Serotonergic drugs : effects on appetite expression and use for the treatment of obesity

AMPK as Target for Intervention in Childhood and Adolescent Obesity

Childhood obesity is a major worldwide health problem. Intervention programs to ameliorate the rate of obesity have been designed and implemented; yet the epidemic has no end near in sight. AMP-activated protein kinase (AMPK) has become one of the most important key elements in energy control, appetite regulation, myogenesis, adipocyte differentiation, and cellular stress management. Obesity is a multifactorial disease, which has a very strong genetic component, especially epigenetic factors. The intrauterine milieu has a determinant impact on adult life, since the measures taken for survival are kept throughout life thanks to epigenetic modification. Nutrigenomics studies the influence of certain food molecules on the metabolome profile, raising the question of an individualized obesity therapy according to metabolic (and probably) genetic features. Metformin, an insulin sensitizing agent, its known to lower insulin resistance and enhance metabolic profile, with an additional weight reduction capacity, via activation of AMPK. Exercise is coadjutant for lifestyle modifications, which also activates AMPK in several ways contributing to glucose and fat oxidation. The following review examines AMPK's role in obesity, applying its use as a tool for childhood and adolescent obesity.

Pharmacological treatment of obesity in children and adolescents: present and future

The prevalence of overweight and obesity is increasing in children and adolescents worldwide raising the question on the approach to this condition because of the potential morbidity, mortality, and economic tolls. Dietetic and behavioral treatments alone have only limited success; consequently, discussion on strategies for treating childhood and adolescent obesity has been promoted. Considering that our knowledge on the physiological systems regulating food intake and body weight is considerably increased, many studies have underlined the scientific and clinical relevance of potential treatments based on management of peripheral or central neuropeptides signals by drugs. In this paper, we analyze the data on the currently approved obesity pharmacological treatment suggesting the new potential drugs.

Novel 6,7,8,9-tetrahydro-5H-1,4,7,10a-tetraaza-cyclohepta[f]indene analogues as potent and selective 5-HT(2C) agonists for the treatment of metabolic disorders

The discovery of a novel series of 5-HT(2C) agonists based on a tricyclic pyrazolopyrimidine scaffold is described. Compounds with good levels of in vitro potency and moderate to good levels of selectivity with respect to the 5-HT(2A) and 5-HT(2B) receptors were identified. One of the analogues (7 g) was found to be efficacious in a sub-chronic weight loss model. A key limitation of the series of compounds was that they were found to be potent inhibitors of the hERG ion channel. Some compounds, bearing polar side chains were identified which showed a much reduced hERG liability however these compounds were sub-optimal in terms of their in vitro potency or selectivity.

A randomized, triple masked, placebo-controlled clinical trial for controlling childhood obesity

BACKGROUND

The efficacy of pharmacological treatment in controlling childhood obesity is controversial. We aimed to compare the effects of three types of drug regimens and placebo on generalized and abdominal obesity among obese children and adolescents who did not succeed to lose weight 3 months after lifestyle modification (diet and exercise).

METHODS

This triple-masked randomized clinical trial was conducted among 180 participants aged 10-16 years. They were assigned randomly to 4 groups of equal number to receive metformin, fluoxetine, a combination of the two drugs, or placebo. The trial lasted for 12 weeks and participants were followed up for an additional 12-week period.

RESULTS

Overall, 91.1% (n=164) of the enrolled participants completed the trial. After the 12-week trial, the body mass index decreased significantly in all groups receiving medications [approximately -1.2 (0.2) kg/m², P<0.05]. This decrease was not significant in the placebo group. Waist circumference decreased significantly in the groups receiving metformin [-2.1 (0.4) cm, P=0.03)] as well as in the group receiving a combination therapy of metformin and fluoxetine [-2.5 (0.4) cm, P=0.01)]. In the 24-week follow-up study, these anthropometric indexes were lower than the baseline in the group that had received a combination therapy of metformin and fluoxetine. No serious drug side-effects were reported.

CONCLUSIONS

A limited period of such treatment may help weight control, and might be used to encourage those children who have been refractory to weight loss for continuing the non-pharmacological programs. Our findings should be confirmed in future studies with a longer follow-up period.

Waterborne fluoxetine disrupts feeding and energy metabolism in the goldfish Carassius auratus

Fluoxetine (FLX) is one of the most commonly detected pharmaceuticals in wastewater and bioaccumulates in wild-caught fish, especially in brain, liver and muscle tissues. Previous studies indicated that FLX is pharmacologically active in fish species exerting anorexigenic effects, but it is not clear whether waterborne FLX has any potential effects on regulating food intake and energy metabolism. In this study, we investigated the effect of two doses of FLX, an environmental concentration of 540 ng/L, and 100-times this concentration (54 μg/L), on feeding and key metabolic parameters in goldfish. Fish were exposed for a period of 28 days and changes in food intake and body mass were assessed. Pair-fed groups were maintained to discern primary FLX-induced effects from secondary metabolic responses induced by the decreased food intake. Additionally, an untreated control group and a fasted group were used to further compare physiological changes in the context of nutritional status of the animals. Significant decreases in food intake and weight gain were recorded in goldfish exposed to 54 μg/L FLX. Furthermore a significant decrease occurred in circulating glucose levels in the group exposed to 540 ng/L FLX. To elucidate potential mechanisms, we investigated gene expression of feeding neuropeptides in the neuroendocrine brain of goldfish as well as gene expression and enzymatic activity of glycolytic and gluconeogenetic enzymes in liver and muscle tissues. The results confirm brain gene expression patterns in line with potential anorexigenic effects in the hypothalamus, with increased expression in corticotropin-releasing factor (CRF) and decreased expression of neuropeptide Y (NPY). With respect to glucose metabolism, liver gene expression of the gluconeogenic enzyme fructose-1,6-bisphosphatase decreased and muscle hexokinase activity increased in fish exposed to 540 ng/L FLX. Overall, this study demonstrated anorectic properties of FLX at a dose of 54 μg/L FLX and moderate but significant effects on glucose metabolism in goldfish exposed to 540 ng/L FLX. Future studies investigating the importance of these changes in fish are warranted.

