Genetic and pharmacological manipulations of the serotonergic system in early life: neurodevelopmental underpinnings of autism-related behavior

Maternal fluoxetine impairs synaptic transmission and plasticity in the medial prefrontal cortex and alters the structure and function of dorsal raphe nucleus neurons in offspring mice

Selective serotonin (5-HT) reuptake inhibitors (SSRIs) are commonly prescribed to women during pregnancy and breastfeeding despite posing a risk of adverse cognitive outcomes and affective disorders for the child. The consequences of SSRI-induced excess of 5-HT during development for the brain neuromodulatory 5-HT system remain largely unexplored. In this study, an SSRI - fluoxetine (FLX) - was administered to C57BL/6 J mouse dams during pregnancy and lactation to assess its effects on the offspring. We found that maternal FLX decreased field potentials, impaired long-term potentiation, facilitated long-term depression and tended to increase the density of 5-HTergic fibers in the medial prefrontal cortex (mPFC) of female but not male adolescent offspring. These effects were accompanied by deteriorated performance in the temporal order memory task and reduced sucrose preference with no change in marble burying behavior in FLX-exposed female offspring. We also found that maternal FLX reduced the axodendritic tree complexity of 5-HT dorsal raphe nucleus (DRN) neurons in female but not male offspring, with no changes in the excitability of DRN neurons of either sex. While no effects of maternal FLX on inhibitory postsynaptic currents (sIPSCs) in DRN neurons were found, we observed a significant influence of FLX exposure on kinetics of spontaneous excitatory postsynaptic currents (sEPSCs) in DRN neurons. Finally, we report that no changes in field potentials and synaptic plasticity were evident in the mPFC of the offspring after maternal exposure during pregnancy and lactation to a new antidepressant, vortioxetine. These findings show that in contrast to the mPFC, long-term consequences of maternal FLX exposure on the structure and function of DRN 5-HT neurons are mild and suggest a sex-dependent, distinct sensitivity of cortical and brainstem neurons to FLX exposure in early life. Vortioxetine appears to exert fewer side effects with regards to the mPFC when compared with FLX.

olf413 an octopamine biogenesis pathway gene is required for axon growth and pathfinding during embryonic nervous system development in Drosophila melanogaster

OBJECTIVE

Neurotransmitters have been extensively studied as neural communication molecules. Genetic associations discovered, and indirect intervention studies in Humans and mammals have led to a general proposition that neurotransmitters have a role in structuring of neuronal network during development. olf413 is a Drosophila gene annotated as coding for dopamine beta-monooxygenase enzyme with a predicted function in octopaminergic pathway. The biological function of this gene is very little worked out. In this study we investigate the requirement of olf413 gene function for octopamine biogenesis and developmental patterning of embryonic nervous system.

RESULT

In our study we have used the newly characterized neuronal specific allele olf413SG1.1, and the gene disruption strain olf413MI02014 to dissect out the function of olf413. olf413 has an enhancer activity as depicted by reporter GFP expression, in the embryonic ventral nerve cord, peripheral nervous system and the somatic muscle bundles. Homozygous loss of function mutants show reduced levels of octopamine, and this finding supports the proposed function of the gene in octopamine biogenesis. Further, loss of function of olf413 causes embryonic lethality. FasII staining of these embryos reveal a range of phenotypes in the central and peripheral motor nerves, featuring axonal growth, pathfinding, branching and misrouting defects. Our findings are important as they implicate a key functional requirement of this gene in precise axonal patterning events, a novel developmental role imparted for an octopamine biosynthesis pathway gene in structuring of embryonic nervous system.

Branched-chain amino acids as adjunctive-alternative treatment in patients with autism: a pilot study

The branched-chain amino acid (BCAA) is a group of essential amino acids that are involved in maintaining the energy balance of a human being as well as the homoeostasis of GABAergic, glutamatergic, serotonergic and dopaminergic systems. Disruption of these systems has been associated with the pathophysiology of autism while low levels of these amino acids have been discovered in patients with autism. A pilot open-label, prospective, follow-up study of the use of BCAA in children with autistic behaviour was carried out. Fifty-five children between the ages of 6 and 18 participated in the study from May 2015 to May 2018. We used a carbohydrate-free BCAA-powdered mixture containing 45·5 g of leucine, 30 g of isoleucine and 24·5 g of valine in a daily dose of 0·4 g/kg of body weight which was administered every morning. Following the initiation of BCAA administration, children were submitted to a monthly psychological examination. Beyond the 4-week mark, BCAA were given to thirty-two people (58·18 %). Six of them (10·9 %) discontinued after 4-10 weeks owing to lack of improvement. The remaining twenty-six children (47·27 %) who took BCAA for longer than 10 weeks displayed improved social behaviour and interactions, as well as improvements in their speech, cooperation, stereotypy and, principally, their hyperactivity. There were no adverse reactions reported during the course of the treatment. Although these data are preliminary, there is some evidence that BCAA could be used as adjunctive treatment to conventional therapeutic methods for the management of autism.

Benefits and Risks of Antidepressant Drugs During Pregnancy: A Systematic Review of Meta-analyses

BACKGROUND

The prescription of antidepressant drugs during pregnancy has been steadily increasing for several decades. Meta-analyses (MAs), which increase the statistical power and precision of results, have gained interest for assessing the safety of antidepressant drugs during pregnancy.

OBJECTIVE

We aimed to provide a meta-review of MAs assessing the benefits and risks of antidepressant drug use during pregnancy.

