Akhmediev Breathers and Peregrine Solitary Waves in a Quadratic Medium

We investigate the formation of optical localized nonlinear structures, evolving upon a non-zero background plane wave, in a dispersive quadratic medium. We show the existence of quadratic Akhmediev breathers and Peregrine solitary waves, in the regime of cascading second-harmonic generation. This finding opens a novel path for the excitation of extreme rogue waves and for the description of modulation instability in quadratic nonlinear optics

Resonant radiation shed by dispersive shock waves

We show that dispersive shock waves resulting from the nonlinearity overbalancing a weak leading-order dispersion can emit resonant radiation owing to higher-order dispersive contributions. We analyze such phenomenon for the defocusing nonlinear Schroedinger equation, giving criteria for calculating the radiated frequency based on the estimate of the shock velocity, revealing also a diversity of possible scenarios depending on the order and magnitude of the dispersive corrections

Parametric Frequency Conversion of Short Optical Pulses Controlled by a CW Background

We predict that parametric sum-frequency generation of an ultra-short pulse may result from the mixing of an ultra-short optical pulse with a quasi-continuous wave control. We analytically show that the intensity, time duration and group velocity of the generated idler pulse may be controlled in a stable manner by adjusting the intensity level of the background pump

Brain aminergic systems and autism-associated risk factors in zebrafish

Brain amines are neurotransmitters that modulate important functions in the central nervous system, including behavior and brain development. Several brain disorders are characterized by impairments in aminergic systems, including autism spectrum disorder (ASD). ASD is characterized by impaired social behavior, difficulty in communication and stereotypies. The etiology of ASD is poorly understood, but both environmental and genetic risk factors are known to play a role on it. Valproic acid (VPA), a drug commonly used to treat bipolar disorder, and mutations in the monoamine oxidase a gene are both environmental and genetic risk factors. Zebrafish shares relevant neurochemical aspects with humans and display a wide range of behaviors, which contribute to its appreciation as a model organism in neuroscience. Thus, this study characterized the phenotypes of zebrafish pharmacologically and genetically challenged with ASD risk factors. Additionally, functional aspects of aminergic neurotransmission in the zebrafish brain were studied through the characterization of animals that lacked vesicular monoamine transporter 2 (vmat2, also known as slc18a2) and monoamine oxidase (mao), relevant genes for aminergic vesicular transport and metabolism, respectively. In the first publication of this thesis, larval zebrafish embryonically exposed to VPA showed a reduction in the number of histaminergic neurons and in the levels of histamine when compared to control animals. The histaminergic system of VPA-exposed larvae was also affected by a downregulation of histidine decarboxylase and histamine receptors. Some of these abnormalities persisted until adulthood along with impaired social behavior. This study brings more attention to a possible involvement of the histaminergic system in the outcomes related to ASD. In the second article, the levels of dopamine, noradrenaline, serotonin and histamine of vmat2 mutants were decreased, whereas levels of dopamine and serotonin metabolites were increased, indicating elevated amine turnover. There were also fewer aminergic immunoreactive cells. Further, in mutants notch1a and pax2a were downregulated in brain proliferative zones. This mutant line may be used in the investigation of how amines transport affects brain development and function, and for use in high-throughput and drug screening. In the third article, mao−/− larvae showed a hyperserotonergic phenotype characterized by extracellular serotonin immunoreactivity that was associated with damage in aminergic systems. They also showed weaker responses to visual and acoustic stimuli, abnormal expression of developmental markers and died within 20 days