Neurotensin-deficient mice show altered responses to antipsychotic drugs

Neurotensin receptor-1 antagonist SR48692 modulation of high-fat diet induced reproductive impairment in male mice

Neurotensin (NTS), a tridecapeptide of the gastrointestinal tract, has been implicated in the facilitation of lipid absorption on ingestion of a high-fat diet (HFD) especially via NTS receptors, NTSR1, NTSR2, and NTSR3, to cause lipid metabolic dysregulation and imbalance of the oxidant-antioxidant system. Oxidative stress induced a negative impact on reproductive function, affecting the reproductive organ and related reproductive hormones. The present study elucidated the efficacy of NTSR1 antagonist SR48692 in the modulation of HFD-induced reproductive impairment in male mice. Swiss albino mice (male, 23 ± 2 g) were maintained (6/group) for eight weeks; Group-I chow diet (CD), Group-II HFD, Group-III (HFD+SR48692L), Group-IV (HFD+SR48692H), Group-V (CD+SR48692L) and Group-VI (CD+SR48692H). SR48692 low (100 µg/kg b.w./SR48692L) and high-dose (400 µg/kg b.w./SR48692H) were given intraperitoneally for the last four weeks. Treatment with low-dose (SR48692L) to HFD-fed mice showed some efficacy in mitigating lipid dysregulation, oxidative stress, and reproductive impairment as evidenced by decreased triglycerides, total cholesterol, low-density lipoprotein cholesterol, leptin, and increased high-density lipoprotein cholesterol, increased antioxidant defense enzymes, reduction of histopathological scores in testis and increase in plasma level of LH, FSH and testosterone compared to that of HFD, but not up to CD. With the high-dose of antagonist (SR48692H) showed more adverse effects even from that of HFD. Treatment of both doses of SR48692 to CD-fed mice these effects become more extended. Less effectiveness of NTSR1 antagonist with the doses tried (low and high) in normalizing the lipid dysregulation and reproductive impairments might be due to the persistence of NTSR2/NTSR3-mediated lipid absorption.

Neurotensin differentially regulates bile acid metabolism and intestinal FXR-bile acid transporter axis in response to nutrient abundance

Studies demonstrate a role for neurotensin (NT) in obesity and related comorbidities. Bile acid (BA) homeostasis alterations are associated with obesity. We determined the effect of NT on BA metabolism in obese and non-obese conditions. Plasma and fecal BA profiles were analyzed by LC-MS/MS in male and female NT^+/+ and NT^-/- mice fed low-fat (LFD) or high-fat diet (HFD) for 6 weeks (early stage of obesity) or greater than 20 weeks (late stage of obesity). The nuclear farnesoid X receptor (FXR) and BA transporter mRNA expression were assessed in ileum, mouse enteroids, and human cell lines. HFD decreased plasma primary and secondary BAs in NT^+/+ mice; HFD-induced decrease of plasma BAs was improved in NT-deficient mice. In NT^+/+ mice, HFD inhibited ileal FXR and BA transporter expression; HFD-decreased expression of FXR and BA transporters was prevented in NT^-/- mice. Compared with LFD-fed NT^+/+ mice, LFD-fed NT^-/- mice had relatively lower levels of ileal FXR and BA transporter expression. Moreover, NT stimulates the expression of FXR and BA transporters in Caco-2 cells; however, stimulated expression of BA transporters was attenuated in NT^-/- enteroids. Therefore, we demonstrate that HFD disrupts the BA metabolism and ileal FXR and BA transporter axis which are improved in the absence of NT, suggesting that NT contributes to HFD-induced disruption of BA metabolism and plays an inhibitory role in the regulation of ileal FXR and BA transporter signaling under obese conditions. Conversely, NT positively regulates the expression of ileal FXR and BA transporters under non-obese conditions. Therefore, NT plays a dual role in obese and non-obese conditions, suggesting possible therapeutic strategies for obesity control.

Effect of clozapine dose and concentration on fasting concentration of appetite regulating peptides

The aim of this study is to analyze whether clozapine serum concentration may affect fasting serum levels of several appetite regulating peptides: CART, PYY(1-36), NPY, AgRP, des-acylated ghrelin, leptin and obestatin. Serum concentration of clozapine and fasting serum levels of des-acylated ghrelin, neuropeptide Y (NPY), agouti-related protein (AgRP), peptide YY (PYY(1-36)), cocaine- and amphetamine-regulated transcript (CART), leptin and obestatin were measured in 30 subjects with schizophrenia on clozapine monotherapy. Leptin concentration was negatively correlated with clozapine dose (r = -0.53, p = 0.002), while NPY concentration was negatively correlated with clozapine concentration (r = -0.55, p = 0.01). Correlations with other peptides were not significant. We cannot conclude that serum concentration of clozapine is directly associated with increased or decreased level of appetite-regulating peptides.

An obligatory role for neurotensin in high-fat-diet-induced obesity

Obesity and its associated comorbidities (for example, diabetes mellitus and hepatic steatosis) contribute to approximately 2.5 million deaths annually and are among the most prevalent and challenging conditions confronting the medical profession. Neurotensin (NT; also known as NTS), a 13-amino-acid peptide predominantly localized in specialized enteroendocrine cells of the small intestine and released by fat ingestion, facilitates fatty acid translocation in rat intestine, and stimulates the growth of various cancers. The effects of NT are mediated through three known NT receptors (NTR1, 2 and 3; also known as NTSR1, 2, and NTSR3, respectively). Increased fasting plasma levels of pro-NT (a stable NT precursor fragment produced in equimolar amounts relative to NT) are associated with increased risk of diabetes, cardiovascular disease and mortality; however, a role for NT as a causative factor in these diseases is unknown. Here we show that NT-deficient mice demonstrate significantly reduced intestinal fat absorption and are protected from obesity, hepatic steatosis and insulin resistance associated with high fat consumption. We further demonstrate that NT attenuates the activation of AMP-activated protein kinase (AMPK) and stimulates fatty acid absorption in mice and in cultured intestinal cells, and that this occurs through a mechanism involving NTR1 and NTR3 (also known as sortilin). Consistent with the findings in mice, expression of NT in Drosophila midgut enteroendocrine cells results in increased lipid accumulation in the midgut, fat body, and oenocytes (specialized hepatocyte-like cells) and decreased AMPK activation. Remarkably, in humans, we show that both obese and insulin-resistant subjects have elevated plasma concentrations of pro-NT, and in longitudinal studies among non-obese subjects, high levels of pro-NT denote a doubling of the risk of developing obesity later in life. Our findings directly link NT with increased fat absorption and obesity and suggest that NT may provide a prognostic marker of future obesity and a potential target for prevention and treatment.

