Role of hypothalamic neuropeptide Y (NPY) in the change of feeding behavior induced by repeated treatment of amphetamine

Critical View on the Usage of Ribavirin in Already Existing Psychostimulant-Use Disorder

Substance-use disorder represents a frequently hidden non-communicable chronic disease. Patients with intravenous drug addiction are at high risk of direct exposure to a variety of viral infections and are considered to be the largest subpopulation infected with the hepatitis C virus. Ribavirin is a synthetic nucleoside analog that has been used as an integral component of hepatitis C therapy. However, ribavirin medication is quite often associated with pronounced psychiatric adverse effects. It is not well understood to what extent ribavirin per se contributes to changes in drug-related neurobehavioral disturbances, especially in the case of psychostimulant drugs, such as amphetamine. It is now well-known that repeated amphetamine usage produces psychosis in humans and behavioral sensitization in animals. On the other hand, ribavirin has an affinity for adenosine A1 receptors that antagonistically modulate the activity of dopamine D1 receptors, which play a critical role in the development of behavioral sensitization. This review will focus on the current knowledge of neurochemical/ neurobiological changes that exist in the psychostimulant drug-addicted brain itself and the antipsychotic-like efficiency of adenosine agonists. Particular attention will be paid to the potential side effects of ribavirin therapy, and the opportunities and challenges related to its application in already existing psychostimulant-use disorder.

Role of hypothalamic leptin-LepRb signaling in NPY-CART-mediated appetite suppression in amphetamine-treated rats

Leptin is an adipose tissue hormone which plays an important role in regulating energy homeostasis. Amphetamine (AMPH) is a drug of appetite suppressant, which exerts its effect by decreasing the expression of hypothalamic neuropeptide Y (NPY) and increasing that of cocaine- and amphetamine-regulated transcript (CART). This study investigated whether leptin, the leptin receptor (LepRb) and the signal transducer and activator of transcription-3 (STAT3) were involved in NPY/CART-mediated appetite suppression in AMPH-treated rats. Rats were given AMPH daily for four days, and changes in the levels of blood leptin and hypothalamic NPY, CART, LepRb, Janus kinases 2 (JAK2), and STAT3 were assessed and compared. During the AMPH treatment, blood leptin levels and hypothalamic NPY expression decreased, with the largest reduction observed on Day 2. By contrast, the expression of hypothalamic CART, LepRb, JAK2, and STAT3 increased, with the maximum response on Day 2. Furthermore, the binding activity of pSTAT3/DNA increased and was expressed in similar pattern to that of CART, LepRb, and JAK2. An intracerebroventricular infusion of NPY antisense 60min prior to AMPH treatment increased the levels of leptin, as well as the expression in LepRb, JAK2, and CART, whereas an infusion of STAT3 antisense decreased these levels and the expression of these parameters. The results suggest that blood leptin and hypothalamic LepRb-JAK2-STAT3 signaling involved in NPY-CART-regulated appetite suppression in AMPH-treated rats. The findings may aid understanding the role of leptin-LepRb during the treatment of anorectic drugs.

Role of oxidative stress in disrupting the function of negative glucocorticoid response element in daily amphetamine-treated rats

Amphetamine (AMPH)-induced appetite suppression is associated with changes in hypothalamic reactive oxygen species (ROS), antioxidants, neuropeptides, and plasma glucocorticoid. This study explored whether ROS and glucocorticoid response element (GRE), which is the promoter site of corticotropin-releasing hormone (CRH) gene, participated in neuropeptides-mediated appetite control. Rats were treated daily with AMPH for four days, and changes in food intake, plasma glucocorticoid and expression levels of hypothalamic neuropeptide Y (NPY), proopiomelanocortin (POMC), superoxide dismutase (SOD), CRH, and glucocorticoid receptor (GR) were examined and compared. Results showed that food intake decreased and NPY gene down-regulated, while POMC, SOD, and CRH gene up-regulated during AMPH treatment. GR and GRE-DNA bindings were disrupted on Day 1 and Day 2 when glucocorticoid levels were still high. Pretreatment with GR inhibitor or ROS scavenger modulated mRNA levels in NPY, POMC, SOD and CRH in AMPH-treated rats. We suggest that disruptions of negative GRE (nGRE) on Day 1 and Day 2 are associated with an increase in oxidative stress during the regulation of NPY/POMC-mediated appetite control in AMPH-treated rats. These results advance the understanding of molecular mechanism in regulating AMPH-mediated appetite suppression.

