A novel neurotensin peptide analog given extracranially decreases food intake and weight in rodents

Hungry for relief: Potential for neurotensin to address comorbid obesity and pain

Chronic pain and obesity frequently occur together. An ideal therapy would alleviate pain without weight gain, and most optimally, could promote weight loss. The neuropeptide neurotensin (Nts) has been separately implicated in reducing weight and pain but could it be a common actionable target for both pain and obesity? Here we review the current knowledge of Nts signaling via its receptors in modulating body weight and pain processing. Evaluating the mechanism by which Nts impacts ingestive behavior, body weight, and analgesia has potential to identify common physiologic mechanisms underlying weight and pain comorbidities, and whether Nts may be common actionable targets for both.

Bee Pollen and Probiotics May Alter Brain Neuropeptide Levels in a Rodent Model of Autism Spectrum Disorders

Neuropeptides play a major role in maintaining normal brain development in children. Dysfunction of some specific neuropeptides can lead to autism spectrum disorders (ASD) in terms of social interaction and repetitive behavior, but the exact underlying etiological mechanisms are still not clear. In this study, we used an animal model of autism to investigate the role of bee pollen and probiotic in maintaining neuropeptide levels in the brain. We measured the Alpha-melanocyte-stimulating hormone (α-MSH), Beta-endorphin (β-End), neurotensin (NT), and substance P (SP) in brain homogenates of six studied groups of rats. Group I served as control, given only PBS for 30 days; Group II as an autistic model treated with 250 mg PPA/kg BW/day for 3 days after being given PBS for 27 days. Groups III-VI were denoted as intervention groups. G-III was treated with bee pollen (BP) 250 mg/kg body weight/day; G-IV with Lactobacillus paracaseii (LB) (109 CFU/mL) suspended in PBS; G-V with 0.2 g/kg body weight/day Protexin^®, a mixture of probiotics (MPB); and G-VI was transplanted with stool from normal animals (FT) for 27 days prior to the induction of PPA neurotoxicity on the last 3 days of study (days 28–30). The obtained data were analyzed through the use of principal component analysis (PCA), discriminant analysis (DA), hierarchical clustering, and receiver operating characteristic (ROC) curves as excellent statistical tools in the field of biomarkers. The obtained data revealed that brain levels of the four measured neuropeptides were significantly reduced in PPA-treated animals compared to healthy control animals. Moreover, the findings demonstrate the ameliorative effects of bee pollen as a prebiotic and of the pure or mixed probiotics. This study proves the protective effects of pre and probiotics against the neurotoxic effects of PPA presented as impaired levels of α-MSH, β-End, NT, and SP.

Time to drink: Activating lateral hypothalamic area neurotensin neurons promotes intake of fluid over food in a time-dependent manner

The lateral hypothalamic area (LHA) is essential for ingestive behavior but has primarily been studied in modulating feeding, with comparatively scant attention on drinking. This is partly because most LHA neurons simultaneously promote feeding and drinking, suggesting that ingestive behaviors track together. A notable exception are LHA neurons expressing neurotensin (LHANts neurons): activating these neurons promotes water intake but modestly restrains feeding. Here we investigated the connectivity of LHANts neurons, their necessity and sufficiency for drinking and feeding, and how timing and resource availability influence their modulation of these behaviors. LHANts neurons project broadly throughout the brain, including to the lateral preoptic area (LPO), a brain region implicated in modulating drinking behavior. LHANts neurons also receive inputs from brain regions implicated in sensing hydration and energy status. While activation of LHANts neurons is not required to maintain homeostatic water or food intake, it selectively promotes drinking during the light cycle, when ingestive drive is low. Activating LHANts neurons during this period also increases willingness to work for water or palatable fluids, regardless of their caloric content. By contrast, LHANts neuronal activation during the dark cycle does not promote drinking, but suppresses feeding during this time. Finally, we demonstrate that the activation of the LHANts → LPO projection is sufficient to mediate drinking behavior, but does not suppress feeding as observed after generally activating all LHANts neurons. Overall, our work suggests how and when LHANts neurons oppositely modulate ingestive behaviors.

Neurohormonal Changes in the Gut–Brain Axis and Underlying Neuroendocrine Mechanisms following Bariatric Surgery

Obesity is a complex, multifactorial disease that is a major public health issue worldwide. Currently approved anti-obesity medications and lifestyle interventions lack the efficacy and durability needed to combat obesity, especially in individuals with more severe forms or coexisting metabolic disorders, such as poorly controlled type 2 diabetes. Bariatric surgery is considered an effective therapeutic modality with sustained weight loss and metabolic benefits. Numerous genetic and environmental factors have been associated with the pathogenesis of obesity, while cumulative evidence has highlighted the gut–brain axis as a complex bidirectional communication axis that plays a crucial role in energy homeostasis. This has led to increased research on the roles of neuroendocrine signaling pathways and various gastrointestinal peptides as key mediators of the beneficial effects following weight-loss surgery. The accumulate evidence suggests that the development of gut-peptide-based agents can mimic the effects of bariatric surgery and thus is a highly promising treatment strategy that could be explored in future research. This article aims to elucidate the potential underlying neuroendocrine mechanisms of the gut–brain axis and comprehensively review the observed changes of gut hormones associated with bariatric surgery. Moreover, the emerging role of post-bariatric gut microbiota modulation is briefly discussed.

