Transcriptional development of the hippocampus and the dorsal-intermediate-ventral axis in rats.

Risk and resilience for neuropsychiatric illnesses are established during brain development, and transcriptional markers of risk may be identifiable in early development. The dorsal-ventral axis of the hippocampus has behavioral, electrophysiological, anatomical, and transcriptional gradients and abnormal hippocampus development is associated with autism, schizophrenia, epilepsy, and mood disorders. We previously showed that differential gene expression along the dorsoventral hippocampus in rats was present at birth (postnatal day 0, P0), and that a subset of differentially expressed genes (DEGs) was present at all postnatal ages examined (P0, P9, P18, and P60). Here, we extend the analysis of that gene expression data to understand the development of the hippocampus as a whole by examining DEGs that change with age. We additionally examine development of the dorsoventral axis by looking at DEGs along the axis at each age. Using both unsupervised and supervised analyses, we find that the majority of DEGs are present from P0 to P18, with many expression profiles presenting peaks or dips at P9/18. During development of the hippocampus, enriched pathways associated with learning, memory, and cognition increase with age, as do pathways associated with neurotransmission and synaptic function. Development of the dorsoventral axis is greatest at P9 and P18 and is marked by DEGs associated with metabolic functions. Our data indicate that neurodevelopmental disorders like epilepsy, schizophrenia and affective disorders are enriched with developmental DEGs in the hippocampus, regardless of dorsoventral location, with the greatest enrichment of these clinical disorders seen in genes whose expression changes from P0-9. When comparing DEGs from the ventral and dorsal poles, the greatest number of neurodevelopmental disorders is enriched with DEGs found at P18. Taken together, the developing hippocampus undergoes substantial transcriptional maturation during early postnatal development, with expression of genes involved in neurodevelopmental disorders also showing maximal expression changes within this developmental period.

Postnatal Development of Functional Projections from Parasubiculum and Presubiculum to Medial Entorhinal Cortex in the Rat.

Neurons in parasubiculum (PaS), presubiculum (PrS), and medial entorhinal cortex (MEC) code for place (grid cells) and head direction. Directional input has been shown to be important for stable grid cell properties in MEC, and PaS and PrS have been postulated to provide this information to MEC. In line with this, head direction cells in those brain areas are present at postnatal day 11 (P11), having directional tuning that stabilizes shortly after eye opening, which is before premature grid cells emerge in MEC at P16. Whether functional connectivity between these structures exists at those early postnatal stages is unclear. Using anatomical tracing, voltage-sensitive dye imaging and single-cell patch recordings in female and male rat brain slices between P2 and P61, we determined when the pathways from PaS and PrS to MEC emerge, become functional, and how they develop. Anatomical connections from PaS and PrS to superficial MEC emerge between P4 and P6. Monosynaptic connectivity from PaS and PrS to superficial MEC was measurable from P9 to P10 onward, whereas connectivity with deep MEC was measurable from P11 to P12. From P14/P15 on, reactivity of MEC neurons to parasubicular and presubicular inputs becomes adult-like and continues to develop until P28-P30. The maturation of the efficacy of both inputs between P9 and P21 is paralleled by maturation of morphological properties, changes in intrinsic properties of MEC principal neurons, and changes in the GABAergic network of MEC. In conclusion, synaptic projections from PaS and PrS to MEC become functional and adult-like before the emergence of grid cells in MEC.SIGNIFICANCE STATEMENT Head direction information, crucial for grid cells in medial entorhinal cortex (MEC), is thought to enter MEC via parasubiculum (PaS) and presubiculum (PrS). Unraveling the development of functional connections between PaS, PrS, and MEC is key to understanding how spatial navigation, an important cognitive function, may evolve. To gain insight into the development, we used anatomical tracing techniques, voltage-sensitive dye imaging, and single-cell recordings. The combined data led us to conclude that synaptic projections from PaS and PrS to MEC become functional and adult-like before eye opening, allowing crucial head direction information to influence place encoding before the emergence of grid cells in rat MEC.

Development and topographic organization of subicular projections to lateral septum in the rat brain.