Effects of drugs of abuse on the central neuropeptide Y system

Neuropeptide Y (NPY), which is widely expressed in the central nervous system is involved in several neuropathologies including addiction. Here we comprehensively and systematically review alterations on the central NPY system induced by several drugs. We report on the effects of psychostimulants [cocaine, amphetamine, methamphetamine, 3,4-methylenedioxymethamphetamine (MDMA) and nicotine], ethanol, and opioids on NPY protein levels and expression of different NPY receptors. Overall, expression and function of NPY and its receptors are changed under conditions of drug exposure, thus affecting several physiologic behaviors, such as feeding, stress and anxiety. Drugs of abuse differentially affect the components of the NPY system. For example methamphetamine and nicotine lead to a consistent increase in NPY mRNA and protein levels in different brain sites whereas ethanol and opioids decrease NPY mRNA and protein expression. Drug-induced alterations on the different NPY receptors show more complex regulation pattern. Manipulation of the NPY system can have opposing effects on reinforcing and addictive properties of drugs of abuse. NPY can produce pro-addictive effects (nicotine and heroin), but can also exert inhibitory effects on addictive behavior (AMPH, ethanol). Furthermore, NPY can act as a neuroprotective agent in chronically methamphetamine and MDMA-treated rodents. In conclusion, manipulation of the NPY system seems to be a potential target to counteract neural alterations, addiction-related behaviors and cognitive deficits induced by these drugs.

Involvement of neuropeptide Y Y1 receptor in the regulation of amphetamine-mediated appetite suppression

Recently, we reported that an initial decrease followed by recovery of food intake was observed during four days of amphetamine (AMPH) treatment and suggested that these changes in response were mediated by changes in neuropeptide Y (NPY) and proopiomelanocortin (POMC). Here we investigated if Y1 receptor (Y1R) and/or Y5 receptor (Y5R) might be involved in this regulation. Rats were treated daily with AMPH for four days. Changes in the expression levels of Y1R, Y5R, melanocortin receptor 3 (MC3R), and NPY were assessed and compared. Results showed that Y1R and MC3R increased, with a maximal increase of about 210% on Day 2 but with a restoration to the normal level on Day 4. In contrast, NPY decreased with a biggest reduction of about 45% on Day 2 and the pattern of expression during AMPH treatment was opposite to those of Y1R and MC3R, while the expression of Y5R was not changed. Central inhibitions of NPY formation or Y1R activity modulated the anorectic response of AMPH and the reciprocal regulation of NPY and MC3R, revealing a crucial role of Y1R in this action. It is suggested that Y1R participates in the reciprocal regulation of NPY- and MC3R-containing neurons in the hypothalamus during the anorectic effect of AMPH. These results may further the understanding of Y1R in the control of eating.

NF-κB knockdown can modulate amphetamine-mediated feeding response

This study determined if transcription factor NF-κB is involved in the effect of amphetamine (AMPH)-mediated feeding response. Moreover, possible roles of hypothalamic neuropeptide Y (NPY) and proopiomelanocortin (POMC) were also investigated. AMPH was administered daily to rats for four days. Changes in NF-κB, NPY and POMC expression were assessed and compared. The NPY gene was down-regulated with maximal response on Day 2 during AMPH treatment, which was consistent with the response to feeding behavior. In contrast, NF-κB and POMC genes were up-regulated, and their expression was increased by about 200% and 450%, respectively, with maximal response on Day 2. Moreover, NF-κB DNA binding ability and expression were increased similar to that of POMC. To examine further if NF-κB was involved, intracerebroventricular infusion of NF-κB antisense oligonucleotide was performed 1 h before the daily AMPH dosing in freely moving rats. Results showed that NF-κB knockdown could modify AMPH anorexia as well as NPY and POMC expression. The present findings prove that cerebral NF-κB participates in AMPH-mediated appetite suppression, possibly by modulating NPY and POMC expression. These results may aid in therapeutic research on AMPH and AMPH-like anti-obesity drugs.

