Zika Virus Infection in the Developing Mouse Produces Dramatically Different Neuropathology Dependent on Viral Strain.

Zika virus (ZIKV) infection during pregnancy has been causally linked to a constellation of neurodevelopmental deformities in the fetus resulting in a disease termed congenital Zika syndrome (CZS). Here we detail how ZIKV infection produces extensive neuropathology in the developing mouse brain and spinal cord of both sexes. Surprisingly, neuropathology differs depending on viral strain with a French Polynesian isolate producing primarily excitotoxicity and a Brazilian isolate being almost exclusively apoptotic but occurring over a prolonged period that is more likely to produce severe hypoplasia. We also show exposure can produce a characteristic pattern of infection that mirrors neuropathology and ultimately results in gross morphological deformities strikingly similar to CZS. This research provides a valuable mouse model mirroring the clinical course of disease that can be used to test potential therapies to improve treatment and gain a better understanding of the disabilities associated with CZS.SIGNIFICANCE STATEMENT Zika virus (ZIKV) infection during pregnancy has been causally linked to a constellation of neurodevelopmental deformities in the fetus resulting in a disease termed congenital Zika syndrome. Despite its devastating effects, very little is known about how ZIKV infection produces fetal neuropathology. Here we detail the temporal progression of ZIKV infection in the mouse brain and spinal cord resulting in massive neurodegeneration of infected regions. We also report a ZIKV strain from a region of Brazil with high levels of microcephaly (abnormally small head circumference) produces particularly devastating neuropathology.

Mild hypothermia ameliorates anesthesia toxicity in the neonatal macaque brain.

Sedatives and anesthetics can injure the developing brain. They cause apoptosis of neurons and oligodendrocytes, impair synaptic plasticity, inhibit neurogenesis and trigger long-term neurocognitive deficits. The projected vulnerable period in humans extends from the third trimester of pregnancy to the third year of life. Despite all concerns, there is no ethically and medically acceptable alternative to the use of sedatives and anesthetics for surgeries and painful interventions. Development of measures that prevent injury while allowing the medications to exert their desired actions has enormous translational value. Here we investigated protective potential of hypothermia against histological toxicity of the anesthetic sevoflurane in the developing nonhuman primate brain. Neonatal rhesus monkeys underwent sevoflurane anesthesia over 5 h. Body temperature was regulated in the normothermic (>36.5 °C), mild hypothermic (35-36.5 °C) and moderately hypothermic (<35 °C) range. Animals were euthanized at 8 h and brains examined immunohistochemically (activated caspase 3) and stereologically to quantify apoptotic neuronal and oligodendroglial death. Sevoflurane anesthesia was well tolerated at all temperatures, with oxygen saturations, end tidal CO2 and blood gases remaining at optimal levels. Compared to controls, sevoflurane exposed brains displayed significant apoptosis in gray and white matter affecting neurons and oligodendrocytes. Mild hypothermia (35-36.5 °C) conferred significant protection from apoptotic brain injury, whereas moderate hypothermia (<35 °C) did not. Hypothermia ameliorates anesthesia-induced apoptosis in the neonatal primate brain within a narrow temperature window (35-36.5 °C). Protection is lost at temperatures below 35 °C. Given the mild degree of cooling needed to achieve significant brain protection, application of our findings to humans should be explored further.

Quantitative ultrasound and apoptotic death in the neonatal primate brain.

Apoptosis is triggered in the developing mammalian brain by sedative, anesthetic or antiepileptic drugs during late gestation and early life. Whether human children are vulnerable to this toxicity mechanism remains unknown, as there are no imaging techniques to capture it. Apoptosis is characterized by distinct structural features, which affect the way damaged tissue scatters ultrasound compared to healthy tissue. We evaluated whether apoptosis, triggered by the anesthetic sevoflurane in the brains of neonatal rhesus macaques, can be detected using quantitative ultrasound (QUS). Neonatal (n = 15) rhesus macaques underwent 5 h of sevoflurane anesthesia. QUS images were obtained through the sagittal suture at 0.5 and 6 h. Brains were collected at 8 h and examined immunohistochemically to analyze apoptotic neuronal and oligodendroglial death. Significant apoptosis was detected in white and gray matter throughout the brain, including the thalamus. We measured a change in the effective scatterer size (ESS), a QUS biomarker derived from ultrasound echo signals obtained with clinical scanners, after sevoflurane-anesthesia in the thalamus. Although initial inclusion of all measurements did not reveal a significant correlation, when outliers were excluded, the change in the ESS between the pre- and post-anesthesia measurements correlated strongly and proportionally with the severity of apoptotic death. We report for the first time in vivo changes in QUS parameters, which may reflect severity of apoptosis in the brains of infant nonhuman primates. These findings suggest that QUS may enable in vivo studies of apoptosis in the brains of human infants following exposure to anesthetics, antiepileptics and other brain injury mechanisms.

Hedgehog regulates cerebellar progenitor cell and medulloblastoma apoptosis.

