Chronic high-fat diet affects food-motivated behavior and hedonic systems in the nucleus accumbens of male rats.

Environmental variations can influence eating and motivated behaviors, as well as the brain's feeding circuits to predisposing overweight and obesity. The identification of mechanisms through which a long-term consumption of caloric-dense palatable foods and its association with early life stress can cause neuroadaptations and possible modify motivational behaviors are relevant to elucidate the mechanisms associated with obesity. Here, we investigated the long-term effects of a chronic high-fat diet (HFD), and its interaction with early social isolation on hedonic feeding responses in adult rats. Rats were subjected, or not, to social isolation between postnatal days 21-28 and were fed a control diet or HFD, for 10 weeks post weaning. Hedonic feeding behavior was evaluated during adulthood and parameters related to the dopaminergic, cannabinoid, and opioid systems were measured in the nucleus accumbens. Animals with chronic HFD intake were less motivated to obtain sweet palatable foods. This reduced motivation did not appear to be associated with less pleasure upon tasting sweet food, as no alteration in reactivity to sweet taste was observed. Interestingly, the animals receiving HFD presented decreased immunocontents of the D1 and CB1 receptors, while the stressed group displayed a reduction in dopamine turnover. In summary, chronic HFD causes a significant motivational impairment for sweet palatable foods; these changes may be associated with a decreased dopaminergic and cannabinoid neurotransmission in the nucleus accumbens. In contrast, a brief social isolation during the prepubertal period was unable to alter the behavioral parameters studied but caused a decreased dopaminergic turnover in the nucleus accumbens of adult rats. These findings highlight the importance of long-term HFD exposure on the modulation of hedonic feeding behavior and related neurochemical systems.

Consumption of a palatable diet rich in simple sugars during development impairs memory of different degrees of emotionality and changes hippocampal plasticity according to the age of the rats.

We investigated the effect of a chronic palatable diet rich in simple sugars on memory of different degrees of emotionality in male adult rats, and on hippocampal plasticity markers in different stages of development. On postnatal day (PND) 21, 45 male Wistar rats were divided in two groups, according to their diet: (1-Control) receiving standard lab chow or (2-Palatable Diet) receiving both standard chow plus palatable diet ad libitum. At PND 60, behavioral tests were performed to investigate memory in distinct tasks. Hippocampal plasticity markers were investigated at PND 28 in half of the animals, and after the behavioral tests. Palatable diet consumption induced an impairment in memory, aversive or not, and increased Na+ , K+ -ATPase activity, both at PND 28, and in the adulthood. Synaptophysin, brain-derived neurotrophic factor (BDNF), and protein kinase B (AKT), and phosphorylated AKT were reduced in the hippocampus at PND 28. However, at PND 75, this diet consumption led to increased hippocampal levels of synaptophysin, spinophilin/neurabin-II, and decreased BDNF and neuronal nitric oxide synthase. These results showed a strongly association of simple sugars-rich diet consumption during the development with memory impairments. Plasticity markers are changed, with results that depend on the stage of development evaluated.

Resilience and Vulnerability to Trauma: Early Life Interventions Modulate Aversive Memory Reconsolidation in the Dorsal Hippocampus.