Possible biomarkers modulating haloperidol efficacy and/or tolerability

Haloperidol (HP) is widely used in the treatment of several forms of psychosis. Despite of its efficacy, HP use is a cause of concern for the elevated risk of adverse drug reactions. adverse drug reactions risk and HP efficacy greatly vary across subjects, indicating the involvement of several factors in HP mechanism of action. The use of biomarkers that could monitor or even predict HP treatment impact would be of extreme importance. We reviewed the elements that could potentially be used as peripheral biomarkers of HP effectiveness. Although a validated biomarker still does not exist, we underlined the several potential findings (e.g., about cytokines, HP metabolites and genotypic biomarkers) which could pave the way for future research on HP biomarkers.

Repeated effects of the neurotensin receptor agonist PD149163 in three animal tests of antipsychotic activity: assessing for tolerance and cross-tolerance to clozapine

Neurotensin is an endogenous neuropeptide closely associated with the mesolimbic dopaminergic system and shown to possess antipsychotic-like effects. In particular, acute neurotensin receptor activation can inhibit conditioned avoidance response (CAR), attenuate phencyclidine (PCP)-induced prepulse inhibition (PPI) disruptions, and reverse PCP-induced hyperlocomotion. However, few studies have examined the long term effects of repeated neurotensin receptor activation and results are inconsistent. Since clinical administration of antipsychotic therapy often requires a prolonged treatment schedule, here we assessed the effects of repeated activation of neurotensin receptors using an NTS1 receptor selective agonist, PD149163, in 3 behavioral tests of antipsychotic activity. We also investigated whether reactivity to the atypical antipsychotic clozapine was altered following prior PD149163 treatment. Using both normal and prenatally immune activated rats generated through maternal immune activation with polyinosinic:polycytidylic acid, we tested PD149163 in CAR, PCP (1.5mg/kg)-induced PPI disruption, and PCP (3.2mg/kg)-induced hyperlocomotion. For each paradigm, rats were first repeatedly tested with vehicle or PD149163 (1.0, 4.0, 8.0mg/kg, sc) along with vehicle or PCP for PPI and hyperlocomotion tests, then challenged with PD149163 after 2 drug-free days. All rats were then challenged with clozapine (5.0mg/kg, sc). During the repeated test period, PD149163 exhibited antipsychotic-like effects in all three models. On the PD149163 challenge day, prior drug treatment only caused a tolerance effect in CAR. This tolerance in CAR was transferrable to clozapine, as it enhanced clozapine tolerance in the same group of animals. Although no tolerance effect was seen in the PD149163 challenge for the PCP-induced hyperlocomotion test, the clozapine challenge showed increased sensitivity in groups previously exposed to repeated PD149163 treatment. Our findings suggest that repeated exposure to NTS1 receptor agonists can induce a dose-dependent tolerance and cross-tolerance to clozapine to some of its behavioral effects but not others.

Striatal dopamine receptor plasticity in neurotensin deficient mice

Schizophrenia is thought to be caused, at least in part, by dysfunction in striatal dopamine neurotransmission. Both clinical studies and animal research have implicated the dopamine neuromodulator neurotensin (NT) in the pathophysiology of schizophrenia. Utilizing male mice lacking the NT gene (NT(-/-)), these studies examined the consequences of NT deficiency on dopaminergic tone and function, investigating (1) dopamine concentrations and dopamine receptor and transporter expression and binding in dopaminergic terminal regions, and (2) the behavioral effects of selective dopamine receptor agonists on locomotion and sensorimotor gating in adult NT(-/-) mice compared to wildtype (NT(+/+)) mice. NT(-/-) mice did not differ from NT(+/+) mice in concentrations of dopamine or its metabolite DOPAC in any brain region examined. However, NT(-/-) mice showed significantly increased D1 receptor, D2 receptor, and dopamine transporter (DAT) mRNA in the caudate putamen compared to NT(+/+) controls. NT(-/-) mice also showed elevated D2 receptor binding densities in both the caudate putamen and nucleus accumbens shell compared to NT(+/+) mice. In addition, some of the behavioral effects of the D1-type receptor agonist SKF-82958 and the D2-type receptor agonist quinpirole on locomotion, startle amplitude, and prepulse inhibition were dose-dependently altered in NT(-/-) mice, showing altered D1-type and D2-type receptor sensitivity to stimulation by agonists in the absence of NT. The results indicate that NT deficiency alters striatal dopamine receptor expression, binding, and function. This suggests a critical role for the NT system in the maintenance of striatal DA system homeostasis and implicates NT deficiency in the etiology of dopamine-associated disorders such as schizophrenia.

