Olig1 exhibits an opposite effect. By analyzing the overlapped differentially expressed genes after expressing individual Olig factor and functional validation, we find that the role of Olig1 is at least partially through the neurite extension factor 1 (Nrsn1). We therefore identify Olig1 as an intrinsic factor that promotes regenerative capacity of injured axons.

BDNF-TrkB signaling orchestrates the buildup process of local sleep

Sleep debt accumulates during wakefulness, leading to increased slow wave activity (SWA) during sleep, an encephalographic marker for sleep need. The use-dependent demands of prior wakefulness increase sleep SWA locally. However, the circuitry and molecular identity of this "local sleep" remain unclear. Using pharmacology and optogenetic perturbations together with transcriptomics, we find that cortical brain-derived neurotrophic factor (BDNF) regulates SWA via the activation of tyrosine kinase B (TrkB) receptor and cAMP-response element-binding protein (CREB). We map BDNF/TrkB-induced sleep SWA to layer 5 (L5) pyramidal neurons of the cortex, independent of neuronal firing per se. Using mathematical modeling, we here propose a model of how BDNF's effects on synaptic strength can increase SWA in ways not achieved through increased firing alone. Proteomic analysis further reveals that TrkB activation enriches ubiquitin and proteasome subunits. Together, our study reveals that local SWA control is mediated by BDNF-TrkB-CREB signaling in L5 excitatory cortical neurons.

miRNA-mediated inhibition of an actomyosin network in hippocampal pyramidal neurons restricts sociability in adult male mice

Social deficits are frequently observed in patients suffering from neurodevelopmental disorders, but the molecular mechanisms regulating sociability are still poorly understood. We recently reported that the loss of the microRNA (miRNA) cluster miR-379-410 leads to hypersocial behavior and anxiety in mice. Here, we show that ablating miR-379-410 in excitatory neurons of the postnatal mouse hippocampus recapitulates hypersociability, but not anxiety. At the cellular level, miR-379-410 loss in excitatory neurons leads to larger dendritic spines, increased excitatory synaptic transmission, and upregulation of an actomyosin gene network. Re-expression of three cluster miRNAs, as well as pharmacological inhibition of the actomyosin activator ROCK, is sufficient to reinstate normal sociability in miR-379-410 knockout mice. Several actomyosin genes and miR-379-410 family members are reciprocally dysregulated in isogenic human induced pluripotent stem cell (iPSC)-derived neurons harboring a deletion present in patients with Williams-Beuren syndrome, characterized by hypersocial behavior. Together, our results show an miRNA-actomyosin pathway involved in social behavior regulation.

Physiological characteristics of neurons in the mammillary bodies align with topographical organization of subicular inputs

The mammillary bodies (MBOs), a group of hypothalamic nuclei, play a pivotal role in memory formation and spatial navigation. They receive extensive inputs from the hippocampus through the fornix, but the physiological significance of these connections remains poorly understood. Damage to the MBOs is associated with various forms of anterograde amnesia. However, information about the physiological characteristics of the MBO is limited, primarily due to the limited number of studies that have directly monitored MBO activity along with population patterns of its upstream partners. Employing large-scale silicon probe recording in mice, we characterize MBO activity and its interaction with the subiculum across various brain states. We find that MBO cells are highly diverse in their relationship to theta, ripple, and slow oscillations. Several of the physiological features are inherited by the topographically organized inputs to MBO cells. Our study provides insights into the functional organization of the MBOs.

Alternating bilateral sensory stimulation alleviates alcohol-induced conditioned place preference via a superior colliculus-VTA circuit

Alcohol is the most widely used addictive substance, potentially leading to brain damage and genetic abnormalities. Despite its prevalence and associated risks, current treatments have yet to identify effective methods for reducing cravings and preventing relapse. In this study, we find that 4-Hz alternating bilateral sensory stimulation (ABS) effectively reduces ethanol-induced conditioned place preference (CPP) in male mice, while 4-Hz flash light does not exhibit therapeutic effects. Whole-brain c-Fos mapping demonstrates that 4-Hz ABS triggers notable activation in superior colliculus GABAergic neurons (SCGABA). SCGABA forms monosynaptic connections with ventral tegmental area dopaminergic neurons (VTADA), which is implicated in ethanol-induced CPP. Bidirectional chemogenetic manipulation of SC-VTA circuit either replicates or blocks the therapeutic effects of 4-Hz ABS on ethanol-induced CPP. These findings elucidate the role of SC-VTA circuit for alleviating ethanol-related CPP by 4-Hz ABS and point to a non-drug and non-invasive approach that might have potential for treating alcohol use disorder.