METHODS

Following Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines, a literature search on PubMed and Web of Science databases was conducted on 25 October, 2021, on MAs assessing the association between antidepressant drug use during pregnancy and health outcomes for the pregnant women, embryo, fetus, newborn, and developing child. Study selection and data extraction were carried out independently and in duplicate by two authors. The methodological quality of included studies was evaluated with the AMSTAR-2 tool. Overlap among MAs was assessed by calculating the corrected covered area. Data were presented in a narrative synthesis, using four levels of evidence.

RESULTS

Fifty-one MAs were included, all but one assessing risks. These provided evidence for a significant increase in the risks for major congenital malformations (selective serotonin reuptake inhibitors, paroxetine, fluoxetine, no evidence for sertraline; eight MAs), congenital heart defects (paroxetine, fluoxetine, sertraline; 11 MAs), preterm birth (eight MAs), neonatal adaptation symptoms (eight MAs), and persistent pulmonary hypertension of the newborn (three MAs). There was limited evidence (only one MA for each outcome) for a significant increase in the risks for postpartum hemorrhage, and with a high risk of bias, for stillbirth, impaired motor development, and intellectual disability. There was inconclusive evidence, i.e., discrepant results, for an increase in the risks for spontaneous abortion, small for gestational age and low birthweight, respiratory distress, convulsions, feeding problems, and for a subsequent risk for autism with an early antidepressant drug exposure. Finally, MAs provided no evidence for an increase in the risks for gestational hypertension, preeclampsia, and for a subsequent risk for attention-deficit/hyperactivity disorder. Only one MA assessed benefits, providing limited evidence for preventing relapse in severe or recurrent depression. Effect sizes were small, except for neonatal symptoms (small to large). Results were based on MAs in which overall methodological quality was low (AMSTAR-2 score = 54.8% ± 12.9%, [19-81%]), with a high risk of bias, notably indication bias. The corrected covered area was 3.27%, which corresponds to a slight overlap.

CONCLUSIONS

This meta-review has implications for clinical practice and future research. First, these results suggest that antidepressant drugs should be used as a second-line treatment during pregnancy (after first-line psychotherapy, according to the guidelines). The risk of major congenital malformations could be prevented by observing guidelines that discourage the use of paroxetine and fluoxetine. Second, to decrease heterogeneity and bias, future MAs should adjust for maternal psychiatric disorders and antidepressant drug dosage, and perform analyses by timing of exposure.

RNA epitranscriptomics dysregulation: A major determinant for significantly increased risk of ASD pathogenesis

Autism spectrum disorders (ASDs) are perhaps the most severe, intractable and challenging child psychiatric disorders. They are complex, pervasive and highly heterogeneous and depend on multifactorial neurodevelopmental conditions. Although the pathogenesis of autism remains unclear, it revolves around altered neurodevelopmental patterns and their implications for brain function, although these cannot be specifically linked to symptoms. While these affect neuronal migration and connectivity, little is known about the processes that lead to the disruption of specific laminar excitatory and inhibitory cortical circuits, a key feature of ASD. It is evident that ASD has multiple underlying causes and this multigenic condition has been considered to also dependent on epigenetic effects, although the exact nature of the factors that could be involved remains unclear. However, besides the possibility for differential epigenetic markings directly affecting the relative expression levels of individual genes or groups of genes, there are at least three mRNA epitranscriptomic mechanisms, which function cooperatively and could, in association with both genotypes and environmental conditions, alter spatiotemporal proteins expression patterns during brain development, at both quantitative and qualitative levels, in a tissue-specific, and context-dependent manner. As we have already postulated, sudden changes in environmental conditions, such as those conferred by maternal inflammation/immune activation, influence RNA epitranscriptomic mechanisms, with the combination of these processes altering fetal brain development. Herein, we explore the postulate whereby, in ASD pathogenesis, RNA epitranscriptomics might take precedence over epigenetic modifications. RNA epitranscriptomics affects real-time differential expression of receptor and channel proteins isoforms, playing a prominent role in central nervous system (CNS) development and functions, but also RNAi which, in turn, impact the spatiotemporal expression of receptors, channels and regulatory proteins irrespective of isoforms. Slight dysregulations in few early components of brain development, could, depending upon their extent, snowball into a huge variety of pathological cerebral alterations a few years after birth. This may very well explain the enormous genetic, neuropathological and symptomatic heterogeneities that are systematically associated with ASD and psychiatric disorders at large.

Development of prefrontal cortex

During evolution, the cerebral cortex advances by increasing in surface and the introduction of new cytoarchitectonic areas among which the prefrontal cortex (PFC) is considered to be the substrate of highest cognitive functions. Although neurons of the PFC are generated before birth, the differentiation of its neurons and development of synaptic connections in humans extend to the 3rd decade of life. During this period, synapses as well as neurotransmitter systems including their receptors and transporters, are initially overproduced followed by selective elimination. Advanced methods applied to human and animal models, enable investigation of the cellular mechanisms and role of specific genes, non-coding regulatory elements and signaling molecules in control of prefrontal neuronal production and phenotypic fate, as well as neuronal migration to establish layering of the PFC. Likewise, various genetic approaches in combination with functional assays and immunohistochemical and imaging methods reveal roles of neurotransmitter systems during maturation of the PFC. Disruption, or even a slight slowing of the rate of neuronal production, migration and synaptogenesis by genetic or environmental factors, can induce gross as well as subtle changes that eventually can lead to cognitive impairment. An understanding of the development and evolution of the PFC provide insight into the pathogenesis and treatment of congenital neuropsychiatric diseases as well as idiopathic developmental disorders that cause intellectual disabilities.