post-fertilization. mao+/- fish were viable and demonstrated impaired social interactions compared with adult mao+/+ siblings. These mutants could be used in investigations aiming to assess the roles of MAOA/B and amines during brain development and to study the behavioral outcomes associated with MAOA/B deficiency. Collectively, the results of the present thesis support zebrafish as a tool to investigate mechanisms underlying ASD. Additionally, it presented two new models to study important aspects of aminergic neurotransmission in zebrafish and its role in brain function and behavior.Aivojen amiinit ovat välittäjäaineita, jotka säätelevät tärkeitä keskushermoston toimintoja, mukaan lukien käyttäytyminen ja aivojen kehitys. Useille aivosairauksille, mukaan lukien autismikirjon häiriöt (ASD), on ominaista aminergisten järjestelmien poikkeavuus. Autismikirjon häiriölle on tyypillistä heikentynyt sosiaalinen käyttäytyminen, kommunikaatiovaikeudet ja stereotypiat. Autismin etiologiaa ymmärretään huonosti, mutta sekä ympäristön että geneettisten riskitekijöiden tiedetään vaikuttavan siihen. Valproiinihappo, yleisesti kaksisuuntaisen mielialahäiriön hoitoon käytetty lääke, ja mutaatiot monoamiinioksidaasin geenissä ovat ympäristöllisiä ja geneettisiä riskitekijöitä. Eläinmallit ovat hyödyllisiä työkaluja, joiden avulla voidaan ymmärtää paremmin mekanismeja ja muutoksia liittyvät aminergisiin hermoston kehityshäiriöihin. Niillä voidaan testata uusia lääkkeitä, jotka voivat vaikuttaa näihin tiloihin liittyviin käyttäytymispoikkeavuuksiin. Seeprakalalla on samoja neurokemiallisia ja toiminnallisia ominaisuuksia ihmisten ja muiden nisäkkäiden kanssa. Nämä ja monet käyttäytymistestit mahdollistavat sen käyttämisen neurotieteen malliorganismina. Tämä tutkimus luonnehti seeprakalan fenotyyppejä, jotka oli farmakologisesti ja geneettisesti altistettu ASD-riskitekijöille. Lisäksi seeprakalan aivojen aminergisen neurotransmission toiminnallisia näkökohtia tutkittiin karakterisoimalla eläimiä, joilta puuttui vesikulaarinen monoamiinikuljettaja 2 (vmat2, joka tunnetaan myös nimellä slc18a2) ja monoamiinioksidaasi (mao), aminergisen rakkulakuljetuksen ja aineenvaihdunnan kannalta oleelliset geenit. Tämän opinnäytetyön ensimmäisessä julkaisussa VPA:lle altistetut seeprakalan toukat osoittivat histaminergisten hermosolujen lukumäärän ja histamiinitasojen pienenemistä verrokkieläimiin verrattuna. VPA:lle altistuneiden toukkien histaminergiseen järjestelmään vaikutti myös histidiinidekarboksylaasin ja histamiinireseptorien väheneminen. Jotkut näistä poikkeavuuksista säilyivät aikuisikään asti heikentyneen sosiaalisen käyttäytymisen ohella. Tämä tutkimus osoittaa histaminergisen järjestelmän mahdollisen osuuden ASD:n mekanismeihin. Toisessa artikkelissa vmat2-mutanttien dopamiinin, noradrenaliinin, serotoniinin ja histamiinin tasot laskivat, kun taas dopamiinin ja serotoniinin metaboliittien tasot nousivat verrokkikaloihin verrattuna, mikä viittaa kohonneeseen amiinien vaihduntaan. Aminergisia hermosoluja oli myös vähemmän. Lisäksi mutanteissa notch1a- ja pax2a-geenien ilmentyminen väheni aivojen proliferatiivisilla alueilla. Tämä mutanttikalalinja voi olla hyödyllinen amiinien osuuden selvittämisessä aivojen kehityksessä, ja sitä voidaan käyttää lääkeaineiden seulonnassa. Kolmannessa artikkelissa mao-mutanttikaloilla todettiin hyperserotonerginen fenotyyppi, jota luonnehti solujen ulkopuolinen serotoniini-immunoreaktiviteetti, joka liittyi aminergisten järjestelmien vaurioon. Mutanttikalojen reaktiot näkö- ja kuuloärsykkeille olivat heikentyneet, kehitystä kuvaavien geenien ilmentyminen oli poikkeava, ja kalat menehtyivät noin 20 päivän ikäisinä. Heterotsygootit säilyivät hyväkuntoisina ja niillä oli normaalista poikkeava sosiaalinen käyttäytyminen verrattuna villityypin kaloihin. Tämä mutanttikalalinja sopii amiinien merkityksen selvittämiseen aivojen kehítyksessä ja mao-vajavuuden merkityksen selvittämiseen käyttäytymisessä. Yhteenvetona tulokset tukevat seeprakalan käyttämistä autismikirjoin häiriöiden mekanismien tutkimuksessa. Tutkimuksessa esitettiin kaksi uutta mallia keskeisten aminergisen hermovälityksen mekanismien tutkimiseksi seeprakalalla ja sen merkityksen selvittämiseksi aivojen toiminnassa ja käyttäytymisessä

