Brain development in rodents and humans: Identifying benchmarks of maturation and vulnerability to injury across species

A new two-hit animal model for schizophrenia research: Consequences on social behavior

Schizophrenia, a profoundly impactful neuropsychiatric disorder, has been the subject of extensive research using animal models. However, certain important aspects remain understudied, including assumed long-term consequences of psychotic episodes on negative symptoms development and progression. Addressing these limitations, we proposed a novel animal model in male rats based on early postnatal immune activation triggered by lipopolysaccharide (LPS), serving as the predisposing factor (1st hit). As the 2nd hit, representing psychotic-like episodes, we implemented a multi-episodic co-treatment with dizocilpine (MK-801) and amphetamine (AMP), spanning multiple developmental periods. The animals were tested in two social behavioral assays in adolescence and adulthood to investigate whether a social deficit would arise. In addition, we evaluated the level of oxytocin (OT), a neuropeptide relevant to social behavior, in selected brain regions. In the social interaction test, when animals could freely interact in the open field and express their social behavioral profile entirely, social behavior decreased in adolescent experimental animals. In the social approach test in the Y maze, all animals, irrespective of treatment, preferred conspecific over an indifferent object and novel rat over a familiar rat. Further, the results revealed that the OT content in the hypothalamus increased with age. In the proposed model, social interaction in the open field was decreased in adolescent but not in adult rats, indicating that the pharmacological manipulations caused only transient age-dependent changes. The study was thus in certain aspects successful in creating a novel approach to model social deficit potentially relevant to schizophrenia; other findings require further investigation.

The association between threatened miscarriage in early pregnancy and depression or anxiety in offspring in late adolescence

BACKGROUND

Adolescent mental health is a known determinant of health across the lifespan underscoring the importance of identifying determining factors. Threatened miscarriage is a common pregnancy complication, yet its influence on child mental health outcomes is unclear. Here we examined the association between pregnancies complicated by threatened miscarriage and the risk of offspring depression or anxiety in late adolescence using the representative longitudinal UK Millennium Cohort Study.

METHODS

Maternal reported data on threatened miscarriage and potential confounders were collected at 9-months postpartum. Data on depression and anxiety were collected as one variable when children were aged 17 years using self-reported doctor diagnosis. Multivariable logistic regression adjusted for several maternal and sociodemographic factors. We examined separate interaction effects for threatened miscarriage and hypertensive disorders of pregnancy, small for gestational age (SGA) and preterm birth.

RESULTS

N = 9521 mother-child dyads were included in the analyses, with n = 574 (6 %) women experiencing a threatened miscarriage, and 978 (10.3 %) children reported depression or anxiety diagnosis. Adjusted results suggested that threatened miscarriage was associated with a 34 % increase in the odds of depression or anxiety (OR: 1.34, 95 % CI 1.03, 1.73). An interaction effect was observed for threatened miscarriage and SGA (OR: 2.09, 95 % CI: 1.01, 4.36) and threatened miscarriage and preterm birth (OR:2.23, 95 % CI: 1.26, 3.95).

CONCLUSION

Threatened miscarriage was associated with an increased odds of depression or anxiety in offspring by age 17 years, albeit residual and unmeasured confounding cannot be ruled out. Future research should examine the potential biological mechanisms mediating this association.

Neuroimmune and behavioral changes elicited by maternal immune activation in mice are ameliorated by early postnatal immune stimulation

Though the etiology of autism spectrum disorder (ASD) is complex and not fully understood, it is believed that genetic risk factors, coupled with early life inflammation may predispose individuals to develop ASD. Maternal immune activation (MIA) is associated with increased incidence of ASD in offspring; however, not all mothers who experience inflammation during pregnancy have children with autism, suggesting that MIA may act as a disease primer that results in ASD pathology when paired with additional inflammatory insults. Here, we tested the hypothesis that MIA is a disease primer by using a two-hit model that combined MIA with a secondary immune stimulation in early life. C57BL/6J mouse dams were treated with polyinosinic-polycytidylic acid (Poly(I:C)) at embyronic day 12.5, and a subset of litters were then treated with the endotoxin lipopolysaccharide (LPS) four days after birth. Offspring were assessed in young adulthood for changes in behavior including sociability, repetitive-like behaviors, and anxiety-like behaviors. Flow cytometry was performed in adulthood to assess changes in immune cell populations in the periphery and in the brain. MIA increased repetitive-like behaviors in male mice and decreased sociability in both sexes. Unexpectedly, the secondary immune stimulation with LPS did not exacerbate changes in social and repetitive-like behaviors in either sex. MIA also altered distribution of cytotoxic CD8 + T cell populations in the periphery and brain of both sexes: CD8 + T cells were elevated in thymus but reduced in spleen, lymph, and brain. Additionally, MIA altered microglia activity in a region-specific manner in male mice, which was also not exacerbated but rather ameliorated when combined with LPS. Our results demonstrate that changes in repetitive-like and social behaviors that are induced by MIA in male mice are not exacerbated by subsequent inflammatory challenge and highlights the importance of considering the timing of stressors in the appearance of developmental pathology.

Differential regulation of GABAA receptor-mediated hyperexcitability at different stages of brain development in focal cortical dysplasia (FCD)

Focal cortical dysplasia (FCD) is a developmental abnormality of cortex commonly linked with drug-resistant seizures. Altered GABAergic activity is a key contributor to interictal discharges in FCD. In FCD, GABAA receptor associated epileptogenicity is dependent upon the age at seizure onset, as differential epileptogenic networks are observed in early and late onset FCD patients. But the contribution of GABAA receptor alteration to epileptogenic networks during development is unclear. We hypothesize that GABAergic signaling in FCD undergoes age-dependent molecular alterations, contributing to the development of distinct epileptogenic networks. In this study, we investigated age-dependent changes in GABA neurotransmitter levels, GABAA receptor α subunit expression, and GABAA receptor-mediated synaptic activity using the BCNU-rat model of FCD. GABA levels, mRNA, and protein expression of GABAA receptor α subunits were determined by HPLC, qPCR and western blot and spontaneous GABAergic activity from pyramidal neurons was recorded using whole cell patch-clamp technique. At postnatal days (P) 12 and 21, reduced expression of α1, 2 and 4 subunits were observed in FCD rats compared to control. Consistent with this, decreased amplitude and frequency of GABAergic events were observed in FCD rats. In contrast, at P30 and P65, decreased GABA levels, without changes in receptor expression, were observed in FCD rats. Consistently, reduction in the frequency of GABAergic events was observed in FCD rats compared to the control. Furthermore, treatment with tetrodotoxin (TTX) revealed that the observed alterations in GABAergic activity were predominantly action potential (AP)-dependent. Our findings indicate that distinct epileptogenic networks exist in FCD during early and late developmental stages. These networks are driven primarily by altered GABAergic activity, with early age changes linked to aberrant GABAA receptor configurations and late age changes associated with abnormal GABA levels.

Maternal N-acetylcysteine supplementation in lactation ameliorates metabolic and cognitive deficits in adult offspring exposed to maternal obesity

Maternal obesity in pregnancy and lactation is linked to metabolic disturbances and neurodevelopmental problems in offspring, increasing the risk of psychiatric disorders in adulthood. We proposed that maternal N-acetyl cysteine (NAC) supplementation during lactation, a critical period for neurodevelopment, potentially protects offspring from developing cognitive impairment in adulthood. Fifteen young female ICR mice were randomly allocated to different experimental groups: high-fat diet (HFD; 60.3% fat before mating, during pregnancy and lactation), HFD-NAC of 300 mg/kg/day during lactation, CD (high-fat diet before mating, during pregnancy, and regular chow control diet of 8.2% fat during lactation), CD-NAC of 300 mg/kg/day during lactation and control group consuming regular chow diet. The serum inflammatory markers of the offspring were evaluated post-weaning, while metabolic markers, microglial density, and cognitive performance were assessed in adulthood using the novel Object Recognition and Morris Water Maze tests. Our results demonstrate maternal obesity during gestation and lactation increased body weight, hepatic steatosis, and microglial cell density in the dentate gyrus (DG) and cortex. Furthermore, these offspring exhibited reduced spatial learning abilities in adulthood, regardless of sex. However, maternal NAC administration during lactation and maternal diet intervention significantly reduced brain microglial density and improved both male and female offspring metabolic profiles. More importantly, NAC supplementation during lactation, regardless of maternal diet, enhanced male offspring's learning ability in adulthood. Our findings indicate that administering NAC to obese mothers during the critical lactation period may offer protection against metabolic disturbances and cognitive deficits in adult offspring previously exposed to maternal obesity.