Serotonin-related rodent models of early-life exposure relevant for neurodevelopmental vulnerability to psychiatric disorders

Mental disorders including depression and anxiety are continuously rising their prevalence across the globe. Early-life experience of individuals emerges as a main risk factor contributing to the developmental vulnerability to psychiatric disorders. That is, perturbing environmental conditions during neurodevelopmental stages can have detrimental effects on adult mood and emotional responses. However, the possible maladaptive neural mechanisms contributing to such psychopathological phenomenon still remain poorly understood. In this review, we explore preclinical rodent models of developmental vulnerability to psychiatric disorders, focusing on the impact of early-life environmental perturbations on behavioral aspects relevant to stress-related and psychiatric disorders. We limit our analysis to well-established models in which alterations in the serotonin (5-HT) system appear to have a crucial role in the pathophysiological mechanisms. We analyze long-term behavioral outcomes produced by early-life exposures to stress and psychotropic drugs such as the selective 5-HT reuptake inhibitor (SSRI) antidepressants or the anticonvulsant valproic acid (VPA). We perform a comparative analysis, identifying differences and commonalities in the behavioral effects produced in these models. Furthermore, this review discusses recent advances on neurodevelopmental substrates engaged in these behavioral effects, emphasizing the possible existence of maladaptive mechanisms that could be shared by the different models.

Neonatal fluoxetine exposure delays reflex ontogeny, somatic development, and food intake similarly in male and female rats

Serotonin (5-HT) acts as a neuromodulator and plays a critical role in brain development. Changes in 5-HT signaling during the perinatal period can affect neural development and may result in behavioral changes in adulthood; however, further investigations are necessary including both sexes to study possible differences. Thus, the aim of this study was to investigate the impact of neonatal treatment with fluoxetine on the development of male and female offspring. The animals were divided into four groups according to sex and treatment. The experimental groups received fluoxetine at 10 mg·kg-1 (1 μL/g of body weight (bw)) and the animals of control group received saline solution 0.9% (1 μL/g of bw) from postnatal days 1-21. In the neonatal period, reflex ontogeny, somatic development, physical features, and food intake were recorded. In the postnatal period (until day 31) bw and post-weaning food intake were recorded. Chronic administration of fluoxetine in the neonatal period caused a delay in the reflex ontogeny and somatic development, as well as reduction of lactation, post-weaning bw, and post-weaning food intake in rats. No difference was found between the sexes. These changes reaffirm that serotonin plays an important role in regulating the plasticity of the brain during the early development period, but without sex differences.

Knowledge-Based Design of Long-Chain Arylpiperazine Derivatives Targeting Multiple Serotonin Receptors as Potential Candidates for Treatment of Autism Spectrum Disorder

Autism spectrum disorder (ASD) includes a group of neurodevelopmental disorders characterized by core symptoms such as impaired social interaction and communication, repetitive and stereotyped behaviors, and restricted interests. To date, there are no effective treatments for these core symptoms. Several studies have shown that the brain serotonin (5-HT) neurotransmission system is altered in both ASD patients and animal models of the disease. Multiple pieces of evidence suggest that targeting 5-HT receptors may treat the core symptoms of ASD and associated intellectual disabilities. In fact, stimulation of the 5-HT_1A receptor reduces repetitive and restricted behaviors; blockade of the 5-HT_2A receptor reduces both learning deficits and repetitive behavior, and activation of the 5-HT₇ receptor improves cognitive performances and reduces repetitive behavior. On such a basis, we have designed novel arylpiperazine derivatives pursuing unprecedently reported activity profiles: dual 5-HT₇/5-HT_1A receptor agonist properties and mixed 5-HT₇ agonist/5-HT_1A agonist/5-HT_2A antagonist properties. Seventeen new compounds were synthesized and tested in radioligand binding assay at the target receptors. We have identified the dual 5-HT_1AR/5-HT₇R agonists 8c and 29 and the mixed 5-HT_1AR agonist/5-HT₇R agonist/5-HT_2AR antagonist 20b. These compounds are metabolically stable in vitro and have suitable central nervous system druglike properties.

Semax, synthetic ACTH(4-10) analogue, attenuates behavioural and neurochemical alterations following early-life fluvoxamine exposure in white rats

Selective serotonin reuptake inhibitors (SSRI) are commonly used to treat depression during pregnancy. SSRIs cross the placenta and may influence the maturation of the foetal brain. Clinical and preclinical findings suggest long-term consequences of SSRI perinatal exposure for the offspring. The mechanisms of SSRI effects on developing brain remain largely unknown and there are no directional approaches for prevention of the consequences of maternal SSRI treatment during pregnancy. The heptapeptide Semax (MEHFPGP) is a synthetic analogue of ACTH(4-10) which exerts marked nootropic and neuroprotective activities. The aim of the present study was to investigate the long-term effects of neonatal exposure to the SSRI fluvoxamine (FA) in white rats. Additionally, the study examined the potential for Semax to prevent the negative consequences of neonatal FA exposure. Rat pups received FA or vehicle injections on postnatal days 1-14, a time period equivalent to 27-40 weeks of human foetal age. After FA treatment, rats were administered with Semax or vehicle on postnatal days 15-28. During the 2nd month of life, the rats underwent behavioural testing, and monoamine levels in brain structures were measured. It was shown that neonatal FA exposure leads to the impaired emotional response to stress and novelty and delayed acquisition of food-motivated maze task in adolescent and young adult rats. Furthermore, FA exposure induced alterations in the monoamine levels in brains of 1- and 2- month-old rats. Semax administration reduced the anxiety-like behaviour, improved learning abilities and normalized the levels of brain biogenic amines impaired by the FA exposure. The results demonstrate that early-life FA exposure in rat pups produces long-term disturbances in their anxiety-related behaviour, learning abilities, and brain monoamines content. Semax exerts a favourable effect on behaviour and biogenic amine system of rats exposed to the antidepressant. Thus, peptide Semax can prevent behavioural deficits caused by altered 5-HT levels during development.