Endogenous CNS expression of neurotensin and neurotensin receptors is altered during the postpartum period in outbred mice

Neurotensin (NT) is a neuropeptide identical in mice and humans that is produced and released in many CNS regions associated with maternal behavior. NT has been linked to aspects of maternal care and previous studies have indirectly suggested that endogenous NT signaling is altered in the postpartum period. In the present study, we directly examine whether NT and its receptors exhibit altered gene expression in maternal relative to virgin outbred mice using real time quantitative PCR (qPCR) across multiple brain regions. We also examine NT protein levels using anti-NT antibodies and immunohistochemistry in specific brain regions. In the medial preoptic area (MPOA), which is critical for maternal behaviors, mRNA of NT and NT receptor 3 (Sort1) were significantly up-regulated in postpartum mice compared to virgins. NT mRNA was also elevated in postpartum females in the bed nucleus of the stria terminalis dorsal. However, in the lateral septum, NT mRNA was down-regulated in postpartum females. In the paraventricular nucleus of the hypothalamus (PVN), Ntsr1 expression was down-regulated in postpartum females. Neurotensin receptor 2 (Ntsr2) expression was not altered in any brain region tested. In terms of protein expression, NT immunohistochemistry results indicated that NT labeling was elevated in the postpartum brain in the MPOA, lateral hypothalamus, and two subregions of PVN. Together, these findings indicate that endogenous changes occur in NT and its receptors across multiple brain regions, and these likely support the emergence of some maternal behaviors.

Persistent gene expression changes in NAc, mPFC, and OFC associated with previous nicotine or amphetamine exposure

Highly addictive drugs like nicotine and amphetamine not only change an individual's behaviour in the short and long-term, they also induce persistent changes in neuronal excitability and morphology. Although research has started to examine the epigenetic changes that occur immediately after drug exposure, there has been little investigation into the persistent modifications to the epigenome that likely moderate the stable maintenance of the neurological changes. Male Long-Evans rats were administered amphetamine, nicotine, or saline for 14 consecutive days, given a 14 day withdrawal period, and then sacrificed. DNA from the mPFC, OFC, and nucleus accumbens (NAc) was used for global DNA methylation analysis and RNA from the same brain regions was used for gene expression analysis. Following the two-week withdrawal period, exposure to amphetamine or nicotine was associated with a decrease in global DNA methylation in each brain region examined. Previous exposure to nicotine was associated with changes in expression of 16 genes (NAc:6, mPFC:5, OFC:5) whereas exposure to amphetamine was associated with changes in expression of 25 genes (NAc:13, OFC:8, mPFC:4). The persistent epigenetic changes associated with exposure to amphetamine and nicotine were region and drug dependent, and differ from the latent epigenetic changes that occur immediately after drug exposure. The changes in DNA methylation are consistent with the gene expression results and provide further support to the notion that DNA methylation is the key regulatory mechanism for experience dependent changes.

Effects of neurotensin gene knockout in mice on the behavioral effects of cocaine

RATIONALE

The neuropeptide neurotensin (NT), which has been implicated in the modulation of dopamine signaling, is expressed in a subset of dopamine neurons and antagonism of the NT receptor has been reported to reduce psychostimulant-induced behavior. Gene knockout (KO) of the neurotensin/neuromedin N precursor provides an approach to delineating possible roles of endogenous NT in psychostimulant-induced responses.

OBJECTIVES

Involvement of NT in cocaine responses was examined by comparing acute and conditioned locomotor responses, conditioned place preference, and sensitization in wild-type (WT), heterozygous, and homozygous NT KO mice.

RESULTS

NT KO mice did not differ from their WT or heterozygous littermates in either baseline or acute cocaine-stimulated locomotor activity. The locomotor stimulant effects of cocaine were slightly prolonged in these mice under some, but not all, experimental conditions. The rewarding effects of cocaine as assessed in the conditioned place preference and conditioned locomotion paradigms were also similar between genotypes at all cocaine doses tested.

CONCLUSIONS

These results suggest that endogenous NT is not involved in cocaine-mediated behaviors in most circumstances, but under some conditions, a slight prolongation of the effects of cocaine was observed in the absence of endogenous NT.

Striatal NTS1 , dopamine D2 and NMDA receptor regulation of pallidal GABA and glutamate release--a dual-probe microdialysis study in the intranigral 6-hydroxydopamine unilaterally lesioned rat

The current microdialysis study elucidates a functional interaction between the striatal neurotensin NTS(1) receptor and the striatal dopamine D(2) and N-methyl-d-aspartic acid (NMDA) receptors in the regulation of striatopallidal gamma-aminobutyric acid (GABA) and glutamate levels after an ipsilateral intranigral 6-hydroxydopamine-induced lesion of the ascending dopamine pathways to the striatum. Lateral globus pallidus GABA levels were higher in the lesioned group while no change was observed in striatal GABA and glutamate levels. The 6-hydroxydopamine-induced lesion did not alter the ability of intrastriatal NT (10 nm) to counteract the decrease in pallidal GABA and glutamate levels induced by the dopamine D(2) -like receptor agonist quinpirole (10 μm). A more pronounced increase in the intrastriatal NMDA- (10 μm) induced increase in pallidal GABA levels was observed in the lesioned group while it attenuated the increase in striatal glutamate levels and amplified the increase in pallidal glutamate levels compared with that observed in the controls. NT enhanced the NMDA-induced increase in pallidal GABA and glutamate and striatal glutamate levels; these effects were counteracted by the NTS(1) antagonist SR48692 (100 nm) in both groups. These findings demonstrate an inhibitory striatal dopamine D(2) and an excitatory striatal NMDA receptor regulation of striatopallidal GABA transmission in both groups. These actions are modulated by NT via antagonistic NTS(1) /D(2) and facilitatory NTS(1) /NMDA receptor-receptor interactions, leading to enhanced glutamate drive of the striatopallidal GABA neurons associated with motor inhibition, effects which all are counteracted by SR48692. Thus, NTS(1) antagonists in combination with conventional treatments may provide a novel therapeutic strategy in Parkinson's disease.