Long-term consumption of fish oil-enriched diet impairs serotonin hypophagia in rats

Hypothalamic serotonin inhibits food intake and stimulates energy expenditure. High-fat feeding is obesogenic, but the role of polyunsaturated fats is not well understood. This study examined the influence of different high-PUFA diets on serotonin-induced hypophagia, hypothalamic serotonin turnover, and hypothalamic protein levels of serotonin transporter (ST), and SR-1B and SR-2C receptors. Male Wistar rats received for 9 weeks from weaning a diet high in either soy oil or fish oil or low fat (control diet). Throughout 9 weeks, daily intake of fat diets decreased such that energy intake was similar to that of the control diet. However, the fish group developed heavier retroperitoneal and epididymal fat depots. After 12 h of either 200 or 300 μg intracerebroventricular serotonin, food intake was significantly inhibited in control group (21-25%) and soy group (37-39%) but not in the fish group. Serotonin turnover was significantly lower in the fish group than in both the control group (-13%) and the soy group (-18%). SR-2C levels of fish group were lower than those of control group (50%, P = 0.02) and soy group (37%, P = 0.09). ST levels tended to decrease in the fish group in comparison to the control group (16%, P = 0.339) and the soy group (21%, P = 0.161). Thus, unlike the soy-oil diet, the fish-oil diet decreased hypothalamic serotonin turnover and SR-2C levels and abolished serotonin-induced hypophagia. Fish-diet rats were potentially hypophagic, suggesting that, at least up to this point in its course, the serotonergic impairment was either compensated by other factors or not of a sufficient extent to affect feeding. That fat pad weight increased in the absence of hyperphagia indicates that energy expenditure was affected by the serotonergic hypofunction.

Brain serotonin system in the coordination of food intake and body weight

An inverse relationship between brain serotonin and food intake and body weight has been known for more than 30 years. Specifically, augmentation of brain serotonin inhibits food intake, while depletion of brain serotonin promotes hyperphagia and weight gain. Through the decades, serotonin receptors have been identified and their function in the serotonergic regulation of food intake clarified. Recent refined genetic studies now indicate that a primary mechanism through which serotonin influences appetite and body weight is via serotonin 2C receptor (5-HT(2C)R) and serotonin 1B receptor (5-HT(1B)R) influencing the activity of endogenous melanocortin receptor agonists and antagonists at the melanocortin 4 receptor (MC4R). However, other mechanisms are also possible and the challenge of future research is to delineate them in the complete elucidation of the complex neurocircuitry underlying the serotonergic control of appetite and body weight.

Efeito do tratamento com triptofano sobre parâmetros do comportamento alimentar em ratos adultos submetidos à desnutrição neonatal

OBJETIVO: Investigou-se os efeitos do tratamento com triptofano sobre o consumo alimentar em ratos adultos, submetidos ou não a desnutrição precoce. MÉTODOS: Sessenta e quatro ratos Wistar machos foram divididos em nutridos (n=32, caseína=17%) e desnutridos (n=32, caseína=8%), de acordo com a dieta materna empregada no período de lactação. Após o desmame, todos os ratos receberam dieta com 23% de proteína. Pesos corporais foram avaliados no sétimo, vigésimo primeiro e septuagésimo dias de vida. Aos setenta dias de idade, cada grupo nutricional foi dividido em subgrupos: Nutrido-Salina (n=16) e Nutrido-Triptofano (n=16), Desnutrido-Salina (n=16) e Desnutrido-Triptofano (n=16). Os grupos receberam diariamente 1,0mL/100g de triptofano, na dose de 50mg/kgP ou salina (0,9%NaCl), durante 14 dias. Neste período foram realizados os estudos dos parâmetros do comportamento alimentar. Posteriormente obteve-se a média do consumo alimentar relativo e a média do ganho de peso relativo. As análises estatísticas foram feitas utilizando os testes t Student e ANOVA seguido de Tukey, com p<0,05. RESULTADOS: As ninhadas de mães alimentadas com dieta hipoproteica mantiveram pesos inferiores comparados com as ninhadas nutridas (p<0,01) até os setenta dias de vida. Os ratos nutridos tratados com triptofano (M=6,88, DP=0,05) reduziram a ingestão alimentar comparados aos nutridos salina (M=7,27, DP=0,08) (p<0,01). Contudo, não houve efeito sobre o ganho de peso. Entre os desnutridos nenhuma diferença foi encontrada. CONCLUSÃO: Nesse estudo, a restrição proteica neonatal alterou a evolução ponderal em ratos. Além disso, a desnutrição precoce tornou os ratos adultos resistentes aos efeitos inibitórios do triptofano sobre a ingestão alimentar.

Combinations of drugs in the Treatment of Obesity

Obesity is a chronic disease associated with excess morbidity and mortality. Clinical treatment, however, currently offers disappointing results, with very high rates of weight loss failure or weight regain cycles, and only two drugs (orlistat and sibutramine) approved for long-term use. Drugs combinations can be an option for its treatment but, although widely used in clinical practice, very few data are available in literature for its validation. Our review focuses on the rationale for their use, with advantages and disadvantages; on combinations often used, with or without studies; and on new perspectives of combinations being studied mainly by the pharmaceutical industry.

Genetic and pharmacological evidence that 5-HT2C receptor activation, but not inhibition, affects motivation to feed under a progressive ratio schedule of reinforcement

Previous work showed that 5-HT(2C) receptor agonists reduce cocaine self-administration on a progressive ratio (PR) schedule of reinforcement, whereas a 5-HT(2C) receptor antagonist enhances responding for cocaine. The present experiments examined the effects of Ro60-0175 (5-HT(2C) agonist) and SB242084 (5-HT(2C) receptor antagonist) in rats on responding for food on a PR schedule; responding was also determined in mice lacking functional 5-HT(2C) receptors. In food-restricted rats, lever pressing reinforced by regular food pellets or sucrose pellets was reduced by Ro60-0175. This effect was blocked by SB242084, and was absent in mice lacking functional 5-HT(2C) receptors. A number of studies examined the effects of SB242084 on responding for food under a variety of conditions. These included manipulation of food type (regular pellets versus sucrose pellets), nutritional status of the animals (food restriction versus no restriction), and rate of progression of the increase in ratio requirements on the PR schedule. In all cases there was no evidence of enhanced responding for food by SB242084. Mice lacking functional 5-HT(2C) receptors did not differ from wildtype mice in responding for food in either food-restricted or non-restricted states. The effects of Ro60-0175 are consistent with its effects on food consumption and motivation to self-administer cocaine. Unlike their effects on cocaine self-administration, pharmacological blockade of 5-HT(2C) receptors, and genetic disruption of 5-HT(2C) receptor function do not alter the motivation to respond for food. Because the 5-HT(2C) receptor exerts a modulatory effect on dopamine function, the differential effects of reduced 5-HT(2C) receptor mediated transmission on responding for food versus cocaine may relate to a differential role of this neurotransmitter in mediating these two behaviours.

