Effect of opioid antagonism on conditioned place preferences to snack foods

Endogenous opioid modulation of food intake and body weight: Implications for opioid influences upon motivation and addiction

This review is part of a special issue dedicated to Opioid addiction, and examines the influential role of opioid peptides, opioid receptors and opiate drugs in mediating food intake and body weight control in rodents. This review postulates that opioid mediation of food intake was an example of "positive addictive" properties that provide motivational drives to maintain opioid-seeking behavior and that are not subject to the "negative addictive" properties associated with tolerance, dependence and withdrawal. Data demonstrate that opiate and opioid peptide agonists stimulate food intake through homeostatic activation of sensory, metabolic and energy-related In contrast, general, and particularly mu-selective, opioid receptor antagonists typically block these homeostatically-driven ingestive behaviors. Intake of palatable and hedonic food stimuli is inhibited by general, and particularly mu-selective, opioid receptor antagonists. The selectivity of specific opioid agonists to elicit food intake was confirmed through the use of opioid receptor antagonists and molecular knockdown (antisense) techniques incapacitating specific exons of opioid receptor genes. Further extensive evidence demonstrated that homeostatic and hedonic ingestive situations correspondingly altered the levels and expression of opioid peptides and opioid receptors. Opioid mediation of food intake was controlled by a distributed brain network intimately related to both the appetitive-consummatory sites implicated in food intake as well as sites intimately involved in reward and reinforcement. This emergent system appears to sustain the "positive addictive" properties providing motivational drives to maintain opioid-seeking behavior.

Influence of the fat/carbohydrate component of snack food on energy intake pattern and reinforcing properties in rodents

Hedonic intake of strongly rewarding foods is independent from biological needs and, thus, a common cause of obesity. The effect of potato chips on energy intake in a snacking model could be explained by their fat/carbohydrate content (FCHc). The present study investigated if the FCHc shapes energy intake patterns and reward processing of satiated rodents. Modulation of energy intake patterns was studied in an established snacking model offering FCHc rich food for 3 × 10 min/day to satiated rats. Reward processing was analyzed by a previously established conditioned place preference tests in satiated mice. The limited access to FCHc rich food led to higher daily energy intake compared to days without access (110 ± 10 vs. 96 ± 5 kcal/day) indicating that fat/carbohydrate intake was not fully compensated by reducing standard chow intake during the rest of the day. Furthermore, fat/carbohydrate snacking led to binge eating episodes with up to 55% of the daily energy intake consumed during limited access. Forced withdrawal from fat/carbohydrate snacking opportunities for six weeks increased the total daily energy intake and the relative amount of energy consumed by FCHc after reintroducing fat/carbohydrate snacking. Snack food and fat/carbohydrate food were powerful food reinforcers in satiated mice in contrast to standard chow. Altogether, these data suggest that the FCHc of snack food has strong reinforcing properties, which are probably responsible for the significant modulation of the amount and pattern of food intake in ad libitum fed animals.

Food-induced reinforcement is abrogated by the genetic deletion of the MT1 or MT2 melatonin receptor in C3H/HeN mice

Palatable food is known for its ability to enhance reinforcing responses. Studies have suggested a circadian variation in both drug and natural reinforcement, with each following its own time course. The goal of this study was to determine the role of the MT1 and MT2 melatonin receptors in palatable snack food-induced reinforcement, as measured by the conditioned place preference (CPP) paradigm during the light and dark phases. C3H/HeN wild-type mice were trained for snack food-induced CPP at either ZT 6 - 8 (ZT: Zeitgeber time; ZT 0 = lights on), when endogenous melatonin levels are low, or ZT 19 - 21, when melatonin levels are high. These time points also correspond to the high and low points for expression of the circadian gene Period1, respectively. The amount of snack food (chow, Cheetos®, Froot Loops® and Oreos®) consumed was of similar magnitude at both times, however only C3H/HeN mice conditioned to snack food at ZT 6 - 8 developed a place preference. C3H/HeN mice with a genetic deletion of either the MT1 (MT1KO) or MT2 (MT2KO) receptor tested at ZT 6 - 8 did not develop a place preference for snack food. Although the MT2KO mice showed a similar amount of snack food consumed when compared to wild-type mice, the MT1KO mice consumed significantly less than either genotype. We conclude that in our mouse model snack food-induced CPP is dependent on time of day and the presence of the MT1 or MT2 receptors, suggesting a role for melatonin and its receptors in snack food-induced reinforcement.

