Ventromedial prefrontal cortex mediates sex differences in persistent cognitive drive for food

Recruitment of hippocampal and thalamic pathways to the central amygdala in the control of feeding behavior under novelty

It is adaptive to restrict eating under uncertainty, such as during habituation to novel foods and unfamiliar environments. However, sustained restrictive eating can become maladaptive. Currently, the neural substrates of restrictive eating are poorly understood. Using a model of feeding avoidance under novelty, our recent study identified forebrain activation patterns and found evidence that the central nucleus of the amygdala (CEA) is a core integrating node. The current study analyzed the activity of CEA inputs in male and female rats to determine if specific pathways are recruited during feeding under novelty. Recruitment of direct inputs from the paraventricular nucleus of the thalamus (PVT), the infralimbic cortex (ILA), the agranular insular cortex (AI), the hippocampal ventral field CA1, and the bed nucleus of the stria terminals (BST) was assessed with combined retrograde tract tracing and Fos induction analysis. The study found that during consumption of a novel food in a novel environment, larger number of neurons within the PVTp and the CA1 that send monosynaptic inputs to the CEA were recruited compared to controls that consumed familiar food in a familiar environment. The ILA, AI, and BST inputs to the CEA were similarly recruited across conditions. There were no sex differences in activation of any of the pathways analyzed. These results suggest that the PVTp-CEA and CA1-CEA pathways underlie feeding inhibition during novelty and could be potential sites of malfunction in excessive food avoidance.

The effect of gender in binge eating behavior in Chinese culture: the serial mediation model of body dissatisfaction and self-acceptance

Introduction

The gender difference of binge eating behavior been highlighted by previous studies. However, psychological mechanisms underlying the gender difference of binge eating behavior remain unclear. This study addressed this issue from a sociocultural perspective.

Methods

Firstly, we investigated the mediation effect of body dissatisfaction on the gender difference of binge eating behavior. Secondly, we examine the serial mediating role of body dissatisfaction and self-acceptance in gender differences of binge eating behavior. Here, we analyzed data from 703 Chinese university students using SPSS 26.0 and SPSS PROCESS.

Results

In Chinese culture, body dissatisfaction and self-acceptance independently or through a serial way mediate the gender differences in binge eating behaviors.

Discussion

We discussed the implications and limitations of the present study.

Learning processes in relapse to alcohol use: lessons from animal models

RATIONALE

Alcohol use is reliably preceded by discrete and contextual stimuli which, through diverse learning processes, acquire the capacity to promote alcohol use and relapse to alcohol use.

OBJECTIVE

We review contemporary extinction, renewal, reinstatement, occasion setting, and sex differences research within a conditioning framework of relapse to alcohol use to inform the development of behavioural and pharmacological therapies.

KEY FINDINGS

Diverse learning processes and corresponding neurobiological substrates contribute to relapse to alcohol use. Results from animal models indicate that cortical, thalamic, accumbal, hypothalamic, mesolimbic, glutamatergic, opioidergic, and dopaminergic circuitries contribute to alcohol relapse through separable learning processes. Behavioural therapies could be improved by increasing the endurance and generalizability of extinction learning and should incorporate whether discrete cues and contexts influence behaviour through direct excitatory conditioning or occasion setting mechanisms. The types of learning processes that most effectively influence responding for alcohol differ in female and male rats.

CONCLUSION

Sophisticated conditioning experiments suggest that diverse learning processes are mediated by distinct neural circuits and contribute to relapse to alcohol use. These experiments also suggest that gender-specific behavioural and pharmacological interventions are a way towards efficacious therapies to prevent relapse to alcohol use.