Adiposopathy: treating pathogenic adipose tissue to reduce cardiovascular disease risk

Excessive adipose tissue is potentially pathogenic due to its mass effects and through adverse metabolic/immune responses, which may lead to cardiovascular disease risk factors (eg, type 2 diabetes mellitus, hypertension, dyslipidemia, and possibly atherosclerosis itself). Positive caloric balance in genetically/environmentally susceptible patients may result in adipocyte hypertrophy, visceral adipose tissue accumulation, and ectopic fat deposition, all causally associated with metabolic disease, and all anatomic manifestations of "adiposopathy" (a term used to describe adipose tissue pathology). Weight loss through improved nutrition, increased physical activity, and weight loss agents (ie, orlistat and sibutramine) improves adiposopathy and improves many metabolic diseases whose prevalence are directly associated with an increase in body fat and sedentary lifestyle. Cannabinoid receptor antagonists improve adiposopathy through weight reduction and favorable metabolic effects upon multiple body organs (including adipocytes). Peroxisome proliferator-activated receptor-gamma agonists may improve adiposopathy through recruitment of functional fat cells and apoptosis of dysfunctional fat cells.

Effects of dietary fat and enterostatin on dopamine and 5-hydroxytrytamine release from rat striatal slices

Studies have demonstrated defects of DA and 5HT neurotransmission in dietary fat induced obese animals. In the present study, we used a perfusion system to assay the release of DA and 5HT from striatal slices preloaded with [(3)H]-DA or [(3)H]-5HT. The release of both DA and 5HT from striatal slices of rats fed a high fat diet for 10 days, but not 3 days, was reduced when compared to striatal slices taken from rats fed a low fat diet. Enterostatin, an endogenous pentapeptide inhibits dietary fat intake when administered peripherally and centrally in animals. The central mechanism for the action of enterostatin is not yet determined even though several mechanisms have been suggested. We have shown that enterostatin enhanced [(3)H]-DA release, but not [(3)H]-5HT release from striatal slices of rats that had been adapted to high fat diet for 10 days. The enterostatin-induced increase in [(3)H]-DA release was blocked by nomifensine. Enterostatin did not alter [(3)H]-DA or [(3)H]-5HT release from striatal slices of rats adapted to high fat or low fat diet feeding for 3 days. These findings suggest that enterostatin may inhibit dietary fat intake by blocking dopamine reuptake transport to increase central striatal DA release from rats that have acquired diminished dopamine signal after an adaptive period of fat consumption.

Tesofensine, a novel triple monoamine reuptake inhibitor, induces appetite suppression by indirect stimulation of alpha1 adrenoceptor and dopamine D1 receptor pathways in the diet-induced obese rat

Tesofensine is a novel monoamine reuptake inhibitor that inhibits both norepinephrine, 5-HT, and dopamine (DA) reuptake function. Tesofensine is currently in clinical development for the treatment of obesity, however, the pharmacological basis for its strong effect in obesity management is not clarified. Using a rat model of diet-induced obesity (DIO), we characterized the pharmacological mechanisms underlying the appetite suppressive effect of tesofensine. DIO rats treated with tesofensine (2.0 mg/kg, s.c.) for 16 days showed significantly lower body weights than vehicle-treated DIO rats, being reflected by a marked hypophagic response. Using an automatized food intake monitoring system during a 12 h nocturnal test period, tesofensine-induced hypophagia was investigated further by studying the acute interaction of a variety of monoamine receptor antagonists with tesofensine-induced hypophagia in the DIO rat. Tesofensine (0.5-3.0 mg/kg, s.c.) induced a dose-dependent and marked decline in food intake with an ED(50) of 1.3 mg/kg. The hypophagic response of tesofensine (1.5 mg/kg, s.c.) was almost completely reversed by co-administration of prazosin (1.0 mg/kg, alpha(1) adrenoceptor antagonist) and partially antagonized by co-administration of SCH23390 (0.03 mg/kg, DA D(1) receptor antagonist). In contrast, tesofensine-induced hypophagia was not affected by RX821002 (0.3 mg/kg, alpha(2) adrenoceptor antagonist), haloperidol (0.03 mg/kg, D(2) receptor antagonist), NGB2904 (0.1 mg/kg, D(3) receptor antagonist), or ritanserin (0.03 mg/kg, 5-HT(2A/C) receptor antagonist). Hence, the mechanism underlying the suppression of feeding by tesofensine in the obese rat is dependent on the drug's ability to indirectly stimulate alpha(1) adrenoceptor and DA D(1) receptor function.

Pharmacological management of appetite expression in obesity

For obese individuals, successful weight loss and maintenance are notoriously difficult. Traditional drug development fails to exploit knowledge of the psychological factors that crucially influence appetite, concentrating instead on restrictive criteria of intake and weight reduction, allied to a mechanistic view of energy regulation. Drugs are under development that may produce beneficial changes in appetite expression in the obese. These currently include glucagon-like peptide-1 analogs such as liraglutide, an amylin analog davalintide, the 5-HT(2C) receptor agonist lorcaserin, the monoamine re-uptake inhibitor tesofensine, and a number of combination therapies such as pramlintide and metreleptin, bupropion and naltrexone, phentermine and topiramate, and bupropion and zonisamide. However, the effects of these treatments on eating behavior remain poorly characterized. Obesity is typically a consequence of overconsumption driven by an individual's natural sensitivity to food stimuli and the pleasure derived from eating. Intuitively, these processes should be effective targets for pharmacotherapy, and behavioral analysis can identify drugs that selectively affect desire to eat, enjoyment of eating, satiation or postmeal satiety. Rational interventions designed specifically to modulate these processes could limit the normally aversive consequences of caloric restriction and maximize an individual's capacity to successfully gain control over their appetite.

