Eating disorder and epilepsy in mice lacking 5-HT2c serotonin receptors

Dynamic 5-HT2C receptor editing in a mouse model of obesity

The central serotonergic signalling system has been shown to play an important role in appetite control and the regulation of food intake. Serotonin exerts its anorectic effects mainly through the 5-HT(1B), 5-HT(2C) and 5-HT(6) receptors and these are therefore receiving increasing attention as principal pharmacotherapeutic targets for the treatment of obesity. The 5-HT(2C) receptor has the distinctive ability to be modified by posttranscriptional RNA editing on 5 nucleotide positions (A, B, C, D, E), having an overall decreased receptor function. Recently, it has been shown that feeding behaviour and fat mass are altered when the 5-HT(2C) receptor RNA is fully edited, suggesting a potential role for 5-HT(2C) editing in obesity. The present studies investigate the expression of serotonin receptors involved in central regulation of food intake, appetite and energy expenditure, with particular focus on the level of 5-HT(2C) receptor editing. Using a leptin-deficient mouse model of obesity (ob/ob), we show increased hypothalamic 5-HT(1A) receptor expression as well as increased hippocampal 5-HT(1A), 5-HT(1B), and 5-HT(6) receptor mRNA expression in obese mice compared to lean control mice. An increase in full-length 5-HT(2C) expression, depending on time of day, as well as differences in 5-HT(2C) receptor editing were found, independent of changes in total 5-HT(2C) receptor mRNA expression. This suggests that a dynamic regulation exists of the appetite-suppressing effects of the 5-HT(2C) receptor in both the hypothalamus and the hippocampus in the ob/ob mice model of obesity. The differential 5-HT(1A), 5-HT(1B) and 5-HT(6) receptor expression and altered 5-HT(2C) receptor editing profile reported here is poised to have important consequences for the development of novel anti-obesity therapies.

Long term impact of prenatal exposure to SSRIs on growth and body weight in childhood: evidence from animal and human studies

Prenatal exposure to SSRIs has the potential to alter fetal 5-HT signalling during critical periods of development: the long-term consequences of which have not been well studied. Of particular interest are the potential long-term effects of prenatal SSRI exposure on growth and body weight in later life, given the role of the serotonergic system in regulating food intake and body weight. Animal studies demonstrate that changes in 5-HT homeostasis during critical periods of fetal development can lead to sex-specific molecular and functional alterations in the serotonergic and HPA systems, leading to an increased risk of overweight in male, but not female, offspring in later life. This review highlights the evidence and the need for studies in humans to determine whether prenatal SSRI exposure is associated with alterations in child growth and body weight and the importance of delineating these effects from those of the underlying maternal illness.

Reduced serotonin reuptake transporter (SERT) function causes insulin resistance and hepatic steatosis independent of food intake

Serotonin reuptake transporter (SERT) is a key regulator of serotonin neurotransmission and a major target of antidepressants. Antidepressants, such as selectively serotonin reuptake inhibitors (SSRIs), that block SERT function are known to affect food intake and body weight. Here, we provide genetic evidence that food intake and metabolism are regulated by separable mechanisms of SERT function. SERT-deficient mice ate less during both normal diet and high fat diet feeding. The reduced food intake was accompanied with markedly elevated plasma leptin levels. Despite reduced food intake, SERT-deficient mice exhibited glucose intolerance and insulin resistance, and progressively developed obesity and hepatic steatosis. Several lines of evidence indicate that the metabolic deficits of SERT-deficient mice are attributable to reduced insulin-sensitivity in peripheral tissues. First, SERT-deficient mice exhibited beta-cell hyperplasia and islet-mass expansion. Second, biochemical analyses revealed constitutively elevated JNK activity and diminished insulin-induced AKT activation in the liver of SERT-deficient mice. SERT-deficient mice exhibited hyper-JNK activity and hyperinsulinemia prior to the development of obesity. Third, enhancing AKT signaling by PTEN deficiency corrected glucose tolerance in SERT-deficient mice. These findings have potential implications for designing selective SERT drugs for weight control and the treatment of metabolic syndromes.

Functional heterogeneity of arcuate nucleus pro-opiomelanocortin neurons: implications for diverging melanocortin pathways

Arcuate nucleus (ARC) pro-opiomelanocortin (POMC) neurons are essential regulators of food intake, energy expenditure, and glucose homeostasis. POMC neurons integrate several key metabolic signals that include neurotransmitters and hormones. The change in activity of POMC neurons is relayed to melanocortin receptors in distinct regions of the central nervous system. This review will summarize the role of leptin and serotonin receptors in regulating the activity of POMC neurons and provide a model in which different melanocortin pathways regulate energy and glucose homeostasis.

Association of variations in TPH1 and HTR2B with gestational weight gain and measures of obesity

Serotonin is involved in appetite regulation and energy homeostasis. Recently, it has been reported that 5-hydroxytryptamine receptor 2B (Htr2b) and tryptophan hydroxylase 1 (Tph1) play major role in β-cell proliferation in mouse during pregnancy. We investigated the genetic association of HTR2B and TPH1 with risk of gestational diabetes mellitus (GDM) and measures of obesity, in 869 Korean GDM women and carefully selected 632 nondiabetic control subjects. Six single-nucleotide polymorphisms (SNPs) in HTR2B and ten SNPs in TPH1 were selected for genotyping according to their tagging status. Genetic variants in HTR2B and TPH1 were not associated with the risk of GDM. In GDM women, SNPs of TPH1 were significantly associated with weight gain during pregnancy. In nondiabetic controls, SNPs of TPH1 were associated with waist circumference and BMI. We also found that a variant of TPH1 (rs623580) was associated with BMI in a genome-wide association study comprised of 8,842 subjects. Although genetic variants in HTR2B and TPH1 were not associated with risk of GDM, we found significant association of these variants with measures of obesity. However, further replication studies in a different population are required to confirm our findings.

5-HT₂c receptor selectivity and structure-activity relationship of N-methyl-N-(1-methylpiperidin-4-yl)benzenesulfonamide analogs

Agonists of the 5-HT(2C) receptor have attracted much attention as therapeutic agents for the treatment of obesity. Subtype selectivity against other 5-HT(2) receptors is one of the most important prerequisites for reducing side effects. We present the synthesis of N-methyl-N-(1-methylpiperidin-4-yl)benzenesulfonamide analogs and their structure-activity relationship studies on 5-HT(2A) and 5-HT(2C) receptors. Although the compounds showed nanomolar activity to the 5-HT(2C) receptor, their selectivity against the 5-HT(2A) receptor was modest to low. Molecular modeling studies using homology modeling and docking simulation revealed that selectivity originated from subtype specific residues. The observed binding modes and receptor-ligand interactions provided us a clue for optimizing the selectivity against the 5-HT(2A) receptor.