Knocking down the transcript of protein kinase C-lambda modulates hypothalamic glutathione peroxidase, melanocortin receptor and neuropeptide Y gene expression in amphetamine-treated rats

It has been reported that neuropeptide Y (NPY) contributes to the behavioral response of amphetamine (AMPH), a psychostimulant. The present study examined whether protein kinase C (PKC)-λ signaling was involved in this action. Moreover, possible roles of glutathione peroxidase (GP) and melanocortin receptor 4 (MC4R) were also examined. Rats were given AMPH daily for 4 days. Hypothalamic NPY, PKCλ, GP and MC4R were determined and compared. Pretreatment with α-methyl-para-tyrosine could block AMPH-induced anorexia, revealing that endogenous catecholamine was involved in regulating AMPH anorexia. PKCλ, GP and MC4R were increased with maximal response on Day 2 during AMPH treatment, which were concomitant with the decreases in NPY. cAMP response element binding protein (CREB) DNA binding activity was increased during AMPH treatment, revealing the involvement of CREB-dependent gene transcription. An interruption of cerebral PKCλ transcript could partly block AMPH-induced anorexia and partly reverse NPY, MC4R and GP mRNA levels to normal. These results suggest that PKCλ participates in regulating AMPH-induced anorexia via a modulation of hypothalamic NPY gene expression and that increases of GP and MC4R may contribute to this modulation. Our results provided molecular evidence for the regulation of AMPH-induced behavioral response.

The development of tolerance to drugs that suppress food intake

Appetite suppressants have been available as weight-reducing aids for over 50 years. The first discovered was amphetamine, which was potent, but possessed undesirable side effects (it is a stimulant and elevates blood pressure). Subsequently, a variety of appetite drugs was developed, all structurally related to amphetamine, but mostly lacking unwanted side effects. Until recently, fenfluramine (FEN) was the most widely used; presently, sibutramine is the most commonly used appetite suppressant. While these appetite suppressants are effective at reducing hunger and food intake when given as a single dose or for short periods of time, their effectiveness diminishes when administered chronically. The biological mechanisms underlying this tolerance have not been carefully studied, but many possibilities have been identified, including the down-regulation in brain of neurotransmitter receptors that might mediate the action of these drugs and adaptive responses of the appetite control circuitry in brain. To date, however, few studies have examined these possibilities in any detail. This article focuses on the question of why appetite suppressants lose efficacy, when given chronically, because this issue is important to the development of the next generation of appetite suppressants. Chronic efficacy should be an issue studied relatively early in the drug development process. This issue is of particular relevance, since obesity treatment is now recognized as a long-term, not a short-term, process. If appetite suppressants are to become a more important tool in obesity treatment, agents that do not lose efficacy when administered for extended periods of time must be identified.

Intracerebral administration of protein kinase A or cAMP response element-binding protein antisense oligonucleotide can modulate amphetamine-mediated appetite suppression in free-moving rats

Although amphetamine (AMPH)-induced appetite suppression has been attributed to its inhibitory action on neuropeptide Y (NPY), an appetite neurotransmitter abundant in the brain, molecular mechanisms underlying this effect are not well known. This study examined the possible role of protein kinase A (PKA) and cAMP response element-binding protein (CREB) signaling in this anorectic effect, and the results showed that both PKA and CREB mRNA levels in hypothalamus were increased following AMPH treatment, which was relevant to a reduction of NPY mRNA level. To determine whether PKA or CREB was involved in the anorectic response, intracerebroventricular infusions of antisense oligonucleotide (or missense control) were performed 60 min before daily AMPH treatment in conscious rats, and results showed that either PKA or CREB knockdown could block AMPH-induced anorexia as well as restore NPY mRNA level, indicating the respective involvement of PKA and CREB signaling in the regulation of NPY gene expression. It is suggested that hypothalamic PKA and CREB signaling may involve the central regulation of AMPH-mediated feeding suppression via the modulation of NPY gene expression.

Cloning, expression and growth promoting action of Red tilapia (Oreochromis sp.) neuropeptide Y

Neuropeptide Y, a 36 amino acid peptide abundantly expressed in the brain, is the most potent orexigenic factor known to date in mammals. It has been shown to be one of the most conserved neuropeptides in vertebrate evolution. It seems that neuropeptide Y functions, in addition to sequence conservation, are also well conserved in fish. In the present study, we cloned and reported the cDNA sequence coding for tilapia 36 aminoacid neuropeptide Y. We express the tilapia neuropeptide Y gene in Escherichia coli driven by T7 promoter. The recombinant neuropeptide Y was purified up to 80% by affinity chromatography. We developed both, a food intake and a growth performance experiment to evaluate the effects of neuropeptide Y administration. Juvenile tilapia receiving recombinant neuropeptide Y (1 microg/g of body weight) by intraperitoneal injection increased food intake compared to controls (p < 0.05). Similarly, in the growth performance experiment, we observed an increase in body weight (p < 0.05) of tilapia fry receiving the same dose of the peptide. Neuropeptide Y treatment had no significant effect on hepatosomatic index and muscle moisture content. On the other hand, muscle protein content was increased in treated animals. These results demonstrate that administration of biologically active E. coli-derived neuropeptide Y resulted in a growth promoting action in fish.

