Molecular Brain

The cerebellar nuclei form the main output structures of the cerebellum and are composed of a deeply conserved set of cell types. Two excitatory cell classes, Class-A and -B, are present in each cerebellar nucleus and mediate all excitatory output of the cerebellum. To provide genetic access to these cell types, here we identified Acan as a marker gene for Class-B cells and generated a knock-in Acan-P2A-Cre mouse line. We demonstrate that this Acan-Cre line selectively labels Class-B neurons in the cerebellar nuclei and validate its use in viral projection tracing. This new mouse line provides a valuable genetic tool to study cerebellar nuclei organization and function.

The hippocampal CA3 subfield is central to associative learning and memory consolidation. The principal cells of the CA3, pyramidal neurons, execute these functions by generating hypersynchronous bursts that feed forward to the CA1. Extensive recurrent collateral connections within the CA3 neuron population are crucial for the generation of this burst activity. Double C2 domain-containing protein (Doc2) and synaptotagmin 7 (Syt7) are high-affinity calcium sensors implicated in asynchronous synaptic vesicle (SV) release and in the exocytosis of dense-core vesicles (DCVs). Additionally, Doc2 is a sensor for miniature neurotransmission, whereas Syt7 is involved in synaptic facilitation and SV replenishment. Both Doc2 and Syt7 are expressed in the hippocampus, but their potential roles in spontaneous excitatory network activity remain unanswered. Using whole-cell recordings in disinhibited acute hippocampal slices obtained from juvenile Doc2- and Syt7- knockout (KO) mice (P15-21), we report increased CA3 burst generation without changes in spontaneous excitatory postsynaptic current (sEPSC) frequency or amplitude. Moreover, the intrinsic properties of CA3 pyramidal neurons, such as the resting membrane potential, firing rate and input resistance, are unchanged. We propose that this novel burst phenotype in Doc2- and Syt7- KO mice is unrelated to changes in SV release but might be mediated by changes in neuropeptide release from DCVs. Regardless of the underlying mechanisms, this work reveals that both proteins act to regulate network activity. The hippocampal CA3 subfield is central to associative learning and memory consolidation. The principal cells of the CA3, pyramidal neurons, execute these functions by generating hypersynchronous bursts that feed forward to the CA1. Extensive recurrent collateral connections within the CA3 neuron population are crucial for the generation of this burst activity. Double C2 domain-containing protein (Doc2) and synaptotagmin 7 (Syt7) are high-affinity calcium sensors implicated in asynchronous synaptic vesicle (SV) release and in the exocytosis of dense-core vesicles (DCVs). Additionally, Doc2 is a sensor for miniature neurotransmission, whereas Syt7 is involved in synaptic facilitation and SV replenishment. Both Doc2 and Syt7 are expressed in the hippocampus, but their potential roles in spontaneous excitatory network activity remain unanswered. Using whole-cell recordings in disinhibited acute hippocampal slices obtained from juvenile Doc2- and Syt7- knockout (KO) mice (P15-21), we report increased CA3 burst generation without changes in spontaneous excitatory postsynaptic current (sEPSC) frequency or amplitude. Moreover, the intrinsic properties of CA3 pyramidal neurons, such as the resting membrane potential, firing rate and input resistance, are unchanged. We propose that this novel burst phenotype in Doc2- and Syt7- KO mice is unrelated to changes in SV release but might be mediated by changes in neuropeptide release from DCVs. Regardless of the underlying mechanisms, this work reveals that both proteins act to regulate network activity.

