Cátia M. Teixeira

Dopamine and serotonin signaling during two sensitive developmental periods differentially impact adult aggressive and affective behaviors in mice

Pharmacologic blockade of monoamine oxidase A (MAOA) or serotonin transporter (5-HTT) has antidepressant and anxiolytic efficacy in adulthood. Yet, genetically conferred MAOA or 5-HTT hypoactivity is associated with altered aggression and increased anxiety/depression. Here we test the hypothesis that increased monoamine signaling during development causes these paradoxical aggressive and affective phenotypes. We find that pharmacologic MAOA blockade during early postnatal development (P2–P21) but not during peri-adolescence (P22−41) increases anxiety- and depression-like behavior in adult (>P90) mice, mimicking the effect of P2–21 5-HTT inhibition. Moreover, MAOA blockade during peri-adolescence, but not P2–21 or P182-201, increases adult aggressive behavior, and 5-HTT blockade from P22–P41 reduced adult aggression. Blockade of the dopamine transporter, but not the norepinephrine transporter, during P22–41 also increases adult aggressive behavior. Thus, P2–21 is a sensitive period during which 5-HT modulates adult anxiety/depression-like behavior, and P22–41 is a sensitive period during which DA and 5-HT bi-directionally modulate adult aggression. Permanently altered DAergic function as a consequence of increased P22–P41 monoamine signaling might underlie altered aggression. In support of this hypothesis, we find altered aggression correlating positively with locomotor response to amphetamine challenge in adulthood. Proving that altered DA function and aggression are causally linked, we demonstrate that optogenetic activation of VTA DAergic neurons increases aggression. It therefore appears that genetic and pharmacologic factors impacting dopamine and serotonin signaling during sensitive developmental periods can modulate adult monoaminergic function and thereby alter risk for aggressive and emotional dysfunction.

GSK-3β overexpression causes reversible alterations on postsynaptic densities and dendritic morphology of hippocampal granule neurons in vivo

Adult hippocampal neurogenesis (AHN) is crucial for the maintenance of hippocampal function. Several neurodegenerative diseases such as Alzheimer’s disease (AD) are accompanied by memory deficits that could be related to alterations in AHN. Here, we took advantage of a conditional mouse model to study the involvement of glycogen synthase kinase-3β (GSK-3β) overexpression (OE) in AHN. By injecting GFP- and PSD95-GFP-expressing retroviruses, we have determined that hippocampal GSK-3β-OE causes dramatic alterations in both dendritic tree morphology and post-synaptic densities in newborn neurons. Alterations in previously damaged neurons were reverted by switching off the transgenic system and also by using a physiological approach (environmental enrichment) to increase hippocampal plasticity. Furthermore, comparative morphometric analysis of granule neurons from patients with AD and from GSK-3β overexpressing mice revealed shared morphological alterations. Taken together, these data indicate that GSK-3β is crucial for hippocampal function, thereby supporting this kinase as a relevant target for the treatment of AD.

Cell-autonomous inactivation of the reelin pathway impairs adult neurogenesis in the hippocampus.

Adult hippocampal neurogenesis is thought to be essential for learning and memory, and has been implicated in the pathogenesis of several disorders. Although recent studies have identified key factors regulating neuroprogenitor proliferation in the adult hippocampus, the mechanisms that control the migration and integration of adult-born neurons into circuits are largely unknown. Reelin is an extracellular matrix protein that is vital for neuronal development. Activation of the Reelin cascade leads to phosphorylation of Disabled-1, an adaptor protein required for Reelin signaling. Here we used transgenic mouse and retroviral reporters along with Reelin signaling gain-of-function and loss-of-function studies to show that the Reelin pathway regulates migration and dendritic development of adult-generated hippocampal neurons. Whereas overexpression of Reelin accelerated dendritic maturation, inactivation of the Reelin signaling pathway specifically in adult neuroprogenitor cells resulted in aberrant migration, decreased dendrite development, formation of ectopic dendrites in the hilus, and the establishment of aberrant circuits. Our findings support a cell-autonomous and critical role for the Reelin pathway in regulating dendritic development and the integration of adult-generated granule cells and point to this pathway as a key regulator of adult neurogenesis. Moreover, our data reveal a novel role of the Reelin cascade in adult brain function with potential implications for the pathogenesis of several neurological and psychiatric disorders.

