Novel neurotensin analog blocks the initiation and expression of nicotine-induced locomotor sensitization

Actions of feeding-related peptides on the mesolimbic dopamine system in regulation of natural and drug rewards

The mesolimbic dopamine system is the primary neural circuit mediating motivation, reinforcement, and reward-related behavior. The activity of this system and multiple behaviors controlled by it are affected by changes in feeding and body weight, such as fasting, food restriction, or the development of obesity. Multiple different peptides and hormones that have been implicated in the control of feeding and body weight interact with the mesolimbic dopamine system to regulate many different dopamine-dependent, reward-related behaviors. In this review, we summarize the effects of a selected set of feeding-related peptides and hormones acting within the ventral tegmental area and nucleus accumbens to alter feeding, as well as food, drug, and social reward.

The impact of adolescent nicotine exposure on alcohol use during adulthood: The role of neuropeptides

Nicotine and alcohol abuse and co-dependence represent major public health crises. Indeed, previous research has shown that the prevalence of alcoholism is higher in smokers than in non-smokers. Adolescence is a susceptible period of life for the initiation of nicotine and alcohol use and the development of nicotine-alcohol codependence. However, there is a limited number of pharmacotherapeutic agents to treat addiction to nicotine or alcohol alone. Notably, there is no effective medication to treat this comorbid disorder. This chapter aims to review the early nicotine use and its impact on subsequent alcohol abuse during adolescence and adulthood as well as the role of neuropeptides in this comorbid disorder. The preclinical and clinical findings discussed in this chapter will advance our understanding of this comorbid disorder's neurobiology and lay a foundation for developing novel pharmacotherapies to treat nicotine and alcohol codependence.

Sex differences in neurotensin and substance P following nicotine self-administration in rats

Investigator-administered nicotine alters neurotensin and substance P levels in Sprague-Dawley rats. This finding suggested a role of the dopamine-related endogenous neuropeptides in nicotine addiction. We sought to extend this observation by determining the responses of neurotensin and substance P systems (assessed using radioimmunoassay) in male and female rats following nicotine self-administration (SA). Male and female Sprague-Dawley were trained to self-administer nicotine, or receive saline infusions yoked to a nicotine-administering rat during daily sessions (1-h; 21 days). Brains were extracted 3 h after the last SA session. Nicotine SA increased tissue levels of neurotensin in the males in the anterior and posterior caudate, globus pallidus, frontal cortex, nucleus accumbens core and shell, and ventral tegmental area. Nicotine SA also increased tissue levels of neurotensin in the females in the anterior caudate, globus pallidus, nucleus accumbens core and shell, but not in the posterior caudate, frontal cortex, or ventral tegmental area. There were fewer sex differences observed in the substance P systems. Nicotine SA increased tissue levels of substance P in both the males and females in the posterior caudate, globus pallidus, frontal cortex, nucleus accumbens shell, and ventral tegmental area. A sex difference was observed in the nucleus accumbens core, where nicotine SA increased tissue levels of substance P in the males, yet decreased levels in the females. The regulation of neuropeptides following nicotine SA may play a role in the susceptibility to nicotine dependence in females and males. Synapse 70:336-346, 2016. © 2016 Wiley Periodicals, Inc.

Neurotensin: A role in substance use disorder?

Neurotensin is a tridecapeptide originally identified in extracts of bovine hypothalamus. This peptide has a close anatomical and functional relationship with the mesocorticolimbic and nigrostriatal dopamine system. Neural circuits containing neurotensin were originally proposed to play a role in the mechanism of action of antipsychotic agents. Additionally, neurotensin-containing pathways were demonstrated to mediate some of the rewarding and/or sensitizing properties of drugs of abuse.This review attempts to contribute to the understanding of the role of neurotensin and its receptors in drug abuse. In particular, we will summarize the potential relevance of neurotensin, its related compounds and neurotensin receptors in substance use disorders, with a focus on the preclinical research.

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.

Neurotensin agonist attenuates nicotine potentiation to cocaine sensitization

Tobacco usage typically precedes illicit drug use in adolescent and young adult populations. Several animal studies suggest nicotine increases the risk for subsequent cocaine abuse, and may be a negative prognostic factor for treatment of cocaine addiction; i.e., a “gateway drug”. Neurotensin (NT) is a 13-amino acid neuropeptide that modulates dopamine, acetylcholine, glutamate, and GABA neurotransmission in brain reward pathways. NT69L, a NT(8-13) analog, blocks behavioral sensitization (an animal model for psychostimulant addiction) to nicotine, and nicotine self-administration in rats. The present study tested the effect of NT69L on the potentiating effects of nicotine on cocaine-induced locomotor sensitization. Male Wistar rats were injected daily for seven days with nicotine or saline (control) followed by four daily injections of cocaine. NT69L was administered 30 min prior to the last cocaine injection. Behavior was recorded with the use of activity chambers. Subchronic administration of nicotine enhanced cocaine-induced behavioral sensitization in Wistar rats, consistent with an hypothesized gateway effect. These behavioral effects of cocaine were attenuated by pretreatment with NT69L. The effect of the neurotensin agonist on cocaine sensitization in the nicotine treated group indicated a possible therapeutic effect for cocaine addiction, even in the presence of enhanced behavioral sensitization induced by nicotine.

