Strain-specific changes in nucleus accumbens transcriptome and motivation for palatable food reward in mice exposed to maternal separation.

Introduction: In humans, adversity in childhood exerts enduring effects on brain and increases the vulnerability to psychiatric diseases. It also leads to a higher risk of eating disorders and obesity. Maternal separation (MS) in mice has been used as a proxy of stress during infancy. We hypothesized that MS in mice affects motivation to obtain palatable food in adulthood and changes gene expression in reward system. Methods: Male and female pups from C57Bl/6J and C3H/HeN mice strains were subjected to a daily MS protocol from postnatal day (PND) 2 to PND14. At adulthood, their motivation for palatable food reward was assessed in operant cages. Results: Compared to control mice, male and female C3H/HeN mice exposed to MS increased their instrumental response for palatable food, especially when the effort required to obtain the reward was high. Importantly, this effect is shown in animals fed ad libitum. Transcriptional analysis revealed 375 genes differentially expressed in the nucleus accumbens of male MS C3H/HeN mice compared to the control group, some of these being associated with the regulation of the reward system (e.g., Gnas, Pnoc). Interestingly, C57Bl/6J mice exposed to MS did not show alterations in their motivation to obtain a palatable reward, nor significant changes in gene expression in the nucleus accumbens. Conclusion: MS produces long-lasting changes in motivation for palatable food in C3H/HeN mice, but has no impact in C57Bl/6J mice. These behavioral alterations are accompanied by drastic changes in gene expression in the nucleus accumbens, a key structure in the regulation of motivational processes.

A Holistic View of the Goto-Kakizaki Rat Immune System: Decreased Circulating Immune Markers in Non- Obese Type 2 Diabetes.

Type-2 diabetes is a complex disorder that is now considered to have an immune component, with functional impairments in many immune cell types. Type-2 diabetes is often accompanied by comorbid obesity, which is associated with low grade inflammation. However,the immune status in Type-2 diabetes independent of obesity remains unclear. Goto-Kakizaki rats are a non-obese Type-2 diabetes model. The limited evidence available suggests that Goto-Kakizaki rats have a pro-inflammatory immune profile in pancreatic islets. Here we present a detailed overview of the adult Goto-Kakizaki rat immune system. Three converging lines of evidence: fewer pro-inflammatory cells, lower levels of circulating pro-inflammatory cytokines, and a clear downregulation of pro-inflammatory signalling in liver, muscle and adipose tissues indicate a limited pro-inflammatory baseline immune profile outside the pancreas. As Type-2 diabetes is frequently associated with obesity and adipocyte-released inflammatory mediators, the pro-inflammatory milieu seems not due to Type-2 diabetes per se; although this overall reduction of immune markers suggests marked immune dysfunction in Goto-Kakizaki rats.

A new experimental design to study inflammation-related versus non-inflammation-related depression in mice.

BACKGROUND: Major depressive disorder (MDD) represents a major public health concern, particularly due to its steadily rising prevalence and the poor responsiveness to standard antidepressants notably in patients afflicted with chronic inflammatory conditions, such as obesity. This highlights the need to improve current therapeutic strategies, including by targeting inflammation based on its role in the pathophysiology and treatment responsiveness of MDD. Nevertheless, dissecting the relative contribution of inflammation in the development and treatment of MDD remains a major issue, further complicated by the lack of preclinical depression models suitable to experimentally dissociate inflammation-related vs. inflammation-unrelated depression. METHODS: While current models usually focus on one particular MDD risk factor, we compared in male C57BL/6J mice the behavioral, inflammatory and neurobiological impact of chronic exposure to high-fat diet (HFD), a procedure known to induce inflammation-related depressive-like behaviors, and unpredictable chronic mild stress (UCMS), a stress-induced depression model notably renowned for its responsivity to antidepressants. RESULTS: While both paradigms induced neurovegetative, depressive-like and anxiety-like behaviors, inflammation and downstream neurobiological pathways contributing to inflammation-driven depression were specifically activated in HFD mice, as revealed by increased circulating levels of inflammatory factors, as well as brain expression of microglial activation markers and enzymes from the kynurenine and tetrahydrobiopterin (BH4) pathways. In addition, serotoninergic and dopaminergic systems were differentially impacted, depending on the experimental condition. CONCLUSIONS: These data validate an experimental design suitable to deeply study the mechanisms underlying inflammation-driven depression comparatively to non-inflammatory depression. This design could help to better understand the pathophysiology of treatment resistant depression.

