Memory impairments and increased GFAP expression in hippocampal astrocytes following hypercaloric diet in rats / Prejuízos de memória e expressão aumentada de GFAP em astrócitos hipocampais após dieta hipercalórica em ratos

ABSTRACT Objective: Hypothalamic inflammation and glial fibrillary acidic protein (GFAP) overexpression in astrocytes are well described in obese animals, as are some cognitive and memory deficits. As the hippocampus plays important roles in the consolidation of information, this investigation aimed to observe the memory function and the astrocyte expression of GFAP in the hippocampus of rats that received either a hypercaloric or a normocaloric diet. Methods: Adult male Wistar rats received a high-fat (cafeteria) or a standard diet for 60 days. On the 61st day, the rats were submitted to the novel object recognition (NOR) test at three and 24 hours after the first contact with objects, to assess short-term and long-term memory, respectively. Thereafter, the rats were euthanized and their brains were collected for GFAP immunohistochemical investigation in the hippocampus (CA1, CA2, CA3 areas) and hypothalamus (periventricular and arcuate nuclei). Astrocytic reactivity was assessed by morphometry. Different white adipose tissue depots and brown adipose tissue were weighed to calculate the adiposity index. Results: The hypercaloric diet increased body weight gain, adiposity index, white adipose tissue weight (epididymal, subcutaneous and retroperitoneal) and brown adipose tissue weight. Rats fed with the hypercaloric diet showed short-term and long-term memory impairments in the NOR test, as well as increased GFAP expression in astrocytes from all analyzed hypothalamic and hippocampal areas. Conclusion: This astrogliosis suggests that the neuroinflammatory response also occurs in the hippocampus and may be involved in the memory losses observed in obese/overweight animals.

RESUMO Objetivo: A inflamação hipotalâmica e a superexpressão da proteína glial fibrilar ácida (GFAP) em astrócitos são bem descritas em animais obesos, assim como déficits cognitivos e de memória. Como o hipocampo desempenha importante papel na consolidação de informações, esta investigação teve como objetivo observar a função da memória e a expressão astrocitária da GFAP no hipocampo de ratos que receberam dieta hipercalórica ou normocalórica. Métodos: Ratos Wistar machos adultos receberam dieta rica em gordura (cafeteria) ou dieta padrão por 60 dias. No 61º dia, os ratos foram submetidos ao teste de reconhecimento de objetos (NOR) 3 e 24 horas após o primeiro contato com os objetos, para avaliação da memória de curto e de longo prazo, respectivamente. Após, os ratos foram eutanasiados e os encéfalos coletados para pesquisa imuno-histoquímica da expressão astrocitária de GFAP no hipocampo (áreas CA1, CA2 e CA3) e no hipotálamo (núcleos periventricular e arqueado). A reatividade astrocitária foi avaliada por morfometria. Diferentes depósitos de tecido adiposo branco e marrom foram pesados para calcular o índice de adiposidade. Resultados: A dieta hipercalórica aumentou o ganho de peso corporal, o índice de adiposidade, o peso do tecido adiposo branco (epididimal, subcutâneo e retroperitoneal) e marrom. Ratos alimentados com dieta hipercalórica apresentaram prejuízos na memória de curto e longo prazo no teste NOR e aumento da expressão de GFAP em astrócitos de todas as áreas hipotalâmicas e hipocampais analisadas. Conclusão: Esta astrogliose sugere que a resposta neuroinflamatória também ocorre no hipocampo, podendo estar envolvida nas perdas de memória observadas em animais obesos/com sobrepeso.

Phytochemical analysis of hydroethanolic extract of Turnera diffusa Willd and evaluation of its effects on astrocyte cell death / Análise fitoquímica do extrato hidroetanólico de Turnera diffusa Willd e avaliação de seus efeitos na morte de astrócitos

ABSTRACT Objective To evaluate the phytochemical composition of hydroethanolic extracts from powdered aerial parts of Turnera diffusa Willd (Turneraceae; T. diffusa), as well as its toxicity in astrocytes. Methods Chemical analyses of hydroethanolic extract from powdered aerial parts ofT. diffusa were carried out using HPLC-DAD-ESI-MS/MS.In vitro assays using astrocytes culture were performed to evaluate cell death. Results Flavone-C, O-diglycosides, such as, luteolin-8-C-[6-deoxy-2-O-rhamnosyl]-xylo-hexos-3-uloside, apigenin-8-C-[6-deoxy-2-O-rhamnosyl]-xylo-hexos-3-uloside and apigenin-7-O-6”-p-coumaroylglucoside were the main compounds found in this hydroethanolic extract. Concentration time-effect demonstrated the toxicity of this extract at a concentration of 1,000µg/mL in astrocyte culture, after 6 and 24 hours of incubation. Conclusion In phytochemical analyses, important antioxidants (mainly flavonoids) were observed. T. diffusa extracts presented cytotoxic effect in high concentrations, leading to increased cell death in astrocyte culture.