Casein kinase 1-epsilon deletion increases mu opioid receptor-dependent behaviors and binge eating1

Genetic and pharmacological studies indicate that casein kinase 1 epsilon (Csnk1e) contributes to psychostimulant, opioid, and ethanol motivated behaviors. We previously used pharmacological inhibition to demonstrate that Csnk1e negatively regulates the locomotor stimulant properties of opioids and psychostimulants. Here, we tested the hypothesis that Csnk1e negatively regulates opioid and psychostimulant reward using genetic inhibition and the conditioned place preference assay in Csnk1e knockout mice. Similar to pharmacological inhibition, Csnk1e knockout mice showed enhanced opioid-induced locomotor activity with the mu opioid receptor agonist fentanyl (0.2 mg/kg i.p.) as well as enhanced sensitivity to low-dose fentanyl reward (0.05 mg/kg). Interestingly, female knockout mice also showed a markedly greater escalation in consumption of sweetened palatable food - a behavioral pattern consistent with binge eating that also depends on mu opioid receptor activation. No difference was observed in fentanyl analgesia in the 52.5°C hot plate assay (0-0.4 mg/kg), naloxone conditioned place aversion (4 mg/kg), or methamphetamine conditioned place preference (0-4 mg/kg). To identify molecular adaptations associated with increased drug and food behaviors in knockout mice, we completed transcriptome analysis via mRNA sequencing of the striatum. Enrichment analysis identified terms associated with myelination and axon guidance and pathway analysis identified a differentially expressed gene set predicted to be regulated by the Wnt signaling transcription factor, Tcf7l2. To summarize, Csnk1e deletion increased mu opioid receptor-dependent behaviors, supporting previous studies indicating an endogenous negative regulatory role of Csnk1e in opioid behavior.

An Open Trial Targeting Food Cue Reactivity and Satiety Sensitivity in Overweight and Obese Binge Eaters

Data suggests that individuals who binge eat are more responsive to food cues in the environment and less sensitive to satiety cues. The aim of this open trial was to evaluate the feasibility, acceptability, and initial effectiveness of a novel treatment grounded in Schachter's externality theory targeting food cue reactivity and satiety responsiveness with obese adults who binge eat. Treatment was provided in groups, and utilized appetite monitoring, cue-exposure treatment, in vivo exercises, self-monitoring, and coping skills. Twenty-eight overweight and obese adults who binge eat (82% female; mean age = 47.5 years [SD = 12.8]; BMI = 38.9 [SD = 10.3]; 79% White non-Hispanic) participated in a 4-month group-based treatment program. Assessments were conducted at baseline, posttreatment, and 3-month follow-up time points. Results indicated that this treatment was well accepted and had high retention at posttreatment. Initial effectiveness showed significant decreases in BMI, and improvements in loss of control and overeating episodes, food responsiveness, and power of food. The majority of results were maintained at the 3-month follow-up time point. This open trial provides preliminary evidence for the feasibility, acceptability, and initial effectiveness of this treatment on both eating disorder symptoms and weight in obese adults who binge eat. Because these data are preliminary, further treatment development and randomized controlled studies are needed.

Endogenous opioids and feeding behavior: A decade of further progress (2004-2014). A Festschrift to Dr. Abba Kastin

Functional elucidation of the endogenous opioid system temporally paralleled the creation and growth of the journal, Peptides, under the leadership of its founding editor, Dr. Abba Kastin. He was prescient in publishing annual and uninterrupted reviews on Endogenous Opiates and Behavior that served as a microcosm for the journal under his stewardship. This author published a 2004 review, "Endogenous opioids and feeding behavior: a thirty-year historical perspective", summarizing research in this field between 1974 and 2003. The present review "closes the circle" by reviewing the last 10 years (2004-2014) of research examining the role of endogenous opioids and feeding behavior. The review summarizes effects upon ingestive behavior following administration of opioid receptor agonists, in opioid receptor knockout animals, following administration of general opioid receptor antagonists, following administration of selective mu, delta, kappa and ORL-1 receptor antagonists, and evaluating opioid peptide and opioid receptor changes in different food intake models.

