Estradiol modulates the anorexic response to central glucagon-like peptide 1

Liraglutide prevents body and fat mass gain in ovariectomized Wistar rats

Estrogens exert beneficial metabolic effects by reducing food intake and enhancing energy expenditure through both central and peripheral mechanisms. The decrease of estrogen, as occurs in ovariectomy (OVX), leads to metabolic disturbances, such as increased body weight, adipose tissue mass, basal blood glucose, and impaired glucose tolerance. These effects can be reversed by reintroducing estrogen. GLP-1 and its receptor agonists, known for their antihyperglycemic properties, also exhibit anorexigenic effects. Besides that, research indicates that GLP-1 analogs can induce metabolic changes peripherally, such as increased fatty acid oxidation and inhibited lipogenesis. Given the shared metabolic actions of GLP-1 and estrogens, we explored whether liraglutide, a GLP-1 agonist, could mitigate the metabolic effects of estrogen deficiency. We tested this hypothesis using ovariectomized rats, a model that simulates menopausal estrogen deficiency, and treated them with either liraglutide or 17β-Estradiol benzoate for 21 days. Ovariectomy resulted in elevated DPP-IV activity in both plasma and inguinal white adipose tissue (iWAT). While estrogen replacement effectively countered the DPP-IV increase in both plasma and iWAT, liraglutide only prevented the rise in iWAT DPP-IV activity. Liraglutide prevented body weight and fat mass gain after ovariectomy to the same extent as estradiol treatment. This can be explained by the lower food intake and food efficiency caused by estradiol and liraglutide. However, liraglutide was associated with increased pro-inflammatory cytokines and inflammatory cells in white adipose tissue. Further research is crucial to fully understand the potential benefits and risks of using GLP-1 receptor agonists in the context of menopause.

The emerging role of glucagon-like peptide 1 in binge eating

Binge eating is a central component of two clinical eating disorders: binge eating disorder and bulimia nervosa. However, the large treatment gap highlights the need to identify other strategies to decrease binge eating. Novel pharmacotherapies may be one such approach. Glucagon-like peptide-1 (GLP-1) is an intestinal and brain-derived neuroendocrine signal with a critical role in promoting glycemic control through its incretin effect. Additionally, the energy balance effects of GLP-1 are well-established; activation of the GLP-1 receptor (GLP-1R) reduces food intake and body weight. Aligned with these beneficial metabolic effects, there are GLP-1R agonists that are currently used for the treatment of diabetes and obesity. A growing body of literature suggests that GLP-1 may also play an important role in binge eating. Dysregulation of the endogenous GLP-1 system is associated with binge eating in non-human animal models, and GLP-1R agonists may be a promising approach to suppress the overconsumption that occurs during binge eating. Here, we briefly discuss the role of GLP-1 in normal energy intake and reward and then review the emerging evidence suggesting that disruptions to GLP-1 signaling are associated with binge eating. We also consider the potential utility of GLP-1-based pharmacotherapies for reducing binge eating behavior.

The estrogenic reduction in water intake stimulated by dehydration involves estrogen receptor alpha and a potential role for GLP-1

It is well documented that estrogens inhibit fluid intake. Most of this research, however, has focused on fluid intake in response to dipsogenic hormone and/or drug treatments in euhydrated rats. Additional research is needed to fully characterize the fluid intake effects of estradiol in response to true hypovolemia. As such, the goals of this series of experiments were to provide a detailed analysis of water intake in response to water deprivation in ovariectomized female rats treated with estradiol. In addition, these experiments also tested if activation of estrogen receptor alpha is sufficient to reduce water intake stimulated by water deprivation and tested for a role of glucagon like peptide-1 in the estrogenic control of water intake. As expected, estradiol reduced water intake in response to 24 and 48 h of water deprivation. The reduction in water intake was associated with a reduction in drinking burst number, with no change in drinking burst size. Pharmacological activation of estrogen receptor alpha reduced intake. Finally, estradiol-treatment caused a leftward shift in the behavioral dose response curve of exendin-4, the glucagon like peptide-1 agonist. While the highest dose of exendin-4 reduced 10 min intake in both oil and estradiol-treated rats, the intermediate dose only reduced intake in rats treated with estradiol. Together, this series of experiments extends previous research by providing a more thorough behavioral analysis of the anti-dipsogenic effect of estradiol in dehydrated rats, in addition to identifying the glucagon like peptide-1 system as a potential bioregulator involved in the underlying mechanisms by which estradiol reduces water intake in the female rat.

