Greater Reward-Related Neuronal Response to Hedonic Foods in Women Compared with Men

Sex-Specific Mechanisms Underlie Long-Term Potentiation at Hippocampus→Medium Spiny Neuron Synapses in the Medial Shell of the Nucleus Accumbens

Sex differences have complicated our understanding of the neurobiological basis of many behaviors that are key for survival. As such, continued elucidation of the similarities and differences between sexes is necessary to gain insight into brain function and vulnerability. The connection between the hippocampus (Hipp) and nucleus accumbens (NAc) is a crucial site where modulation of neuronal activity mediates reward-related behavior. Our previous work demonstrated that long-term potentiation (LTP) of Hipp→NAc synapses is rewarding, and mice can establish learned associations between LTP of these synapses and the contextual environment in which LTP occurred. Here, we investigated sex differences in the mechanisms underlying Hipp→NAc LTP using whole-cell electrophysiology and pharmacology. We observed similarities in basal synaptic strength between males and females and found that LTP occurs postsynaptically with similar magnitudes in both sexes. However, key sex differences emerged as LTP in males required NMDA receptors (NMDAR), whereas LTP in females utilized an NMDAR-independent mechanism involving L-type voltage-gated Ca2+ channels (VGCCs) and estrogen receptor α (ERα). We also uncovered sex-similar features as LTP in both sexes depended on CaMKII activity and occurred independently of dopamine-1 receptor (D1R) activation. Our results have elucidated sex-specific molecular mechanisms for LTP in an integral pathway that mediates reward-related behaviors, emphasizing the importance of considering sex as a variable in mechanistic studies. Continued characterization of sex-specific mechanisms underlying plasticity will offer novel insight into the neurophysiological basis of behavior, with significant implications for understanding how diverse processes mediate behavior and contribute to vulnerability to developing psychiatric disorders.

Relationship between functional connectivity and weight-gain risk of antipsychotics in schizophrenia

BACKGROUND

The mechanisms by which antipsychotic medications (APs) contribute to obesity in schizophrenia are not well understood. Because AP effects on functional brain connectivity may contribute to weight effects, the current study investigated how AP-associated weight-gain risk relates to functional connectivity in schizophrenia.

METHODS

Fifty-five individuals with schizophrenia (final N = 54) were divided into groups based on previously reported AP weight-gain risk (no APs/low risk [N = 19]; moderate risk [N = 17]; high risk [N = 18]). Resting-state functional magnetic resonance imaging (fMRI) was completed after an overnight fast ("fasted") and post-meal ("fed"). Correlations between AP weight-gain risk and functional connectivity were assessed at the whole-brain level and in reward- and eating-related brain regions (anterior insula, caudate, nucleus accumbens).

RESULTS

When fasted, greater AP weight-gain risk was associated with increased connectivity between thalamus and sensorimotor cortex (pFDR = 0.021). When fed, greater AP weight-gain risk was associated with increased connectivity between left caudate and left precentral/postcentral gyri (pFDR = 0.048) and between right caudate and multiple regions, including the left precentral/postcentral gyri (pFDR = 0.001), intracalcarine/precuneal/cuneal cortices (pFDR < 0.001), and fusiform gyrus (pFDR = 0.008). When fed, greater AP weight-gain risk was also associated with decreased connectivity between right anterior insula and ventromedial prefrontal cortex (pFDR = 0.002).

CONCLUSIONS

APs with higher weight-gain risk were associated with greater connectivity between reward-related regions and sensorimotor regions when fasted, perhaps relating to motor anticipation for consumption. Higher weight-gain risk APs were also associated with increased connectivity between reward, salience, and visual regions when fed, potentially reflecting greater desire for consumption following satiety.

