Activity-based anorexia during adolescence does not promote binge eating during adulthood in female rats

OBJECTIVE

Given the frequency of transition from anorexia nervosa to bulimia nervosa, this study investigated whether a history of activity-based anorexia (ABA) during adolescence would promote binge eating during adulthood in female rats.

METHOD

Adolescent rats were given 1-h unlimited access to chow and ad libitum access to a running wheel until body weight reached <80%, indicating the development of ABA. During adulthood, all groups were given 21 days of access to a palatable food for 2 h/day and ad libitum access to chow.

RESULTS

During adolescence, rats in the ABA paradigm developed increased wheel running and decreased food intake, reaching <80% of body weight after 3 days. However, there were no significant differences between groups in the amount of binge food consumed during adulthood.

CONCLUSION

A brief episode of ABA during adolescence did not lead to increased binge eating later in life. Longer-term models are needed to determine whether a propensity toward binge eating may result from more sustained ABA during adolescence.

Bingeing, self-restriction, and increased body weight in rats with limited access to a sweet-fat diet

OBJECTIVE

Prior research has shown that fasting alternated with a diet of standard rodent chow and a 10% sucrose solution produces bingeing on the sucrose, but animals remain at normal body weight. The present study investigated whether restricted access to a highly palatable combination of sugar and fat, without food deprivation, would instigate binge eating and also increase body weight.

METHODS AND PROCEDURES

Male rats were maintained for 25 days on one of four diets: (i) sweet-fat chow for 2 h/day followed by ad libitum standard chow, (ii) 2-h sweet-fat chow only 3 days/week and access to standard chow the rest of the time, (iii) ad libitum sweet-fat chow, or (iv) ad libitum standard chow.

RESULTS

Both groups with 2-h access to the sweet-fat chow exhibited bingeing behavior, as defined by excessively large meals. The body weight of these animals increased due to large meals and then decreased between binges as a result of self-restricted intake of standard chow following binges. However, despite these fluctuations in body weight, the group with 2-h access to sweet-fat chow every day gained significantly more weight than the control group with standard chow available ad libitum.

DISCUSSION

These findings may have implications for the body weight fluctuations associated with binge-eating disorder, as well as the relationship between binge eating and the obesity epidemic.

A high-fat diet prevents and reverses the development of activity-based anorexia in rats

OBJECTIVE

Activity-based anorexia is an animal model of anorexia nervosa in which limited access to standard lab chow combined with voluntary wheel running leads to hypophagia and severe weight loss. This study tested whether activity-based anorexia could be prevented or reversed with palatable foods.

METHOD

Male rats were divided into sedentary or ad libitum-running groups and maintained on 1 h daily access to standard chow plus one of the following: sugar, saccharin, vegetable fat (shortening), or sweet high-fat chow.

RESULTS

Access to the sweet high-fat chow both reversed and prevented the weight loss typical of activity-based anorexia. Vegetable fat attenuated body weight loss, but to a lesser degree than the sweet high-fat diet. The addition of saccharin or sucrose solutions to the standard lab-chow diet had no effect.

CONCLUSION

The results suggest that certain palatable diets may affect the development of, and recovery from, activity-based anorexia.

After daily bingeing on a sucrose solution, food deprivation induces anxiety and accumbens dopamine/acetylcholine imbalance

Bingeing on sugar may activate neural pathways in a manner similar to taking drugs of abuse, resulting in related signs of dependence. The present experiments test whether rats that have been bingeing on sucrose and then fasted demonstrate signs of opiate-like withdrawal. Rats were maintained on 12-h deprivation followed by 12-h access to a 10% sucrose solution and chow for 28 days, then fasted for 36 h. These animals spent less time on the exposed arm of an elevated plus-maze compared with a similarly deprived ad libitum chow group, suggesting anxiety. Microdialysis revealed a concomitant increase in extracellular acetylcholine and decrease in dopamine release in the nucleus accumbens shell. These results did not appear to be due to hypoglycemia. The findings suggest that a diet of bingeing on sucrose and chow followed by fasting creates a state that involves anxiety and altered accumbens dopamine and acetylcholine balance. This is similar to the effects of naloxone, suggesting opiate-like withdrawal. This may be a factor in some eating disorders.

