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Neurotrophin brain-derived neurotrophic factor (BDNF) and neurotransmitter serotonin (5-HT) regulate each other and have been implicated in several neuronal mechanisms, including neuroplasticity. We have investigated the effects of BDNF on serotonergic neurons by deleting BDNF receptor TrkB from serotonergic neurons in the adult brain. The transgenic mice show increased 5-HT and Tph2 levels with abnormal behavioral phenotype. In spite of increased food intake, the transgenic mice are significantly leaner than their wildtype littermates, which may be due to increased metabolic activity. Consistent with increased 5-HT, the proliferation of hippocampal progenitors is significantly increased, however, long-term survival of newborn cells is unchanged. Our data indicates that BDNF-TrkB signaling regulates the functional phenotype of 5-HT neurons with long-term behavioral consequences.

P75 neurotrophic receptor (p75NTR) is an important receptor for the role of neurotrophins in modulating brain plasticity and apoptosis. The current understanding of the role of p75NTR in cellular adaptation following pathological insults remains blurred, which makes p75NTR’s related signaling networks an interesting and challenging initial point of investigation. We identified p75NTR and related genes through extensive data mining of a PubMed literature search including published works related to p75NTR from the past 20 years. Bioinformatic network and pathway analyses of identified genes (n = 235) were performed using ReactomeFIViz in Cytoscape based on the highly reliable Reactome functional interaction network algorithm. This approach merges interactions extracted from human curated pathways with predicted interactions from machine learning. Genome-wide pathway analysis showed total of 16 enriched hierarchical clusters. A total of 278 enriched single pathways were also identified (p p75NTR gene network. This study provides a comprehensive analysis and investigation into the current knowledge of p75NTR signaling networks and pathways. These results also identify several genes and their respective protein products as involved in the p75NTR network, which have not previously been clearly studied in this pathway. These results can be used to generate novel hypotheses to gain a greater understanding of p75NTR in acute brain injuries, neurodegenerative diseases and general response to cellular damage.

Activation state of Parvalbumin (PV) interneurons regulates neuronal plasticity, driving the closure of developmental critical periods and alternating between high and low plasticity states in response to experience in adulthood. We now show that PV plasticity states are regulated through the activation of TrkB neurotrophin receptors. Activation of an optically activatable TrkB (optoTrkB) specifically in PV interneurons switches adult cortical networks into a state of elevated plasticity within minutes by decreasing excitability of PV neurons. OptoTrkB activation induces changes in gene expression related to neuronal plasticity and excitability, and increases the phosphorylation of Kv3.1 channels. OptoTrkB activation shifted cortical networks towards a low PV configuration, promoting oscillatory synchrony and ocular dominance plasticity. Visual plasticity induced by fluoxetine was lost in mice lacking TrkB in PV neurons. Our data suggest a novel mechanism that dynamically regulates PV interneurons configuration state and orchestrates cortical networks during adulthood.Graphical Abstract

Although the precise mechanism of action of antidepressant drugs remains elusive, the neuroplastic hypothesis has gained acceptance during the last two decades. Several studies have shown that treatment with antidepressants such as Fluoxetine is associated with enhanced plasticity in control animals, especially in regions such as the visual cortex, the hippocampus and the medial prefrontal cortex. More recently, the basolateral amygdala has been shown to be affected by Fluoxetine leading to a reopening of critical period-like plasticity in the fear and aggression circuits. One of the key elements triggering this type of brain plasticity are inhibitory networks, especially parvalbumin interneurons. However, recent work on fast-acting antidepressants has shown also an important role for somatostatin interneurons. Here we show that Fluoxetine reorganizes inhibitory circuits through increased expression of the plasticity-related molecule PSA-NCAM which regulates interneuronal structure and connectivity. In addition, we demonstrate that treatment with this antidepressant alters the structure of somatostatin interneurons both at the level of dendritic spines and of axonal en passant boutons. Our findings suggest that new strategies targeting somatostatin interneuron activity might help us to better understand depression and the action of antidepressants.

The network hypothesis of depression proposes that mood disorders reflect problems in information processing within particular neural networks. Antidepressants (AD), including selective serotonin reuptake inhibitors (SSRI), function by gradually improving information processing within these networks. AD have been shown to induce a state of juvenile-like plasticity comparable to that observed during developmental critical periods: Such critical-period-like plasticity allows brain networks to better adapt to extrinsic and intrinsic signals. We have coined this drug-induced state of juvenile-like plasticity 'iPlasticity.' A combination of iPlasticity induced by chronic SSRI treatment together with training, rehabilitation, or psychotherapy improves symptoms of neuropsychiatric disorders and issues underlying the developmentally or genetically malfunctioning networks. We have proposed that iPlasticity might be a critical component of AD action. We have demonstrated that iPlasticity occurs in the visual cortex, fear erasure network, extinction of aggression caused by social isolation, and spatial reversal memory in rodent models. Chronic SSRI treatment is known to promote neurogenesis and to cause dematuration of granule cells in the dentate gyrus and of interneurons, especially parvalbumin interneurons enwrapped by perineuronal nets in the prefrontal cortex, visual cortex, and amygdala. Brain-derived neurotrophic factor (BDNF), via its receptor tropomyosin kinase receptor B, is involved in the processes of synaptic plasticity, including neurogenesis, neuronal differentiation, weight of synapses, and gene regulation of synaptic formation. BDNF can be activated by both chronic SSRI treatment and neuronal activity. Accordingly, the BDNF/tropomyosin kinase receptor B pathway is critical for iPlasticity, but further analyses will be needed to provide mechanical insight into the processes of iPlasticity.

A brief burst-suppressing isoflurane anesthesia has been shown to rapidly alleviate symptoms of depression in a subset of patients, but the neurobiological basis of these observations remains obscure. We show that a single isoflurane anesthesia produces antidepressant-like behavioural effects in the learned helplessness paradigm and regulates molecular events implicated in the mechanism of action of rapid-acting antidepressant ketamine: activation of brain-derived neurotrophic factor (BDNF) receptor TrkB, facilitation of mammalian target of rapamycin (mTOR) signaling pathway and inhibition of glycogen synthase kinase 3β (GSK3β). Moreover, isoflurane affected neuronal plasticity by facilitating long-term potentiation in the hippocampus. We also found that isoflurane increased activity of the parvalbumin interneurons, and facilitated GABAergic transmission in wild type mice but not in transgenic mice with reduced TrkB expression in parvalbumin interneurons. Our findings strengthen the role of TrkB signaling in the antidepressant responses and encourage further evaluation of isoflurane as a rapid-acting antidepressant devoid of the psychotomimetic effects and abuse potential of ketamine.

