Early life handling decreases serotonin turnover in the nucleus accumbens and affects feeding behavior of adult rats.

In our previous studies, we reported that neonatally handled rats have an increased ingestion of sweet food but are resistant to the damaging effects of a chronic exposure to a highly palatable diet. Accumbal serotonin (5-HT) is important for feeding behavior and plays a role in the vulnerability to diet-induced obesity. Therefore, our hypotheses were (1) 5-HT turnover in the nucleus accumbens is altered in neonatally handled animals and plays a role in their differential feeding behavior and (2) if this is so, a chronic pharmacological treatment affecting 5-HT reuptake (chronic imipramine) would be able to revert the behavioral findings. Litters were divided into nonhandled and handled (10 min/day, Days 1-10 after birth). In Experiment 1, we demonstrated that a decreased 5-HT metabolism in the nucleus accumbens was observed in adult handled animals. In Experiment 2, the two previous groups were subdivided and assigned to receive imipramine diluted in water or water alone. After 30 days of treatment, we evaluated their weight gain and feeding behavior. Handled rats weighed less than nonhandled rats, and all imipramine-treated rats showed a reduction in weight gain after 60 days of treatment. Imipramine reverted the increased sweet food consumption seen in neonatally handled rats. We conclude that serotonin is involved in the altered feeding behavior of neonatally handled rats, and this protocol is an important tool for studying the mechanisms by which early life events have a long-term impact on feeding preferences.

Both infantile stimulation and exposure to sweet food lead to an increased sweet food ingestion in adult life.

We have reported that neonatal handling leads to increased sweet food preference in adult life. Our aim was to verify if these differences in feeding behavior appear before puberty, and whether other types of intervention in periadolescence (such as exposure to toys) could interfere with sweet food consumption later in life. Nests of Wistar rats were (1) non-handled or (2) handled (10 min/day) on days 1-10 after birth. Males from these groups were subdivided in two subgroups: one was habituated to sweet food (Froot Loops-Kellogs) in a new environment for 4 days and tested for sweet food preference at age 27 days, before submitting to a new habituation and test for sweet food ingestion again in adult life. The other subgroup was habituated and tested only in adulthood. In another set of experiments, neonatally non-handled rats were exposed or not to a new environment with toys in periadolescence, and tested for sweet food ingestion as adults. Neonatal handling increases sweet food consumption only if the habituation and tests are performed after puberty. Interestingly, infant exposure to sweet food had a similar effect as neonatal handling, since controls that were exposed to sweet food at age 22 to 27 days increased their ingestion as adults. Exposure to toys in periadolescence had the same effect. We suggest that an intervention during the first postnatal days or exposure to an enriched environment later in the pre-pubertal period leads to behavioral alterations that persist through adulthood, such as increased sweet food ingestion.

The fetal programming of food preferences: current clinical and experimental evidence.

Increased energy consumption is one of the major factors implicated in the epidemic of obesity. There is compelling evidence, both clinical and experimental, that fetal paucity of nutrients may have programming effects on feeding preferences and behaviors that can contribute to the development of diseases. Clinical studies in different age groups show that individuals born small for their gestational age (SGA) have preferences towards highly caloric foods such as carbohydrates and fats. Some studies have also shown altered eating behaviors in SGA children. Despite an apparent discrepancy in different age groups, all studies seem to converge to an increased intake of palatable foods in SGA individuals. Small nutrient imbalances across lifespan increase the risk of noncommunicable diseases in adult life. Homeostatic factors such as altered responses to leptin and insulin and alterations in neuropeptides associated with appetite and satiety are likely involved. Imbalances between homeostatic and hedonic signaling are another proposed mechanism, with the mesocorticolimbic dopaminergic pathway having differential reward and pleasure responses when facing palatable foods. Early exposure to undernutrition also programs hypothalamic-pituitary-adrenal axis, with SGA having higher levels of cortisol in different ages, leading to chronic hyperactivity of this neuroendocrine axis. This review summarizes the clinical and experimental evidence related to fetal programming of feeding preferences by SGA.

The effect of neonatal handling on adult feeding behavior is not an anxiety-like behavior.

