Neurotensin agonists: potential in the treatment of schizophrenia

Dissecting the association between psychiatric disorders and neurological proteins: a genetic correlation and two-sample bidirectional Mendelian randomization study

OBJECTIVES

The role of neurological proteins in the development of bipolar disorder (BD) and schizophrenia (SCZ) remains elusive now. The current study aims to explore the potential genetic correlations of plasma neurological proteins with BD and SCZ.

METHODS

By using the latest genome-wide association study (GWAS) summary data of BD and SCZ (including 41,917 BD cases, 11,260 SCZ cases, and 396,091 controls) derived from the Psychiatric GWAS Consortium website (PGC) and a recently released GWAS of neurological proteins (including 750 individuals), we performed a linkage disequilibrium score regression (LDSC) analysis to detect the potential genetic correlations between the two common psychiatric disorders and each of the 92 neurological proteins. Two-sample Mendelian randomisation (MR) analysis was then applied to assess the bidirectional causal relationship between the neurological proteins identified by LDSC, BD and SCZ.

RESULTS

LDSC analysis identified one neurological protein, NEP, which shows suggestive genetic correlation signals for both BD (coefficient = -0.165, p value = 0.035) and SCZ (coefficient = -0.235, p value = 0.020). However, those association did not remain significant after strict Bonferroni correction. Two sample MR analysis found that there was an association between genetically predicted level of NEP protein, BD (odd ratio [OR] = 0.87, p value = 1.61 × 10^-6) and SCZ (OR = 0.90, p value = 4.04 × 10^-6). However, in the opposite direction, there is no genetically predicted association between BD, SCZ, and NEP protein level.

CONCLUSION

This study provided novel clues for understanding the genetic effects of neurological proteins on BD and SCZ.

Association of Neurotensin Receptor 1 Gene Polymorphisms With Defense Mechanisms in Healthy Chinese

Aims: In the central nerve system, neurotensin (NT), and neurotensin receptor 1 (NTR1) modulate the dopamine system. Gene variations in the dopamine system have been demonstrated to influence certain defense mechanisms, but no studies have investigated possible effect of NTR1 gene polymorphisms in the biological determination of these defenses. The present study therefore examined this link. Methods: In 412 healthy Han Chinese, single nucleotide polymorphisms rs6090453C/G, rs6011914C/G, and rs2427422A/G of the NTR1 gene were genotyped, and the defense mechanisms were measured by the self-reporting Defense Style Questionnaire 88. Results: Significant male-specific differences in the projective identification among the rs6090453 genotypes (p = 0.003); in the intermediate defense, reaction formation, and projective identification among the rs6011914 genotypes (p = 0.011, 0.010, and 0.011, respectively); and in the projective identification among the rs2427422 genotypes (p = 0.005) were found when the level of significance was adjusted by the Bonferroni correction. There was no significant difference in any of the defense scores among genotypes of any single nucleotide polymorphism in the total cohort or female subjects (all p > 0.017). The distributions of genotypes between the low and high score subgroups showed significant differences in the rs2427422 genotype distributions for help-rejecting complaining, regression, and projective identification (p = 0.010, 0.022, and 0.044, respectively). Significant differences were found between males and females in 10 defense mechanisms (all P < 0.05). Conclusions: The gene variations in the NTR1 polymorphisms were involved in the biological mechanisms of intermediate defense mechanisms, and this effect was influenced by sex.

Neuropeptides and oligopeptidases in schizophrenia

Schizophrenia (SCZ) is a complex psychiatric disorder with severe impact on patient's livelihood. In the last years, the importance of neuropeptides in SCZ and other CNS disorders has been recognized, mainly due to their ability to modulate the signaling of classical monoaminergic neurotransmitters as dopamine. In addition, a class of enzymes coined as oligopeptidases are able to cleave several of these neuropeptides, and their potential implication in SCZ was also demonstrated. Interestingly, these enzymes are able to play roles as modulators of neuropeptidergic systems, and they were also implicated in neurogenesis, neurite outgrowth, neuron migration, and therefore, in neurodevelopment and brain formation. Altered activity of oligopeptidases in SCZ was described only more recently, suggesting their possible utility as biomarkers for mental disorders diagnosis or treatment response. We provide here an updated and comprehensive review on neuropeptides and oligopeptidases involved in mental disorders, aiming to attract the attention of physicians to the potential of targeting this system for improving the therapy and for understanding the neurobiology underlying mental disorders as SCZ.