Escalated or abnormal aggression induced by early adverse experiences is a growing issue of social concern and urges the development of effective treatment strategies. Here we report that synergistic interactions between psychosocial and biological factors specifically ameliorate escalated aggression induced by early adverse experiences. Rats reared in isolation from weaning until early adulthood showed abnormal forms of aggression and social deficits that were temporarily ameliorated by re-socialization, but aggression again escalated in a novel environment. We demonstrate that when re-socialization was combined with the antidepressant fluoxetine, which has been shown to reactivate juvenile-like state of plasticity, escalated aggression was greatly attenuated, while neither treatment alone was effective. Early isolation induced a permanent, re-socialization-resistant reduction in Bdnf expression in the amygdala and the infralimbic cortex. Only the combined treatment of fluoxetine and re-socialization was able to recover Bdnf expression via epigenetic regulation. Moreover, the behavior improvement after the combined treatment was dependent on TrkB activity. Combined treatment specifically strengthened the input from the ventral hippocampus to the mPFC, suggesting that this pathway is an important mediator of the beneficial behavioral effects of the combined psychosocial and pharmacological treatment of abnormal aggression. Our findings suggest that synergy between pharmacological induction of plasticity and psychosocial rehabilitation could enhance the efficacy of therapies for pathological aggression.

Objective: Rewiring of excitatory glutamatergic neuronal circuits is a major abnormality in epilepsy. Besides the rewiring of excitatory circuit, an abnormal depolarizing GABAergic drive has been hypothesized to participate in the epileptogenic processes. However, a remaining clinically relevant question is whether early post Status Epilepticus (SE) evoked chloride dysregulation is important for the remodeling of aberrant glutamatergic neuronal circuit. Methods: Osmotic mini-pumps were used to infuse intracerebrally a specific inhibitor of depolarizing GABAergic transmission as well as a functionally blocking antibody towards the pan-neurotrophin receptor p75 (p75NTR). The compounds were infused between 2 and 5 days after pilocarpine-induced SE. Immunohistochemistry for NKCC1, KCC2 and ectopic recurrent mossy fiber (rMF) sprouting as well as telemetric EEG and electrophysiological recordings were performed at day 5 and 2 months post-SE. Results: Blockade of NKCC1 after SE with the specific inhibitor bumetanide restored NKCC1 and KCC2 expression, normalized chloride homeostasis and significantly reduced the glutamatergic recurrent mossy fiber sprouting (rMF) within the dentate gyrus. This mechanism partially involves p75NTR signaling as bumetanide application reduced SE-induced p75NTR expression and functional blockade of p75NTR decreased rMF sprouting. The early transient (3days) post-SE infusion of bumetanide reduced rMF sprouting and recurrent seizures in the chronic epileptic phase. Interpretation: Our findings show that early post-SE abnormal depolarizing GABA and p75NTR signalings foster a long lasting rearrangement of glutamatergic network that contributes to the epileptogenic process. This finding defines promising and novel targets to constrain reactive glutamatergic network rewiring in adult epilepsy. This article is protected by copyright. All rights reserved.

Several antidepressant drugs activate tropomyosin-related kinase B (TRKB) receptor, but it remains unclear whether these compounds employ a common mechanism for TRKB activation. Here, using MS, we found that a single intraperitoneal injection of fluoxetine disrupts the interaction of several proteins with TRKB in the hippocampus of mice. These proteins included members of adaptor protein complex-2 (AP-2) involved in vesicular endocytosis. The interaction of TRKB with the cargo-docking ? subunit of the AP-2 complex (AP2M) was confirmed to be disrupted by both acute and repeated fluoxetine treatments. Of note, fluoxetine disrupted the coupling between full-length TRKB and AP2M, but not the interaction between AP2M and the TRKB C-terminal region, indicating that the fluoxetine-binding site in TRKB lies outside the TRKB:AP2M interface. ELISA experiments revealed that in addition to fluoxetine, other chemically diverse antidepressants, such as imipramine, rolipram, phenelzine, ketamine, and its metabolite 2R,6R-hydroxynorketamine, also decreased the interaction between TRKB and AP2M in vitro. Silencing the expression of AP2M in a TRKB-expressing mouse fibroblast cell line (MG87.TRKB) increased cell-surface expression of TRKB and facilitated its activation by brain-derived neurotrophic factor (BDNF), observed as levels of phosphorylated TRKB. Moreover, animals haploinsufficient for the Ap2m1 gene displayed increased levels of active TRKB, along with enhanced cell-surface expression of the receptor in cultured hippocampal neurons. Taken together, our results suggest that disruption of the TRKB:AP2M interaction is a common mechanism underlying TRKB activation by several chemically diverse antidepressants.

Heightened neuronal plasticity expressed during early postnatal life has been thought to permanently decline once critical periods have ended. For example, monocular deprivation is able to shift ocular dominance in the mouse visual cortex during the first months of life, but this effect is lost later in life. However, various treatments, such as the antidepressant fluoxetine, can reactivate a critical period‐like plasticity in the adult brain. When monocular deprivation is supplemented with chronic fluoxetine administration, a major shift in ocular dominance is produced after the critical period has ended. In the current study, we characterized the temporal patterns of fluoxetine‐induced plasticity in the adult mouse visual cortex, using in vivo optical imaging. We found that artificially induced plasticity in ocular dominance extended beyond the duration of the naturally occurring critical period and continued as long as fluoxetine was administered. However, this fluoxetine‐induced plasticity period ended as soon as the drug was not given. These features of antidepressant‐induced plasticity may be useful when designing treatment strategies involving long‐term antidepressant treatment in humans., Various treatments including antidepressant fluoxetine can reinstate developmental‐like plasticity in adult animals. In the current study, we describe patterns of fluoxetine‐induced plasticity in the mouse visual cortex using in vivo optical imaging.

Summary It is unclear how binding of antidepressant drugs to their targets gives rise to the clinical antidepressant effect. We discovered that the transmembrane domain of tyrosine kinase receptor 2 (TRKB), the brain-derived neurotrophic factor (BDNF) receptor that promotes neuronal plasticity and antidepressant responses, has a cholesterol-sensing function that mediates synaptic effects of cholesterol. We then found that both typical and fast-acting antidepressants directly bind to TRKB, thereby facilitating synaptic localization of TRKB and its activation by BDNF. Extensive computational approaches including atomistic molecular dynamics simulations revealed a binding site at the transmembrane region of TRKB dimers. Mutation of the TRKB antidepressant-binding motif impaired cellular, behavioral, and plasticity-promoting responses to antidepressants in vitro and in vivo. We suggest that binding to TRKB and allosteric facilitation of BDNF signaling is the common mechanism for antidepressant action, which may explain why typical antidepressants act slowly and how molecular effects of antidepressants are translated into clinical mood recovery., Graphical Abstract, Highlights • Several antidepressants, including SSRIs and ketamine, directly bind to TRKB • TRKB dimerization at transmembrane region forms a binding pocket for fluoxetine • Antidepressant binding to TRKB facilitates BDNF action and plasticity • Point mutation in TRKB transmembrane region blocks the effects of antidepressants, Direct binding of both typical and fast-acting antidepressants to the BDNF receptor TRKB accounts for cell biological and behavioral actions of antidepressants. This mechanism directly connects antidepressant action to neuronal plasticity and may explain the slow action of typical antidepressants.

