The anorectic effect of SK&F 38393, a selective dopamine D1 receptor agonist: a microstructural analysis of feeding and related behaviour

Role of the striatal dopamine, GABA and opioid systems in mediating feeding and fat intake

Food intake, which is a highly reinforcing behavior, provides nutrients required for survival in all animals. However, when fat and sugar consumption goes beyond the daily needs, it can favor obesity. The prevalence and severity of this health problem has been increasing with time. Besides covering nutrient and energy needs, food and in particular its highly palatable components, such as fats, also induce feelings of joy and pleasure. Experimental evidence supports a role of the striatal complex and of the mesolimbic dopamine system in both feeding and food-related reward processing, with the nucleus accumbens as a key target for reward or reinforcing-associated signaling during food intake behavior. In this review, we provide insights concerning the impact of feeding, including fat intake, on different types of receptors and neurotransmitters present in the striatal complex. Reciprocally, we also cover the evidence for a modulation of palatable food intake by different neurochemical systems in the striatal complex and in particular the nucleus accumbens, with a focus on dopamine, GABA and the opioid system.

Perinatal malnutrition stimulates motivation through reward and enhances drd(1a) receptor expression in the ventral striatum of adult mice

AIM

The aim of this study was to analyze the effects of protein perinatal malnutrition on the function of dopamine DRD1 and DRD2 receptors in regards to motivation and food consumption in adult mice. The study also analyzed the effect of protein perinatal malnutrition on the gene expression of these receptors in the ventral striatum.

METHODS

Wistar lineage mice were divided into two groups according to maternal diet: control (17% casein), n=30 and low protein (8% casein), n=30. Between 30 and 120days of life, the following factors were measured: body weight; the effect of dopamine D1 and D2 agonists on the ingestion of palatable food; the motivational aspect under the action of the D1 (SKF 38393) and D2 Quinpirole dopaminergic agonists; and the gene expression of DRD1 and DRD2 receptors in the ventral striatum.

RESULTS

The body weights of the malnourished animals remained significantly lower than those of the control group from 30 to 120days of life. Malnourished animals ingested a greater quantity of palatable food. There was a decrease in palatable diet consumption in both the control and malnourished groups after the application of D1 and D2 agonists; however, the anorexic effect of the D1 agonist was understated in malnourished animals. Perinatal malnutrition increases the motivational behavior of the animal when food reward is used. There was an increase in gene expression of the DRD1a receptor in the ventral striatum of malnourished animals, and there were no significant changes concerning the DRD2 receptor.

CONCLUSIONS

Perinatal protein malnutrition stimulates hedonic control of eating behavior by promoting increased intake of palatable foods, possibly due to increased expression of dopamine receptor DRD1a in the ventral striatum.

The effect of dopamine on adult hippocampal neurogenesis

Cumulative studies indicated that adult hippocampal neurogenesis might be involved in the action mechanism of antidepressant drugs and/or the pathophysiology of depression. Dopamine (DA) is involved in the regulation of motivation, volition, interest/pleasure, and attention/concentration, all of which are likely to be impaired in depressed patients. Several previous reports suggest that depression may often be accompanied by a relative hypo-dopaminergic state, and some DA receptor agonists are beneficial effects in the treatment for refractory and bipolar depression. In the present study, to clarify the direct effect of DA on neural progenitor cells, we examined the effect of DA on the proliferation of adult rat dentate gyrus-derived neural precursor cells (ADPs). In addition, we examined the effect of DA receptor agonists on adult rat hippocampal neurogenesis in vivo. Results showed that DA promoted the increase of ADPs via D1-like receptor and D1-like receptor agonist promoted the survival of newborn cells in the adult hippocampus. On the contrary, D2-like receptor agonist did not affect both proliferation and survival. These results suggested that DA might play, at least in part, a role in adult hippocampal neurogenesis via D1-like receptor and the activation of D1-like receptor has a therapeutic potential for depression.