Dopamine signaling through dopamine 1 receptors (D1R) and dopamine 2 receptors (D2R) regulates hippocampal synaptic plasticity underlying learning and memory, yet their subcellular localization within the hippocampus is unknown. Here we performed electron microscopic immunocytochemistry to elucidate the distribution of D1R and D2R in subregions of the mouse hippocampus. In CA1 and CA3 stratum radiatum (SR), D1R- and D2R-immunoreactivity was found primarily on pyramidal cell dendritic spines and unmyelinated axons, and to a lesser extent in axon terminals and glia. In both regions, D1R-labeled terminals formed predominantly asymmetric (excitatory-type) synapses on dendritic spines, whereas D2R-labeled terminals formed mainly symmetric (inhibitory-type) synapses on pyramidal cell dendritic shafts. In the dentate gyrus (DG) hilus, D1R-labeling was almost exclusively found in unmyelinated axons and glia. D2R immunoreactivity in the hilus similarly was present in unmyelinated axons and glia but was also detected in dendritic spines originating from mossy cells and in terminals forming symmetric synapses. These findings indicate that dopamine receptors are positioned to influence excitatory and inhibitory signaling in the murine hippocampus. As D1R and D2R exert opposing effects on neuronal signaling, their localization on pyramidal neuron compartments provides a structural substrate for bidirectional modulation of synaptic plasticity and pyramidal cell activity. In addition, the presence of D2Rs on inhibitory terminals contacting pyramidal neurons and hilar interneurons suggests a role in regulating inhibitory circuitry within the hippocampus.

CaMKII promoter is widely used to label and manipulate hippocampal pyramidal neurons via transgenic mouse lines or viral approaches. While it targets most excitatory neurons, a small subset remains unlabeled and often overlooked. We present an AAV-based strategy combined with CaMKII-driven Cre expression to access and study this remaining population. Furthermore, we provide a detailed protocol for in-house AAV production, targeted stereotaxic delivery, and functional validation of targeted neurons through slice electrophysiology and behavior. Graphical abstract O_FIG O_LINKSMALLFIG WIDTH=194 HEIGHT=200 SRC="FIGDIR/small/723440v1_ufig1.gif" ALT="Figure 1"> View larger version (50K): org.highwire.dtl.DTLVardef@3a31ccorg.highwire.dtl.DTLVardef@9b7e90org.highwire.dtl.DTLVardef@92297borg.highwire.dtl.DTLVardef@1e159eb_HPS_FORMAT_FIGEXP M_FIG C_FIG

Sleep spindles are rhythmic electroencephalographic signatures of non-rapid-eye-movement sleep. Their dysregulation has been implicated in several neuropsychiatric illnesses. Spindles have a characteristic waxing and waning shape, but the cellular and circuit mechanisms controlling their shape are not well understood. Recent but sparse research has implied that sleep spindle shape becomes abnormal in post-traumatic stress disorder (PTSD). PTSD patients have dysfunctional GABAA receptors in midline thalamic regions, areas involved in the orchestration of sleep spindles. We modelled this GABAA dysfunction within thalamocortical (TC) neurons using localized CRISPR-Cas9 technology to test the hypothesis that GABA dysfunction would dysregulate sleep spindle shape and cause symptoms of PTSD, in mouse model behavioral evaluations. We found sleep spindles were shorter and abnormally shaped, having lost their characteristic waxing and waning shape, in mice with GABAA receptor knock-down in TC neurons (TC-1KD). TC-1KD mice failed to recover from learned fearful reactions following an aversive stimulus. We tested this with a contextual fear conditioning paradigm using electric foot shocks. A control group with intact GABAA receptors successfully habituated to the fear conditioned location in subsequent visits to that context without foot shocks. In contrast, TC-1KD mice never habituated, suggesting abnormally extended fearful memories. The number of inhibitory post synaptic currents in TC neurons were significantly decreased in vitro, confirming an effective knock-down. Our results imply that abnormally shaped sleep spindles may serve as a biomarker of GABAA receptor dysfunction in TC neurons which may be involved in abnormal fear processing in PTSD. We postulate GABAA receptor dysfunction in TC neurons may be underlying pathophysiology of PTSD and our findings here may inspire the development of screens, diagnostics and objective characteristics of stress related disorders, including PTSD.