Cholesterol is an essential constituent of cell membranes. Recently, the discovery of cholesterol recognition aminoacid consensus (CRAC) on proteins indicated a putative direct, non-covalent interaction between cholesterol and proteins. In the present study, we evaluated the incidence of CRAC motifs, and its inverted version (CARC), in the transmembrane region (TMR) of tyrosine kinase receptor family (RTK) in Caenorhabditis elegans (nematode); Drosophila melanogaster (fruit fly); Danio rerio (zebrafish); Mus musculus (mouse), and Homo sapiens (human) by using in silico methods. We found CRAC motifs across all species analyzed, whereas, CARC motifs, comprising the extracellular side of the TMR, were only found in vertebrates. On top of its contribution to structural properties of cells, cholesterol (or its’ metabolites) regulates a myriad of cellular functions culminating in increased neuronal plasticity in the central nervous system. The tropomyosin-related kinase B (TRKB), a member of RTK family, is also a core participant in neuronal plasticity process. Therefore, focusing on TRKB receptor, we observed high homology in TRKB.TMR and conservation of CARC motifs across multiple organisms. Upon the recognition of conserved CARC motif in the TRKB, we compared the effect of point mutations in CARC on structural changes in the TMR of human TRKB. The alignment of wild-type and mutant TMR indicates small changes across the 5 mutations analyzed (Y434F, Y434C, Y434A, V439K and R428A), indicated by the root-mean-squared deviation (RMSD) values for the superimposed structures, average=2.448Å. The TMR point mutation also impacted the physicochemical properties of the models, measured by solvent accessibility. The mutation of the Y, V or R residues in the CARC motif increased the solvent access in the juxtamembrane portions of the TMR, ranging from 150-500%. In conclusion, it is plausible to consider a potential role for CARC/CRAC motifs in the function of RTK family TMR. The presently described CARC motif in TRKB.TMR may exert its effect by regulating the receptor capability to interact with the polar heads of membrane phospholipids.

BACKGROUND: Activity-dependent release of brain-derived neurotrophic factor (BDNF) in the medial prefrontal cortex (mPFC) is essential for the rapid and sustained antidepressant actions of ketamine, and a recent study shows a similar requirement for vascular endothelial growth factor (VEGF). Since BDNF is reported to stimulate VEGF expression/release in neuroblastoma cells, the present study tested the hypothesis that the actions of BDNF are mediated by VEGF. METHODS: The role of VEGF in the antidepressant behavioral actions of BDNF was tested by intra-mPFC co-infusion of a VEGF neutralizing antibody and by neuron-specific deletion of VEGF. The influence of BDNF on the release of VEGF and the role of VEGF in the neurotrophic actions of BDNF were determined in rat primary cortical neurons. The role of BDNF in the behavioral and neurotrophic actions of VEGF were also determined. RESULTS: The results show that the rapid and sustained antidepressant-like actions of intra-mPFC BDNF are blocked by co-infusion of a VEGF neutralizing antibody, and that neuron-specific mPFC deletion of VEGF blocks the antidepressant-like actions of BDNF. Studies in primary cortical neurons demonstrate that BDNF stimulates the release of VEGF, and that BDNF-induction of dendrite complexity is blocked by a selective VEGF-Flk-1 antagonist. Surprisingly, the results also show reciprocal interactions, indicating that the behavioral and neurotrophic actions of VEGF are dependent on BDNF. CONCLUSIONS: These findings indicate that the antidepressant-like and neurotrophic actions of BDNF require VEGF signaling, but also demonstrate reciprocal interdependence for BDNF in the actions of VEGF.

The activation of TRKB (tropomyosin-related kinase B), the receptor for brain-derived neurotrophic factor (BDNF), is a crucial step in brain plasticity. Several antidepressant drugs are reported to activate TRKB, and animals with compromised BDNF or TRKB system are refractory to these drugs’ effects. However, it remains unclear whether these compounds employ a common mechanism to activate BDNF-TRKB signaling. We have used mass spectrometry to investigate proteins that are co-immunoprecipitated with TRKB from the hippocampus of mice treated with the antidepressant fluoxetine or vehicle. We found that the interaction of several proteins with TRKB was disrupted in fluoxetine-treated brain samples, including several components of the AP-2 complex involved in vesicular endocytosis. Silencing of AP2M (mu subunit) expression in MG87.TRKB fibroblast cell line that overexpresses TRKB led to an increase in the surface positioning of TRKB as well as to a higher response to BDNF, observed as the levels of active TRKB (pTRKB). Consistent with these findings, animals lacking one of the Ap2m1 gene copies also displayed increased levels of active TRKB in the hippocampus. We also addressed the effect of multiple antidepressant drugs on the interaction of TRKB and AP2M by ELISA. Pharmacologically diverse drugs: imipramine, fluoxetine, phenelzine and rolipram, decreased the interaction between TRKB:AP2M, and increased TRKB surface expression levels. However, while the interaction between full length TRKB and AP2M was disrupted by fluoxetine, the interaction between AP2M and the TRKB C-terminal peptide was found resistant to this drug suggesting additional binding sites targeted by fluoxetine or an indirect mechanism of action of the antidepressants. Taken together, our data suggest that the TRKB:AP2M interaction is a potential target for several antidepressants with diverse chemical structures and modes of action, leading to increased exposure of TRKB at the cell surface and facilitated activation by BDNF.