Estradiol and progesterone in female reward-learning, addiction, and therapeutic interventions

Sex steroid hormones like estradiol (E2) and progesterone (P4) guide the sexual organization and activation of the developing brain and control female reproductive behavior throughout the lifecycle; importantly, these hormones modulate functional activity of not just the endocrine system, but most of the nervous system including the brain reward system. The effects of E2 and P4 can be seen in the processing of and memory for rewarding stimuli and in the development of compulsive reward-seeking behaviors like those seen in substance use disorders. Women are at increased risk of developing substance use disorders; however, the origins of this sex difference are not well understood and therapeutic interventions targeting ovarian hormones have produced conflicting results. This article reviews the contribution of the E2 and P4 in females to functional modulation of the brain reward system, their possible roles in origins of addiction vulnerability, and the development and treatment of compulsive reward-seeking behaviors.

Stress and sex-dependent effects on conditioned inhibition of fear

Anxiety and stress-related disorders are highly prevalent and are characterized by excessive fear to threatening and nonthreatening stimuli. Moreover, there is a large sex bias in vulnerability to anxiety and stress-related disorders-women make up a disproportionately larger number of affected individuals compared with men. Growing evidence suggests that an impaired ability to suppress fear in the presence of safety signals may in part contribute to the development and maintenance of many anxiety and stress-related disorders. However, the sex-dependent impact of stress on conditioned inhibition of fear remains unclear. The present study investigated sex differences in the acquisition and recall of conditioned inhibition in male and female mice with a focus on understanding how stress impacts fear suppression. In these experiments, the training context served as the "fear" cue and an explicit tone served as the "safety" cue. Here, we found a possible sex difference in the training requirements for safety learning, although this effect was not consistent across experiments. Reductions in freezing to the safety cue in female mice were also not due to alternative fear behavior expression such as darting. Next, using footshock as a stressor, we found that males were impaired in conditioned inhibition of freezing when the stress was experienced before, but not after, conditioned inhibition training. Females were unaffected by footshock stress when it was administered at either time. Extended conditioned inhibition training in males eliminated the deficit produced by footshock stress. Finally, exposing male and female mice to swim stress impaired safety learning in male mice only. Thus, we found sex × stress interactions in the learning of conditioned inhibition and sex-dependent effects of stress modality. The present study adds to the growing literature on sex differences in safety learning, which will be critical for developing sex-specific therapies for a variety of fear-related disorders that involve excessive fear and/or impaired fear inhibition.

Sex differences in the immediate extinction deficit and renewal of extinguished fear in rats

Extinction learning is central to exposure-based behavioral therapies for reducing fear and anxiety in humans. However, patients with fear and anxiety disorders are often resistant to extinction. Moreover, trauma and stress-related disorders are highly prone to relapse and are twice as likely to occur in females compared to males, suggesting that females may be more susceptible to extinction deficits and fear relapse phenomena. In this report, we tested this hypothesis by examining sex differences in a stress-induced extinction learning impairment, the immediate extinction deficit (IED), and renewal, a common form of fear relapse. In contrast to our hypothesis, there were no sex differences in the magnitude of the immediate extinction deficit in two different rat strains (Long-Evans and Wistar). However, we did observe a sex difference in the renewal of fear when the extinguished conditioned stimulus was presented outside the extinction context. Male Wistar rats exhibited significantly greater renewal than female rats, a sex difference that has previously been reported after appetitive extinction. Collectively, these data reveal that stress-induced extinction impairments are similar in male and female rats, though the context-dependence of extinction is more pronounced in males.

The role of context on responding to an alcohol-predictive cue in female and male rats

