Cannabinoid in the nucleus accumbens enhances the intake of palatable solution

Reduced menthol sensitivity in a prodromal Parkinson's disease model induced by intranasal rotenone treatment

Parkinson's disease (PD) is a neurodegenerative disorder characterized by motor symptoms, and it is associated with several prodromal non-motor symptoms, including an impaired sense of smell, taste and touch. We previously reported that bitter taste impairments occur independently of olfactory impairments in an early-stage PD animal model using short-term intranasal rotenone-treated mice. Cool temperatures also affect bitter taste perception, but it remains unclear whether or not bitter taste impairments result from an altered sensitivity for intraoral cool stimuli. We examined disturbances in the intraoral menthol sensitivity, such as coolness at low concentrations of menthol, using a brief-access test. Once a day, one solution from the 7-concentration series of (-)-menthol (0-2.3 mM) or the bitter taste quinine-HCl (0.3 mM) was randomly presented 20 times for 10 s to water-deprived mice before and 1 week after rotenone treatment. The total number of licks within 20 times was significantly decreased with the presentation of 2.3 mM menthol and quinine-HCl, compared to distilled water in untreated mice, but not in rotenone-treated mice. The correlation between the licks for quinine-HCl and that for menthol was increased after rotenone treatment. In contrast, the 2-bottle choice test for 48 h clarified that menthol sensitivity was increased after rotenone treatment. Furthermore, a thermal place preference test revealed that seeking behavior toward a cold-floored room was increased in the rotenone-treated mice despite the unchanged plantar cutaneous cold sensitivity. These results suggest that taste impairments in this model mice are at least partly due to intraoral somatosensory impairments, accompanied by peripheral/central malfunction.

The conserved endocannabinoid anandamide modulates olfactory sensitivity to induce hedonic feeding in C. elegans

The ability of cannabis to increase food consumption has been known for centuries. In addition to producing hyperphagia, cannabinoids can amplify existing preferences for calorically dense, palatable food sources, a phenomenon called hedonic amplification of feeding. These effects result from the action of plant-derived cannabinoids that mimic endogenous ligands called endocannabinoids. The high degree of conservation of cannabinoid signaling at the molecular level across the animal kingdom suggests hedonic feeding may also be widely conserved. Here, we show that exposure of Caenorhabditis elegans to anandamide, an endocannabinoid common to nematodes and mammals, shifts both appetitive and consummatory responses toward nutritionally superior food, an effect analogous to hedonic feeding. We find that anandamide's effect on feeding requires the C. elegans cannabinoid receptor NPR-19 but can also be mediated by the human CB1 cannabinoid receptor, indicating functional conservation between the nematode and mammalian endocannabinoid systems for the regulation of food preferences. Furthermore, anandamide has reciprocal effects on appetitive and consummatory responses to food, increasing and decreasing responses to inferior and superior foods, respectively. Anandamide's behavioral effects require the AWC chemosensory neurons, and anandamide renders these neurons more sensitive to superior foods and less sensitive to inferior foods, mirroring the reciprocal effects seen at the behavioral level. Our findings reveal a surprising degree of functional conservation in the effects of endocannabinoids on hedonic feeding across species and establish a new system to investigate the cellular and molecular basis of endocannabinoid system function in the regulation of food choice.

Hypothalamic endocannabinoids in obesity: an old story with new challenges

The crucial role of the hypothalamus in the pathogenesis of obesity is widely recognized, while the precise molecular and cellular mechanisms involved are the focus of intense research. A disrupted endocannabinoid system, which critically modulates feeding and metabolic functions, through central and peripheral mechanisms, is a landmark indicator of obesity, as corroborated by investigations centered on the cannabinoid receptor CB1, considered to offer promise in terms of pharmacologically targeted treatment for obesity. In recent years, novel insights have been obtained, not only into relation to the mode of action of CB receptors, but also CB ligands, non-CB receptors, and metabolizing enzymes considered to be part of the endocannabinoid system (particularly the hypothalamus). The outcome has been a substantial expansion in knowledge of this complex signaling system and in drug development. Here we review recent literature, providing further evidence on the role of hypothalamic endocannabinoids in regulating energy balance and the implication for the pathophysiology of obesity. We discuss how these lipids are dynamically regulated in obesity onset, by diet and metabolic hormones in specific hypothalamic neurons, the impact of gender, and the role of endocannabinoid metabolizing enzymes as promising targets for tackling obesity and related diseases.