From neurotoxicity to neuroprotection: Rethinking GABAAR-targeting anesthetics

The brain growth spurt (BGS) represents a pivotal window in neurodevelopment, defined by rapid neurogenesis, heightened synaptogenesis, and the dynamic establishment of neural networks. During this phase, heightened brain plasticity significantly enhances learning and memory abilities, while also increasing the brain's susceptibility to disruptions. Anesthetics, particularly those targeting γ-aminobutyric acid type A receptors (GABAARs), interfere with GABAergic and glutamatergic systems, disrupt brain-derived neurotrophic factor (BDNF) signaling, and exacerbate neurotoxic effects. These agents activate glial cells, induce inflammation, and contribute to oxidative stress, while also disrupting calcium homeostasis and triggering endoplasmic reticulum stress. Furthermore, anesthetics alter the expression of non-coding RNAs, which affects gene regulation and long-term memory formation. The extent of neurotoxic effects is contingent upon a constellation of factors, including the timing, dosage, and frequency of anesthetic exposure, as well as individual susceptibility. Notably, perioperative administration of anesthetic agents has been implicated in long-term cognitive dysfunction, thereby emphasizing the critical importance of precisely modulated dosing regimens and temporally optimized delivery strategies to mitigate potential neurodevelopmental risks. In contrast, neuroactive steroids demonstrate promising neuroprotective potential by modulating GABAAR activity, enhancing BDNF release, and regulating oxidative stress and inflammation. New strategies for preventing and reversing anesthetic-induced neurotoxicity could include novel anesthetic combinations, anti-apoptotic agents, antioxidants, or nutritional supplements. These findings underscore the complex and multifactorial effects of anesthetic agents on the developing brain and emphasize the urgent need to establish and refine anesthetic strategies that safeguard neural integrity during vulnerable windows of neurodevelopment.

Balancing efficacy and safety: The dual impact of antiseizure medications on the developing brain

The number of neurons in the developing brain is greater than typically found in adulthood, and the brain possesses delicate mechanisms to induce the death of excess cells and refine neural circuitry. The correct tuning between the processes of neuronal death and survival generates a mature and functional brain in its complexity and plastic capacity. Epilepsy is a highly prevalent neurological condition worldwide, including among young individuals. However, exposure to the main treatment approaches, the long-term use of Antiseizure Medication (ASM), during the critical period of development can induce a series of changes in this delicate balance. Acting by various mechanisms of action, ASMs may induce an increase in neuronal death, something that translates into deleterious neuropsychiatric effects in adulthood. Several investigations conducted in recent years have brought to light new aspects related to this dynamic, yet many questions, such as the cellular mechanisms of death and the pathophysiology of late effects, still have unresolved elements. In this review, we aimed to explore the mechanisms of action of the most widely used ASMs in the treatment of neonatal epilepsy, the broad aspects of neuronal death in the developing brain and the repercussions of this death and other effects in adulthood. We review the evidence indicating a relationship between exposure to ASMs and the manifestation of associated psychiatric comorbidities in adulthood and discuss some possible mechanisms underlying the induction of this process by morphological and physiological changes in the related behaviors.

A human iPSC-Derived myelination model for investigating fetal brain injuries

Cerebral white matter injuries, such as periventricular leukomalacia, are major contributors to neurodevelopmental impairments in preterm infants. Despite the clinical significance of these conditions, human-relevant models for studying fetal brain development and injury mechanisms remain limited. This study introduces a human iPSC-derived myelination model developed using a microfluidic device. The platform combines spinal cord-patterned neuronal and oligodendrocyte spheroids to recapitulate axon-glia interactions and myelination processes in vitro. The model successfully achieved axonal fascicle formation and compact myelin deposition, as validated by immunostaining and transmission electron microscopy. Functional calcium imaging confirmed neuronal activity within the system, underscoring its physiological relevance. While myelination efficiency was partial, with some axons remaining unmyelinated under the current conditions, this model represents a significant advancement in human myelin biology, offering a foundation for investigating fetal and perinatal brain injuries and related pathologies. Future refinements, such as improved myelination coverage and incorporating additional CNS cell types, will enhance its utility for studying disease mechanisms and enabling high-throughput drug screening.

A graded neonatal mouse model of necrotizing enterocolitis demonstrates that mild enterocolitis is sufficient to activate microglia and increase cerebral cytokine expression

Necrotizing enterocolitis (NEC) is an inflammatory gastrointestinal process that afflicts approximately 10% of preterm infants born in the United States each year, with a mortality rate of 30%. NEC severity is graded using Bell's classification system, from stage I mild NEC to stage III severe NEC. Over half of NEC survivors present with neurodevelopmental impairment during adolescence, a long-term complication that is poorly understood. Although multiple animal models exist, none prospectively controls for NEC severity. We bridge this knowledge gap by characterizing a graded murine model of NEC and studying its relationship with neuroinflammation across a range of NEC severities. Postnatal day 3 (P3) C57BL/6 mice were fed a formula containing different concentrations (0% control, 0.25%, 1%, 2%, and 3%) of dextran sodium sulfate (DSS). P3 mice were fed every 3 hours for 72 hours. We collected data on weight gain and behavior (activity, response, body color) during feeding. At the end of feeding, we collected tissues (intestine, liver, plasma, brain) for immunohistochemistry, immunofluorescence, and cytokine and chemokine analysis. Throughout NEC induction, mice fed higher concentrations of DSS died sooner, lost weight faster, and became sick or lethargic earlier. Intestinal characteristics (dilation, color, friability) were worse in mice fed higher DSS concentrations. Histology revealed small intestinal disarray among all mice fed DSS, while higher DSS concentrations resulted in reduced small intestinal cellular proliferation and increased hepatic and systemic inflammation. In the brain, IL-2, G-CSF, and CXCL1 concentrations increased with higher DSS concentrations, and microglial branching in the hippocampus CA1 was significantly reduced in DSS-fed mice. In conclusion, we characterized a novel graded model of NEC that recapitulates the full range of NEC severities. We showed that mild NEC is sufficient to initiate neuroinflammation and microglia activation. This model will facilitate long-term studies on the neurodevelopmental effects of NEC.

Neurodevelopmental toxicity and mechanism of chlorinated polyfluoroalkyl ether sulfonate alternative F-53B in pubertal male rats

F-53B, a substitute for perfluorooctane sulfonate (PFOS), has attracted considerable concerns due to its frequent detection in environment matrices. However, the potential health risks to mammals, especially neurodevelopmental toxicity, remain unclear. In this study, 3-week-old pubertal male rats were exposed to F-53B at concentrations of 0, 0.15, 1.5, and 15 μg/kg for 3 weeks continuously. Diminished cognitive abilities were observed by morris water maze (MWM) test, F-53B exposure increased the escape latency and decreased the time spent in the target quadrant of rats. Furthermore, F-53B significantly altered neurotransmitter levels in the hippocampus. Molecular docking studies indicated that F-53B might bind to metabotropic glutamate receptor 5 (mGluR5), potentially entering neurons and causing further neurotoxicity. qRT-PCR and western blot analyses were used to assess the expression of genes and proteins related to calcium pathways. Results revealed that F-53B exposure downregulated mRNA expression of ryanodine receptors (RyRs) and the phosphorylation of inositol trisphosphate receptors (IP3Rs), while upregulating sarco/endoplasmic reticulum Ca2+-ATPase2 (SERCA2) levels. F-53B inhibits the IP3/Ca2+ signaling pathway in the rat hippocampus, which may affect ER Ca2+ storage and release functions. Additionally, F-53B reduced the phosphorylation of IP3R, Ca2+/calmodulin-dependent protein kinase II (CaMKII), extracellular signal-regulated kinase 1 and 2 (ERK1/2), and cAMP response element binding protein (CREB), potentially impairing synaptic plasticity and long-term potentiation (LTP), leading to learning and memory deficits. This study reveals that F-53B induced neurodevelopmental toxicity linked to calcium pathway disruption and provides new insight into the potential long-term hazards of F-53B.

Limb Motility and Ambulation as Mechanical Cues in Postnatal Murine Tendon Development

The musculoskeletal system provides structural stability and coordination to enable movement. Tendons have the essential role of efficiently transmitting force generated from muscle contraction to bone for ambulation. In doing so, they resist high mechanical loads. Muscle contraction during embryonic development is required for continued tendon growth and differentiation. Defining the types and magnitudes of loads that act on tendons during the early postnatal periods is quite difficult. This study aimed to reveal whether limb motility and spontaneous physical behaviors in the postnatal phase work as mechanical cues for tendon development, leading to mechanobiological phenomena during postnatal phases in the murine model. Neonatal mice showed gradual limb motility, rollover function, and ambulation patterns during early postnatal phases. Tendons showed lengthening, decreasing the cell density and nuclear roundness concurrently. Scx and Tnmd gene expression showed a tendency to increase with time as well. This study presented a comprehensive time course of limb movement and ambulation with corresponding tendon growth during the postnatal phase. Our chronological analysis of the relationship between changing limb loading and tendon development provides a foundation for future work focused on mechanobiology in tendon development.

The evolving neurobiology of early-life stress

Because early-life stress is common and constitutes a strong risk factor for cognitive and mental health disorders, it has been the focus of a multitude of studies in humans and experimental models. Yet, we have an incomplete understanding of what is perceived as stressful by the developing brain, what aspects of stress influence brain maturation, what developmental ages are particularly vulnerable to stress, which molecules mediate the effects of stress on brain operations, and how transient stressful experiences can lead to enduring emotional and cognitive dysfunctions. Here, we discuss these themes, highlight the challenges and progress in resolving them, and propose new concepts and avenues for future research.

