Expressão de GABA e plasticidade do fenótipo neuroquímico e morfológico de células da Zona Subventricular pós-natal

The subventricular zone (SVZ) is proliferative epithelium that continuously gives rise to new neurons in postnatal and adult mammals. The neurons generated in the SVZ migrate through the rostral migratory stream (RMS) where they differentiate in GABAergic interneurons. A characteristic of these neuron precursors is that they start to express GABA while they are still in the SVZ. This fact can lead to the conclusion that at this time they are already commited to the GABAergic phenotype. However, to affirm this one has to show that the origin of GABA in these cells is the same as in mature neurons. One of the most important steps to define GABAergic commitment in neurons is to demonstrate the expression of glutamic acid decarboxylase (GAD), the synthetic enzyme for GABA in mature neurons. Here we show that SVZ cells display low levels of GAD immunocytochemistry and enzyme activity as compared with the olfactory bulb. We also show that these cells are able to synthesize GABA using an alternative source, the putrescine pathway. To test the importance of putrescine made GABA in vivo, we pharmacolgically inhibited putrescine synthesis through DFMO administration. We observed that this treatment lead to an increase of GAD expression in the SVZ and RMS. We also show here that SVZ cells can display phenotypic plasticity. Co-culturing SVZ explants and dorsal telencephalic slices, a spot of glutamatergic neurogenesis, we observed that a subpopulation of SVZ derived neurons differentiated into GABAergic neurons and another into glutamatergic pyramidal neurons. Our working hypothesis is that the putrescine pathway is a mechanism to synthesize GABA without commitment to the GABAergic phenotype. The release of putrescine derived GABA inhibits GAD expression leaving these neuroblasts in an undifferentiated state. The inhibition of putrescine synthesis caused an upregulation of GAD expression which would lead to GABAergic commitment. If we present these neuroblasts with different signals, as those present in the embryonic dorsal telencephalon, they would show plasticity in their phenotypic fate and differentiate into other neurochemical and morphological phenotypes, one of which is the glutamatergic pyramidal neuron.A zona subventricular (SVZ) é um sítio de contínua neurogênese em mamíferos pós-natos e adultos. Ao longo de toda a vida, os progenitores neuronais gerados destinam-se ao bulbo olfatório (BO) para onde migram através da via migratória rostral (RMS). Uma vez no BO, os novos neurônios se diferenciam em neurônios GABAérgicos que integram-se à circuitaria local. A expressão de GABA inicia ainda na zona germinativa. Essa expressão precoce poderia levar a hipótese de que estes progenitores já estariam comprometidos com o fenótipo GABAérgico. Porém, para demonstrar seu comprometimento GABAérgico, um dos passos necessários é mostrar que a descarboxilase do ácido glutâmico (GAD), a enzima que sintetiza GABA em neurônios maduros, está presente nestas células. Nesta tese mostramos que a expressão e atividade enzimática de GAD, são muito baixas na SVZ. Revelamos que o GABA presente em neurônios imaturos da SVZ provém de uma via de síntese alternativa, a via da putrescina. Para analisar a importância do GABA proveniente de putrescina para estas células realizamos a inibição farmacológica de sua síntese através da administração de DFMO. Observamos que o tratamento com DFMO regula positivamente a expressão de GAD na SVZ e RMS. Mostramos também que os neuroblastos da SVZ que expressam GABA são realmente plásticos quanto a sua escolha de fenótipo neuroquímico. Quando explantes de SVZ são co-cultivados com fatias de telencéfalo embrionário dorsal, sítio de geração de neurônios glutamatérgicos, uma subpopulação se diferencia em neurônios GABAérgicos e outra menor em glutamatérgicos. Sugerimos, portanto, que a via da putrescina permite que neurônios imaturos sintetizem GABA sem, no entanto, haver comprometimento com o fenótipo GABAérgico. Esta produção de GABA parece ser importante para a migração de neuroblastos da SVZ, embora não tenhamos tido sucesso em mostrar um papel na proliferação com o decréscimo na produção do precursor putrescina. Mostramos que a liberação de GABA de putrescina parece ter um papel em inibir a expressão de GAD nestes neuroblastos. Em contrapartida, a subregulação desta sinalização levaria ao comprometimento pelo fenótipo GABAérgico. Se mudarmos os sinais apresentados ás células da SVZ, como àqueles presentes na VZ do telencéfalo embrionário, pelo menos uma de suas subpopulações é capaz de mudar seu destino fenotípico, e diferenciar-se em neurônios glutamatérgicos piramidais

Nootropic effects of LSD: Behavioral, molecular and computational evidence

The therapeutic use of classical psychedelic substances such as d-lysergic acid diethylamide (LSD) surged in recent years. Studies in rodents suggest that these effects are produced by increased neural plasticity, including stimulation of the mTOR pathway, a key regulator of metabolism, plasticity, and aging. Could psychedelic-induced neural plasticity be harnessed to enhance cognition? Here we show that LSD treatment enhanced performance in a novel object recognition task in rats, and in a visuo-spatial memory task in humans. A proteomic analysis of human brain organoids showed that LSD affected metabolic pathways associated with neural plasticity, including mTOR. To gain insight into the relation of neural plasticity, aging and LSD-induced cognitive gains, we emulated the experiments in rats and humans with a neural network model of a cortico-hippocampal circuit. Using the baseline strength of plasticity as a proxy for age and assuming an increase in plasticity strength related to LSD dose, the simulations provided a good fit for the experimental data. Altogether, the results suggest that LSD has nootropic effects.This project was supported by the Beckley Foundation; Fundação de Amparo à Pesquisa do Estado do Rio de Janeiro, Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) – Finance Code 001, Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) (grants 308775/2015-5 and 408145/2016-1), São Paulo Research Foundation grants (2013/07699-0, 2014/10068-4, 2017/25588-1 and 2019/00098-7), intramural grants from D'Or Institute and Federal University of Rio Grande do Norte, and a Juan de la Cierva-Incorporación Scholarship (IJCI-2016-27864) from the Spanish Ministry of Science, Innovation and Universities, and a Newton International Fellowship from the Royal Society.Peer reviewe

