The importance of the period of dietary restriction of the dam on behavior and growth in the rat

Transgenerational effects of caloric restriction on appetite: a meta-analysis

Maternal undernutrition can result in significant alterations to the post-natal offspring phenotype, including body size and behaviour. For example, maternal food restriction has been implicated in offspring hyperphagia, potentially causing increased weight gain and fat accumulation. This could result in obesity and other adverse long-term health effects in offspring. We investigated the link between maternal caloric restriction during gestation and offspring appetite by conducting the first meta-analysis on this topic using experimental data from mammalian laboratory models (i.e. rats and mice). We collected 89 effect sizes from 35 studies, together with relevant moderators. Our analysis revealed weak and statistically non-significant overall effect on offspring's appetite. However, we found that lower protein content of restricted diets is associated with higher food intake in female offspring. Importantly, we show that a main source of variation among studies arises from whether, and how, food intake was adjusted for body mass. This probably explains many of the contradictory results in the field. Based on our results, we recommend using allometric scaling of food intake to body mass in future studies.

Maternal food restriction modulates cerebrovascular structure and contractility in adult rat offspring: effects of metyrapone

Although the effects of prenatal undernutrition on adult cardiovascular health have been well studied, its effects on the cerebrovascular structure and function remain unknown. We used a pair-fed rat model of 50% caloric restriction from day 11 of gestation to term, with ad libitum feeding after birth. We validated that maternal food restriction (MFR) stress is mediated by glucocorticoids by administering metyrapone, a corticosterone synthesis inhibitor, to MFR mothers at day 11 of gestation. At age 8 mo, offspring from Control, MFR, and MFR + Metyrapone groups were killed, and middle cerebral artery (MCA) segments were studied using vessel-bath myography and confocal microscopy. Colocalization of smooth muscle α-actin (SMαA) with nonmuscle (NM), SM1 and SM2 myosin heavy-chain (MHC) isoforms was used to assess smooth muscle phenotype. Our results indicate that artery stiffness and wall thickness were increased, pressure-evoked myogenic reactivity was depressed, and myofilament Ca(2+) sensitivity was decreased in offspring of MFR compared with Control rats. MCA from MFR offspring exhibited a significantly greater SMαA/NM colocalization, suggesting that the smooth muscle cells had been altered toward a noncontractile phenotype. MET significantly reversed the effects of MFR on stiffness but not myogenic reactivity, lowered SMαA/NM colocalization, and increased SMαA/SM2 colocalization. Together, our data suggest that MFR alters cerebrovascular contractility via both glucocorticoid-dependent and glucocorticoid-independent mechanisms.

Metabolic fuels and reproduction in female mammals

A complete reproductive cycle of ovulation, conception, pregnancy, and lactation is one of the most energetically expensive activities that a female mammal can undertake. A reproductive attempt at a time when calories are not sufficiently available can result in a reduced return on the maternal energetic investment or even in the death of the mother and her offspring. Numerous physiological and behavioral mechanisms link reproduction and energy metabolism. Reproductive attempts may be interrupted or deferred when food is scarce or when other physiological processes, such as thermoregulation or fattening, make extraordinary energetic demands. Food deprivation suppresses both ovulation and estrous behavior. The neural mechanisms controlling pulsatile release of gonadotropin-releasing hormone (GnRH) and, consequently, luteinizing hormone secretion and ovarian function appear to respond to minute-to-minute changes in the availability of metabolic fuels. It is not clear whether GnRH-secreting neurons are able to detect the availability of metabolic fuels directly or whether this information is relayed from detectors elsewhere in the brain. Although pregnancy is less affected by fuel availability, both lactational performance and maternal behaviors are highly responsive to the energy supply. When a reproductive attempt is made, changes in hormone secretion have dramatic effects on the partitioning and utilization of metabolic fuels. During ovulatory cycles and pregnancy, the ovarian steroids, estradiol and progesterone, induce coordinated changes in the procurement, ingestion, metabolism, storage, and expenditure of metabolic fuels. Estradiol can act in the brain to alter regulatory behaviors, such as food intake and voluntary exercise, as well as adenohypophyseal and autonomic outputs. At the same time, ovarian hormones act on peripheral tissues such as adipose tissue, muscle, and liver to influence the metabolism, partitioning and storage of metabolic fuels. During lactation, the peptide hormones, prolactin and growth hormone, rather than estradiol and progesterone, are the principal hormones controlling partitioning and utilization of metabolic fuels. The interactions between metabolic fuels and reproduction are reciprocal, redundant, and ubiquitous; both behaviors and physiological processes play vital roles. Although there are species differences in the particular physiological and behavioral mechanisms mediating nutrition-reproduction interactions, two findings are consistent across species: 1) Reproductive physiology and behaviors are sensitive to the availability of oxidizable metabolic fuels. 2) When reproductive attempts are made, ovarian hormones play a major role in the changes in ingestion, partitioning, and utilization of metabolic fuels.

