Carlos E Blanco

The response to hypoxia of arterial chemoreceptors in fetal sheep and new-born lambs.

Carotid chemoreceptor activity was detected in each of fourteen halothane or pentobarbitone anaesthetized exteriorized fetal lambs of 90‐143 days gestational age. Activity was about 5 Hz at a Pa,O2 of 25 mmHg and it increased as Pa,O2 was reduced, either by compressing the umbilical cord or by reducing the (FIO2) oxygen fraction of the gas used to ventilate the ewe. Activity increased briskly when 1‐2 ml CO2‐saturated saline was injected retrogradely into the lingual artery, but not when saline of pH 7.4 or fetal arterial blood was injected. In two fetuses near‐term chemoreceptor activity was recorded continuously whilst the umbilical cord was ligated and ventilation with air started. Activity increased 200‐500% as Pa,O2 fell, but then fell to below control as Pa,O2 rose. We suggest that these changes in activity reflect those occurring naturally at birth. No spontaneous chemoreceptor activity could be detected on the day of birth in twelve pentobarbitone anaesthetized lambs delivered vaginally or by Caesarean section at 135‐146 days. Single baroreceptor activity could however be recorded in these lambs, and chemoreceptor activity could be elicited by hypercapnia. Spontaneous chemoreceptor activity was detected in six of seven lambs more than 2 days old. In eight conscious lambs the steady‐state respiratory response to isocapnic hypoxia was variable on the day of birth. In six of these lambs the response was significantly greater by the third day. We conclude that the arterial chemoreceptors are active and responsive in the fetus, but quiescent in the lamb on the day of birth when Pa,O2 has risen. The hypoxic sensitivity of the chemoreceptors is reset from the fetal to the adult range over the next few days.

Prenatal stress and neonatal rat brain development

Chronic or repeated stress during human fetal brain development has been associated with various learning, behavioral, and/or mood disorders, including depression in later life. The mechanisms accounting for these effects of prenatal stress are not fully understood. The aim of this study was to investigate the effects of prenatal stress on early postnatal brain development, a disturbance of which may contribute to this increased vulnerability to psychopathology. We studied the effects of prenatal stress on fetal growth, stress-induced corticosterone secretion, brain cell proliferation, caspase-3-like activity and brain-derived neurotrophic factor protein content in newborn Fischer 344 rats. In addition to a slight reduction in birth weight, prenatal stress was associated with elevated corticosterone levels (33.8%) after 1 h of maternal deprivation on postnatal day 1, whereas by postnatal day 8 this pattern was reversed (-46.5%). Further, prenatal stress resulted in an approximately 50% decrease in brain cell proliferation just after birth in both genders with a concomitant increase in caspase-3-like activity within the hippocampus at postnatal day 1 (36.1%) and at postnatal day 5 (females only; 20.1%). Finally, brain-derived neurotrophic factor protein content was reduced in both the olfactory bulbs (-24.6%) and hippocampus (-28.2%) of prenatally stressed male offspring at postnatal days 1 and 5, respectively. These detrimental central changes observed may partly explain the increased susceptibility of prenatally stressed subjects to mood disorders including depression in later life.

Prenatal Restraint Stress and Long-Term Affective Consequences

Chronic or repeated stress during critical periods of human fetal brain development has been associated with various learning, behavioral and/or mood disorders in later life. In this investigation, pregnant Fischer 344 rats was individually restrained three times a day for 45 min during the last week of gestation in transparent plastic cylinders while at the same time being exposed to bright light. Control pregnant females were left undisturbed in their home cages. Anxiety and depressive-like behavior was measured in the offspring at an age of 6 months using the open field test, the home cage emergence test and the forced swim test. Prenatally stressed rats spent more time in the corners and less time along the walls of an open field, while no difference in total distance moved was observed. In addition, prenatally stressed rats took more time to leave their home cage in the home cage emergence test. On the other hand, no differences in immobility were observed in the forced swim test. Moreover, prenatally stressed rats showed lower stress-induced plasma corticosterone levels compared with control rats. Prenatal stress (PS) had no effect on the number of 5-bromo-2-deoxyuridine-positive cells – used as a measure for cell proliferation – in the dentate gyrus of these rats. These data further support the idea that PS may perturb normal anxiety-related development. However, the present data also suggest that an adaptive or protective effect of PS should not be ignored. Genetic factors are likely to play a role in this respect.