Subventricular zone progenitors in time and space: generating neuronal diversity

The adult mammalian brain harbors a population of cells around their lateral ventricles capable of giving rise to new neurons throughout life. The so-called subventricular zone (SVZ) is a heterogeneous germinative niche in regard to the neuronal types it generates. SVZ progenitors give rise to different olfactory bulb (OB) interneuron types in accordance to their position along the ventricles. Here, I review data showing the difference between progenitors located along different parts of the SVZ axes and ages. I also discuss possible mechanisms for the origin of this diversity

NMDA Receptor Signaling Is Important for Neural Tube Formation and for Preventing Antiepileptic Drug-Induced Neural Tube Defects

Failure of neural tube closure leads to neural tube defects (NTDs), which can have serious neurological consequences or be lethal. Use of antiepileptic drugs (AEDs) during pregnancy increases the incidence of NTDs in offspring by unknown mechanisms. Here we show that during Xenopus laevis neural tube formation, neural plate cells exhibit spontaneous calcium dynamics that are partially mediated by glutamate signaling. We demonstrate that NMDA receptors are important for the formation of the neural tube and that the loss of their function induces an increase in neural plate cell proliferation and impairs neural cell migration, which result in NTDs. We present evidence that the AED valproic acid perturbs glutamate signaling, leading to NTDs that are rescued with varied efficacy by preventing DNA synthesis, activating NMDA receptors, or recruiting the NMDA receptor target ERK1/2. These findings may prompt mechanistic identification of AEDs that do not interfere with neural tube formation.SIGNIFICANCE STATEMENT Neural tube defects are one of the most common birth defects. Clinical investigations have determined that the use of antiepileptic drugs during pregnancy increases the incidence of these defects in the offspring by unknown mechanisms. This study discovers that glutamate signaling regulates neural plate cell proliferation and oriented migration and is necessary for neural tube formation. We demonstrate that the widely used antiepileptic drug valproic acid interferes with glutamate signaling and consequently induces neural tube defects, challenging the current hypotheses arguing that they are side effects of this antiepileptic drug that cause the increased incidence of these defects. Understanding the mechanisms of neurotransmitter signaling during neural tube formation may contribute to the identification and development of antiepileptic drugs that are safer during pregnancy

NMDA Receptor Signaling Is Important for Neural Tube Formation and for Preventing Antiepileptic Drug-Induced Neural Tube Defects

2018-10-30Failure of neural tube closure leads to neural tube defects (NTDs), which can have serious neurological consequences or be lethal. Use of antiepileptic drugs (AEDs) during pregnancy increases the incidence of NTDs in offspring by unknown mechanisms. Here we show that during Xenopus laevis neural tube formation, neural plate cells exhibit spontaneous calcium dynamics that are partially mediated by glutamate signaling. We demonstrate that N-methyl-D-aspartate (NMDA) receptors are important for the formation of the neural tube and loss of their function induces an increase in neural plate cell proliferation and impairs neural cell migration, which result in NTDs. We present evidence that the AED valproic acid perturbs glutamate signaling, leading to NTDs that are rescued with varied efficacy by preventing DNA synthesis, activating NMDA receptors, or recruiting the NMDA receptor target ERK1/2. These findings may prompt mechanistic identification of AEDs that do not interfere with neural tube formation

Radiological characterization of cerebral phenotype in newborn microcephaly cases from 2015 outbreak in Brazil

<p>Brazil is facing, since October of 2015, an outbreak of microcephalic fetuses. This outbreak is correlated with the beginning of circulation of Zika virus (ZIKV) in the country. Although it is clear that the size of the head is diminished in these fetuses, the brain phenotype associated with these malformations is unknown. We collected computed tomography images of the microcephaly cases from the region of Natal, Rio Grande do Norte, from September 2015 to February 2016. The CT acquisition was performed by a multidetector equipment, Philips Brilliance 64 (Philips Medical Systems; Cleveland, EUA), with tomographic section thickness of 1.0 mm, without administration of iodinated contrast. The protocol for this study was reviewed and approved by the Universidade Federal do Rio Grande do Norte Ethics Committee, certificate of approval CAAE 53111416.7.0000.5537. Role of funding source: The funding agencies had no participation in this work. The microcephalies derived from the current outbreak are associated with intracerebral calcifications, malformation of the ventricular system, migratory disorders in the telencephalon and, in a lower frequency, malformation of the cerebellum and brainstem. The characteristics here described are not usually found in other types of microcephaly. We suggest that this work can be used as a guideline to identify microcephaly cases associated to the current outbreak. </p