The role of serotonin in axon and dendrite growth

The neurotransmitter serotonin (5-hydroxytryptamine, 5-HT) plays multiple roles in the enteric, peripheral, and central nervous systems (CNS). Although its most prominent biological function is as a signal transmission messenger from pre- to postsynaptic neurons, other roles such as shaping brain development and regulating neurite growth have also been described. Here, we review the less well-studied role of 5-HT as a modulator of neurite growth. 5-HT has been shown to regulate neurite growth in multiple systems and species, including in the mammalian CNS. 5-HT predominantly appears to suppress neurite growth, but depending on the model system and 5-HT receptor subtype, in rare cases, it may promote neurite outgrowth and elongation. Failure of axon regeneration in the adult mammalian CNS is a major problem in multiple diseases, and understanding how 5-HT receptors signal opposing effects on neurite growth may lead to novel neuroregenerative therapies, by targeting either 5-HT receptors or their downstream signaling pathways.

5-HT(2C) agonists as therapeutics for the treatment of schizophrenia

The 5-HT(2C) receptor is a highly complex, highly regulated receptor which is widely distributed throughout the brain. The 5-HT(2C) receptor couples to multiple signal transduction pathways leading to engagement of a number of intracellular signaling molecules. Moreover, there are multiple allelic variants of the 5-HT(2C) receptor and the receptor is subject to RNA editing in the coding regions. The complexity of this receptor is further emphasized by the studies suggesting the utility of either agonists or antagonists in the treatment of schizophrenia. While several 5-HT(2C) agonists have demonstrated clinical efficacy in obesity (lorcaserin, PRX-000933), the focus of this review is on the therapeutic potential of 5-HT(2C) agonists in schizophrenia. To this end, the preclinical profile of 5-HT(2C) agonists from a neurochemical, electrophysiological, and a behavioral perspective is indicative of antipsychotic-like efficacy without extrapyramidal symptoms or weight gain. Recently, the selective 5-HT(2C) agonist vabicaserin demonstrated clinical efficacy in a Phase II trial in schizophrenia patients without weight gain and with low EPS liability. These data are highly encouraging and suggest that 5-HT(2C) agonists are potential therapeutics for the treatment of psychiatric disorders.

5-HT(2C) receptor agonists and the control of appetite

The role of serotonin (5-HT) in appetite control is well recognised. 5-HT drugs reduce food intake in rodents in a manner consistent with an enhancement of satiety. In humans, they have been shown to reduce caloric intake, an effect associated with reduced hunger and increased satiety. These effects appear to be mediated, at least in part, by the 5-HT(2C) receptor subtype. 5-HT-acting drugs such as fenfluramine, d-fenfluramine, and sibutramine have provided effective anti-obesity treatments in the past. However, more selective agents are needed that produce the same changes in eating behaviour and induce weight loss without unacceptable side effects. Lorcaserin, a selective 5-HT(2C) receptor agonist, is a novel anti-obesity agent that reduces both energy intake and body weight. The effects of lorcaserin on eating behaviour remain to be characterised as does its behavioural specificity.

Synergistic roles for G-protein γ3 and γ7 subtypes in seizure susceptibility as revealed in double knock-out mice

The functions of different G-protein αβγ subunit combinations are traditionally ascribed to their various α components. However, the discovery of similarly diverse γ subtypes raises the possibility that they may also contribute to specificity. To test this possibility, we used a gene targeting approach to determine whether the closely related γ(3) and γ(7) subunits can perform functionally interchangeable roles in mice. In contrast to single knock-out mice that show normal survival, Gng3(-/-)Gng7(-/-) double knock-out mice display a progressive seizure disorder that dramatically reduces their median life span to only 75 days. Biochemical analyses reveal that the severe phenotype is not due to redundant roles for the two γ subunits in the same signaling pathway but rather is attributed to their unique actions in different signaling pathways. The results suggest that the γ(3) subunit is a component of a G(i/o) protein that is required for γ-aminobutyric acid, type B, receptor-regulated neuronal excitability, whereas the γ(7) subunit is a component of a G(olf) protein that is responsible for A(2A) adenosine or D(1) dopamine receptor-induced neuro-protective response. The development of this mouse model offers a novel experimental framework for exploring how signaling pathways integrate to produce normal brain function and how their combined dysfunction leads to spontaneous seizures and premature death. The results underscore the critical role of the γ subunit in this process.

Rational Drug Design Leading to the Identification of a Potent 5-HT(2C) Agonist Lacking 5-HT(2B) Activity

The 5-HT(2C) receptor is an attractive drug target in the quest for new therapeutics to treat a variety of human disorders. We have previously undertaken a structural optimization campaign that has led to some potent and moderately selective 5-HT(2C) receptor agonists. After expanding our structure-function library, we were able to combine our datasets so as to allow the design of compounds of improved selectivity and potency. We disclose herein the structural optimization of our previously reported 5-HT(2B)/5-HT(2C) agonists, which has led to the identification of a highly selective 5-HT(2C) agonist, (+)-trans-[2-(2-cyclopropylmethoxyphenyl)cyclopropyl]methylamine hydrochloride, with an EC(50) of 55 nM and no detectable agonism at the 5-HT(2B) receptor.

Atypical antipsychotic-induced weight gain: insights into mechanisms of action

Prescriptions for second-generation antipsychotics (SGAs) have surpassed those for first-generation agents in the treatment of schizophrenia and bipolar disorder. While SGAs have the benefit of a much reduced risk of causing movement disorders, they have been associated with weight gain and metabolic effects. These adverse reactions are not uncommon, and threaten to have a significant impact on the patient's health over the long-term treatment that the patient requires. Currently, the aetiology of these effects is not known. This article reviews the data exploring the weight gain phenomenon. The literature was reviewed from searches of PubMed and the references of major articles in the field. The SGAs present a heterogeneous risk for weight gain. In addition, different individuals receiving the same drug can exhibit substantially different weight changes. This pattern suggests that a group of factors are associated with the weight gain phenomenon rather than a single mechanism. Coupled with the genetic profile that the patient brings to the treatment, the risk for SGA-induced weight gain will be different for different drugs and different individuals. Targets for exploration of the weight gain phenomenon include receptor interactions involving serotonin, histamine, dopamine, adrenergic, cannabinoid and muscarinic receptors. The association of SGA-induced weight gain and the role of orexigenic and anorexigenic peptides are reviewed. Also, a brief discussion of genetic factors associated with SGA-induced weight gain is presented, including that of the serotonin 5-HT(2C) receptor gene (HTR2C) and the cannabinoid 1 receptor gene (CNR1). The most promising data associated with SGA-induced weight gain include investigations of the histamine H(1), 5-HT(2A), 5-HT(2C), muscarinic M(3) and adrenergic receptors. In addition, work in the genetic area promises to result in a better understanding of the variation in risk associated with different individuals.