Hippocampal Interneurons Shape Spatial Coding Alterations in Neurological Disorders

Hippocampal interneurons (INs) play a fundamental role in regulating neural oscillations, modulating excitatory circuits, and shaping spatial representation. While historically overshadowed by excitatory pyramidal cells in spatial coding research, recent advances have demonstrated that inhibitory INs not only coordinate network dynamics but also contribute directly to spatial information processing. This review aims to provide a novel integrative perspective on how distinct IN subtypes participate in spatial coding and how their dysfunction contributes to cognitive deficits in neurological disorders such as epilepsy, Alzheimer's disease (AD), traumatic brain injury (TBI), and cerebral hypoxia-ischemia. We synthesize recent findings demonstrating that different IN classes-including parvalbumin (PV)-, somatostatin (SST)-, cholecystokinin (CCK)-, and calretinin (CR)-expressing neurons-exhibit spatially selective activity, challenging traditional views of spatial representation, and influence memory consolidation through network-level interactions. By leveraging cutting-edge techniques such as in vivo calcium imaging and optogenetics, new evidence suggests that INs encode spatial information with a level of specificity previously attributed only to pyramidal cells. Furthermore, we investigate the impact of inhibitory circuit dysfunction in neurological disorders, examining how disruptions in interneuronal activity lead to impaired theta-gamma coupling, altered sharp wave ripples, and destabilized place cell representations, ultimately resulting in spatial memory deficits. This review advances the field by shifting the focus from pyramidal-centered models to a more nuanced understanding of the hippocampal network, emphasizing the active role of INs in spatial coding. By highlighting the translational potential of targeting inhibitory circuits for therapeutic interventions, we propose novel strategies for restoring hippocampal network function in neurological conditions. Readers will gain a comprehensive understanding of the emerging role of INs in spatial representation and the critical implications of their dysfunction, paving the way for future research on interneuron-targeted treatments for cognitive disorders.

Chronic low-level exposure to Pb, Hg, and Cd mixture triggers brain premature aging in rat

Lead (Pb), mercury (Hg), and cadmium (Cd), prevalent neurotoxic heavy metals in the environment, are commonly detected at low concentrations in the blood of the general population. Our previous studies demonstrated that Pb, Hg, and Cd mixture induced neurodevelopmental toxicity even at very low levels. However, the long-term effects of low-level Pb, Hg, Cd exposure on brain aging remain unclear. In this study, female rats were exposed to a mixture of 10 mg/L Pb(CH3COO)2, 0.05 mg/L HgCl2, and 3.5 mg/L CdCl2 via drinking water from mating until offspring weaning. Offspring continued to exposed to heavy metal mixture (3.5 mg/L Pb(CH3COO)2, 0.015 mg/L HgCl2, and 0.5 mg/L CdCl2) for 32 weeks. At 52 weeks of age, brain aging was comprehensively evaluated through behavioral testing, histopathological examination, and telomere assessment. The results revealed that prolonged low-level exposure to the Pb, Hg, and Cd mixture compromised telomeric function by shortening telomere length, inhibiting telomerase activity, and induced neuronal loss in the hippocampal CA1 and CA3 regions. Additionally, Golgi staining revealed disrupted dendritic spines in the hippocampus and altered spine-related signaling pathways (Snk-SPAR pathway). Furthermore, behavioral testing showed that exposure to this mixture impaired spatial memory and social cognition. In conclusion, prolonged exposure to low levels of Pb, Hg, and Cd accelerated brain aging by causing hippocampal telomere dysfunction, neuronal loss, dendritic degeneration, and cognitive decline in rats. These findings offer novel insights into the potential neurotoxic effects of chronic exposure to low-level of Pb, Hg, and Cd mixtures on neurological health.

Early postnatal inhibition of neurosteroid synthesis changes the later-life adverse outcome of neonatal asphyxia in rats

Birth asphyxia (BA) is a common cause of hypoxic-ischemic encephalopathy (HIE), neonatal seizures, and detrimental neurodevelopment. Brain levels of neurosteroids such as allopregnanolone rise in response to acute hypoxic stress, which is thought to represent an endogenous protective mechanism that reduces excitotoxicity in the developing brain. In the present study, we investigated how inhibition of neurosteroid synthesis by the steroid 5α-reductase inhibitor finasteride affects the adverse outcomes of BA/HIE. Intermittent asphyxia was induced in neonatal rats at postnatal day 11. Finasteride (50 mg/kg) was administered immediately before asphyxia. Behavioral and cognitive tests were performed over the subsequent 14 months, which corresponds to ∼50 % of the lifespan of the outbred rat strain used. In contrast to our expectation, finasteride decreased the severity and duration of the neonatal seizures and did not increase mortality. Subsequent behavioral experiments showed no adverse development of motor function, but finasteride-treated rats exhibited increased anxiety-like behavior in the open field, elevated plus-maze, and light-dark box tests. The increased anxiety-like behavior was correlated with enhanced mossy fiber sprouting in the hippocampal CA3a region. While vehicle-treated post-asphyxial rats showed a serious decline in cognitive functions, this was not observed in the finasteride-treated group. One possible explanation of the latter finding is that a significant loss of CA3c neurons in the dorsal hippocampus was only determined in vehicle-treated but not finasteride-treated post-asphyxial rats. Overall, the present study indicates that the role of neurosteroids in BA and its adverse outcome is much more complex than previously thought.

Endogenous Recovery of Hippocampal Function Following Global Cerebral Ischemia in Juvenile Female Mice Is Influenced by Neuroinflammation and Circulating Sex Hormones

Cardiac arrest (CA)-induced global cerebral ischemia (GCI) in childhood often results in learning and memory deficits. We previously demonstrated in a murine CA and cardiopulmonary resuscitation (CA/CPR) mouse model that a cellular mechanism of learning and memory, long-term potentiation (LTP), is acutely impaired in the hippocampus of juvenile males, correlating with deficits in memory tasks. However, little is known regarding plasticity impairments in juvenile females. We performed CA/CPR in juvenile (P21-25) female mice and used slice electrophysiology and hippocampal-dependent behavior to assess hippocampal function. LTP and contextual fear were impaired 7 days after GCI and endogenously recovered by 30 days. LTP remained impaired at 30 days in ovariectomized females, suggesting the surge in gonadal sex hormones during puberty mediates endogenous recovery. Unlike juvenile males, recovery of LTP in juvenile females was not associated with BDNF expression. NanoString transcriptional analysis revealed a potential role of neuroinflammatory processes, and specifically Cd68 pathways, in LTP impairment and hormone-dependent recovery. This was confirmed with staining that revealed increased Cd68 expression in microglia within the hippocampus. We were able to restore LTP in ovariectomized females with chronic and acute PPT administration, implicating estrogen receptor alpha in recovery mechanisms. This study supports a mechanism of endogenous LTP recovery after GCI in juvenile female mice, which differs mechanistically from juvenile males and does not occur in adults of either sex.

Excitotoxic lesion in the corpus callosum of neonatal rats: A model for encephalopathy of prematurity

Encephalopathy of prematurity (EP) can develop in preterm infants exposed to risk factors like extreme prematurity, low birth weight, hypoxia, infections, and inflammation. These factors can induce excitotoxicity in the brain's gray and white matter, leading to the death of neurons and oligodendrocyte progenitors. Understanding the brain mechanisms of EP requires animal models. In this study, we generated an EP model by injecting N-methyl-D-aspartic acid (NMDA) into the corpus callosum (CC) of neonatal male rats on postnatal day (PND) 5. Rats were divided into five groups: Intact, Vehicle, and three doses of NMDA (3, 4, or 5 μg). On PND 20, we measured the volumes of the CC, motor cortex (MC), and lateral ventricles. The 5 µg NMDA dose caused the largest lesion. We later assessed these structures on PNDs 6, 10, 20, and 30 to monitor lesion progression. We also analyzed myelin basic protein (MBP) expression and counted NeuN-positive cells using immunofluorescent markers. NMDA groups showed reduced MBP expression and fewer NeuN-positive cells in the MC. Additionally, NMDA-treated rats exhibited increased motor activity in the open field and reduced fall latencies in the rotarod task compared to controls. In conclusion, our perinatal excitotoxic lesion model in rats demonstrates structural abnormalities, including decreased MBP and loss of NeuN-positive cells, alongside motor and habituation impairments, resembling those seen in human EP.

Perinatal SSRI exposure impacts innate fear circuit activation and behavior in mice and humans

Before assuming its role in the mature brain, serotonin modulates early brain development across phylogenetically diverse species. In mice and humans, early-life SSRI exposure alters the offspring's brain structure and is associated with anxiety and depression-related behaviors beginning in puberty. However, the impact of early-life SSRI exposure on brain circuit function is unknown. To address this question, we examined how developmental SSRI exposure changes fear-related brain activation and behavior in mice and humans. SSRI-exposed mice showed increased defense responses to a predator odor, and stronger fMRI amygdala and extended fear-circuit activation. Likewise, adolescents exposed to SSRIs in utero exhibited higher anxiety and depression symptoms than unexposed adolescents and also had greater activation of the amygdala and other limbic structures when processing fearful faces. These findings demonstrate that increases in anxiety and fear-related behaviors as well as brain circuit activation following developmental SSRI exposure are conserved between mice and humans. These findings have potential implications for the clinical use of SSRIs during human pregnancy and for designing interventions that protect fetal brain development.

