Fetal body weight and the development of the control of the cardiovascular system in fetal sheep

The Vagus Nerve Regulates Immunometabolic Homeostasis in the Ovine Fetus near Term: The Impact on Terminal Ileum

BACKGROUND

Glucosensing elements are widely distributed throughout the body and relay information about circulating glucose levels to the brain via the vagus nerve. However, while anatomical wiring has been established, little is known about the physiological role of the vagus nerve in glucosensing. The contribution of the vagus nerve to inflammation in the fetus is poorly understood. Increased glucose levels and inflammation act synergistically when causing organ injury, but their interplay remains incompletely understood. We hypothesized that vagotomy (Vx) will trigger a rise in systemic glucose levels and this will be enhanced during systemic and organ-specific inflammation. Efferent vagus nerve stimulation (VNS) should reverse this phenotype.

METHODS

Near-term fetal sheep (n = 57) were surgically prepared using vascular catheters and ECG electrodes as the control and treatment groups (lipopolysaccharide (LPS), Vx + LPS, Vx + LPS + selective efferent VNS). The experiment was started 72 h postoperatively to allow for post-surgical recovery. Inflammation was induced with LPS bolus intravenously (LPS group, 400 ng/fetus/day for 2 days; n = 23). For the Vx + LPS group (n = 11), a bilateral cervical vagotomy was performed during surgery; of these n = 5 received double the LPS dose, LPS800. The Vx + LPS + efferent VNS group (n = 8) received cervical VNS probes bilaterally distal from Vx in eight animals. Efferent VNS was administered for 20 min on days 1 and 2 +/10 min around the LPS bolus. Fetal arterial blood samples were drawn on each postoperative day of recovery (-72 h, -48 h, and -24 h) as well as at the baseline and seven selected time points (3-54 h) to profile inflammation (ELISA IL-6, pg/mL), insulin (ELISA), blood gas, and metabolism (glucose). At 54 h post-LPS, a necropsy was performed, and the terminal ileum macrophages' CD11c (M1 phenotype) immunofluorescence was quantified to detect inflammation. The results are reported for p < 0.05 and for Spearman R2 > 0.1. The results are presented as the median (IQR).

RESULTS

Across the treatment groups, blood gas and cardiovascular changes indicated mild septicemia. At 3 h in the LPS group, IL-6 peaked. That peak was decreased in the Vx + LPS400 group and doubled in the Vx + LPS800 group. The efferent VNS sped up the reduction in the inflammatory response profile over 54 h. The M1 macrophage activity was increased in the LPS and Vx + LPS800 groups only. The glucose and insulin concentrations in the Vx + LPS group were, respectively, 1.3-fold (throughout the experiment) and 2.3-fold higher vs. control (at 3 h). The efferent VNS normalized the glucose concentrations.

CONCLUSIONS

The complete withdrawal of vagal innervation resulted in a 72-h delayed onset of a sustained increase in glucose for at least 54 h and intermittent hyperinsulinemia. Under the conditions of moderate fetal inflammation, this was related to higher levels of gut inflammation. The efferent VNS reduced the systemic inflammatory response as well as restored both the concentrations of glucose and the degree of terminal ileum inflammation, but not the insulin concentrations. Supporting our hypothesis, these findings revealed a novel regulatory, hormetic, role of the vagus nerve in the immunometabolic response to endotoxin in near-term fetuses.

Heart Rate Variability Code: Does It Exist and Can We Hack It?

A code is generally defined as a system of signals or symbols for communication. Experimental evidence is synthesized for the presence and utility of such communication in heart rate variability (HRV) with particular attention to fetal HRV: HRV contains signatures of information flow between the organs and of response to physiological or pathophysiological stimuli as signatures of states (or syndromes). HRV exhibits features of time structure, phase space structure, specificity with respect to (organ) target and pathophysiological syndromes, and universality with respect to species independence. Together, these features form a spatiotemporal structure, a phase space, that can be conceived of as a manifold of a yet-to-be-fully understood dynamic complexity. The objective of this article is to synthesize physiological evidence supporting the existence of HRV code: hereby, the process-specific subsets of HRV measures indirectly map the phase space traversal reflecting the specific information contained in the code required for the body to regulate the physiological responses to those processes. The following physiological examples of HRV code are reviewed, which are reflected in specific changes to HRV properties across the signal-analytical domains and across physiological states and conditions: the fetal systemic inflammatory response, organ-specific inflammatory responses (brain and gut), chronic hypoxia and intrinsic (heart) HRV (iHRV), allostatic load (physiological stress due to surgery), and vagotomy (bilateral cervical denervation). Future studies are proposed to test these observations in more depth, and the author refers the interested reader to the referenced publications for a detailed study of the HRV measures involved. While being exemplified mostly in the studies of fetal HRV, the presented framework promises more specific fetal, postnatal, and adult HRV biomarkers of health and disease, which can be obtained non-invasively and continuously.

Sheep as a model for neuroendocrinology research

Animal models remain essential to understand the fundamental mechanisms of physiology and pathology. Particularly, the complex and dynamic nature of neuroendocrine cells of the hypothalamus make them difficult to study. The neuroendocrine systems of the hypothalamus are critical for survival and reproduction, and are highly conserved throughout vertebrate evolution. Their roles in controlling body metabolism, growth and body composition, stress, electrolyte balance, and reproduction, have been intensively studied, and have yielded groundbreaking discoveries. Many of these discoveries would not have been feasible without the use of the domestic sheep (Ovis aries). The sheep has been used for decades to study the neuroendocrine systems of the hypothalamus and has become a model for human neuroendocrinology. The aim of this chapter is to review some of the profound biomedical discoveries made possible by the use of sheep. The advantages and limitations of sheep as a neuroendocrine model will be discussed. While no animal model can perfectly recapitulate a human disease or condition, sheep are invaluable for enabling manipulations not possible in human subjects and isolating physiologic variables to garner insight into neuroendocrinology and associated pathologies.

Effects of maternal ritodrine hydrochloride administration on the heart rate of preterm fetal sheep with intraamniotic inflammation

Ritodrine hydrochloride is used for pregnancy prolongation and intrauterine fetal resuscitation. However, its clinical significance in intraamniotic inflammation during preterm labor and intrauterine fetal distress is unclear. We investigated the effects of maternal ritodrine hydrochloride administration (MRA; 200 μg/min for 2 h, followed by 800 μg/min for 2 h after 24 h) on fetal physiological parameters. For this purpose, we used chronically instrumented pregnant sheep at 113–119 d (term = 145 d) of gestation without (Group 1, n = 5) and with (Group 2, n = 5) intraamniotic inflammation induced by lipopolysaccharide injection into the amniotic cavity. The changes in fetal heart rate (FHR) and short-term variability (STV) and long-term variability (LTV) in FHR, fetal blood pressure, and fetal arterial blood gas (FABG) values were measured before and at 1 and 2 h after initiating MRA. Before MRA, all parameters were similar between Groups 1 and 2; however, there was significantly higher STV in Group 2 than in Group 1 before MRA at 800 μg/min, significantly higher partial arterial pressure of carbon dioxide in FABG in Group 2 than in Group 1 before MRA at 200 μg/min, and significantly lower blood glucose (BG) in Group 2 than in Group 1 before MRA at 800 μg/min. One hour after MRA, the FHR, STV, and LTV were significantly higher at 800 μg/min than those at the baseline in Group 1, as determined by the Friedman test; however, no significant difference was observed in Group 2. Additionally, the FABG pH significantly decreased 1 h after MRA at 800 μg/min in Group 2, whereas FABG lactate and BG significantly increased 2 h after MRA at 800 μg/min in Groups 1 and 2. Thus, short-term MRA at 800 μg/min increased the FHR, STV, and LTV significantly; these values were further modified under intraamniotic inflammation.

A Review on the Vagus Nerve and Autonomic Nervous System During Fetal Development: Searching for Critical Windows

The autonomic nervous system (ANS) is one of the main biological systems that regulates the body's physiology. Autonomic nervous system regulatory capacity begins before birth as the sympathetic and parasympathetic activity contributes significantly to the fetus' development. In particular, several studies have shown how vagus nerve is involved in many vital processes during fetal, perinatal, and postnatal life: from the regulation of inflammation through the anti-inflammatory cholinergic pathway, which may affect the functioning of each organ, to the production of hormones involved in bioenergetic metabolism. In addition, the vagus nerve has been recognized as the primary afferent pathway capable of transmitting information to the brain from every organ of the body. Therefore, this hypothesis paper aims to review the development of ANS during fetal and perinatal life, focusing particularly on the vagus nerve, to identify possible "critical windows" that could impact its maturation. These "critical windows" could help clinicians know when to monitor fetuses to effectively assess the developmental status of both ANS and specifically the vagus nerve. In addition, this paper will focus on which factors-i.e., fetal characteristics and behaviors, maternal lifestyle and pathologies, placental health and dysfunction, labor, incubator conditions, and drug exposure-may have an impact on the development of the vagus during the above-mentioned "critical window" and how. This analysis could help clinicians and stakeholders define precise guidelines for improving the management of fetuses and newborns, particularly to reduce the potential adverse environmental impacts on ANS development that may lead to persistent long-term consequences. Since the development of ANS and the vagus influence have been shown to be reflected in cardiac variability, this paper will rely in particular on studies using fetal heart rate variability (fHRV) to monitor the continued growth and health of both animal and human fetuses. In fact, fHRV is a non-invasive marker whose changes have been associated with ANS development, vagal modulation, systemic and neurological inflammatory reactions, and even fetal distress during labor.

