HPA and sympathoadrenal activity of adult rats perinatally exposed to maternal mild calorie restriction

Maternal Caloric Restriction Implemented during the Preconceptional and Pregnancy Period Alters Hypothalamic and Hippocampal Endocannabinoid Levels at Birth and Induces Overweight and Increased Adiposity at Adulthood in Male Rat Offspring

Exposure to inadequate nutritional conditions in critical windows of development has been associated to disturbances on metabolism and behavior in the offspring later in life. The role of the endocannabinoid system, a known regulator of energy expenditure and adaptive behaviors, in the modulation of these processes is unknown. In the present study, we investigated the impact of exposing rat dams to diet restriction (20% less calories than standard diet) during pre-gestational and gestational periods on: (a) neonatal outcomes; (b) endocannabinoid content in hypothalamus, hippocampus and olfactory bulb at birth; (c) metabolism-related parameters; and (d) behavior in adult male offspring. We found that calorie-restricted dams tended to have a reduced litter size, although the offspring showed normal weight at birth. Pups from calorie-restricted dams also exhibited a strong decrease in the levels of anandamide (AEA), 2-arachidonoylglycerol (2-AG), arachidonic acid (AA) and palmitoylethanolamide (PEA) in the hypothalamus at birth. Additionally, pups from diet-restricted dams displayed reduced levels of AEA in the hippocampus without significant differences in the olfactory bulb. Moreover, offspring exhibited increased weight gain, body weight and adiposity in adulthood as well as increased anxiety-related responses. We propose that endocannabinoid signaling is altered by a maternal caloric restriction implemented during the preconceptional and pregnancy periods, which might lead to modifications of the hypothalamic and hippocampal circuits, potentially contributing to the long-term effects found in the adult offspring.

Maternal separation during nursing alters basal neuroendocrine levels in juvenile and adult rats

INTRODUCTION

Work with different animal models including that of maternal separation during nursing has shown that early adverse experiences such as abuse, maternal abandonment and psychosocial stress may favor the development of various psychopathologies. However, several neuroendocrine changes have not been completely described yet. 

OBJECTIVE

To establish whether maternal separation during nursing modifies the basal levels of neurohormones such as corticosterone, ACTH, oxytocin and vasopressin in juvenile and adult rats (aged 35 and 90 days, respectively). 

MATERIALS AND METHODS

Wistar rats were separated from their mothers for two periods of 3 hours per day during the 21 days of nursing. Once these rats had reached 35 and then 90 days of age, blood samples were taken from both the separated and control groups to obtain serum for immunoenzymatic assays and measure the levels of each of the hormones. 

RESULTS

Concentrations of corticosterone were higher in control adult females in comparison with the rest of the groups and lower in the control adult males. Those of ACTH were higher in the separated young males and females than in the adult groups. Oxytocin levels were significantly higher in the separated adult females in comparison with the other groups and significantly lower in the adult males. With respect to vasopressin, the separated groups had lower concentrations than the young and adult control groups. 

CONCLUSIONS

These results show that the early stress to which rats were submitted produced changes in the basal responses of the hypothalamic-pituitary-adrenal axis, that these responses were distinct in males and females and that they also differed according to age.

Paternal calorie restriction prior to conception alters anxiety-like behavior of the adult rat progeny

The maternal environment influences a broad range of phenotypic outcomes for offspring, with anxiety-like behavior being particularly susceptible to maternal environmental perturbations. Much less is known regarding paternal environmental influences. To investigate this, adult male rats were exposed to 25% calorie restriction (CR) or glucocorticoid elevation (CORT; 200 μg/ml of corticosterone in drinking water) for ∼ 6 weeks prior to breeding. Elevated plus maze (EPM), open field (OF), predator odor (cat urine), and acoustic startle/pre-pulse inhibition (AS/PPI) were characterised in the adult male offspring. Plasma concentrations of corticotrophin-releasing hormone (CRF), adrenocorticotropin hormone (ACTH), and serum leptin were characterised in both sires and offspring. Maternal care received by litters was additionally observed. Expectedly, CR and CORT treatment attenuated weight gain, whilst only CR induced anxiolytic behavior in the EPM. The adult offspring sired by CR males also demonstrated a reduction in weight gain, food intake and serum leptin levels when compared to controls. Moreover, CR offspring demonstrated an anxiolytic-like profile in the EPM and OF, enhanced habituation to the AS pulse, reduced PPI, but no alteration to predator odor induced defensiveness compared to control. CORT offspring failed to demonstrate any behavioral differences from controls, however, exhibited a trend towards reduced ACTH and leptin concentration. Collectively, the results indicate that a reduction in calories in males prior to conception can affect the behavior of adult offspring. The phenotypic transmission of CR experiences from fathers to the progeny could potentially be mediated epigenetically. The role of glucocorticoid elevation and maternal care are also discussed.