Hyperactivity of the dopaminergic system in NTS1 and NTS2 null mice

Neurotensin (NT) is a tridecapeptide that acts as a neuromodulator in the central nervous system mainly through two NT receptors, NTS1 and NTS2. The functional-anatomical interactions between NT, the mesotelencephalic dopamine system, and structures targeted by dopaminergic projections have been studied. The present study was conducted to determine the effects of NT receptor subtypes on dopaminergic function with the use of mice lacking either NTS1 (NTS1(-/-)) or NTS2 (NTS2(-/-)). Basal and amphetamine-stimulated locomotor activity was determined. In vivo microdialysis in freely moving mice, coupled with HPLC-ECD, was used to detect basal and d-amphetamine-stimulated striatal extracellular dopamine levels. In vitro radioligand binding and synaptosomal uptake assays for the dopamine transporters were conducted to test for the expression and function of the striatal pre-synaptic dopamine transporter. NTS1(-/-) and NTS2(-/-) mice had higher baseline locomotor activity and higher basal extracellular dopamine levels in striatum. NTS1(-/-) mice showed higher locomotor activity and exaggerated dopamine release in response to d-amphetamine. Both NTS1(-/-) and NTS2(-/-) mice exhibited lower dopamine D(1) receptor mRNA expression in the striatum relative to wild type mice. Dopamine transporter binding and dopamine reuptake in striatum were not altered. Therefore, lack of either NTS1 or NTS2 alters the dopaminergic system. The possibility that the dysregulation of dopamine transmission might stem from a deficiency in glutamate neurotransmission is discussed. The data strengthen the hypothesis that NT receptors are involved in the pathogenesis of schizophrenia and provide a potential model for the biochemical changes of the disease.

Effect of amphetamine on extracellular concentrations of amino acids in striatum in neurotensin subtype 1 and 2 receptor null mice: a possible interaction between neurotensin receptors and amino acid systems for study of schizophrenia

Neurotensin (NT) is a tridecapeptide that acts as a neuromodulator in the central nervous system mainly through two NT receptors: NTS1 and NTS2. The present study was done to determine the roles of NTS1 and NTS2 on amino acid release in striatum with the use of NTS1 or NTS2 knockout ((-/-)) mice given d-amphetamine. Both NTS1(-/-) and NTS2(-/-) mice had lower extracellular concentrations of D-serine in striatum than did wild type (WT) mice. NTS2(-/-) but not NTS1(-/-) mice also had significantly lower basal concentrations of glutamate in striatum as compared to that for WT mice. Systemic administration of d-amphetamine (4 mg/kg, ip) increased glutamate release by 500% in WT mice, as compared to 300% in NTS2(-/-) mice, and 250% in NTS1(-/-) mice. Additionally, d-amphetamine injection caused a 4-fold increase in GABA release in both WT and NTS2(-/-) mice, but only a 2-fold increase in NTS1(-/-) mice. Therefore, NTS1 and NTS2 modulate basal release of D-serine and glutamate, and also d-amphetamine-induced GABA and glutamate release in striatum. These results provide further support for the involvement of NT receptors in the pathogenesis of schizophrenia and provide a better understanding of the imbalance of amino acid systems through investigation of a DA-based animal model.

Neurotensin induces IL-6 secretion in mouse preadipocytes and adipose tissues during 2,4,6,-trinitrobenzensulphonic acid-induced colitis

Mesenteric fat is known to undergo inflammatory changes after 2,4,6,-trinitrobenzensulphonic acid (TNBS)-induced colitis. Neurotensin (NT) and neurotensin receptor 1 (NTR1) have been shown to play a major role in the pathogenesis of intestinal inflammation. This led us to explore whether NT and NTR1 are expressed in the mesenteric fat depots during TNBS-induced colitis and whether NT participates in the increased interleukin (IL)-6 secretion in this inflammatory response. TNBS-induced inflammation in the colon increases NT and NTR1 expression in mesenteric adipose tissues, including mesenteric preadipocytes. Compared with wild-type mice, NT knockout (KO) mice have reduced TNBS-induced colitis accompanied by diminished inflammatory responses in mesenteric adipose tissue. Specifically, IL-6 and p65 phosphorylation levels in mesenteric fat of NT KO mice are also reduced compared with wild-type mice. Mouse 3T3-L1 preadipocytes express NTR1 and its expression is increased after stimulation of preadipocytes with proinflammatory cytokines. NT stimulation of 3T3-L1 preadipocytes overexpressing NTR1 causes PKCdelta phosphorylation and IL-6 secretion in a time- and dose-dependent fashion. Moreover, NT-mediated IL-6 expression is nuclear factor-kappaB and PKCdelta dependent. We also found that supernatants from NT-exposed 3T3-L1-NTR1 preadipocytes and mesenteric fat obtained from wild-type mice 2 days after TNBS administration stimulate an IL-6-dependent macrophage migration measured by a macrophage migration assay, whereas this response is reduced when mesenteric fat from NT KO mice is used. These results demonstrate an important role for NT in acute colitis and adipose tissue inflammation associated with experimental colitis that involves direct NT proinflammatory responses in preadipocytes.

Hormonal regulation of clonal, immortalized hypothalamic neurons expressing neuropeptides involved in reproduction and feeding

The hypothalamus has been particularly difficult to study at the molecular level because of the inherent cellular heterogeneity and complexity of neuronal circuits within. We have generated a large number of immortalized, clonal cell lines through retroviral gene transfer of the oncogene SV40 T-Ag into primary murine hypothalamic neuronal cell cultures. A number of these neuronal cell lines express neuropeptides linked to the control of feeding behavior and reproduction, including neuropeptide Y (NPY) and neurotensin (NT). We review recent studies on the direct regulation of NPY gene expression by estrogen, and the leptin-mediated control of signal transduction pathways and NT transcription. These studies provide new insights into the direct control of neuropeptide synthesis by hormones and nutrients at a mechanistic level in the individual neuron, not yet possible in the whole brain. Using these novel cell models, we expect to contribute substantially to the understanding of how individual neuronal cell types control overall endocrine function, especially with regard to two of the most well-known roles of distinct peptidergic neurons; these being the control of reproduction and energy homeostasis.

