The effects of early-life undernutrition and subsequent environment on morphological parameters of the rat brain

Programming of cholesterol metabolism by breast or formula feeding

We tested the hypothesis that breast or formula feeding and cholesterol intake during the neonatal period influence cholesterol metabolism and arterial fatty streaks in young adult baboons. Genetic variation was controlled by randomly assigning half-sib sire progeny to a factorial dietary design. We measured serum cholesterol and lipoprotein cholesterol concentrations enzymically and cholesterol production and bile acid excretion rates isotopically. The bile cholesterol saturation index was calculated from enzymic analyses of cholesterol, bile salt and phospholipid concentrations in gallbladder bile. Breast-fed baboons had higher serum VLDL + LDL cholesterol/HDL cholesterol ratios in the early postweaning period (six months) until adulthood (7-8 years) than formula-fed baboons. In adulthood a high cholesterol diet increased bile acid excretion by approximately 40% in formula-fed baboons but did not significantly increase the bile acid excretion rate among breast-fed animals. Adult baboons breast fed as infants also had an approximately 8% lower cholesterol production rate than formula-fed animals and a 20% higher bile cholesterol saturation index. The level of cholesterol in the infant formulas influenced cholesterol metabolism in adulthood but not serum lipoprotein concentrations. As young adults, breast-fed baboons had more extensive arterial fatty streaks than formula-fed baboons. This difference could be accounted for by differences in the lipoprotein ratios. These results demonstrate that breast and formula feeding differentially modify cholesterol metabolism. This may influence the development of chronic diseases.

A “deficient environment” in prenatal life may compromise systems important for cognitive function by affecting BDNF in the hippocampus

The intrauterine environment has the capacity to mold the prenatal nervous system. Particularly, recent findings show that an adverse prenatal environment produces structural defects of the hippocampus, a critical area sub-serving learning and memory functions. These structural changes are accompanied by a disruption in the normal expression pattern of brain-derived neurotrophic factor (BDNF) and its cognate tyrosine kinase B (TrkB) receptor. The important role that the BDNF system plays in neural modeling and learning and memory processes suggests that fetal exposure to unfavorable intrauterine conditions may compromise proper cognitive function in adult life. These findings have implications for disorders that involve a dysfunction in the BDNF system and are accompanied by cognitive deficits.

Birthdates and number of neurons in the serotonergic raphe nuclei in the rat with prenatal protein malnutrition

The effect of prenatal protein deprivation on timing of neurogenesis and on number of neurons generated in the serotonergic dorsal (DR) and median raphe (MR) nuclei of the rat was studied. These neurons are of interest because their neurogenesis occurs during the period of malnutrition and their axonal projections participate in the earliest stages of brain development. In this study, dams were maintained on a 25% casein diet or a 6% casein diet 5 weeks prior to mating and throughout pregnancy. At birth, all pups were cross-fostered to dams on a 25% casein diet. Bromodeoxyuridine, a thymidine analog that is incorporated into nuclear deoxyribonucleic acid during the cell cycle synthetic phase, was used as a marker of neurogenesis. Bromodeoxyuridine was administered on either embryonic day 11, 12, 13 or 14. On postnatal day 30, serial sections of raphe nuclei were processed with bromodeoxyuridine immunocytochemistry to determine the number of raphe cells generated on each day and with Nissl stain to determine the total number of cells generated. There were no significant differences between the two diet groups in timing of generation or in total number of cells generated, indicating that neurogenesis of these early generated neurons appears unaffected by concomitant protein deprivation.

Effect of prenatal protein deprivation on postnatal granule cell generation in the hippocampal dentate gyrus

The effect of prenatal malnutrition, produced by protein deprivation, on postnatal neurogenesis of granule cells in the fascia dentata of the rat hippocampal formation was examined by injecting tritiated thymidine on P8 and P15 and sacrificing the pups on P30, or by injecting on P30 and sacrificing on P90. The number of labeled granule cells was significantly decreased in prenatally malnourished rats injected on P8, and unaffected in those injected on P15. In contrast, the number of labeled granule cells in prenatally malnourished rats was significantly increased in animals injected in P30. The study shows that prenatal malnutrition significantly alters the postnatal pattern of granule cell neurogenesis in rat hippocampal formation and that the effect persists despite nutritional rehabilitation at birth.