NDE1 and NDEL1 from genes to (mal)functions: parallel but distinct roles impacting on neurodevelopmental disorders and psychiatric illness

NDE1 (Nuclear Distribution Element 1, also known as NudE) and NDEL1 (NDE-Like 1, also known as NudEL) are the mammalian homologues of the fungus nudE gene, with important and at least partially overlapping roles for brain development. While a large number of studies describe the various properties and functions of these proteins, many do not directly compare the similarities and differences between NDE1 and NDEL1. Although sharing a high degree structural similarity and multiple common cellular roles, each protein presents several distinct features that justify their parallel but also unique functions. Notably both proteins have key binding partners in dynein, LIS1 and DISC1, which impact on neurodevelopmental and psychiatric illnesses. Both are implicated in schizophrenia through genetic and functional evidence, with NDE1 also strongly implicated in microcephaly, as well as other neurodevelopmental and psychiatric conditions through copy number variation, while NDEL1 possesses an oligopeptidase activity with a unique potential as a biomarker in schizophrenia. In this review, we aim to give a comprehensive overview of the various cellular roles of these proteins in a "bottom-up" manner, from their biochemistry and protein-protein interactions on the molecular level, up to the consequences for neuronal differentiation, and ultimately to their importance for correct cortical development, with direct consequences for the pathophysiology of neurodevelopmental and mental illness.

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.

Neurotensin receptor 1 gene polymorphisms are associated with personality traits in healthy Chinese individuals

AIMS

Neurotensin receptor 1 (NTR1) is a neurotensin (NT) receptor subtype with a high affinity for NT. NT and NTR1 signaling are involved in modulating the dopamine system. Individual variations in the dopamine system have been demonstrated to determine certain dimensions of personality, but no studies have thus far investigated the involvement of the NTR1 in the biological determination of personality. We therefore examined this link in a Chinese Han population.

METHODS

We genotyped 3 single nucleotide polymorphisms (SNPs) (rs6090453C/G, rs6011914C/G, and rs2427422A/G) of the NTR1 gene and collected the data about the personality traits of novelty seeking (NS), harm avoidance (HA), and reward dependence (RD), as well as their subscales (measured by the Tridimensional Personality Questionnaire), in 575 healthy Chinese Han subjects. Then we examined the association between the 3 NTR1 gene polymorphisms and each personality trait.

RESULTS

There were significant differences in the HA2, HA3 and RD1 scores between rs6090453C/G genotypes (F = 3.425, 5.651, 4.054, p = 0.033, 0.004, 0.018, respectively), in the HA2 and total RD scores between rs6011914C/G genotypes (F = 4.080, 3.712, p = 0.017, 0.025, respectively), and in the total RD (χ(2) = 7.301, p = 0.026) and RD3 (F = 4.119, p = 0.017) scores between the rs2427422A/G genotypes. There were significant male-specific differences in the RD1 scores between the rs6090453C/G genotypes (F = 3.334, p = 0.037), in the total HA (F = 3.043, p = 0.049), HA2 (F = 4.472, p = 0.012) and RD3 (χ(2) = 6.997, p = 0.030) scores between the rs6011914C/G genotypes, and in the HA2 (F = 3.177, p = 0.043), total RD (χ(2) = 7.032, p = 0.030), and RD3 (F = 4.563, p = 0.011) scores between the rs2427422A/G genotypes. We also demonstrated a significant female-specific difference in the total RD scores between the rs6011914C/G genotypes (F = 3.677, p = 0.026). There was no significant difference in the total NS and subscale scores between the genotypes of all 3 SNPs (all p > 0.05).

CONCLUSIONS

The variations in the NTR1 gene were involved in the biological mechanisms of HA and RD personality traits; however, the effect is influenced by gender.

Structure-based evolution of subtype-selective neurotensin receptor ligands

Subtype-selective agonists of the neurotensin receptor NTS2 represent a promising option for the treatment of neuropathic pain, as NTS2 is involved in the mediation of μ-opioid-independent anti-nociceptive effects. Based on the crystal structure of the subtype NTS1 and previous structure-activity relationships (SARs) indicating a potential role for the sub-pocket around Tyr11 of NT(8-13) in subtype-specific ligand recognition, we have developed new NTS2-selective ligands. Starting from NT(8-13), we replaced the tyrosine unit by β(2)-amino acids (type 1), by heterocyclic tyrosine bioisosteres (type 2) and peptoid analogues (type 3). We were able to evolve an asymmetric synthesis of a 5-substituted azaindolylalanine and its application as a bioisostere of tyrosine capable of enhancing NTS2 selectivity. The S-configured test compound 2 a, [(S)-3-(pyrazolo[1,5-a]pyridine-5-yl)-propionyl(11)]NT(8-13), exhibits substantial NTS2 affinity (4.8 nm) and has a nearly 30-fold NTS2 selectivity over NTS1. The (R)-epimer 2 b showed lower NTS2 affinity but more than 600-fold selectivity over NTS1.

Plasma Ndel1 enzyme activity is reduced in patients with schizophrenia--a potential biomarker?

