Amphetamine anorexia: antagonism by typical but not atypical neuroleptics

Changes in feeding and locomotion induced by amphetamine analogs in rats

Studies of the biobehavioral actions of psychostimulants commonly focus on locomotion and less commonly on feeding, and only rarely are these measures considered in conjunction within the same animal. The present study compared the impact of (+)-amphetamine and three amphetamine analogs, PAL-287, PAL-313, and PAL-353, on eating and locomotion assessed concurrently using an automated activity/feeding chamber during a daily 45 min session. Each analog is a potent releaser of norepinephrine and of dopamine, but exerts differential serotonin-releasing activity (PAL-287>PAL-313>amphetamine>PAL-353). Rats were tested with each of five doses of drug (0, 2, 4, 8, or 16 micromol/kg, i.p.), given in equimolar concentrations and in random dose order. PAL-353, an analog with minimal serotonin-releasing capacity, markedly stimulated forward locomotion at 2, 4, 8 and 16 micromol/kg, as did amphetamine, whereas PAL-287 and PAL-313 did not. In contrast to the locomotor findings, all four amphetamine-like drugs exerted similar effects on the suppression of food intake. These results suggest that the capacity of an amphetamine analog (i.e. amphetamine and PAL-353) to stimulate serotonin release can diminish its psychostimulant action on locomotion, but does not reliably augment drug-induced hypophagia.

Effects of ICV administration of the alpha1A-adrenoceptor antagonist 5-methylurapidil on concurrent measures of eating and locomotion after cocaine in the rat

Psychostimulants including amphetamine and cocaine induce locomotion and stereotypy and suppress eating. Although the capacity of cocaine to alter locomotion is usually viewed as related to dopamine neurotransmission, recent studies suggest that norepinephrine, acting through alpha1-adrenergic receptors (alpha1-ARs) can facilitate cocaine-stimulated locomotion. Of the three alpha1-AR subtypes (alpha(1A), alpha(1B), and alpha(1D)) identified to date, inactivation of the alpha(1B)-AR subtype diminishes cocaine-stimulated locomotion, whereas the impact of inactivation of the alpha(1A)-AR subtype on either eating or locomotion is unknown. In the present study, we assessed the relative impact of ICV administration of the alpha(1B)-AR antagonist 5-methylurapidil (5-MU) on cocaine-stimulated hyperlocomotion and hypophagia, using a concurrent method [Wellman, P.J., Ho, D.H., Davis, K.W., 2005. Concurrent measures of feeding and locomotion in rats. Physiology of Behavior 84 (5), 769-774.]. Rats were infused ICV with one of 3 doses of 5-MU (0, 3, or 30 nmol) and then injected (i.p.) with 0, 2.5, 5.0, 10.0, or 20.0 mg/kg cocaine HCl on each of five tests. Rats always received the same 5-MU dose, but a different cocaine dose on each trial. Feeding and locomotion were assessed concurrently during a 45-min postinjection period. Significant suppression of eating was noted at 2.5 mg/kg cocaine, a dose that does not alter forward locomotion in the rat. Administration of 5-MU did not alter locomotion in rats treated with saline, but did significantly increase baseline food intake. Neither cocaine-induced hypophagia nor hyperlocomotion was altered by ICV administration of 5-MU. These results suggest that the capacity of alpha1-AR agonists (e.g. phenylpropanolamine) to suppress eating may be related to activation of the alpha(1A)-AR subtype, whereas cocaine does not act through the alpha(1A)-AR subtype to suppress eating nor does this subtype modulate cocaine-induced hyperlocomotion.

Both alpha1-adrenergic and D(1)-dopaminergic neurotransmissions are involved in phenylpropanolamine-mediated feeding suppression in mice

The anorectic action of phenylpropanolamine (PPA) has been attributed to the activation of alpha1 adrenoceptors. It is unknown whether dopamine (DA) receptor subtype was involved in this action. With a treating dose higher than those used in previous reports and a testing period mainly in the dark phase of a circadian rhythm, we found that DA-ergic transmission was also involved in PPA anorexia. Pretreatment of phentolamine or prazosin could partly block PPA-induced anorexia, confirming the involvement of alpha1 adrenoceptor subtype. In addition, pretreatment of haloperidol or SCH 23390 could also partly block PPA anorexia, revealing the involvement of D(1) receptor subtype. Moreover, co-administration of prazosin and SCH 23390 could completely block PPA anorexia, confirming the co-involvement of alpha1 and D(1) receptor subtypes. These findings suggested that both subtypes of alpha1 adrenoceptor and D(1) receptor were involved in the anorectic action of PPA.

