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Previous issue date: 2018-03-12 / Coordena??o de Aperfei?oamento de Pessoal de N?vel Superior - CAPES / Introduction: Child development in adverse environments and conditions, such as with the lack of economic resources or with parental care deprivation, is considered a major risk factor for neurological and psychiatric diseases. Altered cognitive processing is thought to mediate this relationship, however, the neurobiological mechanisms underlying the effects of early adverse experiences on cognition have not yet been fully revealed. Evidence indicates that dopaminergic neurotransmission and the corticotrophinergic system have important functions in the neurobiology of decision-making and risk assessment, which are cognitive processes associated with the functionality of the cerebral cortex. Similarly, working memory is another cognitive domain that underlies cortical activity, and some studies indicate that alterations in neuroimmunologic signaling may contribute to the decline of these higher order cognitive functions.
Objectives: To investigate the effects of impoverished housing conditions during early life on risk assessment processing and its associated cortical neurobiological and epigenetic mechanisms in C57BL/6 adolescent mice. In addition, we investigated the effects maternal care deprivation during early life, and the effects of systemic activation of the toll-type receptor (TLR)-3 on working memory performance, and its associated cortical neurobiological mechanisms in male BALB/c mice.
Methods: Two studies with rodent experimental models were proposed. The first study used a model of impoverished housing from the postnatal day (P) 2 to P9. During adolescence, risk assessment was investigated using a behavioral paradigm that explores the conflict between two biologically relevant stimuli: the motivation to consume a sweet and highly palatable solution while being threatened by predatory olfactory cues. The expression of dopaminergic (Drd1, Drd2) and corticotrophinergic (Cfr, Crfr1) genes in the medial prefrontal cortex (mPFC) were investigated by real-time PCR. The accumulation of histone marks (H3K9me3, H3R2me2s) were assessed at the promoter region of genes associated with behavioral outcomes. In addition, plasma corticosterone levels were assessed by ELISA. In the second study, a rodent model of maternal care deprivation from P2 to P15 was applied. During adolescence, animals were injected with a TLR-3 agonist, which is a viral receptor implicated with inflammatory signaling, and then tested in a working memory task. The expression of pro-inflammatory genes (Nfkb1, Il6 and Tnf-?) and the receptor itself (Tlr3), were performed in the mPFC by real-time PCR.
Results: In the first study, we found increased anxiety-like behavior, increased HPA axis response to stress and impaired RA processing in female adolescent mice, with no effect in males. These sex-specific effects were associated with increased Crfr1 mRNA expression in the medial prefrontal cortex (mPFC), which correlated with an increase in the occupancy of the histone mark H3R2me2s, a histone modification known to be involved in transcriptional activation and epigenetic priming, within the promoter of the Crfr1 gene. In the second study, we found that systemic administration of a TLR-3 agonist can modulate and exacerbate early life stress induced working memory impairments, and that higher gene expression levels of Nfkb1 in the mPFC was associated a lower working memory performance.
Conclusions: The findings of the first study indicated a deleterious effect of impoverished housing exposure on risk assessment processing in females, which could be detrimental for cognitive performance in potentially dangerous situations, and suggest that the epigenetic priming of the Crfr1 gene may represent a critical factor mediating the relationship between early life stress and altered cognitive processing later in life in females. Finally, the findings of the second study demonstrated that the systemic activation of TLR-3 can induce working memory impairments, revealing an important mediating role of the neuroinflammatory signalling in the cerebral cortex associated with the cognitive changes resulting from maternal care deprivation exposure during early in life. / Introdu??o: O desenvolvimento infantil em ambientes e condi??es adversas, como frente a escassez de recursos econ?micos ou de cuidado parental, ? considerado fator de risco para doen?as neurol?gicas e psiqui?tricas. Altera??es em processos cognitivos parecem mediar esta rela??o, contudo, os mecanismos neurobiol?gicos adjacentes aos efeitos de experi?ncias adversas precoces sobre a cogni??o ainda n?o foram completamente revelados. Evid?ncias apontam que a neurotransmiss?o dopamin?rgica e o sistema corticotrofin?rgico possuem importantes fun??es na neurobiologia da tomada de decis?o e avalia??o do risco, que s?o processos cognitivos associados a funcionalidade do c?rtex cerebral. Similarmente, a mem?ria de trabalho ? outro dom?nio cognitivo que envolve atividade cortical, e alguns estudos apontam que altera??es na sinaliza??o neuroimunol?gica podem contribuir para o decl?nio destas fun??es cognitivas superiores.
Objetivos: Investigar o efeito da exposi??o a moradia empobrecida na inf?ncia sobre o processamento cognitivo de avalia??o do risco e mecanismos neurobiol?gicos e epigen?ticos corticais associados em camundongos adolescentes da linhagem C57BL/6. Al?m disso, investigar o efeito da priva??o do cuidado materno na inf?ncia e da ativa??o sist?mica do receptor do tipo toll (TLR)-3 sobre a mem?ria de trabalho e mecanismos neurobiol?gicos corticais associados em camundongos machos adolescentes da linhagem BALB/c.
