Obtaining novel data-driven hypotheses from teaching activities: An example assessing the role of the FKBP5 gene in major depression.

Many clinical and research efforts aim to develop antidepressant drugs for those suffering from major depressive disorder (MDD). Yet, even today, the available treatments are suboptimal and unpredictable, with a significant proportion of patients enduring multiple drug attempts and adverse side effects before a successful response, and, for many patients, no response at all. Thus, a clearer understanding of the mechanisms underlying MDD is necessary. In the 'Brain Development and Disease' class of our Master's program in Cognitive Sciences, we ask students to collect data about the expression of a gene whose altered expression and/or function is related to a brain disorder. The students' final exam assignment consists of writing a research article in which the collected data are discussed in relation to the relevant disorder. In the course of one of these assignments, we identified the FKBP5 gene as a key player uniting two major hypotheses of MDD pathogenesis and treatment response. FKBP5 controls biological processes including immunoregulation and glucocorticoid function, both of which are separately implicated in the development and prognosis of MDD. Gene expression analyses from the human, non-human primate and mouse Allen Brain Atlases revealed that FKBP5 is expressed in brain regions involved in MDD, particularly at ages susceptible to early-life stressors. Data re-analysis from published studies confirmed that FKBP5 expression is upregulated in relevant brain regions in human MDD and preclinical mouse models of MDD. Our experience shows that classes engaging students in data collection and analysis projects may effectively result in novel data-driven hypotheses.

Abnormal Whisker-Dependent Behaviors and Altered Cortico-Hippocampal Connectivity in Shank3b-/- Mice.

Abnormal tactile response is an integral feature of Autism Spectrum Disorders (ASDs), and hypo-responsiveness to tactile stimuli is often associated with the severity of ASDs core symptoms. Patients with Phelan-McDermid syndrome (PMS), caused by mutations in the SHANK3 gene, show ASD-like symptoms associated with aberrant tactile responses. The neural underpinnings of these abnormalities are still poorly understood. Here we investigated, in Shank3b-/- adult mice, the neural substrates of whisker-guided behaviors, a key component of rodents' interaction with the surrounding environment. We assessed whisker-dependent behaviors in Shank3b-/- adult mice and age-matched controls, using the textured novel object recognition (tNORT) and whisker nuisance (WN) test. Shank3b-/- mice showed deficits in whisker-dependent texture discrimination in tNORT and behavioral hypo-responsiveness to repetitive whisker stimulation in WN. Sensory hypo-responsiveness was accompanied by a significantly reduced activation of the primary somatosensory cortex (S1) and hippocampus, as measured by c-fos mRNA induction, a proxy of neuronal activity following whisker stimulation. Moreover, resting-state fMRI showed a significantly reduced S1-hippocampal connectivity in Shank3b mutants, in the absence of altered connectivity between S1 and other somatosensory areas. Impaired crosstalk between hippocampus and S1 might underlie Shank3b-/- hypo-reactivity to whisker-dependent cues, highlighting a potentially generalizable somatosensory dysfunction in ASD.

Somatosensory cortex hyperconnectivity and impaired whisker-dependent responses in Cntnap2-/- mice.

Sensory abnormalities are a common feature in autism spectrum disorders (ASDs). Tactile responsiveness is altered in autistic individuals, with hypo-responsiveness being associated with the severity of ASD core symptoms. Similarly, sensory abnormalities have been described in mice lacking ASD-associated genes. Loss-of-function mutations in CNTNAP2 result in cortical dysplasia-focal epilepsy syndrome (CDFE) and autism. Likewise, Cntnap2-/- mice show epilepsy and deficits relevant with core symptoms of human ASDs, and are considered a reliable model to study ASDs. Altered synaptic transmission and synchronicity found in the cerebral cortex of Cntnap2-/- mice would suggest a network dysfunction. Here, we investigated the neural substrates of whisker-dependent responses in Cntnap2+/+ and Cntnap2-/- adult mice. When compared to controls, Cntnap2-/- mice showed focal hyper-connectivity within the primary somatosensory cortex (S1), in the absence of altered connectivity between S1 and other somatosensory areas. This data suggests the presence of impaired somatosensory processing in these mutants. Accordingly, Cntnap2-/- mice displayed impaired whisker-dependent discrimination in the textured novel object recognition test (tNORT) and increased c-fos mRNA induction within S1 following whisker stimulation. S1 functional hyperconnectivity might underlie the aberrant whisker-dependent responses observed in Cntnap2-/- mice, indicating that Cntnap2 mice are a reliable model to investigate sensory abnormalities that characterize ASDs.