Contingent tolerance to amphetamine hypophagia: new insights into the role of environmental context in the expression of stereotypy

A growing literature attests to the fact that the environment in which a drug is given can have a profound effect on the development and expression of tolerance and sensitization. The dominant paradigm for studying such context-dependency is based on Pavlovian conditioning, in which a distinctive environment serves as a conditioned stimulus. Context dependency is demonstrated when tolerance or sensitization is expressed only in the environment in which the drug was given chronically. An alternative paradigm for studying context-dependency is to manipulate the contingencies of reinforcement operating in the environment in which the drug is administered. For example, tolerance to amphetamine-induced hypophagia is contingent on having access to food while intoxicated [Carlton PL, Wolgin DL. Contingent tolerance to the anorexigenic effects of amphetamine. Physiol Behav 1971;7:221-223]. Such context-dependency can be explained in terms of an instrumental (or operant) conditioning model, in which food serves as a reinforcer for the learned suppression of stereotyped movements that interfere with ingestion. Research based on this model suggests that the expression of sensitized stereotyped responses is subject to an operant level of control.

Limited proteolysis and physiological regulation: an example from thyrotropin-releasing hormone metabolism

Proteases like trypsin, elastase, and many others play important regulatory functions by generating new biologically active molecules through limited proteolysis of larger proteins and peptides. The limited proteolysis of thyrotropin-releasing hormone (TRH) by Pyroglutamate aminopeptidase yields cyclo(His-Pro) or CHP, a new biopeptide associated with a variety of pharmacological activities, including regulation of body temperature, inhibition of prolactin secretion, and modulation of motor functions. Although the mechanism by which CHP elicits these biological activities is not well understood, it appears that the cyclic peptide may function at least in part by modulating central amine transport mechanisms.

Bioactive cyclic dipeptides

Cyclic dipeptides are among the simplest peptide derivatives commonly found in nature. Most cyclic dipeptides found to date appear to have emerged as by-products of fermentation and food processing. However, many are endogenous to members of animal and plant kingdoms; these include cyclo(Pro-Leu), cyclo(Pro-Val), cyclo(Pro-Phe), cyclo(Ala-Leu), cyclo(Pro-Tyr), cyclo(Pro-Trp), and cyclo(His-Pro). Although the five cyclic dipeptides--cyclo(His-Pro), cyclo(Leu-Gly), cyclo(Tyr-Arg), cyclo(Asp-Pro), and cyclo(Pro-Phe)--exhibit interesting physiological and/or pharmacological activities in mammals, only one of these, cyclo(His-Pro), has been conclusively shown to be endogenous to mammals. On the other hand, cyclo(Leu-Gly), cyclo(Tyr-Arg), and cyclo(Asp-Pro) are structurally related to endogenous peptides Pro-Leu-Gly-NH2 (melanocyte-stimulating hormone release inhibiting factor), Tyr-Arg (kyotorphin), and Val-Pro-Asp-Pro-Arg (enterostatin), respectively, which may serve as precursor peptides. It needs to be determined, however, whether these peptides can indeed result from the processing of their respective precursors. In conclusion, it appears that cyclic dipeptides are a relatively unexplored class of bioactive peptides that may hold great promise for the future.

Does cyclo(His-Pro) act like amphetamine?

In many pharmacologic tests, cyclo(His-Pro) (CHP) appears to act like a dopaminergic agonist and augments the actions of amphetamine (AMP). Therefore, to determine whether CHP is an AMP-like peptide, a comparison between CHP and AMP was made using four separate tests known to be AMP-responsive. These include, food intake, locomotor activity, dopamine uptake and modulation of binding sites for amphetamine and mazindol. A decrease in food intake and increase in spontaneous locomotor activity and stereotypy was observed after peripheral administration of amphetamine but not CHP. Chronic CHP administration resulted into a decrease in striatal amphetamine - and increase in mazindol-binding sites; in contrast, chronic amphetamine decreased both amphetamine - and mazindol-binding sites. These results show a clear dissociation between CHP and AMP suggesting that CHP is not an amphetamine-like peptide.