Neurotensin increases mortality and mast cells reduce neurotensin levels in a mouse model of sepsis

Sepsis is a complex, incompletely understood and often fatal disorder, typically accompanied by hypotension, that is considered to represent a dysregulated host response to infection. Neurotensin (NT) is a 13-amino-acid peptide that, among its multiple effects, induces hypotension. We find that intraperitoneal and plasma concentrations of NT are increased in mice after severe cecal ligation and puncture (CLP), a model of sepsis, and that mice treated with a pharmacological antagonist of NT, or NT-deficient mice, show reduced mortality during severe CLP. In mice, mast cells can degrade NT and reduce NT-induced hypotension and CLP-associated mortality, and optimal expression of these effects requires mast cell expression of neurotensin receptor 1 and neurolysin. These findings show that NT contributes to sepsis-related mortality in mice during severe CLP and that mast cells can lower NT concentrations, and suggest that mast cell-dependent reduction in NT levels contributes to the ability of mast cells to enhance survival after CLP.

Neurotensin receptor mechanisms and its modulation of glutamate transmission in the brain: relevance for neurodegenerative diseases and their treatment

The extracellular accumulation of glutamate and the excessive activation of glutamate receptors, in particular N-methyl-D-aspartate (NMDA) receptors, have been postulated to contribute to the neuronal cell death associated with chronic neurodegenerative disorders such as Parkinson's disease. Findings are reviewed indicating that the tridecaptide neurotensin (NT) via activation of NT receptor subtype 1 (NTS1) promotes and reinforces endogenous glutamate signalling in discrete brain regions. The increase of striatal, nigral and cortical glutamate outflow by NT and the enhancement of NMDA receptor function by a NTS1/NMDA interaction that involves the activation of protein kinase C may favour the depolarization of NTS1 containing neurons and the entry of calcium. These results strengthen the hypothesis that NT may be involved in the amplification of glutamate-induced neurotoxicity in mesencephalic dopamine and cortical neurons. The mechanisms involved may include also antagonistic NTS1/D2 interactions in the cortico-striatal glutamate terminals and in the nigral DA cell bodies and dendrites as well as in the nigro-striatal DA terminals. The possible increase in NT levels in the basal ganglia under pathological conditions leading to the NTS1 enhancement of glutamate signalling may contribute to the neurodegeneration of the nigro-striatal dopaminergic neurons found in Parkinson's disease, especially in view of the high density of NTS1 receptors in these neurons. The use of selective NTS1 antagonists together with conventional drug treatments could provide a novel therapeutic approach for treatment of Parkinson's disease.

Neurotensin reduces glutamatergic transmission in the dorsolateral striatum via retrograde endocannabinoid signaling

Neurotensin is a peptide that has been suggested to mimic the actions of antipsychotics, but little is known about how it affects synaptic transmission in the striatum, the major input nucleus of the basal ganglia. In this study we measured the effects of neurotensin on EPSCs from medium spiny projection neurons in the sensorimotor striatum, a region implicated in habit formation and control of motor sequences. We found that bath-applied neurotensin reduced glutamate release from presynaptic terminals, and that this effect required retrograde endocannabinoid signaling, as it was prevented by the CB1 cannabinoid receptor antagonist AM251. Neurotensin-mediated inhibition of striatal EPSCs was also blocked by antagonists of D2-like dopamine receptors and group I metabotropic glutamate receptors, as well as by intracellular calcium chelation and phospholipase C inhibition. These results suggest that neurotensin can indirectly engage an endocannabinoid-mediated negative feedback signal to control glutamatergic input to the basal ganglia.

Medical sequencing at the extremes of human body mass

Body weight is a quantitative trait with significant heritability in humans. To identify potential genetic contributors to this phenotype, we resequenced the coding exons and splice junctions of 58 genes in 379 obese and 378 lean individuals. Our 96-Mb survey included 21 genes associated with monogenic forms of obesity in humans or mice, as well as 37 genes that function in body weight-related pathways. We found that the monogenic obesity-associated gene group was enriched for rare nonsynonymous variants unique to the obese population compared with the lean population. In addition, computational analysis predicted a greater fraction of deleterious variants within the obese cohort. Together, these data suggest that multiple rare alleles contribute to obesity in the population and provide a medical sequencing-based approach to detect them.

Neurotensin: role in psychiatric and neurological diseases

Neurotensin (NT), an endogenous brain-gut peptide, has a close anatomical and functional relationship with the mesocorticolimbic and neostriatal dopamine system. Dysregulation of NT neurotransmission in this system has been hypothesized to be involved in the pathogenesis of schizophrenia. Additionally, NT containing circuits have been demonstrated to mediate some of the mechanisms of action of antipsychotic drugs, as well as the rewarding and/or sensitizing properties of drugs of abuse. NT receptors have been suggested to be novel targets for the treatment of psychoses or drug addiction.

Corticotropin-releasing hormone induces skin vascular permeability through a neurotensin-dependent process

Many skin disorders are associated with increased numbers of activated mast cells and are worsened by stress; however, the mechanism underlying these processes is not understood. Corticotropin-releasing hormone (CRH) is secreted under stress from the hypothalamus, but also in the skin, where it induces mast cell activation and vascular permeability. We investigated the effect of CRH in a number of animal models by using i.v. Evans blue extravasation as a marker of vascular permeability. Intradermal CRH is among the most potent peptides at 100 nM, its effect being nearly comparable to that of neurotensin (NT). Pretreatment of skin injection sites with the NT receptor antagonist SR48692 blocks CRH-induced vascular permeability, which is diminished in NT-/- mice, implying that NT is necessary for the effect of CRH. CRH and NT precursor mRNA are shown to be expressed in both dorsal root ganglia and skin, whereas the latter also expresses mRNA for prohormone convertase 5, an enzyme that cleaves pro-NT into its active form. We also show that the effect of both CRH and NT is absent in W/W(v) mast cell-deficient mice; however, only a fraction of skin mast cells express CRH receptors, as shown by FACS analysis of CRH receptor (CRHR) and c-kit double-positive disaggregated mouse skin mast cells. These findings suggest that CRH induces skin vascular permeability through NT acting on mast cells and that both peptides should be considered in the pathogenesis of skin disorders exacerbated by stress.