Lack of social interaction results in various behavioral abnormalities in rodents, including increased anxiety levels, altered sociability, and impaired cognitive ability. Epigenetic factors regulate gene expression, however, how they contribute to juvenile social isolation (jSI)-induced behavioral alterations remains largely unknown. Here, we focused on the nucleus accumbens (NAc), a critical brain region of the reward system that regulates motivation-related behaviors. We first performed RNA-seq on neuronal nuclei and found alterations in genes related to neuronal function, as well as in transcriptional and epigenetic regulation. Protein-protein interaction (PPI) analysis of differentially expressed genes (DEGs) showed that top key nodes among down-regulated genes include membrane receptors (Ntrk2, Grin3a, and Grik1) and an apoptosis regulator (Bcl2). To further investigate whether jSI-induced gene expression alterations are mediated by histone modifications, we next performed CUT&Tag for four histone modifications (H3K4me1, H3K4me3, H3K27ac, and H3K27me3), and the results implied that epigenetic alterations may also play a role in neuronal function as well as transcriptional regulation. Reanalysis of previously published RNA-seq data on the manipulation of histone modification-associated factors (including Kdm6b, Brd4, and Setd1a) suggested that these enzymes were probably involved in jSI-induced gene expression alterations. Taken together, our comprehensive analysis implies the involvement of histone modification regulation in jSI-related alterations of gene expression in NAc.

The glutamate delta 1 receptor (GluD1) represents a unique subtype of ionotropic glutamate receptors that is strongly expressed in the mammalian striatum. Disruptions of the GRID1 gene, which encodes GluD1, have been associated with neuropsychiatric disorders, including schizophrenia and autism spectrum disorder; however, the role of GluD1 in the brain remains poorly understood. Previous studies in mice have demonstrated that the knockout of striatal GluD1 led to fear-conditioning deficits and depressive-like behaviors. Furthermore, these mice exhibited reduced excitatory input to the striatum due to a loss of thalamostriatal innervation, whereas corticostriatal innervation was unaffected. In this study, we examined whether changes in synapse morphology contribute to the observed functional deficits. We found that the ablation of GluD1 does not affect synaptic targeting patterns of corticostriatal and thalamostriatal terminals, using transmission electron microscopy. We further utilized three-dimensional reconstruction to obtain quantitative data on synapse ultrastructure and found no significant changes in corticostriatal and thalamostriatal synaptic components, including the presynaptic terminal volume, postsynaptic density area and morphology, and postsynaptic dendritic spine volume. These findings support a model in which GluD1 regulates input-specific circuit organization and synaptic connectivity rather than the structural morphology of individual synapses.

Cav1.2 is an L-type voltage-gated Ca2+ channel (VGCC) that supports Ca2+ influx in response to membrane depolarization. Ca2+ entering via Cav1.2 alters gene expression, activates Ca2+-dependent enzymes and has been implicated in synaptic plasticity. ORL-1 is a Gi/o-coupled G protein-coupled receptor (GPCR) that is expressed in the peripheral and central nervous systems. Both Cav1.2 and ORL-1 are expressed in the hippocampus, where they have been implicated in learning and memory. It is well-documented that ORL-1 interacts with another VGCC, Cav2.2. However, less is known about potential interactions between Cav1.2 and ORL-1. Here, we examine the interplay between Cav1.2 (Cav1c, Cav2{delta}-1, Cav{beta}1) and ORL-1 co-expressed in tsA-201 cells by using biochemical, electrophysiological and confocal imaging analysis. Co-immunoprecipitations revealed that ORL-1 independently interacts with Cav1c and Cav2{delta}-1 subunits of the Cav1.2 channel complex. Electrophysiological recordings revealed that co-expression with ORL-1 reduced Cav1.2 peak current density without altering its biophysical properties. Acute perfusion with the ORL-1 receptor agonist nociceptin (1 M) did not alter Cav1.2 current density. Confocal imaging experiments revealed that ORL-1 significantly decreases Cav1.2 plasma membrane expression by disrupting forward trafficking. Interestingly, ORL-1 did not affect Cav1.2 endocytosis. Overall, our results demonstrate a previously unrecognized interaction between ORL-1 and Cav1.2 that alters Cav1.2 membrane expression without affecting biophysical properties.

