Effects of early life interventions and palatable diet on anxiety and on oxidative stress in young rats

Perinatal diet and offspring anxiety: A scoping review

Health behaviors during pregnancy have an impact on the developing offspring. Dietary factors play a role in the development of mental illness: however, less is known about the impact of diet factors during pre-conception, gestation, and lactation on anxiety levels in offspring. This scoping review sought to systematically map the available research involving human and animal subjects to identify nutritional interventions which may have a harmful or protective effect, as well as identify gaps. Studies investigating an association between any perinatal diet pattern or diet constituent and offspring anxiety were included. The number of studies reporting an association with increased or decreased levels of anxiety were counted and presented in figures. A total of 55,914 results were identified as part of a larger scoping review, and 120 articles met the criteria for inclusion. A greater intake of phytochemicals and vitamins were associated with decreased offspring anxiety whereas maternal caloric restriction, protein restriction, reduced omega-3 consumption, and exposure to a high fat diet were associated with higher levels of offspring anxiety. Results were limited by a very large proportion of animal studies. High quality intervention studies involving human subjects are warranted to elucidate the precise dietary factors or constituents that modulate the risk of anxiety in offspring.

Western Diet Consumption During Development: Setting the Stage for Neurocognitive Dysfunction

The dietary pattern in industrialized countries has changed substantially over the past century due to technological advances in agriculture, food processing, storage, marketing, and distribution practices. The availability of highly palatable, calorically dense foods that are shelf-stable has facilitated a food environment where overconsumption of foods that have a high percentage of calories derived from fat (particularly saturated fat) and sugar is extremely common in modern Westernized societies. In addition to being a predictor of obesity and metabolic dysfunction, consumption of a Western diet (WD) is related to poorer cognitive performance across the lifespan. In particular, WD consumption during critical early life stages of development has negative consequences on various cognitive abilities later in adulthood. This review highlights rodent model research identifying dietary, metabolic, and neurobiological mechanisms linking consumption of a WD during early life periods of development (gestation, lactation, juvenile and adolescence) with behavioral impairments in multiple cognitive domains, including anxiety-like behavior, learning and memory function, reward-motivated behavior, and social behavior. The literature supports a model in which early life WD consumption leads to long-lasting neurocognitive impairments that are largely dissociable from WD effects on obesity and metabolic dysfunction.

Neonatal handling increases neurogenesis, BDNF and GR in the hippocampus favoring memory acquisition in rats

Early life is a critical period for the development of the central nervous system (CNS) when the brain undergoes functional organization, neuronal proliferation and migration. This study aimed to evaluate influences and possible interactions of the neonatal handling (NH) on morphologic, biochemical and molecular markers in the hippocampus, as well as on Mu opioid receptors (MOR) immunoreactivity when adolescent rats were exposed to morphine. On postnatal day (PND) 1, male pups were assigned to two experimental groups: unhandled (UH) or neonatal handling (NH), whose procedure was applied from PND2 to PND9. On PND 50, animals were submitted to memory behavioral test, anesthesia and euthanasia for blood collection and hippocampus removal. Animals exposed to NH showed: i) increased levels of proBDNF and brain-derived neurotrophic factor (BDNF); ii) increased memory performance; iii) decreased lipid peroxidation (LP) in plasma and hippocampus; iv) increased antioxidant defenses; v) increased glucocorticoids receptor (GR) levels. Interestingly, our data showed a positive correlation between BDNF and working memory after NH procedure (r² = 0.73; P = 0.006). Animals submitted to NH showed an increased per se of MOR immunoreactivity regardless of morphine exposure, while this increasing was also observed in the UH group after morphine exposure, even in a small extent. NH beneficial influence during early stage of life can be reflected during the development of the puppies, enhancing memory performance, preventing oxidative events and improving molecular targets in hippocampus. Further experimental studies in addition to clinical ones are needed to validate NH protocol as a therapeutic tool.

