Engagement of the brain orexin system in activity-based anorexia behaviour in mice.

While excessive physical activity is common amongst anorexia nervosa (AN) patients, contributing to their low body weight, little is known about the underlying biology and effective treatments targeting the hyperactivity are lacking. Given the role of orexin in arousal, physical activity and energy expenditure, we sought to investigate i) the extent to which orexin neurons are activated during severe anorectic state in the activity-based anorexia (ABA) mouse model, and ii) if the dual orexin receptor antagonist suvorexant can reduce physical activity during ABA. The Fos-TRAP2 technique enable us to visually capture active neurons (Fos expressing) during severe anorectic state in the ABA mouse model, and by immunohistochemistry, determine the extent to which these active neurons are orexin positive. In addition, suvorexant was administered peripherally to ABA mice and running activity was monitored. We found that a large population of orexin neurons in the hypothalamus are activated by ABA and that peripheral administration of suvorexant decreases food anticipatory activity in these mice. We conclude that orexin may be a suitable target to treat hyperactivity in AN and recommend further studies to examine the efficacy of suvorexant in aiding AN patients to control their drive for hyperactivity.

TRAPing Ghrelin-Activated Circuits: A Novel Tool to Identify, Target and Control Hormone-Responsive Populations in TRAP2 Mice.

The availability of Cre-based mouse lines for visualizing and targeting populations of hormone-sensitive cells has helped identify the neural circuitry driving hormone effects. However, these mice have limitations and may not even be available. For instance, the development of the first ghrelin receptor (Ghsr)-IRES-Cre model paved the way for using the Cre-lox system to identify and selectively manipulate ghrelin-responsive populations. The insertion of the IRES-Cre cassette, however, interfered with Ghsr expression, resulting in defective GHSR signaling and a pronounced phenotype in the homozygotes. As an alternative strategy to target ghrelin-responsive cells, we hereby utilize TRAP2 (targeted recombination in active populations) mice in which it is possible to gain genetic access to ghrelin-activated populations. In TRAP2 mice crossed with a reporter strain, we visualized ghrelin-activated cells and found, as expected, much activation in the arcuate nucleus (Arc). We then stimulated this population using a chemogenetic approach and found that this was sufficient to induce an orexigenic response of similar magnitude to that induced by peripheral ghrelin injection. The stimulation of this population also impacted food choice. Thus, the TRAPing of hormone-activated neurons (here exemplified by ghrelin-activated pathways) provides a complimentary/alternative technique to visualize, access and control discrete pathways, linking hormone action to circuit function.

The Orexigenic Force of Olfactory Palatable Food Cues in Rats.

Environmental cues recalling palatable foods motivate eating beyond metabolic need, yet the timing of this response and whether it can develop towards a less palatable but readily available food remain elusive. Increasing evidence indicates that external stimuli in the olfactory modality communicate with the major hub in the feeding neurocircuitry, namely the hypothalamic arcuate nucleus (Arc), but the neural substrates involved have been only partially uncovered. By means of a home-cage hidden palatable food paradigm, aiming to mimic ubiquitous exposure to olfactory food cues in Western societies, we investigated whether the latter could drive the overeating of plain chow in non-food-deprived male rats and explored the neural mechanisms involved, including the possible engagement of the orexigenic ghrelin system. The olfactory detection of a familiar, palatable food impacted upon meal patterns, by increasing meal frequency, to cause the persistent overconsumption of chow. In line with the orexigenic response observed, sensing the palatable food in the environment stimulated food-seeking and risk-taking behavior, which are intrinsic components of food acquisition, and caused active ghrelin release. Our results suggest that olfactory food cues recruited intermingled populations of cells embedded within the feeding circuitry within the Arc, including, notably, those containing the ghrelin receptor. These data demonstrate the leverage of ubiquitous food cues, not only for palatable food searching, but also to powerfully drive food consumption in ways that resonate with heightened hunger, for which the orexigenic ghrelin system is implicated.

A skeleton in the cupboard in ghrelin research: Where are the skinny dwarfs?

