Distribution of serotonin 5-hydroxytriptamine 1B (5-HT(1B)) receptors in the normal rat hypothalamus

Projection-defined median raphe Pet+ subpopulations are diversely implicated in seizure

The raphe nuclei, the primary resource of forebrain 5-HT, play an important but heterogeneous role in regulating subcortical excitabilities. Fundamental circuit organizations of different median raphe (MR) subsystems are far from completely understood. In the present study, using cell-specific viral tracing, Ca2+ fiber photometry and epilepsy model, we map out the forebrain efferent and afferent of different MR Pet+ subpopulations and their divergent roles in epilepsy. We found that PetMR neurons send both collateral and parallel innervations to different downstream regions through different subpopulations. Notably, CA3-projecting PetMR subpopulations are largely distinct from habenula (Hb)-projecting PetMR subpopulations in anatomical distribution and topological organization, while majority of the CA3-projecting PetMR subpopulations are overlapped with the medial septum (MS)-projecting PetMR subpopulations. Further, using Ca2+ fiber photometry, we monitor activities of PetMR neurons in hippocampal-kindling seizure, a classical epilepsy model with pathological mechanisms caused by excitation-inhibition imbalance. We found that soma activities of PetMR neurons are heterogeneous during different periods of generalized seizures. These divergent activities are contributed by different projection-defined PetMR subpopulations, manifesting as increased activities in CA3 but decreased activity in Hb resulting from their upstream differences. Together, our findings provide a novel framework of MR subsystems showing that projection-defined MR Pet+ subpopulations are topologically heterogenous with divergent circuit connections and are diversely implicated in seizures. This may help in the understanding of heterogeneous nature of MR 5-HTergic subsystems and the paradox roles of 5-HTergic systems in epilepsy.

Chemogenetic Activation of Oxytocin Neurons Improves Pain in a Reserpine-induced Fibromyalgia Rat Model

Fibromyalgia (FM) is a syndrome characterized by chronic pain with depression as a frequent comorbidity. However, efficient management of the pain and depressive symptoms of FM is lacking. Given that endogenous oxytocin (OXT) contributes to the regulation of pain and depressive disorders, herein, we investigated the role of OXT in an experimental reserpine-induced FM model. In FM model, OXT-monomeric red fluorescent protein 1 (OXT-mRFP1) transgenic rats exhibited increased depressive behavior and sensitivity in a mechanical nociceptive test, suggesting reduced pain tolerance. Additionally, the development of the FM-like phenotype in OXT-mRFP1 FM model rats was accompanied by a significant reduction in OXT mRNA expression in the magnocellular neurons of the paraventricular nucleus. OXT-mRFP1 FM model rats also had significantly fewer tryptophan hydroxylase (TPH)- and tyrosine hydroxylase (TH)-immunoreactive (ir) neurons as well as reduced serotonin and norepinephrine levels in the dorsal raphe and locus coeruleus. To investigate the effects of stimulating the endogenous OXT pathway, rats expressing OXT-human muscarinic acetylcholine receptor (hM3Dq)-mCherry designer receptors exclusively activated by designer drugs (DREADDs) were also assessed in the FM model. Treatment of these rats with clozapine-N-oxide (CNO), an hM3Dq-activating drug, significantly improved characteristic FM model-induced pathophysiological pain, but did not alter depressive-like behavior. The chemogenetically induced effects were reversed by pre-treatment with an OXT receptor antagonist, confirming the specificity of action via the OXT pathway. These results indicate that endogenous OXT may have analgesic effects in FM, and could be a potential target for effective pain management strategies for this disorder.

Hypothalamic GPCR Signaling Pathways in Cardiometabolic Control

Obesity is commonly associated with sympathetic overdrive, which is one of the major risk factors for the development of cardiovascular diseases, such as hypertension and heart failure. Over the past few decades, there has been a growing understanding of molecular mechanisms underlying obesity development with central origin; however, the relative contribution of these molecular changes to the regulation of cardiovascular function remains vague. A variety of G-protein coupled receptors (GPCRs) and their downstream signaling pathways activated in distinct hypothalamic neurons by different metabolic hormones, neuropeptides and monoamine neurotransmitters are crucial not only for the regulation of appetite and metabolic homeostasis but also for the sympathetic control of cardiovascular function. In this review, we will highlight the main GPCRs and associated hypothalamic nuclei that are important for both metabolic homeostasis and cardiovascular function. The potential downstream molecular mediators of these GPCRs will also be discussed.

CB1/5-HT/GABA interactions and food intake regulation

Despite historically the serotonergic, GABAergic, and cannabinoid systems have been shown to play a crucial role in the central regulation of eating behavior, interest in the study of the interactions of these neurotransmission systems has only now been investigated. Current evidence suggests that serotonin may influence normal and pathological eating behavior in significantly more complex ways than was initially thought. This knowledge has opened the possibility of exploring the potential clinical utility of new therapeutic strategies more effective and safer than the current approaches to treat pathological eating behavior. Furthermore, the nature and complexity of the interactions between these neurotransmitter systems have provided a better understanding of the pathophysiological mechanisms not only of eating behavior and eating disorders but also of some of the comorbidities associated with modulation of cortical circuits, which are involved in high order cognitive processes. Accordingly, in the present chapter, the clinical and experimental findings of the interactions between serotonin, GABA, and cannabinoids are synthesized, emphasizing the pharmacological, neurophysiological, and neuroanatomical aspects that could potentially improve the current therapeutic approaches against pathological eating behavior.

Effect of amisulpride, olanzapine, quetiapine, and aripiprazole single administration on c-Fos expression in vasopressinergic and oxytocinergic neurons of the rat hypothalamic supraoptic nucleus

OBJECTIVE

The goal of this study was to reveal the impact of four types of atypical antipsychotics including amisulpride (AMI), olanzapine (OLA), quetiapine (QUE), and aripiprazole (ARI), with different receptor-affinity profile and dissociation constant, on the activity of hypothalamic supraoptic nucleus (SON) vasopressinergic and oxytocinergic neurons.

METHODS

Male Sprague Dawley rats received a single injection of vehicle (VEH) (0.1 ml/100g), AMI (20 mg/kg), OLA (5 mg/kg), QUE (15 mg/kg/) or ARI (10 mg/kg). Ninety min after treatment, the animals were fixed by transcardial perfusion, the brains removed, and cryocut into serial coronal sections of 35 µm thickness. The sections were processed for c-Fos staining using an avidin-biotin-peroxidase complex and visualized by nickel intensified diaminobenzidine to reach black end product. Afterwards, the sections were exposed to vasopressin (AVP) and oxytocin (OXY) antibodies and the reaction product visualized by biotin-labeled fluorescent Alexa Fluor 568 dye. The data were evaluated from c-Fos and AVP or OXY merged sections.

RESULTS

The present study shows that all four antipsychotics applied induced c-Fos expression in the SON. With respect to the stimulation efficacy of the individual antipsychotics, estimated based on the quantity of c-Fos-labeled AVP and OXY neurons, could be a preferential action assigned to QUE over moderate effect of ARI and lower effect to OLA and reduced effect of AMI (VEH < AMI < OLA < ARI < QUE).

CONCLUSION

The present data for the first time provide an insight into the quantitative pattern of brain activity within the clusters of SON AVP and OXY cells in response to different atypical antipsychotics single treatment.