Feeding neurons integrate metabolic and reproductive states in mice

Balance between metabolic and reproductive processes is important for survival, particularly in mammals that gestate their young. How the nervous system coordinates this balance is an active area of study. Herein, we demonstrate that somatostatin (SST) neurons of the tuberal hypothalamus alter feeding in a manner sensitive to metabolic and reproductive states in mice. Whereas chemogenetic activation of SST neurons increased food intake across sexes, ablation decreased food intake only in female mice during proestrus. This ablation effect was only apparent in animals with low body mass. Fat transplantation and bioinformatics analysis of SST neuronal transcriptomes revealed white adipose as a key modulator of these effects. These studies indicate that SST hypothalamic neurons integrate metabolic and reproductive cues by responding to varying levels of circulating estrogens to modulate feeding differentially based on energy stores. Thus, gonadal steroid modulation of neuronal circuits can be context dependent and gated by metabolic status.

Chronic Semaglutide Treatment in Rats Leads to Daily Excessive Concentration-Dependent Sucrose Intake

Context

The glucagon-like peptide-1 receptor (GLP-1R) agonist semaglutide (SEMA) produces 15% weight loss when chronically administered to humans with obesity.

Methods

In 2 separate experiments, rats received daily injections of either vehicle (VEH) or SEMA starting at 7 µg/kg body weight (BW) and increasing over 10 days to the maintenance dose (70 µg/kg-BW), emulating clinical dose escalation strategies.

Results

During dose escalation and maintenance, SEMA rats reduced chow intake and bodyweight. Experiment 2 meal pattern analysis revealed that meal size, not number, mediated these SEMA-induced changes in chow intake. This suggests SEMA affects neural processes controlling meal termination and not meal initiation. Two-bottle preference tests (vs water) began after 10 to 16 days of maintenance dosing. Rats received either an ascending sucrose concentration series (0.03-1.0 M) and 1 fat solution (Experiment 1) or a 4% and 24% sucrose solution in a crossover design (Experiment 2). At lower sucrose concentrations, SEMA-treated rats in both experiments drank sometimes >2× the volume consumed by VEH controls; at higher sucrose concentrations (and 10% fat), intake was similar between treatment groups. Energy intake of SEMA rats became similar to VEH rats. This was unexpected because GLP-1R agonism is thought to decrease the reward and/or increase the satiating potency of palatable foods. Despite sucrose-driven increases in both groups, a significant bodyweight difference between SEMA- and VEH-treated rats remained.

Conclusion

The basis of the SEMA-induced overconsumption of sucrose at lower concentrations relative to VEH controls remains unclear, but the effects of chronic SEMA treatment on energy intake and BW appear to depend on the caloric sources available.

The role of glucagon-like peptide-1 (GLP-1) in fluid and food intakes in vasopressin-deficient Brattleboro rats

Eating and drinking co-occur and many of the same mechanisms that control one are involved in the control of the other, making it difficult to isolate specific mechanisms for the control of fluid intake. Glucagon-like peptide-1 (GLP-1) is a peptide that seems to be involved in the endogenous control of both ingestive behaviors, but we lack a thorough understanding of how and where GLP-1 is acting to control fluid intake. Vasopressin-deficient Brattleboro rats are a model of hereditary hypothalamic diabetes insipidus that have been used extensively for the study of vasopressin actions in behavior and physiology. Here, we propose that these rats, that eat normally but drink excessively, provide a useful model to dissociate central controls of food and fluid intakes. As an initial step toward establishing this model for these purposes, we focused on GLP-1. Similar to the effect observed after treatment with a GLP-1 receptor (GLP-1R) agonist, the intake difference between wildtype and Brattleboro rats was largely a function in the number of licking bursts, indicating differences in post-ingestive feedback (e.g., satiation). When given central injections of a GLP-1R agonist, the effect on feeding was comparable between wildtype and Brattleboro rats, but the effect of drug on fluid intake was markedly exaggerated in Brattleboro rats. Additionally, Brattleboro rats did not respond to GLP-1R antagonism, whereas wildtype rats did. Taken together, these results suggest that Brattleboro rats exhibit a selective disruption to GLP-1's control of water intake. Overall, these experiments provide foundational studies of the ingestive behavior of Brattleboro rats and demonstrate the potential to use these rats to disentangle the effects of GLP-1 on food and fluid intakes.