Based on studies delivering ghrelin or ghrelin receptor agonists, we have learned a great deal about the importance of the brain ghrelin signalling system for a wide range of physiological processes that include feeding behaviours, growth hormone secretion and glucose homeostasis. Because these processes can be considered as essential to life, the question arises as to why mouse models of depleted ghrelin signalling are not all skinny dwarfs with a host of behavioural and metabolic problems. Here, we provide a systematic detailed review of the phenotype of mice with deficient ghrelin signalling to help better understand the relevance and importance of the brain ghrelin signalling system, with a particular emphasis on those questions that remain unanswered.

The gravitostat protects diet-induced obese rats against fat accumulation and weight gain.

The gravitostat is a novel homeostatic body weight-regulating mechanism, mostly studied in mice, and recently confirmed in obese humans. In the present study, we explored the effect of weight loading on metabolic outcomes, meal patterns and parameters linked to energy expenditure in both obese and lean rats. Diet-induced obese (DIO) and lean rats were implanted with capsules weighing either 15% of biological body weight (load) or empty capsules (1.3% of body weight; controls). Loading protected against fat accumulation more markedly in the DIO group. In line with this, the obesity-related impairment in insulin sensitivity was notably ameliorated in DIO rats upon loading, as revealed by the reduction in serum insulin levels and homeostatic model assessment for insulin resistance index scores. Although 24-hour caloric intake was reduced in both groups, this effect was greater in loaded DIO rats than in loaded lean peers. During days 10-16, after recovery from surgery, loading: (i) decreased meal size in both groups (only during the light phase in DIO rats) but this was compensated in lean rats by an increase in meal frequency; (ii) reduced dark phase locomotor activity only in lean rats; and (iii) reduced mean caloric efficiency in DIO rats. Muscle weight was unaffected by loading in either group. Dietary-obese rats are therefore more responsive than lean rats to loading.

Genetic deletion of the ghrelin receptor (GHSR) impairs growth and blunts endocrine response to fasting in Ghsr-IRES-Cre mice.

OBJECTIVE: The orexigenic hormone ghrelin exerts its physiological effects by binding to and activating the growth hormone secretagogue receptor (GHSR). The recent development of a Ghsr-IRES-Cre knock-in mouse line has enabled to genetically access GHSR-expressing neurons. Inserting a Cre construct using a knock-in strategy, even when following an upstream internal ribosome entry site (IRES) can, however, interfere with expression of a targeted gene, with consequences for the phenotype emerging. This study aimed to phenotype, both physically and metabolically, heterozygous and homozygous Ghsr-IRES-Cre mice, with a view to discovering the extent to which the ghrelin signalling system remains functional in these mice. METHODS: We assessed feeding and arcuate nucleus (Arc) Fos activation in wild-type, heterozygous and homozygous Ghsr-IRES-Cre mice in response to peripherally-administered ghrelin. We also characterised their developmental and growth phenotypes, as well as their metabolic responses upon an overnight fast. RESULTS: Insertion of the IRES-Cre cassette into the 3'-untranslated region of the Ghsr gene led to a gene-dosage GHSR depletion in the Arc. Whereas heterozygotes remained ghrelin-responsive and more closely resembled wild-types, ghrelin had reduced orexigenic efficacy and failed to induce Arc Fos expression in homozygous littermates. Homozygotes had a lower body weight accompanied by a shorter body length, less fat tissue content, altered bone parameters, and lower insulin-like growth factor-1 levels compared to wild-type and heterozygous littermates. Moreover, both heterozygous and homozygous Ghsr-IRES-Cre mice lacked the usual fasting-induced rise in growth hormone (GH) and displayed an exaggerated drop in blood glucose and insulin compared to wild-types. Unexpectedly, fasting acyl-ghrelin levels were allele-dependently increased. CONCLUSIONS: Our data suggest that (i) heterozygous but not homozygous Ghsr-IRES-Cre mice retain the usual responsiveness to administered ghrelin, (ii) the impact of fasting on GH release and glucose homeostasis is altered even when only one copy of the Ghsr gene is non-functional (as in heterozygous Ghsr-IRES-Cre mice) and (iii) homozygous Ghsr-IRES-Cre mice exhibit growth retardation. Of the many transgenic models of suppressed ghrelin signalling, Ghsr-IRES-Cre mice emerge as best representing the full breadth of the expected phenotype with respect to body weight, growth, and metabolic parameters.

Functional and Neurochemical Identification of Ghrelin Receptor (GHSR)-Expressing Cells of the Lateral Parabrachial Nucleus in Mice.