CB1 receptors in the paraventricular nucleus of the hypothalamus modulate the release of 5-HT and GABA to stimulate food intake in rats

Endocannabinoids and their receptors not only contribute to the control of natural processes of appetite regulation and energy balance but also have an important role in the pathogenesis of obesity. CB1 receptors (CB1R) are expressed in several hypothalamic nuclei, including the paraventricular nucleus (PVN), where induce potent orexigenic responses. Activation of CB1R in the PVN induces hyperphagia by modulating directly or indirectly orexigenic and anorexigenic signals; however, interaction among these mediators has not been clearly defined. CB1R mRNA is expressed in serotonergic neurons that innervate the PVN, and activation of 5-HT receptors in the PVN constitutes an important satiety signal. Some GABAergic terminals are negatively influenced by 5-HT, suggesting that the hyperphagic effect of CB1R activation could involve changes in serotonergic and GABAergic signaling in the PVN. Accordingly, the present study was aimed to characterize the neurochemical mechanisms related to the hyperphagic effects induced by activation of CB1R in the PVN, studying in vitro and in vivo changes induced by direct activation these receptors. Here, we have found that the neurochemical mechanisms activated by stimulation of CB1 receptors in the PVN involve inhibition of 5-HT release, resulting in a decrease of serotonergic activity mediated by 5-HT_1A and 5-HT_1B receptors and inducing disinhibition of GABA release to stimulate food intake. In conclusion, these neurochemical changes in the PVN are determinant to the cannabinoid-induced stimulation of food intake. Our findings provide evidence of a functional connection among CB1R and serotonergic and GABAergic systems on the control of appetite regulation mediated by endocannabinoids.

Physiology and Pharmacology of Ejaculation

Ejaculation is the final stage of coitus in mammalian male and is mandatory for natural procreation. Two synchronized phases, emission and expulsion, form the ejaculatory response and involve specific organs and anatomical structures. The peripheral events leading to ejaculation are commanded by autonomic (sympathetic and parasympathetic) and somatic divisions of the nervous system. The autonomic and somatic motor efferents originate in spinal nuclei located in thoracolumbar and lumbosacral segments. Co-ordinated activation of autonomic and somatic spinal nuclei is orchestrated by a group of lumbar spinal interneurons defined as the spinal generator of ejaculation. The generator of ejaculation together with the autonomic and somatic spinal nuclei constitutes a spinal network that is under the strong influence of stimulating or inhibiting genital sensory and supraspinal inputs. A brain circuitry dedicated to ejaculation has been delineated that is part of a more global network controlling other aspects of the sexual response. This circuitry includes discrete neuronal populations distributed in all divisions of the brain. The corollary to the expanded CNS network is the variety of neurotransmitter systems participating in the ejaculatory process. Among them, serotonin neurotransmission plays a key role and its targeting led to the development of the first registered pharmacological treatment of premature ejaculation in human beings. Critical gaps remain in the understanding of neurophysiopharmacology of ejaculation and management of ejaculatory disorders in human beings needs improvement. Because the ejaculatory response in laboratory animals and in human beings shares many similarities, the use of animal models will certainly provide further advances in the field.

Reductions in brain 5-HT1B receptor availability in primarily cocaine-dependent humans

BACKGROUND

Preclinical evidence implicates the serotonin receptor 5-hydroxytryptamine 1B (5-HT1B) in the effects of cocaine. This study explores 5-HT1B in humans by examining receptor availability in vivo in subjects whose primary addiction is cocaine dependence (CD) using positron emission tomography.

METHODS

Study participants included 14 medically healthy subjects with CD (mean age = 41 ± 6 years) who were compared with 14 age-matched healthy control subjects (mean age = 41 ± 8 years) with no past or current history of cocaine or other illicit substance abuse. Participants underwent magnetic resonance imaging followed by positron emission tomography with the highly selective 5-HT1B tracer, [(11)C]P943, for purposes of quantifying regional binding potential. Voxel-based morphometry and gray matter masking also were employed to control for potential partial volume effects.

RESULTS

The [(11)C]P943 positron emission tomography imaging data in nine candidate regions (amygdala, anterior cingulate cortex, caudate, frontal cortex, hypothalamus, pallidum, putamen, thalamus, and ventral striatum) showed significant or nearly significant reductions of regional binding potential in subjects with CD in three regions: anterior cingulate (-16%, p < .01), hypothalamus (-16%, p = .03), and frontal cortex (-7%, p = .08). Voxel-based morphometry showed significant gray matter reductions in the frontal cortex of subjects with CD. After gray matter masking, statistically significant reductions in the [(11)C]P943 regional binding potential were either retained (anterior cingulate, -14%, p = .01; hypothalamus, -20%, p < .01) or achieved (frontal cortex, -14%, p < .01). Whole-brain voxel-wise parameter estimation confirmed these results. Secondary analyses were also significant in some regions for years of cocaine and daily tobacco use.

CONCLUSIONS

The reductions found in this study suggest that 5-HT1B receptors may contribute to the etiology or expression of CD and potentially represent a target for medication development.

Diphtheria toxin treatment of Pet-1-Cre floxed diphtheria toxin receptor mice disrupts thermoregulation without affecting respiratory chemoreception

In genetically-modified Lmx1b(f/f/p) mice, selective deletion of LMX1B in Pet-1 expressing cells leads to failure of embryonic development of serotonin (5-HT) neurons. As adults, these mice have a decreased hypercapnic ventilatory response and abnormal thermoregulation. This mouse model has been valuable in defining the normal role of 5-HT neurons, but it is possible that developmental compensation reduces the severity of observed deficits. Here we studied mice genetically modified to express diphtheria toxin receptors (DTR) on Pet-1 expressing neurons (Pet-1-Cre/floxed DTR or Pet1/DTR mice). These mice developed with a normal complement of 5-HT neurons. As adults, systemic treatment with 2-35μg of diphtheria toxin (DT) reduced the number of tryptophan hydroxylase-immunoreactive (TpOH-ir) neurons in the raphe nuclei and ventrolateral medulla by 80%. There were no effects of DT on minute ventilation (VE) or the ventilatory response to hypercapnia or hypoxia. At an ambient temperature (TA) of 24°C, all Pet1/DTR mice dropped their body temperature (TB) below 35°C after DT treatment, but the latency was shorter in males than females (3.0±0.37 vs. 4.57±0.29days, respectively; p<0.001). One week after DT treatment, mice were challenged by dropping TA from 37°C to 24°C, which caused TB to decrease more in males than in females (29.7±0.31°C vs. 33.0±1.3°C, p<0.01). We conclude that the 20% of 5-HT neurons that remain after DT treatment in Pet1/DTR mice are sufficient to maintain normal baseline breathing and a normal response to CO2, while those affected include some essential for thermoregulation, in males more than females. In comparison to models with deficient embryonic development of 5-HT neurons, acute deletion of 5-HT neurons in adults leads to a greater defect in thermoregulation, suggesting that significant developmental compensation can occur.