International audience; DYX1C1, DCDC2, and KIAA0319 are three of the most replicated dyslexia candidate genes (DCGs). Recently, these DCGs were implicated in functions at the cilium. Here, we investigate the regulation of these DCGs by Regulatory Factor X transcription factors (RFX TFs), a gene family known for transcriptionally regulating ciliary genes. We identify conserved X-box motifs in the promoter regions of DYX1C1, DCDC2, and KIAA0319 and demonstrate their functionality, as well as the ability to recruit RFX TFs using reporter gene and electrophoretic mobility shift assays. Furthermore, we uncover a complex regulation pattern between RFX1, RFX2, and RFX3 and their significant effect on modifying the endogenous expression of DYX1C1 and DCDC2 in a human retinal pigmented epithelial cell line immortalized with hTERT (hTERT-RPE1). In addition, induction of ciliogenesis increases the expression of RFX TFs and DCGs. At the protein level, we show that endogenous DYX1C1 localizes to the base of the cilium, whereas DCDC2 localizes along the entire axoneme of the cilium, thereby validating earlier localization studies using overexpression models. Our results corroborate the emerging role of DCGs in ciliary function and characterize functional noncoding elements, X-box promoter motifs, in DCG promoter regions, which thus can be targeted for mutation screening in dyslexia and ciliopathies associated with these genes.-Tammimies, K., Bieder, A., Lauter, G., Sugiaman-Trapman, D., Torchet, R., Hokkanen, M.-E., Burghoorn, J., Castrén, E., Kere, J., Tapia-Páez, I., Swoboda, P. Ciliary dyslexia candidate genes DYX1C1 and DCDC2 are regulated by Regulatory Factor (RF) X transcription factors through X-box promoter motifs.

Rapid reorganization and stabilization of the actin cytoskeleton in dendritic spines enables cellular processes underlying learning, such as long-term potentiation (LTP). Dendritic spines are enriched in exceptionally short and dynamic actin filaments, but the studies so far have not revealed the molecular mechanisms underlying the high actin dynamics in dendritic spines. Here, we show that actin in dendritic spines is dynamically phosphorylated at tyrosine-53 (Y53) in rat hippocampal and cortical neurons. Our findings show that actin phosphorylation increases the turnover rate of actin filaments and promotes the short-term dynamics of dendritic spines. During neuronal maturation, actin phosphorylation peaks at the first weeks of morphogenesis, when dendritic spines form, and the amount of Y53-phosphorylated actin decreases when spines mature and stabilize. Induction of LTP transiently increases the amount of phosphorylated actin and LTP induction is deficient in neurons expressing mutant actin that mimics phosphorylation. Actin phosphorylation provides a molecular mechanism to maintain the high actin dynamics in dendritic spines during neuronal development and to induce fast reorganization of the actin cytoskeleton in synaptic plasticity. In turn, dephosphorylation of actin is required for the stabilization of actin filaments that is necessary for proper dendritic spine maturation and LTP maintenance.SIGNIFICANCE STATEMENTDendritic spines are small protrusions from neuronal dendrites where the postsynaptic components of most excitatory synapses reside. Precise control of dendritic spine morphology and density is critical for normal brain function. Accordingly, aberrant spine morphology is linked to many neurological diseases. The actin cytoskeleton is a structural element underlying the proper morphology of dendritic spines. Therefore, defects in the regulation of the actin cytoskeleton in neurons have been implicated in neurological diseases. Here, we revealed a novel mechanism for regulating neuronal actin cytoskeleton that explains the specific organization and dynamics of actin in spines. The better we understand the regulation of the dendritic spine morphology, the better we understand what goes wrong in neurological diseases.

Visual Abstract, NETO2 is an auxiliary subunit for kainate-type glutamate receptors that mediate normal cued fear expression and extinction. Since the amygdala is critical for these functions, we asked whether Neto2−/− mice have compromised amygdala function. We measured the abundance of molecular markers of neuronal maturation and plasticity, parvalbumin-positive (PV+), perineuronal net-positive (PNN+), and double positive (PV+PNN+) cells in the Neto2−/− amygdala. We found that Neto2−/− adult, but not postnatal day (P)23, mice had 7.5% reduction in the fraction of PV+PNN+ cells within the total PNN+ population, and 23.1% reduction in PV staining intensity compared with Neto2+/+ mice, suggesting that PV interneurons in the adult Neto2−/− amygdala remain in an immature state. An immature PV inhibitory network would be predicted to lead to stronger amygdalar excitation. In the amygdala of adult Neto2−/− mice, we identified increased glutamatergic and reduced GABAergic transmission using whole-cell patch-clamp recordings. This was accompanied by increased spine density of thin dendrites in the basal amygdala (BA) compared with Neto2+/+ mice, indicating stronger glutamatergic synapses. Moreover, after fear acquisition Neto2−/− mice had a higher number of c-Fos-positive cells than Neto2+/+ mice in the lateral amygdala (LA), BA, and central amygdala (CE). Altogether, our findings indicate that Neto2 is involved in the maturation of the amygdala PV interneuron network. Our data suggest that this defect, together with other processes influencing amygdala principal neurons, contribute to increased amygdalar excitability, higher fear expression, and delayed extinction in cued fear conditioning, phenotypes that are common in fear-related disorders, including the posttraumatic stress disorder (PTSD).

Primary neurons from rodent brain hippocampus and cortex have served as important tools in biomedical research over the years. However, protocols for the preparation of primary neurons vary, which often lead to conflicting results. This report provides a robust and reliable protocol for the production of primary neuronal cultures from the cortex and hippocampus with minimal contribution of non-neuronal cells. The neurons were grown in serum-free media and maintained for several weeks without any additional feeder cells. The neuronal cultures maintained according to this protocol differentiate and by 3 weeks develop extensive axonal and dendritic branching. The cultures produced by this method show excellent reproducibility and can be used for histological, molecular and biochemical methods.

Heightened neuronal plasticity expressed during early postnatal life has been thought to permanently decline once critical periods have ended. For example, monocular deprivation is able to shift ocular dominance in the mouse visual cortex during the first months of life, but this effect is lost later in life. However, various treatments such as the antidepressant fluoxetine can reactivate a critical period-like plasticity in the adult brain. When monocular deprivation is supplemented with chronic fluoxetine administration, a major shift in ocular dominance is produced after the critical period has ended. In the current study, we characterized the temporal patterns of fluoxetine-induced plasticity in the adult mouse visual cortex, using in vivo optical imaging. We found that artificially-induced plasticity in ocular dominance extended beyond the duration of the naturally occurring critical period, and continued as long as fluoxetine was administered. However, this fluoxetine-induced plasticity period ended as soon as the drug was not given. Taken together, our data highlights how a combination of pharmacological treatment and environmental change could be used to improve strategies in antidepressant therapy in humans.

Neuronal networks are refined through an activity-dependent competition during critical periods of early postnatal development. Recent studies have shown that critical period plasticity is influenced by a number of environmental factors, including drugs that are widely used for the treatment of brain disorders. These findings suggest a new paradigm, where pharmacological treatments can be used to open critical period–like plasticity in the adult brain. The plastic networks can then be modified through rehabilitation or psychotherapy to rewire those abnormally wired during development. This kind of combination of pharmacotherapy with physical or psychological rehabilitation may open a new opportunity for a more efficient recovery of a number of neurological and neuropsychiatric disorders.