Early life experiences program lifelong responses to stress. In agreement, resilience and vulnerability to psychopathologies, such as posttraumatic stress disorder (PTSD), have been suggested to depend on the early background. New therapies have targeted memory reconsolidation as a strategy to modify the emotional valence of traumatic memories. Here, we used animal models to study the molecular mechanism through which early experiences may later affect aversive memory reconsolidation. Handling (H)-separation of pups from dams for 10 min-or maternal separation (MS) - 3-h separation-were performed from PDN1-10, using non-handled (NH) litters as controls. Adult males were trained in a contextual fear conditioning (CFC) task; 24 h later, a short reactivation session was conducted in the conditioned or in a novel context, followed by administration of midazolam 3 mg/kg i.p. (mdz), known to disturb reconsolidation, or vehicle; a test session was performed 24 h after. The immunocontent of relevant proteins was studied 15 and 60 min after memory reactivation in the dorsal hippocampus (dHc) and basolateral amygdala complex (BLA). Mdz-treated controls (NH) showed decreased freezing to the conditioned context, consistent with reconsolidation impairment, but H and MS were resistant to labilization. Additionally, MS males showed increased freezing to the novel context, suggesting fear generalization; H rats showed lower freezing than the other groups, in accordance with previous suggestions of reduced emotionality facing adversities. Increased levels of Zif268, GluN2B, ß-actin and polyubiquitination found in the BLA of all groups suggest that memory reconsolidation was triggered. In the dHc, only NH showed increased Zif268 levels after memory retrieval; also, a delay in ERK1/2 activation was found in H and MS animals. We showed here that reconsolidation of a contextual fear memory is insensitive to interference by a GABAergic drug in adult male rats exposed to different neonatal experiences; surprisingly, we found no differences in the reconsolidation process in the BLA, but the dHc appears to suffer temporal desynchronization in the engagement of reconsolidation. Our results support a hippocampal-dependent mechanism for reconsolidation resistance in models of early experiences, which aligns with current hypotheses for the etiology of PTSD.

Sex-dependent effect on mitochondrial and oxidative stress parameters in the hypothalamus induced by prepubertal stress and access to high fat diet.

OBJECTIVE: Some factors related to lifestyle, including stress and high-fat diet (HFD) consumption, are associated with higher prevalence of obesity. These factors can lead to an imbalance between ROS production and antioxidant defenses and to mitochondrial dysfunctions, which, in turn, could cause metabolic impairments, favoring the development of obesity. However, little is known about the interplay between these factors, particularly at early ages, and whether long-term sex-specific changes may occur. Here, we evaluated whether social isolation during the prepubertal period only, associated or not with chronic HFD, can exert long-term effects on oxidative status parameters and on mitochondrial function in the whole hypothalamus, in a sex-specific manner. METHODS: Wistar male and female rats were divided into two groups (receiving standard chow or standard chow + HFD), that were subdivided into exposed or not to social isolation during the prepubertal period. Oxidative status parameters, and mitochondrial function were evaluated in the hypothalamus in the adult age. RESULTS: Regarding antioxidant enzymes activities, HFD decreased GPx activity in the hypothalamus, while increasing SOD activity in females. Females also presented increased total thiols; however, non-protein thiols were lower. Main effects of stress and HFD were observed in TBARS levels in males, with both factors decreasing this parameter. Additionally, HFD increased complex IV activity, and decreased mitochondrial mass in females. Complex I-III activity was higher in males compared to females. CONCLUSION: Stress during the prepubertal period and chronic consumption of HFD had persistent sex-specific effects on oxidative status, as well as on its consequences for the cell and for mitochondrial function. HFD had more detrimental effects on females, inducing oxidative imbalance, which resulted in damage to the mitochondria. This HFD-induced imbalance may be related to the development of obesity.

Neonatal handling impairs intradimensional shift and alters plasticity markers in the medial prefrontal cortex of adult rats.

Stress response can be modulated by neonatal/childhood events. Neonatal handling (NH) is an animal model in which the animals are subjected to brief separations from the dam during the first days of life, and it leads to lower emotionality and behavioral changes in adulthood. The aim of this study was to observe if early events, such as (NH), may program associative learning and behavioral flexibility in adult male rats and if these changes could be related to altered neurochemistry in the medial prefrontal cortex (mPFC). We evaluated proteins related to synaptic plasticity (brain-derived neurotrophic factor [BDNF] and synaptophysin [SYP]) as well as Na+/K+-ATPase activity. Additionally, we evaluated proteins related to the dopaminergic system (tyrosine hydroxylase [TH] and phosphorylated TH [pTH]), since this system appears to be affected in some neonatal interventions. Neonatally handled animals exhibited impairment in simple discrimination and intradimensional shift but not in reversal or compound discrimination; in addition, no alteration in switching from an egocentric spatial to a cued strategy was observed. These effects were accompanied by a decrease in SYP levels and Na+/K+-ATPase activity, suggesting reduced synaptic function. These results indicate that NH increases attention to irrelevant stimuli and/or impairs associative learning, and this is accompanied by neurochemical alterations in the (mPFC).