Antagonism of serotonin receptor 1B decreases viability and promotes apoptosis in the COS canine osteosarcoma cell line

Serotonin receptor 1B (5HTR1B) traditionally exhibits anti-proliferative activity in osteoblasts. We examined the expression and function of 5HTR1B in the COS canine osteosarcoma cell line and normal canine osteoblasts. Equal levels of 5HTR1B gene and protein expression were found between normal and malignant osteoblasts. Treatment with serotonin enhanced viability of osteosarcoma cells but not normal osteoblasts. Challenge with the 5HTR1B agonist anpirtoline caused no change in cell viability. Rather incubation with the specific receptor antagonist SB224289 caused reduction in osteoblast viability, with this effect more substantial in osteosarcoma cells. Investigation of this inhibitory activity showed 5HTR1B antagonism induces apoptosis in malignant cells. Evaluation of phosphorylated levels of CREB and ERK, transcriptional regulators associated with serotonin receptor signalling in osteoblasts, revealed aberrant 5HTR1B signalling in COS. Our results confirm the presence of 5HTR1B in a canine osteosarcoma cell line and highlight this receptor as a possible novel therapeutic target.

Serotonin mediated changes in corticotropin releasing factor mRNA expression and feeding behavior isolated to the hypothalamic paraventricular nuclei

Fenfluramine reduces hunger and promotes body weight loss by increasing central serotonin (5-HT) signaling. More recently, neuropeptides have been linked to the regulation of feeding behavior, metabolism and body weight. To examine possible interactions between 5-HT and neuropeptides in appetite control, fenfluramine (200 nmol/0.5 μl/side) was administered directly into the hypothalamic paraventricular nuclei (PVN) of male rats. Bilateral fenfluramine produced significant hypophagia and increased expression of PVN corticotropin releasing factor (CRF) mRNA and neuropeptide Y (NPY) mRNA in the arcuate nucleus within the first hour after drug administration. Fenfluramine's effects on feeding behavior and mRNA expression were blocked by PVN injections of a 5-HT(1-2) receptor antagonist, metergoline (15 nmol/0.5 μl/side). These data suggest that 5-HT neurons targeting hypothalamic paraventricular CRF neurons may participate in an appetite control circuit for reducing food intake.

The structure of the dorsal raphe nucleus and its relevance to the regulation of sleep and wakefulness

Serotonergic (5-HT) cells in the rat dorsal raphe nucleus (DRN) appear in topographically organized groups. Based on cellular morphology, expression of other neurotransmitters, afferent and efferent connections and functional properties, 5-HT neurons of the DRN have been grouped into six cell clusters. The subdivisions comprise the rostral, ventral, dorsal, lateral, caudal and interfascicular parts of the DRN. In addition to 5-HT cells, neurons containing γ-aminobutyric acid (GABA), glutamate, dopamine, nitric oxide and the neuropeptides corticotropin-releasing factor, substance P, galanin, cholecystokinin, neurotensin, somatostatin, vasoactive intestinal peptide, neuropeptide Y, thyrotropin-releasing hormone, growth hormone, leu-enkephalin, met-enkephalin and gastrin have been characterized in the DRN. Moreover, numerous brain areas have neurons that project to the DRN and express monoamines (norepinephrine, histamine), amino acids (GABA, glutamate), acetylcholine or neuropeptides (orexin, melanin-concentrating hormone, corticotropin-releasing factor and substance P) that directly or indirectly, through local circuits, regulate the activity of 5-HT cells. The 5-HT cells predominate along the midline of the rostral, dorsal and ventral subdivisions of the DRN and outnumber the non-5-HT cells occurring in the raphe nucleus. The GABAergic and glutamatergic neurons are clustered mainly in the lateral and dorsal subdivisions of the DRN, respectively. The 5-HT(1A) receptor is located on the soma and the dendrites of 5-HT neurons and at postsynaptic sites (outside the DRN). It is expressed, in addition, by non-5-HT cells of the DRN. The 5-HT(1B) receptor is located at presynaptic and postsynaptic sites (outside the boundaries of the DRN). It has been described also in the ventromedial DRN where it is expressed by non-5-HT cells. The 5-HT(2A) and 5-HT(2C) receptors are located within postsynaptic structures. At the level of the DRN the 5-HT(2A) and 5-HT(2C) receptor-containing cells are predominantly GABAergic interneurons and projection neurons. Within the boundaries of the DRN the 5-HT(3) receptor is expressed by, among others, glutamatergic interneurons. 5-HT(7) receptors in the DRN are not localized to serotonergic neurons but, at least in part, to GABAergic cells and terminals. The complex structure of the DRN may have important implications for neural mechanisms underlying 5-HT modulation of wakefulness and REM sleep.

Postnatal changes in the expressions of serotonin 1A, 1B, and 2A receptors in ten brain stem nuclei of the rat: implication for a sensitive period

A critical period in respiratory network development occurs in the rat around postnatal days (P) 12-13, when abrupt neurochemical, metabolic, and physiological changes were evident. As serotonin and its receptors are involved in respiratory modulation, and serotonergic abnormality is implicated in sudden infant death syndrome, we hypothesized that 5-HT receptors are significantly downregulated during the critical period. This was documented recently for 5-HT(2A)R in several respiratory nuclei. The present study represents a comprehensive analysis of postnatal development of 5-HT(1A)R and 5-HT(1B)R in 10 brain stem nuclei and 5-HT(2A)R in six nuclei not previously examined. Optical densitometric analysis of immunohistochemically-reacted neurons from P2 to P21 indicated four developmental patterns of expression: (1) Pattern I: a high level of expression at P2-P11, an abrupt and significant reduction at P12, followed by a plateau until P21 (5-HT(1A)R and 5-HT(1B)R in raphé magnus [RM], raphé obscurus [ROb], raphé pallidus [RP], pre-Bötzinger complex [PBC], nucleus ambiguus [Amb], and hypoglossal nucleus [XII; 5-HT(1A)R only]). (2) Pattern II: a high level at P2-P9, a gradual decline from P9 to P12, followed by a plateau until P21 (5-HT(1A)R and 5-HT(1B)R in the retrotrapezoid nucleus (RTN)/parafacial respiratory group (pFRG)). (3) Pattern III: a high level at P2-P11, followed by a gradual decline until P21 (5-HT(1A)R in the ventrolateral subnucleus of solitary tract nucleus [NTS(VL)] and the non-respiratory cuneate nucleus [CN]). (4) Pattern IV: a relatively constant level maintained from P2 to P21 (5-HT(1A)R in the commissural subnucleus of solitary tract nucleus (NTS(COM)); 5-HT(1B)R in XII, NTS(VL), NTS(COM), and CN; and 5-HT(2A)R in RM, ROb, RP, RTN/pFRG, NTS(VL), and NTS(COM)). Thus, a significant reduction in the expression of 5-HT(1A)R, 5-HT(1B)R, and 5-HT(2A)R in multiple respiratory-related nuclei at P12 is consistent with reduced serotonergic transmission during the critical period, thereby rendering the animals less able to respond adequately to ventilatory distress.