Sugar bingeing in rats

Bingeing behavior is characteristic of many eating disorders. This unit describes an animal model of sugar bingeing. This model has been used successfully to elicit behavioral and neurochemical signs of sugar dependence in rats, e.g., indices of bingeing, withdrawal, increased intake after abstinence (deprivation effect), cross-sensitization with amphetamine, and increases in dopamine release in the nucleus accumbens due to repeated bingeing.

Overview of methodological approaches to the study of ingestive behavior

Some examples of procedures used by feeding researchers are discussed in this unit and include ablation of neural function; inhibition of behaviors by selective neurotoxins and antisense oligonucleotides; staining of sensory and motor mechanisms; electrical stimulation of the brain; local injection and microdialysis of nutrients, neurotransmitters, and drugs; autoradiography and in situ hybridization of neurotransmitters with their receptors; electrophysiological techniques for multi- and single-unit recording of cells in the hypothalamus; and gene technology using inbred strains of genetically obese mice.

Accumbens dopamine-acetylcholine balance in approach and avoidance

Understanding systems for approach and avoidance is basic for behavioral neuroscience. Research on the neural organization and functions of the dorsal striatum in movement disorders, such as Huntington's and Parkinson's Disease, can inform the study of the nucleus accumbens (NAc) in motivational disorders, such as addiction and depression. We propose opposing roles for dopamine (DA) and acetylcholine (ACh) in the NAc in the control of GABA output systems for approach and avoidance. Contrary to DA, which fosters approach, ACh release is a correlate or cause of meal satiation, conditioned taste aversion and aversive brain stimulation. ACh may also counteract excessive DA-mediated approach behavior as revealed during withdrawal from drugs of abuse or sugar when the animal enters an ACh-mediated state of anxiety and behavioral depression. This review summarizes evidence that ACh is important in the inhibition of behavior when extracellular DA is high and the generation of an anxious or depressed state when DA is relatively low.

Orexigenic peptides and alcohol intake: differential effects of orexin, galanin, and ghrelin

BACKGROUND

The question is which hypothalamic systems for food intake might play a role in ethanol intake and contribute to alcohol abuse. The peptide orexin was found to exhibit similar properties to galanin in its relation to dietary fat and may therefore be similar to galanin in having a stimulatory effect on alcohol intake.

METHODS

Rats were trained to drink 10% ethanol, implanted with brain cannulas, and then injected in the paraventricular nucleus (PVN), lateral hypothalamus (LH), or nucleus accumbens (NAc) with galanin, orexin-A, and for comparison, ghrelin. Ethanol, food, and water intake were measured at 1, 2, and 4 hours postinjection.

RESULTS

In the PVN, both orexin and galanin significantly increased ethanol intake, whereas ghrelin increased food intake. In the LH, orexin again induced ethanol intake, while ghrelin increased eating. In the NAc, orexin failed to influence ethanol intake but did stimulate food intake.

CONCLUSIONS

In ethanol-drinking rats, injection of orexin or galanin into the appropriate locus in the hypothalamus induced significant ethanol intake instead of food intake. Ghrelin, as a positive control, failed to influence ethanol intake at the same hypothalamic sites. In the NAc, as an anatomical control, orexin augmented eating but not ethanol intake. Thus orexin and galanin in the hypothalamus selectively stimulated ethanol intake at sites where other studies have shown that both ethanol and fat increase expression of the endogenous peptides. Thus, a neural circuit that evolved with the capability to augment food intake is apparently co-opted by ethanol and may serve as a potential positive feedback circuit for alcohol abuse.

