The changes of oligodendrocytes induced by anesthesia during brain development

Neural stem cell-based in vitro bioassay for the assessment of neurotoxic potential of water samples

Intensive agriculture activities, industrialization and growing numbers of wastewater treatment plants along river banks collectively contribute to the elevated levels of neurotoxic pollutants in natural water reservoirs across Europe. We established an in vitro bioassay based upon neural stem cells isolated from the subventricular zone of the postnatal mouse to evaluate the neurotoxic potential of raw wastewater, treated sewage effluent, groundwater and drinking water. The toxic potential of water samples was evaluated employing viability, proliferation, differentiation and migration assays. We found that raw wastewater could reduce the viability and proliferation of neural stem cells, and decreased the neuronal and astrocyte differentiation, neuronal neurite growth, astrocyte growth and cell migration. Treated sewage water also showed inhibitory effects on cell proliferation and migration. Our results indicated that relatively high concentrations of nitrogenous substances, pesticides, mercuric compounds, bisphenol-A, and phthalates, along with some other pollutants in raw wastewater and treated sewage water, might be the reason for the neuroinhibitory effects of these water samples. Our model successfully predicted the neurotoxicity of water samples collected from different sources and also revealed that the incomplete removal of contaminants from wastewater can be problematic for the developing nervous system. The presented data also provides strong evidence that more effective treatments should be used to minimize the contamination of water before release into major water bodies which may be considered as water reservoirs for human usage in the future.

Early Postnatal Exposure to Isoflurane Disrupts Oligodendrocyte Development and Myelin Formation in the Mouse Hippocampus

BACKGROUND

Early postnatal exposure to general anesthetics may interfere with brain development. We tested the hypothesis that isoflurane causes a lasting disruption in myelin development via actions on the mammalian target of rapamycin pathway.

METHODS

Mice were exposed to 1.5% isoflurane for 4 h at postnatal day 7. The mammalian target of rapamycin inhibitor, rapamycin, or the promyelination drug, clemastine, were administered on days 21 to 35. Mice underwent Y-maze and novel object position recognition tests (n = 12 per group) on days 56 to 62 or were euthanized for either immunohistochemistry (n = 8 per group) or Western blotting (n = 8 per group) at day 35 or were euthanized for electron microscopy at day 63.

RESULTS

Isoflurane exposure increased the percentage of phospho-S6-positive oligodendrocytes in fimbria of hippocampus from 22 ± 7% to 51 ± 6% (P < 0.0001). In Y-maze testing, isoflurane-exposed mice did not discriminate normally between old and novel arms, spending equal time in both (50 ± 5% old:50 ± 5% novel; P = 0.999), indicating impaired spatial learning. Treatment with clemastine restored discrimination, as evidenced by increased time spent in the novel arm (43 ± 6% old:57 ± 6% novel; P < 0.001), and rapamycin had a similar effect (44 ± 8% old:56 ± 8% novel; P < 0.001). Electron microscopy shows a reduction in myelin thickness as measured by an increase in g-ratio from 0.76 ± 0.06 for controls to 0.79 ± 0.06 for the isoflurane group (P < 0.001). Isoflurane exposure followed by rapamycin treatment resulted in a g-ratio (0.75 ± 0.05) that did not differ significantly from the control value (P = 0.426). Immunohistochemistry and Western blotting show that isoflurane acts on oligodendrocyte precursor cells to inhibit both proliferation and differentiation. DNA methylation and expression of a DNA methyl transferase 1 are reduced in oligodendrocyte precursor cells after isoflurane treatment. Effects of isoflurane on oligodendrocyte precursor cells were abolished by treatment with rapamycin.

CONCLUSIONS

Early postnatal exposure to isoflurane in mice causes lasting disruptions of oligodendrocyte development in the hippocampus via actions on the mammalian target of rapamycin pathway.

Neuroanesthesiology Update

We provide a synopsis of innovative research, recurring themes, and novel experimental findings pertinent to the care of neurosurgical patients and critically ill patients with neurological diseases. We cover the following broad topics: general neurosurgery, spine surgery, stroke, traumatic brain injury, monitoring, and anesthetic neurotoxicity.

A holistic approach to anesthesia-induced neurotoxicity and its implications for future mechanistic studies

The year 2016 marked the 15th anniversary since anesthesia-induced developmental neurotoxicity and its resulting cognitive dysfunction were first described. Since that time, multiple scientific studies have supported these original findings and investigated possible mechanisms behind anesthesia-induced neurotoxicity. This paper reviews the existing mechanistic literature on anesthesia-induced neurotoxicity in the context of a holistic approach that emphasizes the importance of both neuronal and non-neuronal cells during early postnatal development. Sections are divided into key stages in early neural development; apoptosis, neurogenesis, migration, differentiation, synaptogenesis, gliogenesis, myelination and blood brain barrier/cerebrovasculature. In addition, the authors combine the established literature in the field of anesthesia-induced neurotoxicity with literature from other related scientific fields to speculate on the potential role of non-neuronal cells and to generate new future hypotheses for understanding anesthetic toxicity and its application to the practice of pediatric anesthesia.