Sex modulated the relationship between trait approach motivation and decision-making

It has been observed that one's Behavioral Approach System (BAS) can have an effect on decision-making under uncertainty, although the results have been mixed. To discern the underlying neural substrates, we hypothesize that sex may explain the conflicting results. To test this idea, a large sample of participants was studied using resting state fMRI, utilizing fractional Amplitude of Low Frequency Fluctuations (fALFF) and Resting-State Functional Connectivity (rsFC) techniques. The results of the Iowa Gambling Task (IGT) revealed an interaction between sex and BAS, particularly in the last 60 trials (decision-making under risk). Males with high BAS showed poorer performance than those with low BAS. fALFF analysis showed a significant interaction between BAS group and sex in the left superior occipital gyrus, as well as the functional connectivity between this region and the left ventrolateral prefrontal cortex. Additionally, this functional connectivity was further positively correlated with male performance in the IGT, particularly in the decision-making under risk stage. Furthermore, it was found that the functional connectivity between left ventrolateral prefrontal cortex and left superior occipital gyrus could mediate the relationship between BAS and decision-making in males, particularly in the decision-making under risk stage. These results suggest possible sex-based differences in decision-making, providing an explanation for the inconsistent results found in prior research. Since the research was carried out exclusively with Chinese university students, it is essential to conduct further studies to investigate whether the findings can be generalized.

Sex-specific mechanisms underlie long-term potentiation at hippocampus-nucleus accumbens synapses

Sex differences have complicated our understanding of the neurobiological basis of many behaviors that are key for survival. As such, continued elucidation of the similarities and differences between sexes is necessary in order to gain insight into brain function and vulnerability. The connection between the hippocampus (Hipp) and nucleus accumbens (NAc) is a crucial site where modulation of neuronal activity mediates reward-related behavior. Our previous work demonstrated that long-term potentiation (LTP) of Hipp-NAc synapses is rewarding, and that mice can make learned associations between LTP of these synapses and the contextual environment in which LTP occurred. Here, we investigate sex differences in the mechanisms underlying Hipp-NAc LTP using whole-cell electrophysiology and pharmacology. We found that males and females display similar magnitudes of Hipp-NAc LTP which occurs postsynaptically. However, LTP in females requires L-type voltage-gated Ca 2+ channels (VGCC) for postsynaptic Ca 2+ influx, while males rely on NMDA receptors (NMDAR). Additionally, females require estrogen receptor α (ERα) activity for LTP while males do not. These differential mechanisms converge as LTP in both sexes depends on CAMKII activity and occurs independently of dopamine-1 receptor (D1R) activation. Our results have elucidated sex-specific molecular mechanisms for LTP in an integral excitatory pathway that mediates reward-related behaviors, emphasizing the importance of considering sex as a variable in mechanistic studies. Continued characterization of sex-specific mechanisms underlying plasticity will offer novel insight into the neurophysiological basis of behavior, with significant implications for understanding how diverse processes mediate behavior and contribute to vulnerability to developing psychiatric disorders.

SIGNIFICANCE STATEMENT

Strengthening of Hipp-NAc synapses drives reward-related behaviors. Male and female mice have similar magnitudes of long-term potentiation (LTP) and both sexes have a predicted postsynaptic locus of plasticity. Despite these similarities, we illustrate here that sex-specific molecular mechanisms are used to elicit LTP. Given the bidirectional relationship between Hipp-NAc synaptic strength in mediating reward-related behaviors, the use of distinct molecular mechanisms may explain sex differences observed in stress susceptibility or response to rewarding stimuli. Discovery and characterization of convergent sex differences provides mechanistic insight into the sex-specific function of Hipp-NAc circuitry and has widespread implications for circuits mediating learning and reward-related behavior.

Obesity surgery and neural correlates of human eating behaviour: A systematic review of functional MRI studies