Evidence for sugar addiction: behavioral and neurochemical effects of intermittent, excessive sugar intake

[Avena, N.M., Rada, P., Hoebel B.G., 2007. Evidence for sugar addiction: Behavioral and neurochemical effects of intermittent, excessive sugar intake. Neuroscience and Biobehavioral Reviews XX(X), XXX-XXX]. The experimental question is whether or not sugar can be a substance of abuse and lead to a natural form of addiction. "Food addiction" seems plausible because brain pathways that evolved to respond to natural rewards are also activated by addictive drugs. Sugar is noteworthy as a substance that releases opioids and dopamine and thus might be expected to have addictive potential. This review summarizes evidence of sugar dependence in an animal model. Four components of addiction are analyzed. "Bingeing," "withdrawal," "craving" and "cross-sensitization" are each given operational definitions and demonstrated behaviorally with sugar bingeing as the reinforcer. These behaviors are then related to neurochemical changes in the brain that also occur with addictive drugs. Neural adaptations include changes in dopamine and opioid receptor binding, enkephalin mRNA expression and dopamine and acetylcholine release in the nucleus accumbens. The evidence supports the hypothesis that under certain circumstances rats can become sugar dependent. This may translate to some human conditions as suggested by the literature on eating disorders and obesity.

Effect of ethanol on hypothalamic opioid peptides, enkephalin, and dynorphin: relationship with circulating triglycerides

BACKGROUND

Recent evidence has demonstrated that ethanol intake can stimulate the expression and production of the feeding-stimulatory peptide, galanin (GAL), in the hypothalamic paraventricular nucleus (PVN), and that PVN injection of this peptide, in turn, can increase the consumption of ethanol. To test the hypothesis that other feeding-related systems are involved in ethanol intake, this study examined the effect of ethanol on the hypothalamic opioid peptides, enkephalin (ENK), and dynorphin (DYN).

METHOD

Adult, male Sprague-Dawley rats were trained to voluntarily drink increasing concentrations of ethanol, up to 9% v/v, on a 12-hour access schedule or were given a single injection of ethanol (10% v/v) versus saline vehicle. The effect of ethanol on GAL, ENK, and DYN mRNA was measured using real-time quantitative polymerase chain reaction and radiolabeled in situ hybridization, while radioimmunoassay was used to measure peptide levels. In addition to blood alcohol, circulating levels of triglycerides (TG), leptin, and insulin were also measured.

RESULTS

The data demonstrated that: (1) rats voluntarily drinking 9% v/v ethanol (approximately 2.0 g/kg/d) show a significant increase in GAL, ENK, and DYN mRNA in the PVN compared with water-drinking rats; (2) voluntary consumption of ethanol also increases peptide levels of ENK and DYN in the PVN; (3) acute injection of 10% ethanol (1.0 g/kg of 10% v/v) similarly increases the expression of GAL, ENK, and DYN in the PVN; and (4) ethanol consumption and injection, while having little effect on leptin and insulin, consistently increase circulating levels of TG as well as alcohol, both of which are strongly, positively correlated with peptide expression in the PVN.

CONCLUSIONS

These findings, together with published studies, suggest a possible role for hypothalamic opioid peptides in the drinking of ethanol. Based on evidence that dietary fat and lipid injections stimulate the PVN peptides and injection of the opiates and GAL increase ethanol intake, it is proposed that both TG and alcohol in the circulation, which are elevated by the ingestion or injection of ethanol, are involved in stimulating these peptides in the PVN, which in turn promote further consumption of ethanol.

Feeding and systemic D-amphetamine increase extracellular acetylcholine in the medial thalamus: a possible reward enabling function

Acetylcholine neurons that project forward from the midbrain are known to enable dopaminergic reward functions in the ventral tegmental area. The question is whether acetylcholine might also be released in the mediodorsal thalamus for the same general purposes. Rats with a microdialysis probe lodged in the mediodorsal thalamus were allowed to eat chow for 20 min after 16-h food deprivation or were given varying doses of D-amphetamine when fed ad libitum. The result in both cases was a significant increase in extracellular acetylcholine. During feeding, acetylcholine increased to 177% of baseline. In response to d-amphetamine (2.5 mg/kg), acetylcholine increased to 184%, and with a higher dose (5 mg/kg) to 400% of baseline. It is concluded that midbrain projections to limbic portions of the thalamus provide acetylcholine for behavioral activation. This cholinergic function theoretically plays a role in enabling the limbic circuits that pass through the thalamus for reinforcement of feeding and psychostimulant abuse.