Background Administration of anandamide (AEA) or 2-arachidonoylglycerol (2AG) induces CB1 coupling and activation of TRKB receptors, regulating the neuronal migration and maturation in the developing cortex. However, at higher concentrations AEA also engages vanilloid receptor TRPV1, usually with opposed consequences on behavior. Methods and Results Using primary cell cultures from the cortex of rat embryos (E18) we determined the effects of AEA on phosphorylated TRKB (pTRK). We observed that AEA (at 100 and 200 nM) induced a significant increase in pTRK levels. Such effect of AEA at 100 nM was blocked by pretreatment with the CB1 antagonist AM251 (200 nM) and, at the higher concentration of 200 nM by the TRPV1 antagonist capsazepine (200 nM), but mildly attenuated by AM251. Interestingly, the effect of AEA or capsaicin (a TRPV1 agonist, also at 200 nM) on pTRK was blocked by TRKB.Fc (a soluble form of TRKB able to bind BDNF) or capsazepine, suggesting a mechanism dependent on BDNF release. Using the marble-burying test (MBT) in mice, we observed that the local administration of ACEA (a CB1 agonist) into the prelimbic region of prefrontal cortex (PL-PFC) was sufficient to reduce the burying behavior, while capsaicin or BDNF exerted the opposite effect, increasing the number of buried marbles. In addition, both ACEA and capsaicin effects were blocked by previous administration of k252a (an antagonist of TRK receptors) into PL-PFC. The effect of systemically injected CB1 agonist WIN55,212-2 was blocked by previous administration of k252a. We also observed a partial colocalization of CB1/TRPV1/TRKB in the PL-PFC, and the localization of TRPV1 in CaMK2+ cells. Conclusion Taken together, our data indicate that anandamide engages a coordinated activation of TRKB, via CB1 and TRPV1. Thus, acting upon CB1 and TRPV1, AEA could regulate the TRKB-dependent plasticity in both pre- and postsynaptic compartments.

Amblyopia is a common visual disorder that is treatable in childhood. However, therapies have limited efficacy in adult patients with amblyopia. Fluoxetine can reinstate early-life critical period-like neuronal plasticity and has been used to recover functional vision in adult rats with amblyopia. This phase 2, randomized, double-blind (fluoxetine vs. placebo), multicenter clinical trial examined whether or not fluoxetine can improve visual acuity in amblyopic adults. This interventional trial included 42 participants diagnosed with moderate to severe amblyopia. Subjects were randomized to receive either 20 mg fluoxetine (n=22) or placebo (n=20). During the 10-week treatment period, all subjects performed daily computerized perceptual training and eye patching. There was no significant difference in treatment efficacy between the groups. Visual acuity at the primary endpoint had significantly improved over baseline in both the fluoxetine (-0.167 logMAR) and placebo (-0.194 logMAR) groups (both p < 0.001). Because patching alone is not effective in adults, the visual acuity improvement likely resulted from perceptual training. There was a positive correlation between visual acuity improvement and the perceptual training time. While this study failed to provide evidence that fluoxetine enhances neuroplasticity, our data support the usefulness of perceptual training for vision improvement in adults with amblyopia. Clinical trial registration ID #EudraCT 2010-023216-14.

Background Trichotillomania (TTM) is an impulse control disorder characterized by repetitive hair pulling/trimming. Barbering behavior (BB) observed in laboratory animals is proposed as a model of TTM. The neurobiological basis of TTM is unclear, but involves striatal hyperactivity and hypoactivation of the prefrontal cortex. Methods In this study, we evaluated the BB in knockout mice for the inducible isoform of nitric oxide synthase (NOS2KO) and the consequences of silencing this enzyme in PC12 cell differentiation. Results NOS2KO exhibit exacerbated BB, starting four weeks of age, and increased repetitive movements compared to wild-type mice (WT). The expression of BB was attenuated by repeated treatment with clomipramine, a clinically approved drug to treat TTM in humans, or memantine, an antagonist of NMDA receptors, as well as partial rescue of NOS2 expression in haploinsufficient animals. The silencing of NOS2 expression reduced the MAP2 (microtubule-associated protein 2) levels in activity-induced differentiated PC12 cells. Discussion Our data led us to propose that NOS2 is putatively involved in the neuronal maturation of the inhibitory afferent pathways during neurodevelopment, and such inadequate inhibition of motor programs might be associated to the observed phenotype.

The quantification of the expression of different molecules is a key question in both basic and applied sciences. While protein quantification through molecular techniques leads to the loss of spatial information and resolution, immunohistochemistry is usually associated with time-consuming image analysis and human bias. In addition, the scarce automatic software analysis is often proprietary and expensive and relies on a fixed threshold binarization. Here we describe and share a set of macros ready for automated fluorescence analysis of large batches of fixed tissue samples using FIJI/ImageJ. The quantification of the molecules of interest are based on an automatic threshold analysis of immunofluorescence images to automatically identify the top brightest structures of each image. These macros measure several parameters commonly quantified in basic neuroscience research, such as neuropil density and fluorescence intensity of synaptic puncta, perisomatic innervation and col-localization of different molecules and analysis of the neurochemical phenotype of neuronal subpopulations. In addition, these same macro functions can be easily modified to improve similar analysis of fluorescent probes in human biopsies for diagnostic purposes based on the expression patterns of several molecules.

Amblyopia is a common visual disorder that is treatable in childhood. However, therapies have limited efficacy in adult patients with amblyopia. Fluoxetine can reinstate early-life critical period-like neuronal plasticity and has been used to recover functional vision in adult rats with amblyopia. We conducted a Phase 2, randomized (fluoxetine vs. placebo), double-blind, multicenter clinical trial examined whether or not fluoxetine can improve visual acuity in amblyopic adults. This interventional trial included 42 participants diagnosed with moderate to severe amblyopia. Subjects were randomized to receive either 20 mg fluoxetine (n = 22) or placebo (n = 20). During the 10-week treatment period, all subjects performed daily computerized perceptual training and eye patching. At the primary endpoint, the mean treatment group difference in visual acuity improvement was only 0.027 logMAR units (95% CI: −0.057 to 0.110; p = 0.524). However, visual acuity had significantly improved from baseline to 10 weeks in both fluoxetine (−0.167 logMAR; 95% CI: −0.226 to −0.108; p

Mood disorders are associated with alterations in serotonergic system, deficient BDNF (brain-derived neurotrophic factor) signaling and abnormal synaptic plasticity. Increased degradation and reduced functions of NCAM (neural cell adhesion molecule) have recently been associated with depression and NCAM deficient mice show depression-related behavior and impaired learning. The aim of the present study was to investigate potential changes in serotonergic and BDNF systems in NCAM knock-out mice. Serotonergic nerve fiber density and SERT (serotonin transporter) protein levels were robustly reduced in the hippocampus, prefrontal cortex and basolateral amygdala of adult NCAM(-)(/-) mice. This SERT reduction was already evident during early postnatal development. [(3)H]MADAM binding experiments further demonstrated reduced availability of SERT in cell membranes of NCAM(-)(/-) mice. Moreover, the levels of serotonin and its major metabolite 5-HIAA were down regulated in the brains of NCAM(-)(/-) mice. NCAM(-)(/-) mice also showed a dramatic reduction in the BDNF protein levels in the hippocampus and prefrontal cortex. This BDNF deficiency was associated with reduced phosphorylation of its receptor TrkB. Importantly, chronic administration of antidepressant amitriptyline partially or completely restored these changes in serotonergic and BDNF systems, respectively. In conclusion, NCAM deficiency lead to prominent and persistent abnormalities in brain serotonergic and BDNF systems, which likely contributes to the behavioral and neurobiological phenotype of NCAM(-/-) mice.