Gestational Factors throughout Fetal Neurodevelopment: The Serotonin Link

Serotonin (5-HT) is a critical player in brain development and neuropsychiatric disorders. Fetal 5-HT levels can be influenced by several gestational factors, such as maternal genotype, diet, stress, medication, and immune activation. In this review, addressing both human and animal studies, we discuss how these gestational factors affect placental and fetal brain 5-HT levels, leading to changes in brain structure and function and behavior. We conclude that gestational factors are able to interact and thereby amplify or counteract each other's impact on the fetal 5-HT-ergic system. We, therefore, argue that beyond the understanding of how single gestational factors affect 5-HT-ergic brain development and behavior in offspring, it is critical to elucidate the consequences of interacting factors. Moreover, we describe how each gestational factor is able to alter the 5-HT-ergic influence on the thalamocortical- and prefrontal-limbic circuitry and the hypothalamo-pituitary-adrenocortical-axis. These alterations have been associated with risks to develop attention deficit hyperactivity disorder, autism spectrum disorders, depression, and/or anxiety. Consequently, the manipulation of gestational factors may be used to combat pregnancy-related risks for neuropsychiatric disorders.

Modelling Learning and Memory in Drosophila to Understand Intellectual Disabilities

Neurodevelopmental disorders (NDDs) include a large number of conditions such as Fragile  X  syndrome, autism spectrum disorders and Down syndrome, among others. They are characterized by limitations in adaptive and social behaviors, as well as intellectual disability (ID). Whole-exome and whole-genome sequencing studies have highlighted a large number of NDD/ID risk genes. To dissect the genetic causes and underlying biological pathways, in vivo experimental validation of the effects of these mutations is needed. The fruit fly, Drosophila melanogaster, is an ideal model to study NDDs, with highly tractable genetics, combined with simple behavioral and circuit assays, permitting rapid medium-throughput screening of NDD/ID risk genes. Here, we review studies where the use of well-established assays to study mechanisms of learning and memory in Drosophila has permitted insights into molecular mechanisms underlying IDs. We discuss how technologies in the fly model, combined with a high degree of molecular and physiological conservation between flies and mammals, highlight the Drosophila system as an ideal model to study neurodevelopmental disorders, from genetics to behavior.

Perinatal exposure of rats to the HIV drug efavirenz affects medial prefrontal cortex cytoarchitecture

Efavirenz (EFV) is used for antiretroviral treatment of HIV infection, and successfully inhibits viral replication and mother-to-child transmission of HIV during pregnancy and childbirth. Unfortunately, the drug induces neuropsychiatric symptoms such as anxiety and depressed mood and potentially affects cognitive performance. EFV acts on, among others, the serotonin transporter and serotonin receptors that are expressed in the developing brain. Yet, how perinatal EFV exposure affects brain cytoarchitecture remains unclear. Here, we exposed pregnant and lactating rats to EFV, and examined in the medial prefrontal cortex (mPFC) of their adult offspring the effects of the maternal EFV exposure on cortical architecture. We observed a significant decrease in the number of cells, mainly mature neurons, in the infra/prelimbic and cingulate cortices of adult offspring. Next, we found an altered cortical cytoarchitecture characterized by a significant reduction in deep- and superficial-layer cells. This was accompanied by a sharp increase in programmed cell death, as we identified a significantly higher number of cleaved Caspase-3-positive cells. Finally, the serotonergic and dopaminergic innervation of the mPFC subdomains was increased. Thus, the perinatal exposure to EFV provoked in the mPFC of adult offspring cell death, significant changes in cytoarchitecture, and disturbances in serotonergic and dopaminergic innervation. Our results are important in the light of EFV treatment of HIV-positive pregnant women, and its effect on brain development and cognitive behavior.

Maternal SSRIs experience and risk of ASD in offspring: a review

Antidepressants are extensively used during pregnancy and associated with severe outcomes, including innate malformations, prematurity, and low birth weight, etc. A recent study suggested that prenatal exposure to antidepressants may impair child neurodevelopment process. Thus, the aim of this review is to investigate the potential association between prenatal use of selective 5-HT reuptake inhibitors (SSRIs) and the risk of autism spectrum disorders (ASDs). Twelve studies related to the linkage between SSRI exposure during pregnancy and ASD in children were explored and compiled. However, there is a knowledge gap concerning the potential link between gestational exposure to antidepressants and the risk of ASDs. Despite such limitations, the available data show that some signal exists and signifies that antenatal exposure to SSRIs may increase the risk of ASDs. Thus, there is a vital need for further, large and well-designed research to definitively evaluate the existence and the magnitude of this severe risk.