Monoamine-sensitive developmental periods impacting adult emotional and cognitive behaviors.

Development passes through sensitive periods, during which plasticity allows for genetic and environmental factors to exert indelible influence on the maturation of the organism. In the context of central nervous system development, such sensitive periods shape the formation of neurocircuits that mediate, regulate, and control behavior. This general mechanism allows for development to be guided by both the genetic blueprint as well as the environmental context. While allowing for adaptation, such sensitive periods are also vulnerability windows during which external and internal factors can confer risk to disorders by derailing otherwise resilient developmental programs. Here we review developmental periods that are sensitive to monoamine signaling and impact adult behaviors of relevance to psychiatry. Specifically, we review (1) a serotonin-sensitive period that impacts sensory system development, (2) a serotonin-sensitive period that impacts cognition, anxiety- and depression-related behaviors, and (3) a dopamine- and serotonin-sensitive period affecting aggression, impulsivity and behavioral response to psychostimulants. We discuss preclinical data to provide mechanistic insight, as well as epidemiological and clinical data to point out translational relevance. The field of translational developmental neuroscience has progressed exponentially providing solid conceptual advances and unprecedented mechanistic insight. With such knowledge at hand and important methodological innovation ongoing, the field is poised for breakthroughs elucidating the developmental origins of neuropsychiatric disorders, and thus understanding pathophysiology. Such knowledge of sensitive periods that determine the developmental trajectory of complex behaviors is a necessary step towards improving prevention and treatment approaches for neuropsychiatric disorders.

FIB/SEM technology and high-throughput 3D reconstruction of dendritic spines and synapses in GFP-labeled adult-generated neurons.

The fine analysis of synaptic contacts is usually performed using transmission electron microscopy (TEM) and its combination with neuronal labeling techniques. However, the complex 3D architecture of neuronal samples calls for their reconstruction from serial sections. Here we show that focused ion beam/scanning electron microscopy (FIB/SEM) allows efficient, complete, and automatic 3D reconstruction of identified dendrites, including their spines and synapses, from GFP/DAB-labeled neurons, with a resolution comparable to that of TEM. We applied this technology to analyze the synaptogenesis of labeled adult-generated granule cells (GCs) in mice. 3D reconstruction of dendritic spines in GCs aged 3–4 and 8–9 weeks revealed two different stages of dendritic spine development and unexpected features of synapse formation, including vacant and branched dendritic spines and presynaptic terminals establishing synapses with up to 10 dendritic spines. Given the reliability, efficiency, and high resolution of FIB/SEM technology and the wide use of DAB in conventional EM, we consider FIB/SEM fundamental for the detailed characterization of identified synaptic contacts in neurons in a high-throughput manner.

Tau Isoform with Three Microtubule Binding Domains is a Marker of New Axons Generated from the Subgranular Zone in the Hippocampal Dentate Gyrus: Implications for Alzheimer's Disease

In the adult hippocampal dentate gyrus, newborn granule cells grow dendrites into the molecular layer and send axons into the CA3 region. Several molecular markers have been used to analyze production of these new neurons; however, no good markers for new axons have been described. Here we demonstrate that tau protein isoform with three microtubule binding domains (3R-Tau) is a marker of those axons following an antigen retrieval protocol. By using retrovirus-mediated GFP transduction, GFP can be detected in a period of 7-14 days after viral infection. We also provide a proof of principle demonstration of the power of that labeling showing modulation of 3R-Tau positive axons under physiological conditions (exercise and aging) as well as in a FTDP-17 neurodegenerative model and Alzheimers disease models (mice overexpressing AβPPsw, ind or GSK3β). We conclude that 3R-Tau would be an efficient marker and a valuable tool to study new axons in adult neurogenesis as well as in neurodegenerative processes.

