Periventricular Zone Research Articles

Multiple Critical Periods for Rapamycin Treatment to Correct Structural Defects in Tsc-1-Suppressed Brain.

Tuberous sclerosis complex (TSC) is an autosomal dominant neurogenetic disorder affecting the brain and other vital organs. Neurological symptoms include epilepsy, intellectual disability, and autism. TSC is caused by a loss-of-function mutation in the TSC1 or TSC2 gene. These gene products form a protein complex and normally suppress mammalian target of rapamycin (mTOR) activity. mTOR inhibitors have been used to treat subependymal glioma (SEGA) that is a brain tumor characteristic of TSC. However, neuropathology of TSC also involves dysregulated cortical circuit formation including neuronal migration, axodendritic differentiation, and synapse formation. It is currently unknown to what extent mTOR signaling inhibitors correct an alteration in neuronal morphology that have already formed prior to the treatment. Here, we address the efficacy of rapamycin treatment on neuronal migration and dendrite formation. Using in utero electroporation, we suppressed Tsc1 expression in a fraction of neuronal progenitor cells during the fetal period. In embryonic brain slices, we found that more Tsc1-suppressed cells remained within the periventricular zone, and rapamycin treatment facilitated neuronal migration. Postnatally, Tsc1-suppressed pyramidal neurons showed more complex branching of basal dendrites and a higher spine density at postnatal day (P) 28. Aberrant arborization was normalized by rapamycin administration every other day between P1 and P13 but not P15 and P27. In contrast, abnormal spine maturation improved by rapamycin treatment between P15 and P27 but not P1 and P13. Our results indicate that there are multiple critical windows for correcting different aspects of structural abnormalities in TSC, and the responses depend on the stage of neuronal circuit formation. These data warrant a search for an additional therapeutic target to treat neurological symptoms of TSC.

RND1 regulates migration of human glioblastoma stem-like cells according to their anatomical localization and defines a prognostic signature in glioblastoma.

Despite post-operative radio-chemotherapy, glioblastoma systematically locally recurs. Tumors contacting the periventricular zone (PVZ) show earlier and more distant relapses than tumors not contacting the PVZ. Since glioblastoma stem-like cells (GSCs) have been proposed to play a major role in glioblastoma recurrence, we decided to test whether GSC migration properties could be different according to their anatomical location (PVZ+/PVZ–). For that purpose, we established paired cultures of GSCs from the cortical area (CT) and the PVZ of glioblastoma patient tumors. We demonstrated that PVZ GSCs possess higher migration and invasion capacities than CT GSCs. We highlighted specific transcriptomic profiles in PVZ versus CT populations and identified a down-regulation of the RhoGTPase, RND1 in PVZ GSCs compared to CT GSCs. Overexpression of RND1, dramatically inhibited PVZ GSC migration and conversely, downregulation of RND1 increased CT GSC migration. Additionally, transcriptomic analyses also revealed a down-regulation of RND1 in glioblastoma compared to normal brain. Using the glioblastoma TCGA database, low levels of RND1 were also shown to correlate with a decreased overall survival of patients. Finally, based on signaling pathways activated in patients with low levels of RND1, we identified an RND1low signature of six genes (MET, LAMC1, ITGA5, COL5A1, COL3A1, COL1A2) that is an independent prognostic factor in glioblastoma. These findings contribute to explain the shorter time to progression of patients with PVZ involvement and, point out genes that establish the RND1low signature as key targets genes to impede tumor relapse after treatment.

The Pax2 and Pax6 Transcription Factors in the Optic Nerve and Brain of Trout Oncorhynchus mykiss after a Mechanical Eye Injury

The distribution of the Pax2+ transcription factor in the optic nerve after a mechanical eye injury on the side of damage and in the contralateral nerve has been studied in the trout Oncorhynchus mykiss. It has been found that injury of the optic nerve in this fish species causes Pax2+ reactive astrocytes involved in the initial stages of optic nerve axon regeneration to increase in number, especially in the area of the head and the proximal part of the optic nerve. As the optic nerve in trout is damaged, a significant growth of the heterogeneous population of Pax6+ cells occurs in the brain divisions that have direct retinal inputs, diencephalon, and optic tectum. A part of the Pax6+ cells have an undifferentiated phenotype and are a component of reactive neurogenic niches located in the periventricular zone and parenchymal regions of the brain. Another population of Pax6+ cells has the radial glial phenotype and appears as a result of activation of the constitutive neurogenic domains also within the newly formed reactive neurogenic niches. Thus, due to the optic nerve injury, a pronounced neurogenic response associated with the appearance of reactive neurogenic niches and radial glia arises both in the brain divisions with direct retinal projections and in those lacking the retinal projections as well as in remote regions. The results obtained indicate that the damage to the optic nerve causes an increased reactive neurogenesis in the brain of adult trout.