Ndel1 oligopeptidase interacts with schizophrenia (SCZ) risk gene product DISC1 and mediates several functions related to neurite outgrowth and neuronal migration. Ndel1 also hydrolyzes neuropeptides previously implicated in SCZ, namely neurotensin and bradykinin. Herein, we compared the plasma Ndel1 enzyme activity of 92 SCZ patients and 96 healthy controls (HCs). Ndel1 enzyme activity was determined by fluorimetric measurements of the FRET peptide substrate Abz-GFSPFRQ-EDDnp hydrolysis rate. A 31% lower mean value for Ndel1 activity was observed in SCZ patients compared to HCs (Student's t = 4.36; p < 0.001; Cohen's d = 0.64). The area under the curve (AUC) for the Receiver Operating Characteristic (ROC) curve for Ndel1 enzyme activity and SCZ/HCs status as outcome was 0.70. Treatment-resistant (TR) SCZ patients were shown to present a significantly lower Ndel1 activity compared to non-TR (NTR) patients by t-test analysis (t = 2.25; p = 0.027). A lower enzymatic activity was significantly associated with both NTR (p = 0.002; B = 1.19; OR = 3.29; CI 95% 1.57-6.88) and TR patients (p < 0.001; B = 2.27; OR = 9.64; CI 95% 4.12-22.54). No correlation between Ndel1 enzyme activity and antipsychotic dose, nicotine dependence, and body mass index was observed. This study is the first to show differences in Ndel1 activity in SCZ patients compared to HCs, besides with a significant lower activity for TR patients compared to NTR patients. Our findings support the Ndel1 enzyme activity implications to clinical practice in terms of diagnosis and drug treatment of SCZ.

OBJECTIVE OF THE STUDY

To compare the Ndel1 enzyme activity levels of schizophrenia (SCZ) patients and healthy controls (HCs) and to correlate these values with the clinical profile and response to treatment by measuring the Ndel1 enzyme activity in human plasma.

Neuropeptide receptor ligands as drugs for psychiatric diseases: the end of the beginning?

The search for novel drugs for treating psychiatric disorders is driven by the growing medical need to improve on the effectiveness and side-effect profile of currently available therapies. Given the wealth of preclinical data supporting the role of neuropeptides in modulating behaviour, pharmaceutical companies have been attempting to target neuropeptide receptors for over two decades. However, clinical studies with synthetic neuropeptide ligands have been unable to confirm the promise predicted by studies in animal models. Here, we analyse preclinical and clinical results for neuropeptide receptor ligands that have been studied in clinical trials for psychiatric diseases, including agents that target the receptors for tachykinins, corticotropin-releasing factor, vasopressin and neurotensin, and suggest new ways to exploit the full potential of these candidate drugs.

Neuropeptide S alters anxiety, but not depression-like behaviour in Flinders Sensitive Line rats: a genetic animal model of depression

Neuropeptide S (NPS) and its receptor (NPSR) have been implicated in the mediation of anxiolytic-like behaviour in rodents. However, little knowledge is available regarding the NPS system in depression-related behaviours, and whether NPS also exerts anxiolytic effects in an animal model of psychopathology. Therefore, the aim of this work was to characterize the effects of NPS on depression- and anxiety-related parameters, using male and female rats in a well-validated animal model of depression: the Flinders Sensitive Line (FSL), their controls, the Flinders Resistant Line (FRL), and Sprague-Dawley (SD) rats. We found that FSL showed greater immobility in the forced swim test (FST) than FRL, confirming their phenotype. However, NPS did not affect depression-related behaviour in any rat line. No significant differences in baseline anxiety levels between the FSL and FRL strains were observed, but FSL and FRL rats displayed less anxiety-like behaviour compared to SD rats. NPS decreased anxiety-like behaviour on the elevated plus-maze in all strains. The expression of the NPSR in the amygdala, periventricular hypothalamic nucleus, and hippocampus was equal in all male strains, although a trend towards reduced expression within the amygdala was observed in FSL rats compared to SD rats. In conclusion, NPS had a marked anxiolytic effect in FSL, FRL and SD rats, but did not modify the depression-related behaviour in any strain, in spite of the significant differences in innate level between the strains. These findings suggest that NPS specifically modifies anxiety behaviour but cannot overcome/reverse a genetically mediated depression phenotype.