Foxg1 Upregulation Enhances Neocortical Activity.

Foxg1 is an ancient transcription factor gene orchestrating a number of neurodevelopmental processes taking place in the rostral brain. In this study, we investigated its impact on neocortical activity. We found that mice overexpressing Foxg1 in neocortical pyramidal cells displayed an electroencephalography (EEG) with increased spike frequency and were more prone to kainic acid (KA)-induced seizures. Consistently, primary cultures of neocortical neurons gain-of-function for Foxg1 were hyperactive and hypersynchronized. That reflected an unbalanced expression of key genes encoding for ion channels, gamma aminobutyric acid and glutamate receptors, and was likely exacerbated by a pronounced interneuron depletion. We also detected a transient Foxg1 upregulation ignited in turn by neuronal activity and mediated by immediate early genes. Based on this, we propose that even small changes of Foxg1 levels may result in a profound impact on pyramidal cell activity, an issue relevant to neuronal physiology and neurological aberrancies associated to FOXG1 copy number variations.

Aberrant Somatosensory Processing and Connectivity in Mice Lacking Engrailed-2.

Overreactivity and defensive behaviors in response to tactile stimuli are common symptoms in autism spectrum disorder (ASD) patients. Similarly, somatosensory hypersensitivity has also been described in mice lacking ASD-associated genes such as Fmr1 (fragile X mental retardation protein 1). Fmr1 knock-out mice also show reduced functional connectivity between sensory cortical areas, which may represent an endogenous biomarker for their hypersensitivity. Here, we measured whole-brain functional connectivity in Engrailed-2 knock-out (En2-/-) adult mice, which show a lower expression of Fmr1 and anatomical defects common to Fmr1 knock-outs. MRI-based resting-state functional connectivity in adult En2-/- mice revealed significantly reduced synchronization in somatosensory-auditory/associative cortices and dorsal thalamus, suggesting the presence of aberrant somatosensory processing in these mutants. Accordingly, when tested in the whisker nuisance test, En2-/- but not WT mice of both sexes showed fear behavior in response to repeated whisker stimulation. En2-/- mice undergoing this test exhibited decreased c-Fos-positive neurons (a marker of neuronal activity) in layer IV of the primary somatosensory cortex and increased immunoreactive cells in the basolateral amygdala compared with WT littermates. Conversely, when tested in a sensory maze, En2-/- and WT mice spent a comparable time in whisker-guided exploration, indicating that whisker-mediated behaviors are otherwise preserved in En2 mutants. Therefore, fearful responses to somatosensory stimuli in En2-/- mice are accompanied by reduced basal connectivity of sensory regions, reduced activation of somatosensory cortex, and increased activation of the basolateral amygdala, suggesting that impaired somatosensory processing is a common feature in mice lacking ASD-related genes.SIGNIFICANCE STATEMENT Overreactivity to tactile stimuli is a common symptom in autism spectrum disorder (ASD) patients. Recent studies performed in mice bearing ASD-related mutations confirmed these findings. Here, we evaluated the behavioral response to whisker stimulation in mice lacking the ASD-related gene Engrailed-2 (En2-/- mice). Compared with WT controls, En2-/- mice showed reduced functional connectivity in the somatosensory cortex, which was paralleled by fear behavior, reduced activation of somatosensory cortex, and increased activation of the basolateral amygdala in response to repeated whisker stimulation. These results suggest that impaired somatosensory signal processing is a common feature in mice harboring ASD-related mutations.