Cyclo(His-Pro) potentiates the reduction of food intake induced by amphetamine, fenfluramine, or serotonin

Electrophysiological and pharmacological evidence suggests that cyclo(His-Pro) (cHP) could reduce food intake by modulating the actions of relevant neurotransmitters. We tested this hypothesis by giving rats a combination of cHP or its analogs centrally and an anorectic, amphetamine or fenfluramine, systemically. Compared to saline control, cHP at doses too low to affect food intake by itself significantly potentiated the reduction of food intake by amphetamine. This potentiation is thought to be due to cHP modulation of norepinephrine (NE) action, because at the low dose used amphetamine acts mainly through NE to inhibit food intake. The modulation has specific requirements for cHP structure, since it was mimicked by one but not two other analogs tested. The anorectic effect of fenfluramine was also potentiated and prolonged by cHP at a dose not effective by itself. Since fenfluramine is known to act by increasing brain serotonin (5-HT), the potentiation was apparently a result of an interaction between cHP and 5-HT effects. To examine this interaction more directly, we administered both cHP and 5-HT centrally. Again, cHP potentiated the reduction of food intake caused by 5-HT. Thus the neuromodulation of feeding-relevant neurotransmitter effects, following NE and 5-HT, is probably a mechanism by which cHP reduces food intake.

Facilitation of feeding by nucleus accumbens amphetamine injections: latency and speed measures

Food-deprived rats were offered food in small meal segments, and latency to initiate feeding and time to complete it were recorded for each segment. Bilateral microinjections of d-amphetamine into nucleus accumbens dramatically increased the mean speed with which meal segments were eaten, but had no reliable effect on mean latency to initiate eating of new segments; l-amphetamine had similar but weaker effects. While mean eating speed was increased, this increase resulted from a decrease in the frequency of slow trials and not from an increase in the absolute speed of the fastest trials. These data suggest that amphetamine facilitates feeding by some other means than simple improvement of the motoric capacity of the animal, and they indicate that nucleus accumbens is an important site for amphetamine's established but not widely appreciated facilitory effects on feeding.

Concurrent facilitory and inhibitory effects of amphetamine on stimulation-induced eating

At low doses (0.125 and 0.25 mg/kg, i.p.), amphetamine facilitated eating induced by lateral hypothalamic electrical stimulation. It decreased the frequency threshold for the behavior and it increased the probability of eating across a range of suprathreshold stimulation frequencies; it also accelerated eating, decreasing the average time to eat three 45-mg food pellets across the range of stimulation frequencies tested. At high doses (1.0 and 2.0 mg/kg), amphetamine increased the frequency threshold and decreased the probability of eating across the range of suprathreshold stimulation frequencies; on those trials where eating was observed, however, even these doses of amphetamine accelerated feeding. Several lines of evidence suggest that amphetamine influences feeding through multiple mechanisms, and that present data may be explained by independent facilitory and inhibitory mechanisms, with the inhibitory mechanism less sensitive to low doses but generally dominant when the two mechanisms are both activated by higher doses. Another possibility is that the well-known anorexic effects of amphetamine result at least in part from over-stimulation of the same mechanism as is involved in the more subtle facilitory effects of the drug.

Behavioural microanalysis of the role of dopamine in amphetamine anorexia

A microstructural analysis paradigm was used to study amphetamine anorexia. Doses above 0.40 mg/kg significantly reduced food intake by reducing eating time; in contrast, eating rate was increased at these doses. Examination of the frequency distribution of interresponse times (IRTs) revealed a significant shift to shorter IRTs at doses as low as 0.125 mg/kg. Pimozide blocked amphetamine anorexia at 0.5 and 1.0 mg/kg, suggesting that at both doses amphetamine anorexia has a dopaminergic substrate. However, the atypical neuroleptic thioridazine did not antagonize amphetamine. Furthermore, effects of amphetamine were additive with those of apomorphine, administered at a dose known to suppress feeding by inhibiting mesolimbic DA neurons. These results provide evidence against an involvement of the mesolimbic DA system in amphetamine anorexia.