Adolescent neurodevelopment and substance use: Receptor expression and behavioral consequences

Adolescence is the transitional period between childhood and adulthood, during which extensive brain development occurs. Since this period also overlaps with the initiation of drug use, it is important to consider how substance use during this time might produce long-term neurobiological alterations, especially against the backdrop of developmental changes in neurotransmission. Alcohol, cannabis, nicotine, and opioids all produce marked changes in the expression and function of the neurotransmitter and receptor systems with which they interact. These acute and chronic alterations also contribute to behavioral consequences ranging from increased addiction risk to cognitive or neuropsychiatric behavioral dysfunctions. The current review provides an in-depth overview and update of the developmental changes in neurotransmission during adolescence, as well as the impact of drug exposure during this neurodevelopmental window. While most of these factors have been studied in animal models, which are the focus of this review, future longitudinal studies in humans that assess neural function and behavior will help to confirm pre-clinical findings. Furthermore, the neural changes induced by each drug should also be considered in the context of other contributing factors, such as sex. Further understanding of these consequences can help in the identification of novel approaches for preventing and reversing the neurobiological effects of adolescent substance use.

Combined ∆9-tetrahydrocannabinol and moderate alcohol administration: effects on ingestive behaviors in adolescent male rats

RATIONALE

Whereas co-use of alcohol and marijuana is prevalent in adolescents, the effects of such drug co-exposure on ingestive and cognitive behaviors remain largely unexplored. We hypothesized that co-exposure to alcohol and ∆⁹-tetrahydrocannabinol (THC), the main psychoactive constitute of marijuana, alters feeding behavior and cognition differently from either drug alone.

METHODS

Male rats received daily THC (3-20 mg/kg/day) or oil vehicle through subcutaneous injection or consumption of a cookie with access to saccharin or saccharin-sweetened alcohol during adolescence (P30-45). Barnes maze and sucrose preference tests were applied to assess spatial memory and behavioral flexibility and abstinence-related anhedonia, respectively.

RESULTS

Subcutaneous THC did not affect alcohol intake but dose-dependently increased acute (3 h) chow intake and reduced weight gain. Moderate alcohol consumption reduced the acute hyperphagic effect of subcutaneous THC. By contrast, oral THC at a dose > 5 mg/kg robustly reduced alcohol intake without affecting 3-h chow intake. At this dose, some rats stopped consuming the THC-laced cookies. Furthermore, oral THC reduced weight gain, and co-exposure to alcohol alleviated this effect. Chronic subcutaneous, but not oral, THC reduced sucrose intake during abstinence. Neither treatment impaired cognitive behaviors in the Barnes maze.

CONCLUSION

Moderate alcohol and THC consumption can interact to elicit unique outcomes on ingestive behaviors and energy balance. Importantly, this study established a novel model of voluntary alcohol and THC consumption for studying mechanisms underlying the consequences of adolescent onset co-use of the two drugs.

Effects of an early life experience on rat brain cannabinoid receptors in adolescence and adulthood

Neonatal handling is an experimental model of early life experience associated with resilience in later life challenges, altering the ability of animals to respond to stress. The endocannabinoid system of the brain modulates the neuroendocrine and behavioral effects of stress, while this system is also capable of being modulated by stress exposure itself. The present study has addressed the question of whether neonatal handling in rats could affect cannabinoid receptors, in an age- and sex-dependent manner, using in situ hybridization and receptor binding techniques. Different effects of neonatal handling were observed in adolescent and adult brain on CB1 receptor mRNA and [3H]CP55,940 binding levels, which in some cases were sexually dimorphic. Neonatal handling interfered in the developmental trajectories of CB1 receptor mRNA levels in striatum and amygdaloid nuclei, as well as of [3H]CP55,940 binding levels in almost all regions studied. Adult handled rats showed reduced [3H]CP55,940 binding levels in the prefrontal cortex, striatum, nucleus accumbens and basolateral amygdala, while binding levels in prefrontal cortex of adolescent handled rats were increased. Finally, handling resulted in decreases in female [3H]CP55,940 binding levels in the striatum, nucleus accumbens, CA3 and DG of dorsal hippocampus and basolateral amygdala. Our results suggest that a brief and repeated maternal separation during the neonatal period induces changes on cannabinoid receptors differently manifested between adolescence and adulthood, male and female brain, which could be correlated to their stress response.