In male rats, physical contexts that are associated with alcohol can amplify the response to a discrete, alcohol-predictive conditioned stimulus (CS), and amplify prime-induced reinstatement. Here, we examined these effects as a function of biological sex. Male and female Long-Evans rats were acclimated to drinking ethanol (15% v/v) in their home cages. Next, they were trained to associate an auditory conditioned stimulus (CS) (10 s; white noise or clicker; 15 trials per session) with ethanol delivery (0.2 mL per CS; 3.0 mL per session) into a fluid port for oral intake. Training occurred in a distinctive context containing specific visual, olfactory, and tactile stimuli. During alternating sessions, rats were exposed to a second context wherein they did not receive ethanol. At test, CS trials occurred in both contexts without ethanol delivery. Rats then underwent extinction using repeated unreinforced presentations of the CS in both contexts. An alcohol-primed reinstatement test was then conducted, in which 0.2 mL of ethanol was presented at the start of the session and during the first CS trial, after which no ethanol was delivered for the remainder of the session. At both test and reinstatement, male rats made significantly more CS port-entries in the context associated with alcohol delivery than in the context in which alcohol was never experienced. Unlike males, female rats made a similar number of CS port-entries at the test in both the alcohol context and the neutral context. The reinstatement observed in female rats was also not affected by context. These findings suggest that the capacity of an alcohol-associated context to modulate responding to a discrete, alcohol-predictive cue is less pronounced in female than male rats.

Corticostriatal Suppression of Appetitive Pavlovian Conditioned Responding

The capacity to suppress learned responses is essential for animals to adapt in dynamic environments. Extinction is a process by which animals learn to suppress conditioned responding when an expected outcome is omitted. The infralimbic (IL) cortex to nucleus accumbens shell (NAcS) neural circuit is implicated in suppressing conditioned responding after extinction, especially in the context of operant cocaine-seeking behavior. However, the role of the IL-to-NAcS neural circuit in the extinction of responding to appetitive Pavlovian cues is unknown, and the psychological mechanisms involved in response suppression following extinction are unclear. We trained male Long Evans rats to associate a 10 s auditory conditioned stimulus (CS; 14 trials per session) with a sucrose unconditioned stimulus (US; 0.2 ml per CS) in a specific context, and then following extinction in a different context, precipitated a renewal of CS responding by presenting the CS alone in the original Pavlovian conditioning context. Unilateral, optogenetic stimulation of the IL-to-NAcS circuit selectively during CS trials suppressed renewal. In a separate experiment, IL-to-NAcS stimulation suppressed CS responding regardless of prior extinction and impaired extinction retrieval. Finally, IL-to-NAcS stimulation during the CS did not suppress the acquisition of Pavlovian conditioning but was required for the subsequent expression of CS responding. These results are consistent with multiple studies showing that the IL-to-NAcS neural circuit is involved in the suppression of operant cocaine-seeking, extending these findings to appetitive Pavlovian cues. The suppression of appetitive Pavlovian responding following IL-to-NAcS circuit stimulation, however, does not appear to be an extinction-dependent process.SIGNIFICANCE STATEMENT Extinction is a form of inhibitory learning through which animals learn to suppress conditioned responding in the face of nonreinforcement. We investigated the role of the IL cortex inputs to the NAcS in the extinction of responding to appetitive Pavlovian cues and the psychological mechanisms involved in response suppression following extinction. Using in vivo optogenetics, we found that stimulating the IL-to-NAcS neural circuit suppressed context-induced renewal of conditioned responding after extinction. In a separate experiment, stimulating the IL-to-NAcS circuit suppressed conditioned responding in an extinction-independent manner. These findings can be used by future research aimed at understanding how corticostriatal circuits contribute to behavioral flexibility and mental disorders that involve the suppression of learned behaviors.

Kamishoyosan (a Japanese traditional herbal formula), which effectively reduces the aggressive biting behavior of male and female mice, and potential regulation through increase of Tph1, Tph2, and Esr2 mRNA levels