[Pharmacological and molecular aspects of the regulation of eating behavior. With special reference to the role of catecholamines and effects of amphetamine]

Among the numerous endogenous substances involved in the regulation of feeding behaviours, the catecholamines are in the front rank. The numerous studies devoted to this aspect of catecholamines emphasize the importance and complexity of their intervention. Depending on the cerebral structures on which they act and on whether noradrenaline or dopamine are concerned, orexigenic or anorexigenic effects have been described. Alpha-2 and beta adrenergic receptors as well as D1 and D2 dopaminergic receptors participate in these effects. Amphetamine, which is an indirect catecholaminergic agonist, mobilizes neuronal catecholamines and fosters their various effects. Moreover, it exercises direct effects by its association with sites borne by glycaemia-sensitive neurons. This target seems to be common to a wide variety of anorectic agents. They are thought to reproduce on this hypothalamic "glucostat" the effect of a high blood glucose level, thus triggering off signals of satiety. In this unifying hypothesis, the diverse pharmacological profiles these agents are known to possess would result from associated properties.

Apomorphine anorexia: the role of dopamine receptors in the ventral forebrain

The inhibition of feeding following the administration of apomorphine, systemically or directly into the nucleus accumbens/ventral striatum, was studied using a microstructural analysis paradigm. On systemic administration, apomorphine reduced food consumption, eating rate and eating time; the effects were blocked by sulpiride but not by SCH-23390. Two doses of apomorphine were administered centrally. Both doses reduced total food intake and eating rate; only the higher dose also reduced eating time; all of these effects were blocked by sulpiride pretreatment. Only the lower dose reduced locomotor activity and rearing in the open field. The results suggest that apomorphine reduces eating rate by an action on dopamine (DA) axon terminal autoreceptors. We have previously demonstrated that apomorphine reduces eating time by an action on DA cell body autoreceptors. Therefore, the two populations of DA autoreceptors appear to be differentially involved in behaviour.

Receptor blocking drugs and amphetamine anorexia in human subjects

The interaction between the receptor antagonist thymoxamine (THYM), propranolol (PPL) and metergoline (MTG) with dexamphetamine (d-Amp)-induced anorexia was examined in a series of studies in normal female volunteers. Visual analogue scale (VAS) ratings of hunger were made and food intake was measured using an automated solid food dispenser (AFD). d-Amp (10 mg) significantly depressed hunger ratings compared to placebo in two of the three studies and its effect was countered by the addition of MTG (4 mg). d-Amp significantly reduced food intake compared to placebo in two studies. In all trials the reduction in food intake following d-Amp was significantly greater than would have been predicted from its effect on hunger. THYM (160 mg) and PPL (40 mg) were associated with no changes in food intake when given alone or with d-Amp, MTG increased food intake (but not significantly) and the combined effects of MTG and d-Amp was the algebraic sum of the effect of each; but there appeared to be no true pharmacological interaction between blocker and anorectic. The results indicated that there may be some dissociation between the effect of d-Amp on hunger and food intake but have failed to produce evidence that noradrenergic pathways are involved. The results are consistent with the theories that d-Amp anorexia does not involve the release of 5-hydroxytryptamine (5-HT) but that 5-HT pathways are involved in the feeding process.

Experimental manipulations of eating: advances in animal models for studying anorectic agents

The material set out in this text has been designed to show the wide range of procedures which have the capacity to modify eating behavior--to produce hyper- or hypophagia, to alter the profile of eating patterns, or to adjust dietary preferences and selection. Accordingly, in investigating anorectic drugs it seems necessary to observe the effects of drug actions in a variety of experimental models. This strategy will provide a more complete description of the effect of a drug, will throw light on the mechanism of action, and will provide a more realistic base for predicting the effects of drugs in man.

Amphetamine: effects on meal patterns and macronutrient selection

Catecholaminergic systems, specifically in the region of the lateral perifornical hypothalamus (PFH), have been linked to the inhibition of feeding behavior. The present studies examined the effects of d-amphetamine (AMPH), which is believed to act through the release of endogenous catecholamines (CAs), on spontaneous feeding and appetite regulation in rats. Injection of AMPH directly into the PFH caused a marked suppression of food intake; changes in computer-monitored meal patterns were characterized by an increase in the latency to meal onset and a consequent reduction in meal size and duration. This suggests that hypothalamic AMPH administration may influence primarily the initiation, rather than the termination, of feeding. In other experiments, chronic infusion of AMPH directly into the PFH was shown to suppress 24 hr food intake and body weight gain, indicating the effectiveness of lateral hypothalamic CA stimulation in overriding normal long-term patterns of feeding. The effect of hypothalamic CA stimulation on macronutrient selection was also investigated in groups of rats injected either centrally or peripherally with AMPH, or centrally with the CA agonists, dopamine and epinephrine. Each of these manipulations caused a strong inhibition of protein intake with no effect on carbohydrate, and only a mild suppression of fat ingestion after peripheral AMPH. These selective effects of AMPH on feeding patterns and diet choice, provide support for a role of CA innervation to the lateral hypothalamus in the modulation of natural feeding behavior and macronutrient selection.