Hedonic Eating and the "Delicious Circle": From Lipid-Derived Mediators to Brain Dopamine and Back

Palatable food can be seductive and hedonic eating can become irresistible beyond hunger and negative consequences. This is witnessed by the subtle equilibrium between eating to provide energy intake for homeostatic functions, and reward-induced overeating. In recent years, considerable efforts have been devoted to study neural circuits, and to identify potential factors responsible for the derangement of homeostatic eating toward hedonic eating and addiction-like feeding behavior. Here, we examined recent literature on “old” and “new” players accountable for reward-induced overeating and possible liability to eating addiction. Thus, the role of midbrain dopamine is positioned at the intersection between selected hormonal signals involved in food reward information processing (namely, leptin, ghrelin, and insulin), and lipid-derived neural mediators such as endocannabinoids. The impact of high fat palatable food and dietary lipids on endocannabinoid formation is reviewed in its pathogenetic potential for the derangement of feeding homeostasis. Next, endocannabinoid signaling that regulates synaptic plasticity is discussed as a key mechanism acting both at hypothalamic and mesolimbic circuits, and affecting both dopamine function and interplay between leptin and ghrelin signaling. Outside the canonical hypothalamic feeding circuits involved in energy homeostasis and the notion of “feeding center,” we focused on lateral hypothalamus as neural substrate able to confront food-associated homeostatic information with food salience, motivation to eat, reward-seeking, and development of compulsive eating. Thus, the lateral hypothalamus-ventral tegmental area-nucleus accumbens neural circuitry is reexamined in order to interrogate the functional interplay between ghrelin, dopamine, orexin, and endocannabinoid signaling. We suggested a pivotal role for endocannabinoids in food reward processing within the lateral hypothalamus, and for orexin neurons to integrate endocrine signals with food reinforcement and hedonic eating. In addition, the role played by different stressors in the reinstatement of preference for palatable food and food-seeking behavior is also considered in the light of endocannabinoid production, activation of orexin receptors and disinhibition of dopamine neurons. Finally, type-1 cannabinoid receptor-dependent inhibition of GABA-ergic release and relapse to reward-associated stimuli is linked to ghrelin and orexin signaling in the lateral hypothalamus-ventral tegmental area-nucleus accumbens network to highlight its pathological potential for food addiction-like behavior.

Oleoylethanolamide: The role of a bioactive lipid amide in modulating eating behaviour

Fatty acid ethanolamides are lipid mediators that regulate a plethora of physiological functions. One such bioactive lipid mediator, oleoylethanolamide (OEA), is a potent agonist of the peroxisome proliferator-activated receptor-alpha (PPAR-α), which modulates increased expression of the fatty acid translocase CD36 that enables the regulation of feeding behaviour. Consumption of dietary fat rich in oleic acid activates taste receptors in the gut activating specific enzymes that lead to the formation of OEA. OEA further combines with PPAR-α to enable fat oxidation in the liver, resulting in enhanced energy production. Evidence suggests that sustained ingestion of a high-fat diet abolishes the anorexic signal of OEA. Additionally, malfunction of the enterocyte that transforms oleic acid produced during fat digestion into OEA might be responsible for reduced satiety and hyperphagia, resulting in overweight and obesity. Thus, OEA anorectic signalling may be an essential element of the physiology and metabolic system regulating dietary fat intake and obesity. The evidence reviewed in this article indicates that intake of oleic acid, and thereby the resulting OEA imparting anorexic properties, is dependent on CD36, PPAR-α, enterocyte fat sensory receptors, histamine, oxytocin and dopamine; leading to increased fat oxidation and enhanced energy expenditure to induce satiety and increase feeding latency; and that a disruption in any of these systems will cease/curb fat-induced satiety.

Adolescent cannabinoid exposure effects on natural reward seeking and learning in rats

RATIONALE

Adolescence is characterized by endocannabinoid (ECB)-dependent refinement of neural circuits underlying emotion, learning, and motivation. As a result, adolescent cannabinoid receptor stimulation (ACRS) with phytocannabinoids or synthetic agonists like "Spice" cause robust and persistent changes in both behavior and circuit architecture in rodents, including in reward-related regions like medial prefrontal cortex and nucleus accumbens (NAc).

OBJECTIVES AND METHODS

Here, we examine persistent effects of ACRS with the cannabinoid receptor 1/2 specific agonist WIN55-212,2 (WIN; 1.2 mg/kg/day, postnatal day (PD) 30-43), on natural reward-seeking behaviors and ECB system function in adult male Long Evans rats (PD 60+).