Changes in weight and body mass index during treatment with melperone, clozapine and typical neuroleptics

Melperone is an atypical antipsychotic drug that has been reported to be effective in treatment-resistant schizophrenia and L-DOPA psychosis. There are limited data concerning its effect on weight or body mass index (BMI). Weight and BMI were retrospectively compared in patients with schizophrenia treated with melperone (n=34), clozapine (n=225), or typical neuroleptics (n=74) for up to 3 months. Clozapine resulted in significant increases in weight and BMI from baseline to 6 weeks and 3 months. Neither melperone nor typical neuroleptics resulted in significant weight gain at either time point. Melperone did not result in significant increases in BMI. Weight and BMI were significantly lower with melperone compared with clozapine, but similar to typical neuroleptics. The proportion of melperone patients who experienced a >or=7% weight increase was lower than that in patients treated with clozapine and similar to that in patients treated with typical neuroleptics. Percent change in weight and BMI predicted improvement in BPRS total scores at 3 months in the clozapine group, but not in the melperone or typical neuroleptic groups. Because of the relationship between BMI and cardiovascular risk, melperone deserves further study as both a first line treatment and as an alternative to clozapine in refractory schizophrenia.

Impact of RNA editing on functions of the serotonin 2C receptor in vivo

Transcripts encoding 5-HT(2C) receptors are modified posttranscriptionally by RNA editing, generating up to 24 protein isoforms. In recombinant cells, the fully edited isoform, 5-HT(2C-VGV), exhibits blunted G-protein coupling and reduced constitutive activity. The present studies examine the signal transduction properties of 5-HT(2C-VGV) receptors in brain to determine the in vivo consequences of altered editing. Using mice solely expressing the 5-HT(2C-VGV) receptor (VGV/Y), we demonstrate reduced G-protein coupling efficiency and high-affinity agonist binding of brain 5-HT(2C-VGV) receptors. However, enhanced behavioral sensitivity to a 5-HT(2C) receptor agonist was also seen in mice expressing 5-HT(2C-VGV) receptors, an unexpected finding given the blunted G-protein coupling. In addition, mice expressing 5-HT(2C-VGV) receptors had greater sensitivity to a 5-HT(2C) inverse agonist/antagonist enhancement of dopamine turnover relative to wild-type mice. These behavioral and biochemical results are most likely explained by increases in 5-HT(2C) receptor binding sites in the brains of mice solely expressing 5-HT(2C-VGV) receptors. We conclude that 5-HT(2C-VGV) receptor signaling in brain is blunted, but this deficiency is masked by a marked increase in 5-HT(2C) receptor binding site density in mice solely expressing the VGV isoform. These findings suggest that RNA editing may regulate the density of 5-HT(2C) receptor binding sites in brain. We further caution that the pattern of 5-HT(2C) receptor RNA isoforms may not reflect the pattern of protein isoforms, and hence the inferred overall function of the receptor.

Diminished neural processing of aversive and rewarding stimuli during selective serotonin reuptake inhibitor treatment

BACKGROUND

Selective serotonin reuptake inhibitors (SSRIs) are popular medications for anxiety and depression, but their effectiveness, particularly in patients with prominent symptoms of loss of motivation and pleasure, has been questioned. There are few studies of the effect of SSRIs on neural reward mechanisms in humans.

METHODS

We studied 45 healthy participants who were randomly allocated to receive the SSRI citalopram, the noradrenaline reuptake inhibitor reboxetine, or placebo for 7 days in a double-blind, parallel group design. We used functional magnetic resonance imaging to measure the neural response to rewarding (sight and/or flavor of chocolate) and aversive stimuli (sight of moldy strawberries and/or an unpleasant strawberry taste) on the final day of drug treatment.

RESULTS

Citalopram reduced activation to the chocolate stimuli in the ventral striatum and the ventral medial/orbitofrontal cortex. In contrast, reboxetine did not suppress ventral striatal activity and in fact increased neural responses within medial orbitofrontal cortex to reward. Citalopram also decreased neural responses to the aversive stimuli conditions in key "punishment" areas such as the lateral orbitofrontal cortex. Reboxetine produced a similar, although weaker effect.

CONCLUSIONS

Our findings are the first to show that treatment with SSRIs can diminish the neural processing of both rewarding and aversive stimuli. The ability of SSRIs to decrease neural responses to reward might underlie the questioned efficacy of SSRIs in depressive conditions characterized by decreased motivation and anhedonia and could also account for the experience of emotional blunting described by some patients during SSRI treatment.

Overview on 5-HT receptors and their role in physiology and pathology of the central nervous system

The present review gives an overview on the serotonin (5-hydroxytryptamine; 5-HT) system, its receptors and their relationship to central nervous system physiology and disorders. Additionally, we also introduce the recent knowledge about the 5-HT receptor ligands in preclinical research, clinical trials and as approved drugs.

JL13 has clozapine-like actions on thermoregulatory cutaneous blood flow in rats: Involvement of serotonin 5-HT1A and 5-HT2A receptor mechanisms

