Development Of Cortical Neurons Research Articles

Neuronal development is promoted by weakened intrinsic antioxidant defences due to epigenetic repression of Nrf2

Forebrain neurons have weak intrinsic antioxidant defences compared with astrocytes, but the molecular basis and purpose of this is poorly understood. We show that early in mouse cortical neuronal development in vitro and in vivo, expression of the master-regulator of antioxidant genes, transcription factor NF-E2-related-factor-2 (Nrf2), is repressed by epigenetic inactivation of its promoter. Consequently, in contrast to astrocytes or young neurons, maturing neurons possess negligible Nrf2-dependent antioxidant defences, and exhibit no transcriptional responses to Nrf2 activators, or to ablation of Nrf2's inhibitor Keap1. Neuronal Nrf2 inactivation seems to be required for proper development: in maturing neurons, ectopic Nrf2 expression inhibits neurite outgrowth and aborization, and electrophysiological maturation, including synaptogenesis. These defects arise because Nrf2 activity buffers neuronal redox status, inhibiting maturation processes dependent on redox-sensitive JNK and Wnt pathways. Thus, developmental epigenetic Nrf2 repression weakens neuronal antioxidant defences but is necessary to create an environment that supports neuronal development.

Regulation of cerebral cortex development by Rho GTPases: insights from in vivo studies.

The cerebral cortex is the site of higher human cognitive and motor functions. Histologically, it is organized into six horizontal layers, each containing unique populations of molecularly and functionally distinct excitatory projection neurons and inhibitory interneurons. The stereotyped cellular distribution of cortical neurons is crucial for the formation of functional neural circuits and it is predominantly established during embryonic development. Cortical neuron development is a multiphasic process characterized by sequential steps of neural progenitor proliferation, cell cycle exit, neuroblast migration and neuronal differentiation. This series of events requires an extensive and dynamic remodeling of the cell cytoskeleton at each step of the process. As major regulators of the cytoskeleton, the family of small Rho GTPases has been shown to play essential functions in cerebral cortex development. Here we review in vivo findings that support the contribution of Rho GTPases to cortical projection neuron development and we address their involvement in the etiology of cerebral cortex malformations.

Chemokine receptors and cortical interneuron dysfunction in schizophrenia

Alterations in inhibitory (GABA) neurons, including deficiencies in the GABA synthesizing enzyme GAD67, in the prefrontal cortex in schizophrenia are pronounced in the subpopulations of neurons that contain the calcium-binding protein parvalbumin or the neuropeptide somatostatin. The presence of similar illness-related deficits in the transcription factor Lhx6, which regulates prenatal development of parvalbumin and somatostatin neurons, suggests that cortical GABA neuron dysfunction may be related to disturbances in utero. Since the chemokine receptors CXCR4 and CXCR7 guide the migration of cortical parvalbumin and somatostatin neurons from their birthplace in the medial ganglionic eminence to their final destination in the neocortex, we sought to determine whether altered CXCR4 and/or CXCR7 mRNA levels were associated with disturbances in GABA-related markers in schizophrenia. Quantitative PCR was used to quantify CXCR4 and CXCR7 mRNA levels in the prefrontal cortex of 62 schizophrenia and 62 healthy comparison subjects that were previously characterized for markers of parvalbumin and somatostatin neurons and in antipsychotic-exposed monkeys. We found elevated mRNA levels for CXCR7 (+29%; p<.0001) and CXCR4 (+14%, p=.052) in schizophrenia subjects but not in antipsychotic-exposed monkeys. CXCR7 mRNA levels were inversely correlated with mRNA levels for GAD67, parvalbumin, somatostatin, and Lhx6 in schizophrenia but not in healthy subjects. These findings suggest that higher mRNA levels for CXCR7, and possibly CXCR4, may represent a compensatory mechanism to sustain the migration and correct positioning of cortical parvalbumin and somatostatin neurons in the face of other insults that disrupt the prenatal development of cortical GABA neurons in schizophrenia.

Control of Spontaneous Ca2+ Transients Is Critical for Neuronal Maturation in the Developing Neocortex.