The lateral parabrachial nucleus (lPBN), located in the pons, is a well-recognized anorexigenic center harboring, amongst others, the calcitonin gene-related peptide (CGRP)-expressing neurons that play a key role. The receptor for the orexigenic hormone ghrelin (the growth hormone secretagogue receptor, GHSR) is also abundantly expressed in the lPBN and ghrelin delivery to this site has recently been shown to increase food intake and alter food choice. Here we sought to explore whether GHSR-expressing cells in the lPBN (GHSR lPBN cells) contribute to feeding control, food choice and body weight gain in mice offered an obesogenic diet, involving studies in which GHSR lPBN cells were silenced. We also explored the neurochemical identity of GHSR lPBN cells. To silence GHSR lPBN cells, Ghsr-IRES-Cre male mice were bilaterally injected intra-lPBN with a Cre-dependent viral vector expressing tetanus toxin-light chain. Unlike control wild-type littermates that significantly increased in body weight on the obesogenic diet (i.e., high-fat high-sugar free choice diet comprising chow, lard and 9% sucrose solution), the heterozygous mice with silenced GHSR lPBN cells were resistant to diet-induced weight gain with significantly lower food intake and fat weight. The lean phenotype appeared to result from a decreased food intake compared to controls and caloric efficiency was unaltered. Additionally, silencing the GHSR lPBN cells altered food choice, significantly reducing palatable food consumption. RNAscope and immunohistochemical studies of the lPBN revealed considerable co-expression of GHSR with glutamate and pituitary adenylate cyclase-activating peptide (PACAP), and much less with neurotensin, substance P and CGRP. Thus, the GHSR lPBN cells are important for diet-induced weight gain and adiposity, as well as in the regulation of food intake and food choice. Most GHSR lPBN cells were found to be glutamatergic and the majority (76%) do not belong to the well-characterized anorexigenic CGRP cell population.

Improvement of APOE4-dependent non-cognitive behavioural traits by postnatal cholinergic stimulation in female mice.

The apolipoprotein E (APOE) ε4 allele hastens cognitive decline, but other non-cognitive behaviours, as well as underpinning interactions with the cholinergic system, have not been systematically addressed. Both C57BL/6 and humanised apoE4 female mice were transiently exposed to subclinical doses (0 or 1 mg/kg body weight) of the cholinesterase inhibitor chlorpyrifos (CPF), a widely-used pesticide, from postnatal days 10-15. At 5 months of age, we assessed the impact of APOE4 genotype, postnatal CPF exposure and APOE4 x CPF interactions on anxiety (open field and light-dark tests), stereotypes (digging test) and neophobia (sucrose preference test), as well as on high-fat diet (HFD)-seeking and consumption (scheduled-feeding paradigm). We found that control APOE4 female carriers displayed a robust anxiety-like phenotype, which was accompanied by exaggerated stereotypes and a subtle neophobic response to rewarding foods. In parallel, we observed an amplified "wanting" response for HFD in these mice, which did not entail enhanced "liking". Notably, postnatal CPF ameliorated the anxiety-like and the heightened HFD-seeking responses in adult apoE4 female mice, while caused them to gain weight steadily compared to control peers. In turn, an early-life transient exposure to CPF fostered the over-consumption of HFD during adulthood without affecting how much this reward was "wanted" or the total caloric intake. These data reveal a role for CPF towards fostering "unhealthy" dietary choices. We conclude that the APOE4 genotype modulates non-cognitive behaviours and we provide support for an APOE4-dependent cholinergic dysfunction.

Sex and Exposure to Postnatal Chlorpyrifos Influence the Epigenetics of Feeding-Related Genes in a Transgenic APOE Mouse Model: Long-Term Implications on Body Weight after a High-Fat Diet.

Developmental exposure to toxicants and diet can interact with an individual's genetics and produce long-lasting metabolic adaptations. The different isoforms of the apolipoprotein E (APOE) are an important source of variability in metabolic disorders and influence the response to the pesticide chlorpyrifos (CPF). We aimed to study the epigenetic regulation on feeding control genes and the influence of postnatal CPF exposure, APOE genotype, and sex, and how these modifications impact on the metabolic response to a high-fat diet (HFD). Both male and female apoE3- and apoE4-TR mice were exposed to CPF on postnatal days 10-15. The DNA methylation pattern of proopiomelanocortin, neuropeptide Y, leptin receptor, and insulin-like growth factor 2 was studied in the hypothalamus. At adulthood, the mice were given a HFD for eight weeks. The results highlight the importance of sex in the epigenetic regulation and the implication of CPF treatment and APOE genotype. The body weight progression exhibited sex-dimorphic differences, apoE4-TR males being the most susceptible to the effects induced by CPF and HFD. Overall, these results underscore the pivotal role of sex, APOE genotype, and developmental exposure to CPF on subsequent metabolic disturbances later in life and show that sex is a key variable in epigenetic regulation.

