Autistic traits may arise from atypical sensory experience during postnatal life, but whether there is a causal link between defects in cortical circuitry in the brain, altered sensory processing and social behavior remains unknown. Here, we studied tactile stimuli processing in the barrel cortex (BC) and social interactions in juvenile male mice lacking Cyclin-dependent kinase-like 5 (CDKL5), a model of a severe neurodevelopmental disease showing autistic traits and sensory impairments. We identified in these mice defects of whisker-dependent postnatal sensorimotor reflexes, NMDA receptors-dependent signaling, and dendritic orientation in thalamic inputs-receiving spiny stellate neurons. We also found that CDKL5 is required for mapping and processing whisker-derived tactile stimuli in the BC. Intriguingly, KO mice show autistic traits at P21 that are ameliorated by neonatal CDKL5 replacement in the BC. Our data suggest that CDKL5 is required to link tactile processing in the BC to the onset of social interaction abilities.

Emotional contagion (ECo) represents a fundamental form of empathy. In this study, we used pupillometry to quantify ECo by assessing pupil responses of a mouse watching another mouse receive a tail shock. Pupil dilation effectively measured both direct and vicarious emotional response thresholds at the individual level through psychometric curve analysis. The pupillary ECo response diminished when the observer could not see the demonstrator, suggesting a multisensory process involving vision. Viewing videos of tail-shocked mice elicited a pupil response in the observer. Brain-wide c-Fos mapping revealed a broad network of 88 brain regions activated during ECo, with all areas activated in the demonstrator also engaged in the observer. Additionally, in some brain regions, correlated activation was detected between each observer-demonstrator pair, indicating that ECo promotes a shared neural state. These findings advance our understanding of the neural basis of shared emotions, with implications for analyzing neuropsychiatric disorder models.

MicroRNAs are key regulators of brain gene expression, with miR-29 family notably upregulated from development to adulthood and in aging, and showing links to cognitive decline. However, the extent to which miR-29 levels influence learning and memory processes, and its molecular mediators, remains to be determined. Here, we down- and up-regulated miR-29 levels in the dorsal hippocampus of adult mice to reveal miR-29 role in memory. Inhibition of miR-29 enhanced trace fear memory stability, increased Dnmt3a levels, and promoted DNA methylation in a DNMT3a-dependent manner. In contrast, increasing miR-29 impaired memory performances and decreased Dnmt3a levels, suggesting a destabilization of memory processes. Proteomic and transcriptomic analysis demonstrated that miR-29 antagonism upregulated RNA-binding and synaptic proteins and downregulated inflammation and myelin associated proteins. These results underscore miR-29’s pivotal role in memory persistence, plasticity, and cognitive aging, suggesting that miR-29 modulation could offer potential strategies for cognitive enhancement and age-related memory decline.

Psychedelics have emerged as powerful modulators of neural plasticity, yet whether the atypical psychedelic ibogaine can enhance plasticity remains poorly understood. Here, we investigated whether a single administration of ibogaine can reinstate juvenile-like experience-dependent plasticity in the adult mouse visual cortex, a canonical model for studying neuroplasticity. Adult mice were treated with ibogaine (40 mg/kg, i.p.) or vehicle, and 24 h later subjected to 4 days of monocular deprivation (MD). Behavioral visual acuity was quantified using the optomotor response test, and structural plasticity was assessed through dendritic spine density analysis following Golgi staining. Ibogaine alone did not alter visual acuity or dendritic spine density in non-deprived adults. However, when coupled with MD, ibogaine restored youthful levels of plasticity: MD significantly reduced visual acuity in the deprived eye and decreased dendritic spine density in the binocular visual cortex of ibogaine-treated, but not vehicle-treated, adult mice. To examine mechanistic correlates of these findings, we quantified perineuronal nets (PNNs), parvalbumin-positive interneurons (PVs), and inhibitory synaptic puncta labeled with the vesicular GABA transporter (vGAT). We found that ibogaine reduced PNN and PV staining intensity and density, decreased the proportion of PVs enwrapped by PNNs, and lowered vGAT-positive puncta density. These results show that ibogaine re-establishes experience-dependent plasticity in the adult visual cortex and that this effect is accompanied by reductions in structural and inhibitory “brakes” on plasticity. Our findings suggest that ibogaine’s long-lasting therapeutic actions can arise, at least partially, from its ability to re-open windows of heightened cortical adaptability.