Sleep consolidates episodic memory through a hippocampus-dependent process in adults. Whether and how sleep supports memory consolidation during early life, when hippocampal function is immature, remains unclear. Here, we examined effects of sleep on the consolidation of spatial context, a core component of episodic memory, in toddlers aged 2 -3 years. Toddlers were familiarized with two spatial contexts, followed by a [~]90-min nap or an equivalent wake period. Afterwards, with a hide-and-seek game we tested their ability to relocate toys within these contexts. Only after post-familiarization sleep, the toddlers showed significant context memory and formed stronger associations between toys and specific contexts compared to wakefulness. Contextual memory was positively correlated with spindle density and slow oscillation-spindle phase-amplitude coupling during non-rapid eye movement (NonREM) sleep. Despite hippocampal immaturity, the sleeping toddlers brain seems to engage consolidation processes similar to those in adults to form spatial context memory for the flexible use in novel situations.

Hippocampal area CA2 has recently emerged as a critical region for social recognition memory. Furthermore, this understudied region has been implicated in psychiatric diseases and neurodegenerative diseases. There has been accumulating evidence indicating that the pyramidal neurons (PNs) in area CA2 exhibit functional specializations that correlate with somatic position in stratum pyramidale (sp). In this study, we investigated the morphological differences in dendritic architecture of CA2 PNs with a focus on the radial gradient, i.e., along the deep-superficial axis of the sp. We conducted a comprehensive morphological analysis including Sholl intersection profiles, branching order distributions, root angle distributions, and dendritic cable lengths. We found that CA2 PNs have fewer oblique dendrites and a larger number of tuft-like dendrites as compared to CA1 PNs. Furthermore, within the CA2 population, we found that many of the dendritic structural features gradually changed along the radial axis from deep to superficial somatic location, indicating a continuum of dendritic morphology rather than two sharply defined subtypes of pyramidal neurons. This morphological characterization may serve as a starting point to better understand the corresponding functional organization of CA2. The gradual difference between deeper and superficial CA2 PNs suggests a continuum of their computational capabilities beyond two binary functional classes. In briefUsing several methods, we examine the dendritic morphology of over 130 CA2 and CA1 pyramidal neurons and find that many properties such as the cable length and terminal numbers of the dendritic arbors vary as a with the location of the soma in the pyramidal layer. HighlightsO_LIWe use scholl analysis, graph theory and machine learning techniques to quantify the different dendritic morphologies of CA2 pyramidal neurons. C_LIO_LIMany properties of CA2 pyramidal neuron apical dendrites vary as a function of somatic location in the pyramidal layer. C_LIO_LIMore superficial CA2 pyramidal neurons have longer oblique apical dendrites, and shorter tuft dendrites. C_LI

Stress during critical developmental periods causes lasting neurobiological alterations. Rodent models like neonatal maternal separation (NMS) induce cognitive alterations, particularly spatial memory deficits. Oxytocin (OT) system has been suggested to underlie these consequences, as it is critical for neurodevelopment. This neuropeptide also promotes maternal nurturing, prevents neuroinflammation and displays anxiolytic properties. This study hypothesized that early postnatal OT administration could prevent NMS-induced memory alterations in adult rats. Sprague-Dawley rat pups (both sexes, n=8-12/group) underwent NMS with concomitant intraperitoneal OT injections. At adulthood, novel object recognition and object location tasks were performed. Further investigation was conducted through ex vivo electrophysiological recordings of functional plasticity at Schaffer collateral-CA1 synapses (male, n=7-12/group), alongside RT-qPCR of synaptic, GABAergic, neuro-inflammatory, and oxytocin receptor markers in dorsal CA1 (male, n=4-6/group). NMS induced male-specific spatial memory impairment without affecting recognition memory. Early OT completely prevented spatial memory deficits in NMS males. Electrophysiological recordings revealed that NMS suppressed CA1 long-term potentiation (LTP), and neonatal OT restored it. NMS induced transcript overexpression of neuro-inflammatory markers, GABAergic markers, and synaptic proteins in dorsal CA1. OT treatment normalized or reduced these mRNA expressions, consistent with restoration of CA1 synaptic function. Early postnatal OT prevents NMS-induced spatial memory deficits and hippocampal LTP impairments in male rats, which is associated with normalized or reduced neuro-inflammatory and GABAergic transcript expressions. These findings establish exogenous oxytocin administration during a critical neonatal window as sufficient to prevent male-specific hippocampal dysfunction and cognitive deficits induced by early-life stress, identifying the oxytocinergic system as a promising target for early neuroprotective interventions.