Clozapine is an effective atypical antipsychotic agent, with serious side effects. JL13 [5-(4-methylpiperazin-1-yl)-8-chloropyrido[2,3-b][1,5]benzoxazepine] is a potential new atypical antipsychotic, structurally modified from clozapine to resist oxidation so as to reduce haematological and cardiological side effects. To assess the potential clinical potency of JL13 we tested its action in a newly described animal model based on the ability of clozapine-like agents to affect brain mechanisms controlling sympathetic outflow to thermoregulatory cutaneous vascular beds. We determined whether JL13 has clozapine-like inhibitory actions on alerting-induced falls in tail artery blood flow (sympathetic cutaneous vasomotor alerting responses, SCVARs) in rats, and whether actions on dopamine D(2), and/or 5-HT(1A) receptors are involved in these effects of JL13. The tail artery Doppler flow signal was recorded in conscious freely moving Sprague-Dawley rats before and after alerting stimuli (e.g. cage tap). The percentage fall in flow in response to an alerting stimulus was quantified as a SCVAR index (fall to zero flow implies SCVAR index of 100%, no fall implies 0%). We used pre-treatment with spiperone and WAY100635, before JL13, to assess the role of D(2) and 5-HT(1A) receptors. In addition, the role of 5-HT(2A) receptors in the action of JL13 was assessed by determining whether JL13 prevented and reversed the CNS-mediated tail artery vasoconstricting actions of DOI ((+/-)-1-(2,5-dimethoxy-4-iodophenyl)-2-aminopropane), an agonist at 5-HT(2A) receptors. JL13 (0.0625-5.0mg/kg s.c.) dose-dependently inhibited SCVARs, less potently than clozapine. WAY100635 but not spiperone reduced the inhibition. JL13 prevented and reversed DOI-induced vasoconstriction. Thus JL13 has clozapine-like actions on thermoregulatory cutaneous blood flow, but the drug is 5 times less potent than clozapine. Stimulation of 5-HT(1A) and blockade of 5-HT(2A) receptors may contribute to the effects, but dopamine D(2) receptors are apparently not involved in the action of JL13.

Brain serotonin transporter occupancy by oral sibutramine dosed to steady state: a PET study using (11)C-DASB in healthy humans

Sibutramine is a centrally acting monoamine reuptake inhibitor prescribed as an appetite suppressant in the management of obesity. Its effects are mostly attributable to serotonin and norepinephrine transporter (SERT and NET, respectively) inhibition by its potent metabolites mono-desmethylsibutramine (M1) and di-desmethylsibutramine (M2). However, there is a paucity of in vivo data in humans about mechanisms underlying both clinical efficacy and the dose-independent non-response observed in a minority of patients. Twelve healthy male patients (mean age 41 years) completed a double-blind, placebo-controlled, within-subject crossover investigation of brain SERT occupancy by sibutramine 15 mg daily at steady state. Correlations were measured between occupancy and (i) plasma concentrations of sibutramine, M1 and M2; (ii) appetite suppression. (11)C-DASB PET scans were performed on the HRRT camera. Binding potentials (BP(ND)) were calculated by the Logan reference tissue (cerebellum) method. SERT occupancy was modest (mean 30+/-10%), was similar across brain regions, but varied widely across subjects (15-46%). Occupancy was correlated positively (p=0.09) with M2 concentration, but not with sibutramine or M1. No significant appetite suppression was seen at <25% occupancy and greatest suppression was associated with highest occupancy (25-46%). However, several subjects with occupancy (36-39%) in the higher range had no appetite suppression. SERT occupancy by clinical doses of sibutramine is of modest magnitude and may be mediated predominantly by M2 in humans. 5-HT reuptake inhibition may be necessary but is not sufficient for sibutramine's efficacy in humans, supporting preclinical data suggesting that the hypophagic effect requires the co-inhibition of both SERT and NET.

Approved and Off-Label Uses of Obesity Medications, and Potential New Pharmacologic Treatment Options

Available anti-obesity pharmacotherapy options remain very limited and development of more effective drugs has become a priority. The potential strategies to achieve weight loss are to reduce energy intake by stimulating anorexigenic signals or by blocking orexigenic signals, and to increase energy expenditure. This review will focus on approved obesity medications, as well as potential new pharmacologic treatment options.

Serotonin transporter deficiency increases abdominal fat in female, but not male rats

Depression and abdominal obesity often co-occur, predominantly in women, and are associated with an increased risk for the development of glucose intolerance and subsequently type 2 diabetes. The underlying mechanisms are poorly understood. We found that female, but not male, depression-prone serotonin transporter knockout (SERT(-/-)) rats had a strong increase (54%) in abdominal fat, whereas no increases in plasma concentrations of glucose and insulin were observed. Surprisingly, application of a high-fat, high-sucrose (HFHS)-choice diet, which results in increased abdominal fat deposition and increased plasma glucose levels in wild-type rats, did not result in elevated plasma glucose levels in female SERT(-/-) rats. Our results show that serotonin transporter deficiency affects abdominal fat deposition in a sex-dependent way, but protects against rises in glucose levels, and thereby potentially glucose intolerance. The increased abdominal fat formation could result from serotonin-mediated developmental changes and provides heuristic value for understanding the effects of the depression-associated serotonin transporter promoter polymorphism in humans.

The effects of sibutramine on the microstructure of eating behaviour and energy expenditure in obese women

Given the suggestion that many potential anti-obesity drugs may enhance within-meal satiation, few studies have directly measured the effects of any drug on the microstructure of human eating behaviour. The effects of 7 days dosing with sibutramine 10 mg and 15 mg a day on appetite and energy balance were determined in 30 obese women (BMI 34.6 +/- 3.3 kg/m2, age 46.0 +/- 12.9 years) using a Universal Eating Monitor (UEM) and indirect calorimetry, in a double-blind, placebo-controlled crossover study. At day 7, sibutramine 10 mg and 15 mg reduced food intake by 16.6% and 22.3%, respectively (p < 0.001), compared with placebo. Sibutramine reduced eating rate compared with placebo rather than meal length (10 mg p < 0.05; 15 mg p < 0.001). In addition, sibutramine 10 mg significantly reduced hunger later in the meal (p < 0.05) and sibutramine 15 mg increased fullness early in the meal (p < 0.01), both of which are consistent with enhanced within-meal satiation. Sibutramine had little effect on resting metabolic rate, although 15 mg did significantly reduce respiratory quotient at several time points during the test day. These results provide novel evidence that decreased consumption of a test meal induced by sibutramine is primarily because of reduced eating rate, enhancing the deceleration in cumulative food intake within a meal associated with the development of satiety. Changes in within-meal appetite ratings appear particularly sensitive to drug-induced enhancement of satiation, and may provide key indices for assessing the therapeutic potential of novel anti-obesity drugs.