Changes in eating behaviour including reductions in appetite and food intake, and healthier food cue reactivity, reward, hedonics and potentially also preference, contribute to weight loss and its health benefits after obesity surgery. Functional magnetic resonance imaging (fMRI) has been increasingly used to interrogate the neural correlates of eating behaviour in obesity, including brain reward-cognitive systems, changes after obesity surgery, and links with alterations in the gut-hormone-brain axis. Neural responses to food cues can be measured by changes in blood oxygen level dependent (BOLD) signal in brain regions involved in reward processing, including caudate, putamen, nucleus accumbens, insula, amygdala, orbitofrontal cortex, and top-down inhibitory control, including dorsolateral prefrontal cortex (dlPFC). This systematic review aimed to examine: (i) results of human fMRI studies involving obesity surgery, (ii) important methodological differences in study design across studies, and (iii) correlations and associations of fMRI findings with clinical outcomes, other eating behaviour measures and mechanistic measures. Of 741 articles identified, 23 were eligible for inclusion: 16 (69.6%) longitudinal, two (8.7%) predictive, and five (21.7%) cross-sectional studies. Seventeen studies (77.3%) included patients having Roux-en-Y gastric bypass (RYGB) surgery, six (26.1%) vertical sleeve gastrectomy (VSG), and five (21.7%) laparoscopic adjustable gastric banding (LAGB). The majority of studies (86.0%) were identified as having a very low risk of bias, though only six (27.3%) were controlled interventional studies, with none including randomisation to surgical and control interventions. The remaining studies (14.0%) had a low risk of bias driven by their control groups not having an active treatment. After RYGB surgery, food cue reactivity often decreased or was unchanged in brain reward systems, and there were inconsistent findings as to whether reductions in food cue reactivity was greater for high-energy than low-energy foods. There was minimal evidence from studies of VSG and LAGB surgeries for changes in food cue reactivity in brain reward systems, though effects of VSG surgery on food cue reactivity in the dlPFC were more consistently found. There was consistent evidence for post-operative increases in satiety gut hormones glucagon-like-peptide 1 (GLP-1) and peptide YY (PYY) mediating reduced food cue reactivity after RYGB surgery, including two interventional studies. Methodological heterogeneity across studies, including nutritional state, nature of food cues, post-operative timing, lack of control groups for order effects and weight loss or dietary/psychological advice, and often small sample sizes, limited the conclusions that could be drawn, especially for correlational analyses with clinical outcomes, other eating behaviour measures and potential mediators. This systematic review provides a detailed data resource for those performing or analysing fMRI studies of obesity surgery and makes suggestions to help improve reporting and design of such studies, as well as future directions.

AgRP neuron activity promotes associations between sensory and nutritive signals to guide flavor preference

OBJECTIVE

The learned associations between sensory cues (e.g., taste, smell) and nutritive value (e.g., calories, post-ingestive signaling) of foods powerfully influences our eating behavior [1], but the neural circuits that mediate these associations are not well understood. Here, we examined the role of agouti-related protein (AgRP)-expressing neurons - neurons which are critical drivers of feeding behavior [2; 3] - in mediating flavor-nutrient learning (FNL).

METHODS

Because mice prefer flavors associated with AgRP neuron activity suppression [4], we examined how optogenetic stimulation of AgRP neurons during intake influences FNL, and used fiber photometry to determine how endogenous AgRP neuron activity tracks associations between flavors and nutrients.

RESULTS

We unexpectedly found that tonic activity in AgRP neurons during FNL potentiated, rather than prevented, the development of flavor preferences. There were notable sex differences in the mechanisms for this potentiation. Specifically, in male mice, AgRP neuron activity increased flavor consumption during FNL training, thereby strengthening the association between flavors and nutrients. In female mice, AgRP neuron activity enhanced flavor-nutrient preferences independently of consumption during training, suggesting that AgRP neuron activity enhances the reward value of the nutrient-paired flavor. Finally, in vivo neural activity analyses demonstrated that acute AgRP neuron dynamics track the association between flavors and nutrients in both sexes.

CONCLUSIONS

Overall, these data (1) demonstrate that AgRP neuron activity enhances associations between flavors and nutrients in a sex-dependent manner and (2) reveal that AgRP neurons track and rapidly update these associations. Taken together, our findings provide new insight into the role of AgRP neurons in assimilating sensory and nutritive signals for food reinforcement.

Sex differences in the rapid detection of neutral faces associated with emotional value

BACKGROUND

Rapid detection of faces with emotional meaning is essential for understanding the emotions of others, possibly promoting successful interpersonal relationships. Although few studies have examined sex differences in the ability to detect emotional faces, it remains unclear whether faces with emotional meaning capture the attention of females and males differently, because emotional faces have visual saliency that modulates visual attention. To overcome this issue, we tested the rapid detection of the neutral faces associated with and without learned emotional value, which are all regarded as free from visual saliency. We examined sex differences in the rapid detection of the neutral female and male faces associated with emotional value.

METHODS

First, young adult female and male participants completed an associative learning task in which neutral faces were associated with either monetary rewards, monetary punishments, or no monetary outcomes, such that the neutral faces acquired positive, negative, and no emotional value, respectively. Then, they engaged in a visual search task in which previously learned neutral faces were presented as discrepant faces among newly presented neutral distractor faces. During the visual search task, the participants were required to rapidly identify discrepant faces.