Prenatal protein malnutrition and working memory performance in adult rats

The performance of prenatally protein malnourished rats was examined in 2 different tasks of learning and memory beginning at 90 or 160 days of age. In Experiment 1, a rewarded alternation task, run as a spatial working memory procedure on an elevated T-maze, revealed no differences between the formerly malnourished (6/25) and control (25/25) rats when either a minimal or a 20-s inter-trial delay was used. Neither was there a difference when an additional, and conflicting, 'information' run was given to provide a source of proactive interference. In extinction, the 6/25 rats required significantly more sessions to abolish their learned alternation response than the controls. In Experiment 2, an operant equivalent of the T-maze task was applied which allowed greater control over the delay interval and task difficulty. Each trial consisted of a forced information response, for which a randomly selected lever was presented, followed by a free-choice stage, when both levers were presented. The rats were rewarded for pressing the lever not presented at the information stage. The inter-trial interval was always 30 s. When the information response requirement was 10 presses no group differences were found in acquisition of the alternation response or in task performance at delays of 5, 10, 15 or 30 s between information and choice stages. As task difficulty was increased, the performance of the 6/25 rats improved more than that of the 25/25 rats, such that they performed significantly better at the longest delay when the information response requirement was 2 presses. This superior performance of the experimental animals is discussed. No differences in reversal were detected. It was concluded that there is no straight-forward 'hippocampal syndrome' in prenatally malnourished adult rats. Working memory appears largely unaffected, whereas susceptibility to interference and extinction may be modified, depending upon the test parameters employed.

Developmental delays in offspring of rats undernourished or zinc deprived during lactation

Offspring of rats who were zinc or calorie deprived during lactation were administered a battery of reflex and motor tests from postnatal Day 4 to Day 21. Compared to offspring of ad lib-fed control rats, both zinc deprived and undernourished offspring exhibited developmental delays in reflexes which appeared after the first postnatal week (auditory startle, air righting, and rope descent). As the deficiencies continued the delays appeared to be more pronounced. The zinc deficiency did not add to the deficits associated with calorie restriction alone because there were no significant differences between the zinc deficient and undernourished pups on any of the measures except eye opening. When rehabilitated offspring were tested at 45 and 60 days of age for motor deficits there were no significant impairments resulting from preweaning dietary conditions. However, the growth retardation of zinc deprived and undernourished rats persisted long after dietary rehabilitation was implemented.

Energetic limits on reproduction: maternal food intake

We examined the factors influencing maternal food intake and pup growth in Norway rats. Mother rats allowed pups in naturally large litters to grow at a slower rate than pups in naturally small litters. Pups reared by dams in a warm ambience (26 degrees C) gained weight more slowly than dams at 22 degrees C, and maternal food intake but not weight gain was depressed in the high ambient temperature. Pup growth at 18 degrees C was unimpaired, with those dams eating no more and gaining no less weight than dams at 22 degrees C. Nest material, however, was found to be essential for the successful rearing of young at cooler ambient temperatures. While restriction of food during gestation resulted in a marginally lower weight gain for the pups during the first 2 weeks postpartum, the dams appeared not to mobilize corporal stores or increase their food intake during lactation. Heavy body weight mothers did not eat any more, nor did they gain any less weight nor rear larger pups than light body weight dams. Rat mothers increased their consumption of a diet diluted with non-nutritive fiber to equal the nutritive intake their controls, with their pups not differing in their growth rate. Pups reared by dams eating a high quality diet grew faster than pups with dams on the control diet. Food intake by mother rats is required during lactation relative to the amount of milk that is delivered to the pups, rather than to an absolute amount of food. Lactating females with a concurrent pregnancy neither increase their food intake nor appear to mobilize their corporal stores to deal with the added energetic drain of pregnancy. Indeed, their young grew somewhat more quickly than pups nursed by dams that were simply lactating. Taken as a whole, these results suggest that Norway rat dams apparently do not monitor and defend a maximal pup growth rate. Rather, rat dams seem to continue to defend their own homeostasis, and by doing so, allow the young to grow and survive under a wide variety of circumstances.

Home-orienting behavior in rat pups: the effect of 2 and 3 generations of rehabilitation following intergenerational malnutrition

In an earlier study in this laboratory, we examined home-orienting ability in rats with histories of intergenerational malnutrition that were rehabilitated postnatally with an adequate protein diet (Galler, 1979). Despite increased size and activity, 1st-generation rehabilitated pups showed no improvement in homing ability when compared to malnourished pups. In the current study, offspring of rats with intergenerational malnutrition were rehabilitated for 2 additional generations and tested for homing ability from postnatal Day 4 through Day 12. The pups rehabilitated for 2 and 3 generations did not perform as well as control pups, even though growth and activity returned to normal levels. Furthermore, the rehabilitated pups failed to demonstrate any preference for the nest on all days of testing; in contrast, control pups favored the nest quadrant by Day 8 of life. No significant improvement was evident on any measure from the 2nd to the 3rd generation of rehabilitation.