Snack food intake in ad libitum fed rats is triggered by the combination of fat and carbohydrates

Snack food like potato chips substantially contributes to energy intake in humans. In contrast to basic food, snacks are consumed additionally to other meals and may thereby lead to non-homeostatic energy intake. Snack food is also frequently associated with hedonic hyperphagia, a food intake independent from hunger. Analysis of brain activity patterns by manganese-enhanced MRI has previously revealed that the intake of potato chips in ad libitum fed rats strongly activates the reward system of the rat brain, which may lead to hedonic hyperphagia. The purpose of the present study was to develop a two-choice preference test to identify molecular determinants of snack food triggering extra food intake in ad libitum fed rats. Different kinds of test food were presented three times a day for 10 min each time. To minimize the influence of organoleptic properties, each test food was applied in a homogenous mixture with standard chow. Food intake as well as food intake-related locomotor activity were analyzed to evaluate the effects induced by the test foods in the two-choice preference test. In summary, fat (F), carbohydrates (CH), and a mixture of fat and carbohydrates (FCH) led to a higher food intake compared to standard chow. Notably, potato chip test food (PC) was highly significantly preferred over standard chow (STD) and also over their single main macronutrients F and CH. Only FCH induced an intake comparable to PC. Despite its low energy density, fat-free potato chip test food (ffPC) was also significantly preferred over STD and CH, but not over F, FCH, and PC. Thus, it can be concluded that the combination of fat and carbohydrates is a major molecular determinant of potato chips triggering hedonic hyperphagia. The applied two-choice preference test will facilitate future studies on stimulating and suppressive effects of other food components on non-homeostatic food intake.

Critical role of NMDA but not opioid receptors in the acquisition of fat-conditioned flavor preferences in rats

Animals learn to prefer flavors associated with the intake of dietary fats such as corn oil (CO) solutions. We previously reported that fat-conditioned flavor preferences in rats were relatively unaffected by systemic treatment with dopamine D1 and D2 antagonsits. The present study examined whether systemic opioid (naltrexone, NTX) or NMDA (MK-801) receptor antagonists altered the acquisition and/or expression of CO-CFP. The CFP was produced by training rats to drink one novel flavor (CS+, e.g., cherry) mixed in a 3.5% CO solution and another flavor (CS-, e.g., grape) in a 0.9% CO solution. In expression studies, food-restricted rats drank these solutions in one-bottle sessions (2 h) over 10 d. Subsequent two-bottle tests with the CS+ and CS- flavors mixed in 0.9% CO solutions occurred 0.5h after systemic administration of vehicle (VEH), NTX (0.1-5 mg/kg) or MK-801 (50-200 μg/kg). Rats displayed a robust CS+ preference following VEH treatment (85-88%) which was significantly though moderately attenuated by NTX (69-70%). The lower doses of MK-801 slightly reduced the CS+ preference; the high dose blocked the CS+ preference (49%) but also markedly reduced overall CS intake. In separate acquisition studies, rats received VEH or NTX (0.1, 0.5, 1mg/kg) or MK-801 (100 μg/kg) 0.5h prior to 1-bottle training trials with CS+/3.5% CO and CS-/0.9% CO training solutions. Additional Limited VEH groups were trained with intakes limited to that of the NTX and MK-801 groups. Subsequent two-bottle CS+ vs. CS- tests were conducted without injections. Significant and persistent CS+ preferences were observed in VEH (77-84%) and Limited VEH (88%) groups. NTX treatment during training failed to block the acquisition of CO-CFP although the magnitude of the CS+ preference was reduced by 0.5 (70%) and 1.0 (72%) mg/kg doses relative to the Limited VEH treatment (88%). In contrast, MK-801 (100 μg/kg) treatment during training blocked the acquisition of the CO-CFP. These data suggest a critical role for NMDA, but not opioid receptor signaling in the acquisition of a fat conditioned flavor preferences, and at best limited involvement of NMDA and opioid receptors in the expression of a previously learned preference.