Maternal separation in rodents: a journey from gut to brain and nutritional perspectives.

The developmental period constitutes a critical window of sensitivity to stress. Indeed, early-life adversity increases the risk to develop psychiatric diseases, but also gastrointestinal disorders such as the irritable bowel syndrome at adulthood. In the past decade, there has been huge interest in the gut-brain axis, especially as regards stress-related emotional behaviours. Animal models of early-life adversity, in particular, maternal separation (MS) in rodents, demonstrate lasting deleterious effects on both the gut and the brain. Here, we review the effects of MS on both systems with a focus on stress-related behaviours. In addition, we discuss more recent findings showing the impact of gut-directed interventions, including nutrition with pre- and probiotics, illustrating the role played by gut microbiota in mediating the long-term effects of MS. Overall, preclinical studies suggest that nutritional approaches with pro- and prebiotics may constitute safe and efficient strategies to attenuate the effects of early-life stress on the gut-brain axis. Further research is required to understand the complex mechanisms underlying gut-brain interaction dysfunctions after early-life stress as well as to determine the beneficial impact of gut-directed strategies in a context of early-life adversity in human subjects.

Pharmacological restoration of gut barrier function in stressed neonates partially reverses long-term alterations associated with maternal separation.

RATIONALE: Intestinal permeability plays an important role in gut-brain axis communication. Recent studies indicate that intestinal permeability increases in neonate pups during maternal separation (MS). OBJECTIVES: The present study aims to determine whether pharmacological inhibition of myosin light chain kinase (MLCK), which regulates tight junction contraction and controls intestinal permeability, in stressed neonates, protects against the long-term effects of MS. METHODS: Male Wistar rats were exposed to MS (3 h per day from post-natal day (PND)2 to PND14) or left undisturbed and received daily intraperitoneal injection of a MLCK inhibitor (ML-7, 5 mg/kg) or vehicle during the same period. At adulthood, emotional behaviors, corticosterone response to stress, and gut microbiota composition were analyzed. RESULTS: ML-7 restored gut barrier function in MS rats specifically during the neonatal period. Remarkably, ML-7 prevented MS-induced sexual reward-seeking impairment and reversed the alteration of corticosterone response to stress at adulthood. The effects of ML-7 were accompanied by the normalization of the abundance of members of Lachnospiraceae, Clostridiales, Desulfovibrio, Bacteroidales, Enterorhabdus, and Bifidobacterium in the feces of MS rats at adulthood. CONCLUSIONS: Altogether, our work suggests that improvement of intestinal barrier defects during development may alleviate some of the long-term effects of early-life stress and provides new insight on brain-gut axis communication in a context of stress.

Multi-hit early life adversity affects gut microbiota, brain and behavior in a sex-dependent manner.

The accumulation of adverse events in utero and during childhood differentially increases the vulnerability to psychiatric diseases in men and women. Gut microbiota is highly sensitive to the early environment and has been recently hypothesized to affect brain development. However, the impact of early-life adversity on gut microbiota, notably with regards to sex differences, remains to be explored. We examined the effects of multifactorial early-life adversity on behavior and microbiota composition in C3H/HeN mice of both sexes exposed to a combination of maternal immune activation (lipopolysaccharide injection on embryonic day 17, 120 µg/kg, i.p.), maternal separation (3hr per day from postnatal day (PND)2 to PND14) and maternal unpredictable chronic mild stress. At adulthood, offspring exposed to multi-hit early adversity showed sex-specific behavioral phenotypes with males exhibiting deficits in social behavior and females showing increased anxiety in the elevated plus maze and increased compulsive behavior in the marble burying test. Early adversity also differentially regulated gene expression in the medial prefrontal cortex (mPFC) according to sex. Interestingly, several genes such as Arc, Btg2, Fosb, Egr4 or Klf2 were oppositely regulated by early adversity in males versus females. Finally, 16S-based microbiota profiling revealed sex-dependent gut dysbiosis. In males, abundance of taxa belonging to Lachnospiraceae and Porphyromonadaceae families or other unclassified Firmicutes, but also Bacteroides, Lactobacillus and Alloprevotella genera was regulated by early adversity. In females, the effects of early adversity were limited and mainly restricted to Lactobacillus and Mucispirillum genera. Our work reveals marked sex differences in a multifactorial model of early-life adversity, both on emotional behaviors and gut microbiota, suggesting that sex should systematically be considered in preclinical studies both in neurogastroenterology and psychiatric research.