Feeding Neurons Integrate Metabolic and Reproductive States in Mice

Trade-offs between metabolic and reproductive processes are important for survival, particularly in mammals that gestate their young. Puberty and reproduction, as energetically taxing life stages, are often gated by metabolic availability in animals with ovaries. How the nervous system coordinates these trade-offs is an active area of study. We identify somatostatin neurons of the tuberal nucleus (TNSST) as a node of the feeding circuit that alters feeding in a manner sensitive to metabolic and reproductive states in mice. Whereas chemogenetic activation of TNSST neurons increased food intake across sexes, selective ablation decreased food intake only in female mice during proestrus. Interestingly, this ablation effect was only apparent in animals with a low body mass. Fat transplantation and bioinformatics analysis of TNSST neuronal transcriptomes revealed white adipose as a key modulator of the effects of TNSST neurons on food intake. Together, these studies point to a mechanism whereby TNSST hypothalamic neurons modulate feeding by responding to varying levels of circulating estrogens differentially based on energy stores. This research provides insight into how neural circuits integrate reproductive and metabolic signals, and illustrates how gonadal steroid modulation of neuronal circuits can be context-dependent and gated by metabolic status.

Increased Meal Size but Reduced Meal-Stimulated Plasma Cholecystokinin Concentrations in Women With Obesity

To better understand the physiological basis of obesity in women, we investigated whether obesity or menstrual cycle phase affects laboratory test-meal size or meal-stimulated plasma cholecystokinin (CCK) concentration. Women with healthy weight (body mass index [BMI] of 18.5-24.9 kg/m2, N = 16) or obesity (BMI 30-39.9 kg/m2, N = 20) were tested once in the late-follicular or peri-ovulatory phase (LF/PO) and once in the mid-luteal phase (ML). Meals of ham sandwiches were offered and blood was sampled. Menstrual cycle phases were verified with participants' reports of menses and measurements of progesterone and luteinizing hormone (LH) concentrations. Women with obesity ate significantly larger meals than women with healthy weight, (mean, 711 [95% CI, 402-1013] kJ, P = 0.001, during the LF/PO and 426 [105-734] kJ, P = 0.027, larger during the ML). Women with healthy weight ate smaller meals during LF/PO than ML (decrease, 510 [192-821 kJ], P = 0.008), but women with obesity did not (decrease, 226 [-87-542] kJ, P = 0.15). CCK concentrations 18 to 30 minutes after meal onset were lower in women with obesity than in women with healthy weight during LF/PO (3.6 [3.1-4.1] vs 6.1 [4.5-7.7] pmol/L; P = 0.004), but not during ML, with a significant interaction effect (1.8 [1.2-2.4] pmol/L, P = 0.048). Women with obesity consumed larger meals than women with healthy weight but displayed reduced meal-stimulated plasma CCK concentrations. These data are consistent with the hypothesis that a defect in CCK secretion compromises satiation in obese women and contributes to the development or maintenance of obesity.

Physiological and pharmacological actions of glucagon like peptide-1 (GLP-1) in domestic animals

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GLP-1 improves peripheral glucose uptake in healthy dogs and cats.

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GLP-1 analogues administration in diabetic cats reduces exogenous insulin requirement.

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Dogs cardiomyocytes apoptosis is reduced by GLP-1-derived molecules action.

Analogues of glucagon like peptide-1 (GLP-1) and other drugs that increase this peptide half-life are used worldwide in human medicine to treat type 2 diabetes mellitus (DM) and obesity. These molecules can increase insulin release and satiety, interesting effects that could also be useful in the treatment of domestic animals pathologies, however their use in veterinary medicine are still limited. Considering the increasing incidence of DM and obesity in cats and dogs, the aim of this review is to summarize the available information about the physiological and pharmacological actions of GLP-1 in domestic animals and discuss about its potential applications in veterinary medicine. In diabetic dogs, the use of drugs based on GLP-1 actions reduced blood glucose and increased glucose uptake, while in diabetic cats they reduced glycemic variability and exogenous insulin administration. Thus, available evidence indicates that GLP-1 based drugs could become alternatives to DM treatment in domestic animals. Nevertheless, current data do not provide enough elements to recommend these drugs widespread clinical use.