Chronic Hypoxia Stimulates Periarterial Sympathetic Nerve Development in Chicken Embryo

BackgroundEpidemiological findings suggest an association between low-for-age birth weight and the risk to develop coronary heart diseases in adulthood. During pregnancy, an imbalance between fetal demands and supply may result in permanent alterations of neuroendocrine development in the fetus. We evaluated whether chronic prenatal hypoxia increases arterial sympathetic innervation. Methods and ResultsChicken embryos were maintained from 0.3 to 0.9 of the 21-day incubation period under normoxic (21% O2) or hypoxic conditions (15% O2). At 0.9 incubation, the degree of sympathetic innervation of the embryonic femoral artery was determined by biochemical, histological, and functional (in vitro contractile reactivity) techniques. Chronic hypoxia increased embryonic mortality (32% versus 13%), reduced body weight (21.9±0.4 versus 25.4±0.6 g), increased femoral artery norepinephrine (NE) content (78.4±9.4 versus 57.5±5.0 pg/mm vessel length), and increased the density of periarterial sympathetic nerve fibers (14.4±0.7 versus 12.5±0.6 counts/104 &mgr;m2). Arteries from hypoxic embryos were less sensitive to NE (pD2, 5.99±0.04 versus 6.21±0.10). In the presence of cocaine, however, differences in sensitivity were no longer present. In the embryonic heart, NE content (156.9±11.0 versus 108.1±14.7 pg/mg wet wt) was also increased after chronic hypoxia. ConclusionsIn the chicken embryo, chronic moderate hypoxia leads to sympathetic hyperinnervation of the arterial system. In humans, an analogous mechanism may increase the risk for cardiovascular disease in adult life.

The role of oxygen in prenatal growth: studies in the chick embryo.

The compelling evidence linking small size at birth with later cardiovascular disease has renewed and amplified scientific and clinical interests into the determinants of fetal growth. It is accepted that genes and nutrition control fetal growth; however, prior to this study, it had been impossible to isolate the effect of increases and decreases in fetal oxygenation on the regulation of prenatal growth. We investigated the role of oxygen in the control of fetal growth in the chicken because in contrast to mammals, the effects on the fetus of changes in oxygenation could be isolated, by assessing them directly without alteration to the maternal or placental physiology or maternal nutrition during development. The data show that incubation at high altitude of fertilized eggs laid by sea level hens markedly restricted fetal growth. Incubation at high altitude of fertilized eggs laid by high altitude hens also restricted fetal growth, but to a lesser extent compared to eggs laid by sea level hens. By contrast, incubation at sea level of fertilized eggs laid by high altitude hens not only restored, but enhanced, fetal growth relative to sea level controls. Incubation at high altitude of sea level eggs with oxygen supplementation completely prevented the high altitude‐induced fetal growth restriction. Thus, fetal oxygenation, independent of maternal nutrition during development, has a predominant role in the control of fetal growth. Further, prolonged high altitude residence confers protection against the deleterious effects of hypoxia on fetal growth.

Baroreceptor reflex sensitivity in human neonates: the effect of postmenstrual age

We performed a cross‐sectional study in human infants to determine if indices of R–R interval variability, systolic blood pressure (SBP) variability, and baroreceptor reflex sensitivity change with postmenstrual age (PMA: gestational age + postnatal age). The electrocardiogram, arterial SBP and respiration were recorded in clinically stable infants (PMA, 28–42 weeks) in the quiet sleep state in the first days after birth. (Cross‐)spectral analyses of R–R interval series and SBP series were performed to calculate the power of low‐frequency (LF, indicating baroreceptor reflex activity, 0.04–0.15 Hz) and high‐frequency (HF, indicating parasympathetic activity, individualized between the p‐10 and p‐90 values of respiratory frequency) fluctuations, and transfer function phase and gain. The mean R–R interval, and LF and HF spectral powers of R–R interval series increased with PMA. The mean SBP increased with PMA, but not the LF and HF spectral powers of SBP series. In the LF range, cross‐spectral analysis showed high coherence values (> 0.5) with a consistent negative phase shift between R–R interval and SBP, indicating a ∼3 s lag in R–R interval changes in relation to SBP. Baroreceptor reflex sensitivity, calculated from LF transfer gain, increased significantly with PMA, from 5 (preterm) to 15 ms mmHg−1 (term). Baroreceptor reflex sensitivity correlated significantly with the (LF and) HF spectral powers of R–R interval series, but not with the LF and HF spectral powers of SBP series. The principal conclusions are that baroreceptor reflex sensitivity and spectral power in R–R interval series increase in parallel with PMA, suggesting a progressive vagal maturation with PMA.

Cardiac output distribution in response to hypoxia in the chick embryo in the second half of the incubation time

1 The fetus develops cardiovascular adaptations to protect vital organs in situations such as hypoxia and asphyxia. These include bradycardia, increased systemic blood pressure and redistribution of the cardiac output. The extent to which they involve maternal or placenta influences is not known. The objective of the present work was to study the cardiac output distribution in response to hypoxia in the chick embryo, which is independent of the mother. 2 Fertilized eggs were studied at three incubation times (10‐13 days, 14‐16 days and 17‐19 days of a normal incubation time of 21 days). Eggs were placed in a Plexiglass box in which the oxygen concentration could be changed. Eggs were opened at the air cell and a chorioallantoic vein was catheterized. Cardiac output distribution was measured with 15 μm fluorescent microspheres injected during normoxia, during the last minute of a 5 min period of hypoxia and after 5 min of subsequent reoxygenation. 3 Hypoxia caused a redistribution of the cardiac output in favour of heart (+17 to +160 % of baseline) and brain (+21 to +57 % of baseline) at the expense of liver (‐3 to ‐65 % of baseline), yolk‐sac (‐46 to ‐77 % of baseline) and carcass (‐6 to ‐33 % of baseline). 4 The magnitude of the changes in cardiac output distribution to the heart, brain, liver and carcass in response to hypoxia increased with advancing incubation time. 5 The data demonstrate the development of a protective redistribution of the cardiac output in response to hypoxia in the chick embryo from day 10 of incubation.