Transcriptional involvement of protein kinase C-alpha isozyme in amphetamine-mediated appetite suppression

Amphetamine (AMPH) is known as an anorectic agent. The anorectic action of AMPH has been attributed to its inhibitory action on hypothalamic neuropeptide Y (NPY), an appetite stimulant in the brain. The molecular mechanisms behind this anorectic action of AMPH are still unclear. This study investigated the possible role of protein kinase C (PKC) isotypes in this anorectic action. Results revealed that most PKC isotypes (alpha, betaII, gamma, delta, eta, lambda and zeta), except betaI and epsilon isotypes, were stimulated during a repeated treatment of AMPH. Among these stimulated isotypes, three isotypes (alpha, delta, lambda) were activated and expressed in a similar manner, while the other isotypes were expressed differently and specifically. To determine if PKCalpha was involved in the anorectic response of AMPH, the infusions of antisense oligonucleotide into the brain were performed 1 h before daily AMPH treatment in freely moving rats, and the results showed that PKCalpha knock down could block the anorectic response and restore NPY mRNA levels in AMPH-treated rats. These results suggest that PKC isotypes- (at least the alpha isotype), related modification of NPY gene expression in hypothalamus might play an essential role in the central regulation of AMPH-mediated feeding suppression.

Activations of c-fos/c-jun signaling are involved in the modulation of hypothalamic superoxide dismutase (SOD) and neuropeptide Y (NPY) gene expression in amphetamine-mediated appetite suppression

Amphetamine (AMPH) is known as an anorectic agent. The mechanism underlying the anorectic action of AMPH has been attributed to its inhibitory action on hypothalamic neuropeptide Y (NPY), an appetite stimulant in the brain. This study was aimed to examine the molecular mechanisms behind the anorectic effect of AMPH. Results showed that AMPH treatment decreased food intake, which was correlated with changes of NPY mRNA level, but increased c-fos, c-jun and superoxide dismutase (SOD) mRNA levels in hypothalamus. To determine if c-fos or c-jun was involved in the anorectic response of AMPH, infusions of antisense oligonucleotide into the brain were performed at 1 h before daily AMPH treatment in freely moving rats, and the results showed that c-fos or c-jun knockdown could block this anorectic response and restore NPY mRNA level. Moreover, c-fos or c-jun knockdown could partially block SOD mRNA level that might involve in the modulation of NPY gene expression. It was suggested that c-fos/c-jun signaling might involve in the central regulation of AMPH-mediated feeding suppression via the modulation of NPY gene expression.

Influence of neuropeptide Y (NPY) on food intake and growth of penaeid shrimps Marsupenaeus japonicus and Penaeus semisulcatus (Decapoda: Penaeidae)

The effects of neuropeptide Y (NPY) administered intramuscularly or orally on postlarvae (PLs) of two penaeid species were investigated in this study. In experiment 1, food intake (FI) of Marsupenaeus japonicus PLs (0.96 g), injected with NPY at 0.6 microg per g BW, was investigated within 48 h posttreatment. In experiment 2, oral administration of NPY (at doses of 0, 0.125, 0.25, 0.5 microg g(-1) food) on feed intake and growth performance of Penaeus semisulcatus PLs (0.27 g) was examined for 6 weeks. In experiment 1, NPY injection significantly increased average daily FI of M. japonicus PLs within the first 24 h compared to the control (P<0.05), but its stimulatory effect decreased on the second day (P>0.05). The increase in FI was 33% during the first 24 h and 17% during the next 24 h. In experiment 2, significant (P<0.05) differences were found among the groups in terms of weight gain and food utilization (P<0.05). Mean FI significantly increased (as much as 1.3-fold over the control) when NPY was orally administered at doses from 0.125 to 0.5 microg g(-1) feed. There was a positive relationship between FI and final weight (y=-0.972+2.098x, R(2)=0.81) and between FCE and NPY doses in the diets (y=45.37+3.46x, R(2)=0.91). The present findings indicated for the first time that NPY is a potent stimulator of food intake when administered either intramuscularly or orally to penaeid shrimps.