Prenatal malnutrition effect on pyramidal and granule cell generation in the hippocampal formation

The effects of prenatal malnutrition produced by protein deprivation on the neurogenesis of granule and pyramidal cells in the rat hippocampal formation was investigated by injecting pregnant rats with tritiated thymidine on E12, E16, or E20 and sacrificing the pups on P30. Granule cell neurogenesis was significantly decreased in the pups injected on E20, but not in E12 or E16 groups. There was no effect on the generation of pyramidal cells at the times noted, indicating a differential effect of prenatal malnutrition on the generation of these two different neuronal types in the hippocampal formation.

Importance of prenatal nutrition to the development of a precocial chick

The developmental maturity of hatchling birds varies greatly across the altricial-precocial continuum and these differences are related to the relative proportions of yolk and albumen in a species' egg. In general, the more precocial the chick the greater the proportion of yolk in its egg. Egg composition can also vary within species with unknown consequences for the developing embryo. The present research sought to determine the importance of egg composition to avian development by experimentally removing 1, 2, 4, 8, 12, or 16% of the albumen from eggs of domestic fowl (Gallus gallus). Experimental chicks were paired to control chicks whose eggs were matched on the basis of original mass and laid by the same female but no albumen was removed from their eggs prior to incubation. Decreased levels of albumen significantly decreased chick size at hatch. Experimental subjects, however, had similar growth to controls after 20 days of ad-lib access to food, although sex differences between pairs indicated that the growth of females may be affected differentially by albumen removal. Righting responses were retarded in experimental subjects for the 2 and 4% albumen-removal groups. Egg composition can have important consequences for chick survival simply by influencing body size at hatch and it is suggested that the practice of using overall egg size as a measure of egg "quality" needs to be broadened by considering what is inside the egg as well. In addition, the unique opportunity presented by using an avian model to assess directly the specific influences of protein (albumen) and of fat (yolk) on growth and behavioral development is explored.

Prenatal protein malnutrition alters behavioral state modulation of inhibition and facilitation in the dentate gyrus

We have examined the effects of prenatal protein malnutrition on interneuronally mediated inhibition and facilitation in the dentate gyrus of the rat using the paired-pulse technique. Field potentials were recorded in the dentate gyrus in response to paired stimuli delivered to the perforant path. The paired-pulse index (PPI) was used as a measure of the net short-term facilitation or interneuronally mediated inhibition effective at the time of the paired-pulse test and was computed by dividing the amplitude of the second population spike (p2) by the amplitude of the first population spike (p1). PPIs were classified according to p1 in order to compare PPIs between behavioral states and dietary treatments since population spike amplitudes in the dentate gyrus vary in relation to behavioral state. Testing was performed during 4 behavioral states: slow-wave sleep (SWS), paradoxical sleep (REM), immobile waking (IW) and exploratory locomotion (AW) using interpulse intervals (IPI) from 20 to 400 ms. The magnitude and duration of interneuronally mediated inhibition was significantly increased in prenatal protein malnourished animals when compared with controls. Paired-pulse tests performed using an IPI of 20 ms under the high p1 (p1 greater than median) condition showed significantly smaller PPIs in prenatal protein malnourished rats regardless of behavioral state. For IPIs greater than 20 ms PPIs were consistently smaller in prenatal protein malnourished rats during SWS and IW. These data indicate that both the magnitude and duration of interneuronally mediated inhibition are increased in prenatally malnourished rats. No consistent diet-related differences were found during AW and REM using IPIs greater than 20 ms because interneuronally mediated inhibition was relatively suppressed during these behavioral states for both dietary groups. There was no consistent behavioral state modulation of paired-pulse facilitation (IPI = 40 to 80 ms) or late inhibition (IPI = 400 ms) in either diet group. In addition, a new relation between PPI and IPI was found under the low p1 (p1 greater than median) condition. During AW the PPIs observed using IPIs of 40 and 50 ms were smaller than those observed using IPIs of 30 and 60 ms. This depression interrupts what is generally considered the "facilitatory" phase of paired-pulse response and may indicate an interaction between perforant path stimulation and hippocampal theta rhythm which is masked when p1 amplitude is high.(ABSTRACT TRUNCATED AT 400 WORDS)