Comparative analysis of serotonin receptor (HTR1A/HTR1B families) and transporter (slc6a4a/b) gene expression in the zebrafish brain

In this study we analyze 5-hydroxytryptamine [5-HT]; serotonin) signaling in zebrafish, an increasingly popular vertebrate disease model. We compare and contrast expression of the 5-HT transporter genes slc6a4a and slc6a4b, which identify 5-HT-producing neurons and three novel 5-HT receptors, htr1aa, htr1ab, and htr1bd. slc6a4a and slc6a4b are expressed in the raphe nuclei, retina, medulla oblongata, paraventricular organ, pretectal diencephalic complex, and caudal zone of the periventricular hypothalamus, in line with the expression profiles of homologues from other vertebrates. Our analysis of serotonin transporter (SERT)-encoding genes also identifies parallel genetic pathways used to build the 5-HT system in zebrafish. In cells in which 5-HT is synthesized by tph1, slc6a4b is used for re-uptake, whereas tph2-positive cells utilize slc6a4a. The receptors htr1aa, htr1ab, and htr1bd also show widespread expression in both the larval and adult brain. Receptor expression is seen in the superior raphe nucleus, retina, ventral telencephalon, optic tectum, thalamus, posterior tuberculum, cerebellum, hypothalamus, and reticular formation, thus implicating 5-HT signaling in several neural circuits. We also examine larval brains double-labeled with 5-HTergic and dopaminergic pathway-specific antibodies, to uncover the identity of some 5-HTergic target neurons. Furthermore, comparison of the expression of transporter and receptor genes also allows us to map sites of autoreceptor activity within the brain. We detect autoreceptor activity in the pretectal diencephalic cluster (htr1aa-, htr1ab-, htr1bd-, and slc6a4a-positive), superior raphe nucleus (htr1aa-, htr1ab-, and slc6a4a-positive), paraventricular organ (htr1aa-, htr1ab-, htr1bd-, and slc6a4b-positive), and the caudal zone of the periventricular hypothalamus (htr1ab- and slc6a4b-positive).

5-HT inhibition of rat insulin 2 promoter Cre recombinase transgene and proopiomelanocortin neuron excitability in the mouse arcuate nucleus

A number of anti-obesity agents have been developed that enhance hypothalamic 5-HT transmission. Various studies have demonstrated that arcuate neurons, which express proopiomelanocortin peptides (POMC neurons), and neuropeptide Y with agouti-related protein (NPY/AgRP) neurons, are components of the hypothalamic circuits responsible for energy homeostasis. An additional arcuate neuron population, rat insulin 2 promoter Cre recombinase transgene (RIPCre) neurons, has recently been implicated in hypothalamic melanocortin circuits involved in energy balance. It is currently unclear how 5-HT modifies neuron excitability in these local arcuate neuronal circuits. We show that 5-HT alters the excitability of the majority of mouse arcuate RIPCre neurons, by either hyperpolarization and inhibition or depolarization and excitation. RIPCre neurons sensitive to 5-HT, predominantly exhibit hyperpolarization and pharmacological studies indicate that inhibition of neuronal firing is likely to be through 5-HT_1F receptors increasing current through a voltage-dependent potassium conductance. Indeed, 5-HT_1F receptor immunoreactivity co-localizes with RIPCre green fluorescent protein expression. A minority population of POMC neurons also respond to 5-HT by hyperpolarization, and this appears to be mediated by the same receptor-channel mechanism. As neither POMC nor RIPCre neuronal populations display a common electrical response to 5-HT, this may indicate that sub-divisions of POMC and RIPCre neurons exist, perhaps serving different outputs.

The development of tolerance to drugs that suppress food intake

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

Serotonin increases the excitability of the hypothalamic paraventricular nucleus magnocellular neurons

Recent evidence that 5-hydroxytryptamine (5-HT or serotonin) enhances the release and the gene expression of vasopressin and oxytocin in the hypothalamic paraventricular nucleus (PVN) suggests that 5-HT can excite the PVN magnocellular neurons. The objective of this study was to examine the underlying mechanisms for such excitatory action in the electrophysiologically identified hypothalamic PVN magnocellular neurons in rats using whole-cell patch-clamp. We found that 5-HT weakly depolarizes 33.3% of PVN magnocellular neurons in the presence of tetrodotoxin. A minuscule inward current was produced by 5-HT in 48% of the cells, which was attenuated when the 5-HT(4) antagonist GR113808 or the 5-HT(7) antagonist SB269970 was added. In addition, 5-HT reduced the frequency of miniature inhibitory postsynaptic currents in a dose-dependent manner. This inhibition was mimicked by the 5-HT(1B) agonist CP93129, and reversed in the presence of 5-HT(1B) antagonists cyanopindolol and SB224289. Besides, 5-HT induced a biphasic effect on the frequency of miniature excitatory postsynaptic currents, comprising a transient inhibition and a delayed concentration-dependent excitation (onset latency approximately 5 min). The facilitation was mimicked by the 5-HT(2A/2C) agonist DOI and abolished in the presence of the 5-HT(2C) antagonist RS102221. Our findings reveal that 5-HT directly increases the excitability of the PVN magnocellular neurons via multiple receptor subtypes and mechanisms. This may help understanding the regulation of 5-HT-induced hormone release and feeding behavior in the PVN.

Enterostatin inhibition of dietary fat intake is modulated through the melanocortin system

Enterostatin injected into the amygdala selectively reduces dietary fat intake by an action that involves a serotonergic component in the paraventricular nucleus. We have investigated the role of melanocortin signaling in the response to enterostatin by studies in melanocortin 4 receptor (MC4R) knock out mice and by the use of the MC4R and MC3R antagonist SHU9119, and by neurochemical phenotyping of enterostatin activated cells. We also determined the effect of enterostatin in vivo on the expression of AgRP in the hypothalamus and amygdala of rats and in culture on a GT1-7 neuronal cell line. Enterostatin had no effect on food intake in MC4R knock out mice. SHU9119 i.c.v. blocked the feeding response to amygdala enterostatin in rats. Amygdala enterostatin induced fos activation in alpha-melanocyte stimulating hormone (alpha-MSH) neurons in the arcuate nucleus. Enterostatin also reduced the expression of AgRP in the hypothalamus and amygdala and in GT1-7 cells. These data suggest enterostatin inhibits dietary fat intake through a melanocortin signaling pathway.

Neurons expressing serotonin-1B receptor in the basolateral nuclear group of the amygdala in normally behaving and aggressive dogs

The present study aimed to quantify neurons expressing the serotonin-1B receptor and evaluate numerical differences in normally behaving and pathologically aggressive dogs in order to assess whether the serotonin-1B receptor is involved in pathological canine aggression. Because previous studies have reported structural alterations in the basolateral nuclear group (BNG) of the amygdaloid body of aggressive dogs, this structure was selected as region of interest in the present study. Indirect immunohistochemistry was applied to visualise the serotonin-1B-receptor-positive neurons. Immunoreactivity was located predominantly within the neuronal cell bodies and adjacent neuronal processes. In the aggressive dogs the BNGs contained a significantly higher number of serotonin-1B-receptor-positive neurons compared to the normally behaving dogs. This number was strongly correlated with the total number of neurons per BNG, which was also significantly increased in aggressive dogs compared to normal dogs. The percentage of neurons expressing the serotonin-1B receptor did not differ significantly between both groups. No significant asymmetries were observed for the number and percentage of serotonin-1B-receptor-positive neurons. Potential relationships between the present findings and the etiology of aggressive behaviour, the neuroprotective role of the serotonin-1B receptor and receptor dysfunction are discussed.