Prenatal retinoic acid exposure reveals candidate genes for craniofacial disorders.

Syndromes that display craniofacial anomalies comprise a major class of birth defects. Both genetic and environmental factors, including prenatal retinoic acid (RA) exposure, have been associated with these syndromes. While next generation sequencing has allowed the discovery of new genes implicated in these syndromes, some are still poorly characterized such as Oculo-Auriculo-Vertebral Spectrum (OAVS). Due to the lack of clear diagnosis for patients, developing new strategies to identify novel genes involved in these syndromes is warranted. Thus, our study aimed to explore the link between genetic and environmental factors. Owing to a similar phenotype of OAVS reported after gestational RA exposures in humans and animals, we explored RA targets in a craniofacial developmental context to reveal new candidate genes for these related disorders. Using a proteomics approach, we detected 553 dysregulated proteins in the head region of mouse embryos following their exposure to prenatal RA treatment. This novel proteomic approach implicates changes in proteins that are critical for cell survival/apoptosis and cellular metabolism which could ultimately lead to the observed phenotype. We also identified potential molecular links between three major environmental factors known to contribute to craniofacial defects including maternal diabetes, prenatal hypoxia and RA exposure. Understanding these links could help reveal common key pathogenic mechanisms leading to craniofacial disorders. Using both in vitro and in vivo approaches, this work identified two new RA targets, Gnai3 and Eftud2, proteins known to be involved in craniofacial disorders, highlighting the power of this proteomic approach to uncover new genes whose dysregulation leads to craniofacial defects.

Unlimited sucrose consumption during adolescence generates a depressive-like phenotype in adulthood.

Depression is highly prevalent worldwide, but its etiology is not fully understood. An overlooked possible contributor to the epidemic of depression is feeding styles, particularly at early age when the brain is intensely changing. We have previously reported that unlimited sucrose consumption during adolescence leads to enduring changes in brain reward function. Here, we tested the hypothesis that sucrose consumption during adolescence would lead to a 'depressive-like' phenotype. Adolescent male rats were given unlimited access to 5% sucrose in their home cages from postnatal day 30 to postnatal day 46 and their emotional behavior was subsequently examined at adulthood. Sucrose consumption during adolescence caused anhedonia, decreased motivation for saccharin, increased immobility in the forced swim test and exacerbated anxiety-like behavior. Additionally, sucrose consumption during adolescence decreased cell proliferation in the hippocampus in adulthood. Chronic treatment with imipramine (10 mg/kg) normalized behavior and restored cell proliferation in the hippocampus of adult rats with a history of sucrose consumption during adolescence. A similar sucrose consumption starting at adulthood only increases immobility in the forced swim test, suggesting that sucrose intake affects also adults' behavior but to a lesser degree. Overall, our findings reveal an unsuspected protracted effect of sucrose consumption on behavior and suggest that unlimited sucrose consumption during critical periods of brain development may play an important role in the etiology of reward-related disorders such as depression.

Maternal high-fat diet and early life stress differentially modulate spine density and dendritic morphology in the medial prefrontal cortex of juvenile and adult rats.