Neural activity plays roles in the later stages of development of cortical excitatory neurons, including dendritic and axonal arborization, remodeling, and synaptogenesis. However, its role in earlier stages, such as migration and dendritogenesis, is less clear. Here we investigated roles of neural activity in the maturation of cortical neurons, using calcium imaging and expression of prokaryotic voltage-gated sodium channel, NaChBac. Calcium imaging experiments showed that postmigratory neurons in layer II/III exhibited more frequent spontaneous calcium transients than migrating neurons. To test whether such an increase of neural activity may promote neuronal maturation, we elevated the activity of migrating neurons by NaChBac expression. Elevation of neural activity impeded migration, and induced premature branching of the leading process before neurons arrived at layer II/III. Many NaChBac-expressing neurons in deep cortical layers were not attached to radial glial fibers, suggesting that these neurons had stopped migration. Morphological and immunohistochemical analyses suggested that branched leading processes of NaChBac-expressing neurons differentiated into dendrites. Our results suggest that developmental control of spontaneous calcium transients is critical for maturation of cortical excitatory neurons in vivo: keeping cellular excitability low is important for migration, and increasing spontaneous neural activity may stop migration and promote dendrite formation.

Neuritin, A Neurotrophic Factor in Nervous System Physiology

Neuritin (also known as candidate plasticity gene 15, cpg15) is an activity-induced glycosylphosphatidylinositol- anchored axonal protein and is mainly expressed in the brain. Neuritin mRNA expression is modulated by neurotrophic factors, synaptic activity, hormones, sensory experience, and electroconvulsive seizure therapy. Neuritin has several effects in the nervous system, such as promoting neurite outgrowth, modulating neurite outgrowth during neuronal differentiation, protecting motor neuron axons, promoting dendritic growth, shaping dendritic arbors of target neurons, regulating synaptic plasticity, stabilizing active synapses, promoting synaptic maturation and neuronal migration, promoting the development and maturation of visual cortical neurons, regulating apoptosis of proliferative neurons, and regenerating peripheral nerve and spinal axons. Neuritin is also implicated in cerebral ischemia, depression, and cognitive function in schizophrenia, and it upregulates transient outward K(+) currents in neurons, suggesting that neuritin may be a potential therapeutic target in peripheral and central nervous system diseases. This review focuses on the expression, distribution, and physiological functions of neuritin in the nervous system.

Activated retinoid receptors are required for the migration and fate maintenance of subsets of cortical neurons

Layer-specific cortical neurons are essential components of local, intracortical and subcortical circuits and are specified by complex signaling pathways acting on cortical progenitors. However, whether extrinsic signals contribute to postmitotic cortical neuronal development is unclear. Here we show in mice that retinoic acid (RA) receptors are activated in newly born migrating cortical neurons indicative of endogenous RA in the cortex. Disruption of RA signaling in postmitotic neurons by dominant-negative retinoid receptor RAR403 expression specifically delays late-born cortical neuron migration in vivo. Moreover, prospective layer V-III neurons that express RAR403 fail to maintain their fates and instead acquire characteristics of layer II neurons. This latter phenotype is rescued by active forms of β-catenin at central and caudal but not rostral cortical regions. Taken together, these observations suggest that RA signaling pathways operate postmitotically to regulate the onset of radial migration and to consolidate regional differences in cortical neuronal identity.

Complement inhibition and statins prevent fetal brain cortical abnormalities in a mouse model of preterm birth

