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

Effects of different malnutrition techniques on the behavior of rats tested in the elevated T-maze

The influence of different malnutrition techniques on the behavior of adult animals was investigated in the elevated T-maze (ETM). Control litters (C) were composed by eight pups constantly kept with their mother and fed by a 16%-protein diet ad libitum; protein malnutrition litters (PM) were fed by a 6%-protein diet; protein-calorie malnutrition litters (PCM) were fed with 50% of the 16%-protein diet ingested by C litters; malnutrition by increase in the size of the litter (LLM-number of pups was twice the number of pups in C litters), and malnutrition by separation (SM-litters spent half of the day with non-lactating females). After weaning, all groups received lab chow diet until the test day (70th day). During the test were recorded the basal, avoidance 1, avoidance 2 and escape latencies. The data showed that PM, PCM, LLM and SM animals showed lower increases in avoidance latencies, when compared to their control groups. However, malnutrition did not affect escape latencies. The nature of these alterations seems to be nutritional, as the extra-nutritional factors (i.e. maternal care) differ a lot among the malnutrition techniques. These results suggest that malnutrition, irrespective of the technique, altered the neural mechanisms believed to control defensive behaviors in the ETM.

Neonatal food restriction and binaural ear occlusion interfere with the maturation of cortical motor pyramids in the rat

Golgi-Cox-impregnated pyramidal neurons of layer five motor cortical area were investigated in control, binaural ear-occluded control, undernourished and binaural ear-occluded undernourished Wistar rats of 12, 20 and 30 days of age. In neonatally undernourished, binaural ear-occluded-undernourished and partly in ear-occluded-control subjects, there were significant reductions in both the number and extent of the distal part of the dendritic branches of motor pyramids compared to their controls. Moreover, minimal effects on perikarya measurements were observed. These findings suggest that neonatal undernutrition and the concurrent reduction of auditory cues affect dendritic arbor development and possibly the convergence of the auditory experience upon motor pyramids and may interfere with the neocortical modulation of postural and movements activities.

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.

Response threshold to aversive stimuli in stimulated early protein-malnourished rats

Two animal models of pain were used to study the effects of short-term protein malnutrition and environmental stimulation on the response threshold to aversive stimuli. Eighty male Wistar rats were used. Half of the pups were submitted to malnutrition by feeding their mothers a 6% protein diet from 0 to 21 days of age while the mothers of the other half (controls) were well nourished, receiving 16% protein. From 22 to 70 days all rats were fed commercial lab chow. Half of the animals in the malnourished and control groups were maintained under stimulating conditions, including a 3-min daily handling from 0 to 70 days and an enriched living cage after weaning. The other half was reared in a standard living cage. At 70 days, independent groups of rats were exposed to the shock threshold or to the tail-flick test. The results showed lower body and brain weights in malnourished rats when compared with controls at weaning and testing. In the shock threshold test the malnourished animals were more sensitive to electric shock and environmental stimulation increased the shock threshold. No differences due to diet or environmental stimulation were found in the tail-flick procedure. These results demonstrate that protein malnutrition imposed only during the lactation period is efficient in inducing hyperreactivity to electric shock and that environmental stimulation attenuates the differences in shock threshold produced by protein malnutrition.

Effects of prenatal protein malnutrition on mossy fibers of the hippocampal formation in rats of four age groups

The present study was undertaken to investigate the effect of prenatal protein deprivation on the postnatal development of the mossy fiber plexus of the hippocampal formation on postnatal (P) days 15, 30, 90, and 220. Although there is extensive information about the effects of malnutrition on cell body and dendrite morphology, little attention has been paid to axons or axon plexuses. The mossy fiber plexus represents the dentate gyrus granule cell axonal projection to areas CA4 and CA3 of the hippocampal formation and is readily demonstrated with Timm's heavy metal stain. With the use of this stain, the plexus was measured at 13 levels throughout the hippocampal complex. There was no effect of the diet on the anatomical distribution of the plexus. The current study, however, does show significant effects of prenatal protein malnutrition on postnatal development of the mossy fiber plexus that are age dependent. The prenatally malnourished rats show significant deficits in the total rostro-caudal extent and volume of the plexus on P15, P90, and P220, with the most marked dietary effect on P220. There was no significant diet effect on P30 in either extent or volume.