Reelin Regulates the Maturation of Dendritic Spines, Synaptogenesis and Glial Ensheathment of Newborn Granule Cells

The Reelin pathway is essential for both neural migration and for the development and maturation of synaptic connections. However, its role in adult synaptic formation and remodeling is still being investigated. Here, we investigated the impact of the Reelin/Dab1 pathway on the synaptogenesis of newborn granule cells (GCs) in the young-adult mouse hippocampus. We show that neither Reelin overexpression nor the inactivation of its intracellular adapter, Dab1, substantially alters dendritic spine numbers in these neurons. In contrast, 3D-electron microscopy (focused ion beam milling/scanning electron microscope) revealed that dysregulation of the Reelin/Dab1 pathway leads to both transient and permanent changes in the types and morphology of dendritic spines, mainly altering mushroom, filopodial, and branched GC spines. We also found that the Reelin/Dab1 pathway controls synaptic configuration of presynaptic boutons in the dentate gyrus, with its dysregulation leading to a substantial decrease in multi-synaptic bouton innervation. Lastly, we show that the Reelin/Dab1 pathway controls astroglial ensheathment of synapses. Thus, the Reelin pathway is a key regulator of adult-generated GC integration, by controlling dendritic spine types and shapes, their synaptic innervation patterns, and glial ensheathment. These findings may help to better understanding of hippocampal circuit alterations in neurological disorders in which the Reelin pathway is implicated. Significance Statement The extracellular protein Reelin has an important role in neurological diseases, including epilepsy, Alzheimers disease and psychiatric diseases, targeting hippocampal circuits. Here we address the role of Reelin in the development of synaptic contacts in adult-generated granule cells (GCs), a neuronal population that is crucial for learning and memory and implicated in neurological and psychiatric diseases. We found that the Reelin pathway controls the shapes, sizes, and types of dendritic spines, the complexity of multisynaptic innervations and the degree of the perisynaptic astroglial ensheathment that controls synaptic homeostasis. These findings show a pivotal role of Reelin in GC synaptogenesis and provide a foundation for structural circuit alterations caused by Reelin deregulation that may occur in neurological and psychiatric disorders.

Optogenetic stimulation of DAergic VTA neurons increases aggression

DATICre:ai32 double-mutant mice express ChR2-eYFP in DAergic neurons. Single-mutant mice do not express ChR2-eYFP and served as controls. Fiberoptic cables were implanted into mice with their tips just dorsal to the VTA. Aggressive behavior was assessed in mixed pairs of DATCre:ai32 double-transgenic mice and single-mutant controls. Only one mouse in a pair was stimulated. Aggressive behavior was increased in pairs when DATCre:ai32 double-mutant mice were stimulated when compared to pairs where the single-mutant controls were stimulated. For more information on this topic, please refer to the article by Yu et al. on pages 688–698.

Alzheimer disease-like cellular phenotype of newborn granule neurons can be reversed in GSK-3β-overexpressing mice

Alzheimer disease-like cellular phenotype of newborn granule neurons can be reversed in GSK-3β-overexpressing mice

New Insights into How Serotonin Selective Reuptake Inhibitors Shape the Developing Brain

Development passes through sensitive periods, during which plasticity allows for genetic and environmental factors to exert indelible influence on the maturation of the organism. In the context of central nervous system (CNS) development, such sensitive periods shape the formation of neuro‐circuits that mediate, regulate, and control behavior. This general mechanism allows for development to be guided by both the genetic blueprint, as well as the environmental context. While allowing for adaptation, such sensitive periods are also windows of vulnerability during which external and internal factors can confer risk to brain disorders by derailing adaptive developmental programs. Our group has been particularly interested in developmental periods that are sensitive to serotonin (5‐HT) signaling, and impact behavior and cognition relevant to psychiatry. Specifically, we review a 5‐HT‐sensitive period that impacts fronto‐limbic system development, resulting in cognitive, anxiety, and depression‐related behaviors. We discuss preclinical data to establish biological plausibility and mechanistic insights. We also summarize epidemiological findings that underscore the potential public health implications resulting from the current practice of prescribing 5‐HT reuptake inhibiting antidepressants during pregnancy. These medications enter the fetal circulation, likely perturb 5‐HT signaling in the brain, and may be affecting circuit maturation in ways that parallel our findings in the developing rodent brain. More research is needed to better disambiguate the dual effects of maternal symptoms on fetal and child development from the effects of 5‐HT reuptake inhibitors on clinical outcomes in the offspring. Birth Defects Research 109:924–932, 2017.