Oxidative Stress and Immune System Dysfunction in Autism Spectrum Disorders.

Autism Spectrum Disorders (ASDs) represent a group of neurodevelopmental disorders associated with social and behavioral impairments. Although dysfunctions in several signaling pathways have been associated with ASDs, very few molecules have been identified as potentially effective drug targets in the clinic. Classically, research in the ASD field has focused on the characterization of pathways involved in neural development and synaptic plasticity, which support the pathogenesis of this group of diseases. More recently, immune system dysfunctions have been observed in ASD. In addition, high levels of reactive oxygen species (ROS), which cause oxidative stress, are present in ASD patients. In this review, we will describe the major alterations in the expression of genes coding for enzymes involved in the ROS scavenging system, in both ASD patients and ASD mouse models. In addition, we will discuss, in the context of the most recent literature, the possibility that oxidative stress, inflammation and immune system dysfunction may be connected to, and altogether support, the pathogenesis and/or severity of ASD. Finally, we will discuss the possibility of novel treatments aimed at counteracting the interplay between ROS and inflammation in people with ASD.

Neurobiological bases of autism-epilepsy comorbidity: a focus on excitation/inhibition imbalance.

Autism spectrum disorders (ASD) and epilepsy are common neurological diseases of childhood, with an estimated incidence of approximately 0.5-1% of the worldwide population. Several genetic, neuroimaging and neuropathological studies clearly showed that both ASD and epilepsy have developmental origins and a substantial degree of heritability. Most importantly, ASD and epilepsy frequently coexist in the same individual, suggesting a common neurodevelopmental basis for these disorders. Genome-wide association studies recently allowed for the identification of a substantial number of genes involved in ASD and epilepsy, some of which are mutated in syndromes presenting both ASD and epilepsy clinical features. At the cellular level, both preclinical and clinical studies indicate that the different genetic causes of ASD and epilepsy may converge to perturb the excitation/inhibition (E/I) balance, due to the dysfunction of excitatory and inhibitory circuits in various brain regions. Metabolic and immune dysfunctions, as well as environmental causes also contribute to ASD pathogenesis. Thus, an E/I imbalance resulting from neurodevelopmental deficits of multiple origins might represent a common pathogenic mechanism for both diseases. Here, we will review the most significant studies supporting these hypotheses. A deeper understanding of the molecular and cellular determinants of autism-epilepsy comorbidity will pave the way to the development of novel therapeutic strategies.

The Chemokine CCL2 Mediates the Seizure-enhancing Effects of Systemic Inflammation.

Epilepsy is a chronic disorder characterized by spontaneous recurrent seizures. Brain inflammation is increasingly recognized as a critical factor for seizure precipitation, but the molecular mediators of such proconvulsant effects are only partly understood. The chemokine CCL2 is one of the most elevated inflammatory mediators in patients with pharmacoresistent epilepsy, but its contribution to seizure generation remains unexplored. Here, we show, for the first time, a crucial role for CCL2 and its receptor CCR2 in seizure control. We imposed a systemic inflammatory challenge via lipopolysaccharide (LPS) administration in mice with mesial temporal lobe epilepsy. We found that LPS dramatically increased seizure frequency and upregulated the expression of many inflammatory proteins, including CCL2. To test the proconvulsant role of CCL2, we administered systemically either a CCL2 transcription inhibitor (bindarit) or a selective antagonist of the CCR2 receptor (RS102895). We found that interference with CCL2 signaling potently suppressed LPS-induced seizures. Intracerebral administration of anti-CCL2 antibodies also abrogated LPS-mediated seizure enhancement in chronically epileptic animals. Our results reveal that CCL2 is a key mediator in the molecular pathways that link peripheral inflammation with neuronal hyperexcitability. SIGNIFICANCE STATEMENT: Substantial evidence points to a role for inflammation in epilepsy, but currently there is little insight as to how inflammatory pathways impact on seizure generation. Here, we examine the molecular mediators linking peripheral inflammation with seizure susceptibility in mice with mesial temporal lobe epilepsy. We show that a systemic inflammatory challenge via lipopolysaccharide administration potently enhances seizure frequency and upregulates the expression of the chemokine CCL2. Remarkably, selective pharmacological interference with CCL2 or its receptor CCR2 suppresses lipopolysaccharide-induced seizure enhancement. Thus, CCL2/CCR2 signaling plays a key role in linking systemic inflammation with seizure susceptibility.

