Cue-induced food seeking after punishment is associated with increased Fos expression in the lateral hypothalamus and basolateral and medial amygdala

Characterization of Sonic Hedgehog transcripts in the adult mouse brain: co-expression with neuronal and oligodendroglial markers

In the adult mammalian brain, astrocytes are proposed to be the major Sonic Hedgehog (Shh)-responsive cells. However, the sources of the Shh molecule mediating activation of the pathway are still poorly characterized. The present work investigates the distribution and phenotype of cells expressing Shh mRNA in the adult mouse brain. Using single-molecule fluorescent in situ hybridization (smfISH), we report much broader expression of Shh transcripts in almost all brain regions than originally reported. We identify Shh mRNA in HuC/D+ neuronal populations, including GABAergic (glutamic acid decarboxylase 67, Gad67), cholinergic (choline acetyltransferase, ChAT), dopaminergic (tyrosine hydroxylase, TH), nitrergic (neuronal nitric oxide synthase, nNOS), and in a small population of oligodendroglial cells expressing Sox10 and Olig2 mRNA transcription factors. Further analysis of Shh mRNA in cerebral cortical and hypothalamic neurons suggests that Shh is also expressed by glutamatergic neurons. Interestingly, we did not observe substantial Desert Hedgehog and Indian Hedgehog mRNA signals, nor Shh signals in S100β+ astrocytes and Iba1+ microglial cells. Collectively, the present work provides the most robust central map of Shh-expressing cells to date and underscores the importance of nitrergic neurons in regulating Shh availability to brain cells. Thus, our study provides a framework for future experiments aimed at better understanding of the functions of Shh signaling in the brain in normal and pathological states, and the characterization of novel regulatory mechanisms of the signaling pathway.

Control of energy homeostasis by the lateral hypothalamic area

The lateral hypothalamic area (LHA) is a subcortical brain region that exerts control over motivated behavior, feeding, and energy balance across species. Recent single-cell sequencing studies have defined at least 30 distinct LHA neuron types. Some of these influence specific aspects of energy homeostasis; however, the functions of many LHA cell types remain unclear. This review addresses the rapidly emerging evidence from cell-type-specific investigations that the LHA leverages distinct neuron populations to regulate energy balance through complex connections with other brain regions. It will highlight recent findings demonstrating that LHA control of energy balance extends beyond mere food intake and propose outstanding questions to be addressed by future research.

Opioid growth factor receptor: Anatomical distribution and receptor colocalization in neurons of the adult mouse brain

The opioid growth factor (OGF) is an endogenous peptide that binds to the nuclear-associated receptor (OGFr), and plays a significant role in the proliferation of developing, renewing, and healing tissues. The receptor is widely expressed in a variety of organs, however its distribution in the brain remains unknown. In this study, we investigated the distribution of OGFr in different brain regions of male heterozygous (-/+ Lepr ^db/J), non -diabetic mice and determined the localization of the receptor in three major brain cell types, astrocytes, microglia, and neurons. Immunofluorescence imaging revealed that the highest number of OGFr was in hippocampal CA3 subregion followed by primary motor cortex, hippocampal CA2, thalamus, caudate and hypothalamus in a descending order. Double immunostaining revealed receptor colocalization with neurons and little or no colocalization in microglia and astrocytes. The highest percentage of OGFr positive neurons was identified in the CA3. Hippocampal CA3 neurons play an important role in memory processing, learning and behavior, and motor cortex neurons are important for muscle movement. However, the significance of the OGFr receptor in these brain regions and its relevance in diseased conditions are not known. Our findings provide a basis for understanding the cellular target and interaction of the OGF- OGFr pathway in neurodegenerative diseases such as Alzheimer's, Parkinson's, and stroke where hippocampus and cortex have an important role. This foundational data may also be useful in drug discovery to modulate OGFr by opioid receptor antagonist in various CNS diseases.