The cannabinoid CB1 receptor inverse agonist AM 251 and antagonist AM 4113 produce similar effects on the behavioral satiety sequence in rats

Cannabinoid CB1 inverse agonists such as rimonabant and AM 251 hold therapeutic promise as appetite suppressants, but the extent to which non-motivational factors contribute to their anorectic effects is not fully known. Examination of the behavioral satiety sequence (BSS) in rats, the orderly progression from eating to post-prandial grooming and then resting, has revealed that these compounds preserve the order of events but differ markedly from natural satiation. The most notable difference is that grooming (particularly scratching) is profoundly enhanced at anorectic doses, while eating and resting are diminished, raising the possibility that the anorectic effect is simply secondary to the grooming effect. In the current design, the neutral CB1 antagonist AM 4113, which has been found to lack some of the undesirable effects of AM 251, produced nearly identical effects on the BSS as AM 251. The possibility that competition from enhanced grooming could account for the anorectic effect of AM 4113 was examined by yoking the pattern of disruptions caused by grooming in the AM 4113-treated group to forced locomotion in a different group fed in a modified running wheel. This response competition did not significantly reduce food intake. It was concluded that AM 4113, a CB1 neutral antagonist, produces the same effects on the BSS as AM 251, but that response competition from enhanced grooming may not be a sufficient explanation for the anorectic effects of CB1 antagonists/inverse agonists.

Dopaminergic control of food choice: Contrasting effects of SKF 38393 and quinpirole on high-palatability food preference in the rat

The aim of the present study was to determine the behavioural effects of the selective dopamine D1 receptor agonist, SKF 38393, and of the selective dopamine D2/D3 receptor agonist, quinpirole, on the feeding performance of food-deprived rats in a model of food-preference behaviour. The animals were familiarised with a choice between a high-palatability, high-fat, high-sugar food (chocolate biscuits/cookies) and their regular maintenance diet. Following administration of either SKF 38393 (1.0-10.0 mg/kg, s.c.) or quinpirole (0.03-0.3 mg/kg, s.c.), the animals were observed throughout a 15-min test period, and their feeding behaviour was carefully monitored. Other behavioural categories were also observed. The resulting data were subject to a microstructural analysis to determine the loci of the behavioural effects. The results indicated that SKF 38393 and quinpirole had contrasting effects on the preference for the high-palatability chocolate food. SKF 38393 enhanced the preference, whereas quinpirole eliminated it. These data reinforce the view that forebrain dopamine mechanisms are closely involved in responses to high-palatability energy-dense food constituents, including chocolate. The data also indicate that pharmacological characterization is important, such that dopamine receptor subtypes appear to mediate contrasting effects on food preference for a high-fat, high-sugar food. Hence, brain dopamine appears to be involved in potentially complex ways in determining food preferences, and this may carry implications in the growing evidence for a link between brain dopamine and human obesity.

The anorectic effect of the selective dopamine D1-receptor agonist A-77636 determined by meal pattern analysis in free-feeding rats

Free-feeding rats meet much of their daily energy requirements by consuming food in meals during the nocturnal phase of the night/day cycle. Meal pattern analysis methodology has been developed to record the patterns of meal taken over a 24-h period, and to provide detailed information on a number of meal-related parameters. Previous work indicates that selective dopamine D1-receptor agonists reduce food intake in short-term feeding tests under the control of homeostatic or hedonic factors. In the present study, our aim was to investigate the effects of the dopamine D1-receptor agonist, A-77636 (0.1-1.0 mg/kg, s.c.), administered just prior to the start of the night period, on the free-feeding and drinking patterns of rats maintained on a standard ad libitum diet. The results indicate that A-77636 exerted a suppressant effect on food intake, due principally to a reduction in meal size and duration. We conclude that there is a dopamine D1-receptor involvement in the normal controls of meal size, and that selective D1-receptor agonists may act to limit meal size.

Reduction of anxiety after restricted feeding in the rat: implication for eating disorders

BACKGROUND

Eating-disorder patients exhibit not only abnormal eating attitudes but also pathologic anxiety-like behaviors. The specific nature of the relationship between dieting and anxiety-like behavior is unknown.

METHODS

To investigate the adaptational changes that resulted from chronic restricted scheduled feeding (2-hour access per day for 2 weeks) and subsequent free refeeding, longitudinal changes in the microstructure of feeding behavior were studied in male rats. To study the relationship between restricted feeding and anxiety-like behavior, separate rats were tested in the elevated plus-maze under the following conditions: 1) free feeding; 2) acute food restriction (2-hour access for 1 day); 3) chronic food restriction (for 10 days); or 4) postrecovery (after 10 days of free feeding subsequent to chronic food restriction).