In vivo biomarkers of structural and functional brain development and aging in humans

Brain aging is a major determinant of aging. Along with the aging population, prevalence of neurodegenerative diseases is increasing, therewith placing economic and social burden on individuals and society. Individual rates of brain aging are shaped by genetics, epigenetics, and prenatal environmental. Biomarkers of biological brain aging are needed to predict individual trajectories of aging and the risk for age-associated neurological impairments for developing early preventive and interventional measures. We review current advances of in vivo biomarkers predicting individual brain age. Telomere length and epigenetic clock, two important biomarkers that are closely related to the mechanistic aging process, have only poor deterministic and predictive accuracy regarding individual brain aging due to their high intra- and interindividual variability. Phenotype-related biomarkers of global cognitive function and brain structure provide a much closer correlation to age at the individual level. During fetal and perinatal life, autonomic activity is a unique functional marker of brain development. The cognitive and structural biomarkers also boast high diagnostic specificity for determining individual risks for neurodegenerative diseases.

Fetal Cardiovascular Decompensation During Labor Predicted From the Individual Heart Rate Tracing: A Machine Learning Approach in Near-Term Fetal Sheep Model

Background: When exposed to repetitive umbilical cord occlusions (UCO) with worsening acidemia, fetuses eventually develop cardiovascular decompensation manifesting as pathological hypotensive arterial blood pressure (ABP) responses to fetal heart rate (FHR) decelerations. Failure to maintain cardiac output during labor is a key event leading up to brain injury. We reported that the timing of the event when a fetus begins to exhibit this cardiovascular phenotype is highly individual and was impossible to predict. Objective: We hypothesized that this phenotype would be reflected in the individual behavior of heart rate variability (HRV) as measured by root mean square of successive differences of R-R intervals (RMSSD), a measure of vagal modulation of HRV, which is known to increase with worsening acidemia. This is clinically relevant because HRV can be computed in real-time intrapartum. Consequently, we aimed to predict the individual timing of the event when a hypotensive ABP pattern would emerge in a fetus from a series of continuous RMSSD data. Study Design: Fourteen near-term fetal sheep were chronically instrumented with vascular catheters to record fetal arterial blood pressure, umbilical cord occluder to mimic uterine contractions occurring during human labor and ECG electrodes to compute the ECG-derived HRV measure RMSSD. All animals were studied over a ~6 h period. After a 1-2 h baseline control period, the animals underwent mild, moderate, and severe series of repetitive UCO. We applied the recently developed machine learning algorithm to detect physiologically meaningful changes in RMSSD dynamics with worsening acidemia and hypotensive responses to FHR decelerations. To mimic clinical scenarios using an ultrasound-based 4 Hz FHR sampling rate, we recomputed RMSSD from FHR sampled at 4 Hz and compared the performance of our algorithm under both conditions (1,000 Hz vs. 4 Hz). Results: The RMSSD values were highly non-stationary, with four different regimes and three regime changes, corresponding to a baseline period followed by mild, moderate, and severe UCO series. Each time series was characterized by seemingly randomly occurring (in terms of timing of the individual onset) increase in RMSSD values at different time points during the moderate UCO series and at the start of the severe UCO series. This event manifested as an increasing trend in RMSSD values, which counter-intuitively emerged as a period of relative stationarity for the time series. Our algorithm identified these change points as the individual time points of cardiovascular decompensation with 92% sensitivity, 86% accuracy and 92% precision which corresponded to 14 ± 21 min before the visual identification. In the 4 Hz RMSSD time series, the algorithm detected the event with 3 times earlier detection times than at 1,000 Hz, i.e., producing false positive alarms with 50% sensitivity, 21% accuracy, and 27% precision. We identified the overestimation of baseline FHR variability by RMSSD at a 4 Hz sampling rate to be the cause of this phenomenon. Conclusions: The key finding is demonstration of FHR monitoring to detect fetal cardiovascular decompensation during labor. This validates the hypothesis that our HRV-based algorithm identifies individual time points of ABP responses to UCO with worsening acidemia by extracting change point information from the physiologically related fluctuations in the RMSSD signal. This performance depends on the acquisition accuracy of beat to beat fluctuations achieved in trans-abdominal ECG devices and fails at the sampling rate used clinically in ultrasound-based systems. This has implications for implementing such an approach in clinical practice.

A Proxy for Detecting IUGR Based on Gestational Age Estimation in a Guatemalan Rural Population

In-utero progress of fetal development is normally assessed through manual measurements taken from ultrasound images, requiring relatively expensive equipment and well-trained personnel. Such monitoring is therefore unavailable in low- and middle-income countries (LMICs), where most of the perinatal mortality and morbidity exists. The work presented here attempts to identify a proxy for IUGR, which is a significant contributor to perinatal death in LMICs, by determining gestational age (GA) from data derived from simple-to-use, low-cost one-dimensional Doppler ultrasound (1D-DUS) and blood pressure devices. A total of 114 paired 1D-DUS recordings and maternal blood pressure recordings were selected, based on previously described signal quality measures. The average length of 1D-DUS recording was 10.43 ± 1.41 min. The min/median/max systolic and diastolic maternal blood pressures were 79/102/121 and 50.5/63.5/78.5 mmHg, respectively. GA was estimated using features derived from the 1D-DUS and maternal blood pressure using a support vector regression (SVR) approach and GA based on the last menstrual period as a reference target. A total of 50 trials of 5-fold cross-validation were performed for feature selection. The final SVR model was retrained on the training data and then tested on a held-out set comprising 28 normal weight and 25 low birth weight (LBW) newborns. The mean absolute GA error with respect to the last menstrual period was found to be 0.72 and 1.01 months for the normal and LBW newborns, respectively. The mean error in the GA estimate was shown to be negatively correlated with the birth weight. Thus, if the estimated GA is lower than the (remembered) GA calculated from last menstruation, then this could be interpreted as a potential sign of IUGR associated with LBW, and referral and intervention may be necessary. The assessment system may, therefore, have an immediate impact if coupled with suitable intervention, such as nutritional supplementation. However, a prospective clinical trial is required to show the efficacy of such a metric in the detection of IUGR and the impact of the intervention.

Uterine and umbilical resistance index and fetal heart rate in pregnant bitches of different body weight

The aim of this study was to compare uterine and umbilical artery blood flow and fetal heart rate (FHR) in small, medium and large body weight (BW) dogs during the second half of pregnancy. Purebred pregnant bitches were assigned to one of the following groups according to their BW: small (S; ≤10 kg), medium (M; 11-25 kg) and large (L; >25-45 kg). Uterine and umbilical Doppler and M-mode ultrasonography was conducted every 10 days from Day 30-60 (Day 0 = first day of gestation). From Day 40, uterine and umbilical artery resistance index (RI) progressively and differentially decreased in the three groups (P < 0.01) being less in L than S bitches (P < 0.01). Litter size but not maternal BW (P > 0.1) affected uterine RI on Days 40 (r = 0.39; P < 0.01) and 50 (r = 0.41; P < 0.01). Conversely, on Day 60, maternal BW (r = 0.61; P < 0.01) had an effect on uterine RI while litter size did not (P > 0.1). Fetal heart rate increased from Day 30-50 and decreased to the time of parturition (P < 0.01) without differences among groups at any time point (P > 0.1). Uterine and umbilical blood flow differentially increased throughout mid- and late-pregnancy in breeds with large and small BW. These differences were affected by litter size on Days 40 and 50, and by maternal BW on Day 60. Conversely, during this same period, FHR did not vary among BW groups. Physiological variations should be considered when gestational ultrasonic examination is interpreted in different BW bitches.

Fetal heart rate variability responsiveness to maternal stress, non-invasively detected from maternal transabdominal ECG

PURPOSE

Prenatal stress (PS) during pregnancy affects in utero- and postnatal child brain-development. Key systems affected are the hypothalamic-pituitary-adrenal axis and the autonomic nervous system (ANS). Maternal- and fetal ANS activity can be gauged non-invasively from transabdominal electrocardiogram (taECG). We propose a novel approach to assess couplings between maternal (mHR) and fetal heart rate (fHR) as a new biomarker for PS based on bivariate phase-rectified signal averaging (BPRSA). We hypothesized that PS exerts lasting impact on fHR.

METHODS

Prospective case-control study matched for maternal age, parity, and gestational age during the third trimester using the Cohen Perceived Stress Scale (PSS-10) questionnaire with PSS-10 over or equal 19 classified as stress group (SG). Women with PSS-10 < 19 served as control group (CG). Fetal electrocardiograms were recorded by a taECG. Coupling between mHR and fHR was analyzed by BPRSA resulting in fetal stress index (FSI). Maternal hair cortisol, a memory of chronic stress exposure for 2-3 months, was measured at birth.