Abstract Memory is proposed to depend on neuronal ensembles distributed across multiple brain regions, yet how episodic-like memories are organized across the brain remains unclear. Here we investigated the brain-wide organization of object-place-context (OPC) memory in mice. By mapping c-Fos activation across the brain during memory recall and comparing it to multiple control conditions, we identified a set of brain regions selectively engaged during episodic-like memory retrieval, consistent with the recruitment of a fronto-posterior medial network. Chemogenetic manipulation of learning-activated neuronal ensembles revealed that the selected brain regions are necessary for memory retrieval. Within this network, the retrosplenial cortex emerged as a key region required for successful memory recall, with neuronal ensembles exhibiting properties of engram cells. Electrophysiological recordings during recall revealed distinct novelty-related dynamics across regions. In mPFC, theta power increased during novel exploration, while firing rate increased both immediately before and during interaction with the novel object configuration. In RSP, novelty was associated with a sharp increase in firing rate during exploration. Together, our findings suggest a distributed organization supporting episodic-like memory retrieval in mice, in which a posterior-medial network is activated and necessary for a successful behavioral expression.

Perineuronal nets (PNNs) are specialized, dense extracellular matrix structures that enmesh the cell bodies and dendrites of specific neurons, most notably inhibitory interneurons. Increasing evidence indicates that PNNs serve not merely as passive scaffolds but play an active and essential role in modulating synaptic plasticity and circuit physiology. They critically influence the timing of sensory system critical periods, as well as processes underlying learning, memory, and higher cognitive functions. Furthermore, dysregulation of PNN density and architecture have been associated with conditions like autism, neurodevelopmental disorders, schizophrenia and Alzheimer's disease. Since they are extensively involved in brain function, we discuss the multitude of regulatory factors that govern the formation, maturation, and remodeling of PNNs. In particular, we focus on both molecular and cellular brain-intrinsic mechanisms, highlighting the potential contributions of microglia and astrocyte derived factors. Additionally, we consider the influence of long-range signaling cues, including the metabolic status and peripheral hormones. Analysing this complex network of interactors, we try to highlight the role of PNNs beyond neural plasticity and brain function, in a broader whole-body physiological perspective.

The huge complexity of neuronal circuits arises from a temporarily overlapped influence of genetic and environmental factors (Nature and Nurture). During specific temporal windows of postnatal development, the so-called critical or sensitive periods of plasticity, the brain is particularly susceptible to the effects of experience, though this sensitivity declines with age. The most widely used experimental paradigm for studying critical periods of plasticity is the ocular dominance model in the mammalian visual cortex. Recent advancements in large-scale methodological approaches have enabled the analysis of the cellular and molecular factors regulating plasticity, highlighting the complex interaction among various metabolic and regulatory pathways. Traditionally, genomic and transcriptomic techniques have been employed to investigate the Central Nervous System in a comprehensive manner, including studies on critical period plasticity in the visual cortex. However, it is the technical advancements in proteomic approaches that have established neuroproteomics as a powerful tool for investigating both normal and pathological brain states. Despite its potential, proteomics has been underutilized in studying visual cortical plasticity. Here, we review existing studies and emphasize the importance of exploiting neuroproteomics, and of integrating with other complementary "omic" approaches, to accurately identify the true active cellular agents and ultimate mediators of brain functions.

Cyclin-dependent kinase-like 5 (CDKL5) deficiency disorder (CDD) is a rare neurodevelopmental disorder often associated with gastrointestinal (GI) issues and subclinical immune dysregulation, suggesting a link to the gut microbiota. We analyze the fecal microbiota composition in two CDKL5 knockout (KO) mouse models at postnatal days (P) 25, 32 (youth), and 70 (adulthood), revealing significant microbial imbalances, particularly during juvenile stages. To investigate the role of the intestinal microbiota in CDD and assess causality, we administer antibiotics, which lead to improved visual cortical responses and reduce hyperactivity. Additionally, microglia morphology changes, indicative of altered surveillance and activation states, are reversed. Strikingly, fecal transplantation from CDKL5 KO to wild-type (WT) recipient mice successfully transfers both visual response deficits and hyperactive behavior. These findings show that gut microbiota alterations contribute to the severity of neurological symptoms in CDD, shedding light on the interplay between microbiota, microglia, and neurodevelopmental outcomes.