RESULTS

The effects of chronic food restriction on meal structure diminished within a few days after refeeding. Decreased anxiety-like behavior was seen during acute and chronic food restriction and did not reflect nonspecific behavioral activation. Anxiolytic-like effects persisted after 10 days of refeeding.

CONCLUSIONS

Chronic food restriction produced reductions in anxiety-like behavior that persisted beyond the normalization of food intake patterns. The findings might have etiologic and pathophysiologic relevance for the restrained eating pattern in eating-disorder patients with comorbid anxious symptoms.

Human urocortin II, a selective agonist for the type 2 corticotropin-releasing factor receptor, decreases feeding and drinking in the rat

Corticotropin-releasing factor (CRF) has been hypothesized to modulate consummatory behavior through the Type 2 CRF (CRF(2)) receptor. However, behavioral functions subserved by the CRF(2) receptor remain poorly understood. Recently, human urocortin II (hUcn II), a selective CRF(2) receptor agonist, was identified. To study the effects of this neuropeptide on ingestive behavior, we examined the effects of centrally infused hUcn II (i.c.v. 0, 0.01, 0.1, 1.0, 10.0 micro g) on the microstructure of nose-poke responding for food and water in nondeprived, male rats. Malaise-inducing properties of the peptide were monitored using conditioned taste aversion (CTA) testing. To identify potential sites of action, central induction of Fos protein expression was examined. hUcn II dose dependently reduced the quantity and duration of responding for food and water at doses lower (0.01-1.0 micro g) than that forming a CTA (10 micro g). Effects were most evident during hours 4 to 6 of the dark cycle. Meal pattern analysis showed that hUcn II potently (0.1 micro g) increased the satiating value of food. Rats ate and drank smaller and shorter meals without changing meal frequency. Rats also ate more slowly. hUcn II induced Fos in regions involved in visceral sensory processing and autonomic/neuroendocrine regulation and resembling those activated by appetite suppressants. hUcn II is a promising neuropeptide for investigating the role of the CRF(2) receptor in ingestive behavior.

Cocaine-induced hypophagia and hyperlocomotion in rats are attenuated by prazosin

The present studies examined the effects of antagonizing alpha(1)-adrenoceptors via systemic administration of prazosin on the behavioral actions of cocaine in rats, including induction of locomotion and suppression of eating. In Experiment 1, locomotor activity was monitored in automated chambers for 80 min in adult male rats pretreated with the alpha(1)-adrenoceptor antagonist prazosin (0, 0.5, or 2 mg/kg, i.p.) and then treated (i.p.) with either 0, 10, 20, or 40 mg/kg cocaine hydrochloride. Cocaine dose-dependently increased total distance traveled and the number of stereotypy counts, and significantly decreased rest time. Each dose of prazosin produced a significant attenuation of the locomotor effects of a limited range of cocaine doses (i.e. 10 and/or 20 mg/kg cocaine, but not 40 mg/kg cocaine). Prazosin alone did not alter any measure of locomotion. In Experiment 2, eating and drinking were monitored for 60 min in male rats pretreated with prazosin (0, 1, and 2 mg/kg, i.p.) and then treated with 0, 10, 20, or 40 mg/kg (i.p.) cocaine. Rats pretreated with vehicle exhibited a dose-dependent suppression of eating, but not drinking, to cocaine. The impact of prazosin on cocaine-induced hypophagia paralleled that noted for locomotion in that administration of prazosin significantly attenuated the hypophagic action of 20 mg/kg cocaine, but not that of 40 mg/kg cocaine. These findings confirm earlier studies noting a partial role for alpha(1)-adrenoceptors in the locomotor stimulant actions of cocaine and extend those findings to the feeding-inhibitory actions of cocaine.