Exposure to chlorpyrifos at different ages triggers APOE genotype-specific responses in social behavior, body weight and hypothalamic gene expression.

To date, we have shown that apolipoprotein E (APOE) polymorphisms differentially modulate the neurobehavioral and metabolic effects of chlorpyrifos (CPF), a widely used pesticide, which is detected as residue in food. We previously reported that, after being exposed to CPF, APOE3 subjects exhibit metabolic dysfunctions while APOE4 subjects undergo changes in behavior. In the current study, we investigated the effects of a double exposure to CPF on social behavior and hypothalamic gene expression in apoE-targeted replacement (TR) mice. Male apoE3-and apoE4-TR mice were exposed to CPF at 0 or 1 mg/kg/day on postnatal days 10-15 and then, during adulthood (5 months of age), fed a CPF-supplemented diet (0 or 2 mg/kg/day) for 15 days. During adult exposure to CPF, body weight gain and food intake were monitored. At the end of the adult exposure period, we evaluated social behavior in a three-chamber test, as well as mRNA levels of hypothalamic neuropeptides and receptors related to social behavior and feeding control. Adult CPF exposure increased food intake in general, but only apoE4 mice increased their body weight. Postnatal CPF exposure improved preference for the social contexts in apoE4 mice while adult CPF exposure did the same in apoE3 mice. Anorexigenic-peptide and social-related behavior gene expression decreased as a result of adult CPF exposure in apoE4 mice, and neuropeptide Y was more expressed in apoE4 mice. These results indicate that CPF exposure produces orexigenic and metabolic effects and enlarges individual differences in social behavior, especially in apoE3 mice.

APOE genetic background and sex confer different vulnerabilities to postnatal chlorpyrifos exposure and modulate the response to cholinergic drugs.

Chlorpyrifos (CPF) is an extensively used organophosphate pesticide. Exposure to CPF has been related to neurobehavioral disorders, particularly during neurodevelopment. Apolipoprotein E (apoE) is a lipid and cholesterol carrier and a susceptibility factor for cognitive impairment which can influence the response to toxic exposures. The study was aimed at assessing the effects of postnatal exposure to CPF on object recognition memory and its modulation by sex and APOE genotype. Human apoE3 and apoE4 targeted replacement mice and C57BL/6 mice were postnatally exposed to 0 or 1 mg/kg/day of CPF. Recognition memory was evaluated in an Object Recognition Test (ORT). In order to study the contribution of cholinergic and GABAergic neurotransmitter systems to recognition memory, a pharmacological challenge was included. Sex, genotype and postnatal exposure to CPF were key factors throughout the testing period. Specifically, CPF increased exploratory behavior and impaired discrimination performance. We observed that administering scopolamine, a cholinergic antagonist, was detrimental to recognition memory. However, discrimination in C57BL/6 and apoE4 males improved with the administration of the cholinergic agonist rivastigmine, but the same drug worsened retention in apoE4 females. Finally, the GABAergic agonist alprazolam altered performance in a sex- and genotype-dependent manner. Overall, these results suggest complex interactions between sex, APOE genotype and postnatal CPF exposure and indicate a different functioning of both the cholinergic and GABAergic neurotransmitter system between groups.

Learning, memory and the expression of cholinergic components in mice are modulated by the pesticide chlorpyrifos depending upon age at exposure and apolipoprotein E (APOE) genotype.