Involvement of hypothalamic neuropeptide Y in regulating the amphetamine-induced appetite suppression in streptozotocin diabetic rats

BACKGROUND AND AIM

Amphetamine (AMPH) is a well-known anorectic agent. In normal rats, AMPH-induced anorexia has been attributed to its inhibitory action on hypothalamic neuropeptide Y (NPY), an appetite stimulant in the brain. In diabetic rats, however, if this anorectic response of AMPH might still be observed was uncertain.

METHODS

Rats (including normal, diabetic and insulin-treated diabetic rats) were given daily with saline or AMPH for 6 days. Changes in food intake, plasma glucose level (PGL) and NPY content of these rats were measured and compared.

RESULTS

The AMPH-induced anorectic response was altered in diabetic rats. Although the anorectic effects of AMPH on the first day of dosing were similar between diabetic and control rats, diabetic rats developed tolerance to this anorexia more rapidly than control rats. This alteration was independent of PGL since PGL levels were not changed following AMPH treatment and PGL normalization induced by phlorizin could not restore the level of AMPH anorexia. On the other hand, this alteration was dependent on the action of NPY because NPY contents were decreased following AMPH treatment and the replacement of insulin in diabetic rats could restore both NPY content and AMPH anorexia.

CONCLUSION

These results suggested that the elevated hypothalamic NPY content in diabetic rats was involved in modifying the anorectic response of AMPH.

Amphetamine, an appetite suppressant, decreases neuropeptide Y immunoreactivity in rat hypothalamic paraventriculum

Amphetamine (AMPH) is a well-known anorectic agent. The mechanism underlying the anorectic response of AMPH has been attributed to its inhibitory effect on hypothalamic neuropeptide Y (NPY), an orexigenic peptide in the brain. However, there is still lack of genomic or in situ immunohistochemical evidence to prove it. The present study was aimed to assess the molecular mechanism of AMPH anorexia by immunostaining of hypothalamic NPY protein in the area of paraventricular nucleus (PVN) and by detecting the change of hypothalamic NPY mRNA level using RT-PCR. Results revealed that an AMPH treatment might reduce the expression of NPY at both transcriptional and posttranslational levels. Comparatively, a treatment of clomipramine, a serotonin transporter inhibitor, was unable to reduce NPY mRNA level, revealing the noninvolvement of hypothalamic NPY gene in serotonin anorexia. Our results provided genomic and in situ immunohistochemical evidence to confirm the mediation of hypothalamic NPY neurons in the anorectic action of AMPH.

Dysregulation of striatal dopamine signaling by amphetamine inhibits feeding by hungry mice

Amphetamine (AMPH) releases monoamines, transiently stimulates locomotion, and inhibits feeding. Using a genetic approach, we show that mice lacking dopamine (DA-deficient, or DD, mice) are resistant to the hypophagic effects of a moderate dose of AMPH (2 microg/g) but manifest normal AMPH-induced hypophagia after restoration of DA signaling in the caudate putamen by viral gene therapy. By contrast, AMPH-induced hypophagia in response to the same dose of AMPH is not blunted in mice lacking the ability to make norepinephrine and epinephrine (Dbh(-/-)), dopamine D(2) receptors (D2r(-/-)), dopamine D(1) receptors (D1r(-/-)), serotonin 2C receptors (Htr2c(-/Y)), neuropeptide Y (Npy(-/-)), and in mice with compromised melanocortin signaling (A(y)). We suggest that, at this moderate dose of AMPH, dysregulation of striatal DA is the primary cause of AMPH-induced hypophagia and that regulated striatal dopaminergic signaling may be necessary for normal feeding behaviors.

Immunohistochemical and genomic evidence for the involvement of hypothalamic neuropeptide Y (NPY) in phenylpropranolamine-mediated appetite suppression

Phenylpropanolamine (PPA) is an appetite suppressant. The mechanism for the anorectic effect of PPA has been attributed to its action on the site of hypothalamic paraventriculum. Neuropeptide Y (NPY) is an appetite stimulant that is widely distributed in the site of hypothalamus. It is not clear whether hypothalamic NPY is involved in the anorectic action of PPA. This study was aimed to investigate the mechanism underlying the involvement of NPY gene in the anorectic action of PPA. Results revealed that PPA treatment in rats could decrease both NPY content and mRNA level in the hypothalamus. In addition, the expression of NPY immunoreactivity following PPA treatment was decreased in areas of hypothalamic arcuate nucleus, paraventricular nucleus and periventricular area using immunohistochemical staining, suggesting an involvement of NPYergic pathway in the action of PPA anorexia. Our results provided immunohistochemical and genomic evidence to suggest that PPA might reduce feeding by altering NPY gene expression.