Sucrose sham feeding on a binge schedule releases accumbens dopamine repeatedly and eliminates the acetylcholine satiety response

Drinking a sugar solution on an intermittent schedule can promote sugar bingeing and cause signs of dependence while releasing dopamine repeatedly like a drug of abuse. It is hypothesized that sweet taste alone is sufficient for this effect in sucrose bingeing rats. On the theory that acetylcholine in the nucleus accumbens plays a role in satiety, it is further hypothesized that purging the stomach contents will delay acetylcholine release. Rats with gastric fistulas and nucleus accumbens guide shafts for microdialysis were fed 12 h each day. During the first hour, fistulas were open for the sham-feeding group and closed for the real-feeding group, and 10% sucrose was the only food source. For the remaining 11 h, liquid rodent diet was available as well as the 10% sucrose to provide a balanced diet. In microdialysis tests during the first sugar meal on days 1, 2 and 21, extracellular dopamine increased at least 30% each day in both groups. Acetylcholine also increased during the sugar meals for the real-feeding animals, but not during sham feeding. In conclusion, the taste of sugar can increase extracellular dopamine in the nucleus accumbens without fail in animals on a dietary regimen that causes bingeing and sugar dependency. During sham feeding, the acetylcholine satiation signal is eliminated, and the animals drink more. These findings support the hypothesis that dopamine is released repeatedly in response to taste when bingeing on sweet food, and the acetylcholine satiety effect is greatly reduced by purging; this may be relevant to bulimia nervosa in humans.

Galanin and alcohol dependence: neurobehavioral research

It is known that microinjection of galanin (GAL) intraventricularly or in specific hypothalamic sites increases food consumption and, conversely, the intake of food increases the expression of GAL in hypothalamic sites. Ethanol (EtOH) is a calorie-rich food as well as a drug of abuse. The research reviewed here shows that GAL may play a similar role in alcohol intake. First, experiments in which GAL was microinjected into the third ventricle or the paraventricular nucleus (PVN) showed increases in EtOH consumption. The increase in EtOH consumption occurred during both the light and dark cycles after GAL injection in the third ventricle in rats with limited EtOH access. Injection of GAL did not increase food intake in rats that had been chronically drinking alcohol. GAL receptor blockade reversed these increases. Microinjection of GAL directly into the PVN also increased ad libitum EtOH intake and blockade of these receptors in the PVN inhibited ad libitum EtOH consumption. Secondly, rats administered EtOH showed increases in GAL in the PVN and related hypothalamic sites. EtOH injection and voluntary intake, both ad libitum and limited access, increased GAL gene and peptide expression in the PVN consistently across administration procedures. These experiments show that GAL injection increases alcohol intake and that the intake of alcohol increases GAL, suggesting a positive feedback relationship between alcohol intake and specific hypothalamic GAL systems. Such a relationship may contribute to the motivation to consume excessive alcoholic beverages and the development of alcohol dependence.

Ethanol intake is increased by injection of galanin in the paraventricular nucleus and reduced by a galanin antagonist

Ethanol intake stimulates expression of galanin in several hypothalamic sites, including the paraventricular nucleus. Because injection of galanin in the paraventricular nucleus induces eating, we hypothesized that galanin might also affect ethanol intake. Rats were given ad libitum access to 4% ethanol for 4 weeks and assigned to one of two groups according to levels of ethanol consumption: high levels (>1.5 g/ kg/day) or low levels (<1.0 g/kg/day). In Experiment 1, galanin (1.0 nmol) or Ringer's solution was injected unilaterally into the paraventricular nucleus, with food and water absent during the first 4 h. Galanin significantly increased ethanol intake only in rats that drank high levels of ethanol. In Experiment 2, injection of galanin (0.5 and 1.0 nmol) in the paraventricular nucleus dose-dependently increased ethanol intake with food and water available. The higher dose was also effective in eliciting ethanol intake when tested with food and water absent. In Experiment 3, a test of receptor specificity was provided by injecting rats with the galanin antagonist M-40 (0.5 nmol) or Ringer's solution. Injection of M-40 in the paraventricular nucleus significantly decreased ethanol consumption. In Experiment 4, an anatomic control, with galanin injected 2 mm dorsal to the paraventricular nucleus in the same animals, caused no change in ethanol intake. In conclusion, injection of galanin in the paraventricular nucleus, at a dose known to induce feeding, acted by means of a galanin receptor to potentiate intake of 4% ethanol, even with food and water available as alternate sources of calories and fluid, respectively. Because ethanol can increase expression of galanin mRNA in the paraventricular nucleus, this could set the stage for a positive feedback loop between galanin and ethanol intake.