The cerebellum is one of the most complex structures of the brain composed of a high diversity of GABAergic and glutamatergic neurons. Whereas cerebellar biogenesis has been extensively studied in the mouse, an in-depth characterization of genes and pathways involved in cerebellar specification and maturation in the humans remains overlooked. Here, we used human pluripotent stem cells (hPSC)-derived cerebellar organoids (CRBOs) to study the temporal biogenesis of neuronal subtypes. Our results show that CRBOs acquire caudal neural tube identity at an early stage followed by a time-dependent expression of mature cerebellar neuronal markers in vitro, mimicking human neurodevelopment. CRBOs show the generation of both cerebellar excitatory and inhibitory neurons and the expression of glial cell markers, suggesting the generation of a high variety of cerebellar cell types in vitro. Further, in vitro CRBOs show expression of cerebellar disease associated genes, such as those related to ataxia. Our results establish CRBOs as a valuable platform to explore the mechanisms of human cerebellar development and related disorders.

D-Aspartate (D-Asp) is an endogenous D-amino acid that exhibits a pronounced developmental peak in the mammalian brain, suggesting a potential regulatory role in glutamatergic signaling and neurodevelopment. Disruption of D-Asp homeostasis has been associated with neuropsychiatric disorders characterized by early-life circuit vulnerability, including schizophrenia and autism spectrum disorders. However, its functional impact to hippocampal physiology remains incompletely defined. Here, we investigated how constitutive D-Asp depletion affects synaptic function in the hippocampal CA1 region of Ddo-knock-in (Ddo-KI) mice, in which zygotic overexpression of the D-Asp-degrading enzyme, D-aspartate oxidase (DASPO), results in embryonic and persistent D-Asp deficiency. Electrophysiological recordings were performed in acute hippocampal slices from male and female mice at postnatal day 30 (P30) and day 60 (P60). Basal synaptic transmission, assessed through paired-pulse ratio and spontaneous excitatory/inhibitory events, was unaltered between genotypes, indicating preserved presynaptic release probability and overall excitation/inhibition balance. In contrast, NMDA receptor (NMDAR)-dependent synaptic plasticity was selectively altered, as theta-burst stimulation induced significantly greater long-term potentiation (LTP) in juvenile P30 Ddo-KI mice, whereas this difference was no longer observed at P60. Consistently, patch-clamp recordings revealed a reduced AMPAR/NMDAR ratio in P30 Ddo-KI males, suggesting an increased relative contribution of NMDAR-mediated currents. Importantly, acute bath application of exogenous D-Asp restored LTP to wild-type levels, demonstrating rapid reversibility and supporting a model of homeostatic receptor rebalancing rather than irreversible circuit alterations. Biochemical assays confirmed significantly increased DASPO activity and reduced D-Asp levels in Ddo-KI mice. However, these parameters remained stable between P30 and P60, indicating that the age-dependent plasticity phenotype is unlikely to arise from progressive biochemical changes. Together, these findings indicate that developmental D-Asp deficiency induces a transient, juvenile-specific alteration characterized by enhanced NMDAR-dependent synaptic plasticity, which can be rapidly normalized upon D-Asp re-exposure.