Effects of prenatal protein malnutrition on hippocampal CA1 pyramidal cells in rats of four age groups

The present study was undertaken to investigate the effect of prenatal protein deprivation on area CA1 hippocampal pyramidal cells on postnatal (P) days 15, 30, 90 and 220 using Golgi techniques. Age related changes in both groups and diet related changes between groups were assessed. There were significant diet effects at all four ages, with one of 12 different measurements showing a significant diet effect on P15, five on P30, one on P90, and seven on P220. The most marked effect of the diet was on pyramidal cell dendrite spine density in the stratum moleculare and stratum radiatum, with a different pattern of diet effects in the two strata. In pyramidal cell dendrites in the stratum moleculare, there was a deficit in spine density that was significant at three of the four ages and there were similar age-related changes in the two diet groups. Spines on pyramidal cell dendrites in the stratum radiatum showed a lack of synchrony of age-related changes in the two diet groups, with an increased spine density in the malnourished rats on P30 and a widening deficit in this parameter on P90 and P220. The bimodal distribution to these changes, with most marked deficits occurring on P30 and P220, with an intervening period of apparent "catch-up" on P90, is of interest and may be a significant brain adaptation to malnutrition. The present study is the final of three morphometric studies on the effect of prenatal protein restriction on three key neurons in the hippocampal trisynaptic circuit. When compared to our previous studies on the dentate granule cell and the CA3 pyramidal cell, it is noted that there is an effect of the low protein diet on all these neurons, with the most marked effect on the predominantly postnatally generated dentate granule cells.

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.

Effects of prenatal malnutrition and postnatal nutritional rehabilitation on CA3 hippocampal pyramidal cells in rats of four ages

The effects of prenatal protein malnutrition and postnatal nutritional rehabilitation on CA3 hippocampal pyramidal cells were investigated in rats of 15, 30, 90 and 220 days of age. Female rats were fed either 6% or 25% casein diet 5 weeks before conception. Following delivery, litters born the same day to 6% and 25% casein diet rats were randomly cross-fostered to 25% casein diet dams and maintained on that diet until sacrificed. In 288 rapid-Golgi impregnated cells, we measured somal size, length of the longest apical dendrite, number of apical and basal dendrites intersecting 10 concentric rings 38 microns apart, synaptic spine density in three 50 microns segments of the largest apical dendrite and the thorny excrescence area. Prenatal protein malnutrition produced differential morphological changes on CA3 pyramidal cells. We observed significant decreases of somal size (at 90 and 220 days of age), of length of apical dendrites (at 15 days old), of apical (in 15 day animals) and basal (in 15, 90 and 220 day animals) dendritic branching and of spine density (in 30, 90 and 220 day animals). We also found significant increases of apical dendritic branching in 90 and 220 day old rats. These results indicate that prenatal protein malnutrition affects normal development and produces long-term effects on CA3 pyramidal cells.

Effects of early protein malnutrition and environmental stimulation upon the reactivity to diazepam in two animal models of anxiety

In order to investigate the effects of early protein malnutrition and environmental stimulation upon the response to the anxiolytic properties of diazepam, two animal models of anxiety (elevated plus-maze and light-dark transition tests) were used. Rats were malnourished by feeding their dams a 6% protein diet during the lactation period (0-21 days of age) while well-nourished controls received a 16% protein diet. From 21 to 70 days of age all rats received a balanced lab chow diet. Environmental stimulation consisted of 3-min daily handling from birth to 70 days of age. Additional stimulation was provided from 21 to 70 days of age by rearing the rats in an enriched living cage. Eight groups of rats were studied in a 2 (malnourished or well-nourished) x 2 (stimulated or nonstimulated) x 2 (diazepam or vehicle) design. At 70 days of age, independent groups of rats treated with diazepam (2.5 mg/kg, IP) or vehicle were submitted to testing in the elevated plus-maze or light-dark transition procedures. The results showed that both diazepam and environmental stimulation reduced anxiety in the elevated plus-maze; stimulation changed the anxiolytic response to diazepam and the two diet conditions altered differentially the response to both pharmacological and stimulation procedures. These results suggest that environmental stimulation can affect differentially the behavioral response of malnourished and well-nourished rats treated with diazepam.