RESULTS

538/1500 pregnant women returned the questionnaire, 55/538 (10.2%) mother-child pairs formed SG and were matched with 55/449 (12.2%) consecutive patients as CG. Maternal hair cortisol was 86.6 (48.0-169.2) versus 53.0 (34.4-105.9) pg/mg (p = 0.029). At 36 + 5 weeks, FSI was significantly higher in fetuses of stressed mothers when compared to controls [0.43 (0.18-0.85) versus 0.00 (- 0.49-0.18), p < 0.001].

CONCLUSION

Prenatal maternal stress affects the coupling between maternal and fetal heart rate detectable non-invasively a month prior to birth. Lasting effects on neurodevelopment of affected offspring should be studied.

TRIAL REGISTRATION

Clinical trial registration: NCT03389178.

Vagal contributions to fetal heart rate variability: an omics approach

OBJECTIVE

Fetal heart rate variability (fHRV) is an important indicator of health and disease, yet its physiological origins, neural contributions, in particular, are not well understood. We aimed to develop novel experimental and data analytical approaches to identify fHRV measures reflecting the vagus nerve contributions to fHRV.

APPROACH

In near-term ovine fetuses, a comprehensive set of 46 fHRV measures was computed from fetal pre-cordial electrocardiogram recorded during surgery and 72 h later without (n  =  24) and with intra-surgical bilateral cervical vagotomy (n  =  15).

MAIN RESULTS

The fetal heart rate did not change due to vagotomy. We identify fHRV measures specific to the vagal modulation of fHRV: multiscale time irreversibility asymmetry index (AsymI), detrended fluctuation analysis (DFA) α ₁, Kullback-Leibler permutation entropy (KLPE) and scale-dependent Lyapunov exponent slope (SDLE α).

SIGNIFICANCE

We provide a systematic delineation of vagal contributions to fHRV across signal-analytical domains which should be relevant for the emerging field of bioelectronic medicine and the deciphering of the 'vagus code'. Our findings also have clinical significance for in utero monitoring of fetal health during surgery. Key points •Fetal surgery causes a complex pattern of changes in heart rate variability measures with an overall reduction of complexity or variability. •At 72 h after surgery, many of the HRV measures recover and this recovery is delayed by an intrasurgical cervical bilateral vagotomy. •We identify HRV pattern representing complete vagal withdrawal that can be understood as part of 'HRV code', rather than any single HRV measure. •We identify HRV biomarkers of recovery from fetal surgery and discuss the effect of anticholinergic medication on this recovery.

Fetal Cerebrovascular Maturation: Effects of Hypoxia

The human cerebral vasculature originates in the fourth week of gestation and continues to expand and diversify well into the first few years of postnatal life. A key feature of this growth is smooth muscle differentiation, whereby smooth muscle cells within cerebral arteries transform from migratory to proliferative to synthetic and finally to contractile phenotypes. These phenotypic transformations can be reversed by pathophysiological perturbations such as hypoxia, which causes loss of contractile capacity in immature cerebral arteries. In turn, loss of contractility affects all whole-brain cerebrovascular responses, including those involved in flow-metabolism coupling, vasodilatory responses to acute hypoxia and hypercapnia, cerebral autoregulation, and reactivity to activation of perivascular nerves. Future strategies to minimize cerebral injury following hypoxia-ischemic insults in the immature brain might benefit by targeting treatments to preserve and promote contractile differentiation in the fetal cerebrovasculature. This could potentially be achieved through inhibition of receptor tyrosine kinase-mediated growth factors, such as vascular endothelial growth factor and platelet-derived growth factor, which are mobilized by hypoxic and ischemic injury and which facilitate contractile dedifferentiation. Interruption of the effects of other vascular mitogens, such as endothelin and angiotensin-II, and even some miRNA species, also could be beneficial. Future experimental work that addresses these possibilities offers promise to improve current clinical management of neonates who have suffered and survived hypoxic, ischemic, asphyxic, or inflammatory cerebrovascular insults.

Proposed mechanisms of relative bradycardia

Relative bradycardia is the term used to describe the mechanism where there is dissociation between pulse and temperature. This finding is important to recognize since it may provide further insights into the potential underlying causes of disease. There is no known proposed mechanism to explain this phenomenon. We hypothesize that relative bradycardia is the central mechanism reflecting and influenced potentially by the direct pathogenic effect on the sinoatrial node as well as cross-talk between the autonomic nervous system and immune system. Cardiac pacemaker cells may act as a target for inflammatory cytokines leading to alteration in heart rate dynamics or their responsiveness to neurotransmitters during systemic inflammation. These factors account for the important role of how the host response to infectious and non-infectious causes influences the appearance of relative bradycardia. We propose several methods that may be useful to confirm the proposed theoretical framework to further enhance our understanding of this paradoxical phenomenon. This includes measuring, during the episode of relative bradycardia, proinflammatory and anti-inflammatory cytokines, monitoring heart rate variability (HRV), and assessing underlying comorbidities and outcomes in patients with the same disease.

Non-invasive biomarkers of fetal brain development reflecting prenatal stress: An integrative multi-scale multi-species perspective on data collection and analysis

Prenatal stress (PS) impacts early postnatal behavioural and cognitive development. This process of 'fetal programming' is mediated by the effects of the prenatal experience on the developing hypothalamic-pituitary-adrenal (HPA) axis and autonomic nervous system (ANS). We derive a multi-scale multi-species approach to devising preclinical and clinical studies to identify early non-invasively available pre- and postnatal biomarkers of PS. The multiple scales include brain epigenome, metabolome, microbiome and the ANS activity gauged via an array of advanced non-invasively obtainable properties of fetal heart rate fluctuations. The proposed framework has the potential to reveal mechanistic links between maternal stress during pregnancy and changes across these physiological scales. Such biomarkers may hence be useful as early and non-invasive predictors of neurodevelopmental trajectories influenced by the PS as well as follow-up indicators of success of therapeutic interventions to correct such altered neurodevelopmental trajectories. PS studies must be conducted on multiple scales derived from concerted observations in multiple animal models and human cohorts performed in an interactive and iterative manner and deploying machine learning for data synthesis, identification and validation of the best non-invasive detection and follow-up biomarkers, a prerequisite for designing effective therapeutic interventions.

A Doubly Stochastic Change Point Detection Algorithm for Noisy Biological Signals

Experimentally and clinically collected time series data are often contaminated with significant confounding noise, creating short, noisy time series. This noise, due to natural variability and measurement error, poses a challenge to conventional change point detection methods. We propose a novel and robust statistical method for change point detection for noisy biological time sequences. Our method is a significant improvement over traditional change point detection methods, which only examine a potential anomaly at a single time point. In contrast, our method considers all suspected anomaly points and considers the joint probability distribution of the number of change points and the elapsed time between two consecutive anomalies. We validate our method with three simulated time series, a widely accepted benchmark data set, two geological time series, a data set of ECG recordings, and a physiological data set of heart rate variability measurements of fetal sheep model of human labor, comparing it to three existing methods. Our method demonstrates significantly improved performance over the existing point-wise detection methods.

Perinatal Psychoneuroimmunology: Protocols for the Study of Prenatal Stress and Its Effects on Fetal and Postnatal Brain Development

Prenatal stress (PS) impacts early behavioral, neuroimmune, and cognitive development. Pregnant rat models have been very valuable in examining the mechanisms of such fetal programming. A newer pregnant sheep model of maternal stress offers the unique advantages of chronic in utero monitoring and manipulation. This chapter presents the techniques used to model single and multigenerational stress exposures and their pleiotropic effects on the offspring.

Fetal Sheep Mesenteric Resistance Arteries: Functional and Structural Maturation

BACKGROUND

Fetal blood pressure increases during late gestation; however, the underlying vascular mechanisms are unclear. Knowledge of the maturation of resistance arteries is important to identify the mechanisms and vulnerable periods for the development of vascular dysfunction in adulthood.

METHODS

We determined the functional and structural development of fetal sheep mesenteric resistance arteries using wire myography and immunohistochemistry.

RESULTS

Media mass and distribution of myosin heavy-chain isoforms showed no changes between 0.7 (100 ± 3 days) and 0.9 (130 ± 3 days) gestation. However, from 0.7 to 0.9 gestation, the resting wall tension increased accompanied by non-receptor-dependent (potassium) and receptor-dependent (noradrenaline; endothelin-1) increases in vasocontraction. Angiotensin II had no contractile effect at both ages. Endothelium-dependent relaxation to acetylcholine and prostaglandin E2 was absent at 0.7 but present at 0.9 gestation. Augmented vascular responsiveness was paralleled by the maturation of sympathetic and sensory vascular innervation. Non-endothelium-dependent relaxation to nitric oxide showed no maturational changes. The expression of vasoregulator receptors/enzymes did not increase between 0.7 and 0.9 gestation.

CONCLUSION

Vascular maturation during late ovine gestation involves an increase in resting wall tension and the vasoconstrictor and vasodilator capacity of the mesenteric resistance arteries. Absence of structural changes in the tunica media and the lack of an increase in vasoregulator receptor/enzyme expression suggest that vasoactive responses are due to the maturation of intracellular pathways at this gestational age.