MicroRNAs are key regulators of brain gene expression, with miR-29a notably upregulated from development to adulthood and in aging, and showing links to cognitive decline. However, the extent to which miR-29 levels influence learning and memory processes, and its molecular mediators, remains to be determined. Here, we down- and up-regulated miR-29a levels in the dorsal hippocampus of adult mice to reveal miR-29 role in memory. Inhibiting miR-29a enhanced trace fear memory stability, increased Dnmt3a levels, and affected CpG methylation in gene regulation regions. In contrast, increasing miR-29a impaired memory performances and decreased Dnmt3a levels, suggesting a destabilization of memory processes. Proteomic and transcriptomic analysis demonstrated that miR-29a antagonism upregulated RNA-binding and synaptic proteins and downregulated inflammation and myelin associated proteins. These results underscore miR-29a pivotal role in memory persistence, plasticity, and cognitive aging, suggesting that miR-29a modulation could offer potential strategies for cognitive enhancement and age-related memory decline. ### Competing Interest Statement The authors have declared no competing interest.

Emotional contagion (ECo) represents a fundamental form of empathy. In this study, we used pupillometry to quantify ECo by assessing pupil responses of a mouse watching another mouse receive a tail shock. Pupil dilation effectively measured both direct and vicarious emotional response thresholds at the individual level through psychometric curve analysis. The pupillary ECo response diminished when the observer could not see the demonstrator, suggesting a multisensory process involving vision. Viewing videos of tail-shocked mice was sufficient to elicit a pupil response in the observer. Whole-brain c-Fos mapping revealed a broad network of 88 brain regions activated during ECo, with all areas activated in the demonstrator also engaged in the observer. Additionally, in certain brain regions, correlated activation was detected between each observer-demonstrator pair, indicating that ECo promotes a shared neural state. These findings advance our understanding of the neural basis of empathy, with implications for analyzing neuropsychiatric disorder models. ### Competing Interest Statement The authors have declared no competing interest.

The ability to store, retrieve, and extinguish memories of adverse experiences is an essential skill for animals' survival. The cellular and molecular factors that underlie such processes are only partially known. Using chondroitinase ABC treatment targeting chondroitin sulfate proteoglycans (CSPGs), previous studies showed that the maturation of the extracellular matrix makes fear memory resistant to deletion. Mice lacking the cartilage link protein Crtl1 (Crtl1-KO mice) display normal CSPG levels but impaired CSPG condensation in perineuronal nets (PNNs). Thus, we asked whether the presence of PNNs in the adult brain is responsible for the appearance of persistent fear memories by investigating fear extinction in Crtl1-KO mice. We found that mutant mice displayed fear memory erasure after an extinction protocol as revealed by analysis of freezing and pupil dynamics. Fear memory erasure did not depend on passive loss of retention; moreover, we demonstrated that, after extinction training, conditioned Crtl1-KO mice display no neural activation in the amygdala (Zif268 staining) in comparison to control animals. Taken together, our findings suggest that the aggregation of CSPGs into PNNs regulates the boundaries of the critical period for fear extinction.

Perineuronal nets (PNNs) surround specific neurons in the brain and are involved in various forms of plasticity and clinical conditions. However, our understanding of the PNN role in these phenomena is limited by the lack of highly quantitative maps of PNN distribution and association with specific cell types. Here, we present the first comprehensive atlas of PNN distribution (in Allen Brain Atlas coordinates) and colocalization with parvalbumin (PV) cells for over 600 regions of the adult mouse brain. Data analysis showed that PV expression is a good predictor of PNN aggregation. In the cortex, PNNs are dramatically enriched in layer 4 of all primary sensory areas in correlation with thalamocortical input density, and their distribution mirrors intracortical connectivity patterns. Gene expression analysis identified many PNN correlated genes. Strikingly, PNN anticorrelated transcripts were enriched in synaptic plasticity genes, generalizing PNN role as circuit stability factors. Overall, this atlas offers novel resources for understanding the organizational principles of the brain extracellular matrix.