Interleukin-6 produces behavioral deficits in pre-pubescent mice independent of neuroinflammation

Maternal inflammation during pregnancy increases the offspring's risk of developing autism, ADHD, schizophrenia, and depression. Epidemiologic studies have demonstrated that maternal infections stimulate the production of interleukin-6 (IL-6), which can cross the placenta and fetal blood-brain barrier to alter brain development with functional and behavioral consequences. To model the effects of increased IL-6 between weeks 24-30 of human gestation, we injected male and female mice with 75 ng IL-6 twice daily, from P3 to P6. Our published studies have shown that this increases circulating IL-6 two-fold, alters post-pubescent ultrasonic vocalization patterns, reduces sociability, and increases self-grooming. However, most neurodevelopmental disorders in humans manifest in children as young as 2 years of age. Hence, a critical unexplored question is whether behavioral changes in immune activation models can be detected in pre-pubescent mice. Therefore, we evaluated early communication, sociability, and repetitive behaviors in pre-pubescent mice following the IL-6 treatment. A second open question is whether the cellular and behavioral changes are secondary to systemic or neuroinflammation. To address this question, we profiled 18 cytokines and chemokines in the circulation and CNS and evaluated eight immune cell types in P7 male and female brains following systemic IL-6 administration. We found an increase in ultrasonic vocalizations with simpler morphologies produced by the IL-6-injected male pups and a decrease in frequency in the female vocalizations upon removal from the nest at P7. The IL-6-treated male pups also socially interacted less when introduced to a novel mouse vs. controls as juveniles and spent almost twice as much time grooming themselves, a phenotype not present in the females. Tactile sensitivity was also increased, but only in the IL-6-treated female mice. The IL-6-treated mice had increased circulating IL-6 and IL-7 and reduced IL-13 at P7 that were no longer elevated at P14. There were no changes in brain levels of IL-6, IL-10, IL-13 or IL-17A mRNAs at P7. Altogether, these studies show that changes in the three core behavioral domains associated with several psychiatric disorders can be detected early in pre-pubescent mice following a transient developmental increase in IL-6. Yet, these behavioral alterations do not require neuroinflammation.

β3-Adrenoceptor Agonism to Mimic the Biological Effects of Intrauterine Hypoxia: Taking Great Strides Toward a Pharmacological Artificial Placenta

At different stages of life, from embryonic to postnatal, varying oxygen concentrations modulate cellular gene expression by enhancing or repressing hypoxia-inducible transcription factors. During embryonic/fetal life, these genes encode proteins involved in adapting to a low-oxygen environment, including the induction of specific enzymes related to glycolytic metabolism, erythropoiesis, angiogenesis, and vasculogenesis. However, oxygen concentrations fluctuate during intrauterine life, enabling the induction of tissue-specific differentiation processes. Fetal well-being is thus closely linked to the physiological benefits of a dynamically hypoxic environment. Premature birth entails the precocious exposure of the immature fetus to a more oxygen-rich environment compared to the womb. As a result, preterm newborns face a condition of relative hyperoxia, which alters the postnatal development of organs and contributes to prematurity-related diseases. However, until recently, the molecular mechanism by which high oxygen tension alters normal fetal differentiation remained unclear. In this review, we discuss the research trajectory followed by our research group, which suggests that early exposure to a relatively hyperoxic environment may impair preterm neonates due to reduced expression of the β3-adrenoceptor. Additionally, we explore how these impairments could be prevented through the pharmacological stimulation of the remaining β3-adrenoceptors. Recent preclinical studies demonstrate that pharmacological stimulation of the β3-adrenoceptor can decouple exposure to hyperoxia from its harmful effects, offering a glimpse of the possibility to recreating the conditions typical of intrauterine life, even after premature birth.

Schizophrenia pathology reverse-translated into mouse shows hippocampal hyperactivity, psychosis behaviors and hyper-synchronous events

Decades of research into the function of the medial temporal lobe has driven curiosity around clinical outcomes associated with hippocampal dysfunction, including psychosis. Post-mortem analyses of brain tissue from human schizophrenia brain show decreased expression of the NMDAR subunit GluN1 confined to the dentate gyrus with evidence of downstream hippocampal hyperactivity in CA3 and CA1. Little is known about the mechanisms of the emergence of hippocampal hyperactivity as a putative psychosis biomarker. We have developed a reverse-translation mouse to study critical neural features. We had previously studied a dentate gyrus (DG)-specific GluN1 KO, which displays hippocampal hyperactivity and a psychosis-relevant behavioral phenotype. Here, we expressed an inhibitory DREADD (pAAV-CaMKIIa-hM4D(Gi)-mCherry) in granule cells of the mouse dentate gyrus, and continuously inhibited the region for 21 days in adolescent (6 weeks) and adult (10 weeks) C57BL/6 J mice with DREADD agonist Compound 21 (C21). Following this period, we quantified activity in the hippocampal subfields by assessing cFos expression, hippocampally mediated behaviors, and hippocampal local field potential with an intracerebral probe with continual monitoring over time. DG inhibition during adolescence generates an increase in hippocampal activity in CA3 and CA1, impairs social cognition and spatial working memory, as well as shows evidence of increased activity in local field potentials as spontaneous synchronous bursts of activity, which we term hyper-synchronous events (HSEs) in hippocampus. The same DG inhibition delivered during adulthood in the mouse lacks these outcomes. These results suggest a sensitive period in development in which the hippocampus is susceptible to DG inhibition resulting in hippocampal hyperactivity and psychosis-like behavioral outcomes.

Safety in treatment: Classical pharmacotherapeutics and new avenues for addressing maternal depression and anxiety during pregnancy

We aimed to review clinical research on the safety profiles of antidepressant drugs and associations with maternal depression and neonatal outcomes. We focused on neuroendocrine changes during pregnancy and their effects on antidepressant pharmacokinetics. Pregnancy-induced alterations in drug disposition and metabolism impacting mothers and their fetuses are discussed. We considered evidence for the risks of antidepressant use during pregnancy. Teratogenicity associated with ongoing treatment, new prescriptions during pregnancy, or pausing medication while pregnant was examined. The Food and Drug Administration advises caution regarding prenatal exposure to most drugs, including antidepressants, largely owing to a dearth of safety studies caused by the common exclusion of pregnant individuals in clinical trials. We contrasted findings on antidepressant use with the lack of treatment where detrimental effects to mothers and children are well researched. Overall, drug classes such as selective serotonin reuptake inhibitors and serotonin norepinephrine reuptake inhibitors appear to have limited adverse effects on fetal health and child development. In the face of an increasing prevalence of major mood and anxiety disorders, we assert that individuals should be counseled before and during pregnancy about the risks and benefits of antidepressant treatment given that withholding treatment has possible negative outcomes. Moreover, newer therapeutics, such as ketamine and κ-opioid receptor antagonists, warrant further investigation for use during pregnancy. SIGNIFICANCE STATEMENT: The safety of antidepressant use during pregnancy remains controversial owing to an incomplete understanding of how drug exposure affects fetal development, brain maturation, and behavior in offspring. This leaves pregnant people especially vulnerable, as pregnancy can be a highly stressful experience for many individuals, with stress being the biggest known risk factor for developing a mood or anxiety disorder. This review focuses on perinatal pharmacotherapy for treating mood and anxiety disorders, highlighting the current knowledge and gaps in our understanding of consequences of treatment.

Tracking brain maturation in vivo: functional connectivity, white matter integrity, and synaptic density in developing mice

BACKGROUND

Investigating dynamic changes during normal brain development is essential for understanding neurodevelopmental disorders (NDDs) and assessing the impact of novel therapies for these conditions. Rodent models, with their shorter developmental timeline, offer a valuable alternative to humans. This study aimed to characterise brain maturation in mice using a longitudinal, multimodal imaging approach.

METHODS

We conducted an in vivo imaging study on 31129/Sv mice with a complete longitudinal dataset available for 22 mice. Resting-state functional MRI (rs-fMRI), diffusion tensor imaging (DTI), and [18F]SynVesT-1 PET were used to examine the development of brain functional connectivity (FC), white matter integrity, and synaptic density at three developmental stages: infancy (P14-21), juvenile (P32-42), and adulthood (P87-106).

FINDINGS

From infancy to juvenile age, we observed a significant decrease in FC and synaptic density, alongside increases in fractional anisotropy (FA) and decreases in mean, axial, and radial diffusivity (RD). From juvenile to adult age, synaptic density and FC stabilised, while FA further increased, and RD continued to decrease. The default mode like network was identifiable in mice across all developmental stages.

INTERPRETATION

Our findings mirror established patterns of human brain development, with infant mice allowing us to capture critical brain developmental changes, underscoring the translational relevance of our findings. This study provides a robust framework for normal rodent neurodevelopment and establishes a foundation for future research on NDDs in mice and the impact of novel treatments on neurodevelopment.

FUNDING

Supported by the University of Antwerp, Fonds Wetenschappelijk Onderzoek (FWO), the Queen Elisabeth Medical Foundation, the European Joint Programme on Rare Disease, and Fondation Lejeune.

Lactate Receptor HCAR1 Affects Axonal Development and Contributes to Lactate's Protection of Axons and Myelin in Experimental Neonatal Hypoglycemia

Lactate plays an important role in brain energy metabolism. It contributes to normal brain development and to neuroprotection in diabetic hypoglycemia, but its role in neonatal hypoglycemia is unclear. Moreover, lactate can work as a signaling substance via the lactate receptor HCAR1 (Hydroxycarboxylic acid receptor 1). Recent studies indicate that HCAR1 is protective in mouse models of neonatal hypoxic ischemia and has a role in metabolic regulation in glial cells during hypoglycemia. Here we have studied potential impacts of HCAR1 on axonal and myelin development in the cerebral cortex and corpus callosum of young (P21) wild-type (WT) mice and HCAR1 KO mice and in cortical organotypic brain slice cultures. The HCAR1 KO mice showed lower axonal area relative to WT in both cortex and corpus callosum. However, the myelin area was unaffected by HCAR1 KO. Using particle and colocalization analysis, we show that HCAR1 KO predominantly reduces axonal size in unmyelinated axons. Using an organotypic brain slice model of neonatal hypoglycemia, we find that lactate protects both axonal and myelin development in hypoglycemia, partially via HCAR1. Lastly, live imaging with a pH-sensitive dye on acute cortical brain slices indicates that cellular lactate uptake is influenced by HCAR1. In conclusion, our findings support a role of HCAR1 in axonal development and in lactate's protective effects in hypoglycemia.