One of the main subcortical targets of hippocampal formation efferents is the lateral septum. Previous studies on the subicular projections, as a main output structure of the hippocampus, have shown a clear topographic organization of septal innervation, related to the origin of the fibres along the dorsoventral axis of the subiculum in the adult brain. In contrast, studies on the developing brain depict an extensive rearrangement of subicular projections during the prenatal period, shifting from the medial septum to the lateral septum. Our study aimed to describe the postnatal development of subicular projections to the septum. We injected anterograde tracers into the subiculum of 57 pups of different postnatal ages. Injections covered the proximodistal and dorsoventral axis of the subiculum. The age of the pups at day of tracer injection ranged from the day of birth to postnatal day 30. Analyses revealed that from the first postnatal day projections from subiculum preferentially target the lateral septum. Sparse innervation in the lateral septum was already present in the first few postnatal days, and during the following 3 weeks, the axonal distribution gradually expanded. Subicular projections to the lateral septum are topographically organized depending on the origin along the dorsoventral axis of the subiculum, in line with the adult innervation pattern. Different origins along the proximodistal axis of the subiculum are reflected in changes in the strength of septal innervation. The findings demonstrate that in case of the development of subicular projections, axonal expansion is more prominent than axonal pruning.

Active place avoidance is no more stressful than unreinforced exploration of a familiar environment.

Training in the active place avoidance task changes hippocampus synaptic function, the dynamics of hippocampus local field potentials, place cell discharge, and active place avoidance memory is maintained by persistent PKMζ activity. The extent to which these changes reflect memory processes and/or stress responses is unknown. We designed a study to assess stress within the active place avoidance task by measuring serum corticosterone (CORT) at different stages of training. CORT levels did not differ between trained mice that learned to avoid the location of the mild foot shock, and untrained no-shock controls exposed to the same environment for the same amount of time. Yoked mice, that received unavoidable shocks in the same time sequence as the trained mice, had significantly higher CORT levels than mice in the trained and no-shock groups after the first trial. This increase in CORT disappeared by the fourth trial the following day, and levels of CORT for all groups matched that of home cage controls. The data demonstrate that place avoidance training is no more stressful than experiencing a familiar environment. We conclude that changes in neural function as a result of active place avoidance training are likely to reflect learning and memory processes rather than stress. © 2016 Wiley Periodicals, Inc.

Memory deficits with intact cognitive control in the methylazoxymethanol acetate (MAM) exposure model of neurodevelopmental insult.

Cognitive impairments are amongst the most debilitating deficits of schizophrenia and the best predictor of functional outcome. Schizophrenia is hypothesized to have a neurodevelopmental origin, making animal models of neurodevelopmental insult important for testing predictions that early insults will impair cognitive function. Rats exposed to methylazoxymethanol acetate (MAM) at gestational day 17 display morphological, physiological and behavioral abnormalities relevant to schizophrenia. Here we investigate the cognitive abilities of adult MAM rats. We examined brain activity in MAM rats by histochemically assessing cytochrome oxidase enzyme activity, a metabolic marker of neuronal activity. To assess cognition, we used a hippocampus-dependent two-frame active place avoidance paradigm to examine learning and spatial memory, as well as cognitive control and flexibility using the same environment and evaluating the same set of behaviors. We confirmed that adult MAM rats have altered hippocampal morphology and brain function, and that they are hyperactive in an open field. The latter likely indicates MAM rats have a sensorimotor gating deficit that is common to many animal models used for schizophrenia research. On first inspection, cognitive control seems impaired in MAM rats, indicated by more errors during the two-frame active place avoidance task. Because MAM rats are hyperactive throughout place avoidance training, we considered the possibility that the hyperlocomotion may account for the apparent cognitive deficits. These deficits were reduced on the basis of measures of cognitive performance that account for motor activity differences. However, though other aspects of memory are intact, the ability of MAM rats to express trial-to-trial memory is delayed compared to control rats. These findings suggest that spatial learning and cognitive abilities are largely intact, that the most prominent cognitive deficit is specific to acquiring memory in the MAM neurodevelopmental model, and that hyperactivity can confound assessments of cognition in animal models of mental dysfunction.

Adolescent chemogenetic activation of dopaminergic neurons leads to reversible decreases in amphetamine-induced stereotypic behavior.