Neurotensin secretion after Roux-en-Y gastric bypass, sleeve gastrectomy, and truncal vagotomy with pyloroplasty

OBJECTIVE

Neurotensin (NT) is released from enteroendocrine cells and lowers food intake in rodents. We evaluated postprandial NT secretion in humans after surgeries associated with accelerated small intestinal nutrient delivery, and after Roux-en-Y gastric bypass (RYGB) when glucagon-like peptide-1 (GLP-1) signalling and dipeptidyl peptidase 4 (DPP-4) were inhibited, and during pharmacological treatments influencing entero-pancreatic functions.

METHODS

We measured NT concentrations in plasma from meal studies: (I) after truncal vagotomy with pyloroplasty (TVP), cardia resection +TVP (CTVP), and matched controls (n = 10); (II) after RYGB, sleeve gastrectomy (SG), and in matched controls (n = 12); (III) after RYGB (n = 11) with antagonism of GLP-1 signalling using exendin(9-39) and DPP-4 inhibition using sitagliptin; (IV) after RYGB (n = 11) during a run-in period and subsequent treatment with, sitagliptin, liraglutide (GLP-1 receptor agonist), verapamil (calcium antagonist), acarbose (alpha glucosidase inhibitor), and pasireotide (somatostatin analogue), respectively.

RESULTS

(I) NT secretion was similar after TVP/CTVP (p = 0.9), but increased vs. controls (p < 0.0001). (II) NT secretion was increased after RYGB vs. SG and controls (p < 0.0001). NT responses were similar in SG and controls (p = 0.3), but early postprandial NT concentrations were higher after SG (p < 0.05). (III) Exendin (9-39) and sitagliptin did not change NT responses vs placebo (p > 0.2), but responses were lower during sitagliptin vs. exendin(9-39) (p = 0.03). (IV) Pasireotide suppressed NT secretion (p = 0.004). Sitagliptin tended to lower NT secretion (p = 0.08). Liraglutide, verapamil, and acarbose had no effect (p > 0.9).

CONCLUSION

Neurotensin secretion is increased after surgeries associated with accelerated gastric emptying and lowered by pasireotide.

The Role of Central Neurotensin in Regulating Feeding and Body Weight

The small peptide neurotensin (Nts) is implicated in myriad processes including analgesia, thermoregulation, reward, arousal, blood pressure, and modulation of feeding and body weight. Alterations in Nts have recently been described in individuals with obesity or eating disorders, suggesting that disrupted Nts signaling may contribute to body weight disturbance. Curiously, Nts mediates seemingly opposing regulation of body weight via different tissues. Peripherally acting Nts promotes fat absorption and weight gain, whereas central Nts signaling suppresses feeding and weight gain. Thus, because Nts is pleiotropic, a location-based approach must be used to understand its contributions to disordered body weight and whether the Nts system might be leveraged to improve metabolic health. Here we review the role of Nts signaling in the brain to understand the sites, receptors, and mechanisms by which Nts can promote behaviors that modify body weight. New techniques permitting site-specific modulation of Nts and Nts receptor-expressing cells suggest that, even in the brain, not all Nts circuitry exerts the same function. Intriguingly, there may be dedicated brain regions and circuits via which Nts specifically suppresses feeding behavior and weight gain vs other Nts-attributed physiology. Defining the central mechanisms by which Nts signaling modifies body weight may suggest strategies to correct disrupted energy balance, as needed to address overweight, obesity, and eating disorders.

Therapeutic approaches targeting the neurotensin receptors

Introduction: Neurotensin is a gut-brain peptide hormone, a 13 amino acid neuropeptide found in the central nervous system and in the GI tract. The neurotensinergic system is implicated in various physiological and pathological processes related to neuropsychiatric and metabolic machineries, cancer growth, food, and drug intake. NT mediates its functions through its two G protein-coupled receptors: neurotensin receptor 1 (NTS1/NTSR1) and neurotensin receptor 2 (NTS2/NTSR2). Over the past decade, the role of NTS3/NTSR3/sortilin has also gained importance in human pathologies. Several approaches have appeared dealing with the discovery of compounds able to modulate the functions of this neuropeptide through its receptors for therapeutic gain.Areas covered: The article provides an overview of over four decades of research and details the drug discovery approaches and patented strategies targeting NTSR in the past decade.Expert opinion: Neurotensin is an important neurotransmitter that enables crosstalk with various neurotransmitter and neuroendocrine systems. While significant efforts have been made that have led to selective agonists and antagonists with promising in vitro and in vivo activities, the therapeutic potential of compounds targeting the neurotensinergic system is still to be fully harnessed for successful clinical translation of compounds for the treatment of several pathologies.

Potential roles of neurotensin on cognition in conditions of obese-insulin resistance

Neurotensin is an endogenous tridecapeptide that can be found in both central and peripheral nervous systems. Under normal physiological conditions, neurotensin is involved in the regulation of pain, body temperature, physical activity, appetite as well as learning and memory. In addition, it plays an important role in fat metabolism. Previous studies have demonstrated that alterations of neurotensin levels were associated with several neuropathological conditions such as Alzheimer's disease, mood disorders, and obesity associated eating disorders. Obesity has been shown to be associated with low-grade systemic inflammation, brain inflammation, and cognitive decline. Several pieces of evidence suggest that neurotensin might play a role in cognitive decline following obesity. However, the underlying mechanisms of neurotensin on cognition under obese-insulin resistant condition are still unclear. In this review, the current available evidence from in vitro, in vivo and clinical studies regarding the role of neurotensin in the physiological condition and obesity in association with cognition are comprehensively summarized and discussed. The studies which report controversial findings regarding these issues are also presented and discussed.