Premature babies are particularly vulnerable to brain injury. In this study we focus on cortical brain damage associated with long-term cognitive, behavioral, attentional or socialization deficits in children born preterm. Using a mouse model of preterm birth (PTB), we demonstrated that complement component C5a contributes to fetal cortical brain injury. Disruption of cortical dendritic and axonal cytoarchitecture was observed in PTB-mice. Fetuses deficient in C5aR (−/−) did not show cortical brain damage. Treatment with antibody anti-C5, that prevents generation of C5a, also prevented cortical fetal brain injury in PTB-mice. C5a also showed a detrimental effect on fetal cortical neuron development and survival in vitro. Increased glutamate release was observed in cortical neurons in culture exposed to C5a. Blockade of C5aR prevented glutamate increase and restored neurons dendritic and axonal growth and survival. Similarly, increased glutamate levels – measured by 1HMRS – were observed in vivo in PTB-fetuses compared to age-matched controls. The blockade of glutamate receptors prevented C5a-induced abnormal growth and increased cell death in isolated fetal cortical neurons. Simvastatin and pravastatin prevented cortical fetal brain developmental and metabolic abnormalities -in vivo and in vitro. Neuroprotective effects of statins were mediated by Akt/PKB signaling pathways. This study shows that complement activation plays a crucial role in cortical fetal brain injury in PTL and suggests that complement inhibitors and statins might be good therapeutic options to improve neonatal outcomes in preterm birth.

A comprehensive characterization of the nuclear microRNA repertoire of post-mitotic neurons

MicroRNAs (miRNAs) are small non-coding RNAs with important functions in the development and plasticity of post-mitotic neurons. In addition to the well-described cytoplasmic function of miRNAs in post-transcriptional gene regulation, recent studies suggested that miRNAs could also be involved in transcriptional and post-transcriptional regulatory processes in the nuclei of proliferating cells. However, whether miRNAs localize to and function within the nucleus of post-mitotic neurons is unknown. Using a combination of microarray hybridization and small RNA deep sequencing, we identified a specific subset of miRNAs which are enriched in the nuclei of neurons. Nuclear enrichment of specific candidate miRNAs (miR-25 and miR-92a) could be independently validated by Northern blot, quantitative real-time PCR (qRT-PCR) and fluorescence in situ hybridization (FISH). By cross-comparison to published reports, we found that nuclear accumulation of miRNAs might be linked to a down-regulation of miRNA expression during in vitro development of cortical neurons. Importantly, by generating a comprehensive isomiR profile of the nuclear and cytoplasmic compartments, we found a significant overrepresentation of guanine nucleotides (nt) at the 3′-terminus of nuclear-enriched isomiRs, suggesting the presence of neuron-specific mechanisms involved in miRNA nuclear localization. In conclusion, our results provide a starting point for future studies addressing the nuclear function of specific miRNAs and the detailed mechanisms underlying subcellular localization of miRNAs in neurons and possibly other polarized cell types.

Transient epileptiform signaling during neuronal network development: regulation by external stimulation and bimodal GABAergic activity

A predominance of excitatory activity, with protracted appearance of inhibitory activity, accompanies cortical neuronal development. It is unclear whether or not inhibitory neuronal activity is solicited exclusively by excitatory neurons or whether the transient excitatory activity displayed by developing GABAergic neurons contributes to an excitatory threshold that fosters their conversion to inhibitory activity. We addressed this possibility by culturing murine embryonic neurons on multi-electrode arrays. A wave of individual 0.2–0.4mV signals (“spikes”) appeared between approx. 20–30 days in culture, then declined. A transient wave of high amplitude (>0.5mV) epileptiform activity coincided with the developmental decline in spikes. Bursts (clusters of ≥3 low-amplitude spikes within 0.7s prior to returning to baseline) persisted following this decline.Addition of the GABAergic antagonist bicuculline initially had no effect on signaling, consistent with delayed development of GABAergic synapses. This was followed by a period in which bicuculline inhibited overall signaling, confirming that GABAergic neurons initially display excitatory activity in ex vivo networks. Following the transient developmental wave of epileptiform signaling, bicuculline induced a resurgence of epileptiform signaling, indicating that GABAergic neurons at this point displayed inhibitory activity. The appearance of transition after the developmental and decline of epileptiform activity, rather than immediately after the developmental decline in lower-amplitude spikes, suggests that the initial excitatory activity of GABAergic neurons contributes to their transition into inhibitory neurons, and that inhibitory GABAergic activity is essential for network development.Prior studies indicate that a minority (25%) of neurons in these cultures were GABAergic, suggesting that inhibitory neurons regulate multiple excitatory neurons. A similar robust increase in signaling following cessation of inhibitory activity in an artificial neural network containing 20% inhibitory neurons supported this conclusion. Even a minor perturbation in GABAergic function may therefore foster initiation and/or amplification of seizure activity, as well as perturbations in long-term potentiation.