RESULTS

Female and male participants exhibited comparable learning abilities. The visual search results demonstrated that female participants achieved rapid detection of neutral faces associated with emotional value irrespective of the sex of the faces presented, whereas male participants showed this ability only for male faces.

CONCLUSIONS

Our results demonstrated that sex differences in the ability to rapidly detect neutral faces with emotional value were modulated by the sex of those faces. The results suggest greater sensitivity to faces with emotional significance in females, which might enrich interpersonal communication, regardless of sex.

Neuroimaging Investigations of Obesity: a Review of the Treatment of Sex from 2010

PURPOSE OF REVIEW

To summarize the results of adult obesity neuroimaging studies (structural, resting-state, task-based, diffusion tensor imaging) published from 2010, with a focus on the treatment of sex as an important biological variable in the analysis, and identify gaps in sex difference research.

RECENT FINDINGS

Neuroimaging studies have shown obesity-related changes in brain structure, function, and connectivity. However, relevant factors such as sex are often not considered. We conducted a systematic review and keyword co-occurrence analysis. Literature searches identified 6281 articles, of which 199 met inclusion criteria. Among these, only 26 (13%) considered sex as an important variable in the analysis, directly comparing the sexes (n = 10; 5%) or providing single-sex/disaggregated data (n = 16, 8%); the remaining studies controlled for sex (n = 120, 60%) or did not consider sex in the analysis (n = 53, 27%). Synthesizing sex-based results, obesity-related parameters (e.g., body mass index, waist circumference, obese status) may be generally associated with more robust morphological alterations in men and more robust structural connectivity alterations in women. Additionally, women with obesity generally expressed increased reactivity in affect-related regions, while men with obesity generally expressed increased reactivity in motor-related regions; this was especially true under a fed state. The keyword co-occurrence analysis indicated that sex difference research was especially lacking in intervention studies. Thus, although sex differences in the brain associated with obesity are known to exist, a large proportion of the literature informing the research and treatment strategies of today has not specifically examined sex effects, which is needed to optimize treatment.

Sex-dependent role of orexin deficiency in feeding behavior and affective state of mice following intermittent access to a Western diet - Implications for binge-like eating behavior

Binge eating disorder is a debilitating disease characterized by recurrent episodes of excessive food consumption and associated with psychiatric comorbidities. Despite a growing body of research investigating the neurobiological underpinnings of eating disorders, specific treatments are lacking. Given its fundamental role in feeding behaviors, we investigated the role of the orexin (hypocretin) neuropeptide system in binge-like eating and associated phenotypes. Specifically, we submitted female and male orexin-deficient mice to a paradigm of intermittent access (once weekly for 24 h) to a Western diet (WD) to induce binge-like eating. Additionally, we measured their anxiety-like behavior and plasma corticosterone levels. All mice showed binge-like eating in response to the intermittent WD access, but females did so to a greater extent than males. While orexin deficiency did not affect binge-like eating in this paradigm, we found that female orexin-deficient mice generally weighed more, and they expressed increased hypophagia and stress levels compared to wild-type mice following binge-like eating episodes. These detrimental effects of orexin deficiency were marginal or absent in males. Moreover, male wild-type mice expressed post-binge anxiety, but orexin-deficient mice did not. In conclusion, these results extend our knowledge of orexin's role in dysregulated eating and associated negative affective states, and contribute to the growing body of evidence indicating a sexual dimorphism of the orexin system. Considering that many human disorders, and especially eating disorders, have a strong sex bias, our findings further emphasize the importance of testing both female and male subjects.

Sex Differences in Effects of Mood, Eating-Related Behaviors, and BMI on Food Appeal and Desire to Eat: A Cross-Sectional Survey Study

Although sex differences in food intake have been observed consistently, contributing factors are not well understood. Using a cross-sectional online survey (n = 306; 151 men, 155 women), this study aimed to assess how sex impacts relationships between food ratings (appeal/desire to eat for high-calorie (HC) and low-calorie (LC) food images) and eating-related attitudes/behaviors, body mass index (BMI), and mood. Across participants, increased state- and trait-based hunger, disinhibition, and cravings were associated with both increased HC appeal and desire (p < 0.001). Increased state-based hunger and cravings were associated with greater LC desire (p < 0.001). Greater satiety was associated with decreased desire for both HC and LC (p < 0.001), while greater anxiety was associated with increased desire for both HC and LC (p < 0.001). Significant associations between BMI and food ratings were not observed. Women reported greater dietary restraint, trait-based hunger, disinhibition, eating disorder-related behaviors, depression, and stress compared to men, in addition to greater appeal and familiarity with LC foods (all p < 0.05). Significant effects of sex on the associations between food ratings and eating-related attitudes/behaviors, BMI, and mood were not observed, however. Findings support the importance of considering mood and eating-related attitudes/behaviors in investigations of food cue responsivity.