Enhanced anxiety-like behavior emerges with weight gain in male and female obesity-susceptible rats

Epidemiological data suggest that body mass index and obesity are strong risk factors for depression and anxiety. However, it is difficult to separate cause from effect, as predisposition to obesity may enhance susceptibility to anxiety, or vice versa. Here, we examined the effect of diet and obesity on anxiety-like behaviors in male and female selectively bred obesity-prone and obesity-resistant rats, and outbred Sprague-Dawley rats. We found that when obesity-prone and obesity-resistant rats do not differ in weight or fat mass, measures of anxiety-like behavior in the elevated plus maze and open field are similar between the two groups. However, once weight and fat mass diverge, group differences emerge, with greater anxiety in obesity-prone relative to obesity-resistant rats. This same pattern was observed for males and females. Interestingly, even when obesity-resistant rats were "forced" to gain fat mass comparable to obesity-prone rats (via prolonged access to 60% high-fat diet), anxiety-like behaviors did not differ from lean chow fed controls. In addition, a positive correlation between anxiety-like behaviors and adiposity were observed in male but not in female obesity-prone rats. Finally, diet-induced weight gain in and of itself was not sufficient to increase measures of anxiety in outbred male rats. Together, these data suggest that interactions between susceptibility to obesity and physiological alterations accompanying weight gain may contribute to the development of enhanced anxiety.

Palatable Food Dampens the Long-Term Behavioral and Endocrine Effects of Juvenile Stressor Exposure but May Also Provoke Metabolic Syndrome in Rats

The juvenile period is marked by a reorganization and growth of important brain regions including structures associating with reward seeking behaviors such as the nucleus accumbens (NA) and prefrontal cortex (PFC). These changes are impacted by stressors during the juvenile period and may lead to a predisposition to stress induced psychopathology and abnormal development of brain reward systems. Like in humans, adult rodents engage certain coping mechanisms such as increases in the consumption of calorie-rich palatable foods to reduce stress, but this behavior can lead to obesity and metabolic disorders. In this study, we examined whether stressors during the juvenile period led to increased caloric intake when a palatable diet was accessible, and whether this diet attenuated adult stress responses. In addition, we examined if the stress buffering effects produced by the palatable diet were also accompanied by an offset propensity towards obesity, and by alterations in mRNA expression of dopamine (DA) receptors in the NA and PFC in adulthood. To this end, juvenile male Wistar rats underwent episodic stressor exposure (forced swim, elevated platform stress and restraint) on postnatal days (PD) 27-29 and received access to regular chow or daily limited access to a palatable diet until adulthood. At the age of 2 months, rats were tested on a social interaction test that screens for anxiety-like behaviors and their endocrine responses to an acute stressor. Animals were sacrificed, and their brains processed to detect differences in DA receptor subtype expression in the PFC and NA using qPCR. Results showed that rats that were stressed during the juvenile period displayed higher social anxiety and a sensitized corticosterone response as adults and these effects were attenuated by access to the palatable diet. Nevertheless, rats that experienced juvenile stress and consumed a palatable diet showed greater adiposity in adulthood. Interestingly, the same group displayed greater mRNA expression of DA receptors at the NA. This suggests that access to a palatable diet mitigates the behavioral and endocrine effects of juvenile stressor exposure in adulthood, but at the cost of metabolic imbalances and a sensitized dopaminergic system.

Home alone: a systematic review and meta-analysis on the effects of individual housing on body weight, food intake and visceral fat mass in rodents

Rats and mice are widely used to study environmental effects on psychological and metabolic health. Study designs differ widely and are often characterized by varying (social) housing conditions. In itself, housing has a profound influence on physiology and behaviour of rodents, affecting energy balance and sustainable metabolic health. However, evidence for potential long-term consequences of individual versus social housing on body weight and metabolic phenotype is inconsistent. We conducted a systematic literature review and meta-analyses assessing effects of individual versus social housing of rats and mice, living under well-accepted laboratory conditions, on measures of metabolic health, including body weight, food intake and visceral adipose tissue mass. Seventy-one studies were included in this review; 59 were included in the meta-analysis. Whilst housing did not affect body weight, both food intake and visceral adipose tissue mass were significantly higher in individually compared with socially housed animals. A combination of emotional stress and lack of social thermoregulation likely contributed to these effects. Increased awareness of consequences and improved specifications of housing conditions are necessary to accurately evaluate efficacy of drugs, diets or other interventions on metabolic and other health outcomes because housing conditions are rarely considered as possible moderators of reported outcomes.