Prenatal exposure to 2,3,7,8-tetrachlorodibenzo-p-dioxin produces alterations in cortical neuron development and a long-term dysfunction of glutamate transmission in rat cerebral cortex

2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) is considered one of the most toxic dioxin-like compounds. It is ubiquitous in foodstuffs of animal origin and accumulates in the fatty tissues of animals and humans. Prenatal TCDD exposure has been associated, beside other effects, with persistent impaired cognitive development.In the present study, the effects of maternal exposure to TCDD during pregnancy on cortical neuron development at birth and cortical glutamate transmission in new-born, 14- and 60-day-old rat offspring, were investigated. A single dose (0.7μg/kg) of TCDD dissolved in corn oil was orally administrated to the dams on gestational day 18; controls dams were treated with the vehicle. All the experiments have been performed on the male offspring from vehicle-treated (i.e. control group) and TCDD-treated dams.Primary cultures of cerebral cortical neurons obtained from 1-day-old rats born from mothers exposed to TCDD displayed a reduction in cell viability (MTT assay) and an increase in the number of apoptotic nuclei (nuclear staining with Hoechst 33258) possibly associated with altered dendrite outgrowth (MAP2-immunoreactivity) with respect to control cell cultures. These changes were associated with impairment in cortical glutamate transmission, characterized by a reduction in basal and K+-evoked outflow as well as a decrease in [3H]glutamate uptake. Interestingly, the prenatal TCDD-induced alteration of cortical glutamate signaling is persistent since it was also present in 14- and 60-day-old offspring.Taken together, these results suggest that a single prenatal exposure to TCDD produces alterations in cortical neuron development associated with a long-term dysfunction of glutamate transmission in rat cerebral cortex. The possible relevance of these findings for the understanding of the long-lasting cognitive deficit observed in the offspring from mothers exposed to the toxicant during pregnancy, is discussed.

Effects of prenatal cocaine and heroin exposure on neuronal dendrite morphogenesis and spatial recognition memory in mice

Cocaine and heroin are psychoactive substances frequently used by woman abusers of childbearing age. In this study, we used in utero electroporation labeling technique and novelty recognition models to evaluate the effects of prenatal exposure of mice to cocaine or heroin on the morphological development of cortical neurons and postnatal cognitive functions. Our results showed that prenatal cocaine exposure increased dendrite outgrowth, and prenatal heroin exposure decreased dendrite length and branch number in pyramidal neurons in the somatosensory cortex. Furthermore, although no effects of prenatal cocaine or heroin exposure on novel object recognition were observed, offspring prenatally exposed to cocaine exhibited no exploration preference for objects placed in novel locations, and mice prenatally exposed to heroin showed a reduced tendency of exploration for objects in novel locations. These data demonstrate that maternal cocaine or heroin administration during pregnancy causes morphological alterations in pyramidal neurons in the somatosensory cortex and suggest that prenatal administration of addictive substances may impair short-term spatial memory in adult offspring.

Autism spectrum disorder susceptibility gene TAOK2 affects basal dendrite formation in the neocortex

How neurons develop their morphology is an important question in neurobiology. Here we describe a new pathway that specifically affects the formation of basal dendrites and axonal projections in cortical pyramidal neurons. We report that thousand-and-one-amino acid 2 kinase (TAOK2), also known as TAO2, is essential for dendrite morphogenesis. TAOK2 downregulation impairs basal dendrite formation in vivo without affecting apical dendrites. Moreover, TAOK2 interacts with Neuropilin 1 (Nrp1), a receptor protein that binds the secreted guidance cue Semaphorin 3A (Sema3A). TAOK2 overexpression restores dendrite formation in cultured cortical neurons from Nrp1(Sema-) mice, which express Nrp1 receptors incapable of binding Sema3A. TAOK2 overexpression also ameliorates the basal dendrite impairment resulting from Nrp1 downregulation in vivo. Finally, Sema3A and TAOK2 modulate the formation of basal dendrites through the activation of the c-Jun N-terminal kinase (JNK). These results delineate a pathway whereby Sema3A and Nrp1 transduce signals through TAOK2 and JNK to regulate basal dendrite development in cortical neurons.