Prevalence of prenatal brain abnormalities in fetuses with congenital heart disease: a systematic review

OBJECTIVES

Studies have shown an association between congenital heart defects (CHDs) and postnatal brain abnormalities and neurodevelopmental delay. Recent evidence suggests that some of these brain abnormalities are present before birth. The primary aim of this study was to perform a systematic review to quantify the prevalence of prenatal brain abnormalities in fetuses with CHDs.

METHODS

MEDLINE, EMBASE and The Cochrane Library were searched electronically. Reference lists within each article were hand-searched for additional reports. The outcomes observed included structural brain abnormalities (on magnetic resonance imaging (MRI)) and changes in brain volume (on MRI, three-dimensional (3D) volumetric MRI, 3D ultrasound and phase-contrast MRI), brain metabolism or maturation (on magnetic resonance spectroscopy and phase-contrast MRI) and brain blood flow (on Doppler ultrasound, phase-contrast MRI and 3D power Doppler ultrasound) in fetuses with CHDs. Cohort and case-control studies were included and cases of chromosomal or genetic abnormalities, case reports and editorials were excluded. Proportion meta-analysis was used for analysis. Between-study heterogeneity was assessed using the I(2) test.

RESULTS

The search yielded 1943 citations, and 20 studies (n = 1175 cases) were included in the review. Three studies reported data on structural brain abnormalities, while data on altered brain volume, metabolism and blood flow were reported in seven, three and 14 studies, respectively. The three studies (221 cases) reporting on structural brain abnormalities were suitable for inclusion in a meta-analysis. The prevalence of prenatal structural brain abnormalities in fetuses with CHD was 28% (95% CI, 18-40%), with a similar prevalence (25% (95% CI, 14-39%)) when tetralogy of Fallot was considered alone. These abnormalities included ventriculomegaly (most common), agenesis of the corpus callosum, ventricular bleeding, increased extra-axial space, vermian hypoplasia, white-matter abnormalities and delayed brain development. Fetuses with CHD were more likely than those without CHD to have reduced brain volume, delay in brain maturation and altered brain circulation, most commonly in the form of reduced middle cerebral artery pulsatility index and cerebroplacental ratio. These changes were usually evident in the third trimester, but some studies reported them from as early as the second trimester.

CONCLUSION

In the absence of known major aneuploidy or genetic syndromes, fetuses with CHD are at increased risk of brain abnormalities, which are discernible prenatally. Copyright © 2016 ISUOG. Published by John Wiley & Sons Ltd.

Sleep restriction during pregnancy and its effects on blood pressure and renal function among female offspring

The influence of sleep restriction (SR) during pregnancy on blood pressure and renal function among female adult offspring was investigated. Pregnant Wistar rats were distributed into control and SR groups. The SR was performed between the 14th and 20th days of pregnancy (multiple platforms method for 20 h/day). At 2 months of age, half of the offspring from both groups were subjected to an ovariectomy (ovx), and the other half underwent sham surgery. The groups were as follows: control sham (C_sham), control ovx (C_ovx), SR sham (SR_sham), and SR ovx (SR_ovx). Renal function markers and systolic blood pressure (BPi, indirect method) were evaluated at 4, 6, and 8 months. Subsequently, the rats were euthanized, kidneys were removed, and processed for morphological analyses of glomerular area (GA), number of glomeruli per mm³ (NG), and kidney mass (KM). Increased BPi was observed in the C_ovx, SR_sham, and SR_ovx groups compared to C_sham at all ages. Increased plasma creatinine concentration and decreased creatinine clearance were observed in the SR_sham and SR_ovx groups compared to the C_sham and C_ovx groups. The SR_ovx group showed higher BPi and reduced creatinine clearance compared to all other groups. The SR_ovx group showed reduced values of GA and KM, as well as increased NG, macrophage infiltration, collagen deposit, and ACE1 expression at the renal cortex. Therefore, SR during pregnancy might be an additional risk factor for developing renal dysfunction and increasing BP in female adult offspring. The absence of female hormones exacerbates the changes caused by SR.

Evaluation of feline uterine and umbilical arteries blood flow in a pharmacologically induced abnormal gestation model

The aim of this study was to describe resistance index (RI) and systolic/diastolic ratio (S/D ratio) of uterine and umbilical arteries in an experimental model of abnormal pregnancy in felids. On days 30 to 35 (32 ± 2.9) after mating, 20 domestic short-hair pregnant queens were randomly assigned to one of the following treatment groups: a treated group (TG; n = 8), which received 10 mg/kg of aglepristone subcutaneously twice, 24 hours apart, and a control nontreated group (CG; n = 12). M-mode and Doppler ultrasonographic evaluations were performed at the initiation of the treatment (Day 0) and then every other day during 8 days. In both groups, uterine and umbilical arteries were evaluated by Doppler ultrasound, whereas fetal heart rate was assessed by M-mode ultrasound. Resistance index of uterine artery augmented in TG from Day 2 onward, conversely it decreased in CG (P < 0.01). On Day 8, RI values were 0.64 ± 0.05 vs 0.37 ± 0.01 for TG and CG, respectively. Additionally, S/D ratio of the same artery presented an increase in TG, whereas this ratio diminished in CG (P < 0.01). On Day 8, this parameter showed values of 2.98 ± 0.4 vs 1.62 ± 0.06 for TG and CG, respectively. Resistance index of umbilical artery remained almost unchanged in TG from Day 6 onward, whereas it progressively decreased in CG throughout the course of the study (P < 0.05). On Day 8, RI were 0.89 ± 0.04 and 0.82 ± 0.01, for TG and CG, respectively. Furthermore, on Day 8, S/D ratio of umbilical artery progressively diminished in CG but not in TG (P < 0.01), being 14.7 ± 9.1 vs 5.9 ± 0.3 for TG and CG, respectively. Fetal heart rate was higher in TG than in CG (P < 0.05). Group differences in Doppler parameters appeared on Day 2, when the other clinical or ultrasonographic signs were still absent. It is concluded that blood flow of the uterine and umbilical arteries differed between these normal and abnormal gestations predicting an adverse obstetric outcome.

Decreased neuroinflammation correlates to higher vagus nerve activity fluctuations in near-term ovine fetuses: a case for the afferent cholinergic anti-inflammatory pathway?

Background

Neuroinflammation in utero may contribute to brain injury resulting in life-long neurological disabilities. The pivotal role of the efferent cholinergic anti-inflammatory pathway (CAP) in controlling inflammation, e.g., by inhibiting the HMGB1 release, via the macrophages’ α7 nicotinic acetylcholine receptor (α7nAChR) has been described in adults, but its importance in the fetus is unknown. Moreover, it is unknown whether CAP may also exert anti-inflammatory effects on the brain via the anatomically predominant afferent component of the vagus nerve.

Methods

We measured microglial activation in the ovine fetal brain near term 24 h after the umbilical cord occlusions mimicking human labor versus controls (no occlusions) by quantifying HMGB1 nucleus-to-cytosol translocation in the Iba1+ and α7nAChR+ microglia. Based on multiple clinical studies in adults and our own work in fetal autonomic nervous system, we gauged the degree of CAP activity in vivo using heart rate variability measure RMSSD that reflects fluctuations in vagus nerve activity.

Results

RMSSD correlated to corresponding plasma IL-1β levels at R = 0.57 (p = 0.02, n = 17) and to white matter microglia cell counts at R = −0.89 (p = 0.03). The insult increased the HMGB1 translocation in α7nAChR+ microglia in a brain region-dependent manner (p < 0.001). In parallel, RMSSD at 1 h post insult correlated with cytosolic HMGB1 of thalamic microglia (R = −0.94, p = 0.005), and RMSSD at pH nadir correlated with microglial α7nAChR in the white matter (R = 0.83, p = 0.04). Overall, higher RMSSD values correlated with lower HMGB1 translocation and higher α7nAChR intensity per area in a brain region-specific manner.

Conclusions

Afferent fetal CAP may translate increased vagal cholinergic signaling into suppression of cerebral inflammation in response to near-term hypoxic acidemia as might occur during labor. Our findings suggest a new control mechanism of fetal neuroinflammation via the vagus nerve, providing novel possibilities for its non-invasive monitoring in utero and for targeted treatment.

Electronic supplementary material

The online version of this article (doi:10.1186/s12974-016-0567-x) contains supplementary material, which is available to authorized users.