Activation of lateral hypothalamic area neurotensin-expressing neurons promotes drinking

Animals must ingest water via drinking to maintain fluid homeostasis, yet the neurons that specifically promote drinking behavior are incompletely characterized. The lateral hypothalamic area (LHA) as a whole is essential for drinking behavior but most LHA neurons indiscriminately promote drinking and feeding. By contrast, activating neurotensin (Nts)-expressing LHA neurons (termed LHA Nts neurons) causes mice to immediately drink water with a delayed suppression of feeding. We therefore hypothesized that LHA Nts neurons are sufficient to induce drinking behavior and that these neurons specifically bias for fluid intake over food intake. To test this hypothesis we used designer receptors exclusively activated by designer drugs (DREADDs) to selectively activate LHA Nts neurons and studied the impact on fluid intake, fluid preference and feeding. Activation of LHA Nts neurons stimulated drinking in water-replete and dehydrated mice, indicating that these neurons are sufficient to promote water intake regardless of homeostatic need. Interestingly, mice with activated LHA Nts neurons drank any fluid that was provided regardless of its palatability, but if given a choice they preferred water or palatable solutions over unpalatable (quinine) or dehydrating (hypertonic saline) solutions. Notably, acute activation of LHA Nts neurons robustly promoted fluid but not food intake. Overall, our study confirms that activation of LHA Nts neurons is sufficient to induce drinking behavior and biases for fluid intake. Hence, LHA Nts neurons may be important targets for orchestrating the appropriate ingestive behavior necessary to maintain fluid homeostasis. This article is part of the Special Issue entitled 'Hypothalamic Control of Homeostasis'.

Role of central neurotensin in regulating feeding: Implications for the development and treatment of body weight disorders

The peptide neurotensin (Nts) was discovered within the brain over 40years ago and is implicated in regulating analgesia, body temperature, blood pressure, locomotor activity and feeding. Recent evidence suggests, however, that these disparate processes may be controlled via specific populations of Nts neurons and receptors. The neuronal mediators of Nts anorectic action are now beginning to be understood, and, as such, modulating specific Nts pathways might be useful in treating feeding and body weight disorders. This review considers mechanisms through which Nts normally regulates feeding and how disruptions in Nts signaling might contribute to the disordered feeding and body weight of schizophrenia, Parkinson's disease, anorexia nervosa, and obesity. Defining how Nts specifically mediates feeding vs. other aspects of physiology will inform the design of therapeutics that modify body weight without disrupting other important Nts-mediated physiology.

Lateral Hypothalamic Neurotensin Neurons Orchestrate Dual Weight Loss Behaviors via Distinct Mechanisms

The central mechanism by which neurotensin (Nts) potentiates weight loss has remained elusive. We leveraged chemogenetics to reveal that Nts-expressing neurons of the lateral hypothalamic area (LHA) promote weight loss in mice by increasing volitional activity and restraining food intake. Intriguingly, these dual weight loss behaviors are mediated by distinct signaling pathways: Nts action via NtsR1 is essential for the anorectic effect of the LHA Nts circuit, but not for regulation of locomotor or drinking behavior. Furthermore, although LHA Nts neurons cannot reduce intake of freely available obesogenic foods, they effectively restrain motivated feeding in hungry, weight-restricted animals. LHA Nts neurons are thus vital mediators of central Nts action, particularly in the face of negative energy balance. Enhanced action via LHA Nts neurons may, therefore, be useful to suppress the increased appetitive drive that occurs after lifestyle-mediated weight loss and, hence, to prevent weight regain.

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.

Distinct Types of Feeding Related Neurons in Mouse Hypothalamus

The last two decades of research provided evidence for a substantial heterogeneity among feeding-related neurons (FRNs) in the hypothalamus. However, it remains unclear how FRNs differ in their firing patterns during food intake. Here, we investigated the relationship between the activity of neurons in mouse hypothalamus and their feeding behavior. Using tetrode-based in vivo recording technique, we identified various firing patterns of hypothalamic FRNs, which, after the initiation of food intake, can be sorted into four types: sharp increase (type I), slow increase (type II), sharp decrease (type III), and sustained decrease (type IV) of firing rates. The feeding-related firing response of FRNs was rigidly related to the duration of food intake and, to a less extent, associated with the type of food. The majority of these FRNs responded to glucose and leptin and exhibited electrophysiological characteristics of putative GABAergic neurons. In conclusion, our study demonstrated the diversity of neurons in the complex hypothalamic network coordinating food intake.

Neurotensin Is Coexpressed, Coreleased, and Acts Together With GLP-1 and PYY in Enteroendocrine Control of Metabolism

The 2 gut hormones glucagon-like peptide-1 (GLP-1) and peptide YY (PYY) are well known to be coexpressed, costored, and released together to coact in the control of key metabolic target organs. However, recently, it became clear that several other gut hormones can be coexpressed in the intestinal-specific lineage of enteroendocrine cells. Here, we focus on the anatomical and functional consequences of the coexpression of neurotensin with GLP-1 and PYY in the distal small intestine. Fluorescence-activated cell sorting analysis, laser capture, and triple staining demonstrated that GLP-1 cells in the crypts become increasingly multihormonal, ie, coexpressing PYY and neurotensin as they move up the villus. Proglucagon promoter and pertussis toxin receptor-driven cell ablation and reappearance studies indicated that although all the cells die, the GLP-1 cells reappear more quickly than PYY- and neurotensin-positive cells. High-resolution confocal fluorescence microscopy demonstrated that neurotensin is stored in secretory granules distinct from GLP-1 and PYY storing granules. Nevertheless, the 3 peptides were cosecreted from both perfused small intestines and colonic crypt cultures in response to a series of metabolite, neuropeptide, and hormonal stimuli. Importantly, neurotensin acts synergistically, ie, more than additively together with GLP-1 and PYY to decrease palatable food intake and inhibit gastric emptying, but affects glucose homeostasis in a more complex manner. Thus, neurotensin is a major gut hormone deeply integrated with GLP-1 and PYY, which should be taken into account when exploiting the enteroendocrine regulation of metabolism pharmacologically.