Central nervous control of energy and glucose balance: focus on the central melanocortin system

Studies have suggested that manipulations of the central melanocortin circuitry by pharmacological agents produce robust effects on the regulation of body weight and glucose homeostasis. In this review, we discuss recent findings from genetic mouse models that have further established the physiological relevance of this circuitry in the context of glucose and energy balance. In addition, we will discuss distinct neuronal populations that respond to central melanocortins to regulate food intake, energy expenditure, insulin sensitivity, and insulin secretion, respectively. Finally, multiple hormonal and neural cues (e.g., leptin, estrogen, and serotonin) that use the melanocortin systems to regulate energy and glucose homeostasis will be reviewed. These findings suggest that targeting the specific branches of melanocortin circuits may be potential avenues to combat the current obesity and diabetes epidemics.

Hypothalamic Ahi1 mediates feeding behavior through interaction with 5-HT2C receptor

It is indicated that there are important molecules interacting with brain nervous systems to regulate feeding and energy balance by influencing the signaling pathways of these systems, but relatively few of the critical players have been identified. In the present study, we provide the evidence for the role of Abelson helper integration site 1 (Ahi1) protein as a mediator of feeding behavior through interaction with serotonin receptor 2C (5-HT(2C)R), known for its critical role in feeding and appetite control. First, we demonstrated the co-localization and interaction between hypothalamic Ahi1 and 5-HT(2C)R. Ahi1 promoted the degradation of 5-HT(2C)R through the lysosomal pathway. Then, we investigated the effects of fasting on the expression of hypothalamic Ahi1 and 5-HT(2C)R. Fasting resulted in an increased Ahi1 expression and a concomitant decreased expression of 5-HT(2C)R. Knockdown of hypothalamic Ahi1 led to a concomitant increased expression of 5-HT(2C)R and a decrease of food intake and body weight. Last, we found that Ahi1 could regulate the expression of neuropeptide Y and proopiomelanocortin. Taken together, our results indicate that Ahi1 mediates feeding behavior by interacting with 5-HT(2C)R to modulate the serotonin signaling pathway.

Pharmacogenetics of leptin in antipsychotic-associated weight gain and obesity-related complications

Second-generation antipsychotics can greatly improve symptoms of psychosis-spectrum disorders. Unfortunately, these drugs are associated with weight gain, which increases a patient's risk for developing chronic diseases including Type 2 diabetes, cardiovascular diseases or other obesity-related complications. There are interindividual differences in weight gain resulting from antipsychotic drug use that may be explained by pharmacodynamic characteristics of these agents as well as clinical factors. In addition, genetic variations in pathways associated with satiety are increasingly recognized as potential contributors to antipsychotic-associated weight gain. Polymorphisms in the leptin gene, as well as the leptin receptor gene, are potential pharmacogenetic markers associated with these outcomes. This article summarizes evidence for the associations of the leptin gene and the leptin receptor gene polymorphisms with antipsychotic-induced weight gain, potential mechanisms underlying these relationships, and discusses areas for future pharmacogenetic investigation.

The G protein coupled receptor Gpr153 shares common evolutionary origin with Gpr162 and is highly expressed in central regions including the thalamus, cerebellum and the arcuate nucleus

The Rhodopsin family of G protein coupled receptors (GPCRs) includes the phylogenetic α-group consisting of about 100 human members. The α-group is the only group of GPCRs that has many receptors for biogenic amines which are major drug targets. Several members of this group are orphan receptors and their functions are elusive. In this study we present a detailed phylogenetic and anatomical characterization of the Gpr153 receptor and also attempt to study its functional role. We identified the homologue of Gpr153 in the elephant shark genome and phylogenetic and synteny analyses revealed that Gpr162 and Gpr153 share a common ancestor that split most likely through a duplication event before the divergence of the tetrapods and the teleost lineage. A quantitative real-time PCR study reveals widespread expression of Gpr153 in the central nervous system and all the peripheral tissues investigated. Detailed in situ hybridization on mouse brain showed specifically high expression in the thalamus, cerebellum and the arcuate nucleus. The antisense oligodeoxynucleotide knockdown of Gpr153 caused a slight reduction in food intake and the elevated plus maze test showed significant reduction in the percentage of time spent in the centre square, which points towards a probable role in decision making. This report provides the first detailed characterization of the evolution, expression and primary functional properties of the Gpr153 gene.

Serotonin 2C receptor activates a distinct population of arcuate pro-opiomelanocortin neurons via TRPC channels

VIDEO ABSTRACT

Serotonin 2C receptors (5-HT(2C)Rs) expressed by pro-opiomelanocortin (POMC) neurons of hypothalamic arcuate nucleus regulate food intake, energy homeostasis and glucose metabolism. However, the cellular mechanisms underlying the effects of 5-HT to regulate POMC neuronal activity via 5-HT(2C)Rs have not yet been identified. In the present study, we found the putative transient receptor potential C (TRPC) channels mediate the activation of a subpopulation of POMC neurons by mCPP (a 5-HT(2C)R agonist). Interestingly, mCPP-activated POMC neurons were found to be a distinct population from those activated by leptin. Together, our data suggest that 5-HT(2C)R and leptin receptors are expressed by distinct subpopulations of arcuate POMC neurons and that both 5-HT and leptin exert their actions in POMC neurons via TRPC channels.

Drug discovery targeting human 5-HT(2C) receptors: residues S3.36 and Y7.43 impact ligand-binding pocket structure via hydrogen bond formation

Specific activation of serotonin (5-HT) 5-HT(2C) G protein-coupled receptors may be therapeutic for obesity and neuropsychiatric disorders. Mutagenesis coupled with computational and molecular modeling experiments based on the human β₂ adrenergic receptor structure was employed to delineate the interactions of different ligands at human 5-HT(2C) residues D3.32, S3.36 and Y7.43. No binding of the tertiary amine radioligand ([³H]-mesulergine) could be detected when the 5-HT(2C) D3.32 residue was mutated to alanine (D3.32A). The S3.36A point-mutation greatly reduced affinity of primary amine ligands, modestly reduced affinity of a secondary amine, and except for the 5-HT(2C)-specific agonist N(CH₃)₂-PAT, affinity of tertiary amines was unaffected. Molecular modeling results indicated that the primary amines form hydrogen bonds with the S3.36 residue, whereas, with the exception of N(CH₃)₂-PAT, tertiary amines do not interact considerably with this residue. The Y7.43A point-mutation greatly reduced affinity of 5-HT, yet reduced to a lesser extent the affinity of tryptamine that lacks the 5-hydroxy moiety present in 5-HT; modeling results indicated that the 5-HT 5-hydroxy moiety hydrogen bonds with Y7.43 at the 5-HT(2C) receptor. Additional modeling results showed that 5-HT induced a hydrogen bond between Y7.43 and D3.32. Finally, modeling results revealed two low-energy binding modes for 5-HT in the 5-HT(2C) binding pocket, supporting the concept that multiple agonist binding modes may stabilize different receptor active conformations to influence signaling. Ligand potencies for modulating WT and point-mutated 5-HT(2C) receptor-mediated phospholipase C activity were in accordance with the affinity data. Ligand efficacies, however, were altered considerably by the S3.36A mutation only.