Neuroinflammatory targets and treatments for epilepsy validated in experimental models.

A large body of evidence that has accumulated over the past decade strongly supports the role of inflammation in the pathophysiology of human epilepsy. Specific inflammatory molecules and pathways have been identified that influence various pathologic outcomes in different experimental models of epilepsy. Most importantly, the same inflammatory pathways have also been found in surgically resected brain tissue from patients with treatment-resistant epilepsy. New antiseizure therapies may be derived from these novel potential targets. An essential and crucial question is whether targeting these molecules and pathways may result in anti-ictogenesis, antiepileptogenesis, and/or disease-modification effects. Therefore, preclinical testing in models mimicking relevant aspects of epileptogenesis is needed to guide integrated experimental and clinical trial designs. We discuss the most recent preclinical proof-of-concept studies validating a number of therapeutic approaches against inflammatory mechanisms in animal models that could represent novel avenues for drug development in epilepsy. Finally, we suggest future directions to accelerate preclinical to clinical translation of these recent discoveries.

Noggin-Mediated Retinal Induction Reveals a Novel Interplay Between Bone Morphogenetic Protein Inhibition, Transforming Growth Factor ß, and Sonic Hedgehog Signaling.

It has long been known that the depletion of bone morphogenetic protein (BMP) is one of the key factors necessary for the development of anterior neuroectodermal structures. However, the precise molecular mechanisms that underlie forebrain regionalization are still not completely understood. Here, we show that Noggin1 is involved in the regionalization of anterior neural structures in a dose-dependent manner. Low doses of Noggin1 expand prosencephalic territories, while higher doses specify diencephalic and retinal regions at the expense of telencephalic areas. A similar dose-dependent mechanism determines the ability of Noggin1 to convert pluripotent cells in prosencephalic or diencephalic/retinal precursors, as shown by transplant experiments and molecular analyses. At a molecular level, the strong inhibition of BMP signaling exerted by high doses of Noggin1 reinforces the Nodal/transforming growth factor (TGF)ß signaling pathway, leading to activation of Gli1 and Gli2 and subsequent activation of Sonic Hedgehog (SHH) signaling. We propose a new role for Noggin1 in determining specific anterior neural structures by the modulation of TGFß and SHH signaling.

Hippocampal dysregulation of neurofibromin-dependent pathways is associated with impaired spatial learning in engrailed 2 knock-out mice.

Genome-wide association studies indicated the homeobox-containing transcription factor Engrailed-2 (En2) as a candidate gene for autism spectrum disorders (ASD). Accordingly, En2 knock-out (En2(-/-)) mice show anatomical and behavioral "ASD-like" features, including decreased sociability and learning deficits. The molecular pathways underlying these deficits in En2(-/-) mice are not known. Deficits in signaling pathways involving neurofibromin and extracellular-regulated kinase (ERK) have been associated with impaired learning. Here we investigated the neurofibromin-ERK cascade in the hippocampus of wild-type (WT) and En2(-/-) mice before and after spatial learning testing. When compared with WT littermates, En2(-/-) mice showed impaired performance in the Morris water maze (MWM), which was accompanied by lower expression of the activity-dependent gene Arc. Quantitative RT-PCR, immunoblotting, and immunohistochemistry experiments showed a marked downregulation of neurofibromin expression in the dentate gyrus of both naive and MWM-treated En2(-/-) mice. ERK phosphorylation, known to be induced in the presence of neurofibromin deficiency, was increased in the dentate gyrus of En2(-/-) mice after MWM. Treatment of En2(-/-) mice with lovastatin, an indirect inhibitor of ERK phosphorylation, markedly reduced ERK phosphorylation in the dentate gyrus, but was unable to rescue learning deficits in MWM-trained mutant mice. Further investigation is needed to unravel the complex molecular mechanisms linking dysregulation of neurofibromin-dependent pathways to spatial learning deficits in the En2 mouse model of ASD.