The Therapeutic Effect of the Chinese Herbal Medicine, Rehmanniae Radix Preparata, in Attention Deficit Hyperactivity Disorder via Reversal of Structural Abnormalities in the Cortex

Rehmanniae radix preparata is extracted from wine-steaming the Rehmannia root, a scrophulariaceae plant. It has been used for thousands of years with effects of nourishing kidney-yin, benefiting essence and filling marrow based on traditional Chinese medicine (TCM) theory. Rehmanniae radix preparata has antioxidant, antisenescence, anti-inflammatory, and neuroprotective properties. It is the most popular Traditional Chinese medicinal compound (TCMC) used in attention deficit hyperactivity disorder (ADHD) therapy. However, few studies have been conducted exploring the effects and potential mechanisms of Rehmanniae radix preparata alone on ADHD. Recent studies have shown that Rehmanniae radix preparata inhibits spontaneous activity in mice, improves learning and memory in rats following thalamic arcuate nucleus injury, and exhibits antidepressant effects. Catalpol, an active component of Rehmanniae radix preparata, elevates brain-derived neurotrophic factor (BDNF), and attenuates neuronal apoptosis and energy metabolism failure. ADHD is characterized by hyperactivity-impulsivity and impairments in learning and memory. Its pathomechanism is closely related to structural abnormalities in the cortex that is mediated by dysfunction in neuronal development, apoptosis, and energy metabolism. We hypothesize that Rehmanniae radix preparata may be effective at treating ADHD by alleviating neurodevelopmental abnormalities, neuronal apoptosis, and energy metabolism failure.

Common Defects of Spine Dynamics and Circuit Function in Neurodevelopmental Disorders: A Systematic Review of Findings From in Vivo Optical Imaging of Mouse Models

In vivo optical imaging is a powerful tool for revealing brain structure and function at both the circuit and cellular levels. Here, we provide a systematic review of findings obtained from in vivo imaging studies of mouse models of neurodevelopmental disorders, including the monogenic disorders fragile X syndrome, Rett syndrome, and Angelman syndrome, which are caused by genetic abnormalities of FMR1, MECP2, and UBE3A, as well as disorders caused by copy number variations (15q11-13 duplication and 22q11.2 deletion) and BTBR mice as an inbred strain model of autism spectrum disorder (ASD). Most studies visualize the structural and functional responsiveness of cerebral cortical neurons to sensory stimuli and the developmental and experience-dependent changes in these responses as a model of brain functions affected by these disorders. The optical imaging techniques include two-photon microscopy of fluorescently labeled dendritic spines or neurons loaded with fluorescent calcium indicators and macroscopic imaging of cortical activity using calcium indicators, voltage-sensitive dyes or intrinsic optical signals. Studies have revealed alterations in the density, stability, and turnover of dendritic spines, aberrant cortical sensory responses, impaired inhibitory function, and concomitant failure of circuit maturation as common causes for neurological deficits. Mechanistic hypotheses derived from in vivo imaging also provide new directions for therapeutic interventions. For instance, it was recently demonstrated that early postnatal administration of a selective serotonin reuptake inhibitor (SSRI) restores impaired cortical inhibitory function and ameliorates the aberrant social behaviors in a mouse model of ASD. We discuss the potential use of SSRIs for treating ASDs in light of these findings.

Links between serotonin reuptake inhibition during pregnancy and neurodevelopmental delay/spectrum disorders: A systematic review of epidemiological and physiological evidence

OBJECTIVE

To investigate possible linkages between neurodevelopmental delay and neurodevelopmental spectrum disorders and exposure to medication with effects on serotonin reuptake inhibition during pregnancy.

METHODS

We systematically reviewed the epidemiological literature for studies bearing on this relationship in children born with neurodevelopmental spectrum disorder and related conditions, as well as animal studies giving serotonin reuptake inhibitors to pregnant animals and in addition reviewed the literature for proposals as to possible mechanisms that might link effects on serotonin reuptake with cognitive changes post-partum.The epidemiological studies were analysed to produce Forest plots to illustrate possible relations.

RESULTS

The odds ratio of Autistic Spectrum or related Disorders in children born to women taking serotonin reuptake inhibiting antidepressants during pregnancy in case control studies was 1.95 (95% C.I. 1.63, 2.34) and in prospective cohort studies was 1.96 (95% C.I. 1.33, 2.90).

CONCLUSIONS

There appears to be a link between serotonin reuptake inhibition in pregnancy and developmental delay and spectrum disorders in infancy leading to cognitive difficulties in childhood. More work needs to be done to establish more precisely the nature of the difficulties and possible mechanisms through which this link might be mediated.

Epigenetic adaptation of the placental serotonin transporter gene (SLC6A4) to gestational diabetes mellitus

We tested the hypothesis that gestational diabetes mellitus (GDM) alters the DNA methylation pattern of the fetal serotonin transporter gene (SLC6A4), and examined the functional relevance of DNA methylation for regulation of the SLC6A4 expression in the human placenta. The study included 50 mother-infant pairs. Eighteen mothers were diagnosed with GDM and 32 had normal glucose tolerance (NGT). All neonates were of normal birth weight and born at term by planned Cesarean section. DNA and RNA were isolated from samples of tissue collected from the fetal side of the placenta immediately after delivery. DNA methylation was quantified at 7 CpG sites within the SLC6A4 distal promoter region using PCR amplification of bisulfite treated DNA and subsequent DNA sequencing. SLC6A4 mRNA levels were measured by reverse transcription—quantitative PCR (RT-qPCR). Functional SLC6A4 polymorphisms (5HTTLPR, STin2, rs25531) were genotyped using standard PCR-based procedures. Average DNA methylation across the 7 analyzed loci was decreased in the GDM as compared to the NGT group (by 27.1%, p = 0.037) and negatively correlated, before and after adjustment for potential confounder/s, with maternal plasma glucose levels at the 24th to 28th week of gestation (p<0.05). Placental SLC6A4 mRNA levels were inversely correlated with average DNA methylation (p = 0.010) while no statistically significant association was found with the SLC6A4 genotypes (p>0.05). The results suggest that DNA methylation of the fetal SLC6A4 gene is sensitive to the maternal metabolic state in pregnancy. They also indicate a predominant role of epigenetic over genetic mechanisms in the regulation of SLC6A4 expression in the human placenta. Longitudinal studies in larger cohorts are needed to verify these results and determine to which degree placental SLC6A4 changes may contribute to long-term outcomes of infants exposed to GDM.

