Neurotoxic effects of hallucinogenic drugs 25H-NBOMe and 25H-NBOH in organotypic hippocampal cultures.

Introduction: NBOMes and NBOHs are psychoactive drugs derived from phenethylamines and have hallucinogenic effects due to their strong agonism to serotonin 5-HT2A receptors. Although cases of toxicity associated with the recreational use of substituted phenethylamines are frequently reported, there is a lack of information on the possible neurotoxic effects of NBOMe and NBOH in the brain hippocampus, a major neurogenesis region. Objectives: This study aimed at assessing the phenotypic and molecular effects of prolonged exposure of the hippocampus to the drugs 25H-NBOMe and 25H-NBOH. Methods: The ex vivo organotypic culture model of hippocampal slices (OHC) was used to investigate, by immunofluorescence and confocal microscopy, and transcriptome analyses, the mechanisms associated with the neurotoxicity of 25H-NBOMe and 25H-NBOH. Results: Reduction in the density of mature neurons in the OHCs occurred after two and seven days of exposure to 25H-NBOMe and 25H-NBOH, respectively. After the withdrawal of 25H-NBOMe, the density of mature neurons in the OHCs stabilized. In contrast, up to seven days after 25H-NBOH removal from the culture medium, progressive neuron loss was still observed in the OHCs. Interestingly, the exposure to 25H-NBOH induced progenitor cell differentiation, increasing the density of post-mitotic neurons in the OHCs. Corroborating these findings, the functional enrichment analysis of differentially expressed genes in the OHCs exposed to 25H-NBOH revealed the activation of WNT/Beta-catenin pathway components associated with neurogenesis. During and after the exposure to 25H-NBOMe or 25H-NBOH, gene expression patterns related to the activation of synaptic transmission and excitability of neurons were identified. Furthermore, activation of signaling pathways and biological processes related to addiction and oxidative stress and inhibition of the inflammatory response were observed after the period of drug exposure. Conclusion: 25H-NBOMe and 25H-NBOH disrupt the balance between neurogenesis and neuronal death in the hippocampus and, although chemically similar, have distinct neurotoxicity mechanisms.

Organotypic hippocampal culture model reveals differential responses to highly similar Zika virus isolates.

INTRODUCTION: Zika virus (ZIKV) caused an outbreak in Brazil, in 2015, being associated to microcephaly. ZIKV has a strong neurotropism leading to death of infected cells in different brain regions, including the hippocampus, a major site for neurogenesis. The neuronal populations of the brain are affected differently by ZIKV from Asian and African ancestral lineages. However, it remains to be investigated whether subtle variations in the ZIKV genome can impact hippocampus infection dynamics and host response. OBJECTIVE: This study evaluated how two Brazilian ZIKV isolates, PE243 and SPH2015, that differ in two specific missense amino acid substitutions, one in the NS1 protein and the other in the NS4A protein, affect the hippocampal phenotype and transcriptome. METHODS: Organotypic hippocampal cultures (OHC) from infant Wistar rats were infected with PE243 or SPH2015 and analyzed in time series using immunofluorescence, confocal microscopy, RNA-Seq and RT-qPCR. RESULTS: Unique patterns of infection and changes in neuronal density in the OHC were observed for PE243 and SPH2015 between 8 and 48 h post infection (p.i.). Phenotypic analysis of microglia indicated that SPH2015 has a greater capacity for immune evasion. Transcriptome analysis of OHC at 16 h p.i. disclosed 32 and 113 differentially expressed genes (DEGs) in response to infection with PE243 and SPH2015, respectively. Functional enrichment analysis suggested that infection with SPH2015 activates mostly astrocytes rather than microglia. PE243 downregulated biological process of proliferation of brain cells and upregulated those associated with neuron death, while SPH2015 downregulated processes related to neuronal development. Both isolates downregulated cognitive and behavioral development processes. Ten genes were similarly regulated by both isolates. They are putative biomarkers of early hippocampus response to ZIKV infection. At 5, 7, and 10 days p.i., neuronal density of infected OHC remained below controls, and mature neurons of infected OHC showed an increase in the epigenetic mark H3K4me3, which is associated to a transcriptionally active state. This feature is more prominent in response to SPH2015. CONCLUSION: Subtle genetic diversity of the ZIKV affects the dynamics of viral dissemination in the hippocampus and host response in the early stages of infection, which may lead to different long-term effects in neuronal population.