Food intake and reward mechanisms in patients with schizophrenia: implications for metabolic disturbances and treatment with second-generation antipsychotic agents

Obesity is highly prevalent among patients with schizophrenia and is associated with detrimental health consequences. Although excessive consumption of fast food and pharmacotherapy with such second-generation antipsychotic agents (SGAs) as clozapine and olanzapine has been implicated in the schizophrenia/obesity comorbidity, the pathophysiology of this link remains unclear. Here, we propose a mechanism based on brain reward function, a relevant etiologic factor in both schizophrenia and overeating. A comprehensive literature search on neurobiology of schizophrenia and of eating behavior was performed. The collected articles were critically reviewed and relevant data were extracted and summarized within four key areas: (1) energy homeostasis, (2) food reward and hedonics, (3) reward function in schizophrenia, and (4) metabolic effects of the SGAs. A mesolimbic hyperdopaminergic state may render motivational/incentive reward system insensitive to low salience/palatability food. This, together with poor cognitive control from hypofunctional prefrontal cortex and enhanced hedonic impact of food, owing to exaggerated opioidergic drive (clinically manifested as pain insensitivity), may underlie unhealthy eating habits in patients with schizophrenia. Treatment with SGAs purportedly improves dopamine-mediated reward aspects, but at the cost of increased appetite and worsened or at least not improved opiodergic capacity. These effects can further deteriorate eating patterns. Pathophysiological and therapeutic implications of these insights need further validation via prospective clinical trials and neuroimaging studies.

Serotonin reciprocally regulates melanocortin neurons to modulate food intake

The neural pathways through which central serotonergic systems regulate food intake and body weight remain to be fully elucidated. We report that serotonin, via action at serotonin1B receptors (5-HT1BRs), modulates the endogenous release of both agonists and antagonists of the melanocortin receptors, which are a core component of the central circuitry controlling body weight homeostasis. We also show that serotonin-induced hypophagia requires downstream activation of melanocortin 4, but not melanocortin 3, receptors. These results identify a primary mechanism underlying the serotonergic regulation of energy balance and provide an example of a centrally derived signal that reciprocally regulates melanocortin receptor agonists and antagonists in a similar manner to peripheral adiposity signals.

Omega-3 fatty acids improve appetite in cancer anorexia, but tumor resecting restores it

BACKGROUND

Tumor growth leads to cancer anorexia that is ameliorated using omega-3 fatty acids (omega-3FA). We hypothesize that omega-3FA modulates up-regulation of hypothalamic orexigenic neuropeptide Y (NPY) and down-regulation of anorexigenic alpha melanocyte-stimulating hormone (alpha-MSH) and serotonin 1B receptors (5-HT(1B)-receptors) in tumor-bearing rats.

METHODS

Twenty-eight tumor-bearing rats were fed either chow (TB-Control) or omega-3FA (TB-omega-3FA). When anorexia developed in TB-Control rats, they and a cohort of TB-omega-pi-3 rats were killed. The rest had their tumor resected (R-Control and R-omega-3FA), and when anorexic TB-Controls normalized their food intake, brains were removed for hypothalamic immunocytochemical study of NPY, alpha-MSH, and 5-HT(1B)-receptor antibodies concentrations. Comparison among slides were assessed by image analysis and analyzed by ANOVA and t test.

RESULTS

At anorexia, hypothalamic NPY in arcuate nucleus (ARC) increased by 38% in TB-omega3FA versus TB-Control, whereas alpha-MSH decreased 64% in ARC and 29% in paraventricular nucleus (PVN). Omega-3FA diet in anorexia (TB-omega-3FA vs R-omega-3FA) produced similar qualitative changes of NPY (22% increase) and alpha-MSH (31% decrease) in ARC, with concomitant decrease of 37% in 5-HT(1B)-receptors in PVN, confirming the influence of omega-3FA on the hypothalamic food intake modulators. However, after tumor resection (TB-Control vs R-Control) a 97% increase in NPY and a 62% decrease in alpha-MSH occurred that was significantly greater than in rats fed omega-3FA diet.

CONCLUSION

Tumor resection and omega-3FA modifies hypothalamic food intake activity, up-regulating NPY and down-regulating alpha-MSH and 5-HT(1B)-receptors. Tumor resection in anorexic rats on chow diet restored hypothalamic NPY, alpha-MSH, and food intake quantitatively more than in rats fed omega3FA diet.

Serotonin-1B receptor activity and expression modulate the aggression-stimulating effects of adolescent anabolic steroid exposure in hamsters

Repeated high dose (5.0 mg/kg) anabolic-androgenic steroid (AAS) exposure during adolescence stimulates offensive aggression in male Syrian hamsters. These studies examined whether AAS-induced aggression was regulated by the activity of serotonin (5HT) type-1B receptors and correlated with altered 5HT1B expression. AAS-treated hamsters were tested for offensive aggression following the administration of the 5HT1B agonist anpirtoline (0.125-0.5 mg/kg). Anpirtoline dose-dependently reduced select components of the AAS-induced aggressive response, with significant reductions observed at 0.25 mg/kg. Aggressive, AAS-treated hamsters showed significant decreases in the area covered by 5HT1B-containing neuronal puncta and increases in the number of 5HT1B-containing neuronal somata in select brain regions implicated in aggression control. Together, these data support a role for site-specific alterations in 5HT1B signaling and expression in adolescent AAS-induced aggression.

Hypothalamic integration of immune function and metabolism

The immune and neuroendocrine systems are closely involved in the regulation of metabolism at peripheral and central hypothalamic levels. In both physiological (meals) and pathological (infections, traumas and tumors) conditions immune cells are activated responding with the release of cytokines and other immune mediators (afferent signals). In the hypothalamus (central integration), cytokines influence metabolism by acting on nucleus involved in feeding and homeostasis regulation leading to the acute phase response (efferent signals) aimed to maintain the body integrity. Peripheral administration of cytokines, inoculation of tumor and induction of infection alter, by means of cytokine action, the normal pattern of food intake affecting meal size and meal number suggesting that cytokines acted differentially on specific hypothalamic neurons. The effect of cytokines-related cancer anorexia is also exerted peripherally. Increase plasma concentrations of insulin and free tryptophan and decrease gastric emptying and d-xylose absorption. In addition, in obesity an increase in interleukin (IL)-1 and IL-6 occurs in mesenteric fat tissue, which together with an increase in corticosterone, is associated with hyperglycemia, dyslipidemias and insulin resistance of obesity-related metabolic syndrome. These changes in circulating nutrients and hormones are sensed by hypothalamic neurons that influence food intake and metabolism. In anorectic tumor-bearing rats, we detected upregulation of IL-1beta and IL-1 receptor mRNA levels in the hypothalamus, a negative correlation between IL-1 concentration in cerebro-spinal fluid and food intake and high levels of hypothalamic serotonin, and these differences disappeared after tumor removal. Moreover, there is an interaction between serotonin and IL-1 in the development of cancer anorexia as well as an increase in hypothalamic dopamine and serotonin production. Immunohistochemical studies have shown a decrease in neuropeptide Y (NPY) and dopamine (DA) and an increase in serotonin concentration in tumor-bearing rats, in first- and second-order hypothalamic nuclei, while tumor resection reverted these changes and normalized food intake, suggesting negative regulation of NPY and DA systems by cytokines during anorexia, probably mediated by serotonin that appears to play a pivotal role in the regulation of food intake in cancer. Among the different forms of therapy, nutritional manipulation of diet in tumor-bearing state has been investigated. Supplementation of tumor bearing rats with omega-3 fatty acid vs. control diet delayed the appearance of tumor, reduced tumor-growth rate and volume, negated onset of anorexia, increased body weight, decreased cytokines production and increased expression of NPY and decreased alpha-melanocyte-stimulating hormone (alpha-MSH) in hypothalamic nuclei. These data suggest that omega-3 fatty acid suppressed pro-inflammatory cytokines production and improved food intake by normalizing hypothalamic food intake-related peptides and point to the possibility of a therapeutic use of these fatty acids. The sum of these data support the concept that immune cell-derived cytokines are closely related with the regulation of metabolism and have both central and peripheral actions, inducing anorexia via hypothalamic anorectic factors, including serotonin and dopamine, and inhibiting NPY leading to a reduction in food intake and body weight, emphasizing the interconnection of the immune and neuroendocrine systems in regulating metabolism during infectious process, cachexia and obesity.