Sugar-dependent rats show enhanced responding for sugar after abstinence: Evidence of a sugar deprivation effect

Studies have shown that intermittent sugar availability (12 h/day) produces signs of dependence in rats, including escalation of intake, mu-opioid and dopamine receptor changes, behavioral and neurochemical indices of withdrawal, and cross-sensitization with amphetamine. "Deprivation-effect" paradigms, whereby abstinence from a substance results in enhanced intake, are often used to measure "craving" for drugs of abuse, such as alcohol. The present study used operant conditioning to investigate consumption of sugar after abstinence in rats selected for glucose avidity. The experimental group was trained on a fixed ratio (FR-1) schedule for 25% glucose for 30 min/day for 28 days and also had glucose access in the home cages for an additional 11.5 h daily. The control group had only the 30-min/day access to glucose in the operant chambers. Then, both groups were deprived of glucose for 2 weeks. After this period of abstinence, animals were put back in the operant chambers. The experimental group responded significantly more than ever before, and significantly more than the control group. In conclusion, daily 12-h access to sugar, in the paradigm used, can result in an altered neural state that lasts throughout 2 weeks of abstinence, leading to enhanced intake. Together with previous results, this deprivation effect supports the theory that animals may become dependent on sugar under selected dietary circumstances.

Acetylcholine in the accumbens is decreased by diazepam and increased by benzodiazepine withdrawal: a possible mechanism for dependency

Diazepam is a benzodiazepine used in the treatment of anxiety, insomnia and seizures, but with the potential for abuse. Like the other benzodiazepine anxiolytics, diazepam does not increase dopamine in the nucleus accumbens. This raises the question as to which other neurotransmitter systems are involved in diazepam dependence. The goal was to monitor dopamine and acetylcholine simultaneously following acute and chronic diazepam treatment and after flumazenil-induced withdrawal. Rats were prepared with microdialysis probes in the nucleus accumbens and given diazepam (2, 5 and 7.5 mg/kg) acutely and again after chronic treatment. Accumbens dopamine and acetylcholine decreased, with signs of tolerance to the dopamine effect. When these animals were put into the withdrawal state with flumazenil, there was a significant rise in acetylcholine (145%, P<0.001) with a smaller significant rise in dopamine (124%, P<0.01). It is suggested that the increase in acetylcholine release, relative to dopamine, is a neural component of the withdrawal state that is aversive.