Polymorphisms of the apolipoprotein E (APOE) gene differentially affect neurobiological functions and cognitive performance and confer different vulnerabilities to subclinical exposures to chlorpyrifos (CPF), a pesticide used worldwide. The data reported on this topic suggest a complex interaction between cholinergic signaling and the APOE genotype. To gain greater functional insight into this interaction, we evaluated spatial learning and memory and hippocampal cholinergic expression in young apoE3 and apoE4 transgenic mice exposed to CPF. Male and female mice were exposed to CPF at 0 or 1 mg/kg on postnatal days 10-15 and then, exposed to CPF at 0 or 2 mg/kg for 60 days at 5 months of age. At 6 months of age, mice were tested for spatial skills in a Barnes maze. At the end of the task, animals were killed and gene expression of cholinergic components was assessed in the hippocampus. Our results show that apoE4 female mice performed worse in the spatial task, while postnatal CPF impaired escape strategies and spatial memory in apoE3 mice. In turn, CPF in adulthood improved spatial abilities in apoE4 female mice. Regarding gene expression, choline acetyltransferase (ChAT) and vesicular acetylcholine transporter (VAChT) expression were increased in apoE4 mice. Postnatal exposure to CPF increased ChAT mRNA levels in apoE4 mice, whereas adult exposure to CPF induced changes in acetylcholinesterase-S, α7- and α4-subunit nicotinic receptor expression in apoE4 females. The current findings provide new insights into APOE-dependent cholinergic signaling, which directly affects the response to CPF cholinergic insult, especially in APOE4 subjects.

Impact of Free-Choice Diets High in Fat and Different Sugars on Metabolic Outcome and Anxiety-Like Behavior in Rats.

OBJECTIVE: Rats were exposed to free-choice diets (fat plus one of two different sugar solutions, glucose or sucrose), and the metabolic consequences and impact on locomotor activity and anxiety-like behavior were explored. METHODS: For 3 weeks, 7-week-old male rats were offered either chow only or free-choice high-fat diets differing in their added sugar: no sugar, sucrose, or glucose. In a second experiment, after 2 weeks on the diets, rats were switched from high sucrose to high glucose for two additional weeks. Metabolic end points included body weight, food intake, food choice, glycemic control, metabolic hormones, fat pad weight, brown adipose tissue weight, and gene expression. Behavioral analysis included locomotor and anxiety-like activity in the open field and elevated plus maze. RESULTS: Both sugar diets enhanced adiposity and induced hyperphagia, favoring unhealthier dietary selection above that of the control diets (chow or free-choice high-fat with no sugar). Despite isocaloric intake in the sugar-containing diets, offering glucose instead of sucrose was associated with improved insulin sensitivity. The sugar-containing diets reduced activity (but with movements of increased velocity) and induced an anxiety-like phenotype. CONCLUSIONS: Although free-choice diets negatively impacted on metabolism and anxiety-like behavior, replacing sucrose with glucose improved insulin sensitivity and may therefore be better for health.

Postnatal chlorpyrifos exposure and apolipoprotein E (APOE) genotype differentially affect cholinergic expression and developmental parameters in transgenic mice.

Chlorpyrifos (CPF) is one of the most commonly used organophosphate pesticides in the world. Our previous results described that apolipoprotein E (APOE) polymorphisms are a source of individual differences in susceptibility to CPF. The aim of this study was to assess the physical and biochemical effects of postnatal exposure to CPF in the apoE targeted replacement mouse model. Mice were exposed to CPF at 0 or 1 mg/kg/day from postnatal day 10-15. Physical development, plasma and forebrain cholinesterase (ChE) activity and gene expression in liver and forebrain were evaluated. CPF exposure delays physical maturation and decreases the expression of choline acetyltransferase, α4-subunit and the α7 receptor. CPF decreases the expression of vesicular acetylcholine transporter (VAChT) mRNA in the forebrain only in apoE3 mice. The expression of paraoxonase-2 in the forebrain was also influenced by APOE genotype and CPF. Differences between genotypes were observed in litter size, ChE activity, expression of butyrylcholinesterase and paraoxonase-1 in liver and variants of acetylcholinesterase, VAChT and the α7 receptor in the forebrain. These results support that there are different vulnerabilities to postnatal CPF exposure according to the APOE polymorphism, which in turn affects the cholinergic system and defenses to oxidative stress.

New mechanistic insights on the metabolic-disruptor role of chlorpyrifos in apoE mice: a focus on insulin- and leptin-signalling pathways.