High fat diet intake during pre and periadolescence impairs learning of a conditioned place preference in adulthood

BACKGROUND

Brain regions that mediate learning of a conditioned place preference (CPP) undergo significant development in pre and periadolescence. Consuming a high fat (HF) diet during this developmental period and into adulthood can lead to learning impairments in rodents. The present study tested whether HF diet intake, consumed only in pre and periadolescence, would be sufficient to cause impairments using a CPP procedure.

METHODS

Rats were randomly assigned to consume a HF or a low fat (LF) diet during postnatal days (PD) 21-40 and were then placed back on a standard lab chow diet. A 20-day CPP procedure, using HF Cheetos® as the unconditioned stimulus (US), began either the next day (PD 41) or 40 days later (PD 81). A separate group of adult rats were given the HF diet for 20 days beginning on PD 61, and then immediately underwent the 20-day CPP procedure beginning on PD 81.

RESULTS

Pre and periadolescent exposure to a LF diet or adult exposure to a HF diet did not interfere with the development of a HF food-induced CPP, as these groups exhibited robust preferences for the HF Cheetos® food-paired compartment. However, pre and periadolescent exposure to the HF diet impaired the development of a HF food-induced CPP regardless of whether it was assessed immediately or 40 days after the exposure to the HF diet, and despite showing increased consumption of the HF Cheetos® in conditioning.

CONCLUSIONS

Intake of a HF diet, consumed only in pre and periadolescence, has long-lasting effects on learning that persist into adulthood.

Methamphetamine acts on subpopulations of neurons regulating sexual behavior in male rats

Methamphetamine (Meth) is a highly addictive stimulant. Meth abuse is commonly associated with the practice of sexual risk behavior and increased prevalence of Human Immunodeficiency Virus and Meth users report heightened sexual desire, arousal, and sexual pleasure. The biological basis for this drug-sex nexus is unknown. The current study demonstrates that Meth administration in male rats activates neurons in brain regions of the mesolimbic system that are involved in the regulation of sexual behavior. Specifically, Meth and mating co-activate cells in the nucleus accumbens core and shell, basolateral amygdala, and anterior cingulate cortex. These findings illustrate that in contrast to current belief drugs of abuse can activate the same cells as a natural reinforcer, that is sexual behavior, and in turn may influence compulsive seeking of this natural reward.

Genetic variance contributes to dopamine and opioid receptor antagonist-induced inhibition of intralipid (fat) intake in inbred and outbred mouse strains

Preference for and intake of solid and emulsified fat (intralipid) solutions vary across different mouse strains. Fat intake in rodents is inhibited by dopamine and opioid receptor antagonists, but any variation in these responses as a function of genetic background is unknown. Therefore, the present study compared the ability of dopamine D1-like (SCH23390) and general opioid (naltrexone) receptor antagonism to alter intake of fat emulsions (intralipid) in mice. Two-hour intakes of 5% intralipid were measured (5-120 min) in seven inbred (BALB/c, C57BL/6, C57BL/10, DBA/2, SJL, SWR, 129P3) and one outbred (CD-1) mouse strains following treatment with vehicle, SCH23390 (50-1600 nmol/kg, ip) and naltrexone (0.001-5 mg/kg, sc). SCH23390 significantly, dose-dependently and differentially reduced intralipid intake at all five (DBA/2, SWR, CD-1), four (SJL, C57BL/6), three (129P3) and one (C57BL/10) of the doses tested, but failed to affect intralipid intake in BALB/c mice. Naltrexone significantly, dose-dependently and differentially reduced intralipid intake at all four (DBA/2), three (SWR, SJL), two (CD-1, C57BL/10) and one (C57BL/6, 129P3) of the doses tested, and also failed to affect intralipid intake in BALB/cJ mice. SCH23390 and naltrexone were respectively 13.3-fold and 9.3-fold more potent in inhibiting intralipid intake in the most sensitive (DBA/2) relative to the least sensitive (BALB/c) mouse strains. A strong positive relationship (r=0.91) was observed for the abilities of SCH23390 and naltrexone to inhibit intralipid intake across strains. These findings indicate that dopaminergic and opioid signaling mechanisms differentially control intralipid intake across different mouse strains, suggesting important genetic and pharmacological interactions in the short-term control of rewarding and post-ingestive consequences of fat intake.