Behavioral satiety sequence (BSS) for the diagnosis of drug action on food intake

The Behavioral Satiety Sequence (BSS) is the name given to the orderly transitions of eating, activity grooming and resting measured during the postingestive period. Because the BSS is considered to reflect the operations of natural physiological processes underlying satiety, the sequence can be used to discriminate between different drugs (and other manipulations) that reduce food intake via these natural physiological mechanisms or those that do so by interference. The BSS is only produced by the presence of a caloric load in the gut, and the preabsorptive satiety factors (such as CCK) the caloric load triggers. The BSS is most accurately defined by continuous observation rather than time or event sampling techniques [Partial Time Sampling (PTS) or Momentary Time Sampling (MTS)]. Continuous observation also allows the true duration and true frequency of each behavior to be analyzed. Continuous observation can be used to determine if the profiles associated with the reduction in food intake is caused by nausea, sedation, hyperactivity, or altered palatability of food. At the present time is it possible to identify a number of drugs whose suppression of food intake is associated with the disruption or preservation of the BSS. Drugs that increase synaptic 5-HT activity such d-fenfluramine, fluoxetine. and sibutramine all preserve the BSS and advance the onset of resting. The 5-HT1b/2c agonists mCPP and TFMPP and the 5-HT1b agonist CP-94,253 produce similar effects. However, the 5-HT2 agonist DOI and the 5-HT1a/1b agonist RU-24969 disrupt the BSS by inducing hyperactivity as does amphetamine. The 5-HT2 agonist MK-212 disrupts the BSS by inducing sedation. Selective dopamine agonists, at low doses, such as SKF-38393 (DA1) and LY-171555 (DA2) also preserve the BSS. However, detailed behavioral analysis of the effects of many recently discovered putative satiety factors remains to be carried out.

Dopamine receptor subtype agonists and feeding behavior

Stimulation or blockade of various dopamine receptor subtypes is associated with reduced feeding. For example, D2 receptor agonists suppress feeding in food-deprived and free-feeding rats, and in rats given access to a highly palatable diet. Similarly, reduced food intake is associated with the actions of diverse D1 receptor agonists, and these compounds can interact synergistically with D2 receptor agonists to potentiate reductions in feeding. Using microstructural analysis to compare D1 and D2 agonist effects, specific differences emerge in their modes of action. D1 agonists reduce the duration of feeding, primarily by decreasing the frequency of feeding bouts, whereas D2 agonists reduce the local rate of eating. However, since D1 agonists uniquely reduce feeding in the absence of other behavioral impairments and are less disruptive of the pattern of feeding behavior, it has been suggested that D1 agonists are more likely than D2 agonists to act on central mechanisms regulating food intake. Moreover, only D1 agonists are effective in suppressing sucrose sham-feeding, suggesting that D1 receptor stimulation may promote satiety. Nevertheless, many questions remain. For example, antagonist studies have implicated 5-HT receptor stimulation in the anorectic effects of D1 agonists, suggesting that further pharmacological and behavioral analyses of receptor-subtype agonist effects are required. Above all, recent developments in the classification of dopamine receptor subtypes reveal the need for new studies examining the involvement of D3, D4 and D5 receptors in feeding.

Effects of SCH39166 and domperidone on the meal patterning of male rats

In male rats given free access to food (45 mg pellets) and water, ingestive behavior is structured into meals. The selective dopamine D1 antagonist SCH39166 had little effect on total food intake, meal size, or feeding rate. However, it did produce a marked, dose-related reduction in drinking that resulted from an increase in intermeal interval with unchanged meal size. Possible peripheral and central explanations of this effect are discussed. In a second experiment, the peripheral dopamine D2 antagonist, domperidone, was shown to have little effect on either feeding or drinking. A dose of 10 mg/kg did reduce feeding rate, but this probably represents a central effect, because doses that were only slightly higher have previously been shown to reduce stimulant-induced hyperactivity and stereotypy. These experiments confirm the functional distinction between D1-like and D2-like dopamine receptors in the control of ingestive behavior, with the D1 receptor having a greater role in drinking and central D2 receptors affecting several aspects of feeding behavior.