Brief periods of handling during the neonatal period have been shown to have profound and long-lasting physiological consequences. Previous studies performed in our laboratory have demonstrated that handling the pups during the neonatal period leads to increased sweet food ingestion in adult life. The objective of this study is to verify if this effect could be explained by the enhanced anxiety levels in these animals. Litters were divided in: (1) intact; (2) handled (10 min in an incubator/day) and (3) handled + tactile stimulation (10 min/day). Procedures were performed on days 1-10 after birth. When adults, rats were tested in the elevated plus maze apparatus, light dark exploration test and open field test. They were also tested for sweet food ingestion, being injected with 2 mg/kg diazepam or vehicle 60 min before the test. Handling and handling + tactile stimulation do not alter performance in the plus maze test, but handled rats presented more crossings in the light/dark exploration test and open field (two-way ANOVA). Females also spent more % time in the open arms in the plus maze and more time in the lit compartment in the light/dark test, presenting more crossings in both tests. Both treated rats (handled and handled + tactile stimulation groups) consumed more sweet food than intact ones (two-way ANOVA). When diazepam was injected prior to the measurement of sweet food ingestion, there was no effect of the drug. We suggest that handling during the neonatal period leads to plastic alterations in the central nervous system of these animals, causing an increased ingestion of palatable food in adult life, and this alteration does not express an anxiety-like behavior.

Litter size reduction alters insulin signaling in the ventral tegmental area and influences dopamine-related behaviors in adult rats.

Postnatal overfeeding is a well-known model of early-life induced obesity and glucose intolerance in rats. However, little is known about its impact on insulin signaling in specific brain regions such as the mesocorticolimbic system, and its putative effects on dopamine-related hedonic food intake in adulthood. For this study, rat litters were standardized to 4 (small litter - SL) or 8 pups (control - NL) at postnatal day 1. Weaning was at day 21, and all tests were conducted after day 60 of life in male rats. In Experiment 1, we demonstrated that the SL animals were heavier than the NL at all time points and had decreased AKT/pAKT ratio in the Ventral Tegmental Area (VTA), without differences in the skeletal muscle insulin signaling in response to insulin injection. In Experiment 2, the standard rat chow intake was addressed using an automated system (BioDAQ, Research Diets(®)), and showed no differences between the groups. On the other hand, the SL animals ingested more sweet food in response to the 1 min tail-pinch challenge and did not develop conditioned place preference to sweet food. In Experiment 3 we showed that the SL rats had increased VTA TH content but had no difference in this protein in response to a sweet food challenge, as the NL had. The SL rats also showed decreased levels of dopamine D2 receptors in the nucleus accumbens. Here we showed that early postnatal overfeeding was linked to an altered functioning of the mesolimbic dopamine pathway, which was associated with altered insulin signaling in the VTA, suggesting increased sensitivity, and expression of important proteins of the dopaminergic system.

Neonatal handling alters feeding behavior of adult rats.

Stress during the neonatal period leads to a large number of behavioral and biochemical alterations in adult life. The aim of this study is to verify the effects of handling and tactile stimulation during the first 10 days of life on feeding behavior in adult rats. Litters were divided into (1). intact; (2). handled (10 min/day); and (3). handled and tactile stimulated (10 min/day). Procedures were performed on Days 1-10 after birth. When adults, rats were tested for ingestion of sweet and savory snacks. We also measured body weight, ingestion of standard lab chow, and consumption of water and 1% glucose and 1.5% NaCl solutions. Stressed rats (handling and handling+tactile stimulation groups) consumed more sweet (two-way ANOVA, P=.008) or savory snacks (P=.001) than intact ones. This effect was observed in males and females. There were no differences in body weight, ingestion of standard lab chow, water, or in the ingestion of sweetened or salty solutions between groups. The same animals were tested later in life (15 months of age), and the effect was still evident. We suggest that handling during the neonatal period leads to alterations in the CNS of rats, causing an increased ingestion of palatable food in adult life, and this alteration probably persists throughout the whole life.

Brief daily postpartum separations from the litter alter dam response to psychostimulants and to stress.