Mammalian target of rapamycin (mTOR) pathway has emerged as a key molecular mechanism underlying memory processes. Although mTOR inhibition is known to block memory processes, it remains elusive whether and how an enhancement of mTOR signaling may improve memory processes. Here we found in male mice that the administration of VO-OHpic, an inhibitor of the phosphatase and tensin homolog (PTEN) that negatively modulates AKT-mTOR pathway, enhanced auditory fear memory for days and weeks, while it left short-term memory unchanged. Memory enhancement was associated with a long-lasting increase in immature-type dendritic spines of pyramidal neurons into the auditory cortex. The persistence of spine remodeling over time arose by the interplay between PTEN inhibition and memory processes, as VO-OHpic induced only a transient immature spine growth in the somatosensory cortex, a region not involved in long-term auditory memory. Both the potentiation of fear memories and increase in immature spines were hampered by rapamycin, a selective inhibitor of mTORC1. These data revealed that memory can be potentiated over time by the administration of a selective PTEN inhibitor. In addition to disclosing new information on the cellular mechanisms underlying long-term memory maintenance, our study provides new insights on the molecular processes that aid enhancing memories over time.SIGNIFICANCE STATEMENT The neuronal mechanisms that may help improve the maintenance of long-term memories are still elusive. The inhibition of mammalian-target of rapamycin (mTOR) signaling shows that this pathway plays a crucial role in synaptic plasticity and memory formation. However, whether its activation may strengthen long-term memory storage is unclear. We assessed the consequences of positive modulation of AKT-mTOR pathway obtained by VO-OHpic administration, a phosphatase and tensin homolog inhibitor, on memory retention and underlying synaptic modifications. We found that mTOR activation greatly enhanced memory maintenance for weeks by producing a long-lasting increase of immature-type dendritic spines in pyramidal neurons of the auditory cortex. These results offer new insights on the cellular and molecular mechanisms that can aid enhancing memories over time.

Quality-controlled predictions of deep learning models for cell counting This dataset contains high-resolution images for the visualization of perineuronal nets (PNNs) and parvalbumin-expressing (PV) cells analyzed in the paper: A Comprehensive Atlas of Perineuronal Net Distribution and Colocalization with Parvalbumin in the Adult Mouse Brain. The dataset integrates the raw data published on a previous upload on Zenodo. Cell locations were obtained using two deep-learning models for cell counting (publicly available on GitHub, details in the paper by Ciampi et al., 2022). The output of the deep-learning pipeline was filtered based on the score assigned to each cell prediction, by removing all the PNNs with a score lower than 0.4 and all the PV cells with a score lower than 0.55. Cases of artefactual cell detection were finally removed manually by visual inspection of the images. Content The dataset contains microscopy images of coronal brain slices from 7 adult mice. The objects highlighted in these images represent the final set of PNNs/PV cells that were used in all the analysis of the paper. Folder Structure and file naming conventions There are separate folders for each mouse. Each folder is named with the ID of that mouse. Within each folder, images are assigned a code specifying the channel (C1 for PNNs, C2 for PV cells).

Mutations in the solute carrier family 6-member 8 ( Slc6a8 ) gene, encoding the protein responsible for cellular creatine (Cr) uptake, cause Creatine Transporter Deficiency (CTD), an X-linked neurometabolic disorder presenting with intellectual disability, autistic-like features, and epilepsy. The pathological determinants of CTD are still poorly understood, hindering the development of therapies. In this study, we generated an extensive transcriptomic profile of CTD showing that Cr deficiency causes perturbations of gene expression in excitatory neurons, inhibitory cells, and oligodendrocytes which result in remodeling of circuit excitability and synaptic wiring. We also identified specific alterations of parvalbumin-expressing (PV + ) interneurons, exhibiting a reduction in cellular and synaptic density, and a hypofunctional electrophysiological phenotype. Mice lacking Slc6a8 only in PV + interneurons recapitulated numerous CTD features, including cognitive deterioration, impaired cortical processing and hyperexcitability of brain circuits, demonstrating that Cr deficit in PV + interneurons is sufficient to determine the neurological phenotype of CTD. Moreover, a pharmacological treatment targeted to restore the efficiency of PV + synapses significantly improved cortical activity in Slc6a8 knock-out animals. Altogether, these data demonstrate that Slc6a8 is critical for the normal function of PV + interneurons and that impairment of these cells is central in the disease pathogenesis, suggesting a novel therapeutic venue for CTD.