The medial prefrontal cortex (mPFC) is a key area for the regulation of numerous brain functions including stress response and cognitive processes. This brain area is also particularly affected by adversity during early life. Using an animal model in rats, we recently demonstrated that maternal exposure to a high-fat diet (HFD) prevents maternal separation (MS)-induced gene expression alterations in the developing PFC and attenuates several long-term deleterious behavioral effects of MS. In the present study, we ask whether maternal HFD could protect mPFC neurons of pups exposed to early life stress by examining dendritic morphology and spine density in juvenile [postnatal day (PND) 21] and adult rats submitted to MS. Dams were fed either a control or an HFD throughout gestation and lactation, and pups were submitted to MS from PND2 to PND14. We report that maternal HFD prevents MS-induced spine loss at PND21 and dendritic atrophy at adulthood. Furthermore, we show in adult MS rats that PFC-dependent memory extinction deficits are prevented by maternal HFD. Finally, perinatal HFD exposure reverses gut leakiness following stress in pups and seems to exert an anti-stress effect in dams. Overall, our work demonstrates that maternal HFD affects the developing brain and suggests that nutrition, possibly through gut-brain interactions, could modulate mPFC sensitivity to early stress.

Maternal high-fat diet leads to hippocampal and amygdala dendritic remodeling in adult male offspring.

Early-life exposure to calorie-dense food, rich in fat and sugar, contributes to the increasing prevalence of obesity and its associated adverse cognitive and emotional outcomes at adulthood. It is thus critical to determine the impact of such nutritional environment on neurobehavioral development. In animals, maternal high-fat diet (HFD) consumption impairs hippocampal function in adult offspring, but its impact on hippocampal neuronal morphology is unknown. Moreover, the consequences of perinatal HFD exposure on the amygdala, another important structure for emotional and cognitive processes, remain to be established. In rats, we show that adult offspring from dams fed with HFD (45% from fat, throughout gestation and lactation) exhibit atrophy of pyramidal neuron dendrites in both the CA1 of the hippocampus and the basolateral amygdala (BLA). Perinatal HFD exposure also impairs conditioned odor aversion, a task highly dependent on BLA function, without affecting olfactory or malaise processing. Neuronal morphology and behavioral alterations elicited by perinatal HFD are not associated with body weight changes but with higher plasma leptin levels at postnatal day 15 and at adulthood. Taken together, our results suggest that perinatal HFD exposure alters hippocampal and amygdala neuronal morphology which could participate to memory alterations at adulthood.

[Early life stressful experiences and neuropsychiatric vulnerability: evidences from human and animal models]. / Environnement précoce et vulnérabilité neuropsychiatrique.

The human newborn is highly dependent on parental care for its survival but also for the healthy development of its brain. A large body of literature demonstrates the impact of early life adversity, even during the prenatal period, on the adult's health. The susceptibility to neuropsychiatric diseases is often potentiated by early stress. If there is an agreement that a critical developmental period exists, the mechanisms underlying the long term effects of early life adversity are still poorly understood. Recent studies in animals highlight the involvement of epigenetic processes in the transmission of such vulnerabilities, notably via modifications in germ cells, which can be transmitted in the next generations.

Juvenile obesity enhances emotional memory and amygdala plasticity through glucocorticoids.

In addition to metabolic and cardiovascular disorders, obesity is associated with adverse cognitive and emotional outcomes. Its growing prevalence during adolescence is particularly alarming since recent evidence indicates that obesity can affect hippocampal function during this developmental period. Adolescence is a decisive period for maturation of the amygdala and the hypothalamic-pituitary-adrenal (HPA) stress axis, both required for lifelong cognitive and emotional processing. However, little data are available on the impact of obesity during adolescence on amygdala function. Herein, we therefore evaluate in rats whether juvenile high-fat diet (HFD)-induced obesity alters amygdala-dependent emotional memory and whether it depends on HPA axis deregulation. Exposure to HFD from weaning to adulthood, i.e., covering adolescence, enhances long-term emotional memories as assessed by odor-malaise and tone-shock associations. Juvenile HFD also enhances emotion-induced neuronal activation of the basolateral complex of the amygdala (BLA), which correlates with protracted plasma corticosterone release. HFD exposure restricted to adulthood does not modify all these parameters, indicating adolescence is a vulnerable period to the effects of HFD-induced obesity. Finally, exaggerated emotional memory and BLA synaptic plasticity after juvenile HFD are alleviated by a glucocorticoid receptor antagonist. Altogether, our results demonstrate that juvenile HFD alters HPA axis reactivity leading to an enhancement of amygdala-dependent synaptic and memory processes. Adolescence represents a period of increased susceptibility to the effects of diet-induced obesity on amygdala function.