Long-chain polyunsaturated fatty acids in preterm infants: Status at birth and its influence on postnatal levels

To determine the influence of the prenatal long-chain polyunsaturated fatty acid (LCP) supply on prenatal growth and on postnatal LCP levels, we studied 52 preterm infants and assessed the relations between the LCP status at birth (reflecting the prenatal LCP supply), gestational age and prenatal growth, and the relation between the LCP status at birth and at 37 to 42 weeks of gestational age. After a correction for gestational age at birth, significant relations (p < or = 0.05) were observed between anthropometric measurements at birth (weight, head circumference, and length) and LCP levels in the umbilical artery wall, the LCP content of which reflects the long-term fetal LCP status. Independent of the neonatal diet (human milk or formula), LCP levels in erythrocyte phospholipids at term were positively related to levels in the umbilical artery wall (docosahexaenoic acid (22:6n-3): p < or = 0.0003; arachidonic acid (20:4n-6): p = 0.02). Postnatal diet significantly influenced LCP levels in plasma phospholipids at term (docosahexaenoic acid: p < or = 0.004; arachidonic acid: p = 0.02); formula-fed infants had lower values. We conclude that the LCP status of preterm infants at birth is related to prenatal growth. Moreover, next to the postnatal enteral diet, the LCP status at birth significantly affects LCP levels at term postconceptional age. This finding may warrant further studies of the effects of essential fatty acid-enriched maternal diets during pregnancy on the neonatal LCP status at birth.

Vulnerability versus resilience to prenatal stress in male and female rats; Implications from gene expression profiles in the hippocampus and frontal cortex

Adverse life events during pregnancy may impact upon the developing fetus, predisposing prenatally stressed offspring to the development of psychopathology. In the present study, we examined the effects of prenatal restraint stress (PS) on anxiety- and depression-related behavior in both male and female adult Sprague-Dawley rats. In addition, gene expression profiles within the hippocampus and frontal cortex (FC) were examined in order to gain more insight into the molecular mechanisms that mediate the behavioral effects of PS exposure. PS significantly increased anxiety-related behavior in male, but not female offspring. Likewise, depression-related behavior was increased in male PS rats only. Further, male PS offspring showed increased basal plasma corticosterone levels in adulthood, whereas both PS males and females had lower stress-induced corticosterone levels when compared to controls. Microarray-based profiling of the hippocampus and FC showed distinct sex-dependent changes in gene expression after PS. Biological processes and/or signal transduction cascades affected by PS included glutamatergic and GABAergic neurotransmission, mitogen-activated protein kinase (MAPK) signaling, neurotrophic factor signaling, phosphodiesterase (PDE)/ cyclic nucleotide signaling, glycogen synthase kinase 3 (GSK3) signaling, and insulin signaling. Further, the data indicated that epigenetic regulation is affected differentially in male and female PS offspring. These sex-specific alterations may, at least in part, explain the behavioral differences observed between both sexes, i.e. relative vulnerability versus resilience to PS in male versus female rats, respectively. These data reveal novel potential targets for antidepressant and mood stabilizing drug treatments including PDE inhibitors and histone deacetylase (HDAC) inhibitors.

Prenatal stress in the rat alters 5-HT1A receptor binding in the ventral hippocampus

Exposure of a pregnant woman to physical and/or psychological stress might affect her offspring by promoting the development of various learning, behavioral and/or mood disorders in later life. The 5-HT1A and 5-HT2A receptors are prominently implicated in the modulation of anxiety and mood-related behaviors. Using a semi-quantitative radiolabel immunocytochemical analysis (immunobinding), we studied the effect of prenatal stress on binding of these two receptor subtypes in the hippocampus of 4-week-old male and female Fischer 344 rats. Levels of 5-HT1A immunobinding in the ventral hippocampus, which is primarily implicated in emotional processing, were significantly decreased in male offspring after prenatal stress. A trend towards a decrease was observed in the ventral hippocampus of females. In contrast, 5-HT1A immunobinding within the dorsal hippocampus, which is mainly related to learning and memory, was not affected by prenatal stress in offspring of either gender. Likewise, no significant differences between control and prenatally stressed rats were observed for levels of 5-HT2A immunobinding in either part of the hippocampus or gender. The observed reduction in hippocampal 5-HT1A receptor binding in male offspring after prenatal stress may have important consequences for adult anxiety- and depressive-like behavior.