Endogenous Murine Amyloid-β Peptide Assembles into Aggregates in the Aged C57BL/6J Mouse Suggesting These Animals as a Model to Study Pathogenesis of Amyloid-β Plaque Formation.

Amyloid-β peptide (Aβ), paired helical filament-tau (PHF-tau), and α-synuclein are in the focus of neuroscience research because they aggregate in brains of patients with Alzheimer's and Parkinson's diseases. For this purpose, transgenic mouse models were used containing the human genes for AβPP/presenilin/tau or α-synuclein with the most frequent mutations. This is not ideal because most patients develop sporadic forms of the diseases with no causative single gene defect and furthermore the aggregation of human proteins in man is not necessarily the same in rodents. We hypothesized that for such cases the aged mouse could be an alternative model and analyzed the distribution of endogenous Aβ, PHF-tau, and α-synuclein in mouse brains at different ages. Whereas Aβ was below detectable levels at birth, it was present at high levels in the 15-month-old mouse. Aβ was found in the cytosol and lysosomes of neurons of the temporal cortex, cingulate area, pons, and cerebellum as well as extracellularly in the periventricular zone. Contrary to Aβ, mouse brain was devoid of PHF-tau-positive neurofibrillary tangles. α-Synuclein was detectable in the newborn mouse with highest levels in the marginal zone of the lateral cortex and average levels in the hippocampus, pons, and cerebellum. Brain-area specific differences in the α-synuclein level persisted up to 15 months of age, but increased 3-fold in all areas over time. α-Synuclein resided in the neuropil, but not in intracellular aggregates even in the aged mouse. We suggest the aged mouse as a model to study Aβ plaque formation.

Visual Experience Facilitates BDNF-Dependent Adaptive Recruitment of New Neurons in the Postembryonic Optic Tectum.

Postembryonic brain development is sensitive to environmental input and sensory experience, but the mechanisms underlying healthy adaptive brain growth are poorly understood. Here, we tested the importance of visual experience on larval zebrafish (Danio rerio) postembryonic development of the optic tectum (OT), a midbrain structure involved in visually guided behavior. We first characterized postembryonic neurogenic growth in OT, in which new neurons are generated along the caudal tectal surface and contribute appositionally to anatomical growth. Restricting visual experience during development by rearing larvae in dim light impaired OT anatomical and neurogenic growth, specifically by reducing the survival of new neurons in the medial periventricular gray zone. Neuronal survival in the OT was reduced only when visual experience was restricted for the first 5 d following new neuron generation, suggesting that tectal neurons exhibit an early sensitive period in which visual experience protects these cells from subsequent neuronal loss. The effect of dim rearing on neuronal survival was mimicked by treatment with an NMDA receptor antagonist early, but not later, in a new neuron's life. Both dim rearing and antagonist treatment reduced BDNF production in the OT, and supplementing larvae with exogenous BDNF during dim rearing prevented neuronal loss, suggesting that visual experience protects new tectal neurons through neural activity-dependent BDNF expression. Collectively, we present evidence for a sensitive period of neurogenic adaptive growth in the larval zebrafish OT that relies on visual experience-dependent mechanisms.SIGNIFICANCE STATEMENT Early brain development is shaped by environmental factors via sensory input; however, this form of experience-dependent neuroplasticity is traditionally studied as structural and functional changes within preexisting neurons. Here, we found that restricting visual experience affects development of the larval zebrafish optic tectum, a midbrain structure involved in visually guided behavior, by limiting the survival of newly generated neurons. We found that new tectal neurons exhibit a sensitive period soon after cell birth in which adequate visual experience, likely mediated by neuronal activity driving BDNF production within the tectum, would protect them from subsequent neuronal loss over the following week. Collectively, we present evidence for neurogenic adaptive tectal growth under different environmental lighting conditions.