Prenatal Cocaine Exposure Decreases Parvalbumin-Immunoreactive Neurons and GABA-to-Projection Neuron Ratio in the Medial Prefrontal Cortex

Cocaine abuse during pregnancy produces harmful effects not only on the mother but also on the unborn child. The neurotransmitters dopamine and serotonin are known as the principal targets of the action of cocaine in the fetal and postnatal brain. However, recent evidence suggests that cocaine can impair cerebral cortical GABA neuron development and function. We sought to analyze the effects of prenatal cocaine exposure on the number and distribution of GABA and projection neurons (inhibitory interneurons and excitatory output neurons, respectively) in the mouse cerebral cortex. We found that the prenatal cocaine exposure decreased GABA neuron numbers and GABA-to-projection neuron ratio in the medial prefrontal cortex of 60-day-old mice. The neighboring prefrontal cortex did not show significant changes in either of these measures. However, there was a significant increase in projection neuron numbers in the prefrontal cortex but not in the medial prefrontal cortex. Thus, the effects of cocaine on GABA and projection neurons appear to be cortical region specific. The population of parvalbumin-immunoreactive GABA neurons was decreased in the medial prefrontal cortex following the prenatal cocaine exposure. The cocaine exposure also delayed the developmental decline in the volume of the medial prefrontal cortex. Thus, prenatal cocaine exposure produced persisting and region-specific effects on cortical cytoarchitecture and impaired the physiological balance between excitatory and inhibitory neurotransmission. These structural changes may underlie the electrophysiological and behavioral effects of prenatal cocaine exposure observed in animal models and human subjects.

Up-regulation of Ras/Raf/ERK1/2 signaling impairs cultured neuronal cell migration, neurogenesis, synapse formation, and dendritic spine development

The Ras/Raf/ERK1/2 signaling pathway controls many cellular responses such as cell proliferation, migration, differentiation, and death. In the nervous system, emerging evidence also points to a death-promoting role for ERK1/2 in both in vitro and in vivo models of neuronal death. Recent studies have suggested that abnormal apoptosis in the central nervous system may be involved in the pathogenesis of autism. Two studies reported that both a microdeletion and microduplication on chromosome 16, which includes the MAPK3 gene that encodes ERK1, are associated with autism. In addition, our recent work showed that Ras/Raf/ERK1/2 signaling activities were significantly up-regulated in the frontal cortex of autistic individuals and in the BTBR murine model of autism. To further investigate how Ras/Raf/ERK1/2 up-regulation may lead to the development of autism, we developed a cellular model of Raf/ERK up-regulation by over-expressing c-Raf in cultured cortical neurons (CNs) and cerebellar granule cells (CGCs). We found that Raf/ERK up-regulation stimulates the migration of both CNs and CGCs, and impairs the formation of excitatory synapses in CNs. In addition, we found that Raf/ERK up-regulation inhibits the development of mature dendritic spines in CNs. Investigating the possible mechanisms through which Raf/ERK up-regulation affects excitatory synapse formation and dendritic spine development, we discovered that Raf/ERK up-regulation suppresses the development and maturation of CNs. Together, these results suggest that the up-regulation of the Raf/ERK signaling pathway may contribute to the pathogenesis of autism through both its impairment of cortical neuron development and causing neural circuit imbalances.