Temporal Patterns in Sheep Fetal Heart Rate Variability Correlate to Systemic Cytokine Inflammatory Response: A Methodological Exploration of Monitoring Potential Using Complex Signals Bioinformatics

Fetal inflammation is associated with increased risk for postnatal organ injuries. No means of early detection exist. We hypothesized that systemic fetal inflammation leads to distinct alterations of fetal heart rate variability (fHRV). We tested this hypothesis deploying a novel series of approaches from complex signals bioinformatics. In chronically instrumented near-term fetal sheep, we induced an inflammatory response with lipopolysaccharide (LPS) injected intravenously (n = 10) observing it over 54 hours; seven additional fetuses served as controls. Fifty-one fHRV measures were determined continuously every 5 minutes using Continuous Individualized Multi-organ Variability Analysis (CIMVA). CIMVA creates an fHRV measures matrix across five signal-analytical domains, thus describing complementary properties of fHRV. We implemented, validated and tested methodology to obtain a subset of CIMVA fHRV measures that matched best the temporal profile of the inflammatory cytokine IL-6. In the LPS group, IL-6 peaked at 3 hours. For the LPS, but not control group, a sharp increase in standardized difference in variability with respect to baseline levels was observed between 3 h and 6 h abating to baseline levels, thus tracking closely the IL-6 inflammatory profile. We derived fHRV inflammatory index (FII) consisting of 15 fHRV measures reflecting the fetal inflammatory response with prediction accuracy of 90%. Hierarchical clustering validated the selection of 14 out of 15 fHRV measures comprising FII. We developed methodology to identify a distinctive subset of fHRV measures that tracks inflammation over time. The broader potential of this bioinformatics approach is discussed to detect physiological responses encoded in HRV measures.

Instrumentation of Near-term Fetal Sheep for Multivariate Chronic Non-anesthetized Recordings

The chronically instrumented pregnant sheep has been used as a model of human fetal development and responses to pathophysiologic stimuli such as endotoxins, bacteria, umbilical cord occlusions, hypoxia and various pharmacological treatments. The life-saving clinical practices of glucocorticoid treatment in fetuses at risk of premature birth and the therapeutic hypothermia have been developed in this model. This is due to the unique amenability of the non-anesthetized fetal sheep to the surgical placement and maintenance of catheters and electrodes, allowing repetitive blood sampling, substance injection, recording of bioelectrical activity, application of electric stimulation and in vivo organ imaging. Here we describe the surgical instrumentation procedure required to achieve a stable chronically instrumented non-anesthetized fetal sheep model including characterization of the post-operative recovery from blood gas, metabolic and inflammation standpoints.

Fetal MRI detects early alterations of brain development in Tetralogy of Fallot

OBJECTIVE

Prenatal imaging has identified alterations of brain growth in fetuses with congenital heart disease. However, little is known about the timing of altered brain development and its occurrence in specific congenital heart disease subgroups. This magnetic resonance imaging study aimed to identify early (median, 25 gestational weeks [GW]) changes in fetal total brain (TBV), gray matter (GMV), and subcortical brain (SBV) volumes in Tetralogy of Fallot (TOF) cases in utero.

STUDY DESIGN

Fetal magnetic resonance imaging (1.5 Tesla) was performed in 24 fetuses who were diagnosed with TOF and 24 normal age-matched control fetuses (20-34 GW). TBV, GMV, SBV, intracranial cavity, cerebellar, ventricular, and external cerebrospinal fluid volumes were quantified by manual segmentation based on coronal T2-weighted sequences. Mixed model analyses of variance and t-tests were conducted to compare cases and control fetuses.

RESULTS

TBV was significantly lower (P < .001) in early (<25 GW) and late TOF cases. Both GMV (P = .003) and SBV (P = .001) were affected. The GMV-to-SBV ratio declined in fetuses with TOF (P = .026). Compared with normal fetuses, ventricular volume was increased (P = .0048). External cerebrospinal fluid was enlarged in relation to head size (P < .001). Intracranial cavity volume (P = .314) and cerebellar volume (P = .074) were not significantly reduced in fetuses with TOF.

CONCLUSION

TOF is associated with smaller volumes of gray and white matter and enlarged cerebrospinal fluid spaces. These changes are present at ≤25 GW and indicate altered fetal brain growth in this pathophysiologic entity during early stages of human brain development.

Does heart rate variability reflect the systemic inflammatory response in a fetal sheep model of lipopolysaccharide-induced sepsis?

Fetal inflammatory response occurs during chorioamnionitis, a frequent and often subclinical inflammation associated with increased risk for brain injury and life-lasting neurologic deficits. No means of early detection exist. We hypothesized that systemic fetal inflammation without septic shock will be reflected in alterations of fetal heart rate (FHR) variability (fHRV) distinguishing baseline versus inflammatory response states. In chronically instrumented near-term fetal sheep (n = 24), we induced an inflammatory response with lipopolysaccharide (LPS) injected intravenously (n = 14). Ten additional fetuses served as controls. We measured fetal plasma inflammatory cytokine IL-6 at baseline, 1, 3, 6, 24 and 48 h. 44 fHRV measures were determined continuously every 5 min using continuous individualized multi-organ variability analysis (CIMVA). CIMVA creates an fHRV measures matrix across five signal-analytical domains, thus describing complementary properties of fHRV. Using principal component analysis (PCA), a widely used technique for dimensionality reduction, we derived and quantitatively compared the CIMVA fHRV PCA signatures of inflammatory response in LPS and control groups. In the LPS group, IL-6 peaked at 3 h. In parallel, PCA-derived fHRV composite measures revealed a significant difference between LPS and control group at different time points. For the LPS group, a sharp increase compared to baseline levels was observed between 3 h and 6 h, and then abating to baseline levels, thus tracking closely the IL-6 inflammatory profile. This pattern was not observed in the control group. We also show that a preselection of fHRV measures prior to the PCA can potentially increase the difference between LPS and control groups, as early as 1 h post LPS injection. We propose a fHRV composite measure that correlates well with levels of inflammation and tracks well its temporal profile. Our results highlight the potential role of HRV to study and monitor the inflammatory response non-invasively over time.

Fetal microglial phenotype in vitro carries memory of prior in vivo exposure to inflammation

Objective: Neuroinflammation in utero may result in life-long neurological disabilities. The molecular mechanisms whereby microglia contribute to this response remain incompletely understood.

Methods: Lipopolysaccharide (LPS) or saline were administered intravenously to non-anesthetized chronically instrumented near-term fetal sheep to model fetal inflammation in vivo. Microglia were then isolated from in vivo LPS and saline (naïve) exposed animals. To mimic the second hit of neuroinflammation, these microglia were then re-exposed to LPS in vitro. Cytokine responses were measured in vivo and subsequently in vitro in the primary microglia cultures derived from these animals. We sequenced the whole transcriptome of naïve and second hit microglia and profiled their genetic expression to define molecular pathways disrupted during neuroinflammation.

Results:In vivo LPS exposure resulted in IL-6 increase in fetal plasma 3 h post LPS exposure. Even though not histologically apparent, microglia acquired a pro-inflammatory phenotype in vivo that was sustained and amplified in vitro upon second hit LPS exposure as measured by IL-1β response in vitro and RNAseq analyses. While NFKB and Jak-Stat inflammatory pathways were up regulated in naïve microglia, heme oxygenase 1 (HMOX1) and Fructose-1,6-bisphosphatase (FBP) genes were uniquely differentially expressed in the second hit microglia. Compared to the microglia exposed to LPS in vitro only, the transcriptome of the in vivo LPS pre-exposed microglia showed a diminished differential gene expression in inflammatory and metabolic pathways prior and upon re-exposure to LPS in vitro. Notably, this desensitization response was also observed in histone deacetylases (HDAC) 1, 2, 4, and 6. Microglial calreticulin/LRP genes implicated in microglia-neuronal communication relevant for the neuronal development were up regulated in second hit microglia.

Discussion: We identified a unique HMOX1_down and FBP^up phenotype of microglia exposed to the double-hit suggesting interplay of inflammatory and metabolic pathways. Our findings suggest that epigenetic mechanisms mediate this immunological and metabolic memory of the prior inflammatory insult relevant to neuronal development and provide new therapeutic targets for early postnatal intervention to prevent brain injury.

Autonomic Functioning in Young Adults Born at Extremely Low Birth Weight

Autonomic functioning is altered in infants born at extremely low birth weight (ELBW; <1000 g), but we know little about how such alterations manifest in adulthood. We examined associations between birth weight and resting heart rate (R-R interval), high-frequency (HF) and low-frequency (LF) heart rate variability, and systolic (SBP) and diastolic (DBP) blood pressure, in 60 participants (ages 22-26) born at ELBW and free of major neurosensory impairment, and 79 controls born at normal birth weight (NBW; >2500 g). HF in the smallest-born ELBW participants was significantly lower than in NBW controls. In both groups, greater birth weight was associated with higher HF. Among ELBW survivors, lower birth weight predicted faster heart rate and higher DBP, but neither heart rate nor DBP appeared to be well-coordinated with baroreflex activity (LF), the principal mechanism for short-term blood pressure regulation. Adult autonomic regulation may be significantly altered in those born extremely preterm.