Do similar neural systems subserve aggressive and sexual behaviour in male rats? Insights from c-Fos and pharmacological studies

It is a common belief that male aggressive and sexual behaviour share many of the underlying neurobiological, neurological, pharmacological and neuroendocrine mechanisms. Therefore, we studied brain activation patterns in male rat after performance of aggressive and sexual behaviour and compared serotonergic pharmacology in the same paradigms to delineate possible similarities and differences. Patterns of Fos-immunoreactivity induced by aggressive and sexual encounters of Wild-type male Brown Norway rats were studied to localise the commonly activated (functionally shared) parts of the circuitry, and the specific (functionally different) parts of the neuronal circuitry. Some brain areas (caudal medial preoptic area and medial amygdala) were commonly activated, but other areas (e.g. posterodorsal parts of the medial amygdala, rostral preoptic and premammillary hypothalamus) showed remarkably specific differences in neural activation. 5-HT(1A) receptor agonists inhibit aggressive, but stimulate male sexual behaviour, whereas 5-HT(1B) receptor agonists inhibit both types of behaviour. Selective serotonin reuptake inhibitors share comparable inhibitory effects in aggression and sexual behaviour, although only at relatively high doses. We propose that separate hard-wired neural systems exist in the brain for aggressive and sexual behaviours, modulated via hierarchically 'higher-level' brain areas that are involved in the integration (gating) of the behavioural outcome of an organism.

Normalization of hypothalamic serotonin (5-HT1B) receptor and NPY in cancer anorexia after tumor resection: An immunocytochemical study

Tumor growth leads to anorexia and decreased food intake, the regulation of which is via the integrated hypothalamic peptidergic and monoaminergic system. Serotonin (5-HT), an anorectic monoamine acts primarily via 5-HT 1B-receptors in hypothalamic nuclei while neuropeptide Y (NPY) acts an orexigenic peptide. We previously reported that 5-HT 1B-receptors are up regulated while NPY is down regulated in tumor-bearing (TB)-related anorexia, contributing to food intake reduction. In anorectic TB rats we hypothesize that after tumor resection when food intake has reverted to normal, normalization of 5-HT 1B-receptor and NPY will occur. The aim of this study was to demonstrate normalization of these hypothalamic changes compared to Controls. In anorectic tumor-bearing rats after tumor resection (TB-R) and in sham-operated (Control) rats, distribution of 5-HT 1B-receptors and NPY in hypothalamic nuclei was analyzed using peroxidase antiperoxidase immunocytochemical methods. Image analysis of immunostaining was performed and the data were statistically analyzed. Immunostaining specificity was controlled by omission of primary or secondary antibodies and pre-absorption test. Our results show that after TB-R versus Controls a normalization of food intake, 5-H-1B-receptor and NPY expression in the hypothalamus occurs. These data, discussed in context with our previous studies, support the hypothesis that tumor resection results not only in normalization of food intake but also in reversible changes of anorectic and orexigenic hypothalamic modulators.

Effects of omega-3 fatty acids on orexigenic and anorexigenic modulators at the onset of anorexia

In cancer anorexia, a decrease in food intake (FI) occurs concomitant with changes in orexigenic peptides such as neuropeptide Y (NPY) and anorexigenic peptides such as alpha-melanocyte-stimulating hormone (alpha-MSH) and anorexigenic neurotransmitter serotonin. omega-3 Fatty acid (omega-3FA) inhibits cytokine synthesis, and delays tumor appearance, tumor growth, and onset of anorexia in tumor-bearing rats. We hypothesize that, in cancer anorexia, omega-3FA is associated with quantitative reversal of hypothalamic NPY, alpha-MSH, and serotonin receptor (5-HT(1B)-receptor) enhancing FI. Fischer rats were divided into: MCA tumor bearing fed chow (TB-Chow) or omega-3FA diet (TB-omega-3FA) and controls: non-tumor bearing fed chow (NTB-Chow) or omega-3FA diet (NTB-omega-3FA). Rats were euthanized at anorexia and brains were removed for hypothalamic immunohistochemical study, using NPY, alpha-MSH, and 5-HT(1B)-receptor-specific antibodies and slides assessed by image analysis. Immunostaining specificity was controlled by omission of primary or secondary antibodies and pre-absorption test. At anorexia, FI decreased (P < 0.05) in TB-Chow but did not change in TB-omega-3FA rats. In TB-omega-3FA vs. TB-Chow, NPY immunoreactivity increased 38% in arcuate nucleus (ARC; P < 0.05), and 50% in magnocellular paraventricular nucleus (mPVN; P < 0.05). alpha-MSH decreased 64% in ARC and 29% in mPVN (P < 0.05). 5-HT(1B)-receptor immunoreactivity decreased 13% only in supraoptic nucleus (P < 0.05). No immunoreactivity was found in the control sections. omega-3FA modified hypothalamic peptides and 5-HT-(1B)-receptor immunoreactivity at anorexia, concomitant with an increase in FI, were probably mediated by omega-3FA inhibition of tumor-induced cytokines.

Neuropeptide Y, alpha-melanocyte-stimulating hormone, and monoamines in food intake regulation

Obesity is increasing in severity and prevalence in the United States and represents a major public health issue. No effective pharmacologic treatment leading to sustained weight loss currently exists. The growing interest in the regulation of food intake stems from the current drug treatments for obesity, almost all of which interfere with the monoamine system. Our knowledge of potential interactions between the orexigenic and anorexigenic pathways is limited and fragmented, making the development of targeted drug therapy for obesity difficult. The present review of the interaction of neuropeptides and monoamines emphasizes the complexity of the central mechanisms that regulate feeding behavior. Two main systems are implicated in food intake regulation: neuropeptide Y (NPY) and pro-opiomelanocortin. alpha-Melanocyte-stimulating hormone is a tridecapeptide cleaved from pro-opiomelanocortin that acts to inhibit food intake. The predominant NPY orexigenic receptors are NPY-Y1 and NPY-Y5, and the two anorexigenic melanocortin receptors involved in hypothalamic food intake control are MC3-R and MC4-R. Both neuropeptides interact with monoamines in the hypothalamus to control physiologic states such as hunger, satiation, and satiety. Serotonin suppresses food intake and body weight, acting mainly through the serotonin 1B receptor. Dopamine regulates hunger and satiety by acting in specific hypothalamic areas, through the D1 and D2 receptors. Noradrenaline activation of alpha1- and beta2-adrenoceptors decreases food intake, and stimulation of the alpha2-adrenoceptor increases food intake. A better understanding of the detailed mechanisms underlying the pathogenesis of hyperphagia and hypophagia is needed to develop new therapeutic approaches to obesity.