The role of endogenous neurotensin in psychostimulant-induced disruption of prepulse inhibition and locomotion

The neuropeptide neurotensin (NT) is closely associated with dopaminergic and glutamatergic systems in the rat brain. Central injection of NT into the nucleus accumbens (NAcc) or peripheral administration of NT receptor agonists, reduces many of the behavioral effects of psychostimulants. However, the role of endogenous NT in the behavioral effects of psychostimulants (e.g. DA agonists and NMDA receptor antagonists) remains unclear. Using a NTR antagonist, SR142948A, the current studies were designed to examine the role of endogenous NT in DA receptor agonist- and NMDA receptor antagonist-induced disruption of prepulse inhibition of the acoustic startle response (PPI), locomotor hyperactivity and brain-region specific c-fos mRNA expression. Adult male rats received a single i.p. injection of SR142948A or vehicle followed by D-amphetamine, apomorphine or dizocilpine challenge. SR142948A had no effect on baseline PPI, but dose-dependently attenuated d-amphetamine- and dizocilpine-induced PPI disruption and enhanced apomorphine-induced PPI disruption. SR142948A did not significantly affect either baseline locomotor activity or stimulant-induced hyperlocomotion. Systemic SR142948A administration prevented c-fos mRNA induction in mesolimbic terminal fields (prefrontal cortex, lateral septum, NAcc, ventral subiculum) induced by all three psychostimulants implicating the VTA as the site for NT modulation of stimulant-induced PPI disruption. Further characterization of the NT system may be valuable to find clinical useful compounds for schizophrenia and drug addiction.

DISC1 Pathway in Brain Development: Exploring Therapeutic Targets for Major Psychiatric Disorders

Genetic risk factors for major psychiatric disorders play key roles in neurodevelopment. Thus, exploring the molecular pathways of risk genes is important not only for understanding the molecular mechanisms underlying brain development, but also to decipher how genetic disturbances affect brain maturation and functioning relevant to major mental illnesses. During the last decade, there has been significant progress in determining the mechanisms whereby risk genes impact brain development. Nonetheless, given that the majority of psychiatric disorders have etiological complexities encompassing multiple risk genes and environmental factors, the biological mechanisms of these diseases remain poorly understood. How can we move forward to our research for discovery of the biological markers and novel therapeutic targets for major mental disorders? Here we review recent progress in the neurobiology of disrupted in schizophrenia 1 (DISC1), a major risk gene for major mental disorders, with a particular focus on its roles in cerebral cortex development. Convergent findings implicate DISC1 as part of a large, multi-step pathway implicated in various cellular processes and signal transduction. We discuss links between the DISC1 pathway and environmental factors, such as immune/inflammatory responses, which may suggest novel therapeutic targets. Existing treatments for major mental disorders are hampered by a limited number of pharmacological targets. Consequently, elucidation of the DISC1 pathway, and its association with neuropsychiatric disorders, may offer hope for novel treatment interventions.

Selective agonists for dopamine/neurotensin receptor heterodimers

The neuromodulatory peptide neurotensin has been described to functionally interact with dopaminergic pathways of the human brain. We employed radioligand binding studies to investigate the physical interaction between co-expressed dopamine D(2L) or D₃ and neurotensin NTS₁ or NTS₂ receptors. Substantial cross-inhibitory effects of both receptor subtypes NTS(1) and NTS₂ on the agonist binding of D(2L) or D₃ were detected in the presence of neurotensin. To identify ligand-specific modulation and subtype-dependent differences, the novel dopamine receptor agonists 5 and 6 bearing the 7-OH-DPAT pharmacophore were synthesized. Exceptional ligand specificity was observed for D₃-NTS₂ co-expression, which gave a 20-fold decrease in affinity for biphenylcarboxamide 5 in the presence of neurotensin. Comparing the binding properties of dopaminergic compounds in the presence of neurotensin, dopamine receptor subtype-selective profiles of the cross-inhibitory effect of neurotensin were observed.

Contribution of neurotensin in the immune and neuroendocrine modulation of normal and abnormal enteric function

Among various hormones, which are synthesized by intestinal cells and influence enteric function, neurotensin (NT) has gained scientific attention the last three decades. This neuropeptide, mainly located in neuronal synaptic vesicles of hypothalamus and in neuroendocrine cells of the small bowel, participates in enteric digestive processes, gut motility and intestinal inflammatory mechanisms by cooperating with other regulators such as histamine, substance P and somatostatin. NT plays an important role mainly in intestinal lipid metabolism by cooperating with cholecystokinin and establishes a hormonal brain-gut-adipose tissue connection, which could adjust appetite, weight status and generally eating behavior with the amount and the content (particularly fat) of food intake. Moreover, NT achieves a multi-level control of intestinal motility by cooperating with the enteric- and central nervous system, and other enteric hormones (such as somatostatin). NT regulates motility patterns related to the efficiency of the digestive process, stool emptying, transition from the fasted to the postprandial state and reestablishment of the fasted status. In addition, NT possesses a long-term enteroprotective role towards the intestinal tract, despite the fact that under certain circumstances NT may participate in short-term subcellular pathways promoting an acute inflammatory response. The aim of this review is two-fold. First, is to provide an up-to-date synopsis of the available knowledge regarding the involvement of neurotensin in enteric functional status, and highlight its significance in physiological and pathological conditions. Second, is to propose new research directions concerning the role of neurotensin and other intestinal regulatory peptides in the establishment of the brain-gut axis and in the development of functional disorders of the abdominal tract. Conclusively, to clarify the areas, in which an experimental therapeutic intervention, based on NT analogs, may lead to encouraging results.