Epileptiform activity and cognitive deficits in SNAP-25(+/-) mice are normalized by antiepileptic drugs.

Synaptosomal-associated protein of 25 kDa (SNAP-25) is a protein that participates in the regulation of synaptic vesicle exocytosis through the formation of the soluble NSF attachment protein receptor complex and modulates voltage-gated calcium channels activity. The Snap25 gene has been associated with schizophrenia, attention deficit hyperactivity disorder, and bipolar disorder, and lower levels of SNAP-25 have been described in patients with schizophrenia. We used SNAP-25 heterozygous (SNAP-25(+/-)) mice to investigate at which extent the reduction of the protein levels affects neuronal network function and mouse behavior. As interactions of genotype with the specific laboratory conditions may impact behavioral results, the study was performed through a multilaboratory study in which behavioral tests were replicated in at least 2 of 3 distinct European laboratories. Reductions of SNAP-25 levels were associated with a moderate hyperactivity, which disappeared in the adult animals, and with impaired associative learning and memory. Electroencephalographic recordings revealed the occurrence of frequent spikes, suggesting a diffuse network hyperexcitability. Consistently, SNAP-25(+/-) mice displayed higher susceptibility to kainate-induced seizures, paralleled by degeneration of hilar neurons. Notably, both EEG profile and cognitive defects were improved by antiepileptic drugs. These results indicate that reduction of SNAP-25 expression is associated to generation of epileptiform discharges and cognitive dysfunctions, which can be effectively treated by antiepileptic drugs.

Alterations of Perineuronal Net Expression and Abnormal Social Behavior and Whisker-dependent Texture Discrimination in Mice Lacking the Autism Candidate Gene Engrailed 2.

GABAergic interneurons and perineuronal nets (PNNs) are important regulators of plasticity throughout life and their dysfunction has been implicated in the pathogenesis of several neuropsychiatric conditions, including autism spectrum disorders (ASD). PNNs are condensed portions of the extracellular matrix (ECM) that are crucial for neural development and proper formation of synaptic connections. We previously showed a reduced expression of GABAergic interneuron markers in the hippocampus and somatosensory cortex of adult mice lacking the Engrailed2 gene (En2-/- mice), a mouse model of ASD. Since alterations in PNNs have been proposed as a possible pathogenic mechanism in ASD, we hypothesized that the PNN dysfunction may contribute to the neural and behavioral abnormalities of En2-/- mice. Here, we show an increase in the PNN fluorescence intensity, evaluated by Wisteria floribunda agglutinin, in brain regions involved in social behavior and somatosensory processing. In addition, we found that En2-/- mice exhibit altered texture discrimination through whiskers and display a marked decrease in the preference for social novelty. Our results raise the possibility that altered expression of PNNs, together with defects of GABAergic interneurons, might contribute to the pathogenesis of social and sensory behavioral abnormalities.

Focal clusters of peri-synaptic matrix contribute to activity-dependent plasticity and memory in mice.