Chronic perturbations of neuronal activity can evoke homeostatic and new setpoints for neurotransmission. Using chemogenetics to probe the relationship between neuronal cell types and behavior, we recently found reversible decreases in dopamine (DA) transmission, basal behavior, and amphetamine (AMPH) response following repeated stimulation of DA neurons in adult mice. It is unclear, however, whether altering DA neuronal activity via chemogenetics early in development leads to behavioral phenotypes that are reversible, as alterations of neuronal activity during developmentally sensitive periods might be expected to induce persistent effects on behavior. To examine the impact of developmental perturbation of DA neuron activity on basal and AMPH behavior, we expressed excitatory hM3D(Gq) in postnatal DA neurons in TH-Cre and WT mice. Basal and CNO- or AMPH-induced locomotion and stereotypy was evaluated in a longitudinal design, with clozapine N-oxide (CNO, 1.0 mg/kg) administered across adolescence (postnatal days 15-47). Repeated CNO administration did not impact basal behavior and only minimally reduced AMPH-induced hyperlocomotor response in adolescent TH-CrehM3Dq mice relative to WThM3Dq littermate controls. Following repeated CNO administration, however, AMPH-induced stereotypic behavior robustly decreased in adolescent TH-CrehM3Dq mice relative to controls. A two-month CNO washout period rescued the diminished AMPH-induced stereotypic behavior. Our findings indicate that the homeostatic compensations that take place in response to chronic hM3D(Gq) stimulation during adolescence are temporary and are dependent on ongoing chemogenetic stimulation.

What is optimized in an optimal path?

An animal confronts numerous challenges when constructing an optimal navigational route. Spatial representations used for path optimization are likely constrained by critical environmental factors that dictate which neural systems control navigation. Multiple coding schemes depend upon their ecological relevance for a particular species, particularly when dealing with the third, or vertical, dimension of space.

Circuits underlying social function and dysfunction.

Substantial advances have been made toward understanding the genetic and environmental risk factors for autism, a neurodevelopmental disorder with social impairment as a core feature. In combination with optogenetic and chemogenetic tools to manipulate neural circuits in vivo, it is now possible to use model systems to test how specific neural circuits underlie social function and dysfunction. Here, we review the literature that has identified circuits associated with social interest (sociability), social reward, social memory, dominance, and aggression, and we outline a preliminary roadmap of the neural circuits driving these social behaviors. We highlight the neural circuitry underlying each behavioral domain, as well as develop an interactive map of how these circuits overlap across domains. We find that some of the circuits underlying social behavior are general and are involved in the control of multiple behavioral aspects, whereas other circuits appear to be specialized for specific aspects of social behavior. Our overlapping circuit map therefore helps to delineate the circuits involved in the various domains of social behavior and to identify gaps in knowledge.

Repeated chemogenetic activation of dopaminergic neurons induces reversible changes in baseline and amphetamine-induced behaviors.

RATIONALE: Repeated chemogenetic stimulation is often employed to study circuit function and behavior. Chronic or repeated agonist administration can result in homeostatic changes, but this has not been extensively studied with designer receptors exclusively activated by designer drugs (DREADDs). OBJECTIVES: We sought to evaluate the impact of repeated DREADD activation of dopaminergic (DA) neurons on basal behavior, amphetamine response, and spike firing. We hypothesized that repeated DREADD activation would mimic compensatory effects that we observed with genetic manipulations of DA neurons. METHODS: Excitatory hM3D(Gq) DREADDs were virally expressed in adult TH-Cre and WT mice. In a longitudinal design, clozapine N-oxide (CNO, 1.0 mg/kg) was administered repeatedly. We evaluated basal and CNO- or amphetamine (AMPH)-induced locomotion and stereotypy. DA neuronal activity was assessed using in vivo single-unit recordings. RESULTS: Acute CNO administration increased locomotion, but basal locomotion decreased after repeated CNO exposure in TH-CrehM3Dq mice relative to littermate controls. Further, after repeated CNO administration, AMPH-induced hyperlocomotion and stereotypy were diminished in TH-CrehM3Dq mice relative to controls. Repeated CNO administration reduced DA neuronal firing in TH-CrehM3Dq mice relative to controls. A two-month CNO washout period rescued the decreases in basal locomotion and AMPH response. CONCLUSIONS: We found that repeated DREADD activation of DA neurons evokes homeostatic changes that should be factored into the interpretation of chronic DREADD applications and their impact on circuit function and behavior. These effects are likely to also be seen in other neuronal systems and underscore the importance of studying neuroadaptive changes with chronic or repeated DREADD activation.