RESULTS

WIN ACRS increased palatable food intake, and altered attribution of incentive salience to food cues in a sign-/goal-tracking paradigm. ACRS also blunted hunger-induced sucrose intake, and resulted in increased anandamide and oleoylethanolamide levels in NAc after acute food restriction not seen in controls. ACRS did not affect food neophobia or locomotor response to a novel environment, but did increase preference for exploring a novel environment.

CONCLUSIONS

These results demonstrate that ACRS causes long-term increases in natural reward-seeking behaviors and ECB system function that persist into adulthood, potentially increasing liability to excessive natural reward seeking later in life.

Orexin in Rostral Hotspot of Nucleus Accumbens Enhances Sucrose 'Liking' and Intake but Scopolamine in Caudal Shell Shifts 'Liking' Toward 'Disgust' and 'Fear'

The nucleus accumbens (NAc) contains a hedonic hotspot in the rostral half of medial shell, where opioid agonist microinjections are known to enhance positive hedonic orofacial reactions to the taste of sucrose ('liking' reactions). Within NAc shell, orexin/hypocretin also has been reported to stimulate food intake and is implicated in reward, whereas blockade of muscarinic acetylcholine receptors by scopolamine suppresses intake and may have anti-reward effects. Here, we show that NAc microinjection of orexin-A in medial shell amplifies the hedonic impact of sucrose taste, but only within the same anatomically rostral site, identical to the opioid hotspot. By comparison, at all sites throughout medial shell, orexin microinjections stimulated 'wanting' to eat, as reflected by increases in intake of palatable sweet chocolates. At NAc shell sites outside the hotspot, orexin selectively enhanced 'wanting' to eat without enhancing sweetness 'liking' reactions. In contrast, microinjections of the antagonist scopolamine at all sites in NAc shell suppressed sucrose 'liking' reactions as well as suppressing intake of palatable food. Conversely, scopolamine increased aversive 'disgust' reactions elicited by bitter quinine at all NAc shell sites. Finally, scopolamine microinjections localized to the caudal half of medial shell additionally generated a fear-related anti-predator reaction of defensive treading and burying directed toward the corners of the transparent chamber. Together, these results confirm a rostral hotspot in NAc medial shell as a unique site for orexin induction of hedonic 'liking' enhancement, similar to opioid enhancement. They also reveal distinct roles for orexin and acetylcholine signals in NAc shell for hedonic reactions and motivated behaviors.

Quantitative analysis of performance on a progressive-ratio schedule: effects of reinforcer type, food deprivation and acute treatment with Δ⁹-tetrahydrocannabinol (THC)

Rats' performance on a progressive-ratio schedule maintained by sucrose (0.6M, 50 μl) and corn oil (100%, 25 μl) reinforcers was assessed using a model derived from Killeen's (1994) theory of schedule-controlled behaviour, 'Mathematical Principles of Reinforcement'. When the rats were maintained at 80% of their free-feeding body weights, the parameter expressing incentive value, a, was greater for the corn oil than for the sucrose reinforcer; the response-time parameter, δ, did not differ between the reinforcer types, but a parameter derived from the linear waiting principle (T0), indicated that the minimum post-reinforcement pause was longer for corn oil than for sucrose. When the rats were maintained under free-feeding conditions, a was reduced, indicating a reduction of incentive value, but δ was unaltered. Under the food-deprived condition, the CB1 cannabinoid receptor agonist Δ(9)-tetrahydrocannabinol (THC: 0.3, 1 and 3 mg kg(-1)) increased the value of a for sucrose but not for corn oil, suggesting a selective enhancement of the incentive value of sucrose; none of the other parameters was affected by THC. The results provide new information about the sensitivity of the model's parameters to deprivation and reinforcer quality, and suggest that THC selectively enhances the incentive value of sucrose.

The endocannabinoid system and appetite: relevance for food reward

Mounting evidence substantiates the central role of the endocannabinoid system (ECS) in the modulation of both homeostatic and hedonic elements of appetite and food intake. Conversely, feeding status and dietary patterns directly influence activity of the ECS. Following a general introduction on the functioning of the ECS, the present review specifically addresses its role in the modulation of hedonic eating. Humans possess strong motivational systems triggered by rewarding aspects of food. Food reward is comprised of two components: one appetitive (orienting towards food); the other consummatory (hedonic evaluation), also referred to as 'wanting' and 'liking', respectively. Endocannabinoid tone seems to influence both the motivation to feed and the hedonic value of foods, probably by modifying palatability. Human physiology underlying hedonic eating is still not fully understood. A better understanding of the role of the ECS in the rewarding value of specific foods or diets could offer new possibilities to optimise the balance between energy and nutrient intake for different target groups. These groups include the obese and overweight, and potentially individuals suffering from malnutrition. Examples for the latter group are patients with disease-related anorexia, as well as the growing population of frail elderly suffering from persistent loss of food enjoyment and appetite resulting in malnutrition and involuntary weight loss. It has become clear that the psychobiology of food hedonics is extremely complex and the clinical failure of CB1 inverse agonists including rimonabant (Accomplia®) has shown that 'quick wins' in this field are unlikely.