Adverse childhood experiences and physiological wear-and-tear in midlife: Findings from the 1958 British birth cohort.

Allostatic load (AL) is a measure of overall physiological wear-and-tear over the life course, which could partially be the consequence of early life exposures. AL could allow a better understanding of the potential biological pathways playing a role in the construction of the social gradient in adult health. To explore the biological embedding hypothesis, we examined whether adverse childhood experiences (ACEs) are associated with elevated AL in midlife. We used imputed data on 3,782 women and 3,753 men of the National Child Development Study in Britain followed up seven times. ACEs were measured using prospective data collected at ages 7, 11, and 16. AL was operationalized using data from the biomedical survey collected at age 44 on 14 parameters representing four biological systems. We examined the role of adult health behaviors, body mass index (BMI), and socioeconomic status as potential mediators using a path analysis. ACEs were associated with higher AL for both men and women after adjustment for early life factors and childhood pathologies. The path analysis showed that the association between ACEs and AL was largely explained by early adult factors at age 23 and 33. For men, the total mediated effect was 59% (for two or more ACEs) via health behaviors, education level, and wealth. For women, the mediated effect represented 76% (for two or more ACEs) via smoking, BMI, education level, and wealth. Our results indicate that early psychosocial stress has an indirect lasting impact on physiological wear-and-tear via health behaviors, BMI, and socioeconomic factors in adulthood.

Perinatal high-fat diet increases hippocampal vulnerability to the adverse effects of subsequent high-fat feeding.

Epidemiological observations report an increase in fat consumption associated with low intake of n-3 relative to n-6 polyunsaturated fatty acids (PUFAs) in women of childbearing age. However, the impact of these maternal feeding habits on cognitive function in the offspring is unknown. This study aims to investigate the impact of early exposure to a high-fat diet (HFD) with an unbalanced n-6/n-3 PUFAs ratio on hippocampal function in adult rats. Furthermore, we explored the effects of perinatal HFD combined with exposure to HFD after weaning. Dams were fed a control diet (C, 12% of energy from lipids, n-6/n-3 PUFAs ratio: 5) or HFD (HF, 39% of energy from lipids, n-6/n-3 PUFAs ratio: 39) throughout gestation and lactation. At weaning, offspring were placed either on control (C-C, HF-C) or high-fat (HF-HF) diets. In adulthood, hippocampus-dependent memory was assessed using the water-maze task and potential hippocampal alterations were determined by studying PUFA levels, gene expression, neurogenesis and astrocyte morphology. Perinatal HFD induced long-lasting metabolic alterations and some changes in gene expression in the hippocampus, but had no effect on memory. In contrast, spatial memory was impaired in animals exposed to HFD during the perinatal period and maintained on this diet. HF-HF rats also exhibited low n-3 and high n-6 PUFA levels, decreased neurogenesis and downregulated expression of several plasticity-related genes in the hippocampus. To determine the contribution of the perinatal diet to the memory deficits reported in HF-HF animals, an additional experiment was conducted in which rats were only exposed to HFD starting at weaning (C-HF). Interestingly, memory performance in this group was similar to controls. Overall, our results suggest that perinatal exposure to HFD with an unbalanced n-6/n-3 ratio sensitizes the offspring to the adverse effects of subsequent high-fat intake on hippocampal function.

Anxiety-like behaviour and associated neurochemical and endocrinological alterations in male pups exposed to prenatal stress.