Kamishoyosan (KSS), a Japanese traditional herbal formula, is used to treat symptoms related to the autonomic nervous system in men and women; it is especially known for improving the symptoms of irritability (e.g., bad temper and persistent anger). Although clinical and ethological studies of KSS have been conducted, its efficacy in reducing irritability remains to be validated. In the present study, male and female ddY-strain mice were isolation-reared for 8 weeks (from the third postnatal week) to induce pathologically aggressive biting behavior (ABB), which was used as an indicator of irritability. The ABB of mice toward metal rods was measured using the Aggressive Response Meter. An intraperitoneal administration of KSS (100 mg/kg) effectively reduced ABB in male and female mice at 2 h after the administration; however, this effect was canceled by prior administration of WAY-100635 [a 5-hydroxytryptoamine (5-HT)-1A receptor antagonist; 0.5 mg/kg] and bicuculline (a type-A gamma-aminobutyric acid receptor antagonist; 1.0 mg/kg). Additionally, tamoxifen, ICI-182780, and G-15 (all estrogen receptor antagonists) inhibited the action of KSS in a dose-dependent manner. Furthermore, gene expression of tryptophan hydroxylase (Tph) 1 and Tph2 were increased and 5-HT immunofluorescence was slightly increased in the dorsal raphe nucleus (DRN) of isolation-reared mice administered with KSS. Collectively, these results indicate that KSS effectively reduces ABB in isolation-reared male and female mice through stimulation of 5-HT production in the DRN. Our findings also suggest that gene expression of estrogen receptor (Esr) 2 increased in the DRN might be associated with the reduction of ABB.

Chemogenetic selective manipulation of nucleus accumbens medium spiny neurons bidirectionally controls alcohol intake in male and female rats

The nucleus accumbens (NAc), considered the hub of reward circuitry, is comprised of two medium spiny neuron (MSN) subtypes that are classified by their enrichment of dopamine 1 (D1) or 2 (D2) receptors. While reports indicate that alcohol increases excitatory neurotransmission exclusively on NAc D1-MSNs in male rats, it remains unknown how NAc MSNs control alcohol intake in either sex. Therefore, this study investigated how NAc MSNs mediate alcohol intake by using Drd1a-iCre and Drd2-iCre transgenic rats of both sexes. Intra-NAc infusions of Cre-inducible viral vectors containing stimulatory (hM3Dq) or inhibitory (hM4Di) designer receptors exclusively activated by designer drugs (DREADDs) were delivered after 4-weeks of alcohol intake, and clozapine-N-oxide (CNO) was administered to selectively manipulate NAc MSNs. Our results show that activation of NAc D1-MSNs increased alcohol intake 1-, 4-, and 24-h after the start of drinking while inhibition decreased it 1-h after the start of drinking, with no sex differences observed at any time point. Activation of NAc D2-MSNs had no impact on alcohol intake while inhibition increased alcohol intake in Drd2-iCre rats for 1-h in males and 4-h in females. These findings suggest opposing roles for how NAc D1- and D2-MSNs modulate alcohol intake in rats of both sexes.

Comparing ABA, AAB, and ABC Renewal of Appetitive Pavlovian Conditioned Responding in Alcohol- and Sucrose-Trained Male Rats

Conditioned responding can be renewed by re-exposure to the conditioning context following extinction in a different context (ABA renewal) or by removal from the extinction context (AAB or ABC renewal). ABA renewal is robust in Pavlovian and operant conditioning paradigms. However, fewer studies have investigated AAB and ABC renewal of appetitive conditioning, and those that did predominantly used operant conditioning tasks. Renewal has theoretical relevance for extinction and for exposure-based treatments for substance use disorders that aim to extinguish reactivity to drug-predictive cues. We therefore investigated ABA, AAB, and ABC renewal of Pavlovian conditioned responding to cues that predicted either alcohol or sucrose. Male, Long-Evans rats (Charles River) were exposed to either 15% ethanol (Study 1: “alcohol”) or 10% sucrose (Study 2: “sucrose”) in their home cages. Next, they were trained to discriminate between two auditory stimuli (white noise and clicker; 10 s) in conditioning chambers equipped with distinct olfactory, visual, and tactile contextual stimuli (context A). One conditioned stimulus (CS+) was paired with fluid delivery (0.2 ml/CS+; 3.2 ml/session; alcohol or sucrose in separate experiments), and the second CS (CS−) was not. In all sessions (conditioning, extinction, and test), each CS was presented 16 times/session on a variable-time 67-s schedule, and entries into the fluid port were recorded. CS+ port entries were then extinguished by withholding fluid delivery either in context A or in a second, different context (context B). Next, we assessed ABA, AAB, and ABC renewal in the absence of fluid delivery. During extinction, CS+ port entries were initially elevated in context A relative to context B. ABA renewal of CS+ port entries occurred in both alcohol- and sucrose-trained rats. ABC renewal approached statistical significance when data from both experiments were combined. No AAB renewal was observed, and, in fact, alcohol-trained rats showed AAB suppression. These results corroborate the reliability of ABA renewal and suggest that ABC renewal is a modest effect that may require greater statistical power to detect. From a treatment perspective, the lack of AAB renewal suggests that exposure-based treatments for substance use disorders might benefit from implementation in real-world, drug-use contexts.