Recently, we have provided evidence, suggesting that mice expressing the human apolipoprotein E3 (apoE3) are more prone to develop an obesity-like phenotype and a diabetic profile when subchronically fed a chlorpyrifos (CPF)-supplemented diet. The aim of the current study was to examine the underlying mechanisms through which CPF alters both insulin- and leptin-signalling pathways in an APOE-dependent manner. Both adult apoE3- and E4-targeted replacement and C57BL/6 mice were exposed to CPF at 0 or 2 mg/kg body weight/day through the diet for 8 consecutive weeks. We determined the expression of JAK2, p-JAK2, STAT3, p-STAT3, SOCS3, IRS-1, p-IRS-1, AKT, p-AKT, GSK3ß, p-GSK3ß, and apoE in the liver, as well as hepatic mRNA levels of pon1, pon2, and pon3. CPF markedly disrupted both leptin and insulin homeostasis, particularly in apoE3 mice. Indeed, only CPF-fed apoE3 mice exhibited an increased phosphorylation ratio of STAT3, as well as increased total SOCS3 protein levels. Similarly, the exposure to CPF drastically reduced the phosphorylation ratio of both AKT and GSK3ß, especially in apoE3 mice. Overall, CPF reduced the expression of the three pon genes, principally in C57BL/6 and apoE3 mice. These results provide notable mechanistic insights on the metabolic effects of the pesticide CPF, and attest the increased vulnerability of apoE3 carriers to its metabolic-disruptor role.

Aluminum and Alzheimer's Disease.

Aluminum (Al) is one of the most extended metals in the Earth's crust. Its abundance, together with the widespread use by humans, makes Al-related toxicity particularly relevant for human health.Despite some factors influence individual bioavailability to this metal after oral, dermal, or inhalation exposures, humans are considered to be protected against Al toxicity because of its low absorption and efficient renal excretion. However, several factors can modify Al absorption and distribution through the body, which may in turn progressively contribute to the development of silent chronic exposures that may lately trigger undesirable consequences to health. For instance, Al has been recurrently shown to cause encephalopathy, anemia, and bone disease in dialyzed patients. On the other hand, it remains controversial whether low doses of this metal may contribute to developing Alzheimer's disease (AD), probably because of the multifactorial and highly variable presentation of the disease.This chapter primarily focuses on two key aspects related to Al neurotoxicity and AD, which are metabolic impairment and iron (Fe) alterations. We discuss sex and genetic differences as a plausible source of bias to assess risk assessment in human populations.

Two cholinesterase inhibitors trigger dissimilar effects on behavior and body weight in C57BL/6 mice: The case of chlorpyrifos and rivastigmine.

Cholinesterases (ChE) are common targets of organophosphate (OP) pesticides and play a critical role in the pathology of some dementias. While chlorpyrifos (CPF) remains one of the most commonly used OPs in the world, numerous investigations have reported its neurotoxic potential and highlighted behavioral disturbances upon its administration. Rivastigmine currently serves to treat Alzheimer's disease, but it may induce cholinergic overstimulation in non-demented individuals. The present investigation aimed to compare the acute and delayed effects caused by both ChE inhibitors in adult C57BL/6 male mice. The animals were daily fed either a standard, a CPF- (5mg/kg body weight) or a rivastigmine-supplemented diet (1 or 2mg/kg body weight) for 8 weeks. After the treatment, we established an 8-week washout period to assess recovery. ChE enzyme activity, biomarkers, physical effects, and behavioral alterations were evaluated at different time points during the exposure and after the washout period. Both rivastigmine doses induced a time-dependent weight increase. CPF and rivastigmine inhibited brain acetylcholinesterase following an isoform-specific pattern. As for behavioral assessment, CPF negatively modulated learning strategies and impaired memory in a Barnes maze task at the end of the exposure. On the other hand, the low dose of rivastigmine improved memory recall at the end of the washout period in a Morris water maze. Indeed, our results endorse the positive effects of low doses of rivastigmine following a drug-free period in young mice. Therefore, doses and periodicity of treatment to improve cognition in elderly people upon rivastigmine administration should be revised.

Apolipoprotein E (APOE) genotype and the pesticide chlorpyrifos modulate attention, motivation and impulsivity in female mice in the 5-choice serial reaction time task.