Daily bingeing on sugar repeatedly releases dopamine in the accumbens shell

Most drugs of abuse increase dopamine (DA) in the nucleus accumbens (NAc), and do so every time as a pharmacological response. Palatable food also releases accumbens-shell DA, but in naïve rats the effect can wane during a long meal and disappears with repetition. Under select dietary circumstances, sugar can have effects similar to a drug of abuse. Rats show signs of DA sensitization and opioid dependence when given intermittent access to sucrose, such as alterations in DA and mu-opioid receptors, cross-sensitization with amphetamine and alcohol, and behavioral and neurochemical signs of naloxone-precipitated withdrawal. The present experiment asks whether sucrose-dependent rats release DA each time they binge. We also predict that acetylcholine (ACh), which rises as the end of a meal, will be delayed in rats with intermittent access to sucrose. To create dependency, the experimental group (Daily Intermittent Sucrose) was maintained on a diet of 12-h food deprivation that extended 4 h into the dark, followed by 12-h access to a 10% sucrose solution and chow, daily, for 21 days. As the main result, these rats gradually increased their sucrose intake from 37 to 112 ml per day (from 13 to 20 ml in the first hour of access), and repeatedly increased extracellular DA to 130% of baseline as measured in the NAc shell by microdialysis during the first hour of sucrose access on day 1, day 2 and day 21. Three control groups failed to show a significant increase in extracellular DA on day 21: Sucrose only for 1 h on days 1 and 21 (Sucrose Twice), ad libitum access to sucrose and chow (Daily Ad libitum Sucrose), and intermittent chow instead of sucrose (Daily Intermittent Chow). Acetylcholine measured at the same time as DA, increased significantly toward the end and after each test meal in all groups. In the Daily Intermittent Sucrose group, the highest ACh levels (133%) occurred during the first sample after the sucrose meal ended. In summary, sucrose-dependent animals have a delayed ACh satiation response, drink more sucrose, and release more DA than sucrose- or binge-experienced, but non-dependent animals. These results suggest another neurochemical similarity between intermittent bingeing on sucrose and drugs of abuse: both can repeatedly increase extracellular DA in the NAc shell.

Galanin Microinjection in the Third Ventricle Increases Voluntary Ethanol Intake

BACKGROUND

The neuropeptide galanin increases food intake. Chronic ethanol (EtOH) increases the expression of galanin in the hypothalamus. The research presented here examines the effects of microinjection of galanin in the third ventricle on voluntary alcohol intake.

METHODS

Male Sprague Dawley rats with a cannula in the third ventricle were given access to increasing concentrations of EtOH for 12 hr/day until all acquired a preference for 7% EtOH over water in a two-bottle choice. Rats then received a microinjection of galanin (0, 1, and 3 nmol) alone or in combination with the galanin antagonist M40 (1 nmol) and with M40 alone to determine the effects on EtOH and water intake. Tests were conducted during both the light and dark periods of a 12:12-hr light-dark cycle with food available ad libitum. As a control for galanin-induced calorie intake, both EtOH and food were measured in a subset of rats during the dark.

RESULTS

Microinjections of galanin (1.0 and 3.0 nmol) increased EtOH consumption during both periods of the light-dark cycle. Galanin's effect on ethanol intake during the light was large relative to the very low intake of food and water during this period. Rats increased their intake of EtOH but not food. Receptor specificity for galanin (3 nmol) was shown by the galanin antagonist M40, which blocked the increase in EtOH intake. M40 alone decreased EtOH intake slightly.

CONCLUSIONS

These data show that galanin injected in the third ventricle increases EtOH consumption and that the effect can occur during both the light and the dark periods of the diurnal cycle in the presence of food and water. This suggests that galanin may play a role in augmenting voluntary alcohol intake and perhaps the development of alcohol dependence.

In alcohol-treated rats, naloxone decreases extracellular dopamine and increases acetylcholine in the nucleus accumbens: evidence of opioid withdrawal

Withdrawal from ethanol is aversive. The question is why. As with the withdrawal from morphine, nicotine, diazepam and sugar, the ethanol withdrawal state may involve an increase in nucleus accumbens (NAc) acetylcholine (ACh) causing an alteration of the dopamine (DA)-ACh balance in favor of ACh. Therefore the effects of acute and chronic alcohol (1 gm/kg/day i.p.) treatment on extracellular concentrations of NAc ACh and DA were determined before and after naloxone-precipitated withdrawal. Ethanol initially increased DA to 119% of baseline as measured by microdialysis. This was still the case on the 21st day of ethanol injection when DA increased to 126%. There was no effect of ethanol on ACh. However, naloxone (3 mg/kg s.c.) injected the next day decreased extracellular DA to 83% of baseline and caused a significant rise in ACh to 119%. This state of high ACh combined with low DA may contribute to the aversive aspects of alcohol withdrawal.