Correlating multidimensional fetal heart rate variability analysis with acid-base balance at birth

Fetal monitoring during labour currently fails to accurately detect acidemia. We developed a method to assess the multidimensional properties of fetal heart rate variability (fHRV) from trans-abdominal fetal electrocardiogram (fECG) during labour. We aimed to assess this novel bioinformatics approach for correlation between fHRV and neonatal pH or base excess (BE) at birth.We enrolled a prospective pilot cohort of uncomplicated singleton pregnancies at 38-42 weeks' gestation in Milan, Italy, and Liverpool, UK. Fetal monitoring was performed by standard cardiotocography. Simultaneously, with fECG (high sampling frequency) was recorded. To ensure clinician blinding, fECG information was not displayed. Data from the last 60 min preceding onset of second-stage labour were analyzed using clinically validated continuous individualized multiorgan variability analysis (CIMVA) software in 5 min overlapping windows. CIMVA allows simultaneous calculation of 101 fHRV measures across five fHRV signal analysis domains. We validated our mathematical prediction model internally with 80:20 cross-validation split, comparing results to cord pH and BE at birth.The cohort consisted of 60 women with neonatal pH values at birth ranging from 7.44 to 6.99 and BE from -0.3 to -18.7 mmol L(-1). Our model predicted pH from 30 fHRV measures (R(2) = 0.90, P < 0.001) and BE from 21 fHRV measures (R(2) = 0.77, P < 0.001).Novel bioinformatics approach (CIMVA) applied to fHRV derived from trans-abdominal fECG during labor correlated well with acid-base balance at birth. Further refinement and validation in larger cohorts are needed. These new measurements of fHRV might offer a new opportunity to predict fetal acid-base balance at birth.

Biphasic changes in fetal heart rate variability in preterm fetal sheep developing hypotension after acute on chronic lipopolysaccharide exposure

Perinatal exposure to infection is highly associated with adverse outcomes. Experimentally, acute, severe exposure to gram-negative bacterial lipopolysaccharide (LPS) is associated with increased fetal heart rate variability (FHRV). It is unknown whether FHRV is affected by subclinical infection with or without acute exacerbations. We therefore tested the hypothesis that FHRV would be associated with hypotension after acute on chronic exposure to LPS. Chronically instrumented fetal sheep at 0.7 gestation were exposed to a continuous low-dose LPS infusion (n = 12, 100 ng/kg over 24 h, followed by 250 ng·kg(-1)·24 h(-1) for a further 96 h) or the same volume of saline (n = 10). Boluses of either 1 μg LPS or saline were given at 48, 72, and 96 h. Low-dose infusion was not associated with hemodynamic or FHRV changes. The first LPS bolus was associated with tachycardia and suppression of nuchal electromyographic activity in all fetuses. Seven of twelve fetuses developed hypotension (a fall in mean arterial blood pressure ≥5 mmHg). FHRV was transiently increased only at the onset of hypotension, in association with increased cytokine induction and electroencephalogram suppression. FHRV then fell before the nadir of hypotension, with transient suppression of short-term FHRV. After the second LPS bolus, the hypotension group showed a biphasic pattern of a transient increase in FHRV followed by more prolonged suppression. These findings suggest that infection-related hypotension in the preterm fetus mediates the transient increase in FHRV and that repeated exposure to LPS leads to progressive loss of FHRV.

Protective effect of Euterpe oleracea Mart (açaí) extract on programmed changes in the adult rat offspring caused by maternal protein restriction during pregnancy

Objectives

This study examined the effect of açaí (Euterpe oleracea Mart.) seed extract (ASE) on cardiovascular and renal alterations in adult offspring, whose mothers were fed a low-protein (LP) diet during pregnancy.

Methods

Four groups of rats were fed: control diet (20% protein); ASE (200 mg/kg per day); and LP (6% protein); LP + ASE (6% protein + ASE) during pregnancy. After weaning, all male offspring were fed a control diet and sacrificed at 4 months old. We evaluated the blood pressure, vascular function, serum and urinary parameters, plasma and kidney oxidative damage, and antioxidant activity and renal structural changes.

Key findings

Hypertension and the reduced acetylcholine-induced vasodilation in the LP group were prevented by ASE. Serum levels of urea, creatinine and fractional excretion of sodium were increased in LP and reduced in LP + ASE. ASE improved nitrite levels and the superoxide dismutase and glutathione peroxidase activity in LP, with a corresponding decrease of malondialdehyde and protein carbonyl levels. Kidney volume and glomeruli number were reduced and glomerular volume was increased in LP. These renal alterations were prevented by ASE.

Conclusions

Treatment of protein-restricted dams with ASE provides protection from later-life hypertension, oxidative stress, renal functional and structural changes, probably through a vasodilator and antioxidant activity.

Sampling rate of heart rate variability impacts the ability to detect acidemia in ovine fetuses near-term

BACKGROUND

To evaluate the impact of sampling rate on the predictive capability of continuous fetal heart rate (FHR) variability (fHRV) monitoring for detecting fetal acidemia during labor, we tested the performance of the root mean square of successive differences (RMSSD) in R-R intervals from the ECG when acquired with the sampling rate of 4 Hz currently available in FHR monitors, in comparison to the gold standard of 1000 Hz.

METHODS

Near-term ovine fetuses (N = 9) were chronically prepared with precordial electrodes for recording ECG, vascular catheters for blood sampling, and an umbilical cord occluder. For 1 min every 2.5 min, animals underwent mild partial umbilical cord occlusions (UCO) × 1 h, moderate partial UCO × 1 h, then complete UCO × 2 h, or until arterial pH reached <7.00. Arterial blood samples were drawn at baseline and every 20 min during the UCO series. RMSSD was calculated continuously in 5 min windows using an automated, standardized system (CIMVA.com). RESULTS are presented as mean ± SEM with significance assumed for p < 0.05.

RESULTS

Repetitive UCO resulted in pH decreasing from 7.35 ± 0.01 to 7.00 ± 0.03. In all nine animals, RMSSD increased from 16.7 ± 1.0 ms at baseline to 44.4 ± 2.3 ms, 70 ± 15 min prior to reaching the pH nadir when sampled at 1000 Hz. When sampled at 4 Hz, RMSSD at baseline measured 36.1 ± 6.0 ms and showed no significant increase during the UCO series until the pH nadir was reached. Consequently, early detection of severe hypoxic-acidemia would have been missed in all fetuses.

CONCLUSION

RMSSD as a measure of fHRV when calculated from FHR sampled at 1000 Hz allowed for the early detection of worsening hypoxic-acidemia in each fetus. However, when calculated at the low sampling rate of 4 Hz used clinically, RMSSD remained unchanged until terminally when the nadir pH was reached. For early detection of fetal acidemia during labor, more sensitive means of acquiring FHR are therefore recommended than currently deployed, e.g., trans-abdominal fetal ECG.

Preterm birth has sex-specific effects on autonomic modulation of heart rate variability in adult sheep

INTRODUCTION

Globally, 11% of infants are born preterm. In adulthood, individuals born preterm are at increased risk of cardiovascular morbidity and mortality, but the mechanistic basis of this remains unknown. Clinically overt cardiovascular disease may be preceded by altered cardiac autonomic activity characterised by increased sympathetic activity and/or reduced parasympathetic activity. Thus, altered cardiac autonomic activity in survivors of preterm birth may underlie later cardiovascular risk.

OBJECTIVE

To investigate the impact of gestational age on cardiac autonomic activity in juvenile and adult sheep.

METHODS AND RESULTS

Singleton-bearing ewes were randomised antenatally to spontaneous term birth (TC; n=73) or corticosteroid induced preterm birth (PT; n=60). Cardiac autonomic modulation was assessed using heart rate variability analysis in juvenile and adult offspring. Preterm birth in adult males was associated with altered sympatho-vagal modulation (LFnu: PT 64 ± 4 vs. TC 49 ± 4, p<0.05; LogLF/HF: PT 1.8 ± 0.1 vs. TC 1.5 ± 0.1, p<0.05) and reduced parasympathetic modulation (LogRMSSD: PT 2.9 ± 0.2 vs. TC 3.4 ± 0.1, p<0.05; LogNN50: PT 0.3 ± 0.4 vs. TC 1.6 ± 0.4, p<0.05). Within the range of term birth, each one-day increment in gestational age was associated with a decrement in LFnu in juvenile females and with a decrement in LFnu and LF/HF ratio, but an increment in RMSSD and NN50 in adult females.

CONCLUSIONS

Cardiac autonomic function in adult sheep is affected in a sex-specific manner by gestational age at birth, even within the term range. Altered cardiac autonomic function may contribute to increased later cardiovascular morbidity in those born preterm.

Prenatal development of the fetal thoracic sympathetic trunk in sheep (Ovis aries)

This study aims at clarifying the detailed morphological and topographical changes of the thoracic part of the sympathetic trunk of sheep during fetal development. Bilateral micro-dissection of the thoracic sympathetic trunk was performed on 40 sheep fetuses aged 6-20 weeks (18 males and 22 females) under a stereomicroscope. The cervicothoracic ganglion (CTG) was observed on 75/80 sides (93.7%) and was composed of the caudal cervical and the first thoracic ganglia on 45/80 sides (56.2%), and of the caudal cervical and the first two thoracic ganglia on 30/80 sides (37.5%). The presence of the two last (12th-13th) thoracic ganglia was not constant. The influence of the sex, the side of the body, and the ages of the fetus on the morphology and topography of the thoracic sympathetic trunk in sheep were identified. In spite of the differences in the morphology and topography of the thoracic sympathetic trunk between early and late fetal developments, the morphology and topography of the older fetal thoracic sympathetic trunk tended to be similar to that of the adult sheep. To comprehend the comparative morphology of the fetal thoracic sympathetic trunk more completely, our results were compared with previous studies. Consequently, differences and similarities in the composition and position of the CTG, presence of single caudal cervical ganglion without fusion to the thoracic ganglia, and absence of the thoracic ganglia, and presence of splitting of the interganglionic branch were found among sheep, pig, and human fetuses. Therefore, sheep might be the appropriate animal model to be applied in human sympathetic nervous system.