Hypericum polyanthemum cyclohexane extract potentiates behavioral effects and neurodegeneration induced by nigral infusions of 6-hydroxydopamine in rats.

INTRODUCTION: Parkinson's Disease (PD) is a progressive neurodegenerative disorder, hallmark of which is loss of nigral dopaminergic neurons. Since a Hypericum polyanthemum extract inhibits monoamine reuptake and some of its constituents present cytotoxic properties, the aim of this study was to evaluate the effect of this extract in an animal PD model. METHODS: Adult Wistar rats (110 days old) received 6-hydroxydopamine (6-OHDA) infusions into the right medial forebrain bundle. A cyclohexane extract from aerial parts of H. polyanthemum (POL; 90 mg/kg/administration; gavage) was administered in three different regimens. In Regimens 1 and 2, rats received 3 administrations of POL starting 4 or 24 h after 6-OHDA infusion, respectively. In Regimen 3, these administrations were carried out 1 day before any evaluation of ipsilateral rotational activity induced by methylphenidate (MP, 20 mg/kg, i.p.). MP was administered 10, 45, and 85 days after 6-OHDA infusion in all groups. Nigral tyrosine hydroxylase (TH) immunocontent was evaluated 120 days after 6-OHDA infusion in animals submitted to Regimen 2 only. The effect of POL on apomorphine-induced climbing behavior in non-lesioned adult CF1 mice (60 days old) treated with POL was also evaluated. RESULTS: Regimen 2 increased MP-induced rotational activity and decreased nigral TH levels in 6-OHDA-lesioned rats. Rotational activity was not altered in regimens 1 and 3. In addition, no change in climbing behavior was observed in non-lesioned mice. CONCLUSION: Together, these results indicate that, in 6-OHDA-lesioned rats, a cyclohexane H. polyanthemum extract potentiates neurotoxicity and MP-induced motor asymmetry depending on the time of administration. In the short term, it seems to not act directly on mice dopaminergic receptors.

Sex-specific effects of prepubertal stress and high-fat diet on leptin signaling in rats.

OBJECTIVE: Both stress exposure and high-fat diet (HFD) are contributors to the alarming prevalence of obesity. Leptin is secreted from adipose tissue and regulates appetite and body weight via the JAK-STAT3 pathway in the hypothalamus; it also regulates the hypothalamic-pituitary-thyroid axis, modulating energy homeostasis. Leptin signaling may be impaired by HFD intake, and here we investigate whether social isolation during the prepubertal period, associated with chronic HFD, can exert long-term effects on metabolic parameters in a sex-specific manner. METHODS: Wistar male and female rats were divided into two groups (receiving standard chow or standard chow and HFD), which were subdivided into (1) exposed to social isolation during the prepubertal period or (2) not exposed. RESULTS: HFD induced sex-specific effects on leptin signaling and on the hypothalamic-pituitary-thyroid axis; males receiving HFD presented increased T4 but a reduced T3:T4 ratio and higher caloric efficiency during development. A stress × diet interaction was noted for leptin signaling in males, where pSTAT3 was higher when these factors were applied together. On the other hand, females were more susceptible to early stress, which reduced pSTAT3 in the hypothalamus. CONCLUSION: Both stress during the prepubertal period and chronic consumption of HFD had long-term sex-specific effects on hormonal signaling related to energy balance. However, the effects of HFD were more pronounced in males, whereas prepubertal stress had greater effects on leptin signaling in females.

Impact of High-Fat Diet and Early Stress on Depressive-Like Behavior and Hippocampal Plasticity in Adult Male Rats.