Principles of motivation revealed by the diverse functions of neuropharmacological and neuroanatomical substrates underlying feeding behavior

Circuits that participate in specific subcomponents of feeding (e.g., gustatory perception, peripheral feedback relevant to satiety and energy balance, reward coding, etc.) are found at all levels of the neural axis. Further complexity is conferred by the wide variety of feeding-modulatory neurotransmitters and neuropeptides that act within these circuits. An ongoing challenge has been to refine the understanding of the functional specificity of these neurotransmitters and circuits, and there have been exciting advances in recent years. We focus here on foundational work of Dr. Ann Kelley that identified distinguishable actions of striatal opioid peptide modulation and dopamine transmission in subcomponents of reward processing. We also discuss her work in overlaying these neuropharmacological effects upon anatomical pathways that link the telencephalon (cortex and basal ganglia) with feeding-control circuits in the hypothalamus. Using these seminal contributions as a starting point, we will discuss new findings that expand our understanding of (1) the specific, differentiable motivational processes that are governed by central dopamine and opioid transmission, (2) the manner in which other striatal neuromodulators, specifically acetylcholine, endocannabinoids and adenosine, modulate these motivational processes (including via interactions with opioid systems), and (3) the organization of the cortical-subcortical network that subserves opioid-driven feeding. The findings discussed here strengthen the view that incentive-motivational properties of food are coded by substrates and neural circuits that are distinguishable from those that mediate the acute hedonic experience of food reward. Striatal opioid transmission modulates reward processing by engaging frontotemporal circuits, possibly via a hypothalamic-thalamic axis, that ultimately impinges upon hypothalamic modules dedicated to autonomic function and motor pattern control. We will conclude by discussing implications for understanding disorders of "non-homeostatic" feeding.

Endocannabinoids in amygdala and nucleus accumbens mediate social play reward in adolescent rats

The brain endocannabinoid system plays a crucial role in emotional processes. We have previously identified an important role for endocannabinoids in social play behavior, a highly rewarding form of social interaction in adolescent rats. Here, we tested the hypothesis that endocannabinoid modulation of social play behavior occurs in brain regions implicated in emotion and motivation. Social play increased levels of the endocannabinoid anandamide in the amygdala and nucleus accumbens (NAc), but not in prefrontal cortex or hippocampus of 4- to 5-week-old male Wistar rats. Furthermore, social play increased phosphorylation of CB1 cannabinoid receptors in the amygdala. Systemic administration of the anandamide hydrolysis inhibitor URB597 increased social play behavior, and augmented the associated elevation in anandamide levels in the amygdala, but not the NAc. Infusion of URB597 into the basolateral amygdala (BLA) increased social play behavior, and blockade of BLA CB1 cannabinoid receptors with the antagonist/inverse agonist SR141716A prevented the play-enhancing effects of systemic administration of URB597. Infusion of URB597 into the NAc also increased social play, but blockade of NAc CB1 cannabinoid receptors did not antagonize the play-enhancing effects of systemic URB597 treatment. Last, SR141716A did not affect social play after infusion into the core and shell subregions of the NAc, while it reduced social play when infused into the BLA. These data show that increased anandamide signaling in the amygdala and NAc augments social play, and identify the BLA as a prominent site of action for endocannabinoids to modulate the rewarding properties of social interactions in adolescent rats.