Slow Physical Growth, Delayed Reflex Ontogeny, and Permanent Behavioral as Well as Cognitive Impairments in Rats Following Intra-generational Protein Malnutrition

Environmental stressors including protein malnutrition (PMN) during pre-, neo- and post-natal age have been documented to affect cognitive development and cause increased susceptibility to neuropsychiatric disorders. Most studies have addressed either of the three windows and that does not emulate the clinical conditions of intra-uterine growth restriction (IUGR). Such data fail to provide a complete picture of the behavioral alterations in the F1 generation. The present study thus addresses the larger window from gestation to F1 generation, a new model of intra-generational PMN. Naive Sprague Dawley (SD) dams pre-gestationally switched to LP (8% protein) or HP (20% protein) diets for 45 days were bred and maintained throughout gestation on same diets. Pups born (HP/LP dams) were maintained on the respective diets post-weaningly. The present study aimed to show the sex specific differences in the neurobehavioral evolution and behavioral phenotype of the HP/LP F1 generation pups. A battery of neurodevelopmental reflex tests, behavioral (Open field and forelimb gripstrength test), and cognitive [Elevated plus maze (EPM) and Morris water maze (MWM)] assays were performed. A decelerated growth curve with significantly restricted body and brain weight, delays in apparition of neuro-reflexes and poor performance in the LP group rats was recorded. Intra-generational PMN induced poor habituation-with-time in novel environment exploration, low anxiety and hyperactive like profile in open field test in young and adult rats. The study revealed poor forelimb neuromuscular strength in LP F1 pups till adulthood. Group occupancy plots in MWM test revealed hyperactivity with poor learning, impaired memory retention and integration, thus modeling the signs of early onset Alzehemier phenotype. In addition, a gender specific effect of LP diet with severity in males and favoring female sex was also noticed.

Diet, behavior and immunity across the lifespan

It is increasingly appreciated that perinatal events can set an organism on a life-long trajectory for either health or disease, resilience or risk. One early life variable that has proven critical for optimal development is the nutritional environment in which the organism develops. Extensive research has documented the effects of both undernutrition and overnutrition, with strong links evident for an increased risk for obesity and metabolic disorders, as well as adverse mental health outcomes. Recent work has highlighted a critical role of the immune system, in linking diet with long term health and behavioral outcomes. The present review will summarize the recent literature regarding the interactions of diet, immunity, and behavior.

Calorie restriction and corticosterone elevation during lactation can each modulate adult male fear and anxiety-like behaviour

Early life events, such as calorie restriction (CR) and elevated glucocorticoids, can calibrate the lifelong behavioural and physiological profile of an individual. Stress reactivity in adulthood is particularly sensitive to early life events; however, the consequence to fear and anxiety-like behaviour is less clear. Consequently, the current study sought to examine the effects of post-natal CR and glucocorticoid elevation, long considered powerful programming stimuli, on the subsequent fear and anxiety behaviour of the adult offspring. Rat dams received either corticosterone (200 μg/ml) supplementation in drinking water (CORT) or a 25% CR from post-natal day (PND) 1 to 11. Responses to the elevated plus maze (EPM), open field and a predator odour (TMT; 2,5-dihydro-2,4,5-trimethylthiazoline) were characterised in the adult male offspring. Both treatment conditions resulted in enhanced fear responses to TMT, characterised by heightened risk assessment and increased avoidance of TMT. CORT nursed offspring further demonstrated an anxiogenic profile in the open field. Basal hypothalamic-pituitary-adrenal function was unchanged in CORT adult offspring, whilst corticosterone concentration was elevated by post-natal CR. CR and CORT treated dams both exhibited greater anxiety-like behaviour in the EPM. A modest and temporary enhancement of maternal care was observed in CR and CORT treated dams, with CR dams further exhibiting rapid pup retrieval latencies. The results indicate enhanced emotionality in the adult male progeny of dams exposed to CR and corticosterone supplementation during the post-natal period. The modest enhancement of maternal care observed by both treatments is unlikely to have influenced the behavioural profile of the offspring.