Medial Prefrontal Cortex Neural Plasticity, Orexin Receptor 1 Signaling, and Connectivity with the Lateral Hypothalamus Are Necessary in Cue-Potentiated Feeding

Cognitive processes contribute to the control of feeding behavior and help organism's survival when they support physiological needs. They can become maladaptive, such as when learned food cues drive feeding in the absence of hunger. Associative learning is the basis for cue-driven food seeking and consumption, and behavioral paradigms with Pavlovian cue-food conditioning are well established. Yet, the neural mechanisms underlying circuit plasticity across cue-food learning, cue memory recall, and subsequent food motivation are unknown. Here, we demonstrated the medial prefrontal cortex (mPFC) is a site of learning-induced plasticity and signaling of the neuropeptide orexin within the mPFC mediates cue potentiated feeding (CPF). First, using a marker of neuronal activation, c-fos, we confirmed that the mPFC is activated during CPF. Next, to assess whether the same mPFC neuronal ensemble is activated during cue-food learning and later CPF, we used the Daun02 chemogenetic inactivation method in c-fos-lacZ transgenic male and female rats. Selective inactivation of the mPFC neurons that were active during the last cue-food training session abolished CPF during test, demonstrating that the mPFC is a site of plasticity. We postulated that integration of food cue memory and feeding motivation requires mPFC communications with lateral hypothalamus and showed that disconnection of that system abolished CPF. Then we showed that lateral hypothalamus orexin-producing neurons project to the mPFC. Finally, we blocked orexin receptor 1 signaling in the mPFC and showed that it is a neuromodulator necessary for the cue-driven consumption. Together, our findings identify a causal function for the mPFC in the cognitive motivation to eat.SIGNIFICANCE STATEMENT Obesity has reached epidemic proportions, and the associated health consequences are serious and costly. The causes of obesity are complex because, in addition to physiological energy and nutrient needs, environmental cues can drive feeding through hedonic and cognitive processes. Learned food cues from the environment can powerfully stimulate appetite and food consumption in the absence of hunger. Using an animal model for cue-potentiated feeding, the current study determined the mPFC neuronal plasticity and neuropeptide orexin signaling are critical circuit and neurotransmitter mechanisms involved in this form of cognitive motivation to eat. These findings identify key targets for potential treatment of excessive appetite and overeating.

Updating gender differences in the control of homeostatic and hedonic food intake: Implications for binge eating disorder

In an obesity pandemic context, eating disorders (ED) have arisen as serious illnesses associated with severe disturbances and has a clear gender dependent bias. In this manuscript, we provide an overview of the oestrogen role in the homeostatic and hedonic control of food intake. We draw attention to the role of oestrogens in the various reward processes and their possible implication in the development of ED, a condition much more common in women. In here, we have summarized the most relevant studies conducted in animal models over the last few years. In particular, we want to emphasize on the importance of continuing thorough investigations in female animal models. We believe that understanding the molecular mechanisms that regulate gender differences in food intake may provide new potential targets for ED treatment.