Amphetamine-elicited striatal Fos expression is attenuated in neurotensin null mutant mice

Neurotensin (NT) has been suggested to interact with dopamine systems in different forebrain sites to exert both antipsychotic- and psychostimulant-like effects. We previously found that genetic or pharmacological manipulations that disrupt endogenous NT signaling attenuate antipsychotic drug-induced Fos expression in the dorsolateral and central striatum but not other striatal regions. To assess the role of NT in psychostimulant responses, we examined the ability of d-amphetamine (AMP) to induce Fos in wild-type and NT null mutant mice. AMP-elicited Fos expression was significantly attenuated in the medial striatum of NT null mutant mice, but was unaffected in other striatal territories. Similar results were obtained in rats and mice pretreated with the high affinity neurotensin receptor (NTR1) antagonist SR 48692. The effect of the NTR1 antagonist was particularly apparent in the striatal patch (striosome) compartment, as defined by mu-opioid receptor immunoreactivity. These data suggest that NT is required for the full activation by AMP of medial striatal neurons.

Anorexigenic hormones leptin, insulin, and alpha-melanocyte-stimulating hormone directly induce neurotensin (NT) gene expression in novel NT-expressing cell models

Neurotensin (NT) is implicated in the regulation of energy homeostasis, in addition to its many described physiological functions. NT is postulated to mediate, in part, the effects of leptin in the hypothalamus. We generated clonal, immortalized hypothalamic cell lines, N-39 and N-36/1, which are the first representative NT-expressing cell models available for the investigation of NT gene regulation and control mechanisms. The cell lines express the Ob-Rb leptin receptor neuropeptide Y (NPY)-Y1, Y2, Y4, Y5 receptors, melanocortin 4 receptor, insulin receptor, and the NT receptor. NT mRNA levels are induced by approximately 1.5-fold to twofold with leptin, insulin, and alpha-melanocyte stimulating hormone treatments but not by NPY. Leptin-mediated induction of NT gene expression was biphasic at 10(-11) and 10(-7) M. The leptin responsive region was localized to within -381 to -250 bp of the 5' regulatory region of the NT gene. Furthermore, we demonstrated direct leptin-mediated signal transducers and activators of transcription (STAT) binding to this region at 10(-11) m, but not 10(-7) m leptin, in chromatin precipitation assays. Leptin-induced NT regulation was attenuated by dominant-negative STAT3 protein expression. These data support the hypothesis that NT may have a direct role in the neuroendocrine control of feeding and energy homeostasis.

Neurotensin-Deficient Mice Have Deficits in Prepulse Inhibition: Restoration by Clozapine but Not Haloperidol, Olanzapine, or Quetiapine

Prepulse inhibition (PPI) of the acoustic startle reflex is a commonly used measure of preattentive sensorimotor gating. Disrupted PPI in rodents represents an animal model of the sensorimotor gating deficits characteristic of schizophrenia. The neurotensin (NT) system is implicated in the pathophysiology of schizophrenia, and NT has been hypothesized to act as an endogenous antipsychotic. In rats, NT receptor agonists restore PPI disrupted by dopamine receptor agonists and N-methyl-D-aspartate receptor antagonists, and pretreatment with an NT receptor antagonist blocks restoration of isolation rearing induced deficits in PPI by some antipsychotic drugs. The current studies further scrutinized the role of the NT system in the regulation of PPI and in antipsychotic drug-induced restoration of PPI using NT-null mutant mice (NT-/-). NT-/- mice exhibited significantly higher pulse alone startle amplitudes and disrupted PPI compared with NT+/+ mice. Haloperidol (0.1 mg/kg) and quetiapine (0.5 mg/kg) administered 30 min before PPI testing significantly increased PPI in NT+/+ mice but had no effect on PPI in NT-/- mice. In contrast, clozapine (1.0 mg/kg) significantly increased PPI in both NT-/- and NT+/+ mice, whereas olanzapine (0.5 mg/kg) had no effect on PPI in either NT-/- or NT+/+ mice. In a separate experiment, amphetamine (2.0 mg/kg i.p.) significantly disrupted PPI in NT+/+ mice but not NT-/- mice. These results provide evidence that the effects of antipsychotic drugs (APDs) may be differentially affected by the state of NT neurotransmission and, moreover, that APDs differ in their dependence on an intact NT system.

Neurotensin receptor antagonist SR 142948A alters Fos expression and extrapyramidal side effect profile of typical and atypical antipsychotic drugs

Antipsychotic drugs (APDs) have previously been shown to alter Fos expression in a regionally specific manner. Increases in Fos expression in the nucleus accumbens (NAcc) are common to all clinically effective APDs. In contrast, APD-induced Fos expression increases in the caudate-putamen (CPu) and prefrontal cortex (PFC) are associated with the extrapyramidal side effect liability of typical APDs or the effectiveness against negative symptoms of atypical APDs, respectively. Considerable evidence suggests that the neuropeptide neurotensin (NT) mediates some of the effects of APDs. To determine whether NT neurotransmission is also involved in APD-induced Fos expression in brain regions relevant for therapeutic efficacy, the NT receptor antagonist SR 142948A (10 or 100 microg/kg i.p.) was coadministered with APDs (haloperidol (2.0 mg/kg s.c.), olanzapine (5 mg/kg i.p.), or clozapine (20 mg/kg s.c.)). Fos expression was evaluated in the PFC, NAcc shell, dorsomedial, and dorsolateral CPu and the lateral septum. SR 142948A attenuated haloperidol-induced Fos expression in the CPu but, in contrast, increased olanzapine-induced Fos expression in this brain region. The effects of the NT receptor antagonist were paralleled by its effects on catalepsy in olanzapine--but not haloperidol--treated animals.