A high-fat meal or injection of lipids stimulates ethanol intake

Findings of earlier studies support the idea of a possible relation between dietary fat and ethanol intake, but it is unclear whether acute exposure to fat can increase ethanol consumption directly. In the current series of experiments, we examined whether daily overeating of fat, a single high-fat meal, or the injection of fat can increase ethanol intake. In Experiment 1, adult Sprague-Dawley rats were maintained on a high-fat diet (50% fat) for 7 days and switched subsequently to a laboratory chow diet while being trained to drink 9% ethanol. Rats that had eaten the greatest amount of the high-fat diet subsequently drank the most ethanol. In Experiment 2, a 1-h meal of the high-fat diet (50% fat) produced a significant increase in 7% ethanol consumption in comparison with what occurred after consumption of an equicaloric, low-fat (10% fat) meal. In Experiment 3, the orosensory effect of fat was eliminated with an intraperitoneal injection of a fat emulsion, Intralipid (20% fat, 5.0 ml). The injection of Intralipid, in comparison with saline, increased the ingestion of 9% ethanol. This finding is in contrast to what occurred with injection of an equicaloric, 50% glucose solution, which suppressed ethanol intake. These findings provide new evidence to support a positive relation between dietary fat and the consumption of ethanol.

Sugar-dependent rats show enhanced intake of unsweetened ethanol

Rats show signs of dependence on sugar when it is available intermittently, including bingeing, withdrawal, and cross-sensitization with amphetamine. In the current study, we sought to determine whether sugar-dependent rats would show increased intake of unsweetened ethanol and, conversely, whether intermittent access to ethanol would augment sugar consumption. In Experiment 1, with intermittent versus ad libitum access to ethanol, Sprague-Dawley rats were given escalating concentrations of ethanol (1%, 2%, 4%, 7%, and 9%) over the course of 20 days. Rats in the intermittent ethanol access group, with 12-h daily access, consumed more 4%, 7%, and 9% ethanol during the first hour of access, and more 9% ethanol daily, than did rats in the ad libitum ethanol access group. In Experiment 2, with ethanol as a gateway to sugar intake, the rats from Experiment 1 were switched to 10% sucrose with 12-h daily access for 1 week. Rats in the intermittent ethanol access group consumed significantly more sugar than was consumed by rats in a control group with no prior ethanol experience. In Experiment 3, with sugar as a gateway to ethanol to determine whether sugar dependence leads to increased ethanol intake, four groups were maintained for 21 days according to the following designations: intermittent access to sugar and chow, ad libitum access to sugar and chow, intermittent access to chow, or ad libitum access to chow. Four days later, all groups were switched to intermittent ethanol access, as described in Experiment 1. The group with intermittent access to sugar and chow consumed the most 9% ethanol, supporting the suggestion that sugar dependence alters a rat's proclivity to drink ethanol. These results may relate to the co-morbidity between binge-eating disorders and alcohol intake and the tendency of people abstaining from alcohol to consume excessive amounts of sugar. In conclusion, bingeing on either ethanol or sugar fosters intake of the other.

Opiate-like effects of sugar on gene expression in reward areas of the rat brain

Drugs abused by humans are thought to activate areas in the ventral striatum of the brain that engage the organism in important adaptive behaviors, such as eating. In support of this, we report here that striatal regions of sugar-dependent rats show alterations in dopamine and opioid mRNA levels similar to morphine-dependent rats. Specifically, after a chronic schedule of intermittent bingeing on a sucrose solution, mRNA levels for the D2 dopamine receptor, and the preproenkephalin and preprotachykinin genes were decreased in dopamine-receptive regions of the forebrain, while D3 dopamine receptor mRNA was increased. While morphine affects gene expression across the entire dopamine-receptive striatum, significant differences were detected in the effects of sugar on the nucleus accumbens and adjacent caudate-putamen. The effects of sugar on mRNA levels were of greater magnitude in the nucleus accumbens than in the caudate-putamen. These areas also showed clear differences in the interactions among the genes, especially between D3R and the other genes. This was revealed by a novel multivariate analysis method that identified cooperative interactions among genes, specifically in the nucleus accumbens but not the caudate-putamen. Finally, a role for these cooperative interactions in a load-sharing response to perturbations caused by sugar was supported by the finding of a different pattern of correlations between the genes in the two striatal regions. These findings support a major role for the nucleus accumbens in mediating the effects of naturally rewarding substances and extend an animal model for studying the common substrates of drug addiction and eating disorders.