Probing multiplexed basal dendritic computations using two-photon 3D holographic uncaging

Basal dendrites of layer 5 cortical pyramidal neurons exhibit Na+ and N-methyl-D-aspartate receptor (NMDAR) regenerative spikes and are uniquely poised to influence somatic output. Nevertheless, due to technical limitations, how multibranch basal dendritic integration shapes and enables multiplexed barcoding of synaptic streams remains poorly mapped. Here, we combine 3D two-photon holographic transmitter uncaging, whole-cell dynamic clamp, and biophysical modeling to reveal how synchronously activated synapses (distributed and clustered) across multiple basal dendritic branches are multiplexed under quiescent and in vivo-like conditions. While dendritic regenerative Na+ spikes promote millisecond somatic spike precision, distributed synaptic inputs and NMDAR spikes regulate gain. These concomitantly occurring dendritic nonlinearities enable multiplexed information transfer amid an ongoing noisy background, including under back-propagating voltage resets, by barcoding the axo-somatic spike structure. Our results unveil a multibranch dendritic integration framework in which dendritic nonlinearities are critical for multiplexing different spatial-temporal synaptic input patterns, enabling optimal feature binding.

Emergent perceptual biases from state-space geometry in trained spiking recurrent neural networks

A stimulus held in working memory is perceived as contracted toward the average stimulus. This contraction bias has been extensively studied in psychophysics, but little is known about its origin from neural activity. By training recurrent networks of spiking neurons to discriminate temporal intervals, we explored the causes of this bias and how behavior relates to population firing activity. We found that the trained networks exhibited animal-like behavior. Various geometric features of neural trajectories in state space encoded warped representations of the durations of the first interval modulated by sensory history. Formulating a normative model, we showed that these representations conveyed a Bayesian estimate of the interval durations, thus relating activity and behavior. Importantly, our findings demonstrate that Bayesian computations already occur during the sensory phase of the first stimulus and persist throughout its maintenance in working memory, until the time of stimulus comparison.

Endoplasmic reticulum morphology regulation by RTN4 modulates neuronal regeneration by curbing luminal transport

Cell functions rely on intracellular transport systems distributing bioactive molecules with high spatiotemporal accuracy. The endoplasmic reticulum (ER) tubular network constitutes a system for delivering luminal solutes, including Ca2+, across the cell periphery. How the ER structure enables this nanofluidic transport system is unclear. Here, we show that ER membrane-localized reticulon 4 (RTN4/Nogo) is sufficient to impose neurite outgrowth inhibition in human cortical neurons while acting as an ER morphoregulator. Improving ER transport visualization methodologies combined with optogenetic Ca2+ dynamics imaging and in silico modeling, we observed that ER luminal transport is modulated by ER tubule narrowing and dilation, proportional to the amount of RTN4. Excess RTN4 limited ER luminal transport and Ca2+ release, while RTN4 elimination reversed the effects. The described morphoregulatory effect of RTN4 defines the capacity of the ER for peripheral Ca2+ delivery for physiological releases and thus may constitute a mechanism for controlling the (re)generation of neurites.

Excitatory and inhibitory synapses show a tight subcellular correlation that weakens over development

Neurons receive correlated levels of excitation and inhibition, a feature that is important for proper brain function. However, how this relationship between excitatory and inhibitory inputs is established during the dynamic period of circuit wiring remains unexplored. Using multiple techniques, including in utero electroporation, electron microscopy, and electrophysiology, we reveal a tight correlation in the distribution of excitatory and inhibitory synapses along the dendrites of developing CA1 hippocampal neurons. This correlation was present within short dendritic stretches (<20 μm) and, surprisingly, was most pronounced during early development, sharply declining with maturity. The tight matching between excitation and inhibition was unexpected, as inhibitory synapses lacked an active zone when formed and exhibited compromised evoked release. We propose that inhibitory synapses form as a stabilizing scaffold to counterbalance growing excitation levels. This relationship diminishes over time, suggesting a critical role for a subcellular balance in early neuronal function and circuit formation.