Acute nicotine treatment enhances compulsive-like remifentanil self-administration that persists despite contextual punishment

Opioid use disorder (OUD) and opioid-related deaths remain a significant public health crisis having reached epidemic status globally. OUDs are defined as chronic, relapsing conditions often characterized by compulsive drug seeking despite the deleterious consequences of drug taking. The use of nicotine-containing products has been linked to increased likelihood of prescription opioid misuse, and there exists a significant comorbidity between habitual nicotine use and opioid dependence. In rodent models, nicotine administration nearly doubles the amount of opioids taken in intravenous self-administration paradigms. Here, we examined the effect of acute systemic nicotine administration in male rats on responding for the synthetic opioid remifentanil (RMF) in a contextual punishment paradigm using either an exteroceptive punisher (foot-shock) or an interoceptive punisher (histamine). Nicotine administration, relative to saline, increased RMF intake in both unpunished and punished contexts, regardless of form of punishment, and resulted in significantly higher motivation to obtain RMF in the previously punished context, as measured by progressive ratio breakpoint. Additionally, regardless of context, nicotine-treated rats were slower to extinguish RMF responding following drug removal and displayed higher levels of cue-induced reinstatement than saline-treated controls. Furthermore, these data support that, compared with histamine adulteration, contingent foot-shock is a more potent form of punishment, as histamine punishment failed to support contextual discrimination between the unpunished and punished contexts. In contrast to RMF administration, augmentation of responding for an audiovisual cue by nicotine pretreatment was lost following contextual punishment. In conclusion, acute nicotine administration in adult male rats significantly enhances compulsive-like responding for RMF that persists despite contingent punishment of drug-directed responding.

Sleep dysregulation in binge eating disorder and "food addiction": the orexin (hypocretin) system as a potential neurobiological link

It has been proposed that binge eating reflects a pathological compulsion driven by the "addictive" properties of foods. Proponents of this argument highlight the large degree of phenomenological and diagnostic overlap between binge eating disorder (BED) and substance use disorders (SUDs), including loss of control over how much is consumed and repeated unsuccessful attempts to abstain from consumption, as well as commonalities in brain structures involved in food and drug craving. To date, very little attention has been given to an additional behavioral symptom that BED shares with SUDs-sleep dysregulation-and the extent to which this may contribute to the pathophysiology of BED. Here, we review studies examining sleep outcomes in patients with BED, which collectively point to a heightened incidence of sleep abnormalities in BED. We identify the orexin (hypocretin) system as a potential neurobiological link between compulsive eating and sleep dysregulation in BED, and provide a comprehensive update on the evidence linking this system to these processes. Finally, drawing on evidence from the SUD literature indicating that the orexin system exhibits significant plasticity in response to drugs of abuse, we hypothesize that chronic palatable food consumption likewise increases orexin system activity, resulting in dysregulated sleep/wake patterns. Poor sleep, in turn, is predicted to exacerbate binge eating, contributing to a cycle of uncontrolled food consumption. By extension, we suggest that pharmacotherapies normalizing orexin signaling, which are currently being trialed for the treatment of SUDs, might also have utility in the clinical management of BED.

Choose your path: Divergent basolateral amygdala efferents differentially mediate incentive motivation, flexibility and decision-making

To survive in a complex environment, individuals form associations between environmental stimuli and rewards to organize and optimize reward seeking behaviors. The basolateral amygdala (BLA) uses these learned associations to inform decision-making processes. In this review, we describe functional projections between BLA and its cortical and striatal targets that promote learning and motivational processes central to decision-making. Specifically, we compare and contrast divergent projections from the BLA to the orbitofrontal (OFC) and to the nucleus accumbens (NAc) and examine the roles of these pathways in associative learning, value-guided decision-making, choice behaviors, as well as cue and context-driven drug seeking. Finally, we consider how these projections are involved in disorders of motivation, with a focus on Substance Use Disorder.

Orexin-1 receptor signaling within the lateral hypothalamus, but not bed nucleus of the stria terminalis, mediates context-induced relapse to alcohol seeking

BACKGROUND

The lateral hypothalamic orexin (hypocretin) system has a well-established role in the motivation for reward. This has particular relevance to substance use disorders since orexin-1 receptors play a critical role in alcohol-seeking behavior, acting at multiple nodes in relapse-associated networks.

AIMS

This study aimed to further our understanding of the role of orexin-1 receptor signaling within the lateral hypothalamus and bed nucleus of the stria terminalis, specifically in context-induced relapse to alcohol-seeking following punishment-imposed abstinence.