Effects of the dopamine D1 receptor antagonist SCH 39166 on the ingestive behaviour of alcohol-preferring rats

The present study evaluated the effect of the selective and long-acting dopamine D1 receptor antagonist SCH 39166 on several aspects of the ingestive behaviour of genetically selected alcohol-preferring rats, bred from Sardinian alcohol-preferring rats. The effect of subchronic (8 days) subcutaneous drug administration was evaluated on the simultaneous daily intake of 10% ethanol, food and water. SCH 39166, 0.1 mg/kg, did not significantly modify the intake of the three ingesta. The dose of 1 mg/kg differentially modified rat ingestive behaviour, inhibiting intake of 10% ethanol, without modifying total fluid and food intake. The higher dose of 5 mg/kg produced a non-selective suppression of ingestive behaviour, which was accompanied by behavioural impairment. Acute drug injection was tested on 2-h intake of 10% sucrose, 0.1% saccharin, water or food. The doses of 0.1 and 1 mg/kg markedly inhibited the 2-h intake of 10% sucrose and 0.1% saccharin, but they did not modify either the 2-h water intake in water deprived and water sated rats or the 2-h food intake in food deprived rats. These findings suggest an important role of mechanisms mediated by D1 receptors in the control of alcohol and sweet solution intake, but not in water and food intake. Moreover, they indicate that SCH 39166, in relation to its selectivity and long-lasting activity, is an interesting pharmacological tool to investigate further the role of D1 receptor mechanisms in the control of ingestive behaviour.

Analysis of the effects of intra-accumbens SKF-38393 and LY-171555 upon the behavioural satiety sequence

The outcome of intra-accumbens infusions of the dopamine D1 receptor family agonist SKF-38393 and the D2 receptor family agonist LY-171555 upon measures taken during the behavioural satiety sequence was assessed (0.01 micrograms, 0.1 micrograms, 1.0 micrograms in each case). Each drug was infused either separately, or together as a co-infusion in order to examine the functional relationship between these dopamine receptor subtypes within the nucleus accumbens. Measures of feeding did not change following infusions of SKF-38393 or LY-171555, whether infused separately or together. However, following separate infusion of the lowest dose tested of each drug (0.01 micrograms), the onset of resting was advanced. Moderate to high doses of SKF-38393 and LY-171555 (0.1 micrograms, 1.0 micrograms) infused separately resulted in a marked increase in activity at the expense of resting. Co-infusion of 0.01 micrograms of each drug also resulted in a dramatic increase in activity. Thus, measures of feeding behaviour were unchanged following excitation of D1 and D2 dopamine receptor families within the nucleus accumbens. In marked contrast, locomotor behaviour appeared to be under the potent synergistic control of these receptor families.

Effect of lead exposure on patterns of food intake in weanling rats

The reduction in growth resulting from lead (PB) exposure in weanling rats is consistent with a lowering of the biological set-point for food intake. In this study the effects of lead on the patterns of food intake were examined. For 10 days (from ages 26 to 36 days), female rats were provided with drinking water containing 250 ppm lead as the acetate (n = 6) or equivalent acetate as sodium acetate (n = 6). A computerized system was used to monitor daily food intake at 5-min intervals over 10 successive 23-h periods (each period consisting of 12 h dark, 11 h light). Control rats consumed approximately 75% to 85% of their food intake during the dark phase. Exposure to lead resulted in decreased body weight, tail length, and cumulative food intake. Decreased food intake associated with lead during the first 6 days of exposure was due to a decrease in the size of each meal during the dark phase, which reflected a decrease in the duration of each meal. These results suggest that lead, at least initially, was affecting food-satiety signals to produce a premature termination of food intake during a meal. After 6 days, the lead-exposed rats appear to have adjusted their meal size and meal duration to approximately control values. However, this compensation appears to have occurred at the expense of the daily (nocturnal) number of meals, which decreased slightly (although not significantly) in lead-exposed animals. Thus, the total daily intake of food in lead-treated animals remained depressed relative to control animals.

The effect of B-HT 920, a dopamine D2 agonist, on bar-press feeding in the monkey

Although the dopamine (DA) system has been shown to regulate food intake, the function of the DA receptor subtypes on behavior still remains to be elucidated. In the present study, we examined the effect of B-HT 920, a selective agonist of DA D2 receptors that preferentially affect presynaptic autoreceptors, on both food consumption and execution of a high fixed-ratio bar-press task for food reward in monkeys. Two kinds of bar-press task were used: 1) a cue-triggered bar-press task during the first 40 trials, and 2) a self-paced bar-press task in which the monkeys freely performed bar-press trials until they were satiated. A SC injection of B-HT 920 (25 micrograms/kg) increased food consumption in the home cage. The same facilitatory effect on food consumption was also observed in the operant task condition. During the cue-triggered bar-press task, however, both the latency of the bar-press responses to a cue light and the time required to complete the bar-press trials were prolonged after the injection of B-HT 920. The results suggest that the activation of D2 autoreceptors suppresses the operant food acquisition behavior and increases food consumption through an inhibition of the satiety mechanism rather than an activation of any hunger-related drive.