Neuroinflammation regulates the balance between hippocampal neuron death and neurogenesis in an ex vivo model of thiamine deficiency.

BACKGROUND: Thiamine (vitamin B1) is a cofactor for enzymes of central energy metabolism and its deficiency (TD) impairs oxidative phosphorylation, increases oxidative stress, and activates inflammatory processes that can lead to neurodegeneration. Wernicke-Korsakoff syndrome (WKS) is a consequence of chronic TD, which leads to extensive neuronal death, and is associated with neuropathological disorders, including cognitive deficits and amnesia. The hippocampus is one of the brain areas most affected by WKS. B1 replacement may not be enough to prevent the irreversible cognitive deficit associated with WKS. MATERIALS AND METHODS: An organotypic hippocampal slice culture (OHC) model was developed to investigate, using immunofluorescence and confocal microscopy and transcriptome analysis, the molecular mechanisms underlying the neurodegeneration associated with TD. The effect of anti-inflammatory pharmacological intervention with resveratrol (RSV) was also assessed in B1-deprived OHCs. RESULTS: In OHCs cultured without B1, neuronal density decayed after 5 days and, on the 7th day, the epigenetic markings H3K4me3 and H3K9me3 were altered in mature neurons likely favoring gene transcription. Between the 7th and the 14th day, a pulse of neurogenesis was observed followed by a further massive neuron loss. Transcriptome analysis at day nine disclosed 89 differentially expressed genes in response to B1 deprivation. Genes involved in tryptophan metabolism and lysine degradation KEGG pathways, and those with Gene Ontology (GO) annotations related to the organization of the extracellular matrix, cell adhesion, and positive regulation of synaptic transmission were upregulated. Several genes of the TNF and FoxO signaling pathways and with GO terms related to inflammation were inhibited in response to B1 deprivation. Nsd1, whose product methylates histone H3 lysine 36, was upregulated and the epigenetic marking H3K36me3, associated with negative regulation of neurogenesis, was increased in neurons. Treating B1-deprived OHCs with RSV promoted an earlier neurogenesis pulse. CONCLUSION: Neuroregeneration occurs in B1-deficient hippocampal tissue during a time window. This phenomenon depends on reducing neuroinflammation and, likely, on metabolic changes, allowing acetyl-CoA synthesis from amino acids to ensure energy supply via oxidative phosphorylation. Thus, neuroinflammation is implicated as a major regulator of hippocampal neurogenesis in TD opening a new search space for treating WKS.

Involvement of TRPV4 channels in Aß(40)-induced hippocampal cell death and astrocytic Ca(2+) signalling.

Previous studies suggested that amyloid ß (Aß)-induced disruption of astrocytic Ca(2+) signalling and oxidative stress play a major role in the progression towards neuronal and glial death in Alzheimer's disease. We have recently demonstrated that Ca(2+)-permeable TRPV4 channels are highly expressed in rat hippocampal astrocytes and are involved in oxidative stress-induced cell damage. The aim of this study was to test the hypothesis that TRPV4 channels also contribute to hippocampal damage evoked by Aß. Synthetic Aß40 evoked cell death in hippocampal slice cultures in a concentration (0-20µM) and time (12-48h) dependent manner, after cultures were preconditioned with sublethal concentration of buthionine sulfoximine (1.5µM) which enhanced endogenous ROS production. As demonstrated by propidium iodide fluorescence, damage was observed in the granule cell layer of the dentate gyrus and to a smaller degree in pyramidal neurons of the CA1-CA3 region, as well as in glia cells mainly at the edge of the slice. Immunocytochemistry revealed an altered pattern of TRPV4 and GFAP protein expression, and reactive astrogliosis surrounding pyramidal CA1-CA3 neurons. Neuronal and astrocytic damage was attenuated by the antioxidant Trolox, TRPV4 channel blockers Gd(3+) and ruthenium red (RR), and a specific inhibitor of the redox and Ca(2+)-sensitive phospholipase A2 enzyme (MAFP). In disassociated co-cultures of hippocampal neurons and astrocytes without BSO preconditioning, Aß40 evoked pronounced neuronal damage, enhanced the expression of TRPV4 and GFAP proteins (indicative of reactive astrogliosis), and increased intracellular free Ca(2+) concentration in astrocytes. The latter effect was attenuated by RR and in Ca(2+)-free media. These data show that Aß40 can activate astrocytic TRPV4 channels in the hippocampus, leading to neuronal and astrocytic damage in a Ca(2+) and oxidative stress-dependent manner.