Opioid receptor antagonism in the nucleus accumbens fails to block the expression of sugar-conditioned flavor preferences in rats

In our prior studies, systemic administration of the opioid receptor antagonist naltrexone (NTX) did not block flavor preference conditioning by the sweet taste or post-oral actions of sugar despite reducing intake. Because opioid signaling in the nucleus accumbens (NAc) is implicated in food reward, this study determined if NTX administered into the NAc would block the expression of sugar-conditioned preferences. In Experiment 1, food-restricted rats with bilateral NAc shell or core cannulae were trained to drink a fructose (8%)+saccharin (0.2%) solution mixed with one flavor (CS+) and a less-preferred 0.2% saccharin solution mixed with another flavor (CS-) during one-bottle sessions. Two-bottle tests with the two flavors mixed in saccharin solutions occurred 10 min following total bilateral NAc shell or core doses of 0, 1, 25 and 50 microg of NTX. The rats preferred the CS+ over CS- following vehicle (80%) and all NTX doses in the shell and core. The CS+ preference was reduced to 64% and 72% by 50 microg NTX in the shell and core, although only the core effect was significant. In Experiment 2, food-restricted rats were trained to drink one flavored saccharin solution (CS+) paired with an intragastic (IG) glucose (8%) infusion and a second flavored saccharin solution (CS-) paired with an IG water infusion. In subsequent two-bottle tests, the rats displayed significant preferences for the CS+ (81-91%) that were unaltered by any NTX dose in the shell or core. CS+ intake, however, was reduced by NTX in the shell, but not the core. These data indicate that accumbal opioid antagonism slightly attenuated, but did not block the expression of sugar-conditioned flavor preferences. Therefore, while opioid drugs can have potent effects on sugar intake they appear less effective in altering sugar-conditioned flavor preferences.

The biology of binge eating

OBJECTIVE

To examine the literature on binge eating to gain a better understanding of its biological foundations and their role in eating disorders.

METHOD

Literature review and synthesis.

RESULTS

Research using animal models has revealed several factors that contribute to the development and maintenance of binge eating. These factors, including stress, food restriction, the presence of palatable foods, and environmental conditioning, parallel many of the precursory circumstances leading to binge eating in individuals with bulimia nervosa and binge eating disorder.

DISCUSSION

The animal literature has opened a new avenue to aid in the understanding of the neurobiological basis of binge eating. Future endeavors examining the genetic and environmental correlates of binge eating behavior will further contribute to the understanding of the biological foundations of binge eating and assist with establishing diagnostic criteria and the development of novel treatments for eating disorders marked by binge eating.

Implications of the biology of weight regulation and obesity on the treatment of obesity

PURPOSE

The purposes of this article are to provide a brief review of the complex biology of weight regulation and obesity, to explain some of the effects of diet and exercise on the biology of weight regulation and obesity, and to propose a coherent way to assess and treat people related to weight and obesity.

DATA SOURCES

Scientific publications, clinical guidelines, and government sources.

CONCLUSIONS

Obesity is a complex problem requiring an understanding of how interventions interact with the biology of weight regulation in people who are obese. Promoting health in obese people requires a focus on improving insulin sensitivity.

IMPLICATIONS FOR PRACTICE

Helping individuals maintain normal weight throughout life is important in order to keep the long- and short-term weight signals in balance and reflective of true energy requirements. Exercise is associated with loss of total and abdominal adipose tissue and improved insulin sensitivity. Diets inducing gradual weight loss are less likely to stimulate appetite. Diets should include antioxidants to neutralize the increase in free radical production associated with obesity and exercise. Other interventions in the treatment of obesity may include treating sleep deficits and the dysregulated endocannabinoid system.