Feeding Behavior Survival Circuit: Anticipation & Competition

A decision to eat or not to eat can be beneficial or detrimental to an organism, depending on internal and external conditions. Because feeding is essential for survival, as it replenishes energy and nutrients, in safe environments, its expression is prioritized over other behaviors. Under threat, responding to danger is a higher priority for survival and feeding is paused even in hungry states. Thus, successful expression of feeding behavior requires adaptive control that utilizes cognitive processes to dynamically assess and update internal drives and environmental changes. Recently identified key circuit components, which are important in anticipatory responding based on food memories and predictions and in resolving feeding versus threat avoidance competition, will be discussed within a connectional schema.

Neural substrates of fear-induced hypophagia in male and female rats

Cessation of eating under fear is an adaptive response that aids survival by prioritizing the expression of defensive behaviors over feeding behavior. However, this response can become maladaptive when persistent. Thus, accurate mediation of the competition between fear and feeding is important in health and disease; yet, the underlying neural substrates are largely unknown. The current study identified brain regions that were recruited when a fear cue inhibited feeding in male and female rats. We used a previously established behavioral paradigm to elicit hypophagia with a conditioned cue for footshocks, and Fos imaging to map activation patterns during this behavior. We found that distinct patterns of recruitment were associated with feeding and fear expression, and that these patterns were similar in males and females except within the medial prefrontal cortex (mPFC). In both sexes, food consumption was associated with activation of cell groups in the central amygdalar nucleus, hypothalamus, and dorsal vagal complex, and exposure to food cues was associated with activation of the anterior basolateral amygdalar nucleus. In contrast, fear expression was associated with activation of the lateral and posterior basomedial amygdalar nuclei. Interestingly, selective recruitment of the mPFC in females, but not in males, was associated with both feeding and freezing behavior, suggesting sex differences in the neuronal processing underlying the competition between feeding and fear. This study provided the first evidence of the neural network mediating fear-induced hypophagia, and important functional activation maps for future interrogation of the underlying neural substrates.

Distinct recruitment of the hippocampal, thalamic, and amygdalar neurons projecting to the prelimbic cortex in male and female rats during context-mediated renewal of responding to food cues

Persistent responding to food cues may underlie the difficulty to resist palatable foods and to maintain healthy eating habits. Renewal of responding after extinction is a model of persistent food seeking that can be used to study the underlying neural mechanisms. In context-mediated renewal, a return to the context in which the initial cue-food learning occurred induces robust responding to the cues that were extinguished elsewhere. Previous work found sex differences in context-mediated renewal and in the recruitment of the ventromedial prefrontal cortex (vmPFC) during that behavior. Males exhibited renewal of responding to food cues and had higher Fos induction in the prelimbic area (PL) of the vmPFC, while females failed to exhibit renewal of responding and had lower Fos induction in the PL. The main aim of the current study was to determine key components of the PL circuitry mediating renewal. The focus was on inputs from three areas important in appetitive associative learning and contextual processing: the amygdala, ventral hippocampal formation, and the paraventricular nucleus of the thalamus. The goal was to determine whether neurons from these areas that send direct projections to the PL (identified with a retrograde tracer) are selectively activated (Fos induction) during renewal and whether they are differently recruited in males and females. The Fos induction patterns demonstrated that the PL-projecting neurons in each of these areas were recruited in a sex-specific way that corresponded to the behavioral differences between males and females. These pathways were selectively activated in the male experimental group-the only group that showed renewal behavior. The findings suggest the pathways from the ventral hippocampal formation, paraventricular nucleus of the thalamus, and basolateral amygdala to the PL mediate renewal in males. The lack of recruitment in females suggests that under activation of these pathways may underlie their lack of renewal.