Bullseye's representation of cerebral white matter hyperintensities

Background and purposeVisual rating scales have limited capacities to depict the regional distribution of cerebral white matter hyperintensities (WMH). We present a regional-zonal volumetric analysis alongside a visualization tool to compare and deconstruct visual rating scales. Materials and methods3D T1-weighted, T2-weighted spin-echo and FLAIR images were acquired on a 3T system, from 82 elderly participants in a population-based study. Images were automatically segmented for WMH. Lobar boundaries and distance to ventricular surface were used to define white matter regions. Regional-zonal WMH loads were displayed using bullseye plots. Four raters assessed all images applying three scales. Correlations between visual scales and regional WMH as well as inter and intra-rater variability were assessed. A multinomial ordinal regression model was used to predict scores based on regional volumes and global WMH burdens. ResultsOn average, the bullseye plot depicted a right-left symmetry in the distribution and concentration of damage in the periventricular zone, especially in frontal regions. WMH loads correlated well with the average visual rating scores (e.g. Kendall's tau [Volume, Scheltens]=0.59 CI=[0.53 0.62]). Local correlations allowed comparison of loading patterns between scales and between raters. Regional measurements had more predictive power than global WMH burden (e.g. frontal caps prediction with local features: ICC=0.67 CI=[0.53 0.77], global volume=0.50 CI=[0.32 0.65], intra-rater=0.44 CI=[0.23 0.60]). ConclusionRegional-zonal representation of WMH burden highlights similarities and differences between visual rating scales and raters. The bullseye infographic tool provides a simple visual representation of regional lesion load that can be used for rater calibration and training.

EANM'17.

Aim: Postoperative cognitive dysfunction (POCD) is a common complication after surgery that can have a long-lasting negative impact on the patient’s quality of life. Although the underlying mechanism is still unknown, evidence suggests that neuroinflammation may play an important role. Here we aimed to confirm the presence of neuroinflammation in a rat model of POCD and investigated the impact of the surgical procedure on brain metabolism. Nutrition is believed to affect cognition and brain metabolism and could modulate neuroinflammation. We therefore also evaluated the impact of a multi-nutrient supplementation diet containing anti-inflammatory ingredients on surgery-induced biochemical alterations in the brain and on POCD symptoms. Materials and Methods: POCD after major abdominal surgery in humans was mimicked in rats by exteriorizing the gastrointestinal tract and clamping the mesenteric artery for 30 min. To assess the validity of the model, behavioral changes were evaluated in the first postoperative week. The effects of surgery on neuroinflammation and brain glucose metabolism were monitored noninvasively by positron emission tomography (PET) and postmortem by immunohistochemistry. To assess the effect of nutrition, rats were fed a control diet or investigational diet starting either 2 weeks before or immediately after the surgical intervention. Results: Major surgery caused significant bodyweight loss, reduced exploratory behavior, increased anxiety and tended to decrease spatial memory. [11C]PK11195-PET imaging and immunohistochemistry confirmed the presence of neuroinflammation in several brain regions after surgery. [18F]FDG-PET imaging revealed both increased and decreased brain metabolism in distinct parts of the brain. Dietary intervention started prior to surgery had a positive impact on recovery, resulting in faster gain in bodyweight and normalization of exploratory behavior and spatial memory. This improvement was accompanied by a reversal of astrocyte activation in the periventricular zone and a normalization of brain metabolism in part of the motor cortex. Dietary intervention started after surgery reversed astrocyte activation in cerebellum and the periventricular zone and decreased brain metabolism in the piriform cortex, but had no beneficial effect on anxiety and spatial memory. Conclusion: This study shows that major surgery can be accompanied by neuroinflammation and changes in glucose metabolism in several brain regions. Preventive intervention with a diet containing anti-inflammatory nutrients can affect neuroinflammation and brain metabolism and has a positive effect on the recovery from abdominal surgery in rats. These results indicate that a dietary intervention can have an effect on brain physiology and warrant further investigation of this concept.