Translational Neuroscience Approaches to Understanding Autism.

While autism spectrum disorder affects nearly 2% of children in the United States, little is known with certainty concerning the etiologies and brain systems involved. This is due, in part, to the substantial heterogeneity in the presentation of the core symptoms of autism as well as the great number of co-occurring conditions that are common in autistic individuals. Understanding the neurobiology of autism is further hampered by the limited availability of postmortem brain tissue to determine the cellular and molecular alterations that take place in the autistic brain. Animal models therefore provide great translational value in helping to define the neural systems that constitute the social brain and mediate repetitive behaviors or interests. If they are based on genetic or environmental factors that contribute to autism, organisms from flies to nonhuman primates may serve as models of the neural structure or function of the autistic brain. Ultimately, successful models can also be employed to test the safety and effectiveness of potential therapeutics. This is an overview of the major animal species that are currently used as models of autism, including an appraisal of the advantages and limitations of each.

Assessment of Neurodevelopment in Infants With and Without Exposure to Asymptomatic or Mild Maternal SARS-CoV-2 Infection During Pregnancy.

Importance: Associations between prenatal SARS-CoV-2 exposure and neurodevelopmental outcomes have substantial public health relevance. A previous study found no association between prenatal SARS-CoV-2 infection and parent-reported infant neurodevelopmental outcomes, but standardized observational assessments are needed to confirm this finding. Objective: To assess whether mild or asymptomatic maternal SARS-CoV-2 infection vs no infection during pregnancy is associated with infant neurodevelopmental differences at ages 5 to 11 months. Design, Setting, and Participants: This cohort study included infants of mothers from a single-site prospective cross-sectional study (COVID-19 Mother Baby Outcomes [COMBO] Initiative) of mother-infant dyads and a multisite prospective cohort study (Epidemiology of Severe Acute Respiratory Syndrome Coronavirus 2 in Pregnancy and Infancy [ESPI]) of pregnant individuals. A subset of ESPI participants was subsequently enrolled in the ESPI COMBO substudy. Participants in the ongoing COMBO study were enrolled beginning on May 26, 2020; participants in the ESPI study were enrolled from May 7 to November 3, 2021; and participants in the ESPI COMBO substudy were enrolled from August 2020 to March 2021. For the current analysis, infant neurodevelopment was assessed between March 2021 and June 2022. A total of 407 infants born to 403 mothers were enrolled (204 from Columbia University Irving Medical Center in New York, New York; 167 from the University of Utah in Salt Lake City; and 36 from the University of Alabama in Birmingham). Mothers of unexposed infants were approached for participation based on similar infant gestational age at birth, date of birth, sex, and mode of delivery to exposed infants. Exposures: Maternal symptomatic or asymptomatic SARS-CoV-2 infection. Main Outcomes and Measures: Infant neurodevelopment was assessed using the Developmental Assessment of Young Children, second edition (DAYC-2), adapted for telehealth assessment. The primary outcome was age-adjusted standard scores on 5 DAYC-2 subdomains: cognitive, gross motor, fine motor, expressive language, and receptive language. Results: Among 403 mothers, the mean (SD) maternal age at delivery was 32.1 (5.4) years; most mothers were of White race (240 [59.6%]) and non-Hispanic ethnicity (253 [62.8%]). Among 407 infants, 367 (90.2%) were born full term and 212 (52.1%) were male. Overall, 258 infants (63.4%) had no documented prenatal exposure to SARS-CoV-2 infection, 112 (27.5%) had confirmed prenatal exposure, and 37 (9.1%) had exposure before pregnancy or at an indeterminate time. In adjusted models, maternal SARS-CoV-2 infection during pregnancy was not associated with differences in cognitive (ß = 0.31; 95% CI, -2.97 to 3.58), gross motor (ß = 0.82; 95% CI, -1.34 to 2.99), fine motor (ß = 0.36; 95% CI, -0.74 to 1.47), expressive language (ß = -1.00; 95% CI, -4.02 to 2.02), or receptive language (ß = 0.45; 95% CI, -2.15 to 3.04) DAYC-2 subdomain scores. Trimester of exposure and maternal symptom status were not associated with DAYC-2 subdomain scores. Conclusions and Relevance: In this study, results of a novel telehealth-adapted observational neurodevelopmental assessment extended a previous finding of no association between prenatal exposure to maternal SARS-CoV-2 infection and infant neurodevelopment. Given the widespread and continued high prevalence of COVID-19, these data offer information that may be helpful for pregnant individuals who experience asymptomatic or mild SARS-CoV-2 infections.