Anxiety- and nociception-like behaviours in mature adult mice induced by audiovisual overstimulation during infancy

OBJECTIVES

To evaluate the behavioural effects in adult mice previously subjected to audiovisual overstimulation during infancy and adolescence.

METHODS

Mice aged 21, 26 and 36 days (p21, p26 and p36) underwent auditory (70 db) and visual (flashing lights) stimulation for 2 or 6 h per day until p64; naive animals were used as controls. At p200, tests assessed respectively motor activity (open field test), depression (forced swimming and splash tests), anxiety (hole board, plus maze and marble burying tests, aggression (resident-intruder test), and nociception (von Frey and hot plate tests).

RESULTS

There were no significant (ANOVA, p > 0.05) behavioural changes in forced swimming, splash, hole board, or marble burying tests between overstimulated and naive groups. However, the p21 group showed significantly (ANOVA, p < 0.05) increased anxiety-like behaviour (2 h) in the elevated plus maze test and altered nociceptive behaviour in the von Frey test (2 and 6 h). The p26 group (2 h) displayed significantly reduced rearing behaviours, fewer entries in the plus maze test, and faster reaction times to noxious thermal stimulation (2 h).

CONCLUSION

Audiovisual overstimulation during early development can promote anxiety-like behaviour and affect nociceptive behaviour in adult mice.

Oxytocin Improves Autistic Behaviors by Positively Shifting GABA Reversal Potential via NKCC1 in Early-Postnatal-Stage

Accumulating evidence has identified disrupted oxytocin signaling in both autistic patients and animal models of autism. Nevertheless, the specific timing of the impact of oxytocin on social behavior has remained unclear. Using mouse strains from oxytocin-Cre mice crossed with Cre-dependent chemogenetic mice, oxytocinergic neuronal activity is selectivity manipulated during the early or late postnatal stages and revealed, for the first time, that the suppression of oxytocinergic neurons in the early rather than late postnatal stage led to the emergence of autistic-like behaviors. Notably, significantly reduced oxytocin levels are identified specifically during the early postnatal stage in both valproic acid (VPA)-exposed and Fmr1-KO mouse brains, along with an impairment of the GABA reversal potential and downregulation of the Na+-K+-2Cl- cotransporter (NKCC1) post-birth. Furthermore, chemogenetic activation of oxytocinergic neurons during the early rather than late postnatal stage effectively restored the aberrant NKCC1 expression and GABAA receptor reversal potential and consequently alleviated autistic-like behaviors in VPA-exposed mice. Overall, the results demonstrate that the early postnatal stage may be the unique critical period for oxytocin signaling to regulate GABA reversal potential and promote brain development for prosocial behaviors. These findings suggest an earlier intervention window and strategy for the clinical oxytocin treatment of autism.

Maternal noninfectious fever during pregnancy modulates offspring social behavior in rats: an exploratory study

BACKGROUND

Maternal fever and elevated interleukin-6 (IL-6) during labor are linked to higher risks of neonatal seizures and cerebral palsy. In rats, IL-6-induced maternal fever is associated with neonatal brain inflammation. This study tests the hypothesis that induced maternal noninfectious fever modulates social behavior in rat offspring.

METHODS

Two groups of near-term pregnant rats (n=6/group) received systemic IL-6 and the intracerebroventricular prostaglandin E1 (PGE1) or vehicle solutions. Maternal core temperature was recorded and pups were delivered naturally. Sixteen offspring (n=8/group) underwent Crawley's behavioral sociability assessment at 4-5 months of age.

RESULTS

Injection with PGE1 + IL-6 increased mean ± standard deviation (SD) core maternal temperature by 1.1 ± 0.3°C in the first hour compared to vehicle (P <0.001), with significant effect at 30, 60, and 90 minutes (P <0.05). Both groups preferred the social cue over the empty enclosure (F(1,14)=45.1, P <0.001), but their relative interest differed (Group x Side interaction: F(1,14)=5.1, P =0.033). Offspring of febrile mothers spent significantly less time (mean ± SD) sniffing the stranger rat's enclosure compared to controls (36.9 ± 15.8 vs. 56.3 ± 12.1 seconds, P =0.0154) indicating reduced sociability. However, both groups showed similar interest in social novelty, suggesting that recognition of a new social stimulus was unaffected.

CONCLUSIONS

Pups exposed to PGE1 + IL-6 spent significantly less time than control pups exploring a new rat, suggesting decreased sociability. These results suggest a long-term effect of maternal fever and systemic noninfectious inflammation on offspring social behavior, highlighting the need for further research into the mechanisms underlying these neurodevelopmental changes.

Multi-site investigation of gut microbiota in CDKL5 deficiency disorder mouse models: Targeting dysbiosis to improve neurological outcomes

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.

Elevated brain manganese induces motor disease by upregulating the kynurenine pathway of tryptophan metabolism

Elevated brain levels of the essential metals manganese (Mn), copper, or iron induce motor disease. However, mechanisms of metal-induced motor disease are unclear and treatments are lacking. Elucidating the mechanisms of Mn-induced motor disease is particularly important because occupational and environmental Mn overexposure is a global public health problem. To address this, here we combined unbiased transcriptomics and metabolomics with functional studies in a mouse model of human environmental Mn exposure. Transcriptomics unexpectedly revealed that Mn exposure up-regulated expression of metabolic pathways in the brain and liver. Notably, genes in the kynurenine pathway of tryptophan metabolism, which produces neuroactive metabolites that impact neurological function, were up-regulated by Mn. Subsequent unbiased metabolomics revealed that Mn treatment altered kynurenine pathway metabolites in the brain and liver. Functional experiments then demonstrated that pharmacological inhibition of the first and rate-limiting step of the kynurenine pathway fully rescued Mn-induced motor deficits. Finally, elevated Mn directly activates hypoxia-inducible factor (HIF) transcription factors, and additional mechanistic assays identified a role for HIF1, but not HIF2, in regulating expression of hepatic kynurenine pathway genes under physiological or Mn exposure conditions, suggesting that Mn-induced HIF1 activation may contribute to the dysregulation of the kynurenine pathway in Mn toxicity. These findings (1) identify the upregulation of the kynurenine pathway by elevated Mn as a fundamental mechanism of Mn-induced motor deficits; (2) provide a pharmacological approach to treat Mn-induced motor disease; and (3) should broadly advance understanding of the general principles underlying neuromotor deficits caused by metal toxicity.

Alterations in the ultrasonic vocalization sequences in pups of an autism spectrum disorder mouse model: A longitudinal study over age and sex

Social communication deficit is a hallmark of autism spectrum disorders (ASDs). Mouse ultrasonic-vocalizations (USVs), with communicative significance, are extensively used to probe vocalization-based social communication impairment. Despite the predictable nature of mouse USVs, very few studies have taken advantage of the same. The current work explores USV pup-isolation-call (PIC) features and alterations in structural content of predictive PIC sequences of the well-established in-utero valproic-acid (VPA) exposure-based ASDs model. Our study shows that along with call features, even higher-order USV structures undergo alterations in the ASDs model at all developmental ages and sexes. Confirming prior observations, we found reduced call rates and durations, as well as heightened peak frequencies in ASD model pups. Our data also highlights trends in call features, syllable composition, and transitions across sexes and age. The ASD female mice exhibited higher within group heterogeneity in syllable composition and transition over age compared to ASD males or typically developing males and females. Analysis of sequences of USVs emitted by pups using mutual information between syllables at different positions revealed that dependencies between syllables were higher in typically developing mice of both sexes compared to ASD model pups. In brief, we found that PICs call features were altered in VPA mouse models both for male and female pups and their vocalizations lack the complex syllable sequence order emitted by typically developing ones. Our studies will help establish and further investigate ASD mouse models to get a clearer picture of abnormalities related to social communication deficits over sexes and age.