Baclofen, raclopride, and naltrexone differentially reduce solid fat emulsion intake under limited access conditions

Previous work in rats has demonstrated that an Intermittent (Monday, Wednesday, Friday) schedule of access promotes binge-type consumption of 100% vegetable shortening during a 1-h period of availability. The present study used novel shortening-derived stable solid emulsions of various fat concentrations. These emulsions were the consistency of pudding and did not demonstrate oil and water phase separation previously reported with oil-based liquid emulsions. Male Sprague-Dawley rats were grouped according to schedule of access (Daily or Intermittent) to one of three concentrations (18%, 32%, 56%) of solid fat emulsion. There were no significant Intermittent vs. Daily differences in amount consumed, due to high intakes in all groups. This indicated the acceptability of the emulsions. Baclofen (GABA(B) agonist) and raclopride (D2-like antagonist) both significantly reduced emulsion intake in all Daily groups, but only in the 56% fat Intermittent group. Naltrexone (opioid antagonist), in contrast, significantly reduced 32% and 56% fat emulsion intake in the Intermittent, as well as the Daily groups. These results indicate that the fat intake-reducing effects of GABA(B) activation and D(2) blockade depend upon fat concentration and schedule of fat access, while the fat intake-reducing effects of opioid blockade depend upon fat concentration but not schedule of access.

Opioid-dependent anticipatory negative contrast and binge-like eating in rats with limited access to highly preferred food

Binge eating and an increased role for palatability in determining food intake are abnormal adaptations in feeding behavior linked to eating disorders and body weight dysregulation. The present study tested the hypothesis that rats with limited access to highly preferred food would develop analogous opioid-dependent learned adaptations in feeding behavior, with associated changes in metabolism and anxiety-like behavior. For this purpose, adolescent female Wistar rats were daily food deprived (2 h) and then offered 10-min access to a feeder containing chow followed sequentially by 10-min access to a different feeder containing either chow (chow/chow; n=7) or a highly preferred, but macronutrient-comparable, sucrose-rich diet (chow/preferred; n=8). Chow/preferred-fed rats developed binge-like hyperphagia of preferred diet from the second feeder and anticipatory chow hypophagia from the first feeder with a time course suggesting associative learning. The feeding adaptations were dissociable in onset, across individuals, and in their dose-response to the opioid-receptor antagonist nalmefene, suggesting that they represent distinct palatability-motivated processes. Chow/preferred-fed rats showed increased anxiety-like behavior in relation to their propensity to binge as well as increased feed efficiency, body weight, and visceral adiposity. Chow/preferred-fed rats also had increased circulating leptin levels and decreased growth hormone and 'active' ghrelin levels. Thus, the short-term control of food intake in rats with restricted access to highly preferred foods comes to rely more on hedonic, rather than nutritional, properties of food, through associative learning mechanisms. Such rats show changes in ingestive, metabolic, endocrine, and anxiety-related measures, which resemble features of binge eating disorders or obesity.

Endogenous opiates and behavior: 2006

This paper is the 29th consecutive installment of the annual review of research concerning the endogenous opioid system, now spanning 30 years of research. It summarizes papers published during 2006 that studied the behavioral effects of molecular, pharmacological and genetic manipulation of opioid peptides, opioid receptors, opioid agonists and opioid antagonists. The particular topics that continue to be covered include the molecular-biochemical effects and neurochemical localization studies of endogenous opioids and their receptors related to behavior (Section 2), and the roles of these opioid peptides and receptors in pain and analgesia (Section 3); stress and social status (Section 4); tolerance and dependence (Section 5); learning and memory (Section 6); eating and drinking (Section 7); alcohol and drugs of abuse (Section 8); sexual activity and hormones, pregnancy, development and endocrinology (Section 9); mental illness and mood (Section 10); seizures and neurological disorders (Section 11); electrical-related activity and neurophysiology (Section 12); general activity and locomotion (Section 13); gastrointestinal, renal and hepatic functions (Section 14); cardiovascular responses (Section 15); respiration and thermoregulation (Section 16); and immunological responses (Section 17).