Serotonin and the GI tract

Serotonin (5-hydroxytryptamine, 5-HT) participates in several functions of the gastrointestinal tract. Receptors in seven families (5-HT(1)-5-HT(7)) were identified, many of which are present on enterocytes, intrinsic and extrinsic neurons, interstitial cells, and gut myocytes. Most 5-HT is released from enterochromaffin cells in response to physiologic and pathologic stimuli. Roles of 5-HT in health include control of normal gut motor activity, secretion, and sensation, and regulation of food intake and cell growth. Abnormalities of serotonergic function contribute to symptom genesis in functional bowel disorders, inflammatory and infectious diseases of the gut, emetic responses to varied stimuli, obesity, and dysregulation of cell growth. Therapies acting as agonists or antagonists of 5-HT receptors or that modulate 5-HT reuptake play prominent roles in managing these conditions, although use of many agents is hampered by cardiopulmonary complications. Novel agents are in testing, which may exhibit efficacy without significant toxicity.

Migraine and obesity: epidemiology, mechanisms, and implications

Adipose tissue is a dynamic neuroendocrine organ that is involved in multiple physiological and pathological processes, and when excessive, results in obesity. Clinical and population-based data suggest that migraine and chronic daily headache are associated with obesity, as estimated by anthropometric indices. In addition, translational and basic science research shows multiple areas of overlap between migraine pathophysiology and the central and peripheral pathways regulating feeding. Specifically, neurotransmittors such as serotonin, peptides such as orexin, and adipocytokines such as adiponectin and leptin have been suggested to have roles in both feeding and migraine. In this article, we first review the definition and ascertainment of obesity. This is followed by a review of the clinical and population-based studies evaluating the associations between obesity and chronic daily headache and migraine. We then discuss the central and peripheral pathways involved in the regulation of feeding, where it overlaps with migraine pathophysiology, and where future research may be headed in light of these data.

Appetite suppressants, cardiac valve disease and combination pharmacotherapy

The prevalence of obesity in the United States is a major health problem associated with significant morbidity, mortality, and economic burden. Although obesity and drug addiction are typically considered distinct clinical entities, both diseases involve dysregulation of biogenic amine neuron systems in the brain. Thus, research efforts to develop medications for treating drug addiction can contribute insights into the pharmacotherapy for obesity. Here, we review the neurochemical mechanisms of selected stimulant medications used in the treatment of obesity and issues related to fenfluramine-associated cardiac valvulopathy. In particular, we discuss the evidence that cardiac valve disease involves activation of mitogenic serotonin 2B (5-HT2B) receptors by norfenfluramine, the major metabolite of fenfluramine. Advances in medication discovery suggest that novel molecular entities that target 2 different neurochemical mechanisms, that is, "combination pharmacotherapy," will yield efficacious antiobesity medications with reduced adverse side effects.

Conserved role for the serotonin transporter gene in rat and mouse neurobehavioral endophenotypes

The serotonin transporter knockout (SERT(-/-)) mouse, generated in 1998, was followed by the SERT(-/-) rat, developed in 2006. The availability of SERT(-/-) rodents creates the unique possibility to study the conservation of gene function across species. Here we summarize SERT(-/-) mouse and rat data, and discuss species (dis)similarities in neurobehavioral endophenotypes. Both SERT(-/-) rodent models show a disturbed serotonergic system, altered nociception, higher anxiety, decreased social behavior, as well as increased negative emotionality, behavioral inhibition and decision making. Used to model a wide range of psychiatric disorders, SERT(-/-) rodents may be particularly valuable in research on neurodevelopmental disorders such as depression, anxiety, and possibly autism. We conclude that SERT function is conserved across mice and rats and that their behavioral profile arises from common neurodevelopmental alterations. Because mice and rats have species-specific characteristics that confer differential research advantages, a comparison of the two models has heuristic value in understanding the mechanisms and behavioral outcome of SERT genetic variation in humans.

The anorexic agents, sibutramine and fenfluramine, depress GABA(B)-induced inhibitory postsynaptic potentials in rat mesencephalic dopaminergic cells

BACKGROUND AND PURPOSE

Nutrition is the result of a complex interaction among environmental, homeostatic and reward-related processes. Accumulating evidence supports key roles for the dopaminergic neurons of the ventral midbrain in regulating feeding behaviour. For this reason, in the present study, we have investigated the electrophysiological effects of two centrally acting anorexic agents, fenfluramine and sibutramine, on these cells.

EXPERIMENTAL APPROACH

Rat midbrain slices were used to make intracellular recordings from dopaminergic neurons of the substantia nigra and the ventral tegmental area. Gamma-aminobutyric acid (GABA)-mediated synaptic transmission was assessed from the inhibitory postsynaptic potentials (IPSPs) mediated by GABA(A) and GABA(B) receptors.

KEY RESULTS

Fenfluramine and sibutramine reduced, concentration-dependently, the GABA(B) IPSPs, without affecting the GABA(A)-mediated potentials. This effect is presynaptic, as postsynaptic membrane responses induced by application of a GABA(B) receptor agonist, baclofen, were not affected by the two drugs. Furthermore, the selective 5-hydroxytriptamine 1B (5-HT(1B)) receptor antagonist, SB216641, blocked the reduction of GABA(B) IPSPs caused by fenfluramine and sibutramine, indicating that the receptor mediating this effect is 5-HT(1B).

CONCLUSIONS AND IMPLICATIONS

Two anorexic agents, fenfluramine and sibutramine, induced the activation of 5-HT(1B) receptors located on presynaptic GABAergic terminals, thus reducing the release of GABA. This action can alter the strength of synaptic afferents that modify the activity of dopaminergic neurons, inducing neuronal excitation. Our results reveal an additional mechanism of action for fenfluramine and sibutramine that might contribute to reducing food intake, by influencing the pleasurable and motor aspects of feeding behaviour.