Malnutrition and brain development: an analysis of the effects of inadequate diet during different stages of life in rat

Protein malnutrition or undernutrition can result in abnormal development of the brain. Depending on type, age at onset and duration, different structural and functional deficits can be observed. In the present review, we discuss the neuroanatomical, behavioral, neurochemical and oxidative status changes associated with protein malnutrition or undernutrition at different ages during prenatal and immediately postnatal periods as well as in adult rat. Analysis of all data suggests that protein malnutrition as well as undernutrition induced impaired learning and retention when imposed during the immediately postnatal period and in adulthood, whereas hyperactivity including increased impulsiveness and greater reactivity to aversive stimuli occurred when malnutrition or undernutrition was imposed either pre or postnatally. This general state of hyperreactivity may be linked essentially to an alteration in dopaminergic system. Hence, the present review shows that in spite of the attention devoted in the literature to prenatal effects, cognitive deficits are more serious following malnutrition or undernutrition after birth. We thus clearly establish a special vulnerability to malnutrition after weaning in rats.

Maternal perinatal undernutrition has long-term consequences on morphology, function and gene expression of the adrenal medulla in the adult male rat

Epidemiological studies suggest that maternal undernutrition sensitises to the development of chronic adult diseases, such as type 2 diabetes, hypertension and obesity. Although the physiological mechanisms involved in this 'perinatal programming' remain largely unknown, alterations of stress neuroendocrine systems such as the hypothalamic-pituitary-adrenal (HPA) and sympathoadrenal axes might play a crucial role. Despite recent reports showing that maternal perinatal undernutrition disturbs chromaffin cells organisation and activity in male rats at weaning, its long-term effects on adrenal medulla in adult animals are unknown. Using a rat model of maternal perinatal 50% food restriction (FR50) from the second week of gestation until weaning, histochemistry approaches revealed alterations in noradrenergic chromaffin cells aggregation and in cholinergic innervation in the adrenal medulla of 8-month-old FR50 rats. Electron microscopy showed that chromaffin cell granules exhibited ultrastructural changes in FR50 rats. These morphological changes were associated with reduced circulating levels and excretion of catecholamines. By contrast, catecholamine plasma levels were significantly increased after a 16 or 72 h of fasting, indicating that the responsiveness of the sympathoadrenal system to food deprivation was accentuated in FR50 adult rats. Among 384 pituitary adenylate cyclase-activating polypeptide-sensitive genes, we identified 129 genes (33.6%) that were under expressed (ratio < 0.7) in FR50 animals. A large number of these genes are involved in cytoskeleton remodelling and vesicle trafficking. Taken together, our results show that maternal perinatal undernutrition programmes adrenomedullary function and gene expression in adult male rats. Because catecholamines contribute to metabolic homeostasis, as well as arterial blood pressure regulation, the alterations observed in the adrenal medulla of adult male FR50 rats may participate in the programming of chronic adult diseases.

Calorie restriction at increasing levels leads to augmented concentrations of corticosterone and decreasing concentrations of testosterone in rats

The influence of calorie restriction (CR) on increasing life span, enhancing immunocompetence, and reducing the incidence of age-related diseases is well established. Evidence points to the involvement of neuroendocrine alterations in these beneficial effects. Accordingly, we hypothesized that CR will result in significant alterations to the hormones investigated. Little attention has been directed toward ascertaining the doses of CR required to obtain such alterations and, indeed, whether a dose-response exists. Adult rats were subjected to 1 of 5 dietary regimens: control, CR12.5%, CR25%, CR37.5%, or CR50%. Rats were decapitated 3 weeks following the onset of restriction; and trunk blood was collected and assayed for concentrations of serum adrenocorticotropic hormone, corticosterone, and testosterone, as well as plasma concentrations of noradrenalin and adrenalin. No effect was found as a result of dietary manipulation for serum concentrations of adrenocorticotropic hormone. However, all doses of CR resulted in increased serum corticosterone in a dose-response trend. A dose-response was also observed for serum testosterone, with higher doses of CR associated with lower testosterone. Concentrations of noradrenalin were not found to be altered by any CR dose, although a trend toward a down-regulation at CR50% was observed. Plasma adrenalin displayed a biphasic distribution with reductions observed at CR25% and CR50%, although the down-regulations only attained statistical significance relative to the CR37.5% and not the control group. As well as reporting the effect of CR on multiple hormones within individual animals, these results go some way in determining the optimal levels of CR needed to induce neuroendocrinologic alterations.