Low maternal care is associated with increased oxidative stress in the brain of lactating rats

Maternal care is crucial for offspring development and licking/grooming patterns can be induced by sensorial, neuroendocrine, and metabolic variations in the CNS. Important brain functions, such as learning and memory, can be influenced by oxidative stress, which can also modulate pathophysiological processes (e.g., depression, anxiety, and other psychiatric disorders). This study evaluated oxidative stress in the hippocampus (HP), olfactory bulb (OB), and plasma in Low-Licking (LL) and High-Licking (HL) lactating rats through superoxide dismutase (SOD) and catalase (CAT) activities, DNA damage (comet assay), and dihydrodichlorofluorescein (DCF) oxidation assay. Results demonstrate that in the HP of LL, the activities of SOD and CAT were increased compared to HL. In the OB, the activities of SOD and CAT were also increased in LL. The comet assay in the HP showed that LL had higher levels of basal damage and increased levels of DNA breaks than HL. In the OB, LL also had higher levels of DNA damage. In the plasma, no difference was observed in either SOD or CAT activities, but the DCF oxidation assay revealed that LL had higher levels of ROS production than HL. In conclusion, we observed that LL mothers showed evidence of increased oxidative stress when compared to HL, suggesting that variations in maternal behavior might be related to these biochemical parameters.

Tactile stimulation during different developmental periods modifies hippocampal BDNF and GR, affecting memory and behavior in adult rats

Recent studies have shown that tactile stimulation (TS) in pups is able to prevent and/or minimize fear, anxiety behaviors, and addiction to psychostimulant drugs in adult rats. In these studies, animals have been exposed to handling from postnatal day (PND) 1-21. This study was designed to precisely establish which period of preweaning development has a greater influence of TS on neuronal development. After birth, male pups were exposed to TS from PND1-7, PND8-14, and PND15-21. In adulthood, the different periods of postnatal TS were assessed through behavioral, biochemical, and molecular assessments. Animals that received TS from PND8-14 showed lower anxiety-like symptoms, as observed by decreased anxiety index in elevated plus maze. This same TS period was able to improve rats' working memory by increasing the percentage of alternation rate in Y-maze, and induce better ability to cope with stressful situations, as showed in the defensive burying test by a reduced time of burying behavior. On the other hand, animals receiving TS in the first week of life showed longest cumulative burying time, which is directly related to increased anxiety-like behavior. Moreover, TS from PND8-14 showed lower corticosterone levels and better oxidative status, as observed by decreased lipid peroxidation and increased catalase activity in the hippocampus. Brain-derived neurotrophic factor (BDNF) immunocontent was increased in the hippocampus of animals receiving TS from PND8-14, while glucocorticoid receptors immunocontent was decreased in both TS_1-7 and TS_15-21 , but not TS_8-14 . To the best of our knowledge, this study is the first to show TS can be more efficient if applied over a focused period of neonatal development (PND8-14) and this beneficial influence can be reflected on reduced emotionality and increased ability to address stressful situations in adulthood. © 2016 Wiley Periodicals, Inc.

Involvement of oxidative stress in the regulation of NPY/CART-mediated appetite control in amphetamine-treated rats

Amphetamine (AMPH) treatment can suppress appetite and increase oxidative stress in the brain. AMPH-induced appetite suppression is associated with the regulation of neuropeptide Y (NPY) and cocaine- and amphetamine-regulated transcript (CART) in the hypothalamus. The present study explored whether antioxidants, including glutathione S-transferase (GST) and glutathione peroxidase (GP), were involved in this NPY/CART-mediated appetite control. Rats were treated daily with AMPH for four days. Changes in food intake and expression levels of hypothalamic NPY, CART, GST, and GP were examined and compared. Results showed that, in AMPH-treated rats, (1) food intake and NPY expression decreased, while CART, GST, and GP expression increased; (2) NPY knockdown in the brain enhanced the decrease in NPY and the increases in CART, GST, and GP expression; and (3) central inhibition of reactive oxygen species production decreased GST and GP and modulated AMPH anorexia and the expression levels of NPY and CART. The present results suggest that oxidative stress in the brain participates in regulating NPY/CART-mediated appetite control in AMPH-treated rats. These results may advance the knowledge regarding the molecular mechanism of AMPH-evoked or NPY/CART-mediated appetite suppression.