Extreme high-intensity and ultrabroadband interactions in anisotropic β-BaB_2O_4 crystals

International audienceWe derive unidirectional pulse propagation equations to describe extreme high-intensity and ultra-broadband optical interactions in uniaxial crystals, showing both second-and third-order nonlinear optical susceptivities. We focus our attention on the anisotropic nature of the quadratic and cubic nonlinear response of β−BaB 2 O 4 (BBO) crystals. Two nonlinearly coupled first order (in the propagation coordinate) equations describe the dynamics and interactions of the ordinary and extraordinary field polarizations, and are valid for arbitrarily wide pulse bandwidth. We exploit this model to predict harmonic and supercontinuum generation in BBO crystals under strong and competing influence of quadratic and cubic susceptivities

Nonlinear envelope equation for broadband optical pulses in quadratic media

We derive a nonlinear envelope equation to describe the propagation of broadband optical pulses in second order nonlinear materials. The equation is first order in the propagation coordinate and is valid for arbitrarily wide pulse bandwidth. Our approach goes beyond the usual coupled wave description of $\chi^{(2)}$ phenomena and provides an accurate modelling of the evolution of ultra-broadband pulses also when the separation into different coupled frequency components is not possible or not profitable

Optical Kerr spatiotemporal dark extreme waves

We study the existence and propagation of multidimensional dark non-diffractive and non-dispersive spatiotemporal optical wave-packets in nonlinear Kerr media. We report analytically and confirm numerically the properties of spatiotemporal dark lines, X solitary waves and lump solutions of the (2 + 1)D nonlinear Schrodinger equation (NLSE). Dark lines, X waves and lumps represent holes of light on a continuous wave background. These solitary waves are derived by exploiting the connection between the (2 + 1)D NLSE and a well-known equation of hydrodynamics, namely the (2+1)D Kadomtsev-Petviashvili (KP) equation. This finding opens a novel path for the excitation and control of spatiotemporal optical solitary and rogue waves, of hydrodynamic nature.Comment: arXiv admin note: text overlap with arXiv:1608.08771, arXiv:1602.0846

Abnormal brain development of monoamine oxidase mutant zebrafish and impaired social interaction of heterozygous fish

Monoamine oxidase (MAO) deficiency and imbalanced levels of brain monoamines have been associated with developmental delay, neuropsychiatric disorders and aggressive behavior. Animal models are valuable tools to gain mechanistic insight into outcomes associated with MAO deficiency. Here, we report a novel genetic model to study the effects of mao loss of function in zebrafish. Quantitative PCR, in situ hybridization and immunocytochemistry were used to study neurotransmitter systems and expression of relevant genes for brain development in zebrafish mao mutants. Larval and adult fish behavior was evaluated through different tests. Stronger serotonin immunoreactivity was detected in mao(+/-) and mao(-/-) larvae compared with their mao(+/+) siblings. mao(-/-) larvae were hypoactive, and presented decreased reactions to visual and acoustic stimuli. They also had impaired histaminergic and dopaminergic systems, abnormal expression of developmental markers and died within 20 days post-fertilization. mao(+/-) fish were viable, grew until adulthood, and demonstrated anxiety-like behavior and impaired social interactions compared with adult mao(+/+) siblings. Our results indicate that mao(-/-) and mao(+/-) mutants could be promising tools to study the roles of MAO in brain development and behavior.Peer reviewe