Contributions of dopamine-related genes and environmental factors to highly sensitive personality: a multi-step neuronal system-level approach

Traditional behavioral genetic studies (e.g., twin, adoption studies) have shown that human personality has moderate to high heritability, but recent molecular behavioral genetic studies have failed to identify quantitative trait loci (QTL) with consistent effects. The current study adopted a multi-step approach (ANOVA followed by multiple regression and permutation) to assess the cumulative effects of multiple QTLs. Using a system-level (dopamine system) genetic approach, we investigated a personality trait deeply rooted in the nervous system (the Highly Sensitive Personality, HSP). 480 healthy Chinese college students were given the HSP scale and genotyped for 98 representative polymorphisms in all major dopamine neurotransmitter genes. In addition, two environment factors (stressful life events and parental warmth) that have been implicated for their contributions to personality development were included to investigate their relative contributions as compared to genetic factors. In Step 1, using ANOVA, we identified 10 polymorphisms that made statistically significant contributions to HSP. In Step 2, these polymorphism's main effects and interactions were assessed using multiple regression. This model accounted for 15% of the variance of HSP (p<0.001). Recent stressful life events accounted for an additional 2% of the variance. Finally, permutation analyses ascertained the probability of obtaining these findings by chance to be very low, p ranging from 0.001 to 0.006. Dividing these loci by the subsystems of dopamine synthesis, degradation/transport, receptor and modulation, we found that the modulation and receptor subsystems made the most significant contribution to HSP. The results of this study demonstrate the utility of a multi-step neuronal system-level approach in assessing genetic contributions to individual differences in human behavior. It can potentially bridge the gap between the high heritability estimates based on traditional behavioral genetics and the lack of reproducible genetic effects observed currently from molecular genetic studies.

Cross-receptor interactions between dopamine D2L and neurotensin NTS1 receptors modulate binding affinities of dopaminergics

Dopaminergic systems have been described to functionally interact with the neuromodulatory peptide neurotensin. Employing fluorescence detected coimmunoprecipitation and radioligand binding experiments, we herein demonstrate that coexpression of dopamine D(2L) receptor and the neurotensin receptor subtype NTS(1) leads to physical interaction and the formation of heteromers in transfected human embryonic kidney 293 cells. In this in vitro system, a trans-inhibitory effect on the agonist binding affinity of D(2) was observed in presence of neurotensin. To correlate between the functional properties of dopaminergic agents and the magnitude of neurotensin-induced modulation of D(2L) binding affinities in cells coexpressing D(2L) and NTS(1), a structurally diverse set of dopamine receptor agonists, partial agonists, and antagonists was tested. Ligand specific profiles indicating substantial bias between ligand efficacy and transmodulation were discovered, suggesting a heteromerization-based functional selectivity. In the presence of neurotensin, the novel D(2) agonist FAUC 326 displayed a 34-fold decrease of binding affinity in cells coexpressing D(2L) and NTS(1).

Neurotensin triggers dopamine D2 receptor desensitization through a protein kinase C and beta-arrestin1-dependent mechanism

The peptide neurotensin (NT) is known to exert a potent excitatory effect on the dopaminergic system by inhibiting D2 dopamine (DA) receptor (D2R) function. This regulation is dependent on activation of PKC, a well known effector of the type 1 NT receptor (NTR1). Because PKC phosphorylation of the D2R has recently been shown to induce its internalization, we hypothesized that NT acts to reduce D2R function through heterologous desensitization of the D2R. In the present study, we first used HEK-293 cells to demonstrate that NT induces PKC-dependent D2R internalization. Furthermore, internalization displayed faster kinetics in cells expressing the D2R short isoform, known to act as an autoreceptor in DA neurons, than in cells expressing the long isoform, known to act as a postsynaptic D2R. In patch clamp experiments on cultured DA neurons, overexpression of a mutant D2S lacking three key PKC phosphorylation sites abrogated the ability of NT to reduce D2R-mediated cell firing inhibition. Short interfering RNA-mediated inhibition of β-arrestin1 and dynamin2, proteins important for receptor desensitization, reduced agonist-induced desensitization of D2R function, but only the inhibition of β-arrestin1 reduced the effect of NT on D2R function. Taken together, our data suggest that NT acutely regulates D2 autoreceptor function and DA neuron excitability through PKC-mediated phosphorylation of the D2R, leading to heterologous receptor desensitization.