Effects of Aerobic and Resistance Exercise Training on Carotid Intima-Media Thickness in Abdominal Obese Women

Aims: The purpose of this study was to investigate the effects of a 12-week aerobic and resistance training program on waist circumference (WC) and carotid intima-media thickness (CIMT) in abdominal obese middle-aged women. Methods: Subjects were 40 middle-aged women with abdominal obesity (WC >85 cm) but no specific diseases. Subjects were divided into a combined exercise group (aerobic and resistance exercise) and a control group that did not participate in any lifestyle modification. Carotid variables were measured using B-mode ultrasound. A treadmill exercise test was conducted to directly assess the peak oxygen uptake (VO₂peak). Differences in the carotid variables and relative changes between baseline and after 12 weeks were evaluated. Results: After 12 weeks, body weight (70.6 ± 7.8 to 65.6 ± 6.3 kg, P < 0.05), WC (88.8 ± 3.6 to 85.6 ± 3.1 cm, P < 0.01), total cholesterol (215.5 ± 38.4 to 188.2 ± 25.8 mmHg, P < 0.05), low-density lipoprotein cholesterol (150.5 ± 30.6 to 131.6 ± 22.3 mmHg, P < 0.05), triglycerides (164.5 ± 82.3 to 119.9 ± 60.6 mmHg, P < 0.01), VO₂peak (24.2 ± 6.2 to 28.7 ± 4.4 mL/kg/min, P < 0.01), and CIMT (0.61 ± 0.13 to 0.58 ± 0.12 mm, P < 0.05) were significantly improved in the combined exercise group but not in the control group; changes in CIMT were associated with changes in WC decrease (r = 0.41, P < 0.01) and VO₂peak (r = -0.53, P < 0.01). Conclusions: Combined exercise training in abdominal obese women decreased CIMT; these changes were also associated with reduced WC and improved VO₂peak.

Reward-related neural correlates in adolescents with excess body weight

•

We examined non-food reward related neural correlates of body mass index (BMI) in adolescents.

•

High BMI z-score relates to heightened reward salience during reward anticipation.

•

High BMI z-score relates to heightened reward salience when receiving feedback about reward.

•

Deficits in inhibitory control networks are shown in adolescents with high BMI z-score.

•

Reward and inhibitory control network impairments may lead to impulsive behavior.

The functional and connectivity reward processing in adults with excessive body weight is well documented, though is relatively less researched during adolescence. Given that reward and inhibition may be highly malleable during adolescence, it is unknown how impulsive behaviors, potentially stemming from impaired inhibitory control and heightened sensitivity to rewarding cues, relate to increases in body weight in adolescents. Adolescents (N = 76; mean age = 14.10 years, SD = 1.92) with varied body mass index (BMI) performed a child-friendly monetary incentive delay task during functional magnetic resonance imaging, to study reward processing during the anticipation of rewards (cue) and reactions to feedback about rewards (feedback). Our results show that adolescents with greater BMI z-score show neural activation and ventral striatum connectivity alterations in networks implicated in reward, salience detection, and inhibitory control. These bottom-up reward and top-down inhibitory control networks, as well as interactions between these networks were prevalent during the anticipation period (when the cue is presented) as well as when receiving feedback about whether one has received a reward. Specifically, our results were mainly driven by failure to receive a reward in the feedback period, and the anticipation of a potential reward in the anticipation period. Overall, we provide evidence for heightened reward salience as well as inhibitory control deficits that, in combination, may contribute to the impulsive behaviors that lead to higher BMI in adolescents.

Altered between-network connectivity in individuals prone to obesity

OBJECTIVE

Investigating intrinsic brain functional connectivity may help identify the neurobiology underlying cognitive patterns and biases contributing to obesity propensity. To address this, the current study used a novel whole-brain, data-driven approach to examine functional connectivity differences in large-scale network interactions between obesity-prone (OP) and obesity-resistant (OR) individuals.