Neural manifolds in V1 change with top-down signals from V4 targeting the foveal region

High-dimensional brain activity is often organized into lower-dimensional neural manifolds. However, the neural manifolds of the visual cortex remain understudied. Here, we study large-scale multi-electrode electrophysiological recordings of macaque (Macaca mulatta) areas V1, V4, and DP with a high spatiotemporal resolution. We find that the population activity of V1 contains two separate neural manifolds, which correlate strongly with eye closure (eyes open/closed) and have distinct dimensionalities. Moreover, we find strong top-down signals from V4 to V1, particularly to the foveal region of V1, which are significantly stronger during the eyes-open periods. Finally, in silico simulations of a balanced spiking neuron network qualitatively reproduce the experimental findings. Taken together, our analyses and simulations suggest that top-down signals modulate the population activity of V1. We postulate that the top-down modulation during the eyes-open periods prepares V1 for fast and efficient visual responses, resulting in a type of visual stand-by state.

Astroglial networks control visual responses of superior collicular neurons and sensory-motor behavior

Astroglial networks closely interact with neuronal populations, but their functional contribution to neuronal representation of sensory information remains unexplored. The superior colliculus (SC) integrates multi-sensory information by generating distinct spatial patterns of neuronal functional responses to specific sensory stimulation. Here, we report that astrocytes from the mouse SC form extensive networks in the retinorecipient layer compared to visual cortex. This strong astroglial connectivity relies on high expression of gap-junction proteins. Genetic disruption of this connectivity functionally impairs SC retinotopic and orientation preference responses. These alterations are region specific, absent in primary visual cortex, and associated at the circuit level with a specific impairment of collicular neurons synaptic transmission. This has implications for SC-related visually induced innate behavior, as disrupting astroglial networks impairs light-evoked temporary arrest. Our results indicate that astroglial networks shape synaptic circuit activity underlying SC functional visual responses and play a crucial role in integrating visual cues to drive sensory-motor behavior.

An atlas of GPCRs in dopamine neurons: Identification of the free fatty acid receptor 4 as a regulator of food and water intake

Midbrain dopaminergic neurons (DANs) are subject to extensive metabotropic regulation, but the repertoire of G protein-coupled receptors (GPCRs) present in these neurons has not been mapped. Here, we isolate DANs from Dat-eGFP mice to generate a GPCR atlas by unbiased qPCR array expression analysis of 377 GPCRs. Combined with data mining of scRNA-seq databases, we identify multiple receptors in DAN subpopulations with 38 of these receptors representing the majority of transcripts. We identify 41 receptors expressed in midbrain DANs but not in non-DAN midbrain cells, including the free fatty acid receptor 4 (FFAR4). Functional expression of FFAR4 is validated by ex vivo Ca2+ imaging, and in vivo experiments support that FFAR4 negatively regulates food and water intake and bodyweight. In addition to providing a critical framework for understanding metabotropic DAN regulation, our data suggest fatty acid sensing by FFAR4 as a mechanism linking high-energy intake to the dopamine-reward pathway.

Retrograde adenosine/A2A receptor signaling facilitates excitatory synaptic transmission and seizures

Retrograde signaling at the synapse is a fundamental way by which neurons communicate and neuronal circuit function is fine-tuned upon activity. While long-term changes in neurotransmitter release commonly rely on retrograde signaling, the mechanisms remain poorly understood. Here, we identified adenosine/A2A receptor (A2AR) as a retrograde signaling pathway underlying presynaptic long-term potentiation (LTP) at a hippocampal excitatory circuit critically involved in memory and epilepsy. Transient burst activity of a single dentate granule cell induced LTP of mossy cell synaptic inputs, a BDNF/TrkB-dependent form of plasticity that facilitates seizures. Postsynaptic TrkB activation released adenosine from granule cells, uncovering a non-conventional BDNF/TrkB signaling mechanism. Moreover, presynaptic A2ARs were necessary and sufficient for LTP. Lastly, seizure induction released adenosine in a TrkB-dependent manner, while removing A2ARs or TrkB from the dentate gyrus had anti-convulsant effects. By mediating presynaptic LTP, adenosine/A2AR retrograde signaling may modulate dentate gyrus-dependent learning and promote epileptic activity.