Further evidence for the mediation of both subtypes of dopamine D1/D2 receptors and cerebral neuropeptide Y (NPY) in amphetamine-induced appetite suppression

Amphetamine (AMPH) is known as an anorectic agent. Repeated treatments of AMPH for several days induced a marked anorexia on day 1 followed by a gradual return of food intake to normal level. Previously, using daily food intake (DFI) as an indicator, we found that both dopamine (DA) D1 and D2 receptors were involved in AMPH anorexia. In the present study, using DFI and body weight change (BWC) as indicators, we took a further step to examine whether repeated co-administrations of D1 and D2 agonists might produce an AMPH-like action. Results revealed that repeated co-administrations of D1 and D2 agonists, but not D1 or D2 agonist alone, produced an AMPH-like action (i.e., tolerant DFI and BWC), confirming the previous study. In addition, we examined whether cerebral neuropeptide Y (NPY), an orexigenic neurotransmitter reported to mediate AMPH anorexia, was involved in the anorectic action of D1/D2 co-administration. Our result revealed that injection of NPY antisense into brain could modify the anorectic action of repeated D1/D2 agonists, indicating the involvement of NPY. Taken together, the present results confirmed that both subtypes of D1 and D2 receptors and cerebral NPY were involved in the anorectic action of AMPH.

Effect of amphetamine repeated treatment on the feeding behavior in neuropeptide Y-overexpressing mice

The preset study examined the hypothesis that an increase of brain neuropeptide Y (NPY), an orexigenic peptide, might decrease the action of amphetamine (AMPH), a well-known anorectic agent. Transgenic mice overexpressing the NPY gene were used to compare with the wild-type control. AMPH-induced anorexia is documented to mediate through the release of dopamine (DA), via an activation of D(1)- and D(2)-subtype receptors, to affect the hypothalamic NPY. Thus, co-administration of D(1)/D(2) agonists was also performed to mimic the action of AMPH. The mice of NPY-overexpressing (NPY-OX) and wild-type groups were administered with AMPH or a combination of D(1)/D(2) agonists repeatedly for 5 days. We found that repeated AMPH administration-induced anorexia in wild-type mice was longer (at the initial 3 days) than that in NPY-OX mice (only at the first day). Moreover, repeated co-administration of D(1)/D(2) agonists significantly exerted a continuous anorectic effect in wild-type mice, but exerted a significant effect only at the first day in NPY-OX mice. These results indicated that the anorectic effect of AMPH decayed faster in NPY-OX mice and suggested that NPY expression by the stimuli could counteract the anorectic effect of AMPH. Thus, NPY can be considered to play a functional role in the regulation of AMPH-induced anorexia in mice.

Role of cerebral dopamine but not plasma insulin, leptin and glucocorticoid in the development of tolerance to the anorectic effect of amphetamine

Repeated treatment with amphetamine (AMPH), an anorectic agent, induced a marked anorexia on day 1 followed by a gradual reversion of this anorexia to the normal level of feeding (tolerant anorexia). The mechanism for this tolerant anorexia remained unknown because it might be related with multiple parameters, such as the change of cerebral dopamine (DA) or the plasma levels of insulin, leptin and glucocorticoid. Results revealed that plasma insulin and leptin concentrations remained unchanged during repeated AMPH administration, revealing that these two factors are not involved. Also, glucocorticoids were not required for the development of tolerant anorexia, as this effect could not be prevented by adrenalectomy. However, AMPH-induced anorexia was decreased by the pretreatment of alpha-methyl-p-tyrosine, an inhibitor of central catecholamine synthesis, and was increased by the pretreatment of nomifensine, a blocker of DA transporter that increased extracellular DA content in brain, revealing that the change of DA content could modify the action of tolerant anorexia. It is suggested that the decrease of inhibitory action of DA in brain during repeated AMPH plays a functional role in the development of tolerance to the anorectic response of AMPH.