Association of Birth During the COVID-19 Pandemic With Neurodevelopmental Status at 6 Months in Infants With and Without In Utero Exposure to Maternal SARS-CoV-2 Infection.

Importance: Associations between in utero exposure to maternal SARS-CoV-2 infection and neurodevelopment are speculated, but currently unknown. Objective: To examine the associations between maternal SARS-CoV-2 infection during pregnancy, being born during the COVID-19 pandemic regardless of maternal SARS-CoV-2 status, and neurodevelopment at age 6 months. Design, Setting, and Participants: A cohort of infants exposed to maternal SARS-CoV-2 infection during pregnancy and unexposed controls was enrolled in the COVID-19 Mother Baby Outcomes Initiative at Columbia University Irving Medical Center in New York City. All women who delivered at Columbia University Irving Medical Center with a SARS-CoV-2 infection during pregnancy were approached. Women with unexposed infants were approached based on similar gestational age at birth, date of birth, sex, and mode of delivery. Neurodevelopment was assessed using the Ages & Stages Questionnaire, 3rd Edition (ASQ-3) at age 6 months. A historical cohort of infants born before the pandemic who had completed the 6-month ASQ-3 were included in secondary analyses. Exposures: Maternal SARS-CoV-2 infection during pregnancy and birth during the COVID-19 pandemic. Main Outcomes and Measures: Outcomes were scores on the 5 ASQ-3 subdomains, with the hypothesis that maternal SARS-CoV-2 infection during pregnancy would be associated with decrements in social and motor development at age 6 months. Results: Of 1706 women approached, 596 enrolled; 385 women were invited to a 6-month assessment, of whom 272 (70.6%) completed the ASQ-3. Data were available for 255 infants enrolled in the COVID-19 Mother Baby Outcomes Initiative (114 in utero exposed, 141 unexposed to SARS-CoV-2; median maternal age at delivery, 32.0 [IQR, 19.0-45.0] years). Data were also available from a historical cohort of 62 infants born before the pandemic. In utero exposure to maternal SARS-CoV-2 infection was not associated with significant differences on any ASQ-3 subdomain, regardless of infection timing or severity. However, compared with the historical cohort, infants born during the pandemic had significantly lower scores on gross motor (mean difference, -5.63; 95% CI, -8.75 to -2.51; F1,267 = 12.63; P<.005), fine motor (mean difference, -6.61; 95% CI, -10.00 to -3.21; F1,267 = 14.71; P < .005), and personal-social (mean difference, -3.71; 95% CI, -6.61 to -0.82; F1,267 = 6.37; P<.05) subdomains in fully adjusted models. Conclusions and Relevance: In this study, birth during the pandemic, but not in utero exposure to maternal SARS-CoV-2 infection, was associated with differences in neurodevelopment at age 6 months. These early findings support the need for long-term monitoring of children born during the COVID-19 pandemic.

Serotonin 5-HT1B receptor-mediated behavior and binding in mice with the overactive and dysregulated serotonin transporter Ala56 variant.