Citalopram combined with WAY 100635 inhibits ejaculation and ejaculation-related Fos immunoreactivity

The role of 5-HT (5-hydroxytryptamine, 5-HT)(1A) receptor activation in the sexual side-effects, in particular delayed ejaculation, of selective serotonin reuptake inhibitors (SSRIs) was studied. Male Wistar rats were treated for 15 days with vehicle, the SSRI citalopram (10 mg/kg/day p.o.), the 5-HT(1A) receptor antagonist N-[2-[4-(2-methoxyphenyl)-1-piperazinyl] ethyl]-N-(2-pyridinyl) cyclohexane carboxamide 3HCL (WAY 100635, 0.1 mg/kg/ day s.c.), or both drugs combined. Sexual behavior was assessed weekly. One h after the last sexual behavior test, rat brains were processed for Fos-immunohistochemistry. Acute and chronic citalopram mildly inhibited ejaculation, which was strongly augmented by co-administration of WAY 100635. WAY 100635 alone did not alter sexual behavior. Brain sites associated with ejaculation showed reduced Fos-immunoreactivity in rats treated with both citalopram and WAY 100635. Citalopram reduced Fos-immunoreactivity in the arcuate hypothalamic nucleus, an area that might link serotonergic neurotransmission to ejaculation.

Hypothalamic 5-HT1B-receptor changes in anorectic tumor bearing rats

Serotonin (5-HT) is an anorectic monoamine and its regulatory effects on feeding are mediated primarily via 5-HT1B-receptors localized in the hypothalamic nuclei, which, apart from the brain stem, are among the most crucial areas of food intake regulation. The distribution of 5-HT1B-receptors in the hypothalamic nuclei was studied in tumor-bearing (TB) rats at the onset of anorexia and in sham-operated control rats, using the peroxidase-anti-peroxidase immunocytochemical method and specific polyclonal antiserum. Semiquantitative image analysis of 5-HT1B-receptor immunostaining was performed on high-resolution digital photomicrographs using the NIH Scion Image analysis program and the data were compared using Student's t-test. Immunostaining detected 5-HT1B-receptor proteins in the same hypothalamic structures in the Controls as in the TB rats. Qualitative and semiquantitative analysis revealed a significant increase in 5-HT1B-receptor expression in the magnocellular neurons of paraventricular and supraoptic hypothalamic nuclei in TB rats versus Controls. In contrast, changes were not significant in the parvocellular portion of paraventricular nucleus or in the lateral hypothalamus including perifornical region. These findings emphasize serotonin's influence on the magnocellular hypothalamic nuclei during developing of cancer anorexia, which is associated with a decrease in food intake.

Neurobiologic changes in the hypothalamus associated with weight loss after gastric bypass

BACKGROUND

Effects of Roux-en-Y gastric bypass (RYGB) on hypothalamic food intake regulation have not been investigated. The hypothalamic arcuate nucleus (ARC) and the magnocellular (m) and parvocellular (p) parts of the paraventricular nucleus (PVN) regulate hunger and satiety, and are under control of the orexigenic neuropeptide Y (NPY), and the anorexigenic alpha-melanocyte stimulating hormone (alpha-MSH) and serotonin (5-HT). We hypothesized that after RYGB, weight loss is associated with hypothalamic down regulation of NPY and up regulation of 5-HT and alpha-MSH.

STUDY DESIGN

Obesity was induced in 12 Sprague Dawley rats using a high-energy diet for 7 weeks, and then the rats were divided into three groups (n = 4/group): RYGB, sham-operated pair-fed (PF), and sham-operated ad libitum (obese control). Ten days after operation, immunohistochemical quantification of NPY, alpha-MSH, and 5-HT(1B)-receptors in ARC and PVN was performed. Data were analyzed using ANOVA and Tukey's test.

RESULTS

Body weight decreased in RYGB (417 +/- 21 g; mean +/- SE) and in PF (436 +/- 14 g) rats 10 days after operation compared with obese control rats (484 +/- 15 g; p < 0.05 for each comparison). NPY in ARC, pPVN, and mPVN decreased by 43%, 43%, and 61%, respectively in RYGB and by 55%, 42%, and 71% in PF, respectively, compared with obese controls (p < 0.05 for each pairwise comparison). RYGB versus PF did not show differences. alpha-MSH in ARC, pPVN and mPVN increased by 35%, 175%, and 67%, respectively in RYGB and by 29%, 162%, and 116% in PF, respectively, compared with obese controls (each p < 0.05). In mPVN, alpha-MSH significantly decreased by 23% in RYGB versus PF (p < 0.05). 5-HT-(1B)-receptor in pPVN increased by 58% in RYGB and by 26% in PF, compared with obese controls (p < 0.05). Compared with obese controls, 5HT-(1B)-receptor in mPVN increased by 39% in RYGB (p < 0.05) and by 9% in PF (p > 0.05). An increase of 5-HT-(1B)-receptor in pPVN and mPVN occurred in RYGB versus PF (p < 0.05).

CONCLUSIONS

Obese rats that undergo weight loss after RYGB demonstrate changes in hypothalamic down regulation of NPY and up regulation of alpha-MSH and serotonin.

Nicotine infusion into rat ventromedial nuclei and effects on monoaminergic system

Nicotine increases satiety and reduces food intake (FI). We hypothesize that nicotine influences FI via alteration of serotonin (5HT) and dopamine (DA) concentration in ventromedial nucleus (VMN) and lateral hypothalamic area (LHA). Microdialysis cannulas were implanted into ipsilateral VMN and contralateral LHA. Nicotine or vehicle was infused for 60 min into VMN of overnight food-deprived rats, followed by ad lib food for 40 min. Hypothalamic changes in 5HT and DA concentrations were measured every 20 min. Intra-VMN nicotine induced a long-lasting increase in 5HT concentration and an increase in DA for a short duration in the VMN, associated with an increase in 5HT in the LHA. Our data suggest that the nicotine-induced hypophagia correlates with VMN and LHA monoaminergic changes.

Interleukin-1beta system in anorectic catabolic tumor-bearing rats

PURPOSE OF REVIEW

The onset of cancer anorexia and the accompanying neurological symptoms and signs involve the general influence of cytokines on the brain. Using methylcholanthrene to induce tumors in Fischer 344 rats, we measured various specific components of the cytokine-induced anorectic reaction, including: (1) IL-1beta system components (ligand, signaling receptor, receptor accessory proteins, and receptor antagonist); (2) TNF-alpha; (3) TGF-beta1; and (4) IFN-gamma in the tumor tissue, the liver and the brain.

RECENT FINDINGS

The data show that IL-1beta, TNF-alpha and IFN-gamma messenger RNA were detected in the tumor tissue of anorectic tumor-bearing rats. In brain regions, anorexia is associated with the upregulation of IL-1beta and its receptor mRNA. All other mRNA remained unchanged in the brain regions examined.

SUMMARY

This suggests that IL-1beta and its receptor may play a significant role in this model of cancer-associated anorexia. In vivo, the characterization of cytokine components in the brain may provide data for potential pharmacological interventions to ameliorate the anorexia of disease.