METHODS

We trained inbred male alcohol-preferring rats to self-administer alcohol in one environment or context (Context A) and subsequently punished their alcohol-reinforced lever presses in a different environment (Context B) using contingent foot shock punishment. Finally, we tested rats for relapse-like behavior in either context following systemic, intra-lateral hypothalamus or intra-bed nucleus of the stria terminalis orexin-1 receptor antagonism with SB-334867.

RESULTS/OUTCOMES

We found that systemic orexin-1 receptor antagonism significantly reduced alcohol-seeking in both contexts. Intra-lateral hypothalamus orexin-1 receptor antagonism significantly reduced alcohol-seeking in Context A whereas intra-bed nucleus of the stria terminalis orexin-1 receptor antagonism had no effect on alcohol-seeking behavior.

CONCLUSIONS/INTERPRETATION

Our results suggest a role for the orexin-1 receptor system in context-induced relapse to alcohol-seeking. Specifically, intra-lateral hypothalamus orexin microcircuits contribute to alcohol-seeking.

Resurgence of punishment-suppressed cocaine seeking in rats

Alternative reinforcement-based treatments are among the most effective for reducing substance abuse. However, relapse often occurs when alternative reinforcement ends. Relapse following the loss of alternative reinforcement is called resurgence. An animal model has been used to study basic factors that may ultimately reduce resurgence but uses drug unavailability (i.e., extinction) to reduce drug seeking. In humans, drug abstinence is thought to be a product of aversive consequences associated with drug use rather than extinction. This discrepancy is important because the environmental and neurobiological factors involved in relapse may differ between punished and extinguished behavior. Experiment 1 evaluated resurgence of previously punished cocaine seeking. In Phase 1, rats earned cocaine for pressing levers. In Phase 2, cocaine remained available, but lever pressing also produced mild foot shocks while an alternative response produced food pellets for 1 group but not for another group. In Phase 3, alternative reinforcement and punishment were removed and resurgence of cocaine seeking occurred only in rats previously exposed to alternative reinforcement. In Experiment 2, resurgence was evaluated similarly, except that consequences of cocaine seeking (i.e., punishment and cocaine) remained available during Phase 3. Resurgence did not occur in either group during Experiment 2. The animal models of resurgence developed herein could increase translational utility and improve examination of the environmental and neurobiological factors underlying resurgence of drug seeking. (PsycInfo Database Record (c) 2020 APA, all rights reserved).

Involvement of orexin/hypocretin in the expression of social play behaviour in juvenile rats

Social play is a highly rewarding and motivated behaviour displayed by juveniles of many mammalian species. We hypothesized that the orexin/hypocretin (ORX) system is involved in the expression of juvenile social play behaviour because this system is interconnected with brain regions that comprise the social behaviour and mesocorticolimbic reward networks. We found that exposure to social play increased recruitment of ORX-A neurons in juvenile rats. Furthermore, central administration of ORX-A decreased social play duration, while central blockade of ORX-1 receptors differentially altered social play duration in juvenile rats with low versus high baseline levels of social play (increasing social play in low baseline social play individuals and decreasing social play in high baseline social play individuals). Together, our results provided the first evidence of a role for the ORX system in the modulation of juvenile social play behaviour.

Food Addiction Symptoms and Amygdala Response in Fasted and Fed States

Few studies have investigated the underlying neural substrates of food addiction (FA) in humans using a recognised assessment tool. In addition, no studies have investigated subregions of the amygdala (basolateral (BLA) and central amygdala), which have been linked to reward-seeking behaviours, susceptibility to weight gain, and promoting appetitive behaviours, in the context of FA. This pilot study aimed to explore the association between FA symptoms and activation in the BLA and central amygdala via functional magnetic resonance imaging (fMRI), in response to visual food cues in fasted and fed states. Females (n = 12) aged 18-35 years completed two fMRI scans (fasted and fed) while viewing high-calorie food images and low-calorie food images. Food addiction symptoms were assessed using the Yale Food Addiction Scale. Associations between FA symptoms and activation of the BLA and central amygdala were tested using bilateral masks and small-volume correction procedures in multiple regression models, controlling for BMI. Participants were 24.1 ± 2.6 years, with mean BMI of 27.4 ± 5.0 kg/m² and FA symptom score of 4.1 ± 2.2. A significant positive association was identified between FA symptoms and higher activation of the left BLA to high-calorie versus low-calorie foods in the fasted session, but not the fed session. There were no significant associations with the central amygdala in either session. This exploratory study provides pilot data to inform future studies investigating the neural mechanisms underlying FA.