RATIONALE: Elevated whole-blood serotonin (5-HT) is a robust biomarker in ~ 30% of patients with autism spectrum disorders, in which repetitive behavior is a core symptom. Furthermore, elevated whole-blood 5-HT has also been described in patients with pediatric obsessive-compulsive disorder. The 5-HT1B receptor is associated with repetitive behaviors seen in both disorders. Chronic blockade of serotonin transporter (SERT) reduces 5-HT1B receptor levels in the orbitofrontal cortex (OFC) and attenuates the sensorimotor deficits and hyperactivity seen with the 5-HT1B agonist RU24969. We hypothesized that enhanced SERT function would increase 5-HT1B receptor levels in OFC and enhance sensorimotor deficits and hyperactivity induced by RU24969. OBJECTIVES: We examined the impact of the SERT Ala56 mutation, which leads to enhanced SERT function, on 5-HT1B receptor binding and 5-HT1B-mediated sensorimotor deficits. METHODS: Specific binding to 5-HT1B receptors was measured in OFC and striatum of naïve SERT Ala56 or wild-type mice. The impact of the 5-HT1A/1B receptor agonist RU24969 on prepulse inhibition (PPI) of startle, hyperactivity, and expression of cFos was examined. RESULTS: While enhanced SERT function increased 5-HT1B receptor levels in OFC of Ala56 mice, RU24969-induced PPI deficits and hyperlocomotion were not different between genotypes. Baseline levels of cFos expression were not different between groups. RU24969 increased cFos expression in OFC of wild-types and decreased cFos in the striatum. CONCLUSIONS: While reducing 5-HT1B receptors may attenuate sensorimotor gating deficits, increased 5-HT1B levels in SERT Ala56 mice do not necessarily exacerbate these deficits, potentially due to compensations during neural circuit development in this model system.

A social encounter drives gene expression changes linked to neuronal function, brain development, and related disorders in mice expressing the serotonin transporter Ala56 variant.

Multiple lines of evidence implicate the serotonin (5-HT) system in social function, including biomarker findings in autism spectrum disorder. In mice, knock-in of a rare Gly56Ala substitution in the serotonin transporter (SERT) causes elevated whole blood 5-HT levels, increased 5-HT clearance in the brain, and altered social and repetitive behavior. To further examine the molecular impact of this variant on social response, SERT Ala56 mutant mice and wildtype littermate controls were exposed to a social or non-social stimulus. We examined the differential activation of the prefrontal cortex, lateral amygdala, and medial amygdala, to social stimuli through RNA sequencing. Differentially expressed genes were enriched in axonal guidance signaling pathways, networks related to nervous system development and function, neurological and psychiatric disorders, and behavior. These identified pathways and networks may shed light on the molecular cascades underlying the impact of altered SERT function on social behavior.

Synaptic plasticity/dysplasticity, process memory and item memory in rodent models of mental dysfunction.

Activity-dependent changes in the effective connection strength of synapses are a fundamental feature of a nervous system. This so-called synaptic plasticity is thought to underlie storage of information in memory and has been hypothesized to be crucial for the effects of cognitive behavioral therapy. Synaptic plasticity stores information in a neural network, creating a trace of neural activity from past experience. The plasticity can also change the behavior of the network so the network can differentially transform/compute information in future activations. We discuss these two related but separable functions of synaptic plasticity; one we call "item memory" as it represents and stores items of information in memory, the other we call "process memory" as it encodes and stores functions such as computations to modify network information processing capabilities. We review evidence of item and process memory operations in behavior and evidence that experience modifies the brain's functional networks. We discuss neurodevelopmental rodent models relevant for understanding mental illness and compare two models in which one model, neonatal ventral hippocampal lesion (NVHL) has beneficial adult outcomes after being exposed to an adolescent cognitive experience that is potentially similar to cognitive behavioral therapy. The other model, gestational day 17 methylazoxymethanol acetate (GD17-MAM), does not benefit from the same adolescent cognitive experience. We propose that process memory is altered by early cognitive experience in NVHL rats but not in GD17-MAM rats, and discuss how dysplasticity factors may contribute to the differential adult outcomes after early cognitive experience in the NVHL and MAM models.

Long-Lasting Input-Specific Experience-Dependent Changes of Hippocampus Synaptic Function Measured in the Anesthetized Rat.

How experience causes long-lasting changes in the brain is a central question in neuroscience. The common view is that synaptic function is altered by experience to change brain circuit functions that underlie conditioned behavior. We examined hippocampus synaptic circuit function in vivo, in three groups of animals, to assess the impact of experience on hippocampus function in rats. The "conditioned" group acquired a shock-conditioned place response during a cognitively-challenging, hippocampus synaptic plasticity-dependent task. The no-shock group had similar exposure to the environmental conditions but no conditioning. The home-cage group was experimentally naive. After the one-week retention test, under anesthesia, we stimulated the perforant path inputs to CA1, which terminate in stratum lacunosum moleculare (slm), and to the dentate gyrus (DG), which terminate in the molecular layer. We find synaptic compartment specific changes that differ amongst the groups. The evoked field EPSP (fEPSP) and pre-spike field response are enhanced only at the DG input layer and only in conditioned animals. The DG responses, measured by the population spiking activity and post-spike responses, are enhanced in both the conditioned and no-shock groups compared to home-cage animals. These changes are pathway specific because no differences are observed in slm of CA1. These findings demonstrate long-term, experience-dependent, pathway-specific alterations to synaptic circuit function of the hippocampus.