Tonic regulation of satiety by 5-HT1B receptors in the mouse: converging evidence from behavioural and c-fos immunoreactivity studies?

Activation of 5-HT(1B) receptors is thought to play an important role in the inhibitory influence of serotonin on feeding behaviour and body weight in mammals. Earlier studies have shown that 5-HT(1B)-knockout (KO) mice eat more and are heavier than wild-type (WT) controls and that the selective 5-HT(1B) receptor agonist CP-94,253 reduces food intake in food-deprived mice. Here we characterize the behavioural effects of both CP-94,253 and the selective 5-HT(1B) receptor antagonist SB224289 on feeding and other behaviours within the behavioural satiety sequence, and also report a c-fos mapping study using CP-94,253. CP-94,253 produced a dose-dependent suppression of food intake with a profile consistent with a selective effect on feeding behaviour. These effects were absent or reduced in 5-HT(1B)-KO mice and in WT mice pretreated with SB224289. SB224289 administered alone enhanced food intake consistent with impaired satiation; a similar effect was apparent in 5-HT(1B)-KO mice compared to WT. CP-94,253 induced c-fos in a range of structures previously implicated in the expression of feeding behaviour. These results suggest that the activation of 5-HT(1B) receptors is an important component of endogenous satiation mechanisms in the mouse.

Expression of serotonin receptors and role of serotonin in human prostate cancer tissue and cell lines

BACKGROUND

Increase in the number of serotonin (5-HT) releasing neuroendocrine (NE) cells has been shown to be correlated with tumor progression, loss of androgen dependence, and poor prognosis. Serotonin is a well-known mitogen which mediates a wide variety of physiological effects via multiple receptors, of which receptor subtype 1 (5-HTR1) has been identified in prostate cancer (PC) cell lines. Recently, 5-HT has been found to show growth-promoting activity and to be functionally related to oncogenes.

MATERIALS AND METHODS

Localization, protein content, and mRNA expression of 5-HTR subtype 1A, 1B, and 1D was studied in prostatic tissue (35 patients), metastases, PC cell lines, a benign prostatic stromal cell line (human prostate cell preparation (hPCP)), and xenografts of PC-3 cells by immunohistochemistry (IHC), Western blotting, and RT-PCR, respectively. The growth-inhibition effect of a 5-HT1A antagonist (NAN-190) on PC cell lines was studied using a bromodeoxyuridine (BrdU) assay.

RESULTS

A strong immunoreaction of 5-HTR1A and 1B was demonstrated in high-grade tumor cells (35/35) and a small number of BPH cells, whereas 5-HTR1D was confined to vascular endothelial cells. 5-HTR1A was also demonstrated in PC cells metastasized to lymph node and bone, PC-3, DU145, LNCaP, and in xenografts of PC-3 cells and hPCP. Western blot analysis gave strong bands from PC tissue extracts compared to BPH tissue. Using RT-PCR, 5-HTR1A mRNA was demonstrated in all PC cell lines. An antagonist of 5-HTR1A (NAN-190) inhibited the growth of PC-3, DU145, and LNCaP cells but not of hPCP cells.

CONCLUSIONS

This is the first study demonstrating an overexpression of 5-HTR subtypes 1A and 1B in PC cells, especially in high-grade tumors. Moreover, 5-HT stimulates proliferation of PC cells and 5-HTR1A antagonists inhibit proliferation. Thus, we propose that 5-HT has an important role in tumor progression, especially in the androgen-independent state of the disease. The design of specific antagonists for this type of receptor might be useful for the growth control of androgen-independent tumors.

Tumor anorexia: effects on neuropeptide Y and monoamines in paraventricular nucleus

Paraventricular (PVN) concentrations of neuropeptide Y (NPY), serotonin (5-HT) and dopamine (DA) in anorectic tumor-bearing (TB) rats were measured before and after tumor resection. At onset of anorexia in TB versus non-tumor bearing (NTB) Controls 5-HT increased from 12.19+/-0.49 pg/microg to 14.89+/-0.81 pg/microg ( P<0.05 ) while DA and NPY decreased from 7.34+/-0.42 pg/microg to 4.97+/-0.56 pg/microg and 23.47+/-4.27 pg/microg to 13.64+/-1.44 pg/microg, respectively ( P<0.05 ). After tumor resection, these neuromediators normalized when compared to sham-operated NTB rats. NTB pair-fed Controls were also studied. We conclude that the increased 5-HT and the decreased DA and NPY concentrations in PVN are associated with cancer anorexia and that the NPY food stimulatory effect is linked to serotoninergic and dopaminergic systems in hypothalamus.

Cachexia and obesity: two sides of one coin?

PURPOSE OF REVIEW

Leptin, a member of the interleukin-6 superfamily of proteins, modifies the gene expression and synthetic pathway of both orexigenic (appetite-stimulating) and anorexigenic (appetite-suppressing) molecules in the hypothalamus, thereby controlling adipocyte energy stores. Lack of leptin secretion or the inability of leptin to interact with these molecules via leptin receptors, prevent leptin's effects and lead to obesity. It is not well known, however, how these feeding-regulatory molecules are affected in cachexia associated with cancer and other critical conditions in which cytokines such as interleukin-1 and interleukin-6 may have a key role.

RECENT FINDINGS

Decreased leptin and increased leptin-like signaling by cytokines in the hypothalamus are the hallmark of obesity and cachexia, respectively. Increased orexigenic and impaired anorexigenic signaling produces hyperphagia and obesity, while the reverse applies to anorexia-cachexia in which adaptive feeding response to starvation is lacking or insufficient.

SUMMARY

Imbalanced operation of orexigenic and anorexigenic circuits perturbs the homeostatic loop of body weight regulation leading to either obesity or cachexia. Modifiers of the central effects on appetite and energy metabolism could restore the balance and be effective for treating both conditions. In cachexia this may especially be true when combined with agents that target muscle and protein breakdown.

Decreased NPY innervation of the hypothalamic nuclei in rats with cancer anorexia

Whether the decrease in food intake that occurs at the onset of anorexia in tumor bearing (TB) rats is related to a change in the hypothalamic neuropeptide Y (NPY) system was tested by comparing NPY expression in sham operated Fischer Control and anorectic TB rats. Coronal cryocut sections of their fixed brain were processed by the peroxidase-antiperoxidase method with NPY polyclonal antibodies. NPY-immunoreactive fibers were widely distributed throughout the forebrain, but were most prominent in the hypothalamic paraventricular, suprachiasmatic, arcuate and periventricular nuclei. NPY-immunoreactive neurons were visualized in Control and anorectic TB rats in the preoptic region, the arcuate nucleus, and occasionally in the lateral hypothalamus. Semiquantitative image analysis showed a significant decrease in the NPY immunostaining in some hypothalamic nuclei of the anorectic TB rats, most prominently in the supraoptic nucleus, the parvocellular portion of the paraventricular nucleus, and, to a lesser extent, the suprachiasmatic and arcuate nuclei. No changes in NPY innervation were seen in the ventromedial nucleus and the lateral hypothalamus. The data support the hypothesis of an altered hypothalamic NPY system at the onset of anorexia in TB rats and also reveal the hypothalamic nuclei through which NPY influences food intake.