RESUMO Objetivo Avaliar a composição fitoquímica do extrato hidroetanólico das partes aéreas de Turnera diffusa Willd (Turneraceae; T. diffusa) e sua toxicidade em astrócitos. Métodos Análises químicas do extrato hidroetanólico de partes aéreas de T. diffusa foram feitas por HPLC-DAD-ESI-MS/MS. Os ensaiosin vitro utilizaram culturas de astrócitos para avaliar morte celular. Resultados Flavonas-C, O-diglicosídeos, como, luteolina-8-C-[6-deoxi-2-O-raminosil]-xilo-hexos-3-ulosideo, apigenina-8-C-[6-deoxi-2-O-raminosil]-xilo-hexos-3-ulosideo e apigenina-7-O-6”-p-cumaroilglucosídeo foram os principais constituintes encontrados neste extrato hidroetanólico. Uma curva tempo-concentração demonstrou toxicidade desse extrato na concentração de 1.000µg/mL, na cultura de astrócitos após 6 e 24 horas de incubação. Conclusão Nas análises fitoquímicas, importantes antioxidantes, sobretudo flavonoides, foram observados. Extratos de T. diffusa apresentaram efeitos citotóxicos em altas concentrações, ocasionando aumento de morte celular em cultura de astrócitos.

Analysis of trophic responses in lesioned brain: focus on basic fibroblast growth factor mechanisms

The actions of fibroblast growth factors (FGFs), particularly the basic from (bFGF), have been described in a large number of cells and include mitogenicity, angiogenicity and wound repair. The present review discusses the presence of the bFGF protein and messenger RNA as well as the presence of the FGF receptor messenger RNA in the rodent brain by means of semiquantitative radioactive in situ hybridization in combination with immunohistochemistry. Chemical and mechanical injuries to the brain trigger a reduction in neurotransmitter synthesis and neuronal death which are accompanied by astroglial reaction. The altered synthesis of bFGF following brain lesions or stimulation was analyzed. Lesions of the central nervous system trigger bFGF gene expression by neurons and/or activated astrocytes, depending on the type of lesion and time post-manipulation. The changes in bFGF messenger RNA are frequently accompanied by a subsequente increase of bFGF immunoreactivity in astrocytes in the lesioned pathway. The reactive astrocytes and injured neurons synthesize increased amount of bFGF, which may act as a paracrine/autocrine factor, protecting neurons from death and also stimulating neuronal plasticity and tissue repair.

Localization of NMDA receptors in the cerebral cortex: a schematic overview

The fundamental role of N-methyl-D-aspartate (NMDA) receptors in many cortical functions has been firmly defined, as has its involvement in a number of neurological and psychiatric diseases. However, until recently very little was known about the anatomical localization od NMDA receptors in the cerebral cortex of mammals. The recent application of molecular biological techniques to the study of NMDA receptors has provided specific tolls which have greatly expanded our understading of the localization of NMDA receptors in the cerebral cortex. In particular, immunocytochemical studies on the distribution of cortical NMDA receptors have shown NMDA receptors are preferentially localized on dendritic spines, have disclosed an unknown fraction of presynaptic NMDA receptors on both excitatory and inhibitory axon terminals, and demonstrated that cortical astrocytes do express NMDA receptors. These studies suggest that the effects induced by the activation of NMDA receptors are not due solely to the opening of NMDA channels on neuronal postsynaptic membranes, as previously assumed, but that the activation of presynaptic and glial NMDA receptors may mediate part of these effects.

Control of the phosphorylation of the astrocyte marker glial fibrillary acidic protein (GFP) in the immature rat hippocampus by glutamate and calcium ions: possible key factor in astrocytic plasticity

The present review describes recent research on the regulation by glutamate and Ca2+ of the phosphorylation state of the intermediate filament protein of the astrocytic cytoskeleton, glial fibrillary acidic protein (GFAP), in immature hippocampal slices. The results of this research are discussed against a background of modern knowledge of the functional importance of astrocytes in the brain and of the structure and dynamic properties of intermediate filament proteins. Astrocytes are now recognized as partners with neurons in many aspects of brain function with important roles in neural plasticity. Site-specific phosphorylation of intermediate filament proteins, including GFAP, has been shown to regulate the dynamic equilibrium between the polymerized and depolymerized state of the filaments and to play a fundamental role in mitosis. Glutamate was found to increase the phosphorylation state of GFAP in hippocampal slices from rats in the post-natal age range of 12-16 days in a reaction that was dependent on external Ca2+. The lack of external Ca2+ in the absence of glutamate also increased GFAP phosphorylation to the same extent. These effects of glutamate and Ca2+ were absent in adult hippocampal slices, where the phosphorylation of GFAP was completely Ca2+ -dependent. Studies using specific agonists of glutamate receptors showed that the glutamate response was mediated by a G protein-linked group II metabotropic glutamate receptor (mGluR). Since group II mGluRs do not act by liberating Ca2+ from internal stores, it is proposed that activation of thereceptor by glutamate inhibits Ca2+ entry into the astrocytes andconsequently down-regulates a Ca2+-dependent dephosphorylationcascade regulating the phosphorylation state of GFAP. The functional significance of these results may be related to the narrow developmental window when the glutamate response is present. In the rat brain this window corresponds to the period of massive synaptogenesis during which astrocytes are known to proliferate. Possibly, glutamate liberated from developing synapses during this period may signal an increase in the phosphorylation state of GFAP and a consequent increase in the number of mitotic astrocytes.