Oromotor and somatic taste reactivity during sucrose meals reveals internal state and stimulus palatability after gastric bypass in rats

After Roux-en-Y gastric bypass (RYGB), rats consume less high-energy foods and fluids, though whether this reflects a concomitant change in palatability remains unclear. By measuring behavior during intraorally delivered liquid meals across days (1 water, 8 sucrose sessions), we showed that RYGB rats (RYGB, n = 8/sex) consumed less 1.0 M sucrose than their sham surgery counterparts (SHAM, n = 8 males, n = 11 females) but displayed similarly high levels of ingestive taste reactivity responses at the start of infusions. Relative to water, both groups increased intake of sucrose, and ingestive responses were dominated by tongue protrusions rather than mouth movements. Thus, RYGB animals still found sucrose palatable despite consuming less than the SHAM group. As the intraoral infusion progressed but before meal termination, aversive behavior remained low and both RYGB and SHAM animals showed fewer ingestive responses, predominantly mouth movements as opposed to tongue protrusions. This shift in responsiveness unrelated to surgical manipulation suggests negative alliesthesia, or a decreased palatability, as rats approach satiation. Notably, only in RYGB rats, across sessions, there was a striking emergence of aversive behavior immediately after the sucrose meal. Thus, although lower intake in RYGB rats seems independent of the hedonic taste properties of sucrose, taste reactivity behavior in these animals immediately after termination of a liquid meal appears to be influenced by postoral events and reflects a state of nimiety or excessive consumption. Measurement of taste reactivity behaviors during an intraorally delivered meal represents a promising way to make inferences about internal state in nonverbal preclinical models.

The Effects of Roux-en-Y Gastric Bypass on Glucose- vs. Fructose-Associated Conditioned Flavor Preference

In rodents, repeated single-bottle exposures to distinctly flavored isocaloric glucose and fructose solutions, two sugars with different metabolic pathways, eventually lead to a preference for the former. Because Roux-en-Y gastric bypass (RYGB) surgery decreases preference for and intake of sugar solutions in rats, we tested whether RYGB would curtail the conditioning of a preference for a glucose-paired vs. fructose-paired flavor. RYGB (♂ n=11; ♀ n=10) and sham-operated (SHAM; ♂ n=9; ♀ n=10) rats were trained with a single bottle (30 min/day) containing 8% glucose solution flavored with either 0.05% grape or cherry Kool-Aid (Glu/CS^G) or 8% fructose solution with the alternative Kool-Aid flavor (Fru/CS^F) in an alternating fashion for 8 days. To determine baseline preferences, a 4-day 30-min two-bottle test was used to assess preference for Glu/CS^G vs. Fru/CS^F before training. After training, 2-day 30-min two-bottle tests assessed preference for the a) Glu/CS^G (CS^G-flavored 8% glucose solution) vs Fru/CS^F (CS^F-flavored 8% fructose solution), b) CS^G- vs. CS^F-flavored mixture of 4% glucose & 4% fructose (isocaloric), c) CS^G- vs. CS^F-flavored 0.2% saccharin ("sweet", no calories), and d) CS^G- vs. CS^F-flavored water. During training, only male SHAM rats demonstrated progressively increased intake of Glu/CS^G over Fru/CS^F, and female SHAM rats displayed a trend. RYGB eliminated any difference in single-bottle intake of these solutions during training, regardless of sex. Like their male and female SHAM counterparts, male RYGB rats displayed a conditioned preference for the CS^G-associated stimulus in Tests 1-3. Although female RYGB rats displayed acquisition of the conditioned flavor preference in Test 1, unlike the other groups, when the differential sugar cue between the two solutions was removed in Tests 2 and 3, female rats did not display a CS^G preference. When the sugar and sweetener cues were both removed on Test 4, all groups displayed some generalization decrement. Thus, RYGB does not compromise the ability of rats to learn and express a glucose- vs. fructose-associated conditioned flavor preference when the exact CS used in training is presented in testing. The mechanistic basis for the sex difference in the effect of RYGB on the generalization decrement observed in this type of flavor preference learning warrants further study.