Nitric oxide is a gaseous neuromodulator that displays a core role in several neuronal processes. Beyond regulating the release of neurotransmitters, nitric oxide also plays a role in cell differentiation and maturation in the central nervous system. Although the mode of action of nitric oxide is not fully understood, it involves the activation of soluble guanylate cyclase as well as the nitration and S-nitrosylation of specific amino acid residues in other proteins. Brain-derived neurotrophic factor is a member of neurotrophic factor family and, acting through its receptor tropomyosinrelated kinase B, increases the production of nitric oxide, modulates neuronal differentiation and survival, and plays a crucial role in synaptic plasticity, such as long-term potentiation. Furthermore, nitric oxide is an important regulator of the production of these factors. The aim of the present review is to present a condensed view of the evidence related to the interaction between nitric oxide and brain-derived neurotrophic factor. Additionally, we conducted bioinformatics analysis based on the amino acid sequences of brain-derived neurotrophic factor and tropomyosin-related kinase receptors, and proposed that nitric oxide might nitrate/S-nitrosylate these proteins. Thus, we suggest a putative direct mode of action between these molecules to be further explored.

Recent studies demonstrate that chronic administration of the widely used antidepressant fluoxetine (FLX) promotes neurogenesis, synaptogenesis and synaptic plasticity in the adult hippocampus, cortex and amygdala. However, the mechanisms underlying these effects and how are they related to the clinical antidepressant efficacy are still poorly understood. We show here that chronic FLX administration decreases hippocampus-associated neophobia in naive mice. In parallel, electrophysiological recordings in hippocampal CA3-CA1 circuitry revealed that the FLX treatment resulted in increased short and long-term plasticity likely attributed to changes in presynaptic function. These changes were accompanied by enhancement in the expression of proteins related to vesicular trafficking and release, namely synaptophysin, synaptotagmin 1, MUNC 18 and syntaxin 1. Thus, chronic FLX administration is associated with enhanced synaptic dynamics atypical of mature CA1 synapses, elevated hippocampal plasticity, improved hippocampus-dependent behavior as well as altered expression of synaptic proteins regulating neurotransmitter trafficking and release. The results support the idea that antidepressants can promote neuronal plasticity and show that they can increase the functional dynamic range and information processing in synaptic circuitries. (C) 2017 Elsevier Ltd. All rights reserved.

Several pieces of evidence indicate that elastase-2 (ELA2; chymotrypsin-like ELA2) is an alternative pathway to the generation of angiotensin II (ANG II). Elastase-2 knockout mice (ELA2KO) exhibit alterations in the arterial blood pressure and heart rate. However, there is no data on the behavioral consequences of ELA2 deletion. In this study we addressed this question, submitting ELA2KO and wild-type (WT) mice to several models sensitive to anxiety‐ and depression-like, memory, and repetitive behaviors. Our data indicates a higher incidence of barbering behavior in ELA2KO compared to WT, as well as an anxiogenic phenotype, evaluated in the elevated plus maze (EPM). While a decrease in locomotor activity was observed in ELA2KO in EPM, this feature was not the main source of variation in the other parameters analyzed. The marble burying test (MBT) indicated increase in repetitive behavior, observed by a higher number of buried marbles. The actimeter test indicated a decrease in total activity and confirmed the increase in repetitive behavior. The spatial memory was tested by repeated exposure to the actimeter in a 24h interval. Both ELA2KO and WT exhibited decreased activity compared to the first exposure, without any distinction between the genotypes. However, when submitted to the cued fear conditioning, ELA2KO displayed lower levels of freezing behavior in the extinction session when compared to WT, but no difference was observed during the conditioning phase. Increased levels of BDNF were found in the prefrontal cortex but not in the hippocampus of ELA2KO mice compared to WT. Finally, in silico analysis indicates that ELA2 is putatively able to cleave BDNF, and incubation of the purified enzyme with BDNF led to the degradation of the later. Our data suggested an anxiogenic‐ and antidepressant-like phenotype of ELA2KO, possibly associated with increased levels of BDNF in the prefrontal cortex.

Renin-angiotensin system (RAS) is associated to peripheral fluid homeostasis and cardiovascular function, but recent evidence has also drawn its functional role in the brain. RAS has been described to regulate physiological and behavioral parameters related to stress response, including depressive symptoms. Apparently, RAS can modulate levels of brain derived neurotrophic factor (BDNF) and TRKB, which are important to neurobiology of depression and antidepressant action. However, interaction between BDNF/TRKB system and RAS in models predictive of antidepressant effect has not been investigated before. Accordingly, in the forced swimming test, we observed an antidepressant-like effect of systemic losartan but not with captopril or enalapril treament. Moreover, infusion of losartan into ventral hippocampus (vHC) and prelimbic prefrontal cortex (PL) mimicked the consequences of systemically injected losartan, whereas K252a, a blocker of TRK, infused into these brain areas impaired such effect. PD123319, an antagonist of AT2 receptor (AGTR2), infused into PL but not into vHC, also prevented systemic losartan effect. Cultured cortical cells of rat embryos indicate that angiotensin II (ANG2), possibly through AGTR2, increases the surface levels of TRKB, and favors it’s coupling to FYN, a SRC family kinase. The higher levels of agtr2 in cortical cells were decreased after insult with glutamate, and under this condition an interaction between losartan and ANG2 was achieved. Occurrence of TRKB/AGTR2 heterodimers was also observed, in MG87 cells GFP-tagged AGTR2 co-immunoprecipitated with TRKB. Therefore, antidepressant-like effect of losartan is proposed to occur through a shift of ANG2 binding towards AGTR2, followed by coupling of TRK/FYN and putative TRKB transactivation. Thus, AGTR1 show therapeutic potential as novel antidepressant therapy.