Persistent and reparative neurogenesis in the juvenile masu salmon Oncorhynchus masou telencephalon after mechanical injury

A superficially located periventricular proliferative area with PCNA-immunopositive (PCNA+) cells, which corresponds to the pallial periventricular zone (PVZ) of other fish species, including its dorsal, lateral, and medial compartments, is discovered in the telencephalon of the juvenile masu salmon Oncorhynchus masou. The PCNA+ cells are also identified in the parenchyma of the masu salmon intact brain, and their maximum concentration is observed in the medial zone. After a mechanical injury, the zones of induced neurogenesis—neurogenic niches and sites of secondary neurogenesis surrounded by radial glial fibers—appear in the masu salmon telencephalon. The PVZ of the juvenile masu salmon pallium contains clusters of undifferentiated HuCD-immunopositive (HuCD+) neurons. A change in the HuCD+ cell topography is observed in the mechanically injured masu salmon telencephalon, namely, neurogenic niches in the lateral zone and an increase in the cell distribution density and cell migration patterns in the medial zone. A high level of persistent neurogenesis is characteristic of the juvenile masu salmon brain.

Impact of Proestrus on Gene Expression in the Medial Preoptic Area of Mice.

The antero-ventral periventricular zone (AVPV) and medial preoptic area (MPOA) have been recognized as gonadal hormone receptive regions of the rodent brain that—via wiring to gonadotropin-releasing hormone (GnRH) neurons—contribute to orchestration of the preovulatory GnRH surge. We hypothesized that neural genes regulating the induction of GnRH surge show altered expression in proestrus. Therefore, we compared the expression of 48 genes obtained from intact proestrous and metestrous mice, respectively, by quantitative real-time PCR (qPCR) method. Differential expression of 24 genes reached significance (p < 0.05). Genes upregulated in proestrus encoded neuropeptides (kisspeptin (KP), galanin (GAL), neurotensin (NT), cholecystokinin (CCK)), hormone receptors (growth hormone secretagogue receptor, μ-opioid receptor), gonadal steroid receptors (estrogen receptor alpha (ERα), progesterone receptor (PR), androgen receptor (AR)), solute carrier family proteins (vesicular glutamate transporter 2, vesicular monoamine transporter 2), proteins of transmitter synthesis (tyrosine hydroxylase (TH)) and transmitter receptor subunit (AMPA4), and other proteins (uncoupling protein 2, nuclear receptor related 1 protein). Proestrus evoked a marked downregulation of genes coding for adenosine A2a receptor, vesicular gamma-aminobutyric acid (GABA) transporter, 4-aminobutyrate aminotransferase, tachykinin precursor 1, NT receptor 3, arginine vasopressin receptor 1A, cannabinoid receptor 1, ephrin receptor A3 and aldehyde dehydrogenase 1 family, member L1. Immunocytochemistry was used to visualize the proteins encoded by Kiss1, Gal, Cck and Th genes in neuronal subsets of the AVPV/MPOA of the proestrous mice. The results indicate that gene expression of the AVPV/MPOA is significantly modified at late proestrus including genes that code for neuropeptides, gonadal steroid hormone receptors and synaptic vesicle transporters. These events support cellular and neuronal network requirements of the positive estradiol feedback action and contribute to preparation of the GnRH neuron system for the pre-ovulatory surge release.

Comparative analysis of monoaminergic cerebrospinal fluid-contacting cells in Osteichthyes (bony vertebrates).

Cerebrospinal fluid‐contacting (CSF‐c) cells containing monoamines such as dopamine (DA) and serotonin (5‐HT) occur in the periventricular zones of the hypothalamic region of most vertebrates except for placental mammals. Here we compare the organization of the CSF‐c cells in chicken, Xenopus, and zebrafish, by analyzing the expression of synthetic enzymes of DA and 5‐HT, respectively, tyrosine hydroxylase (TH) and tryptophan hydroxylase (TPH), and draw an evolutionary scenario for this cell population. Due to the lack of TH immunoreactivity in this region, the hypothalamic CSF‐c cells have been thought to take up DA from the ventricle instead of synthesizing it. We demonstrate that a second TH gene (TH2) is expressed in the CSF‐c cells of all the three species, suggesting that these cells do indeed synthetize DA. Furthermore, we found that many CSF‐c cells coexpress TH2 and TPH1 and contain both DA and 5‐HT, a dual neurotransmitter phenotype hitherto undescribed in the brain of any vertebrate. The similarities of CSF‐c cells in chicken, Xenopus, and zebrafish suggest that these characteristics are inherited from the common ancestor of the Osteichthyes. A significant difference between tetrapods and teleosts is that teleosts possess an additional CSF‐c cell population around the posterior recess (PR) that has emerged in specific groups of Actinopterygii. Our comparative analysis reveals that the hypothalamus in mammals and teleosts has evolved in a divergent manner: placental mammals have lost the monoaminergic CSF‐c cells, while teleosts have increased their relative number.