During development, the brain goes through fundamental processes, including organization of neural networks and plasticity. Environmental interventions may change initial brain programming, leading to long-lasting effects and altering the susceptibility to psychopathologies, including depression disorder. It is known that depression is a psychiatric disorder with a high prevalence worldwide, including high rates among adolescents. In this study, we evaluated whether social isolation in the prepubertal period and chronic use of high-fat diet (HFD) may induce depressive-like behavior in male adult rats. We also investigated hippocampal plasticity markers and neurotransmitter systems. We found both social isolation and HFD induced a depressive-like behavior in the forced swimming task. Moreover, chronic HFD reduced synaptic markers in hippocampus, demonstrated by reductions in ßIII-tubulin (neuronal marker), PSD-95, SNAP-25, and neurotrophin-3. The HFD group also presented decreased glutamatergic and GABAergic receptors subunits. On the other hand, stress affected hippocampal brain-derived neurotrophic factor (BDNF) signaling pathways, and increased expression of subunit of the NMDA receptor (NR2A). Both factors (stress and diet) decreased GR in the hippocampus without affecting plasma corticosterone at basal levels. Interactions between early stress and HFD access were observed only in the BNDF receptor (tropomyosin receptor kinase B; TrkB) and synaptophysin. In summary, these findings showed that a brief social isolation and chronic HFD, during a sensitive developmental period, cause depressive-like behavior in adulthood. The mechanisms underlying these behavioral effects may involve changes in the levels of synaptic proteins in hippocampus: HFD consumption appears to affect synaptic markers, while social isolation affected BDNF signaling more significantly.

Early life adversities or high fat diet intake reduce cognitive function and alter BDNF signaling in adult rats: Interplay of these factors changes these effects.

Environmental factors, like early exposure to stressors or high caloric diets, can alter the early programming of central nervous system, leading to long-term effects on cognitive function, increased vulnerability to cognitive decline and development of psychopathologies later in life. The interaction between these factors and their combined effects on brain structure and function are still not completely understood. In this study, we evaluated long-term effects of social isolation in the prepubertal period, with or without chronic high fat diet access, on memory and on neurochemical markers in the prefrontal cortex of rats. We observed that early social isolation led to impairment in short-term and working memory in adulthood, and to reductions of Na(+),K(+)-ATPase activity and the immunocontent of phospho-AKT, in prefrontal cortex. Chronic exposure to a high fat diet impaired short-term memory (object recognition), and decreased BDNF levels in that same brain area. Remarkably, the association of social isolation with chronic high fat diet rescued the memory impairment on the object recognition test, as well as the changes in BDNF levels, Na(+),K(+)-ATPase activity, MAPK, AKT and phospho-AKT to levels similar to the control-chow group. In summary, these findings showed that a brief social isolation period and access to a high fat diet during a sensitive developmental period might cause memory deficits in adulthood. On the other hand, the interplay between isolation and high fat diet access caused a different brain programming, preventing some of the effects observed when these factors are separately applied.

Neonatal handling causes impulsive behavior and decreased pharmacological response to methylphenidate in male adult wistar rats.

Neonatal handling has an impact on adult behavior of experimental animals and is associated with rapid and increased palatable food ingestion, impaired behavioral flexibility, and fearless behavior to novel environments. These symptoms are characteristic features of impulsive trait, being controlled by the medial prefrontal cortex (mPFC). Impulsive behavior is a key component of many psychiatric disorders such as attention deficit hyperactivity disorder (ADHD), manic behavior, and schizophrenia. Others have reported a methylphenidate (MPH)-induced enhancement of mPFC functioning and improvements in behavioral core symptoms of ADHD patients. The aims of the present study were: (i) to find in vivo evidence for an association between neonatal handling and the development of impulsive behavior in adult Wistar rats and (ii) to test whether neonatal handling could have an impact on monoamine levels in the mPFC and the pharmacological response to MPH in vivo. Therefore, experimental animals (litters) were classified as: "non-handled" and "handled" (10[Formula: see text]min/day, postnatal days 1-10). After puberty, they were exposed to either a larger and delayed or smaller and immediate reward (tolerance to delay of reward task). Acute MPH (3[Formula: see text]mg/Kg. i.p.) was used to suppress and/or regulate impulsive behavior. Our results show that only neonatally handled male adult Wistar rats exhibit impulsive behavior with no significant differences in monoamine levels in the medial prefrontal cortex, together with a decreased response to MPH. On this basis, we postulate that early life interventions may have long-term effects on inhibitory control mechanisms and affect the later response to pharmacological agents during adulthood.

Estrogen-dependent effects on behavior, lipid-profile, and glycemic index of ovariectomized rats subjected to chronic restraint stress.