New insights into epileptic spasm generation and treatment from the TTX animal model

Currently, we have an incomplete understanding of the mechanisms underlying infantile epileptic spasms syndrome (IESS). However, over the past decade, significant efforts have been made to develop IESS animal models to provide much-needed mechanistic information for therapy development. Our laboratory has focused on the TTX model and in this paper, we review some of our findings. To induce spasms, tetrodotoxin (TTX) is infused into the neocortex of infant rats. TTX produces a lesion at its infusion site and thus mimics IESS resulting from acquired structural brain abnormalities. Subsequent electrophysiological studies showed that the epileptic spasms originate from neocortical layer V pyramidal cells. Importantly, experimental maneuvers that increase the excitability of these cells produce focal seizures in non-epileptic control animals but never produce them in TTX-infused epileptic rats; instead, epileptic spasms are produced in epileptic rats, indicating a significant transformation in the operations of neocortical networks. At the molecular level, studies showed that the expression of insulin-like growth factor 1 was markedly reduced in the cortex and this corresponded with a loss of presynaptic GABAergic nerve terminals. Very similar observations were made in surgically resected tissue from IESS patients with a history of perinatal strokes. Other experiments in conditional knockout mice indicated that IGF-1 plays a critical role in the maturation of neocortical inhibitory connectivity. This finding led to our hypothesis that the loss of IGF-1 in epileptic animals impairs inhibitory interneuron synaptogenesis and is responsible for spasms. To test this idea, we treated epileptic rats with the IGF-1-derived tripeptide (1-3)IGF-1, which was shown to act through IGF-1's receptor. (1-3)IGF-1 rescued inhibitory interneuron connectivity, restored IGF-1 levels, and abolished spasms. Thus, (1-3)IGF-1 or its analogs are potential novel treatments for IESS following perinatal brain injury. We conclude by discussing our findings in the broader context of the often-debated final common pathway hypothesis for IESS. PLAIN LANGUAGE SUMMARY: We review findings from the TTX animal model of infantile epileptic spasms syndrome, which show that these seizures come from an area of the brain called the neocortex. In this area, the amount of an important growth factor called IGF-1 is reduced, as is the number of inhibitory synapses that play an important role in preventing seizures. Other results indicate that the loss of IGF-1 prevents the normal development of these inhibitory synapses. Treatment of epileptic animals with (1-3)IGF-1 restored IGF-1 levels and inhibitory synapses and abolished spasms. Thus, (1-3)IGF-1 or an analog is a potential new therapy for epileptic spasms.

Fate plasticity of interneuron specification

Neuronal subtype generation in the mammalian central nervous system is governed by competing genetic programs. The medial ganglionic eminence (MGE) produces two major cortical interneuron (IN) populations, somatostatin (Sst) and parvalbumin (Pvalb), which develop on different timelines. The extent to which external signals influence these identities remains unclear. Pvalb-positive INs are crucial for cortical circuit regulation but challenging to model in vitro. We grafted mouse MGE progenitors into diverse 2D and 3D co-culture systems, including mouse and human cortical, MGE, and thalamic models. Strikingly, only 3D human corticogenesis models promoted efficient, non-autonomous Pvalb differentiation, characterized by upregulation of Pvalb maturation markers, downregulation of Sst-specific markers, and the formation of perineuronal nets. Additionally, lineage-traced postmitotic Sst-positive INs upregulated Pvalb when grafted onto human cortical models. These findings reveal unexpected fate plasticity in MGE-derived INs, suggesting that their identities can be dynamically shaped by the environment.

Ongoing loss of viable neurons for weeks after mild hypoxia-ischaemia

Mild hypoxic-ischaemic encephalopathy is common in neonates, and there are no evidence-based therapies. By school age, 30-40% of those patients experience adverse neurodevelopmental outcomes. The nature and progression of mild injury is poorly understood. We studied the evolution of mild perinatal brain injury using longitudinal two-photon imaging of transgenic fluorescent calcium-sensitive and insensitive proteins to provide a novel readout of neuronal viability and activity at cellular resolution in vitro and in vivo. In vitro, perinatal organotypic hippocampal cultures underwent 15-20 min of oxygen-glucose deprivation. In vivo, mild hypoxia-ischaemia was completed at post-natal day 10 with carotid ligation and 15 min of hypoxia (FiO2, 0.08). Consistent with a mild injury, minimal immediate neuronal death was seen in vitro or in vivo, and there was no volumetric evidence of injury by ex vivo MRI 2.5 weeks after injury (n = 3 pups/group). However, in both the hippocampus and neocortex, these mild injuries resulted in delayed and progressive neuronal loss by the second week after injury compared to controls; measured by fluorophore quenching (n = 6 slices/group in vitro, P < 0.001; n = 8 pups/group in vivo, P < 0.01). Mild hypoxia-ischaemia transiently suppressed cortical network calcium activity in vivo for over 2 h after injury (versus sham, n = 13 pups/group; P < 0.01). No post-injury seizures were seen. By 24 h, network activity fully recovered, and there was no disruption in the development of normal cortical activity for 11 days (n = 8 pups/group). The participation in network activity of individual neurons destined to die in vivo was indistinguishable from those that survived up to 4 days post-injury (n = 8 pups/group). Despite a lack of significant immediate neuronal death and only transient disruptions of network activity, mild perinatal brain injury resulted in a delayed and progressive increase of neuronal death in the hippocampus and neocortex. Neurons that died late were functioning normally for days after injury, suggesting a new pathophysiology of neuronal death after mild injury. Critically, the neurons destined to die late demonstrated multiple biomarkers of viability long after mild injury, suggesting their later death may be modified with neuroprotective interventions.

Asynchronous development of the mouse auditory cortex is driven by hemispheric identity and sex

Lateralized auditory processing is essential for specialized functions such as speech processing, typically dominated by the Left Auditory Cortex (ACx) in humans. Hemispheric specializations also occur in the adult mouse ACx, but their developmental origins are unclear. Our study finds that the Left and Right ACx in mice reach developmental milestones at different ages. Thalamocortical responses and maturation of synaptic dynamics develop earlier in the Right ACx than the Left. We show that this timing offset predicts hemisphere-dependent differences in sensory-driven plasticity. Juvenile tone exposure at specific times results in imbalanced adult tone frequency representations in the Right and Left ACx. Additionally, sex influences the timing of plasticity; female Right ACx plasticity occurs before male Right ACx, and female Left ACx aligns with male Right ACx plasticity. Our findings demonstrate that sex and hemispheric identity drive asynchronous development and contribute to functional differences in sensory cortices.

Animal studies reveal downregulation of the Beclin-1 autophagy pathway as shared mechanism in Autism Spectrum Disorder: a systematic review and meta-analysis

BACKGROUND

Autism Spectrum Disorder (ASD) is a heterogeneous neurodevelopmental condition with complex etiology, involving genetic and environmental influences on brain development and behavior. Dysregulation of mammalian target of rapamycin (mTOR) signaling alters neuronal growth and synaptic plasticity, and has emerged as a potential underlying pathway in ASD.

GOAL AND METHODS

To investigate mTOR dysregulation as a common mechanism in ASD, we performed a systematic review, and a meta-analysis of 192 studies examining mTOR signaling in diverse genetic and environmental animal models.

RESULTS

Our random-effects model identified significant alterations in mTOR pathway-related proteins. For several proteins (p-AKT, PTEN, p-mTOR, p-EIF4e, LC3-II, p-S6K and p-S6), subgroup analyses revealed clear species-, sex-, age-, or brain region-specific effects. Interestingly, Beclin-1 was consistently downregulated across all subgroups.

CONCLUSION

Our findings support mTOR-pathway dysregulation in ASD. The observed consistent downregulation of Beclin-1 highlights autophagy as a common mechanism, and provides new leads for novel ASD biomarker and treatment development.

Abscisic Acid Rescues Behavior in Adult Female Mice in Attention Deficit Disorder with Hyperactivity Model of Dopamine Depletion by Regulating Microglia and Increasing Vesicular GABA Transporter Expression

Attention-deficit/hyperactivity disorder (ADHD) is a neurodevelopmental syndrome typically diagnosed in childhood that may persist into adulthood. Its etiology encompasses both genetic and environmental factors, with genetic studies indicating catecholamine dysfunction and epidemiological evidence emphasizing neuroinflammation as a potential trigger. To investigate the roles of inflammation and development processes in ADHD, we conducted a longitudinal behavioral study using female Swiss mice with a dopamine deficit model. We explored the impact of neonatal dopaminergic lesions, treatment with abscisic acid (ABA)-an anti-inflammatory hormone-and developmental changes by comparing behavioral patterns in juvenile and adult mice. Postmortem analyses assessed neuroinflammation through microglial morphology, NLRP3, cytokine expression, and the excitatory/inhibitory (E/I) ratio in specific brain regions. Neonatal dopaminergic lesions induced hyperactivity and hypersensitivity in juvenile mice that persisted into adulthood. In adults, increased social interaction and memory impairment were observed in lesioned mice. Brain development mitigated impulsivity, while ABA treatment reduced locomotor activity, downregulated pain sensitivity, and influenced social interaction, although it did not completely resolve cognitive deficits in lesioned adult mice. In brain regions such as the anterior cingulate cortex (ACC), posterior insular cortex (pIC), and hippocampus, lesions significantly altered microglial morphology. In the ACC, lesions increased IL-1β and TNFα levels, decreased Arg1 mRNA levels, and disrupted the E/I balance. Importantly, ABA treatment restored microglial morphology, normalized IL-1β and Arg1 expression and upregulated vGAT levels. This study demonstrates that dopamine deficits lead to microglia alterations and E/I imbalance, contributing to ADHD symptoms. While some symptoms improve with brain development, targeting microglial health in specific brain regions emerges as a promising therapeutic approach for managing ADHD.