Brain-derived neurotrophic factor (BDNF), together with its cognate receptor tyrosine kinase B (TrkB), plays an essential role in the development and plasticity of the brain and is widely implicated in psychiatric diseases (Autry and Monteggia, 2012). Due to the highly conserved evolutionary lineage of neurotrophins and their receptors in vertebrates, the zebrafish is a well-suited model for this study. The TrkB receptor, also known as NTRK2, has two forms in zebrafish, Ntrk2a and Ntrk2b. The spatio-temporal expression pattern of bdnf and ntrk2b in zebrafish was studied using in situ hybridization. The complementary expression pattern of ntrk2b to bdnf suggests that ntrk2b is the key receptor, unlike its duplicate isoform ntrk2a. Two reverse genetics strategies, morpholino oligonucleotides (MO) and the TILLING mutant, were applied in this study. The loss or complete deletion of ntrk2b had no major effect on the viability, gross phenotype, or swimming behavior of zebrafish. A specific subset of the dopaminergic and serotonergic neuronal population was affected in the morphants and mutants. Downstream signaling transcripts such as bdnf, serta, th2, and tph2 were downregulated and could be rescued by overexpression of the full-length ntrk2b mRNA in the morphants. Pharmacological intervention with a tyrosine kinase inhibitor, K252a, resulted in similar phenotypes. Overall, our results reveal a specific effect of ntrk2b on the two crucial aminergic systems involved in psychiatric disorders and provide an essential tool to study neurotrophin function in modulating neuronal plasticity in the central nervous system.Significance StatementBrain-derived neurotrophic factor (BDNF) and its high-affinity receptor, tyrosine kinase (TrkB/NTRK2), play a major role in regulating the development and plasticity of neural circuits. Additionally, BDNF/TrkB signaling is involved in psychiatric disorders and antidepressant responses. This study presents the complementary gene expression pattern of TrkB and BDNF in zebrafish during the early larval stage and in the adult brain. Our results consistently indicate that BDNF/TrkB signaling has a significant role in the development and maintenance of dopaminergic and serotonergic neuronal populations. Therefore, the ntrk2b-deficient zebrafish model is well suited to studying psychiatric disorders attributed to a dysfunctional monoaminergic system, and could potentially be a valuable model for small molecule drug screening.

Serotonin modulates neuroplasticity, especially during early life, and dysfunctions in both systems likewise contribute to pathophysiology of depression. Recent findings demonstrate that serotonin reuptake inhibitors trigger reactivation of juvenile-like neuroplasticity. How these findings translate to clinical antidepressant treatment in major depressive disorder remains unclear. With this review, we link preclinical with clinical work on serotonin and neuroplasticity to bring two pathophysiologic models in clinical depression closer together. Dysfunctional developmental plasticity impacts on later-life cognitive and emotional functions, changes of synaptic serotonin levels and receptor levels are coupled with altered synaptic plasticity and neurogenesis. Structural magnetic resonance imaging in patients reveals disease-state-specific reductions of gray matter, a marker of neuroplasticity, and reversibility upon selective serotonin reuptake inhibitor treatment. Translational evidence from magnetic resonance imaging in animals support that reduced densities and sizes of neurons and reduced hippocampal volumes in depressive patients could be attributable to changes of serotonergic neuroplasticity. Since ketamine, physical exercise or learning enhance neuroplasticity, combinatory paradigms with selective serotonin reuptake inhibitors could enhance clinical treatment of depression.

Novel hypotheses suggest that antidepressants, such as the selective serotonin reuptake inhibitor fluoxetine, induce neuronal structural plasticity, resembling that of the juvenile brain, although the underlying mechanisms of this reopening of the critical periods still remain unclear. However, recent studies suggest that inhibitory networks play an important role in this structural plasticity induced by fluoxetine. For this reason we have analysed the effects of a chronic fluoxetine treatment in the hippocampus and medial prefrontal cortex (mPFC) of transgenic mice displaying eGFP labelled interneurons. We have found an increase in the expression of molecules related to critical period plasticity, such as the polysialylated form of the neural cell adhesion molecule (PSA-NCAM), GAD67/65 and synaptophysin, as well as a reduction in the number of parvalbumin expressing interneurons surrounded by perineuronal nets. We have also described a trend towards decrease in the perisomatic inhibitory puncta on pyramidal neurons in the mPFC and an increase in the density of inhibitory puncta on eGFP interneurons. Finally, we have found that chronic fluoxetine treatment affects the structure of interneurons in the mPFC, increasing their dendritic spine density. The present study provides evidence indicating that fluoxetine promotes structural changes in the inhibitory neurons of the adult cerebral cortex, probably through alterations in plasticity-related molecules of neurons or the extracellular matrix surrounding them, which are present in interneurons and are known to be crucial for the development of the critical periods of plasticity in the juvenile brain.

Brain network plasticity occurs principally during critical periods in early postnatal life [1]. Chronic treatment with the antidepressant fluoxetine, however, can induce critical period-like plasticity (iPlasticity), such as shift of ocular dominance after monocular deprivation [2]. Fluoxetine activates the neurotrophic BDNF/TrkB pathway and is thought to be a crucial modulator of iPlasticity [3]. We aim to identify the mechanisms of iPlasticity and the neuronal subpopulations expressing TrkB that are responsible for the profound events observed in that process. Especially, Parvalbumin-positive GABAergic interneurons play a major role in regulating synaptic plasticity in the visual cortex [2]. TrkB receptors are highly enriched in Parvalbumin interneurons [4] and closure of critical periods is promoted by maturation of the intracortical Parvalbumin GABAergic network inhibiting critical period and ocular dominance plasticity. It is widely accepted that visual cortex plasticity requires a reduction in Parvalbumin GABAergic interneuron-mediated inhibition resulting in the activation of a large population of pyramidal neurons and subsequent synchronization of the brain network [1]. Given the importance of Parvalbumin in regulating plasticity events, we hypothesize that fluoxetine-induced plasticity in the adult visual cortex is mediated through TrkB receptors expressed in Parvalbumin GABAergic interneurons. We used the validated shift of ocular dominance paradigm as previously described [5] to study visual cortex plasticity, analyzed the data with two-way ANOVA and demonstrate that Parvalbumin GABAergic interneurons are key regulators in ocular dominance plasticity. Using an inhibition approach, we show that in heterozygous Parvalbumin-specific TrkB knockout mice (hPV-TrkB cKO) the fluoxetine-induced shift in ocular dominance is absent (p = 0.6185) while wild-type mice show a robust shift induced by chronic fluoxetine treatment (p = 0.0002). Also, we have developed DIO-optoTrkB, a double-inverted open reading frame lentivirus construct that is dependent on cre-recombinase, for cell type-specific expression in vivo and optogenetic stimulation promotes the dimerization and autophosphorylation of optoTrkB in Parvalbumin interneurons. During the shift in ocular dominance paradigm, specific optogenetic activation of optoTrkB induces the shift in ocular dominance in a stimulation-dependent manner when combined with monocular deprivation of the stronger eye (p 0.03). These data show a strikingly new and opposing role of intracortical inhibition by Parvalbumin GABAergic interneurons in ocular dominance and induction of iPlasticity, offering a new idea about the underlying mechanisms of plasticity during the critical period and adulthood. We propose a new tool to investigate neuropsychological disorders, such as amblyopia and post-traumatic stress disorder, by optically controlling neuronal plasticity in a neuron-specific manner.

