Novel insights from quantitative imaging of the developing cerebellum

5-Bromo-2'-deoxyuridine labeling: historical perspectives, factors influencing the detection, toxicity, and its implications in the neurogenesis

The halopyrimidine 5-bromo-2'-deoxyuridine (BrdU) is an exogenous marker of DNA synthesis. Since the introduction of monoclonal antibodies against BrdU, an increasing number of methodologies have been used for the immunodetection of this synthesized bromine-tagged base analogue into replicating DNA. BrdU labeling is widely used for identifying neuron precursors and following their fate during the embryonic, perinatal, and adult neurogenesis in a variety of vertebrate species including birds, reptiles, and mammals. Due to BrdU toxicity, its incorporation into replicating DNA presents adverse consequences on the generation, survival, and settled patterns of cells. This may lead to false results and misinterpretation in the identification of proliferative neuroblasts. In this review, I will indicate the detrimental effects of this nucleoside during the development of the central nervous system, as well as the reliability of BrdU labeling to detect proliferating neuroblasts. Moreover, it will show factors influencing BrdU immunodetection and the contribution of this nucleoside to the study of prenatal, perinatal, and adult neurogenesis. Human adult neurogenesis will also be discussed. It is my hope that this review serves as a reference for those researchers who focused on detecting cells that are in the synthetic phase of the cell cycle.

Ultrasound of acquired posterior fossa abnormalities in the newborn

Neonatal brain sonography is part of routine clinical practice in neonatal intensive care units, but ultrasound imaging of the posterior fossa has gained increasing attention since the burden of perinatal acquired posterior fossa abnormalities and their impact on motor and cognitive neurodevelopmental outcome have been recognized. Although magnetic resonance imaging (MRI) is often superior, posterior fossa abnormalities can be suspected or detected by optimized cranial ultrasound (CUS) scans, which allow an early and bed-side diagnosis and monitoring through sequential scans over a long period of time. Different ultrasound appearances and injury patterns of posterior fossa abnormalities are described according to gestational age at birth and characteristics of the pathogenetic insult. The aim of this review article is to describe options to improve posterior fossa sequential CUS image quality, including the use of supplemental acoustic windows, to show standard views and normal ultrasound anatomy of the posterior fossa, and to describe the ultrasound characteristics of acquired posterior fossa lesions in preterm and term infants with effect on long-term outcome. The limitations and pitfalls of CUS and the role of MRI are discussed.

3D evaluation of fetal brain structures: reference values and growth curves

Background: The development of the fetal central nervous system is one of the most important fields of research in perinatology. Since the early 1980s, 3 D ultrasound has become one of the major research tools in obstetrics and gynecology.Objective: The aim of this study was to reconstruct thalamus, cerebellum and Cortex volumes of fetal brain and generate, for these volumes, growth curves related to gestational age.Methods: We enrolled 344 pregnant women. Using "Tomographic Ultrasound Imaging" (TUI), in all cases we obtained a satisfying 3 D acquisition of fetal brain. We reconstructed offline thalamus, cerebellum and cortex volumes using "Virtual Organ Computer-Aided AnaLysis" (VOCAL) or 4 D View (GE Healthcare).Results: Among the 344 fetuses examined, we obtained 314 thalamus volumes, 252 cerebellum volumes and 261 cortex volumes and we constructed the reference growth curves.Conclusion: Our study confirms the reliability of cerebral volumes evaluation using 3 D technology and how these cerebral structures grow through gestation.

Hydroxyurea Exposure and Development of the Cerebellar External Granular Layer: Effects on Granule Cell Precursors, Bergmann Glial and Microglial Cells

The current paper presents a histological analysis of the cell death in the cerebellar external granular layer (EGL) following the treatment with a single dose (2 mg/g) of hydroxyurea (HU). The rats were examined at postnatal days (P) 5, 10, and 15, and sacrificed at appropriate times ranging from 6 to 48 h after treatment administration. Studies were done in each cortical lobe (anterior, central, posterior, and inferior). The quantification of several parameters, such as density of 5-bromo-2'-deoxyuridine, TUNEL, vimentin, and tomato lectin-stained cells, revealed that HU compromises the viability of EGL cells. Our results indicate that P10 is a time of high vulnerability to injury. We also show here that the anterior and central lobes are the cortical regions most susceptible to the action of the HU. Additionally, our data also indicate that from 6 to 24 h after HU-exposure is a time-window of high sensibility to this agent. On the other hand, our ultrastructural analysis confirmed that HU administration produces the activation of apoptotic cellular events in the EGL, resulting in a substantial number of dying cells. Different stages of apoptosis can be observed in all cortical lobes at all investigated postnatal ages and survival times. Moreover, we observed that dying neuroblasts were covered by laminar processes of Bergmann glia, and that these unipolar astrocytes presented cytological features of phagocytes engulfing apoptotic bodies and cell debris. The electron microscopy study also revealed the participation of ameboid microglial cells in the phagocytosis of apoptotic cells in the regions of the EGL with extensive cell death.