Heart rate-mediated blood pressure control in preterm fetal sheep under normal and hypoxic-ischemic conditions

BACKGROUND

The understanding of hypoxemia-induced changes in baroreflex function is limited and may be studied in a fetal sheep experiment before, during, and after standardized hypoxic conditions.

METHODS

Preterm fetal lambs were instrumented at 102 d gestation (term: 146 d). At 106 d, intrauterine hypoxia--ischemia was induced by 25 min of umbilical cord occlusion (UCO). Baroreflex-related fluctuations were calculated at 30-min intervals during the first week after UCO by transfer function (cross-spectral) analysis between systolic blood pressure (SBP) and R-R interval fluctuations, estimated in the low-frequency (LF, 0.04-0.15 Hz) band. LF transfer gain (baroreflex sensitivity) and delay (s) reflect the baroreflex function.

RESULTS

Baseline did not differ in LF transfer gain and delay between controls and the UCO group. In controls, LF gain showed postnatal increase. By contrast, LF gain gradually decreased in the UCO group, resulting in significantly lower values 4-7 d after UCO. In the UCO group, LF delay increased and differed significantly from controls.

CONCLUSION

Our results show that intrauterine hypoxia-ischemia results in reduced baroreflex sensitivity over a period of 7 d, indicating limited efficacy to buffer BP changes by adapting heart rate. Cardiovascular dysregulation may augment already present cerebral damage after systemic hypoxia-ischemia in the reperfusion period.

Effects of early- and late-gestational maternal stress and synthetic glucocorticoid on development of the fetal hypothalamus-pituitary-adrenal axis in sheep

Prenatal maternal stress (PMS) programs dysregulation of the hypothalamus-pituitary-adrenal axis (HPAA) in postnatal life, though time periods vulnerable to PMS, are still unclear. We evaluated in pregnant sheep the effect of PMS during early gestation [30-100 days of gestation (dGA); term is 150 dGA] or late gestation (100-120 dGA) on development of fetal HPAA function. We compared the effects of endogenous cortisol with synthetic glucocorticoid (GC) exposure, as used clinically to enhance fetal lung maturation. Pregnant sheep were exposed to repeated isolation stress twice per week for 3 h in a separate box with no visual, tactile, or auditory contact with their flock-mates either during early (n = 7) or late (n = 7) gestation. Additional groups received two courses of betamethasone (BM; n = 7; 2 × 110 μg kg(- 1) body weight, 24 h apart) during late gestation (106/107 and 112/113 dGA, n = 7) or acted as controls (n = 7). Fetal cortisol responses to hypotensive challenge, a physiological fetal stressor, were measured at 112 and 129 dGA, i.e. before and during maturation of the HPAA. Hypotension was induced by fetal infusion of sodium nitroprusside, a potent vasodilator. At 112 dGA, neither PMS nor BM altered fetal cortisol responses. PMS, during early or late gestation, and BM treatment increased fetal cortisol responses at 129 dGA with the greatest increase achieved in stressed early pregnant sheep. Thus, development of the HPAA is vulnerable to inappropriate levels of GCs during long periods of fetal life, whereas early gestation is most vulnerable to PMS.

Doppler ultrasonographic assessment of maternal and fetal blood flow in abnormal canine pregnancy

The aim of this study was to describe the changes of uterine artery, umbilical artery and fetal abdominal aorta, renal and internal carotid arteries blood flow in abnormal canine pregnancy. Twenty-two, Brucella-negative pregnant bitches were retrospectively classified into abnormal (which had either interrupted their pregnancy between days 52 and 60 or had perinatal death >60% of the litter; n=11) and normal (which had delivered healthy puppies at term; n=11). In all the animals, color and pulsed-wave Doppler examinations of uterine artery were conducted every 10 days from Day 20 to 50 from estimated luteinizing hormone peak. Doppler ultrasonography was also conducted in the fetuses to assess umbilical artery, abdominal aorta, renal and internal carotid arteries from Day 40 to 60 of gestation. Throughout the study, resistance index (RI) of uterine, umbilical and fetal renal arteries decreased up to -15% compared to -36% (P<0.01), -11% compared to -23% (P<0.05) and 2% compared to -13% (P<0.05), respectively in the abnormal and normal bitches. Fetal abdominal aorta and internal carotid did not differ between groups (P>0.05). It is concluded that in dogs, uterine artery, umbilical artery and fetal renal artery RI differ between normal and abnormal gestation being useful for the prediction of adverse obstetric outcome.

Effects of maternal breathing rate, psychiatric status, and cortisol on fetal heart rate

Women's experiences during pregnancy are predictive of variation in neurobehavioral profiles in their children. Few studies have assessed these relationships during the prenatal period. In 113 women in the 36(th) -38(th) gestational week (mean age 26.3 ± 5.4 years), electrocardiogram, blood pressure, respiration, salivary cortisol, and fetal heart rate (HR) were measured during baseline, a psychological challenge (Stroop color-word matching task), and a standardized paced breathing protocol. Subjects underwent the Structured Clinical Interview for DSM-IV prior to testing and were grouped as: depressed, co-morbid for depression and anxiety, anxiety disorder only, and control. There was a significant main effect of maternal diagnostic group on fetal HR only during the Stroop task: fetuses of women in the co-morbid group had a greater HR increase compared to controls (p < .05). Overall, fetuses showed robust increases in HR during paced breathing (p < .0001), and there was no significant difference by maternal diagnosis. For both tasks, changes in fetal HR were independent of women's concurrent cardiorespiratory activity. Finally, although cortisol was higher in the co-morbid group (p < .05), across all participants, there was a trend for maternal baseline cortisol to be positively associated with average fetal HR (p = .06). These findings indicate that variation in fetal HR reactivity-an index of emerging regulatory capacities-is likely influenced by multiple acute and chronic factors associated with women's psychobiology.

Fetal and offspring arrhythmia following exposure to nicotine during pregnancy

Although recent studies have demonstrated prenatal nicotine can increase cardiovascular risk in the offspring, it is unknown whether exposure to nicotine during pregnancy also may be a risk for development of arrhythmia in the offspring. In addition, in previous studies of fetal arrhythmia affected by smoking, only two patterns, bradycardia and tachycardia, were observed. The present study examined acute effects of maternal nicotine on the fetal arrhythmia in utero, and chronic influence on offspring arrhythmia at adult stage following prenatal exposure to nicotine. Nicotine was administered to pregnant ewes and rats. In the fetal sheep, intravenous nicotine not only induced changes of fetal heart rate, but also caused cardiac cycle irregularity, single and multiple dropped cardiac cycles. Although maternal nicotine had no influence on fetal blood pH, lactic acid, hemocrit, Na(+), K(+) levels and plasma osmolality, fetal blood PO(2) levels were significantly decreased following maternal nicotine in ewes. In offspring rats at 4-5 months after birth, prenatal exposure to nicotine significantly increased heart rate and premature ventricular contraction in restraint stress. In addition, arrhythmias induced by injection of nicotine were higher in the offspring prenatal exposure to nicotine in utero. The results provide new evidence that exposure to nicotine in pregnancy can cause fetal arrhythmia in various patterns besides tachycardia and bradycardia, the possible mechanisms for nicotine-induced fetal arrhythmia included in utero hypoxia. Importantly, following exposure to nicotine significantly increased risk of arrhythmia in the adult offspring. The finding offers new insight for development of cardiac rhythm problems in fetal origins.

Validation of spontaneous assessment of baroreceptor reflex sensitivity and its relation to heart rate variability in the ovine fetus pre- and near-term

Assessment of baroreceptor reflex sensitivity (BRS) in the ovine fetus provides insight into autonomic cardiovascular regulation. Currently, assessment of BRS relies on vasoactive drugs, but this approach is limited by feasibility issues and by the nonphysiologic nature of the stimulus. Thus we aimed to validate the method of spontaneous BRS assessment against the reference method of using vasoactive drugs in preterm (0.76 gestation, n = 16) and near-term (0.86 gestation, n = 16) chronically instrumented ovine fetuses. The BRS measures derived from the spontaneous and reference methods correlated at both gestational ages (R = 0.67 ± 0.03). The sequence method of spontaneous BRS measures also correlated both to the root mean square of standard deviations (RMSSD), which is a measure of fetal heart rate variability reflecting vagal modulation (R = 0.69 ± 0.03), and to fetal body weight (R = 0.65 ± 0.03), which is a surrogate for growth trajectory of each fetus. The methodology presented may aid in developing new models to study BRS and cardiovascular control in ovine fetus in the last trimester of pregnancy.