Novel therapeutic targets in depression and anxiety: antioxidants as a candidate treatment

There is growing evidence that the imbalance between oxidative stress and the antioxidant defense system may be associated with the development neuropsychiatric disorders, such as depression and anxiety. Major depression and anxiety are presently correlated with a lowered total antioxidant state and by an activated oxidative stress (OS) pathway. The classical antidepressants may produce therapeutic effects other than regulation of monoamines by increasing the antioxidant levels and normalizing the damage caused by OS processes. This chapter provides an overview of recent work on oxidative stress markers in the animal models of depression and anxiety, as well as patients with the aforementioned mood disorders. It is well documented that antioxidants can remove the reactive oxygen species (ROS) and reactive nitrogen species (RNS) through scavenging radicals and suppressing the OS pathway, which further protect against neuronal damage caused oxidative or nitrosative stress sources in the brain, hopefully resulting in remission of depression or anxiety symptoms. The functional understanding of the relationship between oxidative stress and depression and anxiety may pave the way for discovery of novel targets for treatment of neuropsychiatric disorders.

Potential antioxidant and anxiolytic effects of (+)-limonene epoxide in mice after marble-burying test

The present study evaluated anxiolytic activity of (+)-limonene epoxide (EL), through the marble burying test (MBT) assay, and the antioxidant potential in vitro and in vivo in mice hippocampus of adult mice subjected to experimental anxiety protocol. For behavioral studies, and in vivo antioxidant analyses, mice were treated orally with 0.05% Tween 80 dissolved in 0.9% saline solution (vehicle), ascorbic acid 250 mg/kg, diazepam (2 mg/kg) and EL (25, 50 and 75 mg/kg). Results suggest an anxiolytic effect of (+)-limonene epoxide. A reduction in number of buried marbles in groups treated with EL doses of 25, 50 and 75 mg/kg was observed when compared with diazepam and vehicle groups. This reduction was observed after treatments with single and repeated doses, reinforcing the hypothesis of anxiolytic effect. The anxiolytic effect was reversed by pretreatment with flumazenil (25 mg/kg, o.r) in the same way as it was observed with diazepam (2 mg/kg, o.r, positive control), suggesting that these drugs possess a similar mechanism of action. In antioxidant tests in vitro, the concentrations from 0.9 to 7.2 μg/ml were tested. The results of in vitro antioxidant tests demonstrated a 50% inhibitory effective concentration of 0.7342, 1.296 and 1.169 μg/ml against the formation of nitrite ion, hydroxyl radical and reactive substances to thiobarbituric acid, respectively. The treatment with EL reduced the lipid peroxidation level and nitrite content, suggesting an antioxidant role in vivo since it was able to reduce the formation of reactive species derived from oxygen and nitrogen. Furthermore, the EL increased activity of enzymes catalase and superoxide dismutase in mice hippocampus, suggesting that their role may be due to antioxidant upregulation of these enzymes.

Bizarre behaviors and risk assessment in 3xTg-AD mice at early stages of the disease

Bizarre behaviors (stereotyped stretching, stereotyped rearing, backward movements and jumps) were conspicuously elicited in classical unconditioned tests with different levels of anxiogenic conditions. They were characterized for the first time as early-BPSD-like symptoms in 6 month-old male and female 3xTg-AD mice. The pattern of these behaviors differed from that exhibited by their age- and gender-matched NTg counterparts. Confrontation of an open and illuminated field was the best trigger of such behaviors as compared to mild neophobia in the corner test or the choice between two compartments in the dark-light box. Here we also report that increased freezing, delayed thigmotaxis and enhancement of emotional behaviors were early BPSD-like symptoms indicative of their response to low-stressful environments. Independently of the genotype, consistent gender effects pointed toward the relevance of female gender to study bizarre behaviors and risk assessment. The identification of items of behavior and its gender component were relevant to find out bidirectional and selective behavioral long-lasting effects of postnatal handling. This early life treatment reduced freezing and most of the bizarre behaviors whereas potentiated risk assessment and the horizontal locomotor activity. In contrast, vertical exploratory activity was not modified by the treatment. The results also talk in favor of the beneficence of early-life interventions on the behavioral outcome in adulthood in both healthy and disease conditions. As shown, the consideration of bizarre behaviors and risk assessment may become an additional tool for evaluating BPSD-like symptoms in relation to preventive and/or therapeutical strategies targeted at AD. It may also have a role in the evaluation of the potential risk factors for the disease.