Stimulation of accumbens shell cannabinoid CB(1) receptors by noladin ether, a putative endocannabinoid, modulates food intake and dietary selection in rats

Stimulation of cannabinoid CB(1) receptors in nucleus accumbens shell has been shown to stimulate feeding and enhance positive 'liking' reactions to intraoral sucrose. This study examined the behavioural effects of noladin ether and 2-arachidonoylglycerol following infusion into accumbens shell, on chow intake and food preference in high-carbohydrate and high-fat preferring rats. Noladin ether, potently and dose-dependently stimulated chow intake as compared with 2-arachidonoylglycerol in free-feeding rats. In the diet preference paradigm, in which rats were given free access to both, high-carbohydrate (HC) and high-fat (HF) diets simultaneously, an intra-accumbens administration of noladin ether as well as 2-arachidonoylglycerol, preferentially enhanced fat consumption over carbohydrate in both HF- and HC-preferring rats. These effects were significantly attenuated by the CB(1) receptor antagonist, AM 251. These results suggesting that, the endocannabinoids through CB(1) receptors, affects appetite for specific dietary components. Both these agents exert a specific action on eating motivation and possibly promoting eating by enhancing the incentive value of food. Altogether these findings reinforce the idea that the endogenous cannabinoid system in the accumbens shell may be important to augment reward-driven feeding via modulation of CB(1) receptor signalling pathways.

The thrifty lipids: endocannabinoids and the neural control of energy conservation

The 'thrifty gene hypothesis' posits that evolution preferentially selects physiological mechanisms that optimize energy storage to increase survival under alternating conditions of abundance and scarcity of food. Recent experiments suggest that endocannabinoids - a class of lipid-derived mediators that activate cannabinoid receptors in many cells of the body - are key agents of energy conservation. The new evidence indicates that these compounds increase energy intake and decrease energy expenditure by controlling the activity of peripheral and central neural pathways involved in the sensing and hedonic processing of sweet and fatty foods, as well as in the storage of their energy content for future use.

The endocannabinoid system: role in energy regulation

Cannabis sativa has been used since antiquity to treat many ailments, including eating disorders. The primary psychoactive constituent of this plant, Δ(9) -tetrahydrocannabinol (THC) is an FDA approved medication to treat nausea and emesis caused by cancer chemotherapeutic agents as well as to stimulate appetite in AIDS patients suffering from cachexia. The effects of THC are mediated through the endocannabinoid system (ECS), which promotes a positive energy balance through stimulation of appetite as well as shifting homeostatic mechanisms toward energy storage. Here we discuss the physiological function of the ECS in energy balance and the therapeutic potential of targeting this system.

CB1 receptors modulate the intake of a sweetened-fat diet in response to μ-opioid receptor stimulation of the nucleus accumbens

Previous research has demonstrated that concurrent systemic administration of CB(1) cannabinoid and mu-opioid receptor agonists increases feeding in rats. However, the possible neural loci of this cooperative effect have yet to be identified. These studies tested whether the nucleus accumbens shell may be one site of the interactive effects of opioid and cannabinoid ligands on feeding. Injection of the mu-opioid agonist DAMGO (at 0, 0.025, 0.25, or 2.5 µg/0.5 µl/side) directly into the rat nucleus accumbens shell increased feeding on a sweetened-fat diet, and this effect was blocked by pretreatment with either the mu-opioid antagonist naltrexone (20 µg/0.5 µl/side) or the CB(1) antagonist SR141716 (0.5 µg/0.5 µl/side). Activation of nucleus accumbens shell CB(1) receptors with WIN55212-2 alone (at 0.1 or 0.5 µg/0.5 µl/side) had no apparent effect on food intake. However, local injections of the low dose of DAMGO (.025 µg/0.5 µl/side) in this region along with WIN55212-2 (at 0.25 or 0.50 µg/0.5 µl/side) increased feeding above that induced by DAMGO alone. These data suggest an important modulatory role for cannabinoid receptors in the expression of feeding behaviors in response to mu-opioid receptor activation of the nucleus accumbens shell.

Shared brain vulnerabilities open the way for nonsubstance addictions: carving addiction at a new joint?

For more than half a century, since the beginning of formal diagnostics, our psychiatric nosology has compartmentalized the compulsive pursuit of substance (e.g., alcohol, cocaine, heroin, nicotine) from nonsubstance (e.g., gambling, food, sex) rewards. Emerging brain, behavioral, and genetic findings challenge this diagnostic boundary, pointing to shared vulnerabilities underlying the pathological pursuit of substance and nonsubstance rewards. Working groups for the fifth revision of the Diagnostic and Statistical Manual of Mental Disorders, fifth edition (DSM-V), are thus considering whether the nosologic boundaries of addiction should be redrawn to include nonsubstance disorders, such as gambling. This review discusses how neurobiological data from problem gambling, obesity, and "normal" states of attachment (romantic infatuation, sexual attraction, maternal bonds) may help us in the task of carving addictions "at a new joint." Diagnostic recarving may have a positive effect on addiction research, stimulating discovery of "crossover" pharmacotherapies with benefit for both substance and nonsubstance addictions.