To ingest or rest? Specialized roles of lateral hypothalamic area neurons in coordinating energy balance

Survival depends on an organism’s ability to sense nutrient status and accordingly regulate intake and energy expenditure behaviors. Uncoupling of energy sensing and behavior, however, underlies energy balance disorders such as anorexia or obesity. The hypothalamus regulates energy balance, and in particular the lateral hypothalamic area (LHA) is poised to coordinate peripheral cues of energy status and behaviors that impact weight, such as drinking, locomotor behavior, arousal/sleep and autonomic output. There are several populations of LHA neurons that are defined by their neuropeptide content and contribute to energy balance. LHA neurons that express the neuropeptides melanin-concentrating hormone (MCH) or orexins/hypocretins (OX) are best characterized and these neurons play important roles in regulating ingestion, arousal, locomotor behavior and autonomic function via distinct neuronal circuits. Recently, another population of LHA neurons containing the neuropeptide Neurotensin (Nts) has been implicated in coordinating anorectic stimuli and behavior to regulate hydration and energy balance. Understanding the specific roles of MCH, OX and Nts neurons in harmonizing energy sensing and behavior thus has the potential to inform pharmacological strategies to modify behaviors and treat energy balance disorders.

High on food: the interaction between the neural circuits for feeding and for reward

Hunger, mostly initiated by a deficiency in energy, induces food seeking and intake. However, the drive toward food is not only regulated by physiological needs, but is motivated by the pleasure derived from ingestion of food, in particular palatable foods. Therefore, feeding is viewed as an adaptive motivated behavior that involves integrated communication between homeostatic feeding circuits and reward circuits. The initiation and termination of a feeding episode are instructed by a variety of neuronal signals, and maladaptive plasticity in almost any component of the network may lead to the development of pathological eating disorders. In this review we will summarize the latest understanding of how the feeding circuits and reward circuits in the brain interact. We will emphasize communication between the hypothalamus and the mesolimbic dopamine system and highlight complexities, discrepancies, open questions and future directions for the field.

Elucidating the role of neurotensin in the pathophysiology and management of major mental disorders

Neurotensin (NT) is a neuropeptide that is closely associated with, and is thought to modulate, dopaminergic and other neurotransmitter systems involved in the pathophysiology of various mental disorders. This review outlines data implicating NT in the pathophysiology and management of major mental disorders such as schizophrenia, drug addiction, and autism. The data suggest that NT receptor analogs have the potential to be used as novel therapeutic agents acting through modulation of neurotransmitter systems dys-regulated in these disorders.

Diverse roles of neurotensin agonists in the central nervous system

Neurotensin (NT) is a tridecapeptide that is found in the central nervous system (CNS) and the gastrointestinal tract. NT behaves as a neurotransmitter in the brain and as a hormone in the gut. Additionally, NT acts as a neuromodulator to several neurotransmitter systems including dopaminergic, sertonergic, GABAergic, glutamatergic, and cholinergic systems. Due to its association with such a wide variety of neurotransmitters, NT has been implicated in the pathophysiology of several CNS disorders such as schizophrenia, drug abuse, Parkinson's disease (PD), pain, central control of blood pressure, eating disorders, as well as, cancer and inflammation. The present review will focus on the role that NT and its analogs play in schizophrenia, endocrine function, pain, psychostimulant abuse, and PD.

A neurotensin analog, NT69L, attenuates intravenous nicotine self-administration in rats

NT69L is a neurotensin analog that blocks nicotine-induced locomotor activity and has sustained efficacy in a rat model of nicotine-induced sensitization when administered peripherally. Additionally, NT69L attenuates food-reinforcement in rats. The present study tested the effect of acute administration of NT69L on nicotine self-infusion in Sprague-Dawley rats. Rats were trained to self-infuse nicotine intravenously (0.03mg/kg per infusion) following operant training. Once the rats acquired stable responding to nicotine self-infusion they were pretreated with NT69L (1mg/kg, i.p.) or saline 30min before being assessed for nicotine self-infusion. Pretreatment with NT69L significantly attenuated nicotine self-infusion under FR1 (fixed ratio of 1) and FR5 schedule of reinforcement as compared to saline pretreatment. Control rats that were response-independent "yoked" as well as rats that self-infused saline or NT69L showed minimal responses, indicating that nicotine served as a reinforcer. Additionally, NT69L modulated serum corticosterone; brain norepinephrine serotonin; and dopamine receptors mRNA levels altered in the nicotine self-infused rats after a 24h withdrawal period. Pretreatment with NT69L significantly decreased the nicotine-induced increase in serum corticosterone levels and striatal norepinephrine and increased the nicotine-induced reduction in serotonin in both the striatum and the prefrontal cortex (PFC). NT69L might modulate dopamine neurotransmission implicated in the reinforcing effects of nicotine by modulating tyrosine hydroxylase and dopamine receptor mRNA levels in the PFC and striatum. These data support further study of the effects of NT analogs on attenuating the reinforcing effects of psychostimulants.

Evidence of complex involvement of serotonergic genes with restrictive and binge purge subtypes of anorexia nervosa

OBJECTIVES

There is mixed evidence of association of serotoninergic genes with anorexia nervosa (AN), but substantial evidence for the involvement of serotonergic mechanisms in appetite control. This study was designed to investigate possible associations between the two subtypes of AN (Restricting-RAN, and Binge-purging-BPAN) and polymorphisms within five genes encoding for proteins involved in the serotoninergic system.