Perinatal reduction of functional serotonin transporters results in developmental delay

While there is strong evidence from rodent and human studies that a reduction in serotonin transporter (5-HTT) function in early-life can increase the risk for several neuropsychiatric disorders in adulthood, the effects of reduced 5-HTT function on behavior across developmental stages are underinvestigated. To elucidate how perinatal pharmacological and lifelong genetic inactivation of the 5-HTT affects behavior across development, we conducted a battery of behavioral tests in rats perinatally exposed to fluoxetine or vehicle and in 5-HTT(-/-) versus 5-HTT(+/+) rats. We measured motor-related behavior, olfactory function, grooming behavior, sensorimotor gating, object directed behavior and novel object recognition in the first three postnatal weeks and if possible the tests were repeated in adolescence and adulthood. We also measured developmental milestones such as eye opening, reflex development and body weight. We observed that both pharmacological and genetic inactivation of 5-HTT resulted in a developmental delay. Except for hypo-locomotion, most of the observed early-life effects were normalized later in life. In adolescence and adulthood we observed object directed behavior and decreased novel object recognition in the 5-HTT(-/-) rats, which might be related to the lifelong inactivation of 5-HTT. Together, these data provide an important contribution to the understanding of the effects of perinatal and lifelong 5-HTT inactivation on behavior across developmental stages.

Electrophysiological Assessment of Serotonin and GABA Neuron Function in the Dorsal Raphe during the Third Trimester Equivalent Developmental Period in Mice

Alterations in the development of the serotonin system can have prolonged effects, including depression and anxiety disorders later in life. Serotonin axonal projections from the dorsal raphe undergo extensive refinement during the first 2 weeks of postnatal life in rodents (equivalent to the third trimester of human pregnancy). However, little is known about the functional properties of serotonin and GABA neurons in the dorsal raphe during this critical developmental period. We assessed the functional properties and synaptic connectivity of putative serotoninergic neurons and GABAergic neurons in the dorsal raphe during early [postnatal day (P) P5-P7] and late (P15-P17) stages of the third trimester equivalent period using electrophysiology. Our studies demonstrate that GABAergic neurons are hyperexcitable at P5-P7 relative to P15-P17. Furthermore, putative serotonin neurons exhibit an increase in both excitatory and GABAA receptor-mediated spontaneous postsynaptic currents during this developmental period. Our data suggest that GABAergic neurons and putative serotonin neurons undergo significant electrophysiological changes during neonatal development.

Long-term consequences of chronic fluoxetine exposure on the expression of myelination-related genes in the rat hippocampus

The selective serotonin reuptake inhibitor (SSRI) fluoxetine is widely prescribed for the treatment of symptoms related to a variety of psychiatric disorders. After chronic SSRI treatment, some symptoms remediate on the long term, but the underlying mechanisms are not yet well understood. Here we studied the long-term consequences (40 days after treatment) of chronic fluoxetine exposure on genome-wide gene expression. During the treatment period, we measured body weight; and 1 week after treatment, cessation behavior in an SSRI-sensitive anxiety test was assessed. Gene expression was assessed in hippocampal tissue of adult rats using transcriptome analysis and several differentially expressed genes were validated in independent samples. Gene ontology analysis showed that upregulated genes induced by chronic fluoxetine exposure were significantly enriched for genes involved in myelination. We also investigated the expression of myelination-related genes in adult rats exposed to fluoxetine at early life and found two myelination-related genes (Transferrin (Tf) and Ciliary neurotrophic factor (Cntf)) that were downregulated by chronic fluoxetine exposure. Cntf, a neurotrophic factor involved in myelination, showed regulation in opposite direction in the adult versus neonatally fluoxetine-exposed groups. Expression of myelination-related genes correlated negatively with anxiety-like behavior in both adult and neonatally fluoxetine-exposed rats. In conclusion, our data reveal that chronic fluoxetine exposure causes on the long-term changes in expression of genes involved in myelination, a process that shapes brain connectivity and contributes to symptoms of psychiatric disorders.

Improved Stress Control in Serotonin Transporter Knockout Rats: Involvement of the Prefrontal Cortex and Dorsal Raphe Nucleus

Variations in serotonin transporter (5-HTT) expression have been associated with altered sensitivity to stress. Since controllability is known to alter the impact of a stressor through differential activation of the medial prefrontal cortex (mPFC) and dorsal raphe nucleus (DRN), and that these regions are functionally affected by genetic 5-HTT down-regulation, we hypothesized that 5-HTT expression modulates the effect of controllability on stressor impact and coping. Here, we investigated the effects of a signaled stress controllability task or a yoked uncontrollable stressor on behavioral responding and mPFC and DRN activation. 5-HTT(-/-) rats proved better capable of acquiring the active avoidance task than 5-HTT(+/+) animals. Controllability determined DRN activation in 5-HTT(+/+), but not 5-HTT(-/-), rats, whereas controllability-related activation of the mPFC was independent of genotype. These findings suggest that serotonergic activation in the DRN is involved in stress coping in a 5-HTT expression dependent manner, whereas mPFC activation seems to be implicated in control over stress independently of 5-HTT expression. We speculate that alterations in serotonergic feedback in the DRN might be a potential mechanism driving this differential stress coping.