Measuring reward with the conditioned place preference (CPP) paradigm: update of the last decade

Conditioned place preference (CPP) continues to be one of the most popular models to study the motivational effects of drugs and non-drug treatments in experimental animals. This is obvious from a steady year-to-year increase in the number of publications reporting the use this model. Since the compilation of the preceding review in 1998, more than 1000 new studies using place conditioning have been published, and the aim of the present review is to provide an overview of these recent publications. There are a number of trends and developments that are obvious in the literature of the last decade. First, as more and more knockout and transgenic animals become available, place conditioning is increasingly used to assess the motivational effects of drugs or non-drug rewards in genetically modified animals. Second, there is a still small but growing literature on the use of place conditioning to study the motivational aspects of pain, a field of pre-clinical research that has so far received little attention, because of the lack of appropriate animal models. Third, place conditioning continues to be widely used to study tolerance and sensitization to the rewarding effects of drugs induced by pre-treatment regimens. Fourth, extinction/reinstatement procedures in place conditioning are becoming increasingly popular. This interesting approach is thought to model certain aspects of relapse to addictive behavior and has previously almost exclusively been studied in drug self-administration paradigms. It has now also become established in the place conditioning literature and provides an additional and technically easy approach to this important phenomenon. The enormous number of studies to be covered in this review prevented in-depth discussion of many methodological, pharmacological or neurobiological aspects; to a large extent, the presentation of data had to be limited to a short and condensed summary of the most relevant findings.

Disordered eating and food cravings among urban obese African American women

OBJECTIVE

The prevalence of night eating syndrome (NES), binge eating disorder (BED), and bulimia nervosa (BN) and the general experience of food cravings were examined in 88 obese urban African American women.

METHOD

Participants were administered The Questionnaire on Eating and Weight Patterns-R, the Night Eating Syndrome Questionnaire, and the State and Trait Food Cravings Questionnaire, Trait version (FCQ-T).

RESULTS

Twenty-eight percent reported symptoms of eating disorders (18.9% NES, 6.4% recurrent binge eating, 2.2% both NES and recurrent binge eating). Those reporting disordered eating had significantly higher total FCQ-T scores than those not reporting disordered eating. Persons endorsing recurrent binge eating had the highest mean score, followed by those reporting NES. Those who identified themselves as binge eaters and night eaters were not significantly different from each other, but both groups were significantly different than the no eating disorder symptoms group on various subscales of the FCQ-T.

DISCUSSION

Obese African American women report significant levels of NES and binge eating which may contribute to the development and/ or maintenance of obesity.

Conditioned place preferences (CPPs) to high-caloric "snack foods" in rat strains genetically prone vs. resistant to diet-induced obesity: resistance to naltrexone blockade

A previous study in our laboratory using Sprague-Dawley (SD) male rats showed that conditioned place preferences (CPPs) can be learned to two different high-caloric "snack foods"--one high in sugar (Froot Loops cereal: FL) vs. one high in fat (Cheetos: C), and that both preferences were mediated by endogenous opioids. Using the same CPP apparatus and procedures, two genetic sub-strains of SD rats, one selectively bred for diet-induced obesity (DIO) vs. another bred for diet resistance to obesity (DR), were used in this investigation. The experiment determined if (a) CPPs can be created in both strains using the same high-caloric "snack foods" and, (b) if CPPs existed, were they opioid dependent. Four non-deprived groups of eight male rats, half being of each strain, were given 20 min sessions to eat either FL or C in one side of a three-chamber CPP apparatus vs. chow on the opposite side over alternating days of a 20 day period. Each predetermined side had distinctly different environmental cues. Following conditioning, rats were tested during 10 min sessions to see if CPPs existed to the "snack food" trained sides. During conditioning and testing, bodyweights, intakes of foods, and activity were measured. Both FL and C generated strong CPPs that were equivalent in both strains. In contrast to our previous study in the parent strain, doses of 0, 0.50, 1.0, 2.5, and 5.0 mg/kg of the opioid antagonist, naltrexone, had no effect on blocking these CPPs. These results show that (a) DIO and DR rats can learn CPPs (i.e., "exhibit food cravings") as well as their parent strain after periodic access to high-caloric palatable foods, but imply that (b) some physiological system other than the endogenous opioid system mediates such learning.