Contributions of dopamine terminal areas to amphetamine-induced anorexia and adipsia

Systemic injections of amphetamine produce both anorexia and adipsia. Evidence suggests that it is the stimulation of activity by the drug in both noradrenergic and dopaminergic synapses that mediate these effects. The present study examined the contributions of dopamine terminal regions to these effects in rats by microinjecting amphetamine directly into one of six discrete sites (medial frontal cortex, nucleus accumbens, anteromedial caudate nucleus, ventrolateral caudate nucleus, amygdala, or the region surrounding the area postrema) and observing the effects of the injections on eating or drinking. The rats were mildly deprived of either food or water and following microinjection of either amphetamine or saline, were given access to food or water. Injections of amphetamine into either the nucleus accumbens or amygdala caused both anorexia and adipsia but no effects were observed from the other sites. It is suggested that the amphetamine's action on these two sites contributes to the anorexia and adipsia that are observed after systemic injection of the drug. Possible behavioral mechanisms for the effects are discussed.

Apomorphine anorexia: a further pharmacological characterization

Low doses of apomorphine reduce food intake, primarily by decreasing the rate of eating and also by reducing eating time. We have previously reported that the effect on eating time is mediated by dopamine cell body autoreceptors in the ventral tegmental area. The present experiments were designed to elucidate the pharmacological basis of the effect of apomorphine on eating rate. In the first experiment dopamine was also found to reduce food intake, but mainly by an effect on eating time. The peripheral DA antagonist domperidone abolished the effects of DA, but enhanced the effects of apomorphine. In the second experiment phentolamine, yohimbine, propranolol, scopolamine, naloxone and methergoline all failed to reverse the effect of apomorphine on eating rate. However, in the third experiment, effects of apomorphine on total food intake, eating time and eating rate were all blocked by the neuroleptics, pimozide and sulpiride. It is concluded that the reduction of eating rate by apomorphine is also mediated by an interaction with central DA receptors, but that this receptor population is anatomically distinct from that responsible for the effect of apomorphine on eating time.

Analysis of dopamine D1 and D2 receptor involvement in d- and l-amphetamine-induced anorexia in rats

The concept of dopamine receptor subtypes and the recent development of selective dopamine receptor agonists and antagonists raises the possibility of specific subtype involvement in amphetamine-induced anorexia, and, furthermore, provides the means to evaluate the possibility. Using a test of palatable food consumption by nondeprived male rats, our data confirmed a more potent suppressant effect of d-amphetamine on food intake, compared to l-amphetamine (potency ratio 5.32:1). The test proved sensitive, with ED50s of 0.28 mg/kg and 1.49 mg/kg for d- and l-amphetamine, respectively. The modest anorectic effect of 0.3 mg/kg d-amphetamine was completely reversed by the selective dopamine D1 receptor antagonist, SCH 23390, but was not affected by the selective D2 receptor antagonist, sulpiride. A matched feeding-suppressant effect of 1.0 mg/kg l-amphetamine was reversed at one dose of SCH 23390, but was unaffected by sulpiride. Stronger anorectic effects produced by 1.0 mg/kg d-amphetamine and 3.0 mg/kg l-amphetamine were not antagonized either by SCH 23390 or sulpiride. The selective D1 receptor agonist, SKF 38393, produced a dose-dependent reduction in food consumption, without producing behavioural stereotypy. Unlike amphetamine, SKF 38393 is not self-administered, and therefore may provide an example of a novel pharmacological dissociation between anorectic and reinforcing effects of drug treatments mediated by dopamine receptors. Our data implicate dopamine D1 receptors in the control of feeding responses, and suggest that these receptors may mediate the anorectic effect of small-dose amphetamine treatments.