Stress has been shown to negatively affect the immune system, alter the body's metabolism, and play a strong role in the development of mood disorders. These effects are mainly driven through the release of hormones from the hypothalamic-pituitary-adrenal axis (HPA). Additionally, women are more likely to be affected by stress due to the estrogen fluctuation associated with their menstrual cycle. This study aims to evaluate the effect of chronic restraint stress, applied for 30 days, and estrogen replacement on behavior, glucose level, and the lipid profile of ovariectomized rats. Our results suggest that stress increases sweet food consumption in OVX females treated with estradiol (E2), but reduces consumption in animals not treated. Furthermore, stress increases locomotor activity and anxiety as assessed by the Open Field test and in the Elevated Plus Maze. Similarly, our results suggest that E2 increases anxiety in female rats under the same behavioral tests. In addition, stress reduces glucose and TC levels. Moreover, stress increase TG levels in the presence of E2 and decrease in its absence, as well as the estradiol increase TG levels in stressed groups and reduced in non-stressed groups. Our data suggest an important interaction between stress and estrogen, showing that hormonal status can induce changes in the animal's response to stress.

Oxidative stress and DNA damage in older adults that do exercises regularly.

OBJECTIVES: Free radicals may damage lipids, proteins and DNA, which may lead to critical diseases in the aging. This work evaluated levels of malondialdehyde (MDA), glutathione peroxidase (GPx) and DNA damage by comet assay (SCGE) in older adults that do exercises regularly. DESIGN AND METHODS: 110 females, aged 66.3+/-8 years were divided into sedentary (n=54), walking (n=36) and muscle building (n=20) groups. Levels of MDA, GPx and SCGE were measured in venous blood before and after exercise. RESULTS: MDA levels were higher (P<0.005) and GPx levels were lower (P<0.005) in active groups than in sedentary group. SCGE index after physical activity was greater than at baseline (muscle building: P=0.004; walking: P=0.002). CONCLUSIONS: Exercise reduces the diseases risk, but may promote the production of free radicals. It remains unclear whether cell adaptations responsible for health benefits are associated with such events. However we may suggest the existence of a different biochemical pattern for older adults that do exercise regularly.

Estudo pré-analítico e de validação para determinação de malondialdeído em plasma humano por cromatografia líquida de alta eficiência, após derivatização com 2.4-dinitrofenilhidrazina / Preanalytical and validation studies for the determination of malondialdehyde in human plasma through high performance liquid chromatography after derivatization with 2.4-dinitrophenylhydrazine

O malondialdeído (MDA) é um importante biomarcador utilizado na avaliação do estresse oxidativo. O objetivo deste estudo foi desenvolver uma metodologia para a quantificação plasmática de MDA, através de cromatografia líquida de alta eficiência com detecção por arranjo de diodos (CLAE-DAD), após processo de derivatização com 2,4-dinitrofenilhidrazina (DNPH), avaliando as principais variáveis pré-analíticas. A curva de calibração em plasma (0 a 40 µM) apresentou elevada linearidade (r²=0,998). Os principais parâmetros de validação foram: recuperação absoluta: 78 por cento; limite de detecção: 0,11 µM e limite de quantificação: 0,38 µM. Os valores de MDA determinados em indivíduos adultos saudáveis (n=38) foram 3,31 ± 0,38 µM (média ± DP). Estudos de estabilidade do padrão de MDA, reagente derivatizante e MDA plasmáticos, indicaram que a solução padrão pode ser armazenada a -20 e 4 ºC.

Malondialdehyde (MDA) is an important biomarker for the evaluation of oxidative stress status. The aim of this study was to develop a method for plasma MDA quantification by high performance liquid chromatography with diode-array detection (HPLC-DAD), following derivatization with 2,4-dinitrophenylhydrazine (DNPH), evaluating the main preanalytical variables. The calibration curve in plasma (0 to 40 µM) presented high linearity (r² = 0.998). Main validation parameters were: recovery: 78 percent; LOD: 0.11 µM and LOQ: 0.38 µM. The MDA values obtained in healthy volunteers (n=38) were 3.31 ± 0.38 µM (mean ± SD). Stability studies of MDA standard solution and derivatizing reagent and plasma MDA indicated that the standard solution can be stored at -20 and 4 ºC, remaining stable for at least 30 days.