Neuronal and synaptic measurements in the visual cortex of adult rats after undernutrition during normal or artificial rearing

It is possible that the reported effects of early life undernutrition on brain morphology may be due to alterations in mother-infant interactions and not directly to undernutrition. We have investigated this possibility by comparing artificially reared with mother-reared rats. Four groups of black-and-white hooded male rats were reared. These consisted of mother reared control (MRC), mother reared undernourished (MRU), artificially reared control (ARC) and artificially reared undernourished (ARU). Artificially reared rats were raised in isolation away from their mothers from 5 to 21 days of postnatal age. They were fitted with a gastric cannula through which 'milk' was infused automatically. The period of undernutrition lasted from 5 to 25 postnatal days, following which the animals were fed ad libitum until 312 days of age. Rats from each group were then killed by perfusion with buffered 2.5% glutaraldehyde. Pieces of visual cortex from each rat were postfixed in osmium tetroxide and embedded in resin. Stereological procedures at the light and electron microscopical levels were used to estimate the synapse-to-neuron ratios in cortical layers II to IV. Both MRC and ARC rats had about 7000 synapses per neuron. However, this ratio was about 8300 in MRU rats whilst it was only about 5000 in ARU animals. The rearing x nutrition interaction was statistically significant at the 0.1% level. These changes in the synapse-to-neuron ratio were mainly due to alterations in the numerical densities of the synapses rather than that of neurons. These results demonstrate that environmental isolation, as a result of artificial rearing procedures, and concurrent undernutrition during the first three weeks of postnatal life, interact with one another to produce marked morphological changes in the adult rat brain. However, environmental isolation was not, by itself, sufficient to cause permanent changes in interneuronal connectivity.

Effects of early life undernutrition in artificially-reared rats. 2. Subsequent behaviour

Four groups of rat pups were reared: mother-reared control (well-fed) and undernourished (MRC, MRU) and artificially-reared control and undernourished (ARC, ARU). AR rats were fed expressed rats' milk (days 5-7), mixtures of rats' milk and milk substitute (days 8-16), and milk substitute only (days 17-20) by intermittent infusion via a gastric cannula. Undernutrition, imposed from 5-25 days, was effected initially by underfeeding the mother (MRU) or by infusing restricted quantities of milk (ARU). Weaning was at 21 days and undernutrition from 21-25 days was by restricting the supply of solid food. All rats were fed ad lib from 25 days. From 18 weeks, male rats were subjected to 3 behavioural tests: open field, social behaviour (encounters between rats of like treatment group) and bar-pressing for food (CRF, FR5, VI 1', VI 2' and Extinction). Previously undernourished rats responded at higher rates on FR5, received fewer rewards on VI 2' and displayed more aggression during social interaction. These findings may reflect direct effects of nutrition on brain growth. In the open field and social situations ARU were generally less active than ARC animals, whereas MRU and MRC rats differed little. These results are discussed in terms of MRU pups being maternally "buffered" against the worst effects of undernutrition and ARC rats displaying characteristics of "early stimulated" animals.

Effect of intrauterine growth retardation on developmental changes in DNA and [14C]thymidine metabolism in different regions of rat brain: histological and biochemical correlations

Intrauterine growth retardation was induced in the rat by clamping the uterine artery on day 17 of gestation. The effect of hypotrophy on DNA synthesis was studied in two different cerebral structures: hippocampus and cerebellum. Accumulation of DNA in these structures was biochemically measured in parallel to the incorporation of methyl-[14C]thymidine into nucleic acid at different ages and correlated with autoradiography. The various metabolites of thymidine in acid-soluble fraction were determined by using chromatographic procedures. Phosphorylation defects or reduced utilization of thymidine were found in hypotrophic rats and may delay the DNA synthesis. An essay of catch-up occurred with a different timing according to the cerebral region studied. A morphological and DNA synthesis. An essay of catch-up occurred with a different timing according to the cerebral region studied. A morphological and autoradiographic study after incorporation of [3H]thymidine was carried out in parallel. The neuronal and glial components of cytogenesis were analyzed separately and a good correlation was observed between histological and biochemical data in both groups of animals.