Pupil size variations have been associated with changes in brain activity patterns related with specific cognitive factors, such as arousal, attention, and mental effort. The locus coeruleus (LC), a key hub in the noradrenergic system of the brain, is considered to be a key regulator of cognitive control on pupil size, with changes in pupil diameter corresponding to the release of norepinephrine (NE). Advances in eye-tracking technology and open-source software have facilitated accurate pupil size measurement in various experimental settings, leading to increased interest in using pupillometry to track the nervous system activation state and as a potential biomarker for brain disorders. This review explores pupillometry as a non-invasive and fully translational tool for studying cortical plasticity starting from recent literature suggesting that pupillometry could be a promising technique for estimating the degree of residual plasticity in human subjects. Given that NE is known to be a critical mediator of cortical plasticity and arousal, the review includes data revealing the importance of the LC-NE system in modulating brain plasticity and pupil size. Finally, we will review data suggesting that pupillometry could provide a quantitative and complementary measure of cortical plasticity also in pre-clinical studies.

Rett syndrome caused by MECP2 variants is characterized by a heterogenous clinical spectrum accounted for in 60% of cases by hot-spot variants. Focusing on the most frequent variants, we generated in vitro iPSC-neurons from the blood of RTT girls with p.Arg133Cys and p.Arg255*, associated to mild and severe phenotype, respectively, and of an RTT male harboring the close to p.Arg255*, p.Gly252Argfs*7 variant. Truncated MeCP2 proteins were revealed by Western blot and immunofluorescence analysis. We compared the mutant versus control neurons at 42 days for morphological parameters and at 120 days for electrophysiology recordings, including girls’ isogenic clones. A precocious reduced morphological complexity was evident in neurons with truncating variants, while in p.Arg133Cys neurons any significant differences were observed in comparison with the isogenic wild-type clones. Reduced nuclear size and branch number show up as the most robust biomarkers. Patch clamp recordings on mature neurons allowed the assessment of cell biophysical properties, V-gated currents, and spiking pattern in the mutant and control cells. Immature spiking, altered cell capacitance, and membrane resistance of RTT neurons, were particularly pronounced in the Arg255* and Gly252Argfs*7 mutants. The overall results indicate that the specific markers of in vitro cellular phenotype mirror the clinical severity and may be amenable to drug testing for translational purposes.

Exposing animals to an enriched environment (EE) has dramatic effects on brain structure, function, and plasticity. The poorly known "EE-derived signals"mediating the EE effects are thought to be generated within the central nervous system. Here, we shift the focus to the body periphery, revealing that gut microbiota signals are crucial for EE-driven plasticity. Developmental analysis reveals striking differences in intestinal bacteria composition between EE and standard rearing (ST) mice, as well as enhanced levels of short-chain fatty acids (SCFA) in EE mice. Depleting the microbiota of EE mice with antibiotics strongly decreases SCFA and prevents activation of adult ocular dominance plasticity, spine dynamics, and microglia rearrangement. SCFA treatment in ST mice mimics EE induction of ocular dominance plasticity and microglial remodeling. Remarkably, transferring the microbiota of EE mice to ST recipients activates adult ocular dominance plasticity. Thus, experience-dependent changes in gut microbiota regulate brain plasticity.

Background. An ischemic stroke is followed by the remapping of motor representation and extensive changes in cortical excitability involving both hemispheres. Although stimulation of the ipsilesional motor cortex, especially when paired with motor training, facilitates plasticity and functional restoration, the remapping of motor representation of the single and combined treatments is largely unexplored. Objective. We investigated if spatio-temporal features of motor-related cortical activity and the new motor representations are related to the rehabilitative treatment or if they can be specifically associated to functional recovery. Methods. We designed a novel rehabilitative treatment that combines neuro-plasticizing intervention with motor training. In detail, optogenetic stimulation of peri-infarct excitatory neurons expressing Channelrhodopsin 2 was associated with daily motor training on a robotic device. The effectiveness of the combined therapy was compared with spontaneous recovery and with the single treatments (ie optogenetic stimulation or motor training). Results. We found that the extension and localization of the new motor representations are specific to the treatment, where most treatments promote segregation of the motor representation to the peri-infarct region. Interestingly, only the combined therapy promotes both the recovery of forelimb functionality and the rescue of spatio-temporal features of motor-related activity. Functional recovery results from a new excitatory/inhibitory balance between hemispheres as revealed by the augmented motor response flanked by the increased expression of parvalbumin positive neurons in the peri-infarct area. Conclusions. Our findings highlight that functional recovery and restoration of motor-related neuronal activity are not necessarily coupled during post-stroke recovery. Indeed the reestablishment of cortical activation features of calcium transient is distinctive of the most effective therapeutic approach, the combined therapy.