Neuronal activity regulates hippocampal miRNA expression

Neuronal activity regulates a broad range of processes in the hippocampus, including the precise regulation of translation. Disruptions in proper translational control in the nervous system are associated with a variety of disorders that fall in the autistic spectrum. MicroRNA (miRNA) represent a relatively recently discovered player in the regulation of translation in the nervous system. We have conducted an in depth analysis of how neuronal activity regulates miRNA expression in the hippocampus. Using deep sequencing we exhaustively identify all miRNAs, including 15 novel miRNAs, expressed in hippocampus of the adult mouse. We identified 119 miRNAs documented in miRBase but less than half of these miRNA were expressed at a level greater than 0.1% of total miRNA. Expression profiling following induction of neuronal activity by electroconvulsive shock demonstrates that most miRNA show a biphasic pattern of expression: rapid induction of specific mature miRNA expression followed by a decline in expression. These results have important implications into how miRNAs influence activity-dependent translational control.

Serotonin and molecular neuroimaging in humans using PET

The serotonergic system is one of the most important modulatory neurotransmitter systems in the human brain. It plays a central role in major physiological processes and is implicated in a number of psychiatric disorders. Along with the dopaminergic system, it is also one of the phylogenetically oldest human neurotransmitter systems and one of the most diverse, with 14 different receptors identified up to this day, many of whose function remains to be understood. The system's functioning is even more diverse than the number of its receptors, since each is implicated in a number of different processes. This review aims at illustrating the distribution and summarizing the main functions of the serotonin (5-hydroxytryptamin, 5-HT) receptors as well as the serotonin transporter (SERT, 5-HTT), the vesicular monoamine transporter 2, monoamine oxidase type A and 5-HT synthesis in the human brain. Recent advances in in vivo quantification of these different receptors and enzymes that are part of the serotonergic system using positron emission tomography are described.

Does endoplasmic reticulum stress participate in APD-induced hepatic metabolic dysregulation?

Metabolic side effects caused by certain antipsychotic drugs (APDs), in particular clozapine and olanzapine, are now clinically well-documented. However, the potential mechanisms implicated in the metabolic disturbances of these drugs on peripheral tissues remain obscure. Here, we investigated the effects of five frequently prescribed APDs on the Sterol Regulatory Element Binding Protein (SREBP) transcription factor pathways which control lipogenesis and cholesterogenesis, using the Immortalized Human Hepatocyte cell model (IHH). First, clozapine, haloperidol, olanzapine and risperidone activated, at different levels, SREBP-1 activity reflected by an increased expression of SREBP-1 target genes involved in fatty acid biosynthesis (SREBP-1, FAS and/or SCD1) resulting in an accumulation of intracellular lipids. Second, clozapine and haloperidol also stimulated the SREBP-2 pathway associated with an increase in HMGCoAR expression. In contrast, quetiapine did not affect either the SREBP-1 or -2 pathways, but induced a slight accumulation of intracellular lipids. Interestingly, clozapine, haloperidol and olanzapine induced Endoplasmic Reticulum (ER) stress and, more precisely, initiation of the ER stress-activated eIF2α kinase (PERK) branch of the Unfolded Protein Response (UPR). Furthermore, treatment with thapsigargin, which increases intracellular calcium release, induced both ER stress and SREBP-1 and -2 pathway activation, whereas Ca(2+) chelation by BAPTA completely reversed the lipogenic effects and ER stress induction produced by clozapine. Based on these results, we propose that certain APDs induce ER stress via changes in Ca(2+) homeostasis in hepatocytes. This phenomenon potentially underlies a part of their known undesirable hepatic metabolic side effects. This article is part of a Special Issue entitled 'Post-Traumatic Stress Disorder'.

Quantitative analysis of 5HT(2C) receptor RNA editing patterns in psychiatric disorders

Initially identified as an RNA modification in the anticodon loop of tRNAs from animal, plant and eubacterial origin, the deamination of adenosine-to-inosine by RNA editing has become increasingly recognized as an important RNA processing event to generate diversity in both the transcriptome and proteome and is essential for modulating the activity of numerous proteins critical for nervous system function. Here, we focus on the editing of transcripts encoding the 2C-subtype of serotonin receptor (5HT(2C)) to generate multiple receptor isoforms that differ in G-protein coupling efficacy and constitutive activity. 5HT(2C) receptors have been implicated in the regulation of anxiety, components of the stress response, and are thought to play a role in compulsive behavioral disorders, depression and drug addiction. A number of studies have been conducted to assess whether 5HT(2C) editing is altered in individuals suffering from psychiatric disorders, yet the results from these studies have been inconsistent, and thus inconclusive. This review provides a discussion of the challenges involved with characterizing 5HT(2C) editing patterns in human postmortem tissue samples and how differences in quantitative methodology have contributed to the observed inconsistencies between multiple laboratories. Additionally, we discuss new high-throughput sequencing tools, which provide an opportunity to overcome previous methodological challenges, and permit reliable systematic analyses of RNA editing in control and pathologic disease states.

Estradiol increases the anorexia associated with increased 5-HT(2C) receptor activation in ovariectomized rats

Estradiol's inhibitory effect on food intake is mediated, in part, by its ability to increase the activity of meal-related signals, including serotonin (5-HT), which hastens satiation. The important role that postsynaptic 5-HT(2C) receptors play in mediating 5-HT's anorexigenic effect prompted us to investigate whether a regimen of acute estradiol treatment increases the anorexia associated with increased 5-HT(2C) receptor activation in ovariectomized (OVX) rats. We demonstrated that intraperitoneal and intracerebroventricular (i.c.v.) administration of low doses of the 5-HT(2C) receptor agonist meta-chlorophenylpiperazine (mCPP) decreased 1-h dark-phase food intake in estradiol-treated, but not oil-treated, OVX rats. During a longer feeding test, we demonstrated that i.c.v. administration of mCPP decreased 22-h food intake in oil-treated and, to a greater extent, estradiol-treated OVX rats. In a second study, we demonstrated that estradiol increased 5-HT(2C) receptor protein content in the caudal brainstem, but not hypothalamus, of OVX rats. We conclude that a physiologically-relevant regimen of acute estradiol treatment increases sensitivity to mCPP's anorexigenic effect. Our demonstration that this same regimen of estradiol treatment increases 5-HT(2C) receptor protein content in the caudal hindbrain of OVX rats provides a possible mechanism to explain our behavioral findings.