Sub-circuit alterations in dorsal hippocampus structure and function after global neurodevelopmental insult.

Patients with neuropsychiatric and neurological disorders often express limbic circuit abnormalities and deficits in information processing. While these disorders appear to have diverse etiologies, their common features suggest neurodevelopmental origins. Neurodevelopment is a prolonged process of diverse events including neurogenesis/apoptosis, axon pathfinding, synaptogenesis, and pruning, to name a few. The precise timing of the neurodevelopmental insult to these processes likely determines the resulting functional outcome. We used the epilepsy and schizophrenia-related gestational day 17 methylazoxymethanol acetate model to examine the impact of this timed neurodevelopmental insult on principal cell morphology and synaptic network function of the dorsal hippocampus (dHPC) circuit. Our observed structural and functional alterations in dHPC are compartment specific, indicating that adverse global exposure during gestation can produce specific alterations and distort information processing in neural circuits that underlie cognitive abilities.

13-cis-Retinoic acid alters intracellular serotonin, increases 5-HT1A receptor, and serotonin reuptake transporter levels in vitro.

In addition to their established role in nervous system development, vitamin A and related retinoids are emerging as regulators of adult brain function. Accutane (13-cis-retinoic acid, isotretinoin) treatment has been reported to increase depression in humans. Recently, we showed that chronic administration of 13-cis-retinoic acid (13-cis-RA) to adolescent male mice increased depression-related behaviors. Here, we have examined whether 13-cis-RA regulates components involved in serotonergic neurotransmission in vitro. We used the RN46A-B14 cell line, derived from rat embryonic raphe nuclei. This cell line synthesizes serotonin (5-hydroxytryptamine, 5-HT) and expresses the 5-HT(1A) receptor and the serotonin reuptake transporter (SERT). Cells were treated with 0, 2.5, or 10 microM 13-cis-RA for 48 or 96 hrs, and the levels of 5-HT; its metabolite, 5-hydroxyindoleacetic acid (5HIAA); 5-HT(1A) receptor; and SERT were determined. Treatment with 13-cis-RA for 96 hrs increased the intracellular levels of 5-HT and tended to increase intra-cellular 5HIAA levels. Furthermore, 48 hrs of treatment with 2.5 and 10 microM 13-cis-RA significantly increased 5-HT(1A) protein to 168.5 +/- 20.0% and 148.7 +/- 2.2% of control respectively. SERT protein levels were significantly increased to 142.5 +/- 11.1% and 119.2 +/- 3.6% of control by 48 hrs of treatment with 2.5 and 10 microM of 13-cis-RA respectively. Increases in both 5-HT(1A) receptor and SERT proteins may lead to decreased serotonin availability at synapses. Such an effect of 13-cis-RA could contribute to the increased depression-related behaviors we have shown in mice.

MicroRNAs contribute to postnatal development of laminar differences and neuronal subtypes in the rat medial entorhinal cortex.

The medial entorhinal cortex (MEC) is important in spatial navigation and memory formation and its layers have distinct neuronal subtypes, connectivity, spatial properties, and disease susceptibility. As little is known about the molecular basis for the development of these laminar differences, we analyzed microRNA (miRNA) and messenger RNA (mRNA) expression differences between rat MEC layer II and layers III-VI during postnatal development. We identified layer and age-specific regulation of gene expression by miRNAs, which included processes related to neuron specialization and locomotor behavior. Further analyses by retrograde labeling and expression profiling of layer II stellate neurons and in situ hybridization revealed that the miRNA most up-regulated in layer II, miR-143, was enriched in stellate neurons, whereas the miRNA most up-regulated in deep layers, miR-219-5p, was expressed in ependymal cells, oligodendrocytes and glia. Bioinformatics analyses of predicted mRNA targets with negatively correlated expression patterns to miR-143 found that miR-143 likely regulates the Lmo4 gene, which is known to influence hippocampal-based spatial learning.