Effect of oral contraceptives on energy balance in women: A review of current knowledge and potential cellular mechanisms

Body weight management is currently of major concern as the obesity epidemic is still a worldwide challenge. As women face more difficulties to lose weight than men, there is an urgent need to better understand the underlying reasons and mechanisms. Recent data have suggested that the use of oral contraceptive (OC) could be involved. The necessity of utilization and development of contraceptive strategies for birth regulation is undeniable and contraceptive pills appear as a quite easy approach. Moreover, OC also represent a strategy for the management of premenstrual symptoms, acne or bulimia nervosa. The exact impact of OC on body weight remains not clearly established. Thus, after exploring the potential underlying mechanisms by which OC could influence the two side of energy balance, we then provide an overview of the available evidence regarding the effects of OC on energy balance (i.e. energy expenditure and energy intake). Finally, we highlight the necessity for future research to clarify the cellular effects of OC and how the individualization of OC prescriptions can improve long-term weight loss management.

Meal Patterns and Food Choices of Female Rats Fed a Cafeteria-Style Diet Are Altered by Gastric Bypass Surgery

After Roux-en-Y gastric bypass surgery (RYGB), rats tend to reduce consumption of high-sugar and/or high-fat foods over time. Here, we sought to investigate the behavioral mechanisms underlying these intake outcomes. Adult female rats were provided a cafeteria diet comprised of five palatable foodstuffs varying in sugar and fat content and intake was monitored continuously. Rats were then assigned to either RYGB, or one of two control (CTL) groups: sham surgery or a nonsurgical control group receiving the same prophylactic iron treatments as RYGB rats. Post-sur-gically, all rats consumed a large first meal of the cafeteria diet. After the first meal, RYGB rats reduced intake primarily by decreasing the meal sizes relative to CTL rats, ate meals more slowly, and displayed altered nycthemeral timing of intake yielding more daytime meals and fewer nighttime meals. Collectively, these meal patterns indicate that despite being motivated to consume a cafeteria diet after RYGB, rats rapidly learn to modify eating behaviors to consume foods more slowly across the entire day. RYGB rats also altered food preferences, but more slowly than the changes in meal patterns, and ate proportionally more energy from complex carbohydrates and protein and proportionally less fat. Overall, the pattern of results suggests that after RYGB rats quickly learn to adjust their size, eating rate, and distribution of meals without altering meal number and to shift their macronutrient intake away from fat; these changes appear to be more related to postingestive events than to a fundamental decline in the palatability of food choices.

The diverse effects of brain glucagon-like peptide 1 receptors on ingestive behaviour

Glucagon-like peptide 1 (GLP-1) is well known as a gut hormone and also acts as a neuropeptide, produced in a discrete population of caudal brainstem neurons that project widely throughout the brain. GLP-1 receptors are expressed in many brain areas of relevance to energy balance, and stimulation of these receptors at many of these sites potently suppresses food intake. This review surveys the current evidence for effects mediated by GLP-1 receptors on feeding behaviour at a wide array of brain sites and discusses behavioural and neurophysiological mechanisms for the effects identified thus far. Taken together, it is clear that GLP-1 receptor activity in the brain can influence feeding by diverse means, including mediation of gastrointestinal satiation and/or satiety signalling, suppression of motivation for food reward, induction of nausea and mediation of restraint stress-induced hypophagia, but many questions about the organization of this system remain.

Liraglutide improves lipid and carbohydrate metabolism of ovariectomized rats

Considering that post-menopausal women and ovariectomized rodents develop obesity associated with increased visceral fat, this study was developed to investigate if liraglutide, a glucagon-like peptide 1 (GLP1) analogue, could improve the metabolism of estrogen (E2) deficient females. Wistar rats were ovariectomized (OVX), and subdivided in four groups: sham saline, sham liraglutide, OVX saline, and OVX liraglutide. After sixty days, metabolic parameters of blood, heart, liver, brown (BAT) and white adipose tissue (WAT) visceral depots, and, heart oxidative homeostasis, were evaluated. Castration increased the animals' body weight, the relative weight of the WAT depots, hepatic triglycerides and cardiac glycogen content. Liraglutide treatment reversed these effects, decreased WAT depots weight and increased glucose oxidation and lipogenesis in BAT and WAT. In addition, liraglutide enhanced adrenalin (A) lipolytic effect. These results indicate that liraglutide may be a promising treatment to restore lipid homeostasis and prevent weight gain associated with E2 deficiency.