METHODS

In order to carry out this investigation we have conducted a case-control association study on 226 females meeting the criteria for AN, and 678 matched healthy females.

RESULTS

Our data show a significant association between polymorphisms with the gene encoding HTR2A with both AN subtypes, an association between polymorphisms within the genes encoding HTR1D and HTR1B with RAN, and an association between polymorphisms within the gene encoding HTR2C with BPAN. No associations were found for any polymorphisms of the serotonin transporter gene. This outcome indicates a substantial and complex inter-relationship between serotoninergic genes and AN.

CONCLUSIONS

Given these data we hypothesis that the expression or control of expression of several genes of the serotoninergic system, and interactions between these genes, could exert considerable influence over the specific symptomatology of the subtypes of AN.

The novel neurotensin analog NT69L blocks phencyclidine (PCP)-induced increases in locomotor activity and PCP-induced increases in monoamine and amino acids levels in the medial prefrontal cortex

Schizophrenia is a life-long, severe, and disabling brain disorder that requires chronic pharmacotherapy. Because current antipsychotic drugs do not provide optimal therapy, we have been developing novel treatments that focus on receptors for the neuropeptide neurotensin (NT). NT69L, an analog of neurotensin(8-13), acts like an atypical antipsychotic drug in several dopamine-based animal models used to study schizophrenia. Another current animal model utilizes non-competitive antagonists of the NMDA/glutamate receptor, such as the psychotomimetic phencyclidine (PCP). In the present study, we investigated the effects of NT69L on PCP-induced behavioral and biochemical changes in the rat. The top of an activity chamber was modified to allow us to perform microdialysis in rat brain, while simultaneously recording the locomotor activity of a rat. PCP injection significantly increased activity as well as the extracellular concentration of norepinephrine (NE), 5-HT, dopamine (DA), and glutamate in the medial prefrontal cortex (mPFC). Pretreating with NT69L blocked the PCP-induced hyperactivity as well as the increase of DA, 5-HT, NE, and glutamate in mPFC. Interestingly and unexpectedly, NT69L markedly increased glycine levels, while PCP was without effect on glycine levels. Thus, NT69L showed antipsychotic-like effects in this glutamate-based animal model for studying schizophrenia. Previous work from our group suggests that NT69L also has antipsychotic-like effects in dopaminergic and serotonergic rodent models. Taken together, these data suggest that NT69L in particular and NT receptor agonists in general, will be useful as broad-spectrum antipsychotic drugs.

The acute and subchronic effects of a brain-penetrating, neurotensin-1 receptor agonist on feeding, body weight and temperature

The neurotensin-1 (NT1) receptor has been implicated in mediating a number of important neurotensin effects. We have found that PD149163, a selective, brain-penetrating, NT1 receptor agonist, produces a number of therapeutic-like preclinical effects after peripheral administration including pro-cognitive, antipsychotic and anxiolytic effects. In this study, we investigated PD149163's effect on food intake and thermal regulation, two physiological processes thought to be mediated by NT1 receptors. Brown Norway rats and leptin-deficient mice (ob/ob) mice were administered subcutaneous PD149163 (0, 0.1, 0.25, or 1 mg/kg) for ten consecutive days. Weight and 24-h food intake were measured in mice and rats and core body temperature was also measured in rats. PD149163 significantly decreased food intake in rats and ob/ob mice and no tolerance was demonstrated to this effect over the course of the study. PD149163-treated animals exhibited weight loss compared to saline-treated animals. PD149163 produced hypothermia as expected but this effect did show tolerance over the course of the study, unlike feeding. The results suggest that NT1 receptor agonists are candidates for treatment of obesity and that somewhat different mechanisms are involved in NT1-induced feeding regulation and temperature regulation.

Neurotensin agonists: potential in the treatment of schizophrenia

Neurotensin (NT) is a neuropeptide that, for decades, has been implicated in the biology of schizophrenia. It is closely associated with, and is thought to modulate, dopaminergic and other neurotransmitter systems involved in the pathophysiology of various neuropsychiatric diseases, including schizophrenia. This review outlines the neurochemistry and function of the NT system and the data implicating its role in schizophrenia. The data suggest that NT receptor agonists have the potential to be used as novel therapeutic agents for the treatment of schizophrenia, with the added benefits of (i) not causing weight gain, an adverse effect that is problematic with some of the currently used atypical antipsychotic drugs; and (ii) helping patients to stop smoking, a behaviour that is highly prevalent in those with schizophrenia.

The neurotensin receptor agonist NT69L suppresses sucrose-reinforced operant behavior in the rat

NT69L is a neurotensin analog that can be administered peripherally. It blocks amphetamine- and cocaine-induced hyperactivity in rats. It also blocks nicotine-induced locomotor activity and has shown sustained efficacy in a rat model of nicotine-induced sensitization. The present study tested the effect of NT69L on responding for sucrose reinforcement on a continuous reinforcement schedule (CRF) and incrementing (FR1-FR5) discrimination schedule. Male Sprague-Dawley rats, on restricted food intake, were trained to press a lever for sucrose pellets on a CRF and incrementing discrimination schedule of reinforcement. On the following day, the testing session was followed by an extinction session, where lever pressing was not reinforced. Immediately after extinction, a reversal to CRF was implemented to test for relapse. Trained rats were injected with NT69L (1 mg/kg) or saline 30 min before each testing session. Dopamine, tyrosine 3-hydroxylase, and dopamine receptor mRNA levels were determined. NT69L significantly suppressed the lever pressing behavior for sucrose reinforcement on CRF which measures the "hedonic" value of the reward. NT69L also suppressed sucrose self-administration on the incrementing discrimination schedule of reinforcement (FR3-FR5) that is analogous to the motivational incentive. Reversal to CRF was significantly reduced by pretreatment with NT69L. The suppression of sucrose self-administration behavior by pretreatment with NT69L had a pattern similar to that for extinction. The effect of NT69L on dopamine, tyrosine 3-hydroxylase, and dopamine receptor mRNA levels is discussed relative to changes occurring during extinction.