The serotonergic system in Parkinson's disease

Although the cardinal manifestations of Parkinson's disease (PD) are attributed to a decline in dopamine levels in the striatum, a breadth of non-motor features and treatment-related complications in which the serotonergic system plays a pivotal role are increasingly recognised. Serotonin (5-HT)-mediated neurotransmission is altered in PD and the roles of the different 5-HT receptor subtypes in disease manifestations have been investigated. The aims of this article are to summarise and discuss all published preclinical and clinical studies that have investigated the serotonergic system in PD and related animal models, in order to recapitulate the state of the current knowledge and to identify areas that need further research and understanding.

Role of 5-HT(2C) receptor gene variants in antipsychotic-induced weight gain

Antipsychotic-induced weight gain is a serious side effect of antipsychotic medication that can lead to increased morbidity, mortality, and non-compliance in patients. Numerous single nucleotide polymorphisms have been studied for association with antipsychotic-induced weight gain in an attempt to find genetic predictors of this side effect. An ability to predict this side effect could lead to personalized treatment plans for predisposed individuals, which could significantly decrease the prevalence and severity of weight gain. Variations in the serotonin receptor 2c gene (HTR2C) have emerged as promising candidates for prediction of antipsychotic-induced weight gain. Specifically, the well-studied −759C/T promoter polymorphism has been associated with weight gain in diverse populations, although some studies have reported no association. This discrepancy is likely due to heterogeneity in study design with respect to ethnicity, treatment duration, and other variables. Notably, the association between HTR2C and antipsychotic-induced weight gain appears strongest in short-term studies on patients with limited or no previous antipsychotic treatment. Other, less extensively studied promoter polymorphisms (−697C/G, −997G/A, and −1165A/G) have also emerged as potential predictors of antipsychotic-induced weight gain. Conversely, the well-studied intronic polymorphism Cys23Ser does not appear to be associated. With further research on both HTR2C and other genetic and environmental predictors of antipsychotic-induced weight gain, a predictive test could one day be created to screen patients and provide preventative or alternative treatment for those who are predisposed to this serious side effect.

Cell signaling underlying epileptic behavior

Epilepsy is a complex disease, characterized by the repeated occurrence of bursts of electrical activity (seizures) in specific brain areas. The behavioral outcome of seizure events strongly depends on the brain regions that are affected by overactivity. Here we review the intracellular signaling pathways involved in the generation of seizures in epileptogenic areas. Pathways activated by modulatory neurotransmitters (dopamine, norepinephrine, and serotonin), involving the activation of extracellular-regulated kinases and the induction of immediate early genes (IEGs) will be first discussed in relation to the occurrence of acute seizure events. Activation of IEGs has been proposed to lead to long-term molecular and behavioral responses induced by acute seizures. We also review deleterious consequences of seizure activity, focusing on the contribution of apoptosis-associated signaling pathways to the progression of the disease. A deep understanding of signaling pathways involved in both acute- and long-term responses to seizures continues to be crucial to unravel the origins of epileptic behaviors and ultimately identify novel therapeutic targets for the cure of epilepsy.

Pharmacogenetic testing to predict antipsychotic-induced weight gain: a systematic review

Weight gain is an important side effect of antipsychotic drugs. Since the high interindividual difference in weight gain suggests that genetic factors play a role in this weight gain, studies have tried to identify these factors. Most of these studies were carried out in the past few years and focussed largely on receptor polymorphisms, although some tried to explain the variation in weight gain by differences in pharmacokinetics. Unfortunately, the results of these association studies are often conflicting, which makes it hard to apply this genetic knowledge in daily clinical practice. This article summarizes the findings of these association studies and focuses on differences in study methodology in an attempt to explain why study results could have been conflicting. Furthermore, the feasibility of genetic testing in today’s clinical practice is discussed, using a model that consists of four components; analytical validity, clinical validity, clinical utility and ethical, legal and social issues.

The contribution of serotonin 5-HT2C and melanocortin-4 receptors to the satiety signaling of glucagon-like peptide 1 and liraglutide, a glucagon-like peptide 1 receptor agonist, in mice

Glucagon-like peptide 1 (GLP-1), an insulinotropic gastrointestinal peptide produced mainly from intestinal endocrine L-cells, and liraglutide, a GLP-1 receptor (GLP-1R) agonist, induce satiety. The serotonin 5-HT2C receptor (5-HT2CR) and melanoroctin-4 receptor (MC4R) are involved in the regulation of food intake. Here we show that systemic administration of GLP-1 (50 and 200μg/kg)-induced anorexia was blunted in mice with a 5HT2CR null mutation, and was attenuated in mice with a heterozygous MC4R mutation. On the other hand, systemic administration of liraglutide (50 and 100μg/kg) suppressed food intake in mice lacking 5-HT2CR, mice with a heterozygous mutation of MC4R and wild-type mice matched for age. Moreover, once-daily consecutive intraperitoneal administration of liraglutide (100μg/kg) over 3days significantly suppressed daily food intake and body weight in mice with a heterozygous mutation of MC4R as well as wild-type mice. These findings suggest that GLP-1 and liraglutide induce anorexia via different central pathways.

Lorcaserin for the treatment of obesity

Obesity is a worldwide epidemic and there is an urgent need for the development of effective pharmacological therapies that target the metabolic and behavioral factors of body weight regulation. Serotonin (5-HT) has been implicated as a critical factor in the short-term (meal-by-meal) regulation of food intake and pharmaceutical companies have invested millions of dollars to discover and develop drug targets for the serotonergic pathway. Lorcaserin is a novel selective agonist of the 5-HT(2C) receptor for weight loss therapy. Preclinical and clinical studies indicate lorcaserin is well tolerated and not associated with cardiac valvulopathy or pulmonary hypertension suggesting that lorcaserin is a selective 5-HT(2C) receptor agonist and has little or no activation of the 5-HT(2B) and 5-HT(2A) receptors, respectively. Lorcaserin acts to alter energy balance through a reduction in energy intake and without an increase in energy expenditure and achieved the U.S. Food and Drug Administration guidelines for weight loss efficacy. It remains to be determined whether or not lorcaserin will be approved for the long-term management of obesity.

Adipocytes express a functional system for serotonin synthesis, reuptake and receptor activation

AIMS

Serotonergic pathways in the central nervous system (CNS) are activated in the regulation of food intake and body weight. We hypothesized that adipocytes, like other cells of mesenchymal origin, possess serotonin receptors and thus could be regulated by peripherally circulating serotonin.