The selective dopamine uptake inhibitor GBR 12909: its effects on the microstructure of feeding in rats

Previous experiments have investigated the anorectic effects of mazindol and cocaine, both of which can inhibit dopamine (DA) uptake into presynaptic terminals but do not do so selectively. GBR 12909, however, is an example of a potent and selective inhibitor of DA uptake and, therefore, the present study was concerned with investigating its possible effects on feeding behavior in nondeprived rats given access to a sweetened palatable diet. GBR 12909 (5-20 mg/kg, IP) was injected 2 h before a 60 min observation test. It produced a significant reduction in food intake, as a consequence of a reduction in the duration of feeding, without reducing the rate of eating. This anorectic profile is consistent with earlier findings for mazindol and cocaine. The other main behavioral effect of GBR 12909, observed in the present study, was to induce intense sniffing activity, but, unlike cocaine, it did not suppress grooming or induce hyperlocomotion. This selective behavioral effect of GBR 12909 indicates that sniffing can be isolated as one component of a broader array of components typically associated with DA-related stereotyped behavior.

A comparison of the effects of the D1 receptor antagonists SCH 23390 and SCH 39166 on suppression of feeding behavior by the D1 agonist SKF38393

The hypophagic effect of the D1 receptor agonist SKF 38393 is not dose-dependently antagonized by the D1 antagonist SCH 23390. Moreover, the receptor specificity of this interaction remains in question, since SCH 23390 has significant activity at both 5-HT2 and 5-HT1C receptors, and SKF 38393 also interacts with 5-HT1C receptors. To determine the relative significance of these actions, a comparison was made between the anorectic effects in rats of SCH 23390 (0.1-1.0 mg/kg) and the benzonaphthazepine SCH 39166 (0.1-3.0 mg/kg), a D1 antagonist with negligible affinity for 5-HT sites. Both compounds inhibited food-intake dose-dependently, with SCH 23390 being approximately twice as potent as SCH 39166. Behaviorally inactive and active doses of both antagonists were tested in combination with the D1 agonist SKF 38393 (10-56 mg/kg). Neither antagonist was able to produce more than a marginal attenuation of the agonist-induced hypophagia. This demonstrates that previous failures to reverse the behavioral actions of SKF 38393 by SCH 23390 were not due to specific actions of this particular antagonist. Finally, like SCH 23390, SCH 39166 (0.3 mg/kg) was able to attenuate fully the anorectic effects of the D1 agonist SKF 82958 (1.0 and 3.0 mg/kg), demonstrating that neither compound is intrinsically unable to block D1 receptor-mediated hypophagia. The results demonstrate the generality of the D1 antagonist-mediated effect on feeding and call into question the use of SKF 38393 as a D1 agonist in studies of feeding, and perhaps in other contexts as well.

Evidence that neuropeptide Y and dopamine in the perifornical hypothalamus interact antagonistically in the control of food intake

Mapping studies have revealed that the perifornical hypothalamus (PFH) is a primary locus for both the feeding-stimulatory effect of neuropeptide Y (NPY) and the anorectic effect of catecholamines (CAs), suggesting that NPY and CAs may interact antagonistically there. To investigate this, the CA-releasing agent amphetamine (AMPH) was injected through indwelling guide cannulas into the PFH of satiated adult male rats 5 min prior to injection of NPY (78 pmol/0.3 microliters) and food intake was measured 1, 2, and 4 h later. Amphetamine (50-200 nmol) dose-dependently reduced NPY feeding, usually eliminating it at the higher doses. The receptors mediating this effect were investigated by sequential injection of various CA antagonists, AMPH, and NPY into the PFH. Neither the alpha- nor beta-adrenergic receptor antagonists phentolamine (100 nmol) or propranolol (200 nmol) significantly affected AMPH suppression of NPY feeding. In contrast, the dopamine receptor antagonist haloperidol (5 nmol) abolished AMPH suppression of NPY feeding, suggesting that dopamine (DA) mediates the AMPH effect. To examine this, epinephrine (EPI, 50-200 nmol) and DA (25-200 nmol) were tested for suppression of NPY-induced feeding. While EPI had no significant effect, DA at the maximally effective dose (50 nmol) reduced the NPY feeding response by 36% or more. These findings provide convergent evidence for antagonistic interactions between endogenous DA and NPY in the control of eating behavior.