Acid Ceramidase Deficiency in Mice Results in a Broad Range of Central Nervous System Abnormalities

Farber disease is a rare autosomal recessive disorder caused by acid ceramidase deficiency that usually presents as early-onset progressive visceral and neurologic disease. To understand the neurologic abnormality, we investigated behavioral, biochemical, and cellular abnormalities in the central nervous system of Asah1P361R/P361R mice, which serve as a model of Farber disease. Behaviorally, the mutant mice had reduced voluntary locomotion and exploration, increased thigmotaxis, abnormal spectra of basic behavioral activities, impaired muscle grip strength, and defects in motor coordination. A few mutant mice developed hydrocephalus. Mass spectrometry revealed elevations of ceramides, hydroxy-ceramides, dihydroceramides, sphingosine, dihexosylceramides, and monosialodihexosylganglioside in the brain. The highest accumulation was in hydroxy-ceramides. Storage compound distribution was analyzed by mass spectrometry imaging and morphologic analyses and revealed involvement of a wide range of central nervous system cell types (eg,neurons, endothelial cells, and choroid plexus cells), most notably microglia and/or macrophages. Coalescing and mostly perivascular granuloma-like accumulations of storage-laden CD68+ microglia and/or macrophages were seen as early as 3 weeks of age and located preferentially in white matter, periventricular zones, and meninges. Neurodegeneration was also evident in specific cerebral areas in late disease. Overall, our central nervous system studies in Asah1P361R/P361R mice substantially extend the understanding of human Farber disease and suggest that this model can be used to advance therapeutic approaches for this currently untreatable disorder.

GABAergic Neurons and Their Modulatory Effects on GnRH3 in Zebrafish.

γ-Aminobutyric acid (GABA) is a major amino acid neurotransmitter in the vertebrate brain. To provide detailed information on the distribution of the GABA in zebrafish (Danio rerio), neurons were labeled with mCherry driven by the glutamic acid decarboxylase 67 (gad67) promoter. In the transgenic line Tg(gad67:mCherry), mCherry-positive gad67 cell bodies were predominantly localized to the olfactory bulb, pallial zones, subpallium zones, parvocellular preoptic nucleus, periventricular gray zone of optic tectum, torus semicircularis, posterior tuberculum, medial longitudinal fascicle, caudal zone of periventricular hypothalamus, and oculomotor nucleus. mCherry-positive fibers were widely distributed in the olfactory bulbs, subpallium, thalamus, ventral hypothalamic zone, tectum opticum, mesencephalon, and rhombencephalon. mCherry-positive neurons were also observed in the retina and the spinal cord. The anatomical relationships between GABAergic and gonadotrophin-releasing hormone 3 (GnRH3) neurons were investigated by crossing Tg(gad67:mCherry) fish with the previously established Tg(gnrh3:EGFP) transgenic line. GnRH3 cell bodies and fibers were contacted by GABAergic fibers directly in the ventral telencephalon and anterior tuberal nucleus. A subpopulation of GnRH3 neurons in the ventral telencephalic area was also labeled with mCherry, so some GnRH3 neurons are also GABAergic. GABAB receptor agonist (baclofen) and antagonist (CGP55845) treatments indicated that GABAB receptor signaling inhibited gnrh3 expression in larval fish but was stimulatory in adult fish. The expression of pituitary lhβ and fshβ was stimulated by intraperitoneal injection of baclofen in adult fish. We conclude that GABA via GABAB receptors regulates GnRH3 neurons in a developmentally dependent manner in zebrafish.