Bioactive analogs of neurotensin: focus on CNS effects

Neurotensin (NT) is a 13-amino acid neuropeptide found in the central nervous system and in the gastrointestinal tract. It is closely associated anatomically with dopaminergic and other neurotransmitter systems, and evidence supports a role for NT agonists in the treatment of various neuropsychiatric disorders. However, NT is readily degraded by peptidases, so there is much interest in the development of stable NT agonists, that can be injected systemically, cross the blood-brain barrier (BBB), yet retains the pharmacological characteristics of native NT for therapeutic use in the treatment of diseases such as schizophrenia, Parkinson's disease and addiction.

Effects of 5 daily injections of the neurotensin-mimetic NT69L on the expression of neurotensin receptors in rat brain

The effects of one or five daily intraperitoneal injections of a neurotensin (NT) receptor agonist NT69L (2 mg/kg, i.p.) on the expression of NT (NTS), dopamine 1 and 2 receptors, tyrosine hydroxylase, and DOPA decarboxylase using immunohistochemical and real-time PCR were investigated in rats. Except for the striatum, acute injection of NT69L did not affect neurotensin receptors as compared to saline control. However, 5 daily injections of NT69L resulted in down-regulation of both NTS-1 protein and mRNA levels in several brain regions with the striatum showing a dramatic decrease in NTS-1 expression (P<0.05). The down-regulation of NTS-1 in the striatum, hypothalamus, and substania nigra (SN) after 5 daily injections was confirmed by autoradiography. Acute injection of NT69L increased NTS-2 mRNA and protein level in prefrontal cortex (PFC). NTS-3 mRNA expression and protein levels were slightly down-regulated in hypothalamus, periaqueductal gray (PAG), and SN, though the difference was not significant. The results indicated a difference in the profile of NT receptors expression in response to NT69L. Tyrosine hydroxylase (TH) and DOPA decarboxylase (DDC) mRNA was significantly down-regulated in striatum but not in SN. Interestingly, Nurr 1, a transcriptional activator of TH, was dramatically up-regulated in striatum, but down-regulated in PFC, suggesting that different modulating mechanisms may participate in NT69L tolerance in different regions. The present results suggest that distinct NT receptors involved in the effects exerted by NT69L may contribute to the interactions of NT69L with both neural networks and cellular proteins.

Antinociceptive, hypothermic, hypotensive, and reinforcing effects of a novel neurotensin receptor agonist, NT69L, in rhesus monkeys

Neurotensin (NT) is a tridecapeptide found in the nervous system, as well as elsewhere in the body. It has anatomic and functional relationships to dopaminergic neurons in brain. NT has been implicated in the actions of antipsychotic drugs and psychostimulants, and animal studies suggest that neurotensin directly injected into brain has reinforcing effects. Previously, we showed that one of our brain-penetrating analogs of neurotensin, NT69L (N-methyl-L-Arg, L-Lys, L-Pro, L-neo-Trp, L-tert-Leu, L-Leu), has many pharmacological effects in rats including antinociception, hypothermia, and blockade of the hyperactivity caused by psychostimulants (cocaine, D-amphetamine, and nicotine). Since these studies in rats suggest that this compound may have clinical use in humans, we were interested to know what effects NT69L had in primates. NT69L caused a potent antinociceptive effect against capsaicin (0.1 mg)-induced allodynia in 46 degrees C water in rhesus monkeys, inducing 40% of the maximal possible effect at an intravenous dosage of 0.03 mg/kg; its hypotensive effects precluded evaluation of higher dosages. Core temperature measured by rectal probe was modestly reduced at 0.01 and 0.03 mg/kg. In an intravenous self-administration procedure, NT69L was without reinforcing effects at any dose, including those that caused other pharmacological effects, and did not alter cocaine-maintained behavior when administered as a pretreatment.

Effects of repeated injections of the neurotensin analog NT69L on dopamine release and uptake in rat striatum in vitro

The effect of five daily intraperitoneal (i.p.) injections of NT69L on in vitro dopamine release, uptake, and [(3)H]NT binding in rat striatal tissue was investigated. NT69L perfusion increased K(+)-evoked and electrically evoked [(3)H]DA release. NT receptor-1 antagonist SR48692 inhibited the stimulatory effect of NT69L on K+-evoked [(3)H]DA release, but not on electrical depolarization. Pretreatment with NT69L, in vivo, daily for 5 days, did not cause significant change in K(+) evoked [(3)H]DA release, but reduced electrically evoked [(3)H]DA release induced by NT69L perfusion. Repeated perfusion with NT69L in vitro caused marked reduction on K(+)-evoked [(3)H]DA release and no change in electrically evoked [(3)H]DA release. [(3)H]NT binding was not significantly changed by one injection but was decreased after five injections of NT69L. Desensitization to the effects of NT69L in vitro was different depending upon whether tissue was preexposed to the compound in vivo or in vitro. These results provide further proof for the involvement of different NT receptor subtypes in mediating the effect of NT69L on dopamine release evoked by K(+) or electrical depolarization.