Overlapping Peptide Control of Alcohol Self-Administration and Feeding

This article represents the proceedings of a symposium at the 2003 annual meeting of the Research Society on Alcoholism in Fort Lauderdale, FL. The organizers and chairpersons were Mark Egli and Todd E. Thiele. The presentations were (1) Voluntary alcohol consumption is modulated by central melanocortin receptors, by Todd E. Thiele; (2) Central infusion of neuropeptide Y reduces alcohol drinking in alcohol-preferring P rats, by Robert B. Stewart and Nancy E. Badia-Elder; (3) The gut peptide cholecystokinin controls alcohol intake in Sardinian alcohol-preferring rats, by Nori Geary and Maurizio Massi; and (4) Hypothalamic galanin: a possible role in excess alcohol drinking, by Sarah F. Leibowitz and Bartley G. Hoebel.

A diet promoting sugar dependency causes behavioral cross-sensitization to a low dose of amphetamine

Previous research in this laboratory has shown that a diet of intermittent excessive sugar consumption produces a state with neurochemical and behavioral similarities to drug dependency. The present study examined whether female rats on various regimens of sugar access would show behavioral cross-sensitization to a low dose of amphetamine. After a 30-min baseline measure of locomotor activity (day 0), animals were maintained on a cyclic diet of 12-h deprivation followed by 12-h access to 10% sucrose solution and chow pellets (12 h access starting 4 h after onset of the dark period) for 21 days. Locomotor activity was measured again for 30 min at the beginning of days 1 and 21 of sugar access. Beginning on day 22, all rats were maintained on ad libitum chow. Nine days later locomotor activity was measured in response to a single low dose of amphetamine (0.5 mg/kg). The animals that had experienced cyclic sucrose and chow were hyperactive in response to amphetamine compared with four control groups (ad libitum 10% sucrose and chow followed by amphetamine injection, cyclic chow followed by amphetamine injection, ad libitum chow with amphetamine, or cyclic 10% sucrose and chow with a saline injection). These results suggest that a diet comprised of alternating deprivation and access to a sugar solution and chow produces bingeing on sugar that leads to a long lasting state of increased sensitivity to amphetamine, possibly due to a lasting alteration in the dopamine system.

Glutamate release in the nucleus accumbens is involved in behavioral depression during the PORSOLT swim test

An abnormality in glutamate function has been implicated in the neural substrate of depressive disorders. To investigate this in rats, the Porsolt swim test was used to assess the role of glutamate in the nucleus accumbens. Glutamate injected into the nucleus accumbens dose-dependently decreased swimming time on the test day (day 2), whereas N-methyl-D-aspartate antagonists dizocilpine and 2-amino-5-phosphonovalerate increased swimming, like an antidepressant. Dizocilpine injected before the conditioning trial (day 1) did not modify the swimming times during the first day but abolished behavioral depression on day 2. Microdialysis coupled to capillary-zone electrophoresis was then used to determine in vivo changes in glutamate release in 1-min samples during the swim test. On day 1, glutamate increased significantly and reached a maximum of 222% after 3 min of swimming. On day 2, baseline glutamate levels were back to normal, but when the animal was placed in the water, glutamate increased to 419% during the first minute, and the animals swam significantly less. For comparison, tail pinch on consecutive days was used as a nonspecific, repeated stressor while accumbens glutamate levels were measured. Tail pinch on the first day increased glutamate similar to the effect obtained during the first day of swimming; however, a second day of tail pinch decreased glutamate levels, instead of the potentiated response observed during the second day of swimming. These results show that accumbens glutamate plays a role in causing the behavioral aspects of depressed behavior as modeled in the swim test. The accumbens may be a potential site of action for drugs that alter behavioral depression.