Trace amine-associated receptor 1 as a monoaminergic modulator in brain

Brain monoaminergic systems play critical roles in mood, cognition, emotion, reward, learning and attention, and aberrance in brain monoaminergic activity is associated with a variety of neuropsychiatric disorders/diseases. The present commentary focuses on trace amine-associated receptor 1 (TAAR1) and its potential regulatory roles in brain monoaminergic systems. TAAR1 was discovered in 2001 and has been established to be a G-protein-coupled receptor signaling through the cAMP pathway. This receptor is activated by a broad spectrum of agonists, although there are notable species differences in ligand efficacy and potency. TAAR1 is expressed and widely distributed in brain monoaminergic systems and co-localized with the dopamine transporter in a subset of dopaminergic neurons in rhesus monkey and mouse brain substantia nigra. TAAR1 activation by the common biogenic amines, the trace amine beta-phenylethylamine and methamphetamine alters the monoamine transporter function in both mouse and rhesus monkey brain synaptosomes, suggesting a modulatory role for this receptor in the presynaptic regulation of monoaminergic activity. However, little is known about other functional roles of TAAR1 in the brain. With a purpose to promote further studies on this receptor, we herein discuss the recent findings that provide insights into the functional significance and biological relevance of this receptor as a modulator in brain monoaminergic systems.

Selective serotonin reuptake inhibitors modify physiological gastrointestinal motor activities via 5-HT2c receptor and acyl ghrelin

BACKGROUND

Selective serotonin reuptake inhibitors (SSRIs) are widely used to treat anxiety and depressive disorders. These agents may cause upper gastrointestinal (GI) symptoms that lead to their discontinuation. We examined whether SSRIs modify physiologic GI motor activities in freely moving rats.

METHODS

The SSRIs fenfluramine, fluvoxamine, paroxetine, and fluoxetine were administered to 24-hour food-deprived rats, and then GI motility was measured in conscious, freely moving rats using a strain gauge force transducer method. Plasma acyl ghrelin levels were determined by enzyme immunoassay.

RESULTS

Plasma acyl ghrelin levels were analyzed in conjunction with fasted motor activities. Acyl ghrelin was increased in association with the occurrence of Phase III-like contractions of the migrating motor complex in the antrum and duodenum. SSRIs decreased acyl ghrelin and changed Phase III-like contractions to fed-like motor activities. Both effects were blocked by 5-HT2c, but not 5-HT1b, receptor antagonist. Neither melanocortin 4 nor the 3/4 receptor antagonists blocked this motor effect, although they restored the anorexia induced by SSRIs. The improving effect on GI motility by 5-HT2c receptor (5-HT2cR) antagonist disappeared after treatment with a growth-hormone secretagogue receptor antagonist, whereas ghrelin or ghrelin-releasing drug such as TJ-43 changed SSRI-induced fed-like motor activities to fasted activities.

CONCLUSIONS

SSRIs have inhibitory effects on acyl ghrelin and GI motor activities through 5-HT2cR. Our study identifies the importance and divergence of central 5-HT2cR pathways that regulate GI motor activities through ghrelin and feeding/energy metabolism via melanocortin 4 receptor signaling.

Deficit in BDNF does not increase vulnerability to stress but dampens antidepressant-like effects in the unpredictable chronic mild stress

Despite growing evidences of an association between brain-derived neurotrophic factor (BDNF) and antidepressant effects, the neurotrophic hypothesis of depression is challenged by the paucity of direct links between BDNF deficit and depressive-like behaviors. The unpredictable chronic mild stress (UCMS) paradigm might take our understanding a step further by examining whether a decrease in bdnf expression can lead to enhanced vulnerability to stress and prevent antidepressant efficacy in all or specific UCMS-induced alterations. Wild-type bdnf(+/+) and heterozygous bdnf(+/-) mice were exposed to an 8-week UCMS regimen and, from the third week onward, treated with either vehicle or imipramine (20mg/kg/day, ip). Physical, behavioral and biological (plasma corticosterone levels, bdnf expression in the dentate gyrus) measures were further analyzed regarding to the genotype and the treatment. Heterozygous bdnf(+/-) mice displayed hyperactivity and increase of body weight but no enhancement of the sensitivity to stress exposure in all the measures investigated here. In contrast, while imipramine treatment reduced anxiety-like behaviors in the novelty-suppressed feeding test in both genotypes, it decreased aggressiveness in the resident/intruder test and immobility in the tail suspension test in wild-type but not in heterozygous mice. Furthermore, imipramine induced a twofold increase of bdnf expression in the dentate gyrus in both genotypes, while bdnf(+/-) mice displayed roughly half-reduced level for the same treatment. In summary, we demonstrate here that depletion in BDNF dampened the antidepressant effects in several behaviors but failed to increase vulnerability to chronic stress exposure.

Blockade of the serotonin 5-HT2A receptor suppresses cue-evoked reinstatement of cocaine-seeking behavior in a rat self-administration model

The serotonin 5-HT2A receptor (5-HT-sub(2A)R) may play a role in reinstatement of drug-seeking. This study investigated the ability of a selective 5-HT-sub(2A)R antagonist to suppress reinstatement evoked by exposure to cues conditioned to cocaine self-administration. Cocaine self-administration (0.75 mg/kg/0.1 mL/6 s infusion; FR 4) was trained in naïve, free-fed rats to allow interpretation of results independent from changes related to food deprivation stress. Pretreatment with the selective 5-HT-sub(2A)R antagonist M100907 (volinanserin) failed to reduce rates of operant responding for cocaine infusions. On the other hand, M100907 (0.001-0.8 mg/kg ip) significantly suppressed the cue-induced reinstatement of cocaine-seeking behavior following extinction; effective M100907 doses did not alter operant responding for cues previously associated with sucrose self-administration. Importantly, a greater magnitude of active lever presses on the initial extinction session (high extinction responders) predicted the maximal susceptibility to M100907-induced suppression of cue-evoked reinstatement. The findings indicate that blockade of the 5-HT-sub(2A)R attenuates the incentive-motivational effects of cocaine-paired cues, particularly in high extinction responders, and suggests that M100907 may afford a therapeutic advance in suppression of cue-evoked craving and/or relapse.