Estrogen and gut satiety hormones in vagus-hindbrain axis

Estrogens modulate different physiological functions, including reproduction, inflammation, bone formation, energy expenditure, and food intake. In this review, we highlight the effect of estrogens on food intake regulation and the latest literature on intracellular estrogen signaling. In addition, gut satiety hormones, such as cholecystokinin, glucagon-like peptide 1 and leptin are essential to regulate ingestive behaviors in the postprandial period. These peripheral signals are sensed by vagal afferent terminals in the gut wall and transmitted to the hindbrain axis. Here we 1. review the role of the vagus-hindbrain axis in response to gut satiety signals and 2. consider the potential synergistic effects of estrogens on gut satiety signals at the level of vagal afferent neurons and nuclei located in the hindbrain. Understanding the action of estrogens in gut-brain axis provides a potential strategy to develop estrogen-based therapies for metabolic diseases and emphasizes the importance of sex difference in the treatment of obesity.

Maternal High Fat Diet Programs Male Mice Offspring Hyperphagia and Obesity: Mechanism of Increased Appetite Neurons via Altered Neurogenic Factors and Nutrient Sensor AMPK

Maternal high-fat (HF) is associated with offspring hyperphagia and obesity. We hypothesized that maternal HF alters fetal neuroprogenitor cell (NPC) and hypothalamic arcuate nucleus (ARC) development with preferential differentiation of neurons towards orexigenic (NPY/AgRP) versus anorexigenic (POMC) neurons, leading to offspring hyperphagia and obesity. Furthermore, these changes may involve hypothalamic bHLH neuroregulatory factors (Hes1, Mash1, Ngn3) and energy sensor AMPK. Female mice were fed either a control or a high fat (HF) diet prior to mating, and during pregnancy and lactation. HF male newborns were heavier at birth and exhibited decreased protein expression of hypothalamic bHLH factors, pAMPK/AMPK and POMC with increased AgRP. As adults, these changes persisted though with increased ARC pAMPK/AMPK. Importantly, the total NPY neurons were increased, which was consistent with the increased food intake and adult fat mass. Further, NPCs from HF newborn hypothalamic tissue showed similar changes with preferential NPC neuronal differentiation towards NPY. Lastly, the role of AMPK was further confirmed with in vitro treatment of Control NPCs with pharmacologic AMPK modulators. Thus, the altered ARC development of HF offspring results in excess appetite and reduced satiety leading to obesity. The underlying mechanism may involve AMPK/bHLH pathways.

Sexes on the brain: Sex as multiple biological variables in the neuronal control of feeding

Neuronal interactions at the level of vagal, homeostatic, and hedonic circuitry work to regulate the neuronal control of feeding. This integrative system appears to vary across sex and gender in the animal and human worlds. Most feeding research investigating these variations across sex and gender focus on how the organizational and activational mechanisms of hormones contribute to these differences. However, in limited studies spanning both the central and peripheral nervous systems, sex differences in feeding have been shown to manifest not just at the level of the hormonal, but also at the chromosomal, epigenetic, cellular, and even circuitry levels to alter food intake. In this review, we provide a brief orientation to the current understanding of how these neuronal systems interact before dissecting selected studies from the recent literature to exemplify how feeding physiology at all levels can be affected by the various components of sex.