Identification of novel cellular clusters define a specialized area in the cerebellar periventricular zone

The periventricular zone of cerebellum is a germinative niche during the embryonic development, nevertheless its structural organization and functional implications in adult have not been widely studied. Here we disclose the presence of two novel clusters of cells in that area. The first one was named the subventricular cellular cluster (SVCC) and is composed of cells that express glial and neuronal markers. The second was named the ventromedial cord (VMC) and appears as a streak of biciliated cells with microvillosities facing the ventricle, that includes GFAP+ and nestin+ cells organized along the periventricular vasculature. The dorsal limit of the SVCC is associated with myelinated axons of neurons of unknown origin. This paper describes the characteristics and organization of these groups of cells. They can be observed from late embryonic development in the transgenic mouse line GFAP-GFP. The SVCC and VMC expand during early postnatal development but are restricted to the central area of the ventricle in adulthood. We did not find evidence of cell proliferation, cell migration or the presence of fenestrated blood vessels. These findings provide new insights into the knowledge of the cellular composition and structural organization of the periventricular zone of cerebellum.

Modulation of Benzo[a]Pyrene Induced Anxiolytic-Like Behavior by Retinoic Acid in Zebrafish: Involvement of Oxidative Stress and Antioxidant Defense System.

Benzo[a]pyrene (B[a]P) is commonly associated with oxidative stress-induced neurotoxicity. Retinoic acid (RA) has been shown to exhibit neuroprotection in brain, and disruption of RA signaling via excess or deficient RA can lead to oxidative stress. B[a]P contamination in aquatic environment has been shown to lower the internal RA level. Thus, the present study was conducted in wild-type zebrafish to ameliorate the neurotoxic effect of B[a]P by waterborne RA co-supplementation. Findings showed that B[a]P induced anxiolytic-like behavioral response, and altered antioxidant activity in zebrafish is attenuated by RA. Our study also advocated the neurotoxic potential of RA treatment alone in control condition. Previous findings showed that periventricular gray zone (PGZ) of optic tectum (TeO) in zebrafish brain regulates anxiety-like behavior. The augmented pyknotic neuronal counts in PGZ following B[a]P treatment was ameliorated by RA co-supplementation. Further, presence of B[a]P in the cell milieu is known to induce oxidative stress through increase expression of cytochrome P450 1A1 (CYP1A1), an enzyme necessary for metabolic breakdown of both B[a]P and RA. Any deviation from the required concentration of RA leads to production of reactive oxygen species. Further, low availability of RA in cell milieu is known to decrease the expression of Nrf2, a transcription factor necessary for the expression of several antioxidants and antioxidant enzymes. Recent studies also showed that RA increases glutathione synthesis and exhibits neuroprotective properties in brain cells. The findings of the present study address the potential role of exogenous RA co-supplementation as a therapeutic intervention against B[a]P-induced depletion of RA, causing neurotoxicity in zebrafish.

The pretectal connectome in lamprey.

In vertebrates, the pretectum and optic tectum (superior colliculus in mammals) are visuomotor areas that process sensory information and shape motor responses. Whereas the tectum has been investigated in great detail, the pretectum has received far less attention. The present study provides a detailed analysis of the connectivity and neuronal properties of lamprey pretectal cells. The pretectum can be subdivided roughly into three areas based on cellular location and projection pattern: superficial, central, and periventricular. Three different types of pretectal cells could be distinguished based on neuronal firing patterns. One type, the rapid spike-inactivation cells, preferentially lie within the periventricular zone; the other cell types are distributed more generally. In terms of afferentation, the pretectum receives electro- and mechanoreceptive inputs in addition to retinal input. Histological data reveal that a large number of pretectal cells in the superficial and central areas extend dendrites into the optic tract, suggesting a predominant retinal influence even outside of the normal retinal terminal areas. The pretectum receives inhibitory input from the basal ganglia, and input from the pallium (cortex in mammals) and torus semicircularis. In addition, the pretectum is reciprocally connected with the thalamus, tectum, octavolateral area, and habenula. The main pretectal output is to the reticulospinal nuclei, and thus the pretectum indirectly affects the control of movement. Efference copies of some of this output are relayed to the thalamus and tectum. Overall, its extensive circuitry-especially the reciprocal connectivity with other retinorecipient areas-underlines the importance of the pretectum for sensory integration and visuomotor functions. J. Comp. Neurol. 525:753-772, 2017. © 2016 Wiley Periodicals, Inc.