Laminin/β1 integrin signal triggers axon formation by promoting microtubule assembly and stabilization

Axon specification during neuronal polarization is closely associated with increased microtubule stabilization in one of the neurites of unpolarized neuron, but how this increased microtubule stability is achieved is unclear. Here, we show that extracellular matrix (ECM) component laminin promotes neuronal polarization via regulating directional microtubule assembly through β1 integrin (Itgb1). Contact with laminin coated on culture substrate or polystyrene beads was sufficient for axon specification of undifferentiated neurites in cultured hippocampal neurons and cortical slices. Active Itgb1 was found to be concentrated in laminin-contacting neurites. Axon formation was promoted and abolished by enhancing and attenuating Itgb1 signaling, respectively. Interestingly, laminin contact promoted plus-end microtubule assembly in a manner that required Itgb1. Moreover, stabilizing microtubules partially prevented polarization defects caused by Itgb1 downregulation. Finally, genetic ablation of Itgb1 in dorsal telencephalic progenitors caused deficits in axon development of cortical pyramidal neurons. Thus, laminin/Itgb1 signaling plays an instructive role in axon initiation and growth, both in vitro and in vivo, through the regulation of microtubule assembly. This study has established a linkage between an extrinsic factor and intrinsic cytoskeletal dynamics during neuronal polarization.

Expression of mutant N-terminal huntingtin fragment (htt552-100Q) in astrocytes suppresses the secretion of BDNF

Huntington's disease (HD) is an inheritable neurological disorder caused by an abnormal expansion of the polyglutamine tract in the N-terminus of the protein huntingtin (htt). Mutant htt (mhtt) leads to selective neurodegeneration that preferentially affects striatal medium spiny neurons. Although mhtt is also expressed in astrocytes, whether and how astrocyte derived mhtt contributes to the neurodegeneration in HD remains largely unknown. In this study, a glia HD model, using an adenoviral vector to express wild-type and mutant N-terminal huntingtin fragment 1–552 aa (htt552) in rat primary cortical astrocytes, was generated. The influence of htt552 on the protein level of brain-derived neurotrophic factor (BDNF) in astrocytes was evaluated. Immunofluorescence showed that htt552-100Q formed aggregates in some astrocytes. These mhtt aggregates sequestered clathrin immunoreactivities and dispersed the Golgi complex. ELISA and immunofluorescence demonstrated an increase in BDNF levels in the astrocytes expressing htt552-100Q. Western blot analysis showed that there was an increase in pro-BDNF, but a decrease in mature BDNF in the astrocytes expressing htt552-100Q. Furthermore, medium collected from astrocytes expressing htt552-100Q showed a lower level of mature BDNF and less activity in supporting neurite development of primary cortical neurons. These results suggest that aggregates formed by mutant htt552 affect processing and secretion of the BDNF in astrocytes, which might contribute to the neuronal dysfunction and degeneration in HD.

A distinct response to endogenous DNA damage in the development of Nbs1-deficient cortical neurons

Microcephaly is a clinical characteristic for human nijmegen breakage syndrome (NBS, mutated in NBS1 gene), a chromosomal instability syndrome. However, the underlying molecular pathogenesis remains elusive. In the present study, we demonstrate that neuronal disruption of NBS (Nbn in mice) causes microcephaly characterized by the reduction of cerebral cortex and corpus callosum, recapitulating neuronal anomalies in human NBS. Nbs1-deficient neocortex shows accumulative endogenous DNA damage and defective activation of Ataxia telangiectasia and Rad3-related (ATR)-Chk1 pathway upon DNA damage. Notably, in contrast to massive apoptotic cell death in Nbs1-deficient cerebella, activation of p53 leads to a defective neuroprogenitor proliferation in neocortex, likely via specific persistent induction of hematopoietic zinc finger (Hzf) that preferentially promotes p53-mediated cell cycle arrest whilst inhibiting apoptosis. Moreover, Trp53 mutations substantially rescue the microcephaly in Nbs1-deficient mice. Thus, the present results reveal the first clue that developing neurons at different regions of brain selectively respond to endogenous DNA damage, and underscore an important role for Nbs1 in neurogenesis.