Neonatal handling induces several behavioral and neurochemical alterations in pups, including decreased responses to stress and reduced fear in new environments. However, there are few reports in the literature concerning the behavioral effects of this neonatal intervention on the dams during the postpartum period. Therefore, the aim of the current study was to determine if brief postpartum separation from pups has a persistent impact on the dam's stress response and behavior. Litters were divided into two neonatal groups: 1) non-handled and 2) handled [10 min/day, from postnatal day (PND) 1 to 10]. Weaning occurred at PND 21 when behavioral tasks started to be applied to the dams, including sweet food ingestion (PND 21), forced swimming test (PND 28), and locomotor response to a psychostimulant (PND 28). On postpartum day 40, plasma was collected at baseline for leptin assays and after 1 h of restraint for corticosterone assay. Regarding sweet food consumption, behavior during the forced swimming test or plasma leptin levels did not differ between dams briefly separated and non-separated from their pups during the postpartum period. On the other hand, both increased locomotion in response to diethylpropion and increased corticosterone secretion in response to acute stress were detected in dams briefly separated from their pups during the first 10 postnatal days. Taken together, these findings suggest that brief, repeated separations from the pups during the neonatal period persistently impact the behavior and induce signs of dopaminergic sensitization in the dam.

Effects of in utero conditions on adult feeding preferences.

The fetal or early origins of adult disease hypothesis states that environmental factors, particularly nutrition, act in early life to program the risks for chronic diseases in adult life. As eating habits can be linked to the development of several diseases including obesity, diabetes and cardiovascular disease, it could be proposed that persistent food preferences across the life-span in people who were exposed to an adverse fetal environment may partially explain their increased risk to develop metabolic disease later in life. In this paper, we grouped the clinical and experimental evidence demonstrating that the fetal environment may impact the individual's food preferences. In addition, we review the feeding preferences development and regulation (homeostatic and hedonic pathways, the role of taste/olfaction and the reward/pleasure), as well as propose mechanisms linking early life conditions to food preferences later in life. We review the evidence suggesting that in utero conditions are associated with the development of specific food preferences, which may be involved in the risk for later disease. This may have implications in terms of public health and primary prevention during early ages.

Associations between parenting behavior and anxiety in a rodent model and a clinical sample: relationship to peripheral BDNF levels.

Adverse early-life environment is associated with anxiety-like behaviors and disorders. Brain-derived neurotrophic factor (BDNF) is sensitive to this environment and could be a marker of underlying brain changes. We aimed at evaluating the development of anxiety-like behaviors in a rat model of early adversity, as well as the possible association with BDNF levels. Similar associations were investigated in a sample of adolescent humans. For the rat study, Wistar rat litters were divided into: early-life stress (ELS, limited access to nesting material) and control groups. Maternal behavior was observed from days 1 to 9 of life and, as adults, rats were subjected to behavioral testing and BDNF measurements in plasma, hippocampus, amygdala and periaqueductal gray. For the human study, 129 adolescents were evaluated for anxiety symptoms and perceived parental care. Serum BDNF levels and the Val66Met polymorphism of the BDNF gene were investigated. We found that ELS dams showed more pure contact, that is, contact with low care and high control, toward pups, and their adult offspring demonstrated higher anxiety-like behaviors and plasma BDNF. Also the pure contact correlated positively with adult peripheral BDNF. Similarly in humans, there was a positive correlation between maternal overprotection and serum BDNF only in Met carriers. We also found negative correlations between maternal warmth and separation anxiety, social phobia and school phobia. Finally, our translational approach revealed that ELS, mediated through variations in maternal care, is associated with anxiety in both rats and humans and increased peripheral BDNF may be marking these phenomena.

Exposure to maternal smoking during fetal life affects food preferences in adulthood independent of the effects of intrauterine growth restriction.

Experimental animal studies have shown that nicotine exposure during gestation alters the expression of fetal hypothalamic neuropeptides involved in the control of appetite. We aimed to determine whether the exposure to maternal smoking during gestation in humans is associated with an altered feeding behavior of the adult offspring. A longitudinal prospective cohort study was conducted including all births from Ribeirão Preto (São Paulo, Brazil) between 1978 and 1979. At 24 years of age, a representative random sample was re-evaluated and divided into groups exposed (n = 424) or not (n = 1586) to maternal smoking during gestation. Feeding behavior was analyzed using a food frequency questionnaire. Covariance analysis was used for continuous data and the χ 2 test for categorical data. Results were adjusted for birth weight ratio, body mass index, gender, physical activity and smoking, as well as maternal and subjects' schooling. Individuals exposed to maternal smoking during gestation ate more carbohydrates than proteins (as per the carbohydrate-to-protein ratio) than non-exposed individuals. There were no differences in the consumption of the macronutrients themselves. We propose that this adverse fetal life event programs the individual's physiology and metabolism persistently, leading to an altered feeding behavior that could contribute to the development of chronic diseases in the long term.