The external granule layer (EGL) is a proliferative region that produces over 90% of the neurons in the cerebellum but can also malignantly transform into a cerebellar tumor called the medulloblastoma (the most common malignant brain tumor in children). Current dogma considers Hedgehog stimulation a potent proliferative signal for EGL neural progenitor cells (NPCs) and medulloblastomas. However, the Hedgehog pathway also acts as a survival signal in the neural tube where it regulates dorsoventral patterning by controlling NPC apoptosis. Here we show that Hedgehog stimulation is also a potent survival signal in the EGL and medulloblastomas that produces a massive apoptotic response within hours of signal loss in mice. This toxicity can be produced by numerous Hedgehog antagonists (vismodegib, cyclopamine, and jervine) and is Bax/Bak dependent but p53 independent. Finally, since glucocorticoids can also induce EGL and medulloblastoma apoptosis, we show that Hedgehog's effects on apoptosis can occur independent of glucocorticoid stimulation. This effect may play a major role in cerebellar development by directing where EGL proliferation occurs thereby morphologically sculpting growth. It may also be a previously unknown major therapeutic effect of Hedgehog antagonists during medulloblastoma therapy. Results are discussed in terms of their implications for both cerebellar development and medulloblastoma treatment.

Propylene glycol produces excessive apoptosis in the developing mouse brain, alone and in combination with phenobarbital.

INTRODUCTION: Propylene glycol (PG) is a common solvent used in medical preparations. It is generally recognized as safe at regulated concentrations; however, its apoptotic potential is unknown. RESULTS: PG triggered widespread apoptotic neurodegeneration with the greatest damage at postnatal day 7 (P7). Significant apoptosis was observed at doses as low as 2 ml/kg. These findings have implications for the safety of drug preparations used in pediatric medicine. The anticonvulsant phenobarbital (PB), which alone produces apoptosis in the immature central nervous system (CNS) is prepared in 68% PG and 10% ethanol (EtOH). We assessed whether PG contributes to the neurotoxic potential of PB. The agents (both at subtoxic doses) produce significantly more apoptosis when used in combination. DISCUSSION: In conclusion, finding an alternative non-apoptotic solvent that can be used as a substitute for PG may be beneficial to patients. METHODS: C57BL/6 mice (P4-30) were exposed to PG to examine whether PG could produce apoptosis in the developing CNS.

Glucocorticoid receptor stimulation and the regulation of neonatal cerebellar neural progenitor cell apoptosis.

Glucocorticoids are used to treat respiratory dysfunction associated with premature birth but have been shown to cause neurodevelopmental deficits when used therapeutically. Recently, we established that acute glucocorticoid exposure at clinically relevant doses produces neural progenitor cell apoptosis in the external granule layer of the developing mouse cerebellum and permanent decreases in the number of cerebellar neurons. As the cerebellum naturally matures and neurogenesis is no longer needed, the external granule layer decreases proliferation and permanently disappears during the second week of life. At this same time, corticosterone (the endogenous rodent glucocorticoid) release increases and a glucocorticoid-metabolizing enzyme that protects the external granule layer against glucocorticoid receptor stimulation (11ß-Hydroxysteroid-Dehydrogenase-Type 2; HSD2) naturally disappears. Here we show that HSD2 inhibition and raising corticosterone to adult physiological levels both can independently increase neural progenitor cell apoptosis in the neonatal mouse. Conversely, glucocorticoid receptor antagonism decreases natural physiological apoptosis in this same progenitor cell population suggesting that endogenous glucocorticoid stimulation may regulate apoptosis in the external granule layer. We also found that glucocorticoids which HSD2 can effectively metabolize generate less external granule layer apoptosis than glucocorticoids this enzyme is ineffective at breaking down. This finding may explain why glucocorticoids that this enzyme can metabolize are clinically effective at treating respiratory dysfunction yet seem to produce no neurodevelopmental deficits. Finally, we demonstrate that both acute and chronic glucocorticoid exposures produce external granule layer apoptosis but without appropriate control groups this effect becomes masked. These results are discussed in terms of their implications for glucocorticoid therapy and neurodevelopment during the perinatal period.

Lithium protects against glucocorticoid induced neural progenitor cell apoptosis in the developing cerebellum.

Respiratory dysfunction is one of the most common causes of death associated with premature birth (Barton et al., 1999). In the United States, 7-10% of pregnant women receive antenatal glucocorticoid (GC) therapy (Matthews et al., 2004), while approximately 19% of very low birth weight infants receive postnatal GC therapy (Jobe, 2009). Clinical research suggests that GC treatment causes permanent neuromotor and cognitive deficits (Yeh et al., 2004) and stunts cerebellar growth (Parikh et al., 2007; Tam et al., 2011). We previously reported that GC-mediated neural progenitor cell (NPC) apoptosis may be responsible for cerebellar neuropathology (Maloney et al., 2011; Noguchi et al., 2008, 2011). The goal of the current study was to determine whether lithium protects NPCs from GC neuroapoptosis in vivo and in vitro. Given that it protects against a range of brain insults, we hypothesized that lithium would significantly attenuate GC induced NPC toxicity. We report that acute lithium pretreatment provides potent, cell-intrinsic neuroprotection against GC induced NPC toxicity in vivo and in vitro.