SATB Homeobox Proteins Regulate Trophoblast Stem Cell Renewal and Differentiation

The morphogenesis of the hemochorial placenta is dependent upon the precise expansion and differentiation of trophoblast stem (TS) cells. SATB homeobox 1 (SATB1) and SATB2 are related proteins that have been implicated as regulators of some stem cell populations. SATB1 is highly expressed in TS cells, which prompted an investigation of SATB1 and the related SATB2 as regulators of TS cells. SATB1 and SATB2 were highly expressed in rat TS cells maintained in the stem state and rapidly declined following induction of differentiation. SATB proteins were also present within the rat placenta during early stages of its morphogenesis and disappeared as gestation advanced. Silencing Satb1 or Satb2 expression decreased TS cell self-renewal and increased differentiation, whereas ectopic expression of SATB proteins promoted TS cell expansion and blunted differentiation. Eomes, a key transcriptional regulator of TS cells, was identified as a target for SATB proteins. SATB knockdown decreased Eomes transcript levels and promoter activity, whereas SATB ectopic expression increased Eomes transcript levels and promoter activity. Electrophoretic mobility shift assay as well as chromatin immunoprecipitation analyses demonstrated that SATB proteins physically associate with a regulatory site within the Eomes promoter. We conclude that SATB proteins promote TS cell renewal and inhibit differentiation. These actions are mediated in part by regulating the expression of the TS cell stem-associated transcription factor, EOMES.

Prenatal fluoxetine exposure induces life-long serotonin 5-HT 3 receptor-dependent cortical abnormalities and anxiety-like behaviour

Selective serotonin reuptake inhibitors (SSRIs) are the first choice of drugs to treat depression and anxiety during pregnancy. However, there is evidence that in utero exposure to SSRIs leads to adverse effects in offspring. Here we show that in mice, the adverse effects of the widely used antidepressant and SSRI fluoxetine are critically dependent on the 5-HT 3 receptor, the only ligand-gated ion channel in the family of serotonin receptors. In utero exposure to fluoxetine induces anxiety-like behavior in wildtype, but not in mice lacking the 5-HT 3 receptor. In addition to this behavioral phenotype, these mice show life-long abnormalities of cortical cytoarchitecture, which can be reversed in vitro by pharmacological block of 5-HT 3 receptors. Moreover, the effect of fluoxetine on the development of cortical neurons is absent in 5-HT 3 receptor knockout mice. These findings pinpoint the pivotal role of serotonergic signaling during development and provide a novel basis to investigate the adverse effects of the use of fluoxetine during pregnancy. This article is part of a Special Issue entitled ‘Post-Traumatic Stress Disorder’.

Effects of the genotoxic agent 5-bromo-2′-deoxyuridine with or without pre-pubertal gonadectomy on brain monoamines and their metabolites in female rats

A nucleotide analog 5-bromo-2′-deoxyuridine (BrdU) is a genotoxic compound. Previous studies have demonstrated that prenatal treatment of rodents with BrdU affects the development of cortical neurons, reduces dopamine levels, and elevates serotonin (5-HT) levels in the striatum in adult male offspring from BrdU-treated dams. Moreover, prenatal BrdU-treated rats show locomotor hyperactivity in both males and females. This study investigated sexual dimorphism in the effect of prenatal BrdU on monoamine metabolism. Sprague–Dawley rats were treated with BrdU on gestational days 9–15 (50 mg/kg, i.p.) and monoamine metabolism was examined in female rats at 10 weeks of age. The influence of pre-pubertal gonadectomy on the effects of BrdU was also investigated. BrdU-treated females showed elevations of dopamine and 5-HT levels in the striatum; reductions in dopamine, dihydroxyphenylacetic acid, or homovanillic acid (HVA) in the hypothalamus or the midbrain; and elevated HVA and 5-HT in the hippocampus. Pre-pubertal gonadectomy had a suppressive effect on striatal dopamine levels in prenatal BrdU-treated females. The present data indicate sexual dimorphic effects of prenatal BrdU-treatment in striatal dopamine metabolism but not in serotonergic metabolism and suggest a contribution of the increasing gonadal hormones that accompany puberty to this sex difference.