Altered Resting-State Functional Activity in Patients With Autism Spectrum Disorder: A Quantitative Meta-Analysis

Background: There is accumulating evidence showing that patients with autism spectrum disorder (ASD) have obvious changes in resting-state functional brain activity. So far, there have been no meta-analyses of the resting-state brain activity alterations in patients with ASD. We attempted to explore the resting-state functional activity changes in patients with ASD, possibly providing a new perspective for investigating the pathophysiology of patients with ASD.

Methods: We screened relevant studies published before August 2017 in PubMed, Ovid, Web of Science, China National Knowledge Infrastructure (CNKI), and the Wan-fang database. Fifteen resting-state functional neural activity datasets (including 382 patients and 348 healthy controls) were included. Through the use of the effect-size signed differential mapping (ES-SDM) method, we carried out a meta-analysis of resting-state functional activity studies of patients with ASD.

Results: Compared with healthy controls, patients with ASD showed hyperactivity in the right supplementary motor area, middle frontal gyrus, inferior frontal gyrus, the left precentral gyrus, and the bilateral cerebellum hemispheric lobule (VIII/IX), and hypoactivity in the right middle temporal gyrus, superior temporal gyrus, and the left precuneus, posterior cingulate cortex, median cingulate cortex, and bilateral cerebellum (crus I).

Conclusion: This meta-analysis indicates that patients with ASD have significant and robust resting-state brain activity alterations in the language comprehension network, inferior-posterior cerebellum, default mode network (DMN), and cerebellar crus I. These brain regions may serve as specific regions of interest for further studies of ASD, which will allow us to further clarify the neurobiological mechanisms in patients with ASD.

Periconceptional maternal dairy-rich dietary pattern is associated with prenatal cerebellar growth

Background

Maternal nutrition during pregnancy has been related to intrauterine brain development and neurodevelopmental disabilities in adult life. We aim to investigate associations between periconceptional maternal dietary patterns and prenatal cerebellar growth from the first trimester onwards.

Materials and methods

126 women with singleton non-malformed pregnancies were enrolled before 8 weeks of gestation in the Rotterdam periconceptional cohort between 2013 and 2015. Periconceptional maternal dietary patterns were extracted from food frequency questionnaires and associated with blood biomarkers and micronutrient intakes. Serial two-dimensional and three-dimensional ultrasound scans were performed at 9, 11, 22, 26 and 32 weeks of gestation for transcerebellar diameter (TCD) measurement. Linear mixed models were estimated to investigate associations between periconceptional maternal dietary patterns and longitudinal TCD measurements as a function of gestational age.

Results

We performed a median of 4 scans per pregnancy, resulting in 570 total datasets. The success rate of TCD measurements was 87% (range 65–100%), depending on gestational age. The Mediterranean, Western, egg-rich and dairy-rich dietary patterns were extracted, explaining 37.2% of the overall variance of food intake in this population. The dairy-rich dietary pattern was positively associated with cerebellar growth trajectories (β = 0.02 (95% CI: 0.01; 0.03) √mm, p = 0.01). Maternal strong adherence to this dietary pattern increased TCD measurements by 0.8 standard deviation scores (SDs) compared to weak adherence, reflected in increased TCD estimates of 0.44 mm at 9 weeks (+6.8%), 0.88 mm at 22 weeks (+3.6%), and 1.17 mm at 32 weeks (+2.8%). No significant associations were detected for the Mediterranean, Western and egg-rich dietary patterns.

Conclusions

This study shows a positive association between periconceptional maternal adherence to a dairy-rich dietary pattern and human prenatal TCD measurements as a proxy of cerebellar growth. Next step is the investigation of the impact on neurodevelopmental outcomes in the offspring.