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.

Effect of protein malnutrition on CA3 hippocampal pyramidal cells in rats of three ages

Prenatal and postnatal protein deprivation effects on CA3-hippocampal pyramidal cells were investigated in 30-, 90- and 220-day-old rats. Female rats were fed either a 6% or a 25% casein diet 5 wk before conception and the litters were maintained on their respective diet until sacrificed. In 216 rapid Golgi-impregnated cells, we measured somal size, length and diameter of apical dendrite, number of apical dendrites intersecting 10 concentric rings 38 microns apart, thorny excrescence area and length, head diameter and density of synaptic spines on 50-microns segments of apical dendrite. The present experiments showed that malnutrition produced significant reductions of somal size in animals at 220 days of age. There were significant reductions of apical dendrite diameters in animals of 30 and 90 days, and of density and head diameter of synaptic spines at the three ages studied, and significant decrease of the thorny excrescence area at 220 days of age. At this latter age, dendritic branching was significantly decreased in the last four rings representing the area into which the perforant pathway projects. In 30-day malnourished rats, dendritic branching showed a significant increase in rings 4-6 representing the area in which the Schaffer collaterals synapse. The location of the deficit in dendritic spines corresponds to the sites where mossy fibers synapse on the apical dendrites of CA3 neurons. Age-related changes normally observed in control rats (e.g., the 30-day-old control group showed the smallest somal size and 220-day-old controls the largest size) failed to occur in the malnourished rats. The deficits in spine density and dendritic branching (in animals of 220 days old) were similar to those found in our previous studies on fascia dentata.

Prenatal malnutrition and development of the brain

In this review, we have summarized various aspects as to how prenatal protein malnutrition affects development of the brain and have attempted to integrate several broad principles, concepts, and trends in this field in relation to our findings and other studies of malnutrition insults. Nutrition is probably the single greatest environmental influence both on the fetus and neonate, and plays a necessary role in the maturation and functional development of the central nervous system. Prenatal protein malnutrition adversely affects the developing brain in numerous ways, depending largely on its timing in relation to various developmental events in the brain and, to a lesser extent, on the type and severity of the deprivation. Many of the effects of prenatal malnutrition are permanent, though some degree of amelioration may be produced by exposure to stimulating and enriched environments. Malnutrition exerts its effects during development, not only during the so-called brain growth spurt period, but also during early organizational processes such as neurogenesis, cell migration, and differentiation. Malnutrition results in a variety of minimal brain dysfunction-type syndromes and ultimately affects attentional processes and interactions of the organism with the environment, in particular producing functional isolation from the environment, often leading to various types of learning disabilities. In malnutrition insult, we are dealing with a distributed, not focal, brain pathology and various developmental failures. Quantitative assessments show distorted relations between neurons and glia, poor formation of neuronal circuits and alterations of normal regressive events, including cell death and axonal and dendritic pruning, resulting in modified patterns of brain organization. Malnutrition insult results in deviations in normal age-related sequences of brain maturation, particularly affecting coordinated development of various cell types and, ultimately, affecting the formation of neuronal circuits and the commencing of activity of neurotransmitter cell types and, ultimately, affecting the formation of neuronal circuits and the commencing of activity of neurotransmitter systems. It is obvious that such diffuse type "lesions" can be adequately assessed only by interdisciplinary studies across a broad range of approaches, including morphological, biochemical, neurophysiological, and behavioral analyses.

Effects of environmental enrichment on cortical depth and Morris-maze performance in B6D2F2 mice exposed prenatally to ethanol

Pregnant mice were fed a liquid diet with 25% of the calories as ethanol from day 5 to 17 of gestation; controls received equivalent amounts of diet with maltose-dextrin substituted isocalorically for the ethanol. Two male weanlings from each litter were assigned randomly to an enriched or isolated environmental condition. After 6 weeks in these environments measures of brain growth were obtained, including thickness of frontal, parietal, and occipital cortex (study 1), or their behavioral capabilities were assessed in a Morris water maze (study 2). Ethanol decreased birth weight (both studies), postweaning body weight (study 2), and brain weight (study 1), while the enriched animals in both studies were heavier. Ethanol decreased the thickness of the occipital cortex only. All groups demonstrated learning by showing a decrease in latency to locate the hidden platform over the 5 days of testing; this was supported by their spending most time in the target quadrant during the probe trial. The latencies of the enriched animals were shorter than the isolated; covariance analysis indicated that this was not due solely to their faster swimming speed.