Antidepressant treatments enhance plasticity and increase neurogenesis in the adult brain, but it has been unclear how these effects influence mood. We propose that like environmental enrichment and exercise, antidepressant treatments enhance adaptability by increasing structural variability within the nervous system at many levels, from proliferating precursors to immature synaptic contacts. Conversely, sensory deprivation and chronic stress reduce this structural variability. Activity-dependent competition within the mood-related circuits, guided by rehabilitation, then selects for the survival and stabilization of those structures that best represent the internal or external milieu. Increased variability together with competition-mediated selection facilitates normal function, such as pattern separation within the dentate gyrus and other mood-related circuits, thereby enhancing adaptability towards novel experiences.

Growing interest in long-term visualization of cortical structure and function requires methods that allow observation of an intact cortex in longitudinal imaging studies. Here we describe a detailed protocol for the "transparent skull" (TS) preparation based on skull clearing with cyanoacrylate, which is applicable for long-term imaging through the intact skull in mice. We characterized the properties of the TS in imaging of intrinsic optical signals and compared them with the more conventional cranial window preparation. Our results show that TS is less invasive, maintains stabile transparency for at least two months, and compares favorably to data obtained from the conventional cranial window. We applied this method to experiments showing that a four-week treatment with the antidepressant fluoxetine combined with one week of monocular deprivation induced a shift in ocular dominance in the mouse visual cortex, confirming that fluoxetine treatment restores critical-period-like plasticity. Our results demonstrate that the TS preparation could become a useful method for long-term visualization of the living mouse brain.

Neurotrophic factors, particularly brain-derived neurotrophic factor (BDNF) and other members of the neurotrophin family, are central mediators of the activity-dependent plasticity through which environmental experiences, such as sensory information are translated into the structure and function of neuronal networks. Synthesis, release and action of BDNF is regulated by neuronal activity and BDNF in turn leads to trophic effects such as formation, stabilization and potentiation of synapses through its high-affinity TrkB receptors. Several clinically available drugs activate neurotrophin signaling and neuronal plasticity. In particular, antidepressant drugs rapidly activate TrkB signaling and gradually increase BDNF expression, and the behavioral effects of antidepressants are mediated by and dependent on BDNF signaling through TrkB at least in rodents. These findings indicate that antidepressants, widely used drugs, effectively act as TrkB activators. They further imply that neuronal plasticity is a central mechanism in the action of antidepressant drugs. Indeed, it was recently discovered that antidepressants reactivate a state of plasticity in the adult cerebral cortex that closely resembles the enhanced plasticity normally observed during postnatal critical periods. This state of induced plasticity, known as iPlasticity, allows environmental stimuli to beneficially reorganize networks abnormally wired during early life. iPlasticity has been observed in cortical as well as subcortical networks and is induced by several pharmacological and non-pharmacological treatments. iPlasticity is a new pharmacological principle where drug treatment and rehabilitation cooperate; the drug acts permissively to enhance plasticity and rehabilitation provides activity to guide the appropriate wiring of the plastic network. Optimization of iPlastic drug treatment with novel means of rehabilitation may help improve the efficacy of available drug treatments and expand the use of currently existing drugs into new indications.

Rewiring of excitatory glutamatergic neuronal circuits is a major abnormality in epilepsy. Besides the rewiring of excitatory circuits, an abnormal depolarizing γ-aminobutyric acidergic (GABAergic) drive has been hypothesized to participate in the epileptogenic processes. However, a remaining clinically relevant question is whether early post-status epilepticus (SE) evoked chloride dysregulation is important for the remodeling of aberrant glutamatergic neuronal circuits.Osmotic minipumps were used to infuse intracerebrally a specific inhibitor of depolarizing GABAergic transmission as well as a functionally blocking antibody toward the pan-neurotrophin receptor p75 (p75Blockade of NKCC1 after SE with the specific inhibitor bumetanide restored NKCC1 and KCC2 expression, normalized chloride homeostasis, and significantly reduced the glutamatergic rMF sprouting within the dentate gyrus. This mechanism partially involves p75Our findings show that early post-SE abnormal depolarizing GABA and p75

Inputs to sensory cortices are known to compete for target innervation through an activity-dependent mechanism during critical periods. To investigate whether this principle also applies to association cortices such as the medial prefrontal cortex (mPFC), we produced a bilateral lesion during early development to the ventral hippocampus (vHC), an input to the mPFC, and analyzed the intensity of the projection from another input, the basolateral amgydala (BLA). We found that axons from the BLA had a higher density of “en passant” boutons in the mPFC of lesioned animals. Furthermore, the density of neurons labeled with retrograde tracers was increased, and neurons projecting from the BLA to the mPFC showed increased expression of FosB. Since neonatal ventral hippocampal lesion has been used as an animal model of schizophrenia, we investigated its effects on behavior and found a negative correlation between the density of retrogradely labeled neurons in the BLA and the reduction of the startle response in the prepulse inhibition test. Our results not only indicate that the inputs from the BLA and the vHC compete for target innervation in the mPFC during postnatal development but also that subsequent abnormal rewiring might underlie the pathophysiology of neuropsychiatric disorders such as schizophrenia.

There is evidence that developmental-like plasticity can be reactivated in the adult visual cortex. Although activity-dependent transcription factors underlying the process of plasticity reactivation are currently unknown, recent studies point towards NPAS4 as a candidate gene for the occurrence of plasticity in the adult visual system. Here, we addressed whether NPAS4 is involved in the reinstatement of plasticity by using the monocular deprivation protocol and long-term fluoxetine treatment as a pharmacological strategy that restores plasticity in adulthood. A combination of molecular assays for gene expression and epigenetic analysis, gene delivery by lentiviral infection, shRNA interference and electrophysiology as a functional read-out, revealed a previously unknown role for the transcription factor NPAS4 in the regulation of adult visual cortical plasticity. We found that NPAS4 overexpression restores ocular dominance plasticity in adult naive animals whereas NPAS4 down-regulation prevents the plastic outcome caused by fluoxetine in adulthood. Our findings lead the way to the identification of novel therapeutic targets for pathological conditions where reorganization of neuronal networks would be beneficial in adult life.