Effects of Hydroxyurea Exposure on the Rat Cerebellar Neuroepithelium: an Immunohistochemical and Electron Microscopic Study Along the Anteroposterior and Mediolateral Axes

We present a histological study of the cell death of cerebellar neuroepithelial neuroblasts following treatment with the cytotoxic agent hydroxyurea (HU) during the embryonic life. Pregnant rats were treated with a single dose of HU (300 mg/kg) at embryonic days 13, 14, or 15 of gestation, and their fetuses were studied from 5 to 35 h after treatment to elucidate the mechanisms of HU-induced fetotoxicity. Quantification of several parameters such as the density of pyknotic, mitotic, and PCNA-immunoreactive cells indicated that HU compromises the survival of the cerebellar neuroepithelium neuroblasts. On the other hand, our light and electron microscopic investigations during the course of prenatal development indicated that HU leads to two types of cell death: apoptosis and cells presenting cytoplasmic vacuolization, altered organelles, and a recognizable cell nucleus. Both modalities of cell death resulted in a substantial loss of cerebellar neuroepithelium cells. Current results suggest that HU exposure during gestation is toxic to the cerebellar neuroepithelium. Moreover, they allow to examine the mechanisms of HU-induced toxicity during the early development of the central nervous system. Our data also suggest that it is essential to avoid underestimating the adverse effects of HU when administered during early prenatal life.

Postnatal Migration of Cerebellar Interneurons

Due to its continuing development after birth, the cerebellum represents a unique model for studying the postnatal orchestration of interneuron migration. The combination of fluorescent labeling and ex/in vivo imaging revealed a cellular highway network within cerebellar cortical layers (the external granular layer, the molecular layer, the Purkinje cell layer, and the internal granular layer). During the first two postnatal weeks, saltatory movements, transient stop phases, cell-cell interaction/contact, and degradation of the extracellular matrix mark out the route of cerebellar interneurons, notably granule cells and basket/stellate cells, to their final location. In addition, cortical-layer specific regulatory factors such as neuropeptides (pituitary adenylate cyclase-activating polypeptide (PACAP), somatostatin) or proteins (tissue-type plasminogen activator (tPA), insulin growth factor-1 (IGF-1)) have been shown to inhibit or stimulate the migratory process of interneurons. These factors show further complexity because somatostatin, PACAP, or tPA have opposite or no effect on interneuron migration depending on which layer or cell type they act upon. External factors originating from environmental conditions (light stimuli, pollutants), nutrients or drug of abuse (alcohol) also alter normal cell migration, leading to cerebellar disorders.

Autism genes are selectively targeted by environmental pollutants including pesticides, heavy metals, bisphenol A, phthalates and many others in food, cosmetics or household products

The increasing incidence of autism suggests a major environmental influence. Epidemiology has implicated many candidates and genetics many susceptibility genes. Gene/environment interactions in autism were analysed using 206 autism susceptibility genes (ASG's) from the Autworks database to interrogate ∼1 million chemical/gene interactions in the comparative toxicogenomics database. Any bias towards ASG's was statistically determined for each chemical. Many suspect compounds identified in epidemiology, including tetrachlorodibenzodioxin, pesticides, particulate matter, benzo(a)pyrene, heavy metals, valproate, acetaminophen, SSRI's, cocaine, bisphenol A, phthalates, polyhalogenated biphenyls, flame retardants, diesel constituents, terbutaline and oxytocin, inter alia showed a significant degree of bias towards ASG's, as did relevant endogenous agents (retinoids, sex steroids, thyroxine, melatonin, folate, dopamine, serotonin). Numerous other suspected endocrine disruptors (over 100) selectively targeted ASG's including paraquat, atrazine and other pesticides not yet studied in autism and many compounds used in food, cosmetics or household products, including tretinoin, soy phytoestrogens, aspartame, titanium dioxide and sodium fluoride. Autism polymorphisms influence the sensitivity to some of these chemicals and these same genes play an important role in barrier function and control of respiratory cilia sweeping particulate matter from the airways. Pesticides, heavy metals and pollutants also disrupt barrier and/or ciliary function, which is regulated by sex steroids and by bitter/sweet taste receptors. Further epidemiological studies and neurodevelopmental and behavioural research is warranted to determine the relevance of large number of suspect candidates whose addition to the environment, household, food and cosmetics might be fuelling the autism epidemic in a gene-dependent manner.