Effects of neurotensin-2 receptor deletion on sensorimotor gating and locomotor activity

Endogenous neurotensin (NT) has been implicated in brain processes relevant to schizophrenia as well as the therapeutic effects of antipsychotic drugs (APDs) used to treat this disorder. Converging evidence suggests that NT1 receptors mediate the antipsychotic-like effects of NT, such as prepulse inhibition (PPI) elevation. However, the role of NT2 receptors in these effects is not known. To investigate the contribution of NT2 receptors to the regulation of PPI, we measured baseline PPI and acoustic startle response (ASR), in male and female wild type (WT) and NT2 knockout (KO) mice. For comparison, we also measured locomotor activity. Baseline PPI was significantly elevated in both male (P<0.01) and female (P<0.01) NT2 KO compared to WT mice, while ASR was significantly decreased in KO mice of both genders (P<0.01). In contrast, female but not male KO mice exhibited significantly less baseline ambulations (P<0.05). These data support the regulation of baseline PPI, ASR and locomotor activity by endogenous NT acting at the NT2 receptor. Further studies investigating the role of NT2 receptors in the modulation of APD-like effects are warranted.

Chronic NT69L potently prevents drug-induced disruption of prepulse inhibition without causing tolerance

NT69L is a neurotensin receptor agonist with antipsychotic-like activity. NT69L blocks apomorphine-induced climbing in rats with no effect on stereotypic behavior, attenuates d-amphetamine-induced hyperactivity, and blocks pharmacologically induced disruption of prepulse inhibition (PPI) of the startle response. Repeated administration of NT69L results in tolerance to some, but not to all of its effects. Because schizophrenic patients require long-term treatment, chronic (21-day) administration of NT69L was tested in PPI with comparisons to chronic haloperidol and clozapine treatment. Sprague-Dawley rats received acute or 21 daily, subcutaneous injections of NT69L (1.0mg/kg). On days 1 and 21 the NT69L injection was followed 30 min later by treatment with either saline; the dopamine agonist, d-amphetamine (5.0mg/kg); or the serotonin 5-HT(2A) psychotomimetic receptor agonist [1-(2,5-dimethoxy-4-iodophenyl)-2-aminopropane] DOI (0.5mg/kg). Experiments were repeated with either haloperidol (1mg/kg) or clozapine (20mg/kg) in place of NT69L. Acute injection of NT69L significantly blocked d-amphetamine and DOI disruption of PPI. As with the acute injection, 21 daily administrations of NT69L also blocked d-amphetamine- and DOI-induced disruption of PPI. The data show that animals do not develop tolerance to the antipsychotic-like effects of NT69L when tested in the PPI of the startle response. The persistent efficacy of NT69L with chronic treatment provides further support for the therapeutic use of neurotensin (NT) agonists to treat schizophrenia and possibly other disorders that are characterized by PPI deficits. The modulatory role of NT69L on the dopaminergic and serotonergic neurotransmission systems both of which are implicated in the pathophysiology of schizophrenia is discussed.

NT79: A novel neurotensin analog with selective behavioral effects

Neurotensin, a tridecapeptide, is widely distributed in the brain and gastrointestinal tract. It possesses analgesic, hypothermic, and antipsychotic-like properties. Neurotensin's effects are mediated mainly through two receptor subtypes, NTS1 and NTS2. Activation of NTS1 has been implicated in most of the pharmacological effects of neurotensin but is associated with hypothermia and hypotension. We report on a novel neurotensin analog with higher selectivity to NTS2, namely, NT79, which exhibits selective behavioral effects. NT79 was tested in animal models for pain (thermal-hot plate test; visceral-acetic acid-induced writhing test), and in animal models that are predictive of antipsychotic-like effects (apomorphine-induced climbing; d-amphetamine-induced hyperactivity; disruption of prepulse inhibition). Its effects on body temperature and on blood pressure were also determined. Neurochemical changes in extracellular neurotransmitters were measured using in vivo microdialysis while the rats were simultaneously evaluated for acetic acid-induced writhing with and without pretreatment with NT79. Binding data at molecularly cloned hNTS1 and hNTS2 suggest selectivity for hNTS2. NT79 blocked the acetic acid-induced writhing with an ED(50) of 0.14 microg/kg while having no effect on thermal nociception. The writhing was paralleled by an increase in 5-HT which was attenuated by NT79. NT79 demonstrated antipsychotic-like effects by blocking apomorphine-induced climbing, d-amphetamine-induced hyperactivity, and reducing d-amphetamine- and DOI-induced disruption of prepulse inhibition. Uniquely, it caused no significant hypothermia and was without effect on blood pressure. NT79, with its higher selectivity to NTS2, may be potentially useful to treat visceral pain, and psychosis without concomitant side effects of hypothermia or hypotension.