Nonlinear properties of vagal and sympathetic modulations of heart rate variability in ovine fetus near term

Fetal heart rate (FHR) monitoring is commonly used although clinical studies questioned its diagnostic value. Sophisticated FHR variability (fHRV) measures such as fHRV complexity may improve the sensitivity and specificity of FHR monitoring. A more detailed understanding of the physiology underlying fHRV complexity is essential to harness its use for monitoring fetal health. To examine the specific effects of vagal and sympathetic modulations on fHRV complexity, we blocked vagal activity with atropine and sympathetic activity with propranolol in near-term fetal sheep ( n = 7, 0.85 gestation). Under these conditions, we analyzed the linear and nonlinear parts of fHRV complexity from autonomic information flow. Overall fHRV complexity decreased with both drugs compared with nonrapid eye movement sleep baseline ( P < 0.05). With atropine, this was because of a decrease of the linear part of fHRV complexity on the long-term time scale ( P < 0.05), suggesting that vagal modulation of fHRV is adequately described by linear fHRV measures. With propranolol, the nonlinear part of fHRV complexity decreased on the short-term time scale ( P < 0.05), suggesting that sympathetic influences on fHRV can be detected by the nonlinear part of fHRV complexity. Thus the complex interplay of vagal and sympathetic modulations of fHRV is reflected differently and specifically in the linear and nonlinear properties of fHRV complexity, and on different time scales. Analysis of linear and nonlinear properties of fHRV may improve sensitivity and specificity of FHR monitoring.

Is baroreflex control of sympathetic activity and heart rate active in the preterm fetal sheep?

The arterial baroreflex is a fundamental reflex that buffers rapid changes in arterial blood pressure (BP) via regulation of the heart rate and sympathetic nerve activity to the vasculature. In adults a sigmoidal relationship between BP and both heart rate and sympathetic nerve activity is well documented. Its role in blood pressure control before birth is unclear. Preterm babies have a high incidence of low BP, especially in the first few days of life, which could be related, in part, to immaturity of the baroreflex. In the present study, we investigated the baroreflex control of fetal heart rate and renal sympathetic nerve activity (RSNA) in preterm fetal sheep in utero (102 ± 1 days of gestation; term 140 days). Phenylephrine was associated with a significant increase in BP from 38 ± 2 to 58 ± 3 mmHg and a decrease in heart rate (HR) from 177 ± 4 to 116 ± 8 beats per minute (bpm). Sodium nitroprusside was associated with a significant fall in BP from 38 ± 2 to 26 ± 1 mmHg and an increase in HR from 182 ± 4 to 274 ± 8 bpm. However, the time between the 50% changes in BP and HR was significantly greater after hypotension than hypertension (31 ± 8 s vs. 14 ± 5 s, P < 0.05). No significant changes in RSNA occurred with either stimulus. This suggests that there are different maturational tempos for the components of the central autonomic response to altered blood pressure.

Adverse effects of antenatal glucocorticoids on cerebral myelination in sheep

OBJECTIVE

To determine in fetal sheep the effect of betamethasone on myelination in relation to stage of myelination, number of treatment courses, dose, and route of administration.

METHODS

Fetal expression of myelin basic protein (MBP), a marker of mature oligodendrocytes and myelin, was determined between 0.27 and 0.93 gestation. Short-term betamethasone effects were examined 24 hours after one maternal intramuscular treatment course (weight adjusted to equal the clinical dose of 2 x 8 mg betamethasone to a 70-kg woman) at 0.63, 0.75, and 0.87 gestation or after continuous 48-hour fetal intravenous infusion at 0.75 and 0.87 gestation. Lasting effects were examined 20 days after one and two treatment courses weight-adapted to the clinical dose of 2 x 8 mg or 2 x 12 mg betamethasone at 0.75 gestation.

RESULTS

Myelin basic protein immunoreactivity was first detected in the internal capsule at 0.53 gestation, followed by the centrum semiovale, the superficial white matter, and corpus callosum at 0.63 gestation. Within 24 hours after treatment, betamethasone reduced the number of mature oligodendrocytes and MBP immunoreactivity. The effect decreased with gestational age. Maternal and fetal betamethasone administration had similar effects. Loss of MBP immunoreactivity was not reversed 20 days after two treatment courses, independent of dose.

CONCLUSION

Betamethasone-induced delayed cerebral myelination is dependent on the stage of brain development in sheep. Betamethasone-related disturbances in myelination and any potential contribution to childhood behavior deficits need to be confirmed in clinical studies.

Heart rate variability analysis allows early asphyxia detection in ovine fetus

Fetal heart rate (FHR) monitoring is commonly used to predict asphyxia but clinical and experimental studies have questioned its diagnostic value. We examined the usefulness of fetal heart rate variability (fHRV) measures in detecting early asphyxia using chronically instrumented fetal sheep under normoxic (n = 6) and asphyxic conditions (3 umbilical cord occlusions, n = 6). The occlusions consistently led to pH decreases from 7.35 +/- 0.01 to 7.09 +/- 0.03 ( P < .05). FHR showed biphasic deceleration during each occlusion, associated with increasing arterial blood pressure ( P < .05). RMSSD, an index of vagal modulation of fHRV, increased consistently during repeated occlusion induced FHR decelerations ( P < .05). Under normoxic conditions, RMSSD did not change during FHR decelerations and decreased during FHR accelerations ( P < .05). Our results suggest that an increase of RMSSD in association with FHR decelerations reflects initial vagal activation during fetal asphyxia. RMSSD may accurately identify asphyxic fetuses early. Clinical validation is needed.

Protein restriction during gestation and/or lactation causes adverse transgenerational effects on biometry and glucose metabolism in F1 and F2 progenies of rats

Substantial evidence suggests that poor intrauterine milieu elicited by maternal nutritional disturbance may programme susceptibility in the fetus to later development of chronic diseases, such as obesity, hypertension, cardiovascular disease and diabetes. One of the most interesting features of fetal programming is the evidence from several studies that the consequences may not be limited to the first-generation offspring and that it can be passed transgenerationally. In the present study, female rats (F0) were fed either a normal-protein diet [control diet (C); 19 g of protein/100 g of diet] or a low-protein diet [restricted diet (R); 5 g of protein/100 g of diet]. The offspring were termed according to the period and the types of diet the dams were fed, i.e. CC, RC, CR and RR (first letter indicates the diet during gestation and the second the diet during lactation). At 3 months of age, F1 females were bred to proven males, outside the experiment, to produce F2 offspring. At weaning, F2 offspring were divided by gender. RC1 offspring (with the number indicating the filial generation) were born with low birthweight, but afterwards they had catch-up growth, reaching the weight of the CC1 offspring. The increased glycaemia in RC1 offspring was associated with insulin resistance. CR1 and RR1 offspring had impaired growth with no changes in glucose metabolism. RC2 offspring had high BM (body mass) at birth, which was sustained over the whole experiment in male offspring. The F2 generation had more alteration in glucose metabolism than the F1 generation. CR2 and RC2 offspring had hyperglycaemia accompanied by hyperinsulinaemia and insulin resistance in both genders. CR2 offspring had an increase in body adiposity with hyperleptinaemia. In conclusion, low protein during gestation improves BM, fat mass and growth rate in F1 rats, but has adverse effects on glucose and leptin metabolism, resulting in insulin resistance in adult F1 and F2 offspring. Low protein during lactation has adverse effects on glucose, insulin and leptin metabolism, resulting in insulin resistance in adult F2 offspring. These findings suggest that low protein during gestation and/or lactation can be passed transgenerationally to the second generation.

Male disadvantage? Fetal sex and cardiovascular responses to asphyxia in preterm fetal sheep

Clinically and experimentally male fetuses are at significantly greater risk of dying or suffering injury at birth, particularly after premature delivery. We undertook a retrospective cohort analysis of 60 female and 65 male singleton preterm fetal sheep (103–104 days, 0.7 gestation) with mean arterial blood pressure (MAP), heart rate, and carotid and femoral blood flow recordings during 25 min of umbilical cord occlusion in utero. Occlusions were stopped early if fetal MAP fell below 8 mmHg or if there was asystole for >20 s. Fetuses that were able to complete the full 25-min period of occlusion showed no differences between sexes for any cardiovascular responses. Similar numbers of occlusions were stopped early in males (mean: 21 min, n = 16) and females (mean: 23 min, n = 16); however, they showed different responses. Short-occlusion males ( n = 16) showed a slower initial fall in femoral vascular conductance, followed by greater bradycardia, hypotension, and associated organ hypoperfusion compared with full-occlusion fetuses. In contrast, short-occlusion females ( n = 16) showed a significantly more rapid early increase in femoral vascular conductance than the full-occlusion fetuses, followed by worsening of bradycardia and hypotension that was intermediate to the full-occlusion fetuses and short-occlusion males. Among all fetuses, MAP at 15 min of occlusion, corresponding with the time of the maximal rate of fall, was correlated with postmortem weight in males ( R2 = 0.07) but not females. In conclusion, male and female fetuses showed remarkably similar chemoreflex and hemodynamic responses to severe asphyxia, but some males did show impaired hemodynamic adaptation within the normal weight range.