Recent findings show that effective integration of novel information in the brain requires coordinated processes of homo- and heterosynaptic plasticity. In this work, we hypothesize that activity-dependent remodeling of the peri-synaptic extracellular matrix (ECM) contributes to these processes. We show that clusters of the peri-synaptic ECM, recognized by CS56 antibody, emerge in response to sensory stimuli, showing temporal and spatial coincidence with dendritic spine plasticity. Using CS56 co-immunoprecipitation of synaptosomal proteins, we identify several molecules involved in Ca2+ signaling, vesicle cycling, and AMPA-receptor exocytosis, thus suggesting a role in long-term potentiation (LTP). Finally, we show that, in the CA1 hippocampal region, the attenuation of CS56 glycoepitopes, through the depletion of versican as one of its main carriers, impairs LTP and object location memory in mice. These findings show that activity-dependent remodeling of the peri-synaptic ECM regulates the induction and consolidation of LTP, contributing to hippocampal-dependent memory.

Action of Botulinum Neurotoxin E Type in Experimental Epilepsies.

Botulinum neurotoxins (BoNTs) are zinc endopeptidases produced by the Clostridium genus of anerobic bacteria, largely known for their ability to cleave synaptic proteins, leading to neuromuscular paralysis. In the central nervous system, BoNTs are known to block the release of glutamate neurotransmitter, and for this reason, researchers explored the possible therapeutic action in disorders characterized by neuronal hyperactivity, such as epilepsy. Thus, using multidisciplinary approaches and models of experimental epilepsy, we investigated the pharmacological potential of BoNT/E serotype. In this review, written in memory of Prof. Matteo Caleo, a pioneer in these studies, we go back over the hypotheses and experimental approaches that led us to the conclusion that intrahippocampal administration of BoNT/E (i) displays anticonvulsant effects if prophylactically delivered in a model of acute generalized seizures; (ii) does not have any antiepileptogenic action after the induction of status epilepticus; (iii) reduces frequency of spontaneous seizures in a model of recurrent seizures if delivered during the chronic phase but in a transient manner. Indeed, the control on spontaneous seizures stops when BoNT/E effects are off (few days), thus limiting its pharmacological potential in humans.

Autism Spectrum Disorder with Epilepsy: A Research Protocol for a Clinical and Genetic Study.

Autism spectrum disorder (ASD) is a common neurodevelopmental condition affecting ~1% of people worldwide. Core ASD features present with impaired social communication abilities, repetitive and stereotyped behaviors, and atypical sensory responses and are often associated with a series of comorbidities. Among these, epilepsy is frequently observed. The co-occurrence of ASD and epilepsy is currently thought to result from common abnormal neurodevelopmental pathways, including an imbalanced excitation/inhibition ratio. However, the pathological mechanisms involved in ASD-epilepsy co-morbidity are still largely unknown. Here, we propose a research protocol aiming to investigate electrophysiological and genetic features in subjects with ASD and epilepsy. This study will include a detailed electroencephalographic (EEG) and blood transcriptomic characterization of subjects with ASD with and without epilepsy. The combined approach of EEG and transcriptomic studies in the same subjects will contribute to a novel stratification paradigm of the heterogeneous ASD population based on quantitative gene expression and neurophysiological biomarkers. In addition, our protocol has the potential to indicate new therapeutic options, thus amending the current condition of absence of data and guidelines for the treatment of ASD with epilepsy.

Gene Expression Profiling in Trigeminal Ganglia from Cntnap2-/- and Shank3b-/- Mouse Models of Autism Spectrum Disorder.

Sensory difficulties represent a crucial issue in the life of autistic individuals. The diagnostic and statistical manual of mental disorders describes both hyper- and hypo-responsiveness to sensory stimulation as a criterion for the diagnosis autism spectrum disorders (ASD). Among the sensory domain affected in ASD, altered responses to tactile stimulation represent the most commonly reported sensory deficits. Although tactile abnormalities have been reported in monogenic cohorts of patients and genetic mouse models of ASD, the underlying mechanisms are still unknown. Traditionally, autism research has focused on the central nervous system as the target to infer the neurobiological bases of such tactile abnormalities. Nonetheless, the peripheral nervous system represents the initial site of processing of sensory information and a potential site of dysfunction in the sensory cascade. Here we investigated the gene expression deregulation in the trigeminal ganglion (which directly receives tactile information from whiskers) in two genetic models of syndromic autism (Shank3b and Cntnap2 mutant mice) at both adult and juvenile ages. We found several neuronal and non-neuronal markers involved in inhibitory, excitatory, neuroinflammatory and sensory neurotransmission to be differentially regulated within the trigeminal ganglia of both adult and juvenile Shank3b and Cntnap2 mutant mice. These results may help in disentangling the multifaced complexity of sensory abnormalities in autism and open avenues for the development of peripherally targeted treatments for tactile sensory deficits exhibited in ASD.