Risk factors for sedentary behavior in young adults: similarities in the inequalities.

Physical activity is a known protective factor, with benefits for both metabolic and psychological aspects of health. Our objective was to verify early and late determinants of physical activity in young adults. A total of 2063 individuals from a birth cohort in Ribeirão Preto, Brazil, were studied at the age of 23-25 years. Poisson regression was performed using three models: (1) early model considering birth weight, gestational age, maternal income, schooling and smoking; (2) late model considering individual's gender, schooling, smoking and body mass index; and (3) combined (early + late) model. Physical activity was evaluated using the International Physical Activity Questionnaire, stratifying the individuals into active or sedentary. The general rate of sedentary behavior in the sample was 49.6%. In the early model, low birth weight (relative risk (RR) = 1.186, confidence interval (95%CI) 1.005-1.399) was a risk factor for sedentary activity. Female gender (RR = 1.379, 95%CI = 1.259-1.511) and poor schooling (RR = 1.126, 95%CI = 1.007-1.259) were associated with sedentary behavior in the late model. In the combined model, only female gender and participant's schooling remained significant. An interaction between birth weight and individual's schooling was found, in which sedentary behavior was more prevalent in individuals born with low birth weight only if they had higher educational levels. Variables of early development and social insertion in later life interact to determine an individual's disposition to practice physical activities. This study may support the theoretical model 'Similarities in the inequalities', in which opposed perinatal backgrounds have the same impact over a health outcome in adulthood when facing unequal social achievement during the life-course.

Early life experience alters behavioral responses to sweet food and accumbal dopamine metabolism.

Neonatal handling in rats persistently alters behavioral parameters and responses to stress. Such animals eat more sweet food in adult life, without alterations in lab chow ingestion. Here, we show that neonatally handled rats display greater incentive salience to a sweet reward in a runway test; however they are less prone to conditioned place preference and show less positive hedonic reactions to sweet food. When injected with methylphenidate (a dopamine mimetic agent), non-handled rats increase their sweet food ingestion in the fasted state, while neonatally handled rats do not respond. We did not observe any differences regarding baseline general ambulatory activity between the groups. A lower dopamine metabolism in the nucleus accumbens was observed in handled animals, without differences in norepinephrine content. We suggest that early handling leads to a particular response to positive reinforcers such as palatable food, in a very peculiar fashion of higher ingestion but lower hedonic impact, as well as higher incentive salience, but diminished dopaminergic metabolism in the nucleus accumbens.

Brief daily postpartum separations from the litter alter dam response to psychostimulants and to stress

Neonatal handling induces several behavioral and neurochemical alterations in pups, including decreased responses to stress and reduced fear in new environments. However, there are few reports in the literature concerning the behavioral effects of this neonatal intervention on the dams during the postpartum period. Therefore, the aim of the current study was to determine if brief postpartum separation from pups has a persistent impact on the dam's stress response and behavior. Litters were divided into two neonatal groups: 1) non-handled and 2) handled [10 min/day, from postnatal day (PND) 1 to 10]. Weaning occurred at PND 21 when behavioral tasks started to be applied to the dams, including sweet food ingestion (PND 21), forced swimming test (PND 28), and locomotor response to a psychostimulant (PND 28). On postpartum day 40, plasma was collected at baseline for leptin assays and after 1 h of restraint for corticosterone assay. Regarding sweet food consumption, behavior during the forced swimming test or plasma leptin levels did not differ between dams briefly separated and non-separated from their pups during the postpartum period. On the other hand, both increased locomotion in response to diethylpropion and increased corticosterone secretion in response to acute stress were detected in dams briefly separated from their pups during the first 10 postnatal days. Taken together, these findings suggest that brief, repeated separations from the pups during the neonatal period persistently impact the behavior and induce signs of dopaminergic sensitization in the dam.