Sleep-related eating disorder as a cause of obstructive sleep apnea

A patient with obesity resulting from sleep-related eating disorder demonstrated signs and symptoms of obstructive sleep apnea (OSA). Incarceration restricted access to food during the night, leading to weight loss and clinical improvement. Release from prison allowed recurrence of unrestricted sleep-eating, recurrent obesity, and documented OSA. Successful treatment of sleep-related eating disorder can result in improvement in coexisting OSA.

Cocaine: a microstructural analysis of its effects on feeding and associated behaviour in the rat

Cocaine (5.6-30 mg/kg, i.p.) was administered to nondeprived male rats trained to eat a palatable sweetened mash. Over a 60-min period, their behaviour was observed and recorded for a microstructural analysis. Cocaine suppressed feeding in a dose-dependent manner (significantly at 10 mg/kg and greater), and this was due in the main to a reduction in the frequency of eating bouts. In contrast, the mean duration of eating bouts was unaffected, except at the highest dose, 30 mg/kg. In addition, the rate of eating was not significantly affected by cocaine at any dose. Time-course data revealed that cocaine, at anorectic doses (10-30 mg/kg), initially suppressed feeding completely, and the duration of this suppression was proportional to the dose. In effect, cocaine delayed the initiation of feeding, thus bringing about the reduction in the number of eating bouts. Cocaine caused some stimulation of locomotor activity and rearing to the side of the observation tank, but did not affect rearing away from the centre, or immobility. Grooming proved to be very sensitive to cocaine's suppressant effect, with substantial inhibition occurring at 5.6 mg/kg (a sub-anorectic dose). These data are compared with previously published work with D-amphetamine and are contrasted with results for selective D1 and D2 dopamine receptor agonists.

Selective dopamine D-1 receptor agonists, SK&F 38393 and CY 208-243 reduce sucrose sham-feeding in the rat

Gastric-fistulated rats were trained to sham-feed a 10% sucrose solution in a 60 min test. The selective dopamine D-1 receptor agonists, SK&F 38393 (3 and 10 mg/kg, s.c.) and CY 208-243 (1 and 3 mg/kg, s.c.) both produced dose-related reductions in sham-feeding. These effects were present in the first 5 min of the test period, and persisted throughout the remainder of the test. The data confirm and extend results for an anorectic effect of SK&F 38393 and demonstrate, for the first time, a similar anorectic effect of CY 208-243.

Evidence for dopamine D-1 receptor-mediated facilitatory and inhibitory effects on feeding behaviour in rats

Early studies on dopamine agonists and feeding behaviour showed that apomorphine, administered either centrally or systemically, reduced food intake. While this anorectic effect was later analysed in some detail, it was also recognized that, under some circumstances, apomorphine could increase food consumption. Once the distinction between dopamine D-1 and D-2 receptors had been drawn, and receptor-specific agonists and antagonists had become available, the way was clear to investigate the potential roles of D-1 and D-2 receptor subtypes in relation to ingestional behaviour. This paper reviews evidence which indicates, first of all, that D-1 receptor agonists reduce food intake relatively specifically and that the effect cannot be attributed to the induction of intrusive mouth movements or to general behavioural changes (e.g. increased arousal or sedation). We show that dopamine D-1 agonists reduce sucrose sham-feeding in the gastric-fistulated rat. Secondly, however, we provide initial evidence that D-1 agonist activity can have a facilitatory effect on feeding behaviour. More specifically, the D-1 agonist, SKF 38393, increased the response to a highly palatable food in a food-preference test. This result is compared with published reports that injections of either D-amphetamine or morphine into the nucleus accumbens increases feeding behaviour. We speculate that D-1 receptors in the nucleus accumbens may be involved in the mediation of preference for more palatable foods.