Effects of essential fatty acid deficiency during late gestation on brain N-acetylneuraminic acid metabolism and behaviour in the progeny

1. Rat dams given a diet containing 100 g maize oil/kg for approximately two weeks before mating and during the first 14 d of gestation, were given the same diet or one containing 100 g hydrogenated coconut oil/kg (essential fatty acid (EFA)-deficient) in place of maize oil until parturition. After parturition the dams were given the same diets and all progeny were weaned to the maize oil diet at 21 d of age. Brain N-acetylneuraminic acid (NeuNAc) content as well as neuraminidase (sialidase; (EC 3.2.1.18), and cytidine monophosphate N-acetylneuraminic acid synthetase (CMP-NeuNAc synthetase) activities were measured at days, 7, 14, 21 and 168 in the progeny. Y-maze learning was measured at 168 d. 2. Brain weight was independent of dietary fat at all ages. 3. Lack of EFA in the maternal diet during gestation and lactation depressed ganglioside and glycoprotein NeuNAc levels and the activities of sialidase and CMP-NeuNAc synthetase. 4. Maternal dietary deprivation of EFA irreversibly impaired learning behaviour of the progeny. A relationship exists between early exposure to EFA deficiency and learning potential of the progeny.

Prenatal undernutrition: effects on behavior, brain chemistry and neuroanatomy in rats

The behavior and cerebral effects of prenatal protein-calorie undernutrition were investigated in newborn and postweanling rat pups. At birth, prenatally undernourished (PU) animals showed a deficit in body weight; however, by day 15 the difference was diminished and not significant. On days 13-18, PU pups required more trials for reversal learning of a water-escape response in a T-maze than control (C) pups; however, on days 31-35, there were no difference between groups when trained to learn an active-avoidance response. Assessment of brain development showed that at birth, DNA and protein content was severely reduced in PU animals; however, normalization was noted in regional sections of the brain at 35 days of age. Brainstem reticular cells from PU pups at birth show less dendritic arborization and less terminal branching cells from C pups. The results are discussed in terms of a delayed rate of maturation.

[Birth weight, Röhrer weight index and postnatal growth]

Foi estudada a relação entre peso ao nascer, índice ponderal de Röhrer e o crescimento de crianças no primeiro ano de vida, em 2 grupos de crianças. Verificou-se que crianças que nasceram com índice ponderal baixo (2,50 e menos) e peso igual ou inferior a 3.000 g. apresentaram um retardo no crescimento, medido pelo peso, pois aos 12 meses pesaram cerca de 1.500 g. a menos que as que nasceram com índice ponderal normal (2,51 e mais). Crianças que nasceram com índice ponderal normal, qualquer que tivesse sido o peso ao nascer, no final do primeiro ano de vida apresentavam, nos 2 grupos, o mesmo peso. Concluiu-se que crianças que nasceram com índice ponderal igual ou menor que 2,50 e, ao mesmo tempo, com peso igual ou inferior a 3.000 g. apresentaram um retardo do crescimento, medido pelo peso. A grande vantagem da técnica utilizada foi o fato de que não houve necessidade da determinação da idade gestacional.

Protein malnutrition induced during gestation: its effect on pup development and maternal behavior

Repeated time-lapse photographic observations were used to examine the ontogeny of behavioral development in prenatally malnourished rat pups following birth. Pups born to dams receiving a low protein diet (7% casein by weight) were fostered at birth to well-nourished dams and behavioral observations were made at 4-day intervals. Dams nursing gestationally malnourished pups were observed to spend more time in the nesting area with their pups towards the end of lactation. Moreover, the behavioral development (locomotion, feeding, and rearing and climbing activity) of gestationally malnourished offspring was depressed when compared to their controls. The results indicate that prenatal undernutrition alters the behavioral development of the offspring and maternal behavior of the dam in a manner which reduces the exposure of the pup to the immediate environment.

The effects of prenatal and postnatal protein malnutrition of physical and motor development of the rat

The effects of protein malnutrition in the early stages of mammalian life have been found to be pervasive and frequently very persistent. We conducted this experiment to investigate the relative effects of protein deficiency during prenatal and/or postnatal (preweaning) stages of development in order to evaluate the effects of the timing of protein malnutrition and its duration and found significant deficits on a variety of measures of physical and motor development. Animals maintained on low protein diets both prenatally and postnatally showed the greatest developmental deficits whereas animals maintained on low protein diets either prenatally or postnatally were developmentally intermediate relative to animals maintained on normal diets.