Epidemiological studies suggest that emotional liability in infancy could be a predictor of anxiety-related disorders in the adulthood. Rats exposed to prenatal restraint stress ("PRS rats") represent a valuable model for the study of the interplay between environmental triggers and neurodevelopment in the pathogenesis of anxious/depressive like behaviours. Repeated episodes of restraint stress were delivered to female Sprague-Dawley rats during pregnancy and male offspring were studied. Ultrasonic vocalization (USV) was assessed in pups under different behavioural paradigms. After weaning, anxiety was measured by conventional tests. Expression of GABA(A) receptor subunits and metabotropic glutamate (mGlu) receptors was assessed by immunoblotting. Plasma leptin levels were measured using a LINCOplex bead assay kit. The offspring of stressed dams emitted more USVs in response to isolation from their mothers and showed a later suppression of USV production when exposed to an unfamiliar male odour, indicating a pronounced anxiety-like profile. Anxiety like behaviour in PRS pups persisted one day after weaning. PRS pups did not show the plasma peak in leptin levels that is otherwise seen at PND14. In addition, PRS pups showed a reduced expression of the γ2 subunit of GABA(A) receptors in the amygdala at PND14 and PND22, an increased expression of mGlu5 receptors in the amygdala at PND22, a reduced expression of mGlu5 receptors in the hippocampus at PND14 and PND22, and a reduced expression of mGlu2/3 receptors in the hippocampus at PND22. These data offer a clear-cut demonstration that the early programming triggered by PRS could be already translated into anxiety-like behaviour during early postnatal life.

ROCK inhibition prevents tau hyperphosphorylation and p25/CDK5 increase after global cerebral ischemia.

Rho-kinase (ROCK) is a downstream effector of RhoA, which has been associated with growth cone collapse and retraction in neurons. ROCK inhibition has been shown to protect against ischemic damage, thereby improving short-term collateral flow, inhibiting platelet aggregation, leukocyte adhesion, and preventing neuronal death. However, little is known about the long-term effects of ROCK inhibition on behavior and neuroprotection. The consequence of ROCK inhibition on ischemic rats' learning and spatial memory after 30 days of intracerebroventricular treatment was evaluated. It was found that Y27632 (ROCK inhibitor) reduced neurodegenerative markers, such as Fluoro-Jade, PHF (paired helicoidal filaments) immunoreactivity, and p25 protein levels, in the hippocampus of ischemic animals and improved learning and spatial memory tasks. However, Y27632 alone impaired sham animals' long-term memory. These findings demonstrated the beneficial impact of ROCK inhibition on tauopathy and altered p25 protein levels following global cerebral ischemia.

Effect of prenatal stress on alcohol preference and sensitivity to chronic alcohol exposure in male rats.

RATIONALE: In rats, prenatal restraint stress (PRS) induces persistent behavioral and neurobiological alterations leading to a greater consumption of psychostimulants during adulthood. However, little is known about alcohol vulnerability in this animal model. OBJECTIVES: We examined in adolescent and adult male Sprague Dawley rats the long-lasting impact of PRS exposure on alcohol consumption. METHODS: PRS rats were subjected to a prenatal stress (three daily 45-min sessions of restraint stress to the mothers during the last 10 days of pregnancy). Alcohol preference was assessed in a two-bottle choice paradigm (alcohol 2.5%, 5%, or 10% versus water), in both naïve adolescent rats and adult rats previously exposed to a chronic alcohol treatment. Behavioral indices associated with incentive motivation for alcohol were investigated. Finally, plasma levels of transaminases (marker of hepatic damages) and ΔFosB levels in the nucleus accumbens (a potential molecular switch for addiction) were evaluated following the chronic alcohol exposure. RESULTS: Alcohol preference was not affected by PRS. Contrary to our expectations, stressed and unstressed rats did not display signs of compulsive alcohol consumption. The consequences of the alcohol exposure on locomotor reactivity and on transaminase levels were more prominent in PRS group. Similarly, PRS potentiated alcohol-induced ΔFosB levels in the nucleus accumbens. CONCLUSION: Our data suggest that negative events occurring in utero do not modulate alcohol preference in male rats but potentiate chronic alcohol-induced molecular neuroadaptation in the brain reward circuitry. Further studies are needed to determine whether the exacerbated ΔFosB upregulation in PRS rats could be extended to other reinforcing stimuli.