Automated Segmentation of the Mouse Body Language to Study Stimulus-Evoked Emotional Behaviors.

Understanding the neural basis of emotions is a critical step to uncover the biological substrates of neuropsychiatric disorders. To study this aspect in freely behaving mice, neuroscientists have relied on the observation of ethologically relevant bodily cues to infer the affective content of the subject, both in neutral conditions or in response to a stimulus. The best example of that is the widespread assessment of freezing in experiments testing both conditioned and unconditioned fear responses. While robust and powerful, these approaches come at a cost: they are usually confined within selected time windows, accounting for only a limited portion of the complexity of emotional fluctuation. Moreover, they often rely on visual inspection and subjective judgment, resulting in inconsistency across experiments and questionable result interpretations. To overcome these limitations, novel tools are arising, fostering a new avenue in the study of the mouse naturalistic behavior. In this work we developed a computational tool [stimulus-evoked behavioral tracking in 3D for rodents (SEB3R)] to automate and standardize an ethologically driven observation of freely moving mice. Using a combination of machine learning-based behavioral tracking and unsupervised cluster analysis, we identified statistically meaningful postures that could be used for empirical inference on a subsecond scale. We validated the efficacy of this tool in a stimulus-driven test, the whisker nuisance (WN) task, where mice are challenged with a prolonged and invasive whisker stimulation, showing that identified postures can be reliably used as a proxy for stimulus-driven fearful and explorative behaviors.

At the Crossroad Between Resiliency and Fragility: A Neurodevelopmental Perspective on Early-Life Experiences.

Postnatal development of the brain is characterized by sensitive windows during which, local circuitry are drastically reshaped by life experiences. These critical periods (CPs) occur at different time points for different brain functions, presenting redundant physiological changes in the underlying brain regions. Although circuits malleability during CPs provides a valuable window of opportunity for adaptive fine-tuning to the living environment, this aspect of neurodevelopment also represents a phase of increased vulnerability for the development of a variety of disorders. Consistently, accumulating epidemiological studies point to adverse childhood experience as a major risk factor for many medical conditions, especially stress- and anxiety-related conditions. Thanks to creative approaches to manipulate rodents' rearing environment, neurobiologist have uncovered a pivotal interaction between CPs and early-life experiences, offering an interesting landscape to improve our understanding of brain disorders. In this short review, we discuss how early-life experience impacts cellular and molecular players involved in CPs of development, translating into long-lasting behavioral consequences in rodents. Bringing together findings from multiple laboratories, we delineate a unifying theory in which systemic factors dynamically target the maturation of brain functions based on adaptive needs, shifting the balance between resilience and vulnerability in response to the quality of the rearing environment.

Immune dysfunction in the cerebellum of mice lacking the autism candidate gene Engrailed 2.

Immune system dysfunction has been described in autism spectrum disorder. Here we tested the hypothesis that cerebellar defects are accompanied by immune dysfunction in adult mice lacking the autism-candidate gene Engrailed 2 (En2). Gene ontology analyses revealed that biological processes related to immune function were over-represented in the cerebellar transcriptome of En2-/- mice. Pro-inflammatory molecules and chemokines were reduced in the En2-/- cerebellum compared to controls. Conversely, pro-inflammatory molecules were increased in the peripheral blood of mutant mice. Our results suggest a link between immune dysfunction and cerebellar defects detected in En2-/- mice.