Molecular underpinnings of prefrontal cortex development in rodents provide insights into the etiology of neurodevelopmental disorders

The prefrontal cortex (PFC), seat of the highest-order cognitive functions, constitutes a conglomerate of highly specialized brain areas and has been implicated to have a role in the onset and installation of various neurodevelopmental disorders. The development of a properly functioning PFC is directed by transcription factors, guidance cues and other regulatory molecules and requires the intricate and temporal orchestration of a number of developmental processes. Disturbance or failure of any of these processes causing neurodevelopmental abnormalities within the PFC may contribute to several of the cognitive deficits seen in patients with neurodevelopmental disorders. In this review, we elaborate on the specific processes underlying prefrontal development, such as induction and patterning of the prefrontal area, proliferation, migration and axonal guidance of medial prefrontal progenitors, and their eventual efferent and afferent connections. We furthermore integrate for the first time the available knowledge from genome-wide studies that have revealed genes linked to neurodevelopmental disorders with experimental molecular evidence in rodents. The integrated data suggest that the pathogenic variants in the neurodevelopmental disorder-associated genes induce prefrontal cytoarchitectonical impairments. This enhances our understanding of the molecular mechanisms of prefrontal (mis)development underlying the four major neurodevelopmental disorders in humans, that is, intellectual disability, autism spectrum disorders, attention deficit hyperactivity disorder and schizophrenia, and may thus provide clues for the development of novel therapies.

Impact of prenatal environmental stress on cortical development

Prenatal exposure of the developing brain to various types of environmental stress increases susceptibility to neuropsychiatric disorders such as autism, attention deficit hyperactivity disorder and schizophrenia. Given that even subtle perturbations by prenatal environmental stress in the cerebral cortex impair the cognitive and memory functions, this review focuses on underlying molecular mechanisms of pathological cortical development. We especially highlight recent works that utilized animal exposure models, human specimens or/and induced Pluripotent Stem (iPS) cells to demonstrate: (1) molecular mechanisms shared by various types of environmental stressors, (2) the mechanisms by which the affected extracortical tissues indirectly impact the cortical development and function, and (3) interaction between prenatal environmental stress and the genetic predisposition of neuropsychiatric disorders. Finally, we discuss current challenges for achieving a comprehensive understanding of the role of environmentally disturbed molecular expressions in cortical maldevelopment, knowledge of which may eventually facilitate discovery of interventions for prenatal environment-linked neuropsychiatric disorders.

Allergic fetal priming leads to developmental, behavioral and neurobiological changes in mice

The state of the mother's immune system during pregnancy has an important role in fetal development and disruptions in the balance of this system are associated with a range of neurologic, neuropsychiatric and neurodevelopmental disorders. Epidemiological and clinical reports reveal various clues that suggest a possible association between developmental neuropsychiatric disorders and family history of immune system dysfunction. Over the past three decades, analogous increases have been reported in both the incidence of neurodevelopmental disorders and immune-related disorders, particularly allergy and asthma, raising the question of whether allergic asthma and characteristics of various neurodevelopmental disorders share common causal links. We used a mouse model of maternal allergic asthma to test this novel hypothesis that early fetal priming with an allergenic exposure during gestation produces behavioral deficits in offspring. Mothers were primed with an exposure to ovalbumin (OVA) before pregnancy, then exposed to either aerosolized OVA or vehicle during gestation. Both male and female mice born to mothers exposed to aerosolized OVA during gestation exhibited altered developmental trajectories in weight and length, decreased sociability and increased marble-burying behavior. Moreover, offspring of OVA-exposed mothers were observed to have increased serotonin transporter protein levels in the cortex. These data demonstrate that behavioral and neurobiological effects can be elicited following early fetal priming with maternal allergic asthma and provide support that maternal allergic asthma may, in some cases, be a contributing factor to neurodevelopmental disorders.

Characterization of a mammalian prosencephalic functional plan

Hypothalamic organizational concepts have greatly evolved as the primary hypothalamic pathways have been systematically investigated. In the present review, we describe how the hypothalamus arises from a molecularly heterogeneous region of the embryonic neural tube but is first differentiated as a primary neuronal cell cord (earliest mantle layer). This structure defines two axes that align onto two fundamental components: a longitudinal tractus postopticus(tpoc)/retinian component and a transverse supraoptic tract(sot)/olfactory component. We then discuss how these two axonal tracts guide the formation of all major tracts that connect the telencephalon with the hypothalamus/ventral midbrain, highlighting the existence of an early basic plan in the functional organization of the prosencephalic connectome.

Perinatal Influences of Valproate on Brain and Behaviour: An Animal Model for Autism

Valproic acid or valproate (VPA) is an anti-convulsant and mood stabiliser effective in treating epilepsy and bipolar disorders. Although in adults VPA is well tolerated and safe, there is convincing evidence that it has teratogenic properties, ranging from mild neurodevelopmental changes to severe congenital malformations. In particular, studies involving humans and other animals have shown that prenatal exposure to VPA can induce developmental abnormalities reminiscent of autism spectrum disorder (ASD). In this chapter, we discuss the connection between VPA and ASD, evaluate the VPA animal model of ASD, and describe the possible molecular mechanisms underlying VPA's teratogenic properties.