Endogenous neurotensin attenuates dopamine-dependent locomotion and stereotypy

The neuropeptide neurotensin (NT) is highly sensitive to changes in dopaminergic signaling in the striatum, and is thought to modulate dopamine-mediated behaviors. To explore the interaction of NT with the dopamine system, we utilized mice with a targeted deletion of dopamine synthesis specifically in dopaminergic neurons. Dopamine levels in dopamine-deficient (DD) mice are less than 1% of control mice, and they require daily administration of the dopamine precursor L-dihydroxyphenylalanine (L-DOPA) for survival. DD mice are supersensitive to the effects of dopamine, becoming hyperactive relative to control mice in the presence of L-DOPA. We show that 24 h after L-DOPA treatment, when DD mice are in a "dopamine-depleted" state, Nt mRNA levels in the striatum of DD mice are similar to those in control mice. Administration of L-DOPA or L-DOPA plus the L-amino acid decarboxylase inhibitor, carbidopa, (C/L-DOPA) induced Nt expression in the striatum of DD mice. The dopamine D1 receptor antagonist, SCH23390, blocked C/L-DOPA-induced Nt. To test the hypothesis that this striatal Nt expression modulated dopamine-mediated behavior in DD mice, we administered SR 48692, an antagonist of the high affinity NT receptor, together with L-DOPA or C/L-DOPA. L-DOPA-induced hyperlocomotion and C/L-DOPA-induced stereotypy were potentiated by peripheral administration of SR 48692. Furthermore, intrastriatal microinjections of SR 48692 augmented L-DOPA-induced hyperlocomotion. These results demonstrate a dynamic regulation of striatal Nt expression by dopamine via D1 receptors in DD mice, and point to a physiological role for endogenous striatal NT in counteracting motor behaviors induced by an overactive dopamine system.

Blockade of neurotensin receptors affects differently hypo-locomotion and catalepsy induced by haloperidol in mice

Antipsychotic drug treatment increases neurotensin (NT) neurotransmission, and the exogenous administration of NT produces antipsychotic-like effects in rodents. In order to investigate whether "endogenous" NT may act as a natural occurring antipsychotic or may mediate antipsychotic drug activity, the effects of the selective NT receptor antagonists SR 48692 and SR 142948A were analyzed in different behavioural tests of locomotor activity using vehicle, amphetamine, or haloperidol in mice. SR 48692 (0.1-1 mg/kg, i.p.) and SR 142948A (0.03-0.1 mg/kg, i.p.) failed to affect mouse spontaneous locomotor activity and amphetamine-induced (2.5 mg/kg, i.p.) hyper-locomotion. However, SR 48692 (0.1 and 0.3 mg/kg, i.p.) and SR 142948A (0.03 and 0.05 mg/kg, i.p.) significantly alleviated the reduction of locomotor activity elicited by haloperidol (0.01 and 0.04 mg/kg, s.c.) in vehicle- or amphetamine-treated mice. Finally, SR 48692 (0.3 mg/kg, i.p.) and SR 142948A (0.05 and 0.1 mg/kg, i.p.) increased mouse catalepsy produced by haloperidol (0.3 mg/kg, s.c.). The present results indicate that while endogenous NT is not involved in the modulation of either mouse spontaneous locomotor activity or amphetamine-induced hyper-locomotion, it might act by enhancing the therapeutic effects of haloperidol and by attenuating the extrapyramidal side effects elicited by this antipsychotic.

The transcription factor NGFI-B (Nur77) and retinoids play a critical role in acute neuroleptic-induced extrapyramidal effect and striatal neuropeptide gene expression

Despite extensive investigation, the cellular mechanisms responsible for neuroleptic actions remain elusive. We have previously shown that neuroleptics modulated the expression of some members of the ligand-activated transcription factors (nuclear receptors) including the nerve-growth factor inducible gene B (NGFI-B or Nur77) and retinoid X receptor (RXR) isoforms. Using genetic and pharmacological approaches, we investigated the role of NGFI-B and retinoids in acute behavioral and biochemical responses to dopamine antagonists. NGFI-B knockout (KO) mice display a profound alteration of haloperidol-induced catalepsy and striatal neuropeptide gene expression. Haloperidol-induced increase of striatal enkephalin mRNA is totally abolished in NGFI-B KO mice whereas the increase of neurotensin mRNA expression is reduced by 50%. Interestingly, catalepsy induced by raclopride, a specific dopamine D(2)/D(3) antagonist is completely abolished in NGFI-B-deficient mice whereas the cataleptic response to SCH 23390, a dopamine D(1) agonist, is preserved. Accordingly, the effects of haloperidol on striatal c-fos, Nor-1, and dynorphin mRNA expression are also preserved in NGFI-B-deficient mice. The cataleptic response and the increase of enkephalin mRNA expression induced by haloperidol can also be suppressed by administration of retinoid ligands 9-cis retinoic acid and docosahexaenoic acid. In addition, we demonstrate that haloperidol enhances colocalization of NGFI-B and RXRgamma1 isoform mRNAs, suggesting that both NGFI-B and a RXR isoform are highly coexpressed after haloperidol administration. Our data demonstrate, for the first time, that NGFI-B and retinoids are actively involved in the molecular cascade induced by neuroleptic drugs.

Endogenous neurotensin facilitates visceral nociception and is required for stress-induced antinociception in mice and rats

Central neurotensin (NT) administration can both facilitate and inhibit somatic and visceral nociception, depending on the dose and administration site. NT microinjection in the rostroventral medulla facilitates nociception at low doses, while NT antagonist microinjection can markedly attenuate nociception, supporting the hypothesis that endogenous NT facilitates nociception. However, higher doses of NT produce a mu-opioid receptor-independent analgesia, similar to that resulting from various intense stressors. Furthermore, intense stress results in increased NT expression in several hypothalamic nuclei that have been implicated in stress-induced antinociception (SIAN); however, there is little direct evidence that endogenous NT is required for SIAN. We have investigated the role of endogenous NT in both basal visceral nociception and SIAN using both NT knockout mice and pharmacological approaches in rats. Visceral nociception was monitored by measuring visceromotor responses during colorectal distension both prior to and following water avoidance stress. Visceral nociception was significantly attenuated in both NT knockout mice and rats pre-treated with the NT antagonist SR 48692. Disruption of NT signaling also blocked SIAN, revealing a novel stress-induced hyperalgesic response that was significantly greater in female than in male rats. NT was also required for acetic acid-induced hyperalgesia. These results indicate that endogenous NT normally facilitates visceral pain responses, is required for irritant-induced hyperalgesia, and plays a critical role in SIAN.