M?todos: Foram propostos dois estudos com modelos experimentais murinos. O primeiro estudo utilizou um modelo de moradia empobrecida do dia p?s-natal (P) 2 ao P9. Quando os animais encontravam-se no per?odo da adolesc?ncia, o processamento de avalia??o do risco foi investigado por uma tarefa que explora um conflito entre dois est?mulos biologicamente fundamentais na vida de um roedor, a motiva??o de consumir uma solu??o doce e altamente palat?vel (leite condensado) tendo que se expor a pistas olfativas de um predador natural, o coiote. Os n?veis de express?o de genes dopamin?rgicos (Drd1, Drd2) e corticotrofin?rgicos (Cfr, Crfr1) no c?rtex medial pr?-frontal (mPFC) foram investigados por PCR em tempo real. Os n?veis de altera??es de histonas (H3K9me3, H3R2me2s) foram avaliados na regi?o promotora de genes associados aos desfechos comportamentais. Adicionalmente, os n?veis de corticosterona plasm?tica foram avaliados por ELISA. No segundo estudo, o modelo de adversidade utilizado foi o de priva??o do cuidado materno do P2 ao P15. Similarmente, quando os animais encontravam-se no per?odo da adolesc?ncia, ocorreu a administra??o sist?mica de um agonista de TLR-3, um receptor viral relacionado a sinaliza??o inflamat?ria, e posteriormente os animais foram testados em uma tarefa de mem?ria de trabalho. Os n?veis de express?o g?nica de genes pr?-inflamat?rios (Nfkb1, Il6 e Tnf-?) e do pr?prio receptor (Tlr3), foram avaliados no mPFC por PCR em tempo real.
Resultados: no primeiro estudo, observou-se um aumento de comportamentos do tipo ansioso, maior responsividade do eixo Hipot?lamo-Pituit?ria-Adrenal (HPA) e uma diminui??o do processamento de avalia??o do risco nas f?meas expostas a moradia empobrecida, ao passo que n?o ocorreram altera??es nos animais machos. A diminui??o de avalia??o do risco foi associada a um aumento na express?o de Crfr1 no mPFC, o que se correlacionou com um aumento dos n?veis de H3R2me2s na regi?o promotora deste gene. No segundo estudo, observou-se que a ativa??o sist?mica de TLR-3 exacerbou os preju?zos de mem?ria de trabalho decorrentes da exposi??o a priva??o do cuidado materno, e este efeito correlacionou-se aos n?veis de express?o de Nfkb1 no mPFC.
Conclus?es: os achados do estudo 1 indicam um efeito delet?rio da exposi??o a moradia prec?ria na inf?ncia sobre o processamento de avalia??o do risco em f?meas, revelando um preju?zo espec?fico referente ao engajamento cognitivo frente a situa??es potencialmente perigosas. Al?m disso, evidenciou-se um efeito a n?vel epigen?tico de regula??o da express?o cortical de Crfr1, indicando um importante papel deste gene sobre a rela??o entre pobreza na inf?ncia e altera??es cognitivas em f?meas adolescentes. Por fim, os achados do estudo 2 demonstraram que a ativa??o sist?mica do TLR-3 pode exacerbar os preju?zos de mem?ria de trabalho induzidos pelo estresse precoce, revelando um papel mediador da sinaliza??o neuroinflamat?ria no c?rtex cerebral relacionada as altera??es cognitivas decorrentes da exposi??o a priva??o do cuidado materno.
| Identifer | oai:union.ndltd.org:IBICT/oai:tede2.pucrs.br:tede/8087 |
| Date | 12 March 2018 |
| Creators | Viola, Thiago Wendt |
| Contributors | Grassi-Oliveira, Rodrigo |
| Publisher | Pontif?cia Universidade Cat?lica do Rio Grande do Sul, Programa de P?s-Gradua??o em Medicina/Pediatria e Sa?de da Crian?a, PUCRS, Brasil, Escola de Medicina |
| Source Sets | IBICT Brazilian ETDs |
| Language | Portuguese |
| Detected Language | English |
| Type | info:eu-repo/semantics/publishedVersion, info:eu-repo/semantics/doctoralThesis |
| Format | application/pdf |
| Source | reponame:Biblioteca Digital de Teses e Dissertações da PUC_RS, instname:Pontifícia Universidade Católica do Rio Grande do Sul, instacron:PUC_RS |
| Rights | info:eu-repo/semantics/openAccess |
| Relation | 3098206005268432148, 500, 500, 500, 600, 600, -224747486637135387, -969369452308786627, -8067417953925345752, 2075167498588264571 |
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