Organophosphate pesticides - and chlorpyrifos (CPF) in particular - contribute to a wide range of neurobehavioural disorders. Most experimental research focuses on learning and memory processes, while other behaviours remain understudied. The isoforms of the human apolipoprotein E (apoE) confer different cognitive skills on their carriers, but data on this topic are still limited. The current study was performed to assess whether the APOE genotypic variability differently modulates the effects of CPF on attentional performance, inhibitory control and motivation. Human apoE targeted replacement adult female mice (apoE2, apoE3 and apoE4) were trained to stably perform the 5-choice serial reaction time task (5-CSRTT). Animals were then subjected to daily dietary CPF (3.75 mg/kg body weight) for 4 weeks. After CPF exposure, we established a 4-week CPF-free period to assess recovery. All individuals acquired the task, apoE2 mice showed enhanced learning, while apoE4 mice displayed increased premature and perseverative responding. This genotype-dependent lack of inhibitory control was reversed by CPF. Overall, the pesticide induced protracted impairments in sustained attention and motivation, and it reduced anticipatory responding. ApoE3 mice exhibited delayed attentional disruptions throughout the wash-out period. Taken together, these findings provide notable evidence on the emergence of CPF-related attentional and motivational deficits.

Attentional performance, impulsivity, and related neurotransmitter systems in apoE2, apoE3, and apoE4 female transgenic mice.

RATIONALE: The apolipoprotein E (apoE) genotype influences cognitive performance in humans depending on age and sex. While the detrimental role of the apoE4 isoform on spatial learning and memory has been well-established in humans and rodents, less is known on its impact on the executive functions. OBJECTIVES: We aimed to evaluate the effect of apoE isoforms (apoE2, apoE3, apoE4) on visuospatial attention and inhibitory control performance in female transgenic mice, and to determine the neurochemical and neuropharmacological basis of this potential relationship. METHODS: Female mice carrying apoE2, apoE3, and apoE4 were trained in the five-choice serial reaction time task (5-CSRTT). Upon a stable performance, we manipulated the inter-trial interval and the stimulus duration to elicit impulsive responding and engage attention respectively. We further performed a pharmacological challenge by administering cholinergic and GABAergic agents. Finally, we analyzed the levels of brain amino acids and monoamines by using reversed phase high-performance liquid chromatography (HPLC). RESULTS: ApoE4 mice showed a deficient inhibitory control as revealed by increased perseveration and premature responding. When attention was challenged, apoE4 mice also showed a higher drop in accuracy. The adverse effect of scopolamine on the task was attenuated in apoE4 mice compared to apoE2 and apoE3. Furthermore, apoE4 mice showed less dopamine in the frontal cortex than apoE2 mice. CONCLUSIONS: We confirmed that the apoE genotype influences attention and inhibitory control in female transgenic mice. The influence of apoE isoforms in the brain neuromodulatory system may explain the cognitive and behavioral differences attributable to the genotype.

Adulthood dietary exposure to a common pesticide leads to an obese-like phenotype and a diabetic profile in apoE3 mice.

Increasing evidence links the widespread exposure to organophosphate (OP) pesticides to the global epidemics of type 2 diabetes and obesity. Our recent data highlighted gene×environment interactions: mice expressing the human apolipoprotein E3 (apoE3) isoform were more prone to develop obesity than those expressing apoE2 or apoE4 upon dietary challenge with chlorpyrifos (CPF), the most used OP worldwide. Thus, we aimed to further explore the contribution of the APOE3 genotype on the emergence of obesity and related metabolic dysfunctions upon subchronic exposure to CPF. Seven-month-old targeted replacement apoE3 and C57BL/6N male mice were orally exposed to CPF at 0 or 2mg/kg body weight/day for 8 consecutive weeks. We examined body weight status, food and water intake, lipid and glucose homeostasis, metabolic biomarkers concentrations, insulin levels and insulin resistance, and leptin and ghrelin profiles. CPF exposure generally increased food ingestion, glucose and total cholesterol concentrations, and tended to elevate acyl ghrelin levels. Nonetheless, excess weight gain and increased leptin levels were inherent to apoE3 mice. Moreover, the propensity towards a diabetic profile was markedly higher in these animals than in C57BL/6N, as they showed a higher homeostatic model assessment for insulin resistance index and higher insulin levels. Although both genotypes were metabolically affected by CPF, the results of the present investigation revealed that apoE3 mice were the most vulnerable to developing obesity and related disturbances following CPF administration through the diet. Since the APOE3 genotype is the most prevalent worldwide, current findings have particular implications for human health.