Anti-oxidative and DNA Protecting Effects of Flavonoids-rich Scutellaria Lateriflora

Scutellaria lateriflora (American skullcap), a native plant of North America, has been used by Americans and Europeans as a nerve tonic for more than 200 years. In vivo studies have shown anxiolytic activity of S. lateriflora in animals and humans. However, the neuroprotective mechanisms of S. lateriflora are not fully understood. Oxidative stress plays a vital role in the neurodegenerative and neuropsychiatric diseases such as anxiety, Alzheimer's disease, depression, and Parkinson's disease. Bioactive compounds present in various medicinal plants neutralize or scavenge toxic free radicals and thus suppress oxidative stress. Therefore, the objective of this study was to investigate the antioxidant effects of S. lateriflora. The antioxidant potential of aqueous or ethanolic extracts of S. lateriflora was determined in mouse brain tissue using various biochemical assays. Protective effects of S. lateriflora against oxidative stress induced DNA fragmentation was determined using plasmid DNA. The ethanolic and aqueous extracts scavenged the 1,1-diphenyl-2-picrylhydrazyl (DPPH) radicals. The ethanolic extract reduced tert-butyl peroxide-induced reactive oxygen species (ROS) and lipid peroxides in the mouse brain homogenates. Furthermore, the ethanolic extract of S. lateriflora protected hydrogen peroxide-UV induced cleavage of supercoiled plasmid DNA. In conclusion, S. lateriflora exhibited significant antioxidant effects. The current findings posit S. lateriflora as one of the potential experimental herbal drugs that should be screened for its therapeutic potential against various oxidative stress associated mental disorders.

Developmental post-natal stress can alter the effects of pre-natal stress on the adult redox balance

Across diverse vertebrate taxa, stressful environmental conditions during development can shape phenotypic trajectories of developing individuals, which, while adaptive in the short-term, may impair health and survival in adulthood. Regardless, the long-lasting benefits or costs of early life stress are likely to depend on the conditions experienced across differing stages of development. Here, we used the Japanese quail (Coturnix coturnix japonica) to experimentally manipulate exposure to stress hormones in developing individuals. We tested the hypothesis that interactions occurring between pre- and post-natal developmental periods can induce long-term shifts on the adult oxidant phenotype in non-breeding sexually mature individuals. We showed that early life stress can induce long-term alterations in the basal antioxidant defences. The magnitude of these effects depended upon the timing of glucocorticoid exposure and upon interactions between the pre- and post-natal stressful stimuli. We also found differences among tissues with stronger effects in the erythrocytes than in the brain in which the long-term effects of glucocorticoids on antioxidant biomarkers appeared to be region-specific. Recent experimental work has demonstrated that early life exposure to stress hormones can markedly reduce adult survival (Monaghan et al., 2012). Our results suggest that long-term shifts in basal antioxidant defences might be one of the potential mechanisms driving such accelerated ageing processes and that post-natal interventions during development may be a potential tool to shape the effects induced by pre-natally glucococorticoid-exposed phenotypes.

Diet-regulated anxiety

A substantial proportion of noncommunicable disease originates in habitual overconsumption of calories, which can lead to weight gain and obesity and attendant comorbidities. At the other end of the spectrum, the consequences of undernutrition in early life and at different stages of adult life can also have major impact on wellbeing and quality of life. To help address some of these issues, greater understanding is required of interactions with food and contemporary diets throughout the life course and at a number of different levels: physiological, metabolic, psychological, and emotional. Here we review the current literature on the effects of dietary manipulation on anxiety-like behaviour. This evidence, assembled from study of preclinical models of diet challenge from gestation to adult life, supports a role for diet in the important connections between psychology, physiology, and behaviour. Analogous processes in the human population in our current obesogenic environment are likely to contribute to individual and societal challenges in this area.