METHODS

In vivo studies: four Sprague-Dawley rats were given daily serotonin (5HT) injections subcutaneously (s.c., 25 mg/kg) for 5 days; four controls received saline. In a long-term study, 12 rats were given serotonin s.c. for 4 months, 10 controls received saline. Body weight was registered throughout the studies, and visceral adipose tissue and plasma were collected and analysed. Adipocytes were isolated from normal rat visceral abdominal adipose tissue and analysed for the expression of serotonin receptors, the serotonin transporter (5HTT/SERT), activation of serotonin synthesis (tryptophan hydroxylase 1, Tph1) and secretion and serotonin-induced leptin regulation by RT-PCR and protein analyses.

RESULTS

Hyperserotoninergic rats had significantly lower body weight (-7.4 and -6.8%) and plasma leptin levels (-44 and -38%) than controls, after both short- and long-term serotonin treatment, respectively, whereas plasma ghrelin levels were unaffected. Compared to controls, serotonin induced a 40-fold upregulation of 5HTT mRNA in visceral adipose tissue after 5 days of treatment. In vitro experiments showed that adipocytes express serotonin receptors, Tph1 and 5HTT, synthesize and secrete serotonin and that serotonin regulates leptin in mature adipocytes.

CONCLUSIONS

These findings show that serotonin may regulate adipocyte function in a direct manner via the blood circulation and/or paracrine and autocrine mechanisms, and not only indirectly via the CNS as previously assumed.

Role of the evolutionarily conserved starvation response in anorexia nervosa

This review will summarize recent findings concerning the biological regulation of starvation as it relates to anorexia nervosa (AN), a serious eating disorder that mainly affects female adolescents and young adults. AN is generally viewed as a psychosomatic disorder mediated by obsessive concerns about weight, perfectionism and an overwhelming desire to be thin. By contrast, the thesis that will be developed here is that, AN is primarily a metabolic disorder caused by defective regulation of the starvation response, which leads to ambivalence towards food, decreased food consumption and characteristic psychopathology. We will trace the starvation response from yeast to man and describe the central role of insulin (and insulin-like growth factor-1 (IGF-1))/Akt/ F-box transcription factor (FOXO) signaling in this response. Akt is a serine/threonine kinase downstream of the insulin and IGF-1 receptors, whereas FOXO refers to the subfamily of Forkhead box O transcription factors, which are regulated by Akt. We will also discuss how initial bouts of caloric restriction may alter the production of neurotransmitters that regulate appetite and food-seeking behavior and thus, set in motion a vicious cycle. Finally, an integrated approach to treatment will be outlined that addresses the biological aspects of AN.

Role of peripheral serotonin in glucose and lipid metabolism

PURPOSE OF REVIEW

Two independent serotonin systems exist, one in the brain and the other in the periphery. Serotonin is a well known monoaminergic neurotransmitter in the central nervous system and it is known to regulate feeding behavior, meal size, and body weight. On the other hand, there is much less evidence for the role of serotonin as a gastrointestinal hormone, particularly with respect to its effects on glucose and lipid metabolism. This review summarizes our current understanding of the role of peripheral serotonin on glucose and lipid metabolism and the implications of this for further research.

RECENT FINDINGS

The enterochromaffin cells of the gastrointestinal tract produce peripheral serotonin postprandially. In mice, it induces a decrease in the concentration of circulating lipids as well as hyperglycemia and hyperinsulinemia through its action on several serotonin receptors. Further, serotonin metabolites act as endogenous agonists for peroxisome proliferator-activated receptor γ and serotonin accelerates adipocyte differentiation via serotonin receptor 2A and 2C. Studies of serotonin are likely to provide new insights into the field of lipid accumulation and metabolism.

SUMMARY

Recent studies show new physiological functions of peripheral serotonin, linked to glucose and lipid metabolism. Peripheral serotonin may serve as an attractive new therapeutic target for the treatment of metabolic disorders in the near future.

Selective serotonin 5-HT(2C) receptor activation suppresses the reinforcing efficacy of cocaine and sucrose but differentially affects the incentive-salience value of cocaine- vs. sucrose-associated cues

Serotonin (5-HT) controls affective and motivational aspects of palatable food and drug reward and the 5-HT(2C) receptor (5-HT(2C)R) has emerged as a key regulator in this regard. We have evaluated the efficacy of a selective 5-HT(2C)R agonist, WAY 163909, in cocaine and sucrose self-administration and reinstatement assays employing parallel experimental designs in free-fed rats. WAY 163909 dose-dependently reduced the reinforcing efficacy of cocaine (ID(50) = 1.19 mg/kg) and sucrose (ID(50) = 0.7 mg/kg) as well as reinstatement (ID(50) = 0.5 mg/kg) elicited by exposure to cocaine-associated contextual cues, but not sucrose-associated contextual cues. The ID(50) of WAY 163909 predicted to decrease the reinforcing efficacy of cocaine or sucrose as well as reinstatement upon exposure to cocaine-associated cues was ∼5-12-fold lower than that predicted to suppress horizontal ambulation (ID(50) = 5.89 mg/kg) and ∼2-5-fold lower than that predicted to suppress vertical activity (ID(50) = 2.3 mg/kg). Thus, selective stimulation of the 5-HT(2C)R decreases the reinforcing efficacy of cocaine and sucrose in freely-fed rats, but differentially alters the incentive-salience value of cocaine- vs. sucrose-associated cues at doses that do not impair locomotor activity. Future research is needed to tease apart the precise contribution of 5-HT(2C)R neurocircuitry in reward and motivation and the learning and memory processes that carry the encoding for associations between environmental cues and consumption of rewarding stimuli. A more complete preclinical evaluation of these questions will ultimately allow educated proof-of-concept trials to test the efficacy of selective 5-HT(2C)R agonists as adjunctive therapy in chronic health maladies including obesity, eating disorders and drug addiction.