Astrocytes contain cell-autonomous circadian clocks, but how astrocyte-enriched clock-controlled genes feed back onto the circadian clock remains poorly understood. Here, we identify transmembrane protein 44 (Tmem44) as an astrocyte-enriched circadian transcript whose protein product regulates clock protein abundance through translational control. Tmem44 mRNA oscillated in cultured mouse cortical astrocytes in a BMAL1-dependent manner, whereas TMEM44 protein was constitutively expressed and localized to the endoplasmic reticulum. Acute Tmem44 knockdown reduced BMAL1 and PER2 protein levels without altering their mRNA levels or degradation kinetics, and dampened the amplitude and advanced the phase of Per2-luciferase circadian rhythms. SUnSET assays revealed that Tmem44 knockdown decreased global nascent protein synthesis. Proximity labeling and co-immunoprecipitation further showed that TMEM44 associates with ribosomal proteins and ER-associated translational machinery. Importantly, global protein synthesis exhibited circadian oscillation in synchronized astrocytes, and this rhythmic translation was abolished by Tmem44 knockdown. These findings identify TMEM44 as an astrocyte-enriched, ER-resident translational regulator that supports rhythmic protein synthesis and sustains proper amplitude and phase of the astrocyte circadian clock.

Cystatin-related epididymal spermatogenic (CRES) is a member of a reproductive subgroup of family 2 cystatins and part of a functional amyloid-containing extracellular matrix (ECM) with host defense functions in the epididymal lumen. CRES and the endogenous epididymal amyloid matrix exhibit high plasticity, forming distinct amyloid structures, with antimicrobial functions tailored to specific bacterial strains. We recently demonstrated that CRES/CRES amyloid is also present in the mammalian brain ECM. In this study, we utilized a CRES knockout (KO) mouse model to determine if the loss of CRES altered the structure of the hippocampal and cortical ECM and impacted brain function. We report that CRES KO male and female mice exhibited sex-specific structural changes in both the loose/interstitial and perineuronal net (PNN) ECM. Additionally, young CRES KO males--but not females--displayed deficits in learning, memory and executive functioning when compared to WT controls. In contrast, older CRES KO males did not exhibit behavioral deficits, a finding that correlated with the observation of a similar PNN ECM structure when compared to WT mice. Our data suggest that CRES functions as a regulatory or structural component of the brain ECM, contributing to its sex-specific structural organization and plasticity, affecting sex-specific behaviors of learning and memory.

Protein kinases are important regulators of sleep in animals, but their loss-of-function mutations usually show moderate phenotypes. We report here that sucrose non-fermenting related kinase (SNRK), a member of the AMP-activated protein kinase-related kinase (ARK) family, plays an essential role in sleep regulation: Snrk gene knockout resulted in a profound loss of night-time sleep phenotype, much stronger than that of the well-known ARK member Sik3. This phenotype was completely rescued by neuronal SNRK expression. SNRK in adulthood was required for sleep. Catalytic and regulatory sites in SNRK were important for sleep. A chemoconnectomic (CCT) screen revealed SNRK functioning in cholinergic neurons whose activation is known to inhibit sleep. Sleep loss in SNRK mutants was rescued by pharmacological blockade of nicotinic acetylcholine receptors. Our findings have uncovered a fundamental role for SNRK in cholinergic neurons to regulate sleep.

The hippocampus and its projection targets constitute hippocampal output circuits that are essential for memory, navigation, and emotional regulation. Although cortical and subcortical regions receiving hippocampal projections have been well characterized, it remains unclear how hippocampal signals are processed within these projection target regions. To precisely understand information processing in hippocampal output circuits, it is therefore important to gain genetic access to neuronal subpopulations receiving direct hippocampal inputs for structural and functional analyses. Anterograde transsynaptic transduction using adeno-associated virus (AAV) serotype 1 has emerged as a powerful approach for targeting postsynaptic neurons, but its application is limited by unintended retrograde transport, which leads to false-positive labeling in reciprocally connected circuits. Here, we developed a direction-selective anterograde transsynaptic transduction by combining AAV vectors with distinct infection properties and an intersectional gene expression system. Using the hippocampal-entorhinal circuit, we identified an optimal viral combination that enables predominantly anterograde transsynaptic labeling. We further applied this method to map hippocampal projections to reciprocally connected regions, including the amygdala, providing a robust approach for dissecting complex hippocampal output circuits.