Focus on HTR2C: A possible suggestion for genetic studies of complex disorders

HTR2C is one of the most relevant and investigated serotonin receptors. Its role in important brain structures such as the midbrain, the lateral septal complex, the hypothalamus, the olfactory bulb, the pons, the choroid plexus, the nucleus pallidus, the striatum and the amygdala, the nucleus accumbens and the anterior cingulated gyrus candidate it as a promising target for genetic association studies. The biological relevance of these brain structures is reviewed by way of the focus on HTR2C activity, with a special attention paid to psychiatric disorders. Evidence from the genetic association studies that dealt with HTR2C is reviewed and discussed alongside the findings derived from the neuronatmic investigations. The reasons for the discrepancies between these two sets of reports are discussed. As a result, HTR2C is shown to play a pivotal role in many different psychiatric behaviors or psychiatric related disrupted molecular balances, nevertheless, genetic association studies brought inconsistent results so far. The most replicated association involve the feeding behavior and antipsychotic induced side effects, both weight gain and motor related: Cys23Ser (rs6318) and -759C/T (rs3813929) report the most consistent results. The lack of association found in other independent studies dampens the clinical impact of these reports. Here, we report a possible explanation for discrepant findings that is poorly or not at all usually considered, that is that HTR2C may exert different or even opposite activities in the brain depending on the structure analyzed and that mRNA editing activity may compensate possible genetically controlled functional effects. The incomplete coverage of the HTR2C variants is proposed as the best cost-benefit ratio bias to fix. The evidence of brain area specific HTR2C mRNA editing opens a debate about how the brain can differently modulate stress events, and process antidepressant treatments, in different brain areas. The mRNA editing activity on HTR2C may play a major role for the negative association results.

The neurotensin-1 receptor agonist PD149163 blocks fear-potentiated startle

Preliminary evidence suggests that the neuropeptide, neurotensin (NT) may regulate fear/anxiety circuits. We investigated the effects of PD149163, a NT1 receptor agonist, on fear-potentiated startle (FPS). Sprague Dawley rats were trained to associate a white light with a mild foot shock. In one experiment, animals were treated with either subcutaneous vehicle or PD149163 (0.01, 0.1 or 1.0 mg/kg) 24 h after training. Twenty minutes later their acoustic startle response in the presence or absence of the white light was tested. In a second experiment, saline and 1.0 mg/kg PD149163 were tested using a separate group of rats. In the first experiment, PD149163 produced a non-significant decrease in baseline acoustic startle at all three doses. As expected, saline-treated rats exhibited significant FPS. An ANOVA of percentage FPS revealed no significant effect of treatment group overall but the high dose group did not display FPS strongly suggesting an FPS effect at this dose. This finding was confirmed in the second experiment where the high dose of PD149163 reduced percent FPS relative to saline (P < 0.05). These data suggest that systemically administered NT1 agonists modulate the neural circuitry that regulates fear and anxiety to produce dose-dependent anxiolytic-like effects on FPS.

Biology of neurotensin: revisited study

The tridecapeptide neurotensin (NT) acts in the mammalian brain as a primary neurotransmitter or neuromodulator of classical neurotransmitters. Morphological and functional in vitro and in vivo studies have demonstrated the existence of close interactions between NT and dopamine both in limbic and in striatal brain regions. Additionally, biochemical and neurochemical evidence indicates that in these brain regions NT also plays a crucial role in the regulation of the aminoacidergic signalling. Immune cells, such as lymphocytes, macrophages and mast cells are reported to be activated by neuropeptides, such as neurotensin; this activation leads to cytokine and immunoglobulin production. In addition, neurotensin increases calcium level and the production of nitric oxide. Therefore neurotensin is deeply involved in immunity and inflammation but its real function still remains to be elucidated.

[Development of antipsychotic drug: new directions]

The treatment of psychotic disorders has been dramatically changed by the discovery, in 1952, of antipsychotic activity of chlorpromazine and the definition of criteria for a new therapeutic class. Since then, although major improvements were done in terms of neurological tolerance and easiness to handle, today's antipsychotics are highly similar to former ones. Those treatments do not answer to all expectations of patients or practitioners, in particular regarding their metabolic or cardiologic side effects and potency to reduce cognitive deficit. Moreover, despite increasing understanding of the pathophysiology of schizophrenic disorders, this new knowledge is not or very little used in the field of therapeutics, justifying to resume research efforts to improve therapeutics in psychotic disorders. The development of a new medication follows several steps, based on precise strategies and regulations. The main streams of research concern compounds that act on dopaminergic, serotoninergic or peptidergic systems.