Upregulating mTOR/S6 K Pathway by CASTOR1 Promotes Astrocyte Proliferation and Myelination in Gpam-/--induced mouse model of cerebral palsy

GPAM, a key enzyme for lipid synthesis, is predominantly expressed in astrocytes (ASTs), where it facilitates lipid supply for myelin formation. Our previous studies identified GPAM as a novel causative gene for cerebral palsy (CP) and led to the development of a CP mouse model with GPAM deficiency (Gpam-/-). The model closely recapitulated the clinical phenotype of children with CP, due to the restricted proliferation of ASTs in the brain, reduced the amount of lipid, thinner brain white matter, and myelin dysplasia. The mammalian target of rapamycin (mTOR) pathway plays an important role in cell proliferation and lipid synthesis. Cytosolic arginine sensor (CASTOR1) interacts with GATOR2 to regulate mTOR complex 1 (mTORC1). Targeted degradation of CASTOR1 can activate the mTOR pathway. However, it remains unclear the involvement of mTOR pathway in neurological diseases such as CP. In this study, we demonstrated that the mTOR pathway was inhibited in Gpam-/- mice. Notably, CASTOR1 could regulate the activity of mTOR/S6K pathway, functioning as a negative upstream regulator. Furthermore, inhibition of CASTOR1 upregulated mTOR/S6K signaling, promoting astrocyte proliferation and myelination, which in turn enhanced motor function in the Gpam-/--induced CP mouse model. Collectively, these findings reveal the role of astrocytic mTOR in the pathogenesis of CP mice, broaden the therapeutic strategies, and provide a promising candidate target for CP treatment.

The shifting landscape of the preterm brain

Preterm birth remains a significant global health concern despite advancements in neonatal care. While survival rates have increased, the long-term neurodevelopmental consequences of preterm birth persist. Notably, the profile of the preterm infant has shifted, with infants at earlier gestational ages surviving and decreased rates of gross structural injury secondary to intracranial hemorrhage. However, these infants are still vulnerable to insults, including hypoxia-ischemia, inflammation, and disrupted in utero development, impinging on critical developmental processes, which can lead to neuronal and oligodendrocyte injury and impaired brain function. Consequently, preterm infants often experience a range of neurodevelopmental disorders, such as cognitive impairment and behavioral problems. Here, we address mechanisms underlying preterm brain injury and explore existing and new investigational therapeutic strategies. We discuss how gestational age influences brain development and how interventions, including pharmacological and non-pharmacological approaches, mitigate the effects of preterm birth complications and improve the long-term outcomes of preterm infants.

Time- and sex-dependent effects of juvenile social isolation on mouse brain morphology

During early life stages, social isolation disrupts the proper brain growth and brain circuit formation, which is associated with the risk of mental disorders and cognitive deficits in adulthood. Nevertheless, the impact of juvenile social isolation on brain development, particularly regarding variations across age and sex, remains poorly understood. Here, we investigate the effects of social isolation stress (SIS) during early (3-5 weeks old) or late (5-7 weeks old) juvenile period on brain morphology in adult male and female mice using ultra high-field MRI (11.7 T). We found that both early and late SIS in female mice led to volumetric increases in multiple brain regions, such as the medial prefrontal cortex (mPFC) and hippocampus. Correlation tractography revealed that the fiber tracts in the right corpus callosum and right amygdala were positively correlated with SIS in female mice. In male mice, early SIS resulted in small volumetric increases in the isocortex, whereas late SIS led to reductions in the isocortex and hypothalamus. Furthermore, early SIS caused a negative correlation, while late SIS exhibited a positive correlation, with fiber tracts in the corpus callosum and amygdala in male mice. Using a Random Forest classifier, we achieved effective discrimination between socially isolated and control conditions in the brain volume of female mice, with the limbic areas playing a key role in the model's accuracy. Finally, we discovered that SIS led to context fear generalization in a sex-dependent manner. Our findings highlight the importance of considering both the time- and sex-dependent effects of juvenile SIS on brain development and emotional processing, providing new insights into its long-term consequences.

An update on mammalian and non-mammalian animal models for biomarker development in neurodegenerative disorders

Neurodegeneration is one of the leading factor for death globally, affecting millions of people. Developing animal models are critical to understand biological processes and comprehend pathological hallmarks of neurodegenerative diseases. For decades, many animal models have served as excellent tools to determine the disease progression, develop diagnostic methods and design novel therapies against distinct pathologies. Here, we provide a comprehensive overview of both, mammalian and non-mammalian animal models, with a focus on three most common and aggressive neurodegenerative disorders: Alzheimer's disease, Parkinson's disease and Spinocerebellar ataxia-1. We highlight various approaches including transgene, gene transfer, and chemically-induced methods used to develop disease models. In particular, we discuss applications of both non-mammalian and mammalian contributions in research on neurodegeneration. It is exciting to learn the roles of animal models in disease pathomechanisms, identifying biomarkers and hence devising novel interventions to treat neuropathological conditions.

Astrocyte Extracellular Matrix Modulates Neuronal Dendritic Development

Major developmental events occurring in the hippocampus during the third trimester of human gestation and neonatally in altricial rodents include rapid and synchronized dendritic arborization and astrocyte proliferation and maturation. We tested the hypothesis that signals sent by developing astrocytes to developing neurons modulate dendritic development in vivo. First, we altered neuronal development by exposing neonatal (third trimester-equivalent) mice to ethanol, which increased dendritic arborization in hippocampal pyramidal neurons. We next assessed concurrent changes in the mouse astrocyte translatome by translating ribosomal affinity purification (TRAP)-seq. We followed up on ethanol-inhibition of astrocyte Chpf2 and Chsy1 gene translation because these genes encode biosynthetic enzymes of chondroitin sulfate glycosaminoglycan (CS-GAG) chains (extracellular matrix components that inhibit neuronal development and plasticity) and have not been explored before for their roles in dendritic arborization. We report that Chpf2 and Chsy1 are enriched in astrocytes, and their translation is inhibited by ethanol, which also reduces the levels of CS-GAGs measured by Liquid Chromatography/Mass Spectrometry. Finally, astrocyte-conditioned medium derived from Chfp2-silenced astrocytes increased neurite length and branching of hippocampal neurons in vitro, mechanistically linking changes in CS-GAG biosynthetic enzymes in astrocytes to altered neuronal development. These results demonstrate that CS-GAG biosynthetic enzymes in astrocytes regulate dendritic arborization in developing neurons and are involved in ethanol-induced altered neuronal development.

Novel peptidomimetic compounds attenuate hypoxic-ischemic brain injury in neonatal rats

Hypoxic-ischemic (HI) brain injury is a common neurological problem in neonates. The postsynaptic density protein-95 (PSD-95) is an excitatory synaptic scaffolding protein that regulates synaptic function, and represents a potential therapeutic target to attenuate HI brain injury. Syn3 and d-Syn3 are novel high affinity cyclic peptides that bind the PDZ3 domain of PSD-95. We investigated the neuroprotective efficacy of Syn3 and d-Syn3 after exposure to HI in neonatal rodents. Postnatal (P) day-7 rats were treated with Syn3 and d-Syn3 at zero, 24, and 48-h after carotid artery ligation and 90-min of 8 % oxygen. Hemispheric volume atrophy and Iba-1 positive microglia were quantified by cresyl violet and immunohistochemical staining. Treatment with Syn3 and d-Syn3 reduced tissue volume loss by 47.0 % and 41.0 % in the male plus female, and by 42.1 % and 65.0 % in the male groups, respectively. Syn3 reduced tissue loss by 52.3 % in females. D-Syn3 reduced Iba-1 positive microglia/DAPI ratios in the pooled group, males, and females. Syn3 effects were observed in the pooled group and females. Changes in Iba-1 positive microglia/DAPI cellular ratios correlated directly with reduced hemispheric volume loss, suggesting that Syn3 and d-Syn3 provide neuroprotection in part by their effects on Iba-1 positive microglia. The pathogenic cis phosphorylated Thr231 in Tau (cis P-tau) is a marker of neuronal injury. Cis P-tau was induced in cortical cells of the placebo-treated pooled group, males and females after HI, and reduced by treatment with d-Syn3. Therefore, treatment with these peptidomimetic agents exert neuroprotective effects after exposure of neonatal subjects to HI related brain injury.

Expanding the neuroimmune research toolkit with in vivo brain organoid technologies

Human pluripotent stem cell-derived microglia-like cells (MLCs) and brain organoid systems have revolutionized the study of neuroimmune interactions, providing new opportunities to model human-specific brain development and disease. Over the past decade, advances in protocol design have improved the fidelity, reproducibility and scalability of MLC and brain organoid generation. Co-culturing of MLCs and brain organoids have enabled direct investigations of human microglial interactions in vitro, although opportunities remain to improve microglial maturation and long-term survival. To address these limitations, innovative xenotransplantation approaches have introduced MLCs, organoids or neuroimmune organoids into the rodent brain, providing a vascularized environment that supports prolonged development and potential behavioral readouts. These expanding in vitro and in vivo toolkits offer complementary strategies to study neuroimmune interactions in health and disease. In this Perspective, we discuss the strengths, limitations and synergies of these models, highlighting important considerations for their future applications.