Serotonin-related pathways and developmental plasticity: relevance for psychiatric disorders

Risk for adult psychiatric disorders is partially determined by early-life alterations occurring during neural circuit formation and maturation. In this perspective, recent data show that the serotonin system regulates key cellular processes involved in the construction of cortical circuits. Translational data for rodents indicate that early-life serotonin dysregulation leads to a wide range of behavioral alterations, ranging from stress-related phenotypes to social deficits. Studies in humans have revealed that serotonin-related genetic variants interact with early-life stress to regulate stress-induced cortisol responsiveness and activate the neural circuits involved in mood and anxiety disorders. Emerging data demonstrate that early-life adversity induces epigenetic modifications in serotonin-related genes. Finally, recent findings reveal that selective serotonin reuptake inhibitors can reinstate juvenile-like forms of neural plasticity, thus allowing the erasure of long-lasting fear memories. These approaches are providing new insights on the biological mechanisms and clinical application of antidepressants.

Genetic, psychosocial, and demographic factors associated with social disinhibition in Mexican-origin youth

INTRODUCTION

The genetic heritability for sensation-seeking tendencies ranges from 40 to 60%. Sensation-seeking behaviors typically manifest during adolescence and are associated with alcohol and cigarette experimentation in adolescents. Social disinhibition is an aspect of sensation-seeking that is closely tied to cigarette and alcohol experimentation.

METHODS

We examined the contribution of candidate genes to social disinhibition among 1132 Mexican origin youth in Houston, Texas, adjusting for established demographic and psychosocial risk factors. Saliva samples were obtained at baseline in 2005-06, and social disinhibition and other psychosocial data were obtained in 2008-09. Participants were genotyped for 672 functional and tagging SNPs potentially related to sensation-seeking, risk-taking, smoking, and alcohol use.

RESULTS

Six SNPs were significantly associated with social disinhibition scores, after controlling for false discovery and adjusting for population stratification and relevant demographic/psychosocial characteristics. Minor alleles for three of the SNPs (rs1998220 on OPRM1; rs9534511 on HTR2A; and rs4938056 on HTR3B) were associated with increased risk of social disinhibition, while minor alleles for the other three SNPs (rs1003921 on KCNC1; rs16116 downstream of NPY; and rs16870286 on LINC00518) exhibited a protective effect. Age, linguistic acculturation, thrill and adventure-seeking, and drug and alcohol-seeking were all significantly positively associated with increased risk of social disinhibition in a multivariable model (P < 0.001).

CONCLUSIONS

These results add to our knowledge of genetic risk factors for social disinhibition. Additional research is needed to verify whether these SNPs are associated with social disinhibition among youth of different ethnicities and nationalities, and to elucidate whether and how these SNPs functionally contribute to social disinhibition.

Effects of neonatal fluvoxamine administration on the physical development and activity of the serotoninergic system in white rats

Selective serotonin reuptake inhibitors (SSRIs), including fluvoxamine, are widely used to treat depressive disorders in pregnant women. These antidepressants effectively penetrate through the placental barrier, affecting the fetus during the critical phase of neurodevelopment. Some clinical studies have linked prenatal exposure to SSRIs with increased neonatal mortality, premature birth, decreased fetal growth and delay in psychomotor development. However, the effects of prenatal exposure to SSRIs remain unknown. The administration of SSRIs in rodents during the first postnatal weeks is considered as an model for studying the effects of prenatal SSRIs exposure in human. The aim of this work was to study the acute effects of chronic fluvoxamine (FA) administration in white rat pups. The study was carried out in male and female rat pups treated with FA (10 mg/kg/day, intraperitoneally) from postnatal days 1 to 14. The lethality level, body weight, age of eye opening, and motor reflex maturation were recorded. The contents of biogenic amines and their metabolites in different brain structures were also determined. It was shown that neonatal FA administration led to increased lethality level, reduced body weight, and delayed maturation of motor reflexes. Furthermore, increased noradrenalin level in hypothalamus, serotonin level in hippocampus and serotonin metabolite 5-HIAA level in frontal cortex, hypothalamus, hippocampus, and striatum were observed in drug-treated animals compared to the control group. We can conclude that the altered activity of the serotoninergic system induced by fluvoxamine administration at early developmental stages leads to a delay in physical and motor development.

The attribution of incentive salience to an appetitive conditioned cue is not affected by knockout of the serotonin transporter in rats

Understanding the neurobiological basis underlying individual differences in conditioned stimulus (CS) sensitivity is pertinent, given that excessive conditioned responses to CSs is a key feature of anxiety-related disorders and drug addiction. We have previously shown that behaviour of serotonin transporter knockout (5-HTT(-/-)) rats-mimicking the common 5-HTT promoter polymorphism in humans-is strongly driven by Pavlovian CSs. To investigate whether the knockout rats attribute greater incentive salience to CSs, we tested the 5-HTT(-/-) rats and their wild-type counterparts in the sucrose-reinforced sign-versus goal-tracking task. We also assessed whether motivational properties of the unconditioned stimulus (sucrose pellet) are involved in the individual differences under investigation, by testing the animals in a sucrose-reinforced progressive ratio schedule of reinforcement. We found no genotype differences in sign-versus goal-tracking behavior, despite that progressive ratio responding was increased in 5-HTT(-/-) rats. In conclusion, the high CS sensitivity in 5-HTT(-/-) rats cannot be explained by enhanced incentive salience attribution to the CS as measured by the sign- versus goal-tracking paradigm. Rather, 5-HTT(-/-) rats may be more sensitive to the motivational properties of the unconditioned stimulus.