Central and peripheral contributions to the enhancement of amphetamine anorexia by desmethylimipramine (DMI)

Intrahypothalamic administration of amphetamine to rats increased food intake, but pre-treatment with the alpha-receptor antagonist phentolamine unmasked an anorexic effect commensurate with that seen after peripheral amphetamine administration. Pretreatment with systemic DMI increased anorexia after peripheral or central amphetamine administration, but the enhancement of centrally-induced anorexia was small. It is concluded that enhancement of the anorexic effect of peripherally administered amphetamine by DMI is primarily a peripheral phenomenon, with interactions within the central nervous system making a relatively minor contribution.

Changes in amphetamine-induced anorexia and stereotypy during chronic treatment with antidepressant drugs

Amphetamine-induced anorexia and stereotyped behaviour were studied in rats, following pretreatment with the antidepressants DMI, inprindole and mianserin. A complex drug-dependent and dose-dependent pattern of results was obtained. Acute pretreatment with DMI and iprindole enhanced amphetamine anorexia and stereotypy; at high doses only, the enhancement of anorexia disappeared during chronic treatment. Mianserin had no effects acutely, but chronic treatment with high doses attenuated anorexia and enhanced stereotypy. High doses of all three drugs attenuated anorexia and enhanced stereotypy during withdrawal. The most parsimonious account of these results is that the acute affects of DMI and iprindole are artefactual, and that chronic administration of all three antidepressants increased dopaminergic function and decreased beta-adrenergic function.

Dissociable effects of 6-OHDA-induced lesions of neostriatum on anorexia, locomotor activity and stereotypy: the role of behavioural competition

The effect of 6-OHDA-induced lesions of neostriatum on locomotor activity, stereotypy and anorexia induced by amphetamine (0.5 mg/kg, 1.5 mg/kg and 5.0 mg/kg IP) was examined. Lesioned rats demonstrated attenuated stereotypy and anorexia but enhanced locomotor activity to amphetamine. Biochemical analysis of dopamine and noradrenaline in specific forebrain areas demonstrated significant dopamine depletion in neostriatum. Dopamine levels in mesolimbic, frontal cortex and hypothalamic areas, and noradrenaline in frontal cortex and hypothalamic areas, were not significantly reduced. The data were interpreted in terms of a response incompatibility hypothesis. It is proposed that stereotyped responses mediated by nigrostriatal dopamine neurones are incompatible with eating. In addition, it is suggested that a second form of competition, at the neuro-anatomical level, occurs between mesolimbic and nigrostriatal systems for motor output pathways and the ultimate expression of behaviour. The role of noradrenaline in amphetamine anorexia is also discussed.

The effect of d-amphetamine and haloperidol alone and in combination on milk drinking in rats

The effects of d-amphetamine (0.5-4.0 mg/kg IP) and haloperidol (0.015-1.0 mg/kg IP) alone and in combination on intake of a sweetened milk solution were determined in rats. Experimental sessions consisted of a 15-min access to the milk solution once a day, 7 days a week. d-Amphetamine was administered 15 min prior to the session and haloperidol was administered 60 min prior to the session. The interaction of these compounds was determined by repeated determination of the dose-response function for d-amphetamine in combination with different doses of haloperidol. When given alone, each drug produced a dose-dependent decrease in milk intake. In combination with haloperidol, the decrement caused by d-amphetamine was shifted to lower doses in a dose-dependent manner. Isobolographic analysis of the interaction indicates that the intermediate doses (0.03-0.06 mg/kg) of haloperidol were additive and the highest doses (0.12-0.25 mg/kg) of haloperidol were infraadditive with d-amphetamine. Dose-dependent neuropharmacological actions of these compounds may account for dose-dependent interactions.

Potent anorexic-like effects of RDS-127 (2-di-n-propylamino-4,7-dimethoxyindane) in the rat: a comparison with other dopamine-receptor agonists