Differential antagonism of the effects of dopamine D1-receptor agonists on feeding behavior in the rat

A series of experiments was conducted to examine the effects of dopamine D1 receptor agonists on food intake in rats. In the first experiment, the D1 agonist SKF 38393 (3.0-30.0 mg/kg) dose-dependently suppressed feeding during a 40 min food-access period, both in food-deprived rats and in non-deprived rats fed a highly palatable diet. Non-deprived rats were more sensitive to these effects of SKF 38393. Using the limited-access, food-deprivation procedure, a comparison was made between the anorectic effects of three D1 agonists with differing intrinsic efficacies and receptor selectivities. Rank order of potencies for reducing food intake was SKF 82958 > SKF 77434 > SKF 38393 (ED50 values: 0.7, 3.6 and 15.7 mg/kg, respectively). Dose-related, surmountable antagonism by the D1 antagonist SCH 23390 (0.01 and 0.03 mg/kg) was only obtained with SKF 82958 (0.1-10.0 mg/kg). In contrast to the other compounds, the effects of SKF 38393 were not appreciably altered by the D1 antagonist. The effects of SKF 82958 were also antagonized by the D2 receptor antagonist spiperone (0.05 and 0.1 mg/kg), although not in a dose-dependent manner. The present results support a role for D1 receptors in central feeding mechanisms. They also suggest that the effects of SKF 38393 on feeding may not be mediated exclusively by the D1 receptor and, further, that SKF 38393 may not serve well in behavioral studies as a prototypical D1 agonist. The results also demonstrate the need for comparisons among several compounds in studies of D1 mediated behavioral effects.

Dopaminergic control of locomotion, mouthing, snout contact, and grooming: opposing roles of D1 and D2 receptors

The study compares the behavioral profiles induced in rats (N = 118) by the D2-dopaminergic receptor agonist quinpirole (0.03 and 0.5 mg/kg), and the D1-agonist SKF38393 (1.25-40 mg/kg), and both agonists administered together. Locomotion and snout contact frequency were reduced by the low but increased by the high dose of quinpirole; SKF38393 also reduced these behaviors and attenuated the effect of the high quinpirole dose. Only the high dose of quinpirole increased the duration of snout contact bouts and the frequency of mouthing; SKF38393 had no effect but in combination with the high dose of quinpirole, it enhanced the performance of these behaviors greatly. The duration of mouthing bouts was not affected by either agonist but was greatly extended when SKF38393 was administered together with the high dose of quinpirole. Grooming was inhibited by both the low and the high dose of quinpirole, and stimulated by the injection of SKF38393 or its addition to the low dose of quinpirole. These findings suggest that snout contact is controlled by modulating the frequency of episodes whereas mouthing is controlled by modulating the duration of episodes. Moreover, although they do not disprove the prevailing notion of D1-D2 receptor synergism, the present data are consistent also with an oppositional model of D1-D2 receptor interaction in the regulation of locomotion, snout contact, mouthing, and grooming in intact animals.

Multiple cholecystokinin (CCK) receptors and CCK-monoamine interactions are instrumental in the control of feeding

Almost two decades ago, exogenous cholecystokinin (CCK) was shown to suppress food consumption in rats. Since then, CCK has been detected not only in peripheral tissue but extensively throughout the central nervous system. Furthermore, specific CCK receptors have been described, and a distinction drawn between CCK-A and CCK-B receptors. Recently, potent, orally active CCK antagonists, which show a high degree of selectivity for either CCK-A or CCK-B receptors, have been introduced. The present report reviews recent evidence obtained in studies using devazepide (a selective CCK-A receptor antagonist) and L-365,260 (a selective CCK-B/gastrin receptor antagonist). Both compounds increased food consumption and postponed the onset of satiety in well-satiated rats. L-365,260 was more potent, suggesting that central CCK-B type receptors may mediate the satiety effects of endogenously released CCK. Only devazepide was effective in blocking the feeding-suppressant effect of exogenous CCK, indicating that CCK-A type receptors mediate this effect. In a second series of studies, devazepide but not L-365,260 antagonized the anorectic effect of either d-fenfluramine or systemically administered 5-HT. Hence, CCK-A type receptors appear to be involved in the anorectic effects of these serotonergic drugs. We propose that CCK and 5-HT mechanisms involved in mediating satiety are mutually interdependent. Possible interactions between CCK and catecholaminergic mechanisms are also briefly considered.