METHODS

OR (N = 24) and OP (N = 25) adults completed functional magnetic resonance imaging (fMRI) during rest. Large-scale brain networks were identified using independent component analysis (ICA). Voxel-specific between-network connectivity analysis assessed correlations between ICA component time series' and individual voxel time series, identifying regions strongly connected to many networks, i.e., "hubs".

RESULTS

Significant group differences in between-network connectivity (OP vs. OR; FDR-corrected) were observed in bilateral basal ganglia (left: q = 0.009; right: q = 0.010) and right dorsolateral prefrontal cortex (dlPFC; q = 0.026), with OP>OR. Basal ganglia differences were largely driven by a more strongly negative correlation with a lateral sensorimotor network in OP, with dlPFC differences driven by a more strongly negative correlation with an inferior visual network in OP.

CONCLUSIONS

Greater between-network connectivity was observed in the basal ganglia and dlPFC in OP, driven by stronger associations with lateral sensorimotor and inferior visual networks, respectively. This may reflect a disrupted balance between goal-directed and habitual control systems and between internal/external monitoring processes.

Sex differences in the human reward system: convergent behavioral, autonomic and neural evidence

Several studies have suggested that females and males differ in reward behaviors and their underlying neural circuitry. Whether human sex differences extend across neural and behavioral levels for both rewards and punishments remains unclear. We studied a community sample of 221 young women and men who performed a monetary incentive task known to engage the mesoaccumbal pathway and salience network. Both stimulus salience (behavioral relevance) and valence (win vs loss) varied during the task. In response to high- vs low-salience stimuli presented during the monetary incentive task, men showed greater subjective arousal ratings, behavioral accuracy and skin conductance responses (P < 0.006, Hedges' effect size g = 0.38 to 0.46). In a subsample studied with functional magnetic resonance imaging (n = 44), men exhibited greater responsiveness to stimulus salience in the nucleus accumbens, midbrain, anterior insula and dorsal anterior cingulate cortex (P < 0.02, g = 0.86 to 1.7). Behavioral, autonomic and neural sensitivity to the valence of stimuli did not differ by sex, indicating that responses to rewards vs punishments were similar in women and men. These results reveal novel and robust sex differences in reward- and punishment-related traits, behavior, autonomic activity and neural responses. These convergent results suggest a neurobehavioral basis for sexual dimorphism observed in the reward system, including reward-related disorders.

Sex Differences in Demand for Highly Palatable Foods: Role of the Orexin System

BACKGROUND

The prevalence of eating disorders, including binge eating disorder, is significantly higher in women. These findings are mirrored by preclinical studies, which indicate that female rats have a higher preference for palatable food and show greater binge-like eating compared with male rats.

METHODS

Here, we describe a novel within-session behavioral-economic paradigm that allows for the simultaneous measurement of the intake at null cost (Q0) and normalized demand elasticity (α) of 3 types of palatable food (low fat, high fat, and chocolate sucrose pellets) via demand curve analysis. In light of evidence that the orexin (hypocretin) system is critically involved in reward and feeding behaviors, we also examined the role of orexin function in sex differences of economic demand for palatable foods.

RESULTS

The novel within-session behavioral-economic approach revealed that female rats have higher intake (demand) than males for all palatable foods at low cost (normalized to body weight) but no difference in intake at higher prices, indicating sex-dependent differences in the hedonic, but not motivational, aspects of palatable food. Immediately following behavioral-economic testing, we observed more orexin-expressing neurons and Fos expression (measure of recent neural activation) in these neurons in female rats compared with male rats. Moreover, the orexin-1 receptor antagonist SB334867 reduced both low- and high-cost intake for palatable food in both male and female rats.

CONCLUSIONS

These findings provide evidence of higher demand at low prices for palatable food in females and indicate that these behavioral differences may be associated with sexual dimorphism in orexin system function.

Development and validation of a short form Children's power of Food Scale

OBJECTIVE

To develop and validate a shortened form of the Children's Power of Food Scale (C-PFS), which measures anticipated reward from consuming highly palatable foods (i.e., hedonic hunger). Presently, two gaps exist with the C-PFS: the need for a shorter tighter measure, and evidence to support similar item function across populations.