Protein expression in the nucleus accumbens of rats exposed to developmental vitamin D deficiency

INTRODUCTION

Developmental vitamin D (DVD) deficiency is a candidate risk factor for schizophrenia. Animal models have confirmed that DVD deficiency is associated with a range of altered genomic, proteomic, structural and behavioural outcomes in the rat. Because the nucleus accumbens has been implicated in neuropsychiatric disorders, in the current study we examined protein expression in this region in adult rats exposed to DVD deficiency

METHODS

Female Sprague Dawley rats were maintained on a vitamin D deficient diet for 6 weeks, mated and allowed to give birth, after which a diet containing vitamin D was reintroduced. Male adult offspring (n = 8) were compared to control male (n = 8). 2-D gel electrophoresis-based proteomics and mass spectroscopy were used to investigate differential protein expression.

RESULTS

There were 35 spots, mapped to 33 unique proteins, which were significantly different between the two groups. Of these, 22 were down-regulated and 13 up-regulated. The fold changes were uniformly small, with the largest FC being -1.67. Within the significantly different spots, three calcium binding proteins (calbindin1, calbindin2 and hippocalcin) were altered. Other proteins associated with DVD deficiency related to mitochondrial function, and the dynamin-like proteins.

CONCLUSIONS

Developmental vitamin D deficiency was associated with subtle changes in protein expression in the nucleus accumbens. Disruptions in pathways related to calcium-binding proteins and mitochondrial function may underlie some of the behavioural features associated with animal models of developmental vitamin D deficiency.

Pharmacology of neuropeptide S in mice: therapeutic relevance to anxiety disorders

RATIONALE

Neuropeptide S (NPS) and its receptor (NPSR) comprise a recently deorphaned G protein-coupled receptor system. Recent reports implicate NPS in the mediation of anxiolytic-like activity in rodents.

OBJECTIVES

To extend the characterization of NPS, the present studies examined the in vitro pharmacology of mouse NPSR and the in vivo pharmacology of NPS in three preclinical mouse models predictive of anxiolytic action: the four-plate test (FPT), elevated zero maze (EZM), and stress-induced hyperthermia (SIH). The ability of NPS to produce antidepressant-like effects in the tail suspension test (TST) was also investigated.

RESULTS

In vitro, mouse NPS 1-20 (mNPS 1-20) and the C-terminal glutamine-truncated mouse NPS 1-19 bound mNPSR with high affinity (Ki = 0.203 +/- 0.060, 0.635 +/- 0.141 nM, respectively) and potently activated intracellular calcium release (EC50 = 3.73 +/- 1.08, 4.10 +/- 1.25 nM). NPS produced effects in vivo consistent with anxiolytic-like activity. In FPT, NPS increased punished crossings (minimal effective dose [MED]: mNPS 1-20 = 0.2 microg, mNPS(1-19) = 0.02 microg), similar to the reference anxiolytic, alprazolam (MED 0.5 microg). NPS increased the percentage of time spent in the open quadrants of EZM (MED: mNPS 1-20 = 0.1 microg, mNPS 1-19 = 1.0 microg), like the reference anxiolytic, chlordiazepoxide (MED 56 microg). In SIH, NPS attenuated stress-induced increases in body temperature similar to alprazolam but with a large potency difference between the NPS peptides (MED: mNPS 1-20 = 2.0 microg, mNPS 1-19 = 0.0002 microg) and mNPS 1-20 increased baseline temperature. Unlike fluoxetine, NPS did not effect immobility time in TST, indicating a lack of antidepressant-like activity.

CONCLUSIONS

These data provide an important confirmation and expansion of the anxiolytic-like effects of NPS and implicate the NPS system as a novel target for anxiolytic drug discovery.

Mesolimbic dopamine and cortico-accumbens glutamate afferents as major targets for the regulation of the ventral striato-pallidal GABA pathways by neurotensin peptides

The tridecapeptide neurotensin (NT) acts in the mammalian brain as a primary neurotransmitter or neuromodulator of classical neurotransmitters. Morphological and functional in vitro and in vivo studies have demonstrated the existence of close interactions between NT and dopamine both in limbic and in striatal brain regions. Additionally, biochemical and neurochemical evidence indicates that in these brain regions NT plays also a crucial role in the regulation of the aminoacidergic signalling. It is suggested that in the nucleus accumbens the regulation of prejunctional dopaminergic transmission induced by NT may be primarily due to indirect mechanism(s) involving mediation via the aminoacidergic neuronal systems with increased glutamate release followed by increased GABA release in the nucleus accumbens rather than a direct action of the peptide on accumbens dopaminergic terminals. The neurochemical profile of action of NT in the control of the pattern of dopamine, glutamate and GABA release in the nucleus accumbens differs to a substantial degree from that shown by the peptide in the dorsal striatum. The neuromodulatory NT mechanisms in the regulation of the ventral striato-pallidal GABA pathways are discussed and their relevance for schizophrenia is underlined.