BDNF and TrkB in the preterm and near-term ovine fetal brain and the effect of intermittent umbilical cord occlusion

Nutrition and Brain Development

All nutrients are essential for brain development, but pre-clinical and clinical studies have revealed sensitive periods of brain development during which key nutrients are critical. An understanding of these nutrient-specific sensitive periods and the accompanying brain regions or processes that are developing can guide effective nutrition interventions as well as the choice of meaningful circuit-specific neurobehavioral tests to best determine outcome. For several nutrients including protein, iron, iodine, and choline, pre-clinical and clinical studies align to identify the same sensitive periods, while for other nutrients, such as long-chain polyunsaturated fatty acids, zinc, and vitamin D, pre-clinical models demonstrate benefit which is not consistently shown in clinical studies. This discordance of pre-clinical and clinical results is potentially due to key differences in the timing, dose, and/or duration of the nutritional intervention as well as the pre-existing nutritional status of the target population. In general, however, the optimal window of success for nutritional intervention to best support brain development is in late fetal and early postnatal life. Lack of essential nutrients during these times can lead to long-lasting dysfunction and significant loss of developmental potential.

Morphological Characterization of the Developing Greater Cane Rat (Thryonomys swinderianus) Brain

Developmental mode along the altricial-precocial spectrum is well known to be influenced by brain development and maturation. The greater cane rat (GCR) is an indigenous precocial African rodent with uncommon phenotypes and life traits. This study was therefore designed to characterize and describe distinctive external developmental features in the prenatal GCR brain across the entire gestational length using the emergence and differentiation of external features of the brain vesicles. Four gross morphometric brain parameters (weight, length, width, and height) were evaluated and expressed as mean ± SEM. Relationship between all brain morphometrics and gestation length were analyzed using one-way ANOVA and linear regression. Developmental milestones in the prenatal GCR were then compared with closely related precocial mammals. The earliest time point with gross observable features in the prenatal GCR brain was at gestation day (GD) 60. The period with the most remarkable gross developmental features was noted between GD80 and GD100. Some of these gross features include differentiation of the cerebellar plate into vermis and lateral lobes, emergence of the piriform lobes, mammillary bodies, colliculi bodies, cerebral peduncles, and primordial pons. By GD130, most gross topographic neural features were already established. Cerebellar lobation and patterning at GD130 were the last recognizable gross developmental features noticed in the prenatal GCR brain. This coincided with the time of first eye opening in the GCR fetus. The developmental pattern observed in the prenatal GCR brain is similar to those noted in precocial rodent like the guinea pig. However, the onset of these milestones was delayed, and their duration was relatively shorter in the GCR. This study provides a frame of baseline reference of morphological brain features in the GCR embryos and fetuses that will be useful for fetal age estimation, for home grown neurodevelopmental and eco-toxicological studies, as this rodent is being proposed as a research model.

Astragaloside IV improves neurobehavior and promotes hippocampal neurogenesis in MCAO rats though BDNF-TrkB signaling pathway

Astragaloside IV (AST) as the main active ingredient of Astragalus membranaceus. Clinical and laboratory-based studies have demonstrated the effects of AST on cerebral protection and angiogenesis after ischemia stroke. In addition, several reports investigated the effect of AST on proliferation of neural stem cells. The current study was aimed to evaluate the influence of AST on neurogenesis in hippocampal dentate gyrus (DG) of MCAO rats and to explore the possible mechanisms. In this study, the neurobehavioral tests (Ludmila Belayev 12-point scoring, Screen test, fore limb placing test) had been employed to investigate the effect of AST treatment against functional deficit of MCAO rats. The immunofluorescence staining, western-blot and qRT-PCR was performed to evaluate the effects of AST on proliferation, differentiation and maturity of neural stemr cells in hippocampus. Moreover, we investigated the possible mechanism of the AST treatment in promoting neurogenesis after ischemic stroke. The findings indicated that AST treatment ameliorated the neurobehavior of MCAO rats. The results indicated that AST treatment possessed the potential to improve proprioceptive sense and motor function of MCAO rats. AST treatment sustained neuronal viability and stimulates sensorimotor integration functional recovery in MCAO rats. The results suggested that AST improved neurobehavior deficit after ischemic stroke. Furthermore, AST promoted neurogenesis through upregulating the expressing of BNDF/TrkB signaling pathway. Therefore AST might be a promising therapeutic agent for ischemic stroke.

Atypical fetal development: Fetal alcohol syndrome, nutritional deprivation, teratogens, and risk for neurodevelopmental disorders and psychopathology

Accumulating evidence indicates that the fetal environment plays an important role in brain development and sets the brain on a trajectory across the life span. An abnormal fetal environment results when factors that should be present during a critical period of development are absent or when factors that should not be in the developing brain are present. While these factors may acutely disrupt brain function, the real cost to society resides in the long-term effects, which include important mental health issues. We review the effects of three factors, fetal alcohol exposure, teratogen exposure, and nutrient deficiencies, on the developing brain and the consequent risk for developmental psychopathology. Each is reviewed with respect to the evidence found in epidemiological and clinical studies in humans as well as preclinical molecular and cellular studies that explicate mechanisms of action.