Modification of food intake and motor activity was investigated following administration of amphetamine (AMP), apomorphine (APO) and three novel 2-aminoindanes (2-AI): 2-di-n-propylaminoindane (JPC-60-36), 2-di-n-propylamino-5,6-dimethoxyindane (JPC-211) and 2-di-n-propylamine-4,7-dimethoxyindane (RDS-127). These compounds demonstrated dose- and time-related inhibition of food intake in male rats which were habituated to eating 4 hr each day. The ranked potencies were as follows: RDS-127 greater than AMP = APO greater than JPC-60-36 and JPC-211 was inactive. 2-di-n-Propylamine-4,7-dimethoxyindane (RDS-127) did not increase motor activity in a dose range that Significantly inhibited food intake (66% of control intake with 0.08 mumol/kg). Food intake inhibition was blocked by pimozide, but not by propranolol or phentolamine. The anorectic-like actions of RDS-127 were long-lasting (greater than 4 hr) and RDS-127 was approximately 3-fold more potent than amphetamine or apomorphine in producing increased locomotor activity; the other 2-aminoindanes were less potent in producing hyperactivity. Hyperactivity responses were blocked by pimozide, but not by alpha-methyl-p-tyrosine. These results suggest that 2-aminoindanes may modify motor behaviors, at least in part, via direct stimulation of dopamine receptors. The structure-activity relationships of 2-aminoindanes on locomotor activity and inhibition of food intake are discussed.

Microstructural analysis of the involvement of beta-receptors in amphetamine anorexia

Rats were trained to take food by pushing the door of the pellet dispenser in an operant chamber. Log survivor analysis of the inter-response time frequency distribution was used to determine whether or not an animal was eating, at any time during a thirty minute session. This information was used to compute eating time, eating rate, and the mean length of bouts of eating and gaps between eating bouts. Video-recordings confirmed that the method discriminated eating from not eating with an accuracy of approximately ninety percent. Amphetamine (0.5 mg/kg) significantly reduced total food intake and eating time, and increased gap length; propranolol (5 mg/kg) significantly increased eating time and bout length. Following propranolol pretreatment, amphetamine significantly reduced eating time and bout length but also significantly increased eating rate; as a result there was no significant decrease in total food intake. The possible mediation of these effects by beta-adrenergic and dopaminergic systems is discussed.

The effect of neurotensin on food consumption in the rat

The effect of neurotensin on feeding behavior were studied in rats. Intracerebroventricular administration of neurotensin (3.3-30 micrograms) produced a dose-related decrease in food intake in 24 h food deprived rats. Acute intracerebroventricular injection of neurotensin (30 micrograms) shortly after the ingestion of a novel flavor did not produce a flavor aversion during testing 48 h later, suggesting that reduction of food intake by low doses of centrally administered neurotensin is not related to a conditioned taste aversion. Intracerebroventricularly administered thyrotropin-releasing hormone (2.2 micrograms) also inhibited food intake and appeared to attenuate slightly the inhibition of food intake induced by 10 micrograms neurotensin.

Anorectic effect of lisuride and other ergot derivatives in the rat

Three ergot derivatives, lisuride, lergotrile and bromocriptine, given to rats trained to eat 4 h a day, induced a dose- and time-related anorexia. They were more potent in this context than either amphetamine or fenfluramine. Lisuride and lergotrile failed to increase locomotor activity or to induce stereotyped behaviour at doses corresponding to the ID50 on food intake. At this dose, bromocriptine slightly stimulated motor activity. The anorectic effect of the three compounds was selectively antagonized by blockers of dopamine (DA) receptors in the central nervous system but not by either inhibiton of catecholamine synthesis or blockade of alpha- or beta-adrenoceptors or of serotonergic receptors. Also two blockers of 'peripheral' DA receptors failed to antagonize ergoline-induced anorexia. These findings indicate that stimulation of DA receptors involved in feeding behaviour was responsible for the anorexigenic effect of the ergot derivatives investigated. In most instances this effect occurred at dose levels which failed to induce central stimulant effects.

Characterisation of adjustments to the structure of feeding behaviour following pharmacological treatment: effects of amphetamine and fenfluramine and the antagonism produced by pimozide and methergoline

An observational procedure for examining the micro-structure of eating has been employed to establish the characteristic behaviour patterns displayed after various pharmacological manipulations. Using a double dissociation design it was shown that amphetamine and fenfluramine gave rise to quite distinctive readjustments to the structure of feeding behaviour. Amphetamine anorexia was characterised by a long initial delay, following which feeding was typified by infrequent short bursts of rapid eating. These effects were antagonised by the dopamine receptor blocking agent, pimozide. Fenfluramine exerted a more restricted pattern of action characterised by a marked slowing of the rate of eating. This effect was countered by the serotonin receptor blocking agent methergoline. These data throw light on the way in which pharmacological agents may impede food consumption and upon the neurochemical systems believed to be involved in the expression of feeding behaviour.