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Early postnatal exposure to isoflurane causes cognitive deficits and disrupts development of newborn hippocampal neurons via activation of the mTOR pathway.

ABSTRACT: Clinical and preclinical studies indicate that early postnatal exposure to anesthetics can lead to lasting deficits in learning and other cognitive processes. The mechanism underlying this phenomenon has not been clarified and there is no treatment currently available. Recent evidence suggests that anesthetics might cause persistent deficits in cognitive function by disrupting key events in brain development. The hippocampus, a brain region that is critical for learning and memory, contains a large number of neurons that develop in the early postnatal period, which are thus vulnerable to perturbation by anesthetic exposure. Using an in vivo mouse model we demonstrate abnormal development of dendrite arbors and dendritic spines in newly generated dentate gyrus granule cell neurons of the hippocampus after a clinically relevant isoflurane anesthesia exposure conducted at an early postnatal age. Furthermore, we find that isoflurane causes a sustained increase in activity in the mechanistic target of rapamycin pathway, and that inhibition of this pathway with rapamycin not only reverses the observed changes in neuronal development, but also substantially improves performance on behavioral tasks of spatial learning and memory that are impaired by isoflurane exposure. We conclude that isoflurane disrupts the development of hippocampal neurons generated in the early postnatal period by activating a well-defined neurodevelopmental disease pathway and that this phenotype can be reversed by pharmacologic inhibition.

SUBMITTER: Kang E

PROVIDER: S-EPMC5500005 | biostudies-literature | 2017 Jul

REPOSITORIES: biostudies-literature

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Early postnatal exposure to isoflurane causes cognitive deficits and disrupts development of newborn hippocampal neurons via activation of the mTOR pathway.

Kang Eunchai E Jiang Danye D Ryu Yun Kyoung YK Lim Sanghee S Kwak Minhye M Gray Christy D CD Xu Michael M Choi Jun H JH Junn Sue S Kim Jieun J Xu Jing J Schaefer Michele M Johns Roger A RA Song Hongjun H Ming Guo-Li GL Mintz C David CD

PLoS biology 20170706 7

Clinical and preclinical studies indicate that early postnatal exposure to anesthetics can lead to lasting deficits in learning and other cognitive processes. The mechanism underlying this phenomenon has not been clarified and there is no treatment currently available. Recent evidence suggests that anesthetics might cause persistent deficits in cognitive function by disrupting key events in brain development. The hippocampus, a brain region that is critical for learning and memory, contains a la ...[more]

PMID: 28683067

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Project description:BACKGROUND:Epigenetic modulation may play a role in anesthesia related phenotypes, such as cognitive impairment or memory loss, especially with exposure to anesthetics in the vulnerable phase of brain development. While isoflurane anesthesia can evoke neuroinflammation and neuroapoptosis in young animals, we investigated in a permanent hippocampal cell line (HT22) and in primary hippocampal neurons in an a priori in vitro analysis, whether isoflurane exposure 1) evokes DNA methylation changes in genes involved in apoptosis and inflammation, and 2) results observed in a permanent hippocampal cell line are comparable to primary hippocampal neurons. In case of methylation changes in specific genes, (3) mRNA analysis was performed to assess possible effects on gene expression. METHODS:HT22 cells and primary mouse hippocampal neurons were exposed to 3% isoflurane for 4 h and DNA (each 6 single experiments) and RNA (3 single independent experiments) were extracted. Methylation analysis (EpiTect Methyl II PCR Array Systems, Qiagen) included the methylation status of 66 genes involved in apoptosis, cytokine production, inflammatory response, and autoimmunity. Quantitative Real-Time PCR was performed using the Quantitect SYBR Green Kit on a Step One Plus. RESULTS:Methylation status was markedly different between immortalized HT22 cells and cultured primary hippocampal neurons without isoflurane exposure. Of 66 genes investigated, 29 were methylated to a significantly greater degree in HT22 cells compared to primary hippocampal neurons. In cultured primary hippocampal neurons, in contrast, there was a greater methylation in several genes involved in inflammation, accompanied with significant downregulation of C-X-C motif chemokine 12 with isoflurane exposure (p?=?0.023). CONCLUSIONS:We demonstrate marked differences in gene methylation between HT22 cells and cultured primary hippocampal neurons without isoflurane exposure, with a greater methylation of several genes involved in inflammation upon isoflurane exposure and significant downregulation of Cxcl12 mRNA expression in primary hippocampal neurons. Accordingly, further investigations of anesthesia related DNA methylation should be performed with special consideration being given to the choice of cells targeted for such investigations.

Project description:BackgroundGiardiasis and zinc deficiency have been identified as serious health problems worldwide. Although Zn depletion is known to occur in giardiasis, no work has investigated whether changes occur in brain structures.MethodsThree groups of gerbils were used: control (1), orogastrically inoculated on day 3 after birth with trophozoites of two isolates of Giardia intestinalis (HGINV/WB) group (2 and 3). Estimates were made at five ages covering: establishment of infection, Giardia population growth, natural parasite clearance and a post-infection age. QuantiChrome zinc assay kit, cresyl violet staining and TUNEL technique were used.ResultsA significant decrease (p<0.01) in tissue zinc was observed and persisted after infection. Cytoarchitectural changes were observed in 75% of gerbils in the HGINV or WB groups. Ectopic pyramidal neurons were found in the cornus ammonis (CA1-CA3). At 60 and 90 days of age loss of lamination was clearly visible in CA1. In the dentate gyrus (DG), thinning of the dorsal lamina and abnormal thickening of the ventral lamina were observed from 30 days of age. In the cerebellum, we found an increase (p<0.01) in the thickness of the external granular layer (EGL) at 14 days of age that persisted until day 21 (C 3 ± 0.3 μm; HGINV 37 ± 5 μm; WB 28 ± 3 μm); Purkinje cell population estimation showed a significant decrease; a large number of apoptotic somas were observed scattered in the molecular layer; in 60 and 90 days old gerbils we found granular cell heterotopia and Purkinje cell ectopia. The pattern of apoptosis was different in the cerebellum and hippocampus of parasitized gerbils.ConclusionThe morphological changes found suggest that neuronal migration is affected by zinc depletion caused by giardiasis in early postnatal life; for the first time, the link between giardiasis-zinc depletion and damaged brain structures is shown. This damage may explain the psychomotor/cognitive delay associated with giardiasis. These findings are alarming. Alterations in zinc metabolism and signalling are known to be involved in many brain disorders, including autism.

Dataset Information

Early postnatal exposure to isoflurane causes cognitive deficits and disrupts development of newborn hippocampal neurons via activation of the mTOR pathway.

Publications

Early postnatal exposure to isoflurane causes cognitive deficits and disrupts development of newborn hippocampal neurons via activation of the mTOR pathway.

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