A human iPSC-derived midbrain neural stem cell model of prenatal opioid exposure and withdrawal: A proof of concept study

A growing body of clinical literature has described neurodevelopmental delays in infants with chronic prenatal opioid exposure and withdrawal. Despite this, the mechanism of how opioids impact the developing brain remains unknown. Here, we developed an in vitro model of prenatal morphine exposure and withdrawal using healthy human induced pluripotent stem cell (iPSC)-derived midbrain neural progenitors in monolayer. To optimize our model, we identified that a longer neural induction and regional patterning period increases expression of canonical opioid receptors mu and kappa in midbrain neural progenitors compared to a shorter protocol (OPRM1, two-tailed t-test, p =  0.004; OPRK1, p =  0.0003). Next, we showed that the midbrain neural progenitors derived from a longer iPSC neural induction also have scant toll-like receptor 4 (TLR4) expression, a key player in neonatal opioid withdrawal syndrome pathophysiology. During morphine withdrawal, differentiating neural progenitors experience cyclic adenosine monophosphate overshoot compared to cell exposed to vehicle (p =  0.0496) and morphine exposure conditions (p, =  0.0136, 1-way ANOVA). Finally, we showed that morphine exposure and withdrawal alters proportions of differentiated progenitor cell fates (2-way ANOVA, F =  16.05, p <  0.0001). Chronic morphine exposure increased proportions of nestin positive progenitors (p =  0.0094), and decreased proportions of neuronal nuclear antigen positive neurons (NEUN) (p =  0.0047) compared to those exposed to vehicle. Morphine withdrawal decreased proportions of glial fibrillary acidic protein positive cells of astrocytic lineage (p =  0.044), and increased proportions of NEUN-positive neurons (p <  0.0001) compared to those exposed to morphine only. Applications of this paradigm include mechanistic studies underscoring neural progenitor cell fate commitments in early neurodevelopment during morphine exposure and withdrawal.

Dissociation of circadian rhythms in adolescent rats affects object recognition and spatial recognition memories

The T22 protocol is an animal model of forced internal desynchronization, in which rats are exposed to an 11:11 light-dark (LD) cycle. This non-invasive protocol induces the dissociation of circadian rhythms in adult rats, making it possible to study the effects of circadian disruption on physiological and behavioral processes such as learning, memory, and emotional responses. However, the effects of circadian dissociation during other developmental stages, such as adolescence, remain unexplored. Adolescence is a period marked by significant changes in sleep patterns and increased exposure to bright light at night, making it essential to investigate how circadian dissociation may affect this phase of development. This study aimed to evaluate the circadian rhythmicity, cognitive performance and anxiety-like behavior in adolescent Wistar rats under the alignment (aligned T22 group) or misalignment (misaligned T22 group) phases of the T22 cycle. A third group of adolescent rats was maintained in a normal 12:12 LD cycle during the experiment and was used as control group (T24 group). Compared to the control group, adolescent rats under both phases of the T22 cycle exhibited a dissociated circadian rhythm of the locomotor activity and deficits in object recognition memory tasks, without impairments in tasks related to emotional responses. These findings indicate that forced desynchronization impairs recognition memory in adolescent rats, suggesting potential cognitive consequences of internal desynchronization during this critical developmental phase, with relevant implications for public health discussions.

Pretreatment with oleuropein protects the neonatal brain from hypoxia-ischemia by inhibiting apoptosis and neuroinflammation

Hypoxic-ischemic (HI) encephalopathy is a cerebrovascular injury caused by oxygen deprivation to the brain and remains a major cause of neonatal mortality and morbidity worldwide. Therapeutic hypothermia is the current standard of care but it does not provide complete neuroprotection. Our aim was to investigate the neuroprotective effect of oleuropein (Ole) in a neonatal (seven-day-old) mouse model of HI. Ole, a secoiridoid found in olive leaves, has previously shown to reduce damage against cerebral and other ischemia/reperfusion injuries. Here, we administered Ole as a pretreatment prior to HI induction at 20 or 100 mg/kg. A week after HI, Ole significantly reduced the infarct area and the histological damage as well as white matter injury, by preserving myelination, microglial activation and the astroglial reactive response. Twenty-four hours after HI, Ole reduced the overexpression of caspase-3 and the proinflammatory cytokines IL-6 and TNF-α. Moreover, using UPLC-MS/MS we found that maternal supplementation with Ole during pregnancy and/or lactation led to the accumulation of its metabolite hydroxytyrosol in the brains of the offspring. Overall, our results indicate that pretreatment with Ole confers neuroprotection and can prevent HI-induced brain damage by modulating apoptosis and neuroinflammation.

Glycogen Synthase Kinase-3β Inhibitor VP3.15 Ameliorates Neurogenesis, Neuronal Loss and Cognitive Impairment in a Model of Germinal Matrix-intraventricular Hemorrhage of the Preterm Newborn

Advances in neonatology have significantly reduced mortality rates due to prematurity. However, complications of prematurity have barely changed in recent decades. Germinal matrix-intraventricular hemorrhage (GM-IVH) is one of the most severe complications of prematurity, and these children are prone to suffer short- and long-term sequelae, including cerebral palsy, cognitive and motor impairments, or neuropsychiatric disorders. Nevertheless, GM-IVH has no successful treatment. VP3.15 is a small, heterocyclic molecule of the 5-imino-1,2,4-thiadiazole family with a dual action as a phosphodiesterase 7 and glycogen synthase kinase-3β (GSK-3β) inhibitor. VP3.15 reduces neuroinflammation and neuronal loss in other neurodegenerative disorders and might ameliorate complications associated with GM-IVH. We administered VP3.15 to a mouse model of GM-IVH. VP3.15 reduces the presence of hemorrhages and microglia in the short (P14) and long (P110) term. It ameliorates brain atrophy and ventricle enlargement while limiting tau hyperphosphorylation and neuronal and myelin basic protein loss. VP3.15 also improves proliferation and neurogenesis as well as cognition after the insult. Interestingly, plasma gelsolin levels, a feasible biomarker of brain damage, improved after VP3.15 treatment. Altogether, our data support the beneficial effects of VP3.15 in GM-IVH by ameliorating brain neuroinflammatory, vascular and white matter damage, ultimately improving cognitive impairment associated with GM-IVH.

N, N-dimethyltryptamine (DMT) in rodent brain: Concentrations, distribution, and recent pharmacological data

Renewed interest in the clinical use of psychedelic drugs acknowledges their therapeutic effectiveness. It has also provided a changing frame of reference for older psychedelic drug study data, especially regarding concentrations of N, N-dimethyltryptamine (DMT) reported in rodent brains and recent discoveries in DMT receptor interactions in rat brain neurons and select brain areas. The mode of action of DMT in its newly defined role as a neuroplastogen, its effectiveness in treating neuropsychiatric disorders, and its binding to intracellular sigma-1 and 5HT2a receptors may define these possible roles. Recent data also show psychedelics promote neuroplasticity via activation of sigma-1 receptors associated with the endoplasmic reticulum and binding to 5-HT2a receptors predominantly related to the intracellular membrane of the Golgi apparatus in cortical neurons and the failure of DMT to occupy cell surface 5-HT2a receptors. While DMT has been proposed as the endogenous ligand for sigma-1, there is no identified ligand for intracellular 5-HT2a receptors, which serotonin cannot acquire. DMT is proposed to be the missing endogenous ligand. These data further suggest that DMT may be involved in brain development in rat pups. Brain levels of DMT have also been shown to be elevated by stress in the rat and appear to be under an inducible, adaptive, physiological regulatory system control. With DMT acting as the natural ligand for intracellular 5HT2a receptors in the Golgi, it may also explain the subjective effects observed from the administration of psychedelics in general and define some of the natural roles for DMT in particular.

From Circuits to Lifespan: Translating Mouse and Human Timelines with Neuroimaging-Based Tractography

Animal models are commonly used to investigate developmental processes and disease risk, but humans and model systems (e.g., mice) differ substantially in the pace of development and aging. The timeline of human developmental circuits is well known, but it is unclear how such timelines compare with those in mice. We lack age alignments across the lifespan of mice and humans. Here, we build upon our Translating Time resource, which is a tool that equates corresponding ages during development. We collected 1,125 observations from age-related changes in body, bone, dental, and brain processes to equate corresponding ages across humans, mice, and rats to boost power for comparison across humans and mice. We acquired high-resolution diffusion MR scans of mouse brains (n = 16) of either sex at sequential stages of postnatal development [postnatal day (P)3, 4, 12, 21, 60] to track brain circuit maturation (e.g., olfactory association, transcallosal pathways). We found heterogeneity in white matter pathway growth. Corpus callosum growth largely ceases days after birth, while the olfactory association pathway grows through P60. We found that a P3-4, mouse equates to a human at roughly GW24 and a P60 mouse equates to a human in teenage years. Therefore, white matter pathway maturation is extended in mice as it is in humans, but there are species-specific adaptations. For example, olfactory-related wiring is protracted in mice, which is linked to their reliance on olfaction. Our findings underscore the importance of translational tools to map common and species-specific biological processes from model systems to humans.

Sleep and circadian rhythm activity alterations during adolescence in a mouse model of neonatal fentanyl withdrawal syndrome

Fentanyl, a highly potent synthetic opioid, is a major contributor to the ongoing opioid epidemic. During adulthood, fentanyl is known to induce pronounced sleep and circadian disturbances during use and withdrawal. Children exposed to opioids in utero are likely to develop neonatal opioid withdrawal syndrome, and display sleep disturbances after birth. However, it is currently unknown how neonatal opioid withdrawal from fentanyl impacts sleep and circadian rhythms in mice later in life. To model neonatal opioid withdrawal syndrome, mice were treated with fentanyl from postnatal days 1 through 14, analogous to the third trimester of human gestation. After weaning, fentanyl and saline treated mice underwent non-invasive sleep and circadian rhythm monitoring during adolescence postnatal days 23 through 30. Neonatal fentanyl exposure led to an increase in the percent time spent in rapid eye movement sleep across days. Thus, neonatal fentanyl exposure leads to altered sleep-wake states during adolescence in mice.