METHOD

Ninth grade students (N = 3277; 14.1 ± 0.4 years; 53.5% Female; 47% Hispanic) from 10 Los Angeles high schools completed the C-PFS and other surveys in class. Factor analysis, graded response modeling, and differential item functioning explored the structure of the 15 C-PFS items and identified a reduced set that parsimoniously taps hedonic hunger across the latent continuum and exhibits item-level invariance across sex, race/ethnicity, and weight status. Construct validity was examined via associations of self-reported dietary intake, impulsivity, and body mass index (BMI) to C-PFS scores.

RESULTS

Factor analytic models supported a single, primary dimension of hedonic hunger that accounted for 61% of the variance across all 15-items (α = 0.94). Adequate severity, discriminatory ability, and non-overlapping item-difficulty were observed for 11-items, of which 9-items were found to have item-level invariance across demographic and weight status groupings. Poor performing items were removed to create a 9-item scale (C-PFS-9; α = 0.93). Construct validity was demonstrated as higher C-PFS-9 scores were significantly related to greater sweet (β = 0.32, [95%CI = 0.23, 0.41], p < .001) and fatty food intake (β = 0.34, [95%CI = 0.26, 0.43], p < .001) and impulsivity resulting from positive (β = 0.11, [95%CI = 0.02, 0.21], p < .05) and negative mood (β = 0.36, [95%CI = 0.28, 0.45], p < .001). Females, relative to males, reported higher C-PFS-9 scores (β = 0.10, [95%CI = 0.02, 0.17], p < .05) and associations with BMI were mixed.

CONCLUSION

The C-PFS-9 possesses excellent psychometric properties and retains the original construct coverage of hedonic hunger without a marked decrease in information obtained.

Sex and Feeding Status Differently Affect Natural Reward Seeking Behavior in Olfactory Bulbectomized Rats

Substance abuse and depression are common psychiatric disorders with a high rate of comorbidity. Both conditions affect differently men and women and preclinical research has showed many sex differences in drug addiction and depression. The most common approach for modeling depression-addiction comorbidity is the combination of the intravenous drug self-administration and the olfactory bulbectomy (OBX) models in rats. Such a combination has revealed enhanced drug-taking and drug-seeking behaviors in OBX rats, but no study has investigated so far potential sex differences in operant responding and motivation for natural reinforcers in OBX rats. This study investigated for the first time operant self-administration of palatable food pellets in male and female OBX rats under different feeding status, i.e., ad libitum vs. restricted food, and schedules of reinforcement, i.e., a continuous ratio schedule fixed ratio 1 (FR1) vs. a complex (FR5_(x)) second order schedule of reinforcement. In the FR1 experiment, OBX rats of both sexes exhibited lower operant responding and intake of palatable food pellets than sham-operated controls, with food restriction leading to increased operant responding in both OBX and SHAM groups. Female rats showed higher responding than males but this effect was abolished by the OBX lesion. Similarly, in the (FR5_(x)) second order schedule of reinforcement both male and female OBX rats showed lower responding and food intake, with SHAM and OBX females showing higher operant responding than corresponding male groups. Overall, our findings showed that: (i) responding for food was lower in OBX than in SHAM rats under both FR1 and (FR5_(x)) schedules of reinforcement; (ii) sex and food restriction affect operant responding for palatable food; and (iii) the suppressing effect of OBX lesion on food intake was consistently present in both sexes and represents the most robust factor in the analysis. This may represent anhedonia which is associated with depressive-like phenotype and palatable food self-administration may serve as a robust behavioral index of anhedonia in the OBX model.

Neurobiological characteristics underlying metabolic differences between males and females

The hypothalamus is the main integrating center for metabolic control. Our understanding of how hypothalamic circuits function to control appetite and energy expenditure has increased dramatically in recent years, due to the rapid rise in the incidence of obesity and the search for effective treatments. Increasing evidence indicates that these treatments will most likely differ between males and females. Indeed, sex differences in metabolism have been demonstrated at various levels, including in two of the most studied neuronal populations involved in metabolic control: the anorexigenic proopiomelanocortin neurons and the orexigenic neuropeptide Y/Agouti-related protein neurons. Here we review what is known to date regarding the sex differences in these two neuronal populations, as well as other neuronal populations involved in metabolic control and glial cells.