Neurotensin agonists block the prepulse inhibition deficits produced by a 5-HT2A and an alpha1 agonist

RATIONALE

Neurotensin (NT) agonists have been proposed as potential antipsychotics based exclusively upon their ability to inhibit dopamine-2 (D2) receptor transmission. Several other pharmacological mechanisms have been implicated in enhancing the antipsychotic profile produced by D2 inhibition alone. These include inhibition of 5-HT2A and alpha1-adrenoceptors. Recently, we reported that systemic administration of the neurotensin agonist PD149163 blocks deficits in prepulse inhibition (PPI) of the startle reflex produced by the 5-HT2A receptor agonist DOI. This suggested that NT agonists could inhibit 5-HT2A modulation of neurotransmission.

OBJECTIVE

To determine if other peripherally administered NT agonists shared this effect, we examined the effects of NT69L, another NT agonist, on DOI-induced PPI deficits. In addition, to determine if NT agonists also inhibit alpha1-adrenoceptor neurotransmission, we examined the effects of PD149163 and NT69L on PPI deficits induced by the alpha1-adrenoceptor agonist, cirazoline.

METHODS

In the NT69L/DOI study, rats received subcutaneous (SC) injections of NT69L (0, 0.1, 1, or 2 mg/kg) followed 30 min later by SC saline or DOI (0.5 mg/kg). In the NT agonist/cirazoline studies, animals received SC injections of either PD149163 (0, 0.01, 0.1, or 1 mg/kg) or NT69L (0, 0.01, 0.1, or 1 mg/kg) followed 30 min later by SC saline or cirazoline (0.7 mg/kg). Animals were tested in startle chambers 20 min later.

RESULTS

In all three experiments the PPI disruption produced by DOI and cirazoline was blocked by the NT agonists.

CONCLUSIONS

These findings provide strong evidence that NT agonists inhibit 5-HT2A and alpha1-adrenoceptor modulation of neurotransmission, pharmacological effects that, in conjunction with their known inhibition of dopamine transmission, strengthen the antipsychotic potential of NT agonists.

Selective tolerance to the hypothermic and anticataleptic effects of a neurotensin analog that crosses the blood-brain barrier

NT69L, a neurotensin analog that crosses the blood-brain barrier, reduces body temperature, reverses apomorphine-induced climbing, haloperidol-induced catalepsy, and D-amphetamine- and cocaine-induced locomotor activity in rats. In this study we tested the development of tolerance to these effects of NT69L in rats. The blockade of apomorphine-induced climbing behavior and D-amphetamine- and cocaine-induced hyperactivity seen after a single acute injection did not show significant change with repeated daily injections of NT69L. Thus, for example, NT69L after five daily injections at a fixed dosage was as effective at reversing cocaine-induced hyperactivity as after the first injection. On the other hand, repeated daily injections of NT69L resulted in a diminished hypothermic response and a diminished anticataleptic effect against haloperidol. The effect of NT69L on blood glucose, cortisol, and thyroxine (T(4)) were all back to control levels after five daily injections. Thus, tolerance developed to NT69L after the first injection, when it was tested for causing hypothermia, blockade of haloperidol-induced catalepsy, and change in blood glucose, cortisol and T(4) levels. Since tolerance did not develop to the effects of drugs acting as direct (apomorphine) or indirect (D-amphetamine and cocaine) agonists at dopamine receptors over the course of 5 days, these findings suggest a selective role of neurotensin in the modulation of dopamine neurotransmission. Furthermore, due to the lack of development of tolerance, NT69L or similar analogs might be useful in modulating certain behavioral effects of psychostimulants or have potential use as an antipsychotic drug in humans.

Current topics: brain penetrating neurotensin analog

Neurotensin (NT) is a neuropeptide found in the central nervous system and gastrointestinal tract. It is closely associated with dopaminergic and other neurotransmitter systems, and evidence supports a role for NT in various neuropsychiatric disorders. Because NT is readily degraded by peptidases, our group has developed various NT agonists that can be injected systemically, cross the blood brain barrier (BBB), yet retain the characteristics of native NT. The most widely studied and successful of these compounds, called NT69L, holds promise as a therapeutic agent for Parkinson's disease, schizophrenia, psychostimulant abuse and nicotine dependence, and serves as a tool to study the cellular and molecular effects of NT.

The effects of systemic NT69L, a neurotensin agonist, on baseline and drug-disrupted prepulse inhibition

Centrally administered neurotensin (NT) produces behavioral and biochemical effects that are very similar to the effects of antipsychotic drugs. Therefore, there is much interest in the potential use of NT agonists as antipsychotic drugs. We have previously reported that PD149163, a NT(8-13) analogue, produced effects on prepulse inhibition (PPI) of startle after systemic administration that were suggestive of an atypical antipsychotic-like drug profile. To determine if these effects are shared by other peripherally administered NT agonists, we tested the effects of NT69L, a recently developed NT agonist that penetrates the CNS, on drug-induced PPI deficits. In the first experiment, rats received subcutaneous (s.c.) injections of NT69L (vehicle, 0.08, 0.25, and 1.0mg/kg) followed 30min later by subcutaneous saline or D-amphetamine (2.0mg/kg). In the second experiment, NT69L injections were followed by saline or the non-competitive NMDA antagonist dizocilpine (0.1mg/kg). Both D-amphetamine and dizocilpine significantly decreased PPI as expected. In the first experiment, NT69L significantly increased PPI levels at baseline and after D-amphetamine. In the second experiment, NT69L attenuated PPI deficits produced by dizocilpine, without increasing baseline PPI. In addition, NT69L had no effect on startle magnitude. The effects of NT69L in these studies were similar in some ways to the effects of PD149163 and were also consistent with the preclinical effects of atypical antipsychotic drugs. These data provide further support for the notion that NT agonists may have use as novel antipsychotic drugs. Furthermore, the ability of NT69L and PD149163 to attenuate dizocilpine-disrupted PPI, an antipsychotic drug effect not mediated by dopamine, suggests that NT agonists may produce some of their antipsychotic-like effects by modulating neurotransmitter systems other than dopamine, such as serotonin, noradrenaline or glutamate.