Resurgence of a target behavior suppressed by a combination of punishment and alternative reinforcement

Differential-reinforcement-based treatments involving extinction of target problem behavior and reinforcement of an alternative behavior are highly effective. However, extinction of problem behavior is sometimes difficult or contraindicated in clinical settings. In such cases, punishment instead of extinction may be used in combination with alternative reinforcement. Although it is well documented that omitting alternative reinforcement can produce recurrence (i.e., resurgence) of behavior previously suppressed by extinction plus alternative reinforcement, it remains unclear if resurgence similarly occurs for behavior previously suppressed by punishment plus alternative reinforcement. The present experiment examined this question with rats. In Phase 1, a target behavior (lever pressing) was reinforced with food pellets. In Phase 2, the target behavior continued to be reinforced, but it also produced mild foot shock and an alternative behavior (nose poking) also produced food. Finally, all consequences were removed and resurgence of target behavior occurred. Resurgence did not occur for another group that similarly received punishment of target behavior in Phase 2 but not alternative reinforcement. These results indicate that resurgence was a product of the history of exposure to and then removal of alternative reinforcement and that the removal of punishment alone did not produce resurgence of target behavior.

Anterior Insular Cortex is Critical for the Propensity to Relapse Following Punishment-Imposed Abstinence of Alcohol Seeking

Humans with alcohol use disorder typically abstain because of the negative consequences associated with excessive drinking, and exposure to contexts previously associated with alcohol use can trigger relapse. We used a rat model that captures a characteristic of this human condition: namely voluntary abstinence from alcohol use because of contingent punishment. There is substantial variability in the propensity to relapse following extended periods of abstinence, and this is a critical feature preventing the successful treatment of alcohol use disorder. Here we examined relapse following acute or prolonged abstinence. In male alcohol preferring P rats, we found an increased propensity to relapse in Context B, the punishment context after prolonged abstinence. Next, we found that neither alcohol intake history nor the motivational strength of alcohol predicted the propensity to relapse. We next examined the putative circuitry of context-induced relapse to alcohol seeking following prolonged abstinence using Fos as a marker of neuronal activation. The anterior insular cortex (AI) was the only brain region examined where Fos expression correlated with alcohol seeking behavior in Context B after prolonged abstinence. Finally, we used local infusion of GABAA and GABAB receptor agonists (muscimol + baclofen) to show a causal role of the AI in context-induced relapse in Context B, the punishment context after prolonged abstinence. Our results show that there is substantial individual variability in the propensity to relapse in the punishment-associated context after prolonged abstinence, and this is mediated by activity in the AI.SIGNIFICANCE STATEMENT A key feature of alcohol use disorder is that sufferers show an enduring propensity to relapse throughout their lifetime. Relapse typically occurs despite the knowledge of adverse consequences including health complications or relationship breakdowns. Here we use a recently developed rodent model that recapitulates this behavior. After an extended period of abstinence, relapse propensity is markedly increased in the "adverse consequence" environment, akin to humans with alcohol use disorder relapsing in the face of adversity. From a circuitry perspective, we demonstrate a causal role of the anterior insular cortex in relapse to alcohol seeking after extended abstinence following punishment imposed voluntary cessation of alcohol use.

Neuropharmacology of compulsive eating

Compulsive eating behaviour is a transdiagnostic construct observed in certain forms of obesity and eating disorders, as well as in the proposed construct of 'food addiction'. Compulsive eating can be conceptualized as comprising three elements: (i) habitual overeating, (ii) overeating to relieve a negative emotional state, and (iii) overeating despite adverse consequences. Neurobiological processes that include maladaptive habit formation, the emergence of a negative affect, and dysfunctions in inhibitory control are thought to drive the development and persistence of compulsive eating behaviour. These complex psychobehavioural processes are under the control of various neuropharmacological systems. Here, we describe the current evidence implicating these systems in compulsive eating behaviour, and contextualize them within the three elements. A better understanding of the neuropharmacological substrates of compulsive eating behaviour has the potential to significantly advance the pharmacotherapy for feeding-related pathologies.This article is part of a discussion meeting issue 'Of mice and mental health: facilitating dialogue between basic and clinical neuroscientists'.

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.