Annual Research Review: Transgenic mouse models of childhood-onset psychiatric disorders

Childhood-onset psychiatric disorders, such as attention deficit hyperactivity disorder (ADHD), autism spectrum disorder (ASD), mood disorders, obsessive compulsive spectrum disorders (OCSD), and schizophrenia (SZ), affect many school-age children, leading to a lower quality of life, including difficulties in school and personal relationships that persist into adulthood. Currently, the causes of these psychiatric disorders are poorly understood, resulting in difficulty diagnosing affected children, and insufficient treatment options. Family and twin studies implicate a genetic contribution for ADHD, ASD, mood disorders, OCSD, and SZ. Identification of candidate genes and chromosomal regions associated with a particular disorder provide targets for directed research, and understanding how these genes influence the disease state will provide valuable insights for improving the diagnosis and treatment of children with psychiatric disorders. Transgenic mouse models are one important approach in the study of human diseases, allowing for the use of a variety of experimental approaches to dissect the contribution of a specific chromosomal or genetic abnormality in human disorders. While it is impossible to model an entire psychiatric disorder in a single mouse model, these models can be extremely valuable in dissecting out the specific role of a gene, pathway, neuron subtype, or brain region in a particular abnormal behavior. In this review we discuss existing transgenic mouse models for childhood-onset psychiatric disorders. We compare the strength and weakness of various transgenic mouse models proposed for each of the common childhood-onset psychiatric disorders, and discuss future directions for the study of these disorders using cutting-edge genetic tools.

Functional consequences of two HTR2C polymorphisms associated with antipsychotic-induced weight gain

BACKGROUND

Genetic variation in the promoter region of HTR2C encoding for the 5-HT(2C) receptor is associated with antipsychotic-induced weight gain. Several studies have investigated the regulatory potential of associated variants using gene-reporter systems. Establishing associated polymorphisms as causal variants may aid in the identification of the molecular mechanisms of phenotypic variation.

AIMS & METHODS

To this end we examined the binding of nuclear factors from rat hypothalamus to two polymorphisms in HTR2C, rs3813929 (-759C/T) and rs518147 (-697C/G) using electromobility shift assays. For rs518147, allele-specific RNA folding was also investigated.

RESULTS

Both polymorphisms bound nuclear factors, identifying the sequence fragments as regulatory elements. Importantly, rs3813929 (-759C/T) altered DNA-protein interactions with the weight gain-resistant allele abolishing the formation of two complexes. The formation of allele-specific RNA loops was also observed for rs518147.

CONCLUSION

These data establish rs3813929 (-759C/T) as a functional polymorphism and suggest disruption of DNA-protein interactions as a mechanism by which HTR2C expression is perturbed leading to an influence on antipsychotic-induced weight gain.

Polymorphisms of the HTR2C gene and antipsychotic-induced weight gain: an update and meta-analysis

AIMS

This study aims to test for possible associations between the gene coding for the 5-HT2C receptor and antipsychotic-induced weight gain.

MATERIALS & METHODS

Four HTR2C polymorphisms (rs498207, C-759T, G-697C and Ser23Cys) were investigated in our sample of 205 chronic schizophrenia patients.

RESULTS

Significant over-representation of the C-G-Cys23 haplotype in patients with weight gain (OR: 1.93; 95% CI: 1.04-3.56; p = 0.0015) was found. Similarly, haplotype analyses of percentage weight change were also significant (p = 0.029) for the C-G-Cys23 haplotype associated with the highest average percent weight gain. Observations in the polymorphisms are consistent with previous studies. An updated meta-analysis of nine previous studies plus our current sample suggest that the -759C allele is associated with antipsychotic-induced weight gain.

CONCLUSION

Additional studies, including the resequencing of the region surrounding the HTR2C promoter, and functional studies of the promoter polymorphisms, may elucidate the mechanism underlying this genetic association.

Asenapine: a review of its use in the management of mania in adults with bipolar I disorder

Asenapine is an atypical antipsychotic agent available in sublingual formulations (5 or 10 mg) and indicated in the US (Saphris) for the acute treatment, as monotherapy or adjunctive therapy, of manic and mixed episodes and in the EU (Sycrest) for the treatment of moderate to severe manic episodes, in adult patients with bipolar I disorder. In two large (both n = 480), well designed, 3-week trials in adult patients with bipolar I disorder, asenapine monotherapy was significantly more effective than placebo at improving mania symptoms, as assessed using the Young Mania Rating Scale total score (YMRS; primary endpoint), with significant differences between the asenapine and placebo groups occurring after 2 days of treatment. In both trials, Clinical Global Impression for Bipolar Disorder (CGI-BP) scale mania severity scores exceeded those of placebo. In one trial, response and remission rates exceeded those of placebo. In a 9-week extension study that recruited completers from the monotherapy trials, there were no significant differences between asenapine and olanzapine groups in terms in Montgomery-Åsberg Depression Rating Scale (MADRS) scores, CGI-BP mania severity scores, YMRS response rates or YMRS remission rates during the extension phase. In the extension study, the efficacy of asenapine monotherapy appeared to be maintained over 40 weeks (total treatment duration of 52 weeks). In a 12-week trial of asenapine as adjunctive therapy to lithium or valproate, asenapine was more effective than placebo in improving manic symptoms, based on the difference between groups in the YMRS total score at week 3 (primary endpoint). Most adverse events associated with asenapine were of mild to moderate severity, with <7% of asenapine recipients experiencing serious adverse events (vs 7% with placebo). In a pooled analysis of the monotherapy trials, the most common adverse events (occurring in ≥ 5% of patients and at twice the incidence of placebo) reported during acute phase asenapine monotherapy for bipolar mania were somnolence, dizziness, extrapyramidal symptoms (EPS, other than akathisia) and increased bodyweight, which were similar in nature to those occurring during longer-term monotherapy with asenapine. EPS did not worsen in severity during longer-term asenapine monotherapy. Asenapine had minimal effects on plasma glucose, lipid and prolactin levels over both short- and longer-term treatment periods, and had little pro-arrhythmogenic potential. Further active comparator trials and longer-term tolerability and safety data are required. In the meantime, asenapine is a further option for the management of manic and/or mixed symptoms in patients with bipolar I disorder and may be of particular value for patients who are at high risk for metabolic abnormalities.

Lorcaserin, a 5-HT(2C) receptor agonist, reduces body weight by decreasing energy intake without influencing energy expenditure

CONTEXT

Lorcaserin, a selective 5-hydroxytryptamine (5-HT)(2C) receptor agonist, reduces body weight. It is unclear whether weight loss is due to reduced energy intake (EI) or also to enhanced energy expenditure (EE).

OBJECTIVE

This study tested the effect of lorcaserin on EI and EE.

DESIGN, PARTICIPANTS, AND INTERVENTION

In a double-blind, randomized, placebo-controlled trial, 57 (39 women) overweight and obese (body mass index, 27-45 kg/m(2)) adults were randomized to placebo (n = 28) or 10 mg twice daily lorcaserin (n = 29) for 56 d. Weight maintenance was imposed during d 1-7. Beginning on d 8, participants followed a diet and exercise plan targeting a 600 kcal/d deficit.

OUTCOMES

At baseline and after 7 and 56 d of treatment, we measured body weight, body composition (dual x-ray absorptiometry), blood pressure, heart rate, EI at lunch and dinner, subjective appetite ratings, and 24-h EE and 24-h-respiratory quotient (RQ), measured by indirect calorimetry in a respiratory chamber.