Phasic dopamine responses to a food-predictive cue are suppressed by the glucagon-like peptide-1 receptor agonist Exendin-4

Phasic dopamine activity is evoked by reliable predictors of food reward and plays a role in cue-triggered, goal-directed behavior. While this important signal is modulated by physiological state (e.g. hunger, satiety), the mechanisms by which physiological state is integrated by dopamine neurons is only beginning to be elucidated. Activation of central receptors for glucagon-like peptide-1 (GLP-1R) via long-acting agonists (e.g., Exendin-4) suppresses food intake and food-directed motivated behavior, in part, through action in regions with dopamine cell bodies, terminals, and/or neural populations that directly target the mesolimbic dopamine system. However, the effects of GLP-1R activation on cue-evoked, phasic dopamine signaling remain unknown. Here, in vivo fiber photometry was used to capture real-time signaling dynamics selectively from dopamine neurons in the ventral tegmental area of male and female transgenic (tyrosine hydroxylase-Cre; TH:Cre+) rats trained to associate an audio cue with the brief availability of a sucrose solution. Cue presentation evoked a brief spike in dopamine activity. Administration of Exendin-4 (Ex4; 0, 0.05, 0.1 μg) to the lateral ventricle both dose-dependently suppressed sucrose-directed behaviors and the magnitude of cue-evoked dopamine activity. Moreover, the amplitude of cue evoked dopamine activity was significantly correlated with subsequent sucrose-directed behaviors. While female rats exhibited overall reduced dopamine responses to the sucrose-paired cue relative to males, there was no significant interaction with Ex4. Together, these findings support a role for central GLP-1Rs in modulating a form of dopamine signaling that influences approach behavior and provide a potential mechanism whereby GLP-1 suppresses food-directed behaviors.

Ovarian Hormones Mediate Changes in Adaptive Choice and Motivation in Female Rats

In female rodents, sexual receptivity is coordinated with cyclic changes in the release of gonadal hormones. Increases in estradiol (E) and progesterone (P) during proestrus and estrus not only induce ovulation but also modulate behaviors that increase the likelihood that the female will find a mate and reproduce. This includes changes in receptive behaviors, such as lordosis, as well as changes in appetitive or proceptive behaviors, including motivation. Interestingly, the direction of these changes in motivation is dependent on the type of reward that is being pursued. While induction of sexual receptivity by E and P increases motivation for access to a male, motivation for a palatable food reward is decreased. These concurrent changes may facilitate adaptive choice across the estrous cycle; females bias their choice for sex when fertilization is most likely to occur, but for food when copulation is unlikely to result in impregnation. In order to test this hypothesis, we developed a novel paradigm to measure the motivated choice between a palatable food reward and access to a male conspecific. Ovariectomized, hormone primed females were trained to operantly respond for both food and sex on a fixed interval (FI) schedule. After training, unprimed and primed females were tested in a chamber that allows them to choose between food and sex while still requiring responding on the FI schedule for reach reward. From this we can not only determine the impact of hormone priming on female choice for food or sex, but also how this is reflected by changes in motivation for each specific reward, as measured by the average number of responses made during each fixed interval. Induction of sexual receptivity by hormone priming biases choice toward sex over food and this change is accompanied by an increase in motivation for sex but a decrease in motivation for food. This work provides evidence in support of a novel framework for understanding how the release of ovarian hormones over the course of the estrous cycle modulates adaptive behavioral choice in females by directly assessing motivation via operant responding when multiple rewards are available.

Neuroendocrine drivers of risk and resilience: The influence of metabolism & mitochondria

The manifestation of risk versus resilience has been considered from varying perspectives including genetics, epigenetics, early life experiences, and type and intensity of the challenge with which the organism is faced. Although all of these factors are central to determining risk and resilience, the current review focuses on what may be a final common pathway: metabolism. When an organism is faced with a perturbation to the environment, whether internal or external, appropriate energy allocation is essential to resolving the divergence from equilibrium. This review examines the potential role of metabolism in the manifestation of stress-induced neural compromise. In addition, this review details the current state of knowledge on neuroendocrine factors which are poised to set the tone of the metabolic response to a systemic challenge. The goal is to provide an essential framework for understanding stress in a metabolic context and appreciation for key neuroendocrine signals.

Vagal Interoceptive Modulation of Motivated Behavior

In addition to regulating the ingestion and digestion of food, sensory feedback from gut to brain modifies emotional state and motivated behavior by subconsciously shaping cognitive and affective responses to events that bias behavioral choice. This focused review highlights evidence that gut-derived signals impact motivated behavior by engaging vagal afferents and central neural circuits that generally serve to limit or terminate goal-directed approach behaviors, and to initiate or maintain behavioral avoidance.