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.

NT69L blocks ethanol-induced increase of dopamine and glutamate levels in striatum of mouse

Recent study shows that NT69L, an analog of neurotensin (NT) (8-13), reduces ethanol consumption and preference in mice through modulation of neurotensin receptor subtype one. The current study showed that NT69L significantly decreased ethanol-induced increase of dopamine and glutamate levels in striatum of mouse. These data suggest that NT69L prevents ethanol consumption through the modulation of both dopaminergic and glutamatergic systems implicated in ethanol addiction. NT agonists may provide novel treatment for alcohol addiction.

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.

Neurotensin agonists as an alternative to antipsychotics

Neurotensin (NT) is a 13 amino acid neuropeptide that is found in the central nervous system and in the gastrointestinal tract. In brain, this peptide is prominently associated anatomically with dopaminergic, as well as other neurotransmitter systems. Based on animal studies, already decades old, researchers have hypothesised that NT receptor agonists will have antipsychotic properties in patients. However, to date no one has obtained a non-peptide NT receptor agonist. Therefore, there has been great interest in obtaining peptide analogues of NT, that, unlike NT resist degradation by peptidases and cross the blood-brain barrier, yet have the pharmacological characteristics of native NT, for therapeutic use in the treatment of schizophrenia, as well as other neuropsychiatric diseases such as Parkinson's disease and addiction to psychostimulants. In this review, we present the rationale for development of NT receptor agonists for treatment of certain central nervous system diseases, as well as a review of those peptide agonists that are in early stages of development.

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.

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.

Synthesis and evaluation of novel multimeric neurotensin(8–13) analogs

Neurotensin(8-13) is a hexapeptide with subnanomolar affinity to the neurotensin receptor 1 which is expressed with high incidence in several human tumor entities. Thus, radiolabeled neurotensin(8-13) might be used for tumor targeting. However, its application is limited by insufficient metabolic stability. The present study aims at improving metabolic stability by the synthesis of multimeric neurotensin(8-13) derivatives rather than commonly employed chemical modifications of the peptide itself. Thus, different dimeric and tetrameric peptides carrying C- or N-terminal attached neurotensin(8-13) moieties have been synthesized and their binding affinity toward the neurotensin receptor has been determined. The results demonstrate that branched compounds containing neurotensin(8-13) attached via its C-terminus only show low receptor affinities, whilst derivatives with neurotensin(8-13) attached via the N-terminus show IC50 values in the nanomolar range. Moreover, within the multimeric neurotensin(8-13) derivatives with neurotensin(8-13) attached via the N-terminus an increasing number of branching units lead to higher binding affinities toward the neurotensin receptor.

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.

Neurobiologic basis of nicotine addiction and psychostimulant abuse: a role for neurotensin?

Addiction to psychostimulant drugs such as nicotine, amphetamine, and cocaine is a serious public health problem for which there is a paucity of accepted forms of pharmacotherapy. Nicotine dependence has become more frequently associated with psychiatric illness in recent decades, and patients who have schizophrenia are at highest risk and have the poorest prognosis for stopping their addiction. Possible mechanisms for this association include self-medication, with nicotine attenuating attentional deficits and negative symptoms. Neurotensin has been postulated to be an endogenous neuroleptic, and the performance of neurotensin analogues in animal models of addiction makes such compounds intriguing candidates for treatment of addiction in high-risk psychiatric populations.

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.

Proteomic analysis of nicotine-associated protein expression in the striatum of repeated nicotine-treated rats

Through the proteomic analysis using 2-dimensional electrophoresis, the nicotine addiction-associated proteins were extensively screened in the striatum of rat brains. The nicotine addiction was developed by repeated nicotine injection (0.4mg/kg s.c.), twice daily for 7 days, followed by one challenge injection after a 3 day withdrawal period, and then confirmed by observing a 2.3-fold increase in locomoter activity. The 3 up- and 4 down-regulated proteins were selected and identified to be zinc-finger binding protein-89 (ZBP-89), 2'3'-cyclic nucleotide 3'-phosphodiesterase 1, deoxyribonuclease 1-like 3 (DNase1l3), tandem pore domain halothane inhibited K(+) channel (THIK-2), brain-specific hyaluronan-binding protein (BRAL-1), death effector domain-containing DNA binding protein (DEDD), and brain-derived neurotrophic factor (BDNF) by mass spectrophotometric fingerprinting. Among them, the expression patterns of ZEB-89, DNase1l3, THIK-2, DEDD, and BDNF mRNAs were found to be coincident with those of cognate proteins, by using RT-PCR analysis. These proteins could be suggested as drug targets to develop a new therapy for nicotine-associated diseases, as well as the clues to understand the mechanism of nicotine.

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: 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.