Neurological outcomes of animal models of uterine artery ligation and relevance to human intrauterine growth restriction: a systematic review

AIM

This review explores the molecular, neurological, and behavioural outcomes in animal models of uterine artery ligation. We analyse the relevance of this type of model to the pathological and functional phenotypes that are consistent with cerebral palsy and its developmental comorbidities in humans.

METHOD

A literature search of the PubMed database was conducted for research using the uterine artery ligation model published between 1990 and 2013. From the studies included, any relevant neuroanatomical and behavioural deficits were then summarized from each document and used for further analysis.

RESULTS

There were 25 papers that met the criteria included for review, and several outcomes were summarized from the results of these papers. Fetuses with growth restriction demonstrated a gradient of reduced body weight with a relative sparing of brain mass. There was a significant reduction in the size of the somatosensory cortex, hippocampus, and corpus callosum. The motor cortex appeared to be spared of identifiable deficits. Apoptotic proteins were upregulated, while those important to neuronal survival, growth, and differentiation were downregulated. Neuronal apoptosis and astrogliosis occurred diffusely throughout the brain regions. White matter injury involved oligodendrocyte precursor maturation arrest, hypomyelination, and an aberrant organization of existing myelin. Animals with growth restriction demonstrated deficits in gait, memory, object recognition, and spatial processing.

INTERPRETATION

This review concludes that neuronal death, white matter injury, motor abnormalities, and cognitive deficits are important outcomes of uterine artery ligation in animal models. Therefore, this is a clinically relevant type of model, as these findings resemble deficits in human cerebral palsy.

Microtubule-associated protein 2 and synaptophysin in the preterm and near-term ovine fetal brain and the effect of intermittent umbilical cord occlusion

We have determined the change in immunoreactivity (IR) for microtubule-associated protein 2 (MAP-2) and synaptophysin (SYN) as markers for dendritic and presynaptic nerve development, respectively, in the ovine fetal brain with advancing gestation and in response to intermittent umbilical cord occlusion (UCO), which might then contribute to adverse neurodevelopment. Fetal sheep (control and experimental groups preterm at 111-115 and near term at 132-138 days of gestation; term = 145 days) were studied over 4 days with UCOs performed by inflation of an occluder cuff for 90 seconds every 30 minutes for 3 to 5 hours each day. Animals were then euthanized and fetal brains assessed for IR of MAP-2 and SYN. In control animals, the IR of SYN increased in the gray matter with advancing gestation consistent with a developmental increase in presynaptic vesicles and/or nerve terminals as expected; however, the IR of MAP-2 decreased in all brain regions studied, suggesting concurrent refinement in dendritic branching and spine development. Intermittent UCO as studied with marked but limited hypoxemia resulted in a decrease in IR of SYN for the brain regions of the preterm animals when protein turnover is higher and indicates decreased presynaptic vesicle formation; whereas, MAP-2 IR was selectively increased in the hippocampus CA1 and thalamus of the near-term animals, consistent with reactive dendritic change and heightened vulnerability for neuronal injury. As such, intermittent cord compressions in the ovine fetus can impact protein markers for dendritic and presynaptic nerve development depending on their timing, which might then lead to alterations in synapse formation and neuronal circuitry.

Experimental modelling of the consequences of brief late gestation asphyxia on newborn lamb behaviour and brain structure

Brief but severe asphyxia in late gestation or at the time of birth may lead to neonatal hypoxic ischemic encephalopathy and is associated with long-term neurodevelopmental impairment. We undertook this study to examine the consequences of transient in utero asphyxia in late gestation fetal sheep, on the newborn lamb after birth. Surgery was undertaken at 125 days gestation for implantation of fetal catheters and placement of a silastic cuff around the umbilical cord. At 132 days gestation (0.89 term), the cuff was inflated to induce umbilical cord occlusion (UCO), or sham (control). Fetal arterial blood samples were collected for assessment of fetal wellbeing and the pregnancy continued until birth. At birth, behavioral milestones for newborn lambs were recorded over 24 h, after which the lambs were euthanased for brain collection and histopathology assessments. After birth, UCO lambs displayed significant latencies to (i) use all four legs, (ii) attain a standing position, (iii) find the udder, and (iv) successfully suckle - compared to control lambs. Brains of UCO lambs showed widespread pathologies including cell death, white matter disruption, intra-parenchymal hemorrhage and inflammation, which were not observed in full term control brains. UCO resulted in some preterm births, but comparison with age-matched preterm non-UCO control lambs showed that prematurity per se was not responsible for the behavioral delays and brain structural abnormalities resulting from the in utero asphyxia. These results demonstrate that a single, brief fetal asphyxic episode in late gestation results in significant grey and white matter disruption in the developing brain, and causes significant behavioral delay in newborn lambs. These data are consistent with clinical observations that antenatal asphyxia is causal in the development of neonatal encephalopathy and provide an experimental model to advance our understanding of neuroprotective therapies.