RESULTS

After 7 d of weight maintenance, EI was significantly (P < 0.01) reduced with lorcaserin but not placebo (mean ± sem for lorcaserin, -286 ± 86 kcal; placebo, -147 ± 89 kcal). After 56 d, lorcaserin resulted in significantly larger reductions in body weight (lorcaserin, -3.8 ± 0.4 kg; placebo, -2.2 ± 0.5 kg; P < 0.01), EI (lorcaserin, -470 ± 87 kcal; placebo, -205 ± 91 kcal; P < .05), and appetite ratings than in placebo. Changes in 24-h EE and 24-h RQ did not differ between groups, even after 24-h EE was adjusted for body weight and composition. Compared with placebo, lorcaserin had no effect on systolic or diastolic blood pressure or heart rate after 56 d.

CONCLUSIONS

Lorcaserin reduces body weight through reduced EI, not altered EE or RQ.

Modulatory role of serotonin on feeding behavior

The appearance, the odor, and the flavor of foods, all send messages to the encephalic area of the brain. The hypothalamus, in particular, plays a key role in the mechanisms that control the feeding behavior. These signals modulate the expression and the action of anorexigenic or orexigenic substances that influence feeding behavior. The serotonergic system of neurotransmission consists of neurons that produce and liberate serotonin as well as the serotonin-specific receptor. It has been proven that some serotonergic drugs are effective in modulating the mechanisms of control of feeding behavior. Obesity and its associated illnesses have become significant public health problems. Some drugs that manipulate the serotonergic systems have been demonstrated to be effective interventions in the treatment of obesity. The complex interplay between serotonin and its receptors, and the resultant effects on feeding behavior have become of great interest in the scientific community.

The use of serotonergic drugs to treat obesity--is there any hope?

Surgical interventional strategies for the treatment of obesity are being implemented at an increasing rate. The safety and feasibility of these procedures are questionable for most overweight or obese individuals. The use of long-term pharmacotherapy options, on the other hand, can target a greater portion of the obese population and provide early intervention to help individuals maintain a healthy lifestyle to promote weight loss. Medications that act on the central serotonergic pathways have been a relative mainstay for the treatment of obesity for the last 35 years. The clinical efficacy of these drugs, however, has been encumbered by the potential for drug-associated complications. Two drugs that act, albeit by different mechanisms, on the central serotonergic system to reduce food intake and decrease body weight are sibutramine and lorcaserin. Sibutramine is a serotonin and norepinephrine reuptake inhibitor, whereas lorcaserin is a selective 5HT_2C receptor agonist. The recent worldwide withdrawal of sibutramine and FDA rejection of lorcaserin has changed the landscape not only for serotonin-based therapeutics specifically, but for obesity pharmacotherapy in general. The purpose of this review is to focus on the importance of the serotonergic system in the control of feeding and its potential as a target for obesity pharmacotherapy. Advances in refining and screening more selective receptor agonists and a better understanding of the potential off-target effects of serotonergic drugs are needed to produce beneficial pharmacotherapy.

Association between HTR2C polymorphisms and metabolic syndrome in patients with schizophrenia treated with atypical antipsychotics

BACKGROUND

Previous research indicates that common single-nucleotide polymorphisms (SNPs) in the serotonin 5-HT2C receptor gene (HTR2C) are associated with metabolic syndrome (MetS) related to antipsychotic treatment. This study analyzes a large sample of patients with schizophrenia treated with atypical antipsychotics to determine whether variation in the HTR2C is associated with MetS.

METHODS

Six tag SNPs, capturing all common genetic variations in the HTR2C gene in the Han population, were genotyped in 456 Chinese schizophrenic inpatients treated with atypical antipsychotics (clozapine: 171, olanzapine: 91, and risperidone: 194).

RESULTS

Single-marker based analysis shows that of the six HTR2C SNPs, the rs498177 SNP showed a significant association with MetS in female patients, and the C allele was associated with an increased risk of MetS (for genotype TT/TC/CC: MetS vs. non-MetS=50%/27%/23% vs. 69%/28%/3%, and for allele T/C: MetS vs. non-MetS=63%/37% vs. 83%/17%, p=0.0007). Haplotype analysis shows that the A-C type of rs521018-rs498177 in the HTR2C gene significantly decreased the risk of MetS (corrected p=0.0108) in female patients.

CONCLUSIONS

The results of this study support the role of HTR2C genetic variants in susceptibility to MetS in patients treated with atypical antipsychotics. However, this association is gender-dependent.

Control of hippocampal theta rhythm by serotonin: role of 5-HT2c receptors

The hippocampus plays an important role in learning and memory and has been implicated in a number of diseases, including epilepsy, anxiety and schizophrenia. A prominent feature of the hippocampal network is the capability to generate rhythmic oscillations. Serotonergic modulation is known to play an important role in the regulation of theta rhythm. 5-HT2c receptors represent a specific target of psychopharmacology and, in particular, the behavioral effects of the 5-HT2c receptor agonist mCPP have been thoroughly tested. The present study used this compound and the selective 5-HT2c receptor antagonist SB-242084 to elucidate the role of 5-HT2c receptors in the generation of hippocampal oscillations. Hippocampal EEG was recorded and the power in the theta frequency range was monitored in different behaviors in freely-moving rats and after brainstem stimulation in anesthetized animals. We found that in freely-moving rats, mCPP suppressed hippocampal theta rhythm and the effect was stronger during REM sleep than during waking theta states. Under urethane anesthesia, mCPP decreased the power for both spontaneous and elicited theta rhythm in a dose-dependent manner and the 5-HT2c antagonist reversed this effect. The results of this study demonstrate that 5-HT2c receptors are important element of the serotonergic modulation of hippocampal theta oscillations and thus pharmacological interactions with these receptors can modulate physiological and pathological processes associated with limbic theta activity.

Pharmacogenetics and schizophrenia

The wide interindividual variability in clinical response and tolerability of antipsychotic medications has led investigators to postulate that these variabilities may be under genetic control. Although not always consistent, there are promising indications from emergent pharmacogenetic studies that efficacy of antipsychotic medications for the various symptom domains of psychopathology in schizophrenia may be genetically regulated. This is an encouraging approach. Moreover, there are also suggestive findings that the side-effect profiles of second-generation antipsychotic medications and their propensity to cause weight gain and glucose and lipid abnormalities as well as tardive dyskinesia may be related to pharmacogenetic factors in this patient population. Ultimately, such approaches could drive choices of antipsychotic medication based on the likelihood of clinical response and development of side effects in light of a particular patient's genetic profile. In the future, this targeted approach (personalized medicine) may become informative for clinicians choosing an antipsychotic medication for an individual patient with schizophrenia.