Brain endocannabinoid system is involved in fluoxetine-induced anorexia

In order to describe the effects of chronic fluoxetine administration on the brain endocannabinoid system in lean and obese Zucker rats, brain immunostaining for the CB1 and CB1-phosphorylated cannabinoid receptors was carried out. Obese Zucker rats showed significantly increased the numbers of neural cells positively immunostained for the CB1-phosphorylated receptor in the striatum, compared to their lean litter-mates. Chronic fluoxetine administration decreased the number of neural cells immunostained for CB1-phosphorylated receptor in several striatal and hippocampal regions of obese Zucker rats, compared to controls treated with saline. In contrast, no change in CB1-phosphorylated receptor immunostaining was observed in fluoxetine-treated lean rats, with respect to controls. Taken together, these results suggest the involvement of the hippocampal and striatal endocannabinoid receptor system in fluoxetine-induced anorexia in lean and obese Zucker rats.

Pharmacological targeting of the serotonergic system for the treatment of obesity

The attenuation of food intake as induced by an increase in serotonergic (5-hydroxytryptamine, 5-HT) efficacy has been a target of antiobesity pharmacotherapies. However, the induction of tolerance and/or side-effects limited the clinical utility of the earliest serotonin-related medications. With the global prevalence of obesity rising, there has been renewed interest in the manipulation of the serotonergic system as a point of pharmacological intervention. The serotonin(2C) receptor (5-HT(2C)R), serotonin(1B) (rodent)/serotonin(1Dbeta) (human) receptor (5-HT(1B/1Dbeta)R) and serotonin(6) receptor (5-HT(6)R) represent the most promising serotonin receptor therapeutic targets. Canonical serotonin receptor compounds have given way to a myriad of novel receptor-selective ligands, many of which have observable anorectic effects. Here we review serotonergic compounds reducing ingestive behaviour and discuss their clinical potential for the treatment of obesity.

Impact of regional 5-HT depletion on the cognitive enhancing effects of a typical 5-ht(6) receptor antagonist, Ro 04-6790, in the Novel Object Discrimination task

RATIONALE

Selective 5-ht(6) receptor antagonists like Ro 04-6790 prolong memory in many rodent preclinical paradigms, possibly by blocking tonic 5-HT-evoked GABA release and allowing disinhibition of cortico-limbic glutamatergic and cholinergic neurones. If this is the case, behavioural responses to Ro 04-6790 should be abolished by depletion of endogenous 5-HT, and selective lesions of dorsal raphé (DR) or median raphé (MR) 5-HT pathways would allow the neuroanatomical substrates underlying the cognitive effects of 5-ht(6) receptor antagonists to be elucidated.

OBJECTIVES

This study compared the effect of Ro 04-6790 on novel object discrimination (NOD) before and after sham or 5,7-dihydroxytryptamine (5,7-DHT)-induced lesions produced by injection into the lateral ventricles (LV), DR or MR.

MATERIALS AND METHODS

NOD tests used a 4 h inter-trial interval (ITI) and Ro 04-6790 (10 mg kg(-1) i.p.) was administered 20 min before the familiarization trial. Brain region-specific 5-HT depletion was assessed by high performance liquid chromatography with electrochemical detection (HPLC-ED).

RESULTS

Widespread LV or selective MR, but not DR lesions, abolished the ability of Ro 04-6790 to delay natural forgetting. Successful performance of all lesioned rats in subsequent 'drug-free' NOD tests using a 1 h ITI excluded the possibility of any confounding effects on visual acuity or motivation.

CONCLUSIONS

The ability of Ro 04-6790 to prolong object recognition memory requires blockade of MR 5-HT function. Because DR lesions did not produce the expected depletion of striatal 5-HT an additional contribution of DR inputs to this region cannot be completely excluded.

Serotonergic mechanisms in addiction-related memories

Drug-associated memories are a hallmark of addiction and a contributing factor in the continued use and relapse to drugs of abuse. Repeated association of drugs of abuse with conditioned stimuli leads to long-lasting behavioral responses that reflect reward-controlled learning and participate in the establishment of addiction. A greater understanding of the mechanisms underlying the formation and retrieval of drug-associated memories may shed light on potential therapeutic approaches to effectively intervene with drug use-associated memory. There is evidence to support the involvement of serotonin (5-HT) neurotransmission in learning and memory formation through the families of the 5-HT(1) receptor (5-HT(1)R) and 5-HT(2)R which have also been shown to play a modulatory role in the behavioral effects induced by many psychostimulants. While there is a paucity of studies examining the effects of selective 5-HT(1A)R ligands, the available dataset suggests that 5-HT(1B)R agonists may inhibit retrieval of cocaine-associated memories. The 5-HT(2A)R and 5-HT(2C)R appear to be integral in the strong conditioned associations made between cocaine and environmental cues with 5-HT(2A)R antagonists and 5-HT(2C)R agonists possessing potency in blocking retrieval of cocaine-associated memories following cocaine self-administration procedures. The complex anatomical connectivity between 5-HT neurons and other neuronal phenotypes in limbic-corticostriatal brain structures, the heterogeneity of 5-HT receptors (5-HT(X)R) and the conflicting results of behavioral experiments which employ non-specific 5-HT(X)R ligands contribute to the complexity of interpreting the involvement of 5-HT systems in addictive-related memory processes. This review briefly traces the history of 5-HT involvement in retrieval of drug-cue associations and future targets of serotonergic manipulation that may reduce the impact that drug cues have on addictive behavior and relapse.

Neuropharmacology of human appetite expression

The regulation of appetite relies on the integration of numerous episodic (meal) and tonic (energy storage) generated signals in energy regulatory centres within the central nervous system (CNS). These centers provide the pharmacological potential to modify human appetite (hunger and satiety) to increase or decrease caloric intake, or to normalize aberrant eating behavior. With regard to obesity, the satiety enhancing anti-obesity drug sibutramine has proved effective at reducing body weight. Additionally, the endocannabinoid CB(1) antagonist rimonabant has recently been approved for use in Europe (but not in the US). A 5-HT(2C) agonist lorcaserin is also currently undergoing large-scale clinical trials, but the effect of the drug on human appetite is unknown as yet. Appetite enhancing drugs such as magestrol acetate and dronabiol are currently used to promote weight gain. Finally, sibutramine, selective serotonergic reuptake inhibitors such as fluoxetine and some anti-epileptic drugs have all been used to normalise aberrant eating behaviour. All these drugs act by modifying the expression of human appetite. An assessment of a drug's effects on caloric intake and feelings of hunger and satiety is necessary before they can be considered for clinical use.