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.

Pharmacological approaches for the treatment of obesity

The high incidence of obesity, its multifactorial nature, the complexity and lack of knowledge of the bodyweight control system, and the scarcity of adequate therapeutics have fuelled anti-obesity drug development during a considerable number of years. Irrespective of the efforts invested by researchers and companies, few products have reached a minimum level of effectiveness, and even fewer are available in medical practice. As a consequence of anti-obesity research, our knowledge of the bodyweight control system increased but, despite this, the pharmacological approaches to the treatment of obesity have not resulted yet in effective drugs. This review provides a panoramic of the multiple different approaches developed to obtain workable drugs. These approaches, however, rely in only four main lines of action: control of energy intake, mainly through modification of appetite;control of energy expenditure, essentially through the increase of thermogenesis;control of the availability of substrates to cells and tissues through hormonal and other metabolic factors controlling the fate of the available energy substrates; andcontrol of fat reserves through modulation of lipogenesis and lipolysis in white adipose tissue. A large proportion of current research is centred on neuropeptidic control of appetite, followed by the development of drugs controlling thermogenic mechanisms and analysis of the factors controlling adipocyte growth and fat storage. The adipocyte is also a fundamental source of metabolic signals, signals that can be intercepted, modulated and used to force the brain to adjust the mass of fat with the physiological means available. The large variety of different approaches used in the search for effective anti-obesity drugs show both the deep involvement of researchers on this field and the large amount of resources devoted to this problem by pharmaceutical companies. Future trends in anti-obesity drug research follow closely the approaches outlined; however, the increasing mass of information on the molecular basis of bodyweight control and obesity will in the end prevail in our search for effective and harmless anti-obesity drugs.

Antiparkinson-like effects of a novel neurotensin analog in unilaterally 6-hydroxydopamine lesioned rats

Parkinson's disease is a neuropathological disorder involving the degeneration of dopamine neurons in the substantia nigra, with the resultant loss of their terminals in the striatum. This dopamine loss causes most of the motor disturbances associated with the disease. One animal model of Parkinson's disease involves destruction of the nigrostriatal pathway with a neurotoxin (6-hydroxydopamine) injected into this pathway. In unilaterally lesioned animals, injection of D-amphetamine causes rotation towards the lesioned side, while injection of apomorphine acting upon supersensitive postsynaptic dopamine receptors causes rotation away from the lesioned side. In this study, we tested the effects of acute and subchronic injection of a neurotensin analog (NT69L) on the rotational behavior induced by D-amphetamine (5 mg/kg) or apomorphine (600 microg/kg) in unilaterally 6-hydroxydopamine lesioned rats. Pretreatment of animals with intraperitoneal injections of NT69L (1 mg/kg) resulted in a significant reduction of apomorphine-induced contralateral rotation and D-amphetamine-induced ipsilateral rotation in these lesioned rats with an ED(50) of 40 and 80 microg/kg, respectively. After three daily injections of NT69L, its effects on this rotational behavior were unchanged, suggesting that no tolerance develops to this effect of NT69L.

A novel neurotensin analog blocks cocaine- and D-amphetamine-induced hyperactivity

Neurotensin is a tridecapeptide that exhibits selective anatomic and neurochemical interactions with dopaminergic systems. Since dopaminergic neurotransmission underlies many of the behavioral properties of psychostimulants, and since neurotensin has been implicated in modulating dopaminergic neurotransmitter systems, we tested the effect of our novel neurotensin analog, NT69L (N-methyl-Arg(8),L-Lys(9),L-neo-Trp(11),tert-Leu(12)]neurotensin-(8-13)), on hyperactivity caused by cocaine and D-amphetamine. Previously, we showed that NT69L reduces body temperature, blocks apomorphine-induced climbing, and haloperidol-induced catalepsy. In this study, NT69L blocked the hyperactivity induced by both cocaine and D-amphetamine administered at three different doses each, when this peptide was injected intraperitoneally. These results provide further evidence for the involvement of the neurotensin system in some of the behavioral properties of psychostimulants and suggest that NT69L may find clinical application in patients who abuse this class of compounds.

Neurotensin: peptide for the next millennium

Neurotensin is an endogenous tridecapeptide neurotransmitter (pGlu-Leu-Tyr-Glu-Asn-Lys-Pro-Arg-Arg-Pro-Try-Ile-Leu-OH) that was discovered by Carraway and Leeman in bovine hypothalami in the early 1970s. Since then this peptide has been the subject of a multitude of articles detailing discoveries related to its activity, receptors, localization, synthesis, and interactions with other systems. This review article does not intend to summarize again all the history of this fascinating peptide and its receptors, since this has been done quite well by others. The reader will be directed to these other reviews, where appropriate. Instead, this review attempts to provide a summary of current knowledge about neurotensin, why it is an important peptide to study, and where the field is heading. Special emphasis is placed on the behavioral studies, particularly with reference to agonists, antagonists, and antisense studies, as well as, the interaction of neurotensin with other neurotransmitters.