Effects of prenatal protein deprivation on postnatal development of granule cells in the fascia dentata

The effect of prenatal protein deprivation on the postnatal development of granule cells in the fascia dentata in the rat was studied at 15, 30, 90, and 220 days of age. The granule cells showed a significant reduction in cell size, decreased number of synaptic spines throughout their dendritic extent, and reduced complexity of dendritic branching in the outer two-thirds of the molecular layer. All of these deficits were present at 15 days and persisted throughout the study (220 days). The least deficits in synaptic spine density occurred at 90 days and in dendritic branching at 30 days. Partial restitution of earlier, more severe deficits was associated primarily with maturational events occurring in the protein deprived rats, whereas later increases in deficits were related primarily to a failure of the protein deprived rats to keep pace with neuronal development occurring in the controls. The present results are similar to those noted in our previous study in this journal of the effect of a low protein diet (8% casein) on these neurons that extended from pregnancy until the time of sacrifice at 30, 90, and 220 days of age (Cintra et al., '90; 532:271-277). Taken together, these two studies suggest that the postnatal adaptation of the granule cells to prenatal protein deprivation is primarily due to events that occur during pregnancy and that the site of predilection for the deficit is their dendrites in the outer two-thirds of the molecular layer of the fascia dentata.

Effects of protein undernutrition on the dentate gyrus in rats of three age groups

The effect of an 8% casein and a control 25% casein diet on the granule cells in the dorsal blade of the dentate gyrus of the rat hippocampal formation was studied at 30, 90 and 220 days of age. Female rats were fed either an 8% or 25% casein diet 5 weeks prior to conception and the litters were maintained on these respective diets until killed. In rapid-Golgi-impregnated cells, we measured major and minor axes of the soma of the dentate granule neurons, the number of spines on 50-microns segments of proximal, middle and terminal regions of the largest dendrite per granule cell and the number of dendrites intersecting 8 concentric rings 38 microns apart. At all 3 ages studied undernourished rats showed, when compared to controls, significant reductions of the major and minor axes of the somata and significant reductions in the number of spines on dendrites in the middle and terminal dendritic segments. Dendritic branching was significantly reduced in undernourished rats compared to controls in all but the 4th concentric rings, with the greatest effect being seen on the outer 3 concentric rings at 90 and 220 days of age. The location of the deficit in dendritic synaptic spines and the greatest deficit in dendritic branching correspond to the sites of termination of the lateral and medial perforant pathway projection to the dentate gyrus on the terminal and middle dendritic segments of the granule cells. The deficits noted in the granule cells of the dentate gyrus in this study were more severe than those found in our previous studies on the effect of the low protein diet in these same rats on visual cortical pyramidal cells and on the 3 cell types in the nucleus raphe dorsalis and nucleus locus coeruleus.

Early-life malnutrition selectively retards the development of distal- but not proximal-cue navigation

The effects of early-life malnutrition on the distal-cue and proximal-cue versions of the Morris (1981) water maze were studied with different-aged rats. Consistent with the existing literature, malnutrition only mildly influenced the distal-cue navigation of relatively old pups (30 day olds). Pups 20-27 days old, however, displayed no evidence of distal-cue navigation if they had been malnourished previously. Malnutrition had no effect on proximal-cue based navigation by pups at any age. The effect of malnutrition on distal-cue performance could not be attributed to any general debilitating effects, sensory, motor, or motivational deficits. Instead, it appears to selectively influence the development of the neural system (perhaps the hippocampus and related structures) more directly involved in learning to utilize distal cues.

Malnutrition and group brain- and body-weight variability: data in search of a hypothesis

Chronic malnutrition, which may be induced by a number of different experimental manipulations, appears, from a survey of the literature, to lead to greater relative whole-brain-weight variability in affected groups compared with controls; there is a tendency for the same pattern to emerge in the case of body-weight variability. A hypothesis which might throw some light on this general trend is proposed.

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.