Reduced alcohol drinking in adult rats exposed to sucrose during adolescence.

Intake of sweet-alcoholic drinks during adolescence is believed to favor alcohol abuse and dependence in adulthood. This study examined the influence of early exposure to ethanol with or without sucrose on the consumption of sweet or alcoholic solutions in adulthood. Adolescent rats (from post-natal day 30-46) were given continuous free access to tap water and either 5% sucrose, 5% ethanol or mixed 5% sucrose-5% ethanol. The control group was given access to water only. Upon reaching adulthood (post-natal day 60), rats were tested for saccharin (sweet), quinine (bitter) and ethanol consumption using a two-bottle free-choice paradigm. The results indicated that pre-exposure to ethanol did not alter the intake of sweet or ethanol solutions in adulthood. However, rats exposed to sucrose during adolescence showed a decreased consumption of both sweet and ethanol solutions. Because alcohol has a sweet taste component, an additional group of rats, pre-exposed to either 5% sucrose or water during adolescence, was tested for intravenous ethanol self-administration (preventing oral sensory stimulation) and in a new model of simultaneous access to oral saccharin and intravenous ethanol that results in higher total ethanol intake. Relative to controls, sucrose-exposed rats showed reduced operant self-administration of saccharin, yet no differences were found for intravenous ethanol self-administration. Altogether, these findings indicate that sucrose exposure during adolescence persistently affected the perception of sweet taste reward and thereby alcohol's acceptance in adulthood.

Sugar overconsumption during adolescence selectively alters motivation and reward function in adult rats.

BACKGROUND: There has been a dramatic escalation in sugar intake in the last few decades, most strikingly observed in the adolescent population. Sugar overconsumption has been associated with several adverse health consequences, including obesity and diabetes. Very little is known, however, about the impact of sugar overconsumption on mental health in general, and on reward-related behavioral disorders in particular. This study examined in rats the effects of unlimited access to sucrose during adolescence on the motivation for natural and pharmacological rewards in adulthood. METHODOLOGY/PRINCIPAL FINDINGS: Adolescent rats had free access to 5% sucrose or water from postnatal day 30 to 46. The control group had access to water only. In adulthood, rats were tested for self-administration of saccharin (sweet), maltodextrin (non-sweet), and cocaine (a potent drug of abuse) using fixed- and progressive-ratio schedules, and a concentration-response curve for each substance. Adult rats, exposed or not exposed to sucrose, were tested for saccharin self-administration later in life to verify the specificity of adolescence for the sugar effects. Sugar overconsumption during adolescence, but not during adulthood, reduced the subsequent motivation for saccharin and maltodextrin, but not cocaine. This selective decrease in motivation is more likely due to changes in brain reward processing than changes in gustatory perception. CONCLUSIONS/SIGNIFICANCE: Sugar overconsumption induces a developmental stage-specific chronic depression in reward processing that may contribute to an increase in the vulnerability to reward-related psychiatric disorders.

Impaired interleukin-1beta and c-Fos expression in the hippocampus is associated with a spatial memory deficit in P2X(7) receptor-deficient mice.

Recent evidence suggests that interleukin-1beta (IL-1beta), which was originally identified as a proinflammatory cytokine, is also required in the brain for memory processes. We have previously shown that IL-1beta synthesis in the hippocampus is dependent on P2X(7) receptor (P2X(7)R), which is an ionotropic receptor of ATP. To substantiate the role of P2X(7)R in both brain IL-1beta expression and memory processes, we examined the induction of IL-1beta mRNA expression in the hippocampus of wild-type (WT) and homozygous P2X(7) receptor knockout mice (P2X(7)R(-/-)) following a spatial memory task. The spatial recognition task induced both IL-1beta mRNA expression and c-Fos protein activation in the hippocampus of WT but not of P2X(7)R(-/-) mice. Remarkably, P2X(7)R(-/-) mice displayed spatial memory impairment in a hippocampal-dependant task, while their performances in an object recognition task were unaltered. Taken together, our results show that P2X(7)R plays a critical role in spatial memory processes and the associated hippocampal IL-1beta mRNA synthesis and c-Fos activation.