Early life low intensity stress experience modifies acute stress effects on juvenile brain cell proliferation of European sea bass (D. Labrax)

Early life adversity may be critical for the brain structural plasticity that in turn would influence juvenile behaviour. To address this, we questioned whether early life environment has an impact on stress responses latter in life, using European sea bass, Dicentrarchus labrax, as a model organism. Unpredictable chronic low intensity stress (UCLIS), using a variety of moderate intensity stressors, was applied during two early ontogenetic stages, flexion or formation all fins. At juvenile stage, fish were exposed to acute stress and plasma cortisol, brain mRNA expression of corticosteroid receptors’ genes (gr1, gr2, mr) and brain cell proliferation (using BrdU immunohistochemistry) were determined in experimental and matched controls. UCLIS treatment specifically decreased brain gr1 expression in juveniles, but had no effect on the juvenile brain cell proliferation pattern within the major neurogenic zones studied of dorsal (Dm, Dld) and ventral (Vv) telencephalic, preoptic (NPO) areas, periventricular tectum gray zone (PGZ) and valvula cerebellum (VCe). In contrast, exposure to acute stress induced significant plasma cortisol rise, decreases of cerebral cell proliferation in juveniles, not previously exposed to UCLIS, but no effect detected on the expression levels of gr1, gr2 and mr in all groups of different early life history. Interestingly, juveniles with UCLIS history showed modified responses to acute stress, attenuating acute stress-induced cell proliferation decreases, indicating a long-lasting effect of early life treatment. Taken together, early life mild stress experience influences an acute stress plasticity end-point, cerebral cell proliferation, independently of the stress-axis activation, possibly leading to more effective coping styles.

Optic nerve input-dependent regulation of neural stem cell proliferation in the optic tectum of adult zebrafish.

Adult neurogenesis attracts broad attention as a possible cure for neurological disorders. However, its regulatory mechanism is still unclear. Therefore, they have been studying the cell proliferation mechanisms of neural stem cells (NSCs) using zebrafish, which have high regenerative potential in the adult brain. The presence of neuroepithelial-type NSCs in the optic tectum of adult zebrafish has been previously reported. In the present study, it was first confirmed that NSCs in the optic tectum decrease or increase in proportion to projection of the optic nerves from the retina. At 4 days after optic nerve crush (ONC), BrdU-positive cells decreased in the optic tectum's operation side. In contrast, at 3 weeks after ONC, BrdU-positive cells increased in the optic tectum's operation side. To study the regulatory mechanisms, they focused on the BDNF/TrkB system as a regulatory factor in the ONC model. It was found that bdnf was mainly expressed in the periventricular gray zone (PGZ) of the optic tectum by using in situ hybridization. Interestingly, expression level of bdnf significantly decreased in the optic tectum at 4 days after ONC, and its expression level tended to increase at 3 weeks after ONC. They conducted rescue experiments using a TrkB agonist and confirmed that decrease of NSC proliferation in the optic tectum by ONC was rescued by TrkB signal activation, suggesting stimuli-dependent regulation of NSC proliferation in the optic tectum of adult zebrafish. © 2016 Wiley Periodicals, Inc. Develop Neurobiol 77: 419-437, 2017.

Withania somnifera Leaf Extract Ameliorates Benzo[a]pyrene-Induced Behavioral and Neuromorphological Alterations by Improving Brain Antioxidant Status in Zebrafish (Danio rerio).

The aquatic environment provides a sink for the environmental pollutants that have potential to induce oxidative stress by altering neurobehavioral response of aquatic animals. Benzo[a]pyrene (B[a]P), a polycyclic aromatic hydrocarbon is known to induce oxidative stress in the brain. Withania somnifera has been used traditionally for its neuroprotective effect in experimental models of neurological disorders. The present study is aimed to evaluate the neuroprotective potential of Withania somnifera leaf extract (WSLE) following exposure to waterborne B[a]P. Wild-type zebrafish (Danio rerio) were designated as naive, control (dimethyl sulfoxide), WSLE, B[a]P, and B[a]P + WSLE groups. Behavioral studies showed reversal in scototaxis (anxiety-like) behavior in B[a]P group and was restored by WSLE cosupplementation in B[a]P + WSLE group. B[a]P-induced altered antioxidant status was ameliorated by WSLE in the B[a]P + WSLE group. Previous studies showed that the periventricular gray zone (PGZ) of the optic tectum in zebrafish brain regulates scototaxis (anxiety-like) behavior. Our histopathological observation showed a significant increase in the pyknotic neuronal counts in PGZ of the B[a]P group and was ameliorated by WSLE cosupplementation. The study showed that the reversal in scototaxis behavior following exposure to waterborne B[a]P might be associated with neuromorphological alterations in PGZ, whereas a pioneer ethnopharmacological approach of WSLE cosupplementation showed its neuroprotective role to restore normal scototaxis of zebrafish. Future research directing toward understanding the role of visual circuit involved with impaired scototaxis behavior in zebrafish might provide new pathological outcomes following exposure to B[a]P.