The hippocampus participates in crucial functions such as memory consolidation, spatial processing and emotional regulation that require diverse input from multiple cortical areas that is funneled through the upper layers of the entorhinal cortex (EC), mostly from layer II to the dentate gyrus (DG). Traditional models described 200,000 EC layer II neurons projecting to 1 million granule cells (GCs) in the rat, rendering low divergence (1:5), with each EC neuron establishing about 18,000 synapses with GCs and each GC receiving about 4,000 synapses from EC neurons. In this manuscript, we update this model of connectivity incorporating new features described in the last three decades that include updated populations of EC layer II neurons obtained with design-based stereology, a revised definition of EC layer II based on molecular criteria and selecting reelin expressing neurons as the only layer II neurons projecting to the hippocampus. The updated model shows [~]80,000 neurons from EC layer II projecting to the DG, [~]45,000 from the medial entorhinal cortex (MEC) and [~]35,000 from the lateral entorhinal cortex (LEC) with high divergence of 1:20 and 1:30. We also show that EC layer II neurons may establish [~]90,000-115,000 synapses on GCs, while GCs receive about 8,000 synapses from EC layer II neurons. We estimate a [~]25% redundancy in the connectivity, so each EC neuron may contact [~]68,000-86,000 GCs and each GC would be contacted by [~]3000 neurons from MEC and 3,000 from LEC. In addition, we quantitatively assess a potential projection of mossy cells to the medial molecular layer described in mice, which could have a potential impact on GC inhibition. Overall, we produced a detailed, complete, and updated quantitative model of EC projections to the DG that reveals a much more divergent and richer projection than previously described, with implications for functional models (e.g.: pattern separation) and more widely for building realistic hippocampal models or establishing comparisons across species.

Long-term potentiation (LTP) is a key cellular mechanism underlying learning and memory, but its conservation across species remains unclear. Using nonhuman primates (NHPs), we examined hippocampal synaptic plasticity at Schaffer collateral- CA1 synapses. Theta-burst stimulation (TBS) reliably induced LTP in NHPs, comparable to rodents. However, unlike rodents, TBS in NHPs readily engaged synaptic tagging and capture (STC), indicating a lower threshold for associative plasticity. This was accompanied by increased expression of plasticity-related proteins, including PKM{zeta} and BDNF, suggesting enhanced recruitment of protein synthesisdependent stabilization mechanisms. These findings reveal a species-specific divergence in the molecular regulation of persistent synaptic plasticity and identify an evolutionary specialization in mechanisms supporting associative memory. Together, our results highlight limitations of rodent models in fully capturing human-relevant memory processes and underscore the importance of primate systems for translational neuroscience.

Sleep disturbances are common among individuals with schizophrenia and can exacerbate disruptions in cognitive processes like learning and memory. Elucidating pharmacologically targetable molecular pathways perturbed by schizophrenia genes may uncover new treatment avenues. Here, we investigated the relationship of the schizophrenia-associated gene znf804a with sleep and circadian pathways. Using multi-day behavior tracking, we showed that znf804a zebrafish mutants displayed changes in sleep and circadian behaviors when light cues were removed. Through bulk RNA sequencing of fish raised under normal light cycling and dark-only conditions, we identified altered gene expression in the core and auxiliary pathways controlling circadian rhythms. Expression of fbxl3a, which encodes a modulator of the core negative feedback regulator of the clock, decreased in a dose-dependent manner as znf804a mutant copy number increased. Further analysis also revealed shifts in the relative abundance of specific transcripts, including idh1, suggesting znf804a could influence transcript processing or stability. Together, these findings link a ZNF804A ortholog to sleep and circadian behaviors and identify the regulation of fbxl3a and transcript processing as candidate mechanisms through which this schizophrenia risk gene may influence circadian biology.