Effects of differential environments on the cerebral anatomy of rats as a function of previous and subsequent housing conditions

After 1 month in enriched or impoverished environments, groups of rats were housed for an additional month in either the same or the opposite environment. The cross-over design allowed us to see whether or not the cerebral effects of differential environments are modified by subsequent housing conditions, and also whether or not such effects might be influenced by previous experience. Differential housing for 1 month was associated with significant alterations in the weight and length of the cerebrum, the thickness of the occipital cortex, and the relative number of neurons and oligodendrocytes, and no change in the ratio of astrocytes to neurons. The effects of enrichment were not reduced in animals that were previously impoverished. When impoverishment followed enrichment, certain effects appeared to diminish, notably, the increase in cortical thickness. Other effects, however, such as the increase in the ratio of oligodendrocytes to neurons, were very stable. The gross cerebral alterations associated with differential housing did not differ significantly after 2 as opposed to 1 month's exposure, but the effects on neuronal density and the ratio of oligodendrocytes to neurons in layers V and VI of the cortex were, paradoxically, significantly smaller with the longer duration. We suggest that this decrease is due to the continuation of processes induced in the first month of differential experience rather than to their dissipation.

Is hippocampal function in the adult rat impaired by early protein or protein-calorie deficiencies?

Much of the development of the rat's hippocampal formation occurs postnatally, which suggests that this structure, like the cerebellum, may be especially vulnerable to early postnatal malnutrition. Radial-maze performance and spontaneous alternation, two kinds of behavior requiring the integrity of the hippocampus, were assessed to determine whether hippocampal function in the adult rat is impaired as a result of protein restriction in either the preweaning, the postweaning or both stages of development. In three experiments the performance of protein-malnourished rats in 8- and 12-arm mazes did not differ significantly from that of well-nourished rats. In a fourth experiment levels of spontaneous alternation in protein-malnourished rats were like those of normal well-nourished animals. Thus, the present experiments provide no evidence that hippocampal function is impaired as a consequence of early protein deprivation. For the most part, a critical review of earlier studied of undernourished rats supports a similar conclusion.

The comparative effects of early-life undernutrition and subsequent differential environments on the dendritic branching of pyramidal cells in rat visual cortex

Male rats were either undernourished or fed normally from birth to day 21, after which time food was made freely available. At 1 month of age littermate pairs from both nutritional groups were housed in either enriched or impoverished conditions for 30 days and then killed for brain measurements. Significant deficits due to undernutrition were observed in the weight and size of the cerebrum, but not in the thickness or area of the visual cortex. Although there were large differences of between 21 and 39% in the number of higher-order basal dendrites of layers II and III pyramidal cells, and of about 19% in the distal ring intersections, none except the fourth-order branches and intersections at 100 micron from the cell body approached statistical significance. Changes in cerebral weight and size also occurred as a result of differential housing, with the enriched rats showing increased values relative to their impoverished littermates. In contrast to the nutritional treatment, differential housing significantly affected cortical thickness and area, as well as basal dendritic branching of the pyramidal cells. Enriched rats had relative increases of 26% in the number of fifth-order branches and 45-80% in the number of distal ring intersections.

The separate and combined effects of early undernutrition and environmental complexity at different ages on cerebral measures in rats

Rats were either undernourished or fed normally during the suckling period, then at 1 and 5 months of age littermates were housed in enriched or impoverished environments for 30 days. The undernutrition caused lasting reductions in the weight and size of the cerebrum and in parameters of the hippocampus, but significant deficits were not observed in the thickness and area of the occipital cortex. Differential housing differed from early undernutrition in that its largest effects were on cortical parameters, but the effects of the two conditions did partly overlap. This meant that some nutritionally induced deficits could be modified later by manipulating environmental complexity. The cerebral response of the previously undernourished rats to differential environments was not distinguishable from that of well-fed controls on the basis of the gross anatomical changes that were measured. Furthermore, no significant differences were found between the environmental effects in young and mature rats, although the latter's response tended to be somewhat less for most parameters.