Distinct intracellular signaling mediates C-MET regulation of dendritic growth and synaptogenesis.

Hepatocyte growth factor (HGF) activation of the MET receptor tyrosine kinase influences multiple neurodevelopmental processes. Evidence from human imaging and mouse models shows that, in the forebrain, disruptions in MET signaling alter circuit formation and function. One likely means of modulation is by controlling neuron maturation. Here, we examined the signaling mechanisms through which MET exerts developmental effects in the neocortex. In situ hybridization revealed that hgf is located near MET-expressing neurons, including deep neocortical layers and periventricular zones. Western blot analyses of neocortical crude membranes demonstrated that HGF-induced MET autophosphorylation peaks during synaptogenesis, with a striking reduction in activation between P14 and P17 just before pruning. In vitro analysis of postnatal neocortical neurons assessed the roles of intracellular signaling following MET activation. There is rapid, HGF-induced phosphorylation of MET, ERK1/2, and Akt that is accompanied by two major morphological changes: increases in total dendritic growth and synapse density. Selective inhibition of each signaling pathway altered only one of the two distinct events. MAPK/ERK pathway inhibition significantly reduced the HGF-induced increase in dendritic length, but had no effect on synapse density. In contrast, inhibition of the PI3K/Akt pathway reduced HGF-induced increases in synapse density, with no effect on dendritic length. The data reveal a key role for MET activation during the period of neocortical neuron growth and synaptogenesis, with distinct biological outcomes mediated via discrete MET-linked intracellular signaling pathways in the same neurons. © 2016 Wiley Periodicals, Inc. Develop Neurobiol 76: 1160-1181, 2016.

Localization of P450 Aromatase in The Brain of Adult Catfish Heteropneustes fossilis and Regional Distribution of Estradiol-17β and Testosterone: Gender and Seasonal Differences

P450 aromatase is the key enzyme that converts aromatizable androgens to estrogens. It is coded by the gene that exists in two forms: ovarian type and brain type. In the present study, we localized aromatase protein and gene (brain type) by immunocytochemical and in situ hybridization techniques, respectively, and the gene expression by RT-PCR. Aromatase immunoreactivity and transcript signals were observed in basophils of the proximal pars distalis of the pituitary, purported to be the gonadotrophs. The transcript signals were detected in the periventricular grey zone of optic tectum (PGZ), ventral telencephalic region, and radial glial cells lining the telencephalon, hypothalamus and olfactory bulb. Transcript levels of cyp19a1b showed sex, seasonal and regional differences. We measured testosterone (T) and estradiol-17β (E2) levels by specific ELISA kits. In the brain, T level is low in comparison to E2 level. Testosterone level is higher in postspawning phase and lower in spawning phase. The dimorphic expression varied with seasons, being higher in males in the preparatory and prespawning phases. E2 level is higher in female brain than in male brain especially in the preparatory and prespawning phases. E2 level is the highest in prespawning phase and lowest in postspawning phase. The steroids showed brain regional distribution with significant seasonal and dimorphic variations. Olfactory bulb has the highest T: E2 ratio in the resting, preparatory and prespawning phases in comparisons to other brain regions. All brain regions elicited a high level of E2, which showed dimorphic and seasonal variations, indicating high rate of aromatization. Differential levels of aromatase transcript, E2 and T in brain regions suggest a high level of neuroestrogen formation and E2 involvement in various neuroendocrine functions such as regulating spawning behaviour, plasticity, neurogenesis, etc.