Neurotensin agonists: possible drugs for treatment of psychostimulant abuse

Although many neuropeptides have been implicated in the pathophysiology of psychostimulant abuse, the tridecapeptide neurotensin holds a prominent position in this field due to the compelling literature on this peptide and psychostimulants. These data strongly support the hypothesis that a neurotensin agonist will be clinically useful to treat the abuse of psychostimulants, including nicotine. This paper reviews the evidence for a role for neurotensin in stimulant abuse and for a neurotensin agonist for its treatment.

Neurotensin: dual roles in psychostimulant and antipsychotic drug responses

Central administration of neurotensin (NT) results in a variety of neurobehavioral effects which, depending upon the administration site, resemble the effects of antipsychotic drugs (APDs) and psychostimulants. All clinically effective APDs exhibit significant affinities for dopamine D(2) receptors, supporting the hypothesis that an increase in dopaminergic tone contributes to schizophrenic symptoms. Psychostimulants increase extracellular dopamine (DA) levels and chronics administration can produce psychotic symptoms over time. APDs and psychostimulants induce Fos and NT expression in distinct striatal subregions, suggesting that changes in gene expression underlie some of their effects. To gain insight into the functions of NT, we analyzed APD and psychostimulant induction of Fos in NT knockout mice and rats pretreated with the NT antagonist SR 48692. In both NT knockout mice and rats pretreated with SR 48692, haloperidol-induced Fos expression was markedly attenuated in the dorsolateral striatum; amphetamine-induced Fos expression was reduced in the medial striatum. These results indicate that NT is required for the activation of specific subpopulations of striatal neurons in distinct striatal subregions in response to both APDs and psychostimulants. This review integrates these new findings with previous evidence implicating NT in both APD and psychostimulant responses.

Neuropeptides, food intake and body weight regulation: a hypothalamic focus

Energy homeostasis is controlled by a complex neuroendocrine system consisting of peripheral signals like leptin and central signals, in particular, neuropeptides. Several neuropeptides with anorexigenic (POMC, CART, and CRH) as well as orexigenic (NPY, AgRP, and MCH) actions are involved in this complex (partly redundant) controlling system. Starvation as well as overfeeding lead to changes in expression levels of these neuropeptides, which act downstream of leptin, resulting in a physiological response. In this review the role of several anorexigenic and orexigenic (hypothalamic) neuropeptides on food intake and body weight regulation is summarized.

Targeted inactivation of the neurotensin type 1 receptor reveals its role in body temperature control and feeding behavior but not in analgesia

Three subtypes of neurotensin receptor have been described, two members of the heptahelical transmembrane domain G protein-coupled receptor superfamily NT-1R and NT-2R, and NT-3R unrelated to this family. We have generated NT-1R deficient (NT-1R(-/-)) mice. NT-1R(-/-) mice were born at the expected Mendelian frequency without obvious abnormalities and they were fertile. The NT-induced analgesia on the writhing induced by phenyl-p-benzoquinone administration remained at wild-type levels in the NT-1R(-/-) mice demonstrating that the NT-1R is not implicated in the analgesic effect of NT in this test. The NT-1R(-/-) mice were hyperthermic; their body temperature was not affected by intracerebroventricular (i.c.v.) administration of NT, contrasting with the hypothermia induced in NT-1R(+/+) mice. NT-1R(-/-) mice showed a small significant increase in body weight compared to the NT-1R(+/+) congeners as early as 10 weeks after birth, correlated with a higher food intake. NT-1R(-/-) mice showed similar spontaneous locomotion to the control littermates, but did not respond to i.c.v. NT-induced hypolocomotion. I.c.v. injection of NT inhibited feeding in fasted wild-type mice, but had no effect on feeding of the NT-1R(-/-) mice. I.c.v. administration of the orexigenic neuropeptide Y (NPY) stimulated feeding to the same extent in both wild-type and NT-1R(-/-) mice. This analysis of NT-1R-deficient mice shows that the NT-1R does not play a role in NT-induced analgesia, but that it is clearly implicated in thermal and feeding regulation, weight control, and NT-induced hypolocomotion.

Neurotensin analog selective for hypothermia over antinociception and exhibiting atypical neuroleptic-like properties

Neurotensin (NT) is a tridecapeptide neurotransmitter in the central nervous system. It has been implicated in the therapeutic effects of neuroleptics. Central activity of NT can only be demonstrated by direct injection into the brain, since it is readily degraded by peptidases in the periphery. We have developed many NT(8-13) analogs that are resistant to peptidase degradation and can cross the blood-brain barrier (BBB). In this study, we report on one of these analogs, NT77L. NT77L induced hypothermia (ED(50)=6.5 mg/kg, i.p.) but induced analgesia only at the highest dose examined (20 mg/kg, i.p.). Like the atypical neuroleptic clozapine, NT77L blocked the climbing behavior in rats induced by the dopamine agonist apomorphine (600 microg/kg) with an ED(50) of 5.6 mg/kg (i.p.), without affecting the licking and the sniffing behaviors. By itself NT77L did not cause catalepsy, but it moderately reversed haloperidol-induced catalepsy with an ED(50) of 6.0 mg/kg (i.p.). Haloperidol alone did not lower body temperature, but it potentiated the body temperature lowering effect of NT77L. In studies using in vivo microdialysis NT77L showed similar effects on dopamine turnover to those of clozapine, and significantly different from those of haloperidol in the striatum. In the prefrontal cortex, NT77L significantly increased serotonergic transmission as evidenced by increased 5-hydroxyindole acetic acid:5-hydroxytryptamine (5-HIAA:5-HT) ratio. Thus, NT77L selectively caused hypothermia, over antinociception, while exhibiting atypical neuroleptic-like effects.