Blockade of adenosine A2A receptor counteracts neuropeptide-S-induced hyperlocomotion in mice

Pathophysiological and therapeutic implications of neuropeptide S system in neurological disorders

Neuropeptide S (NPS) is a 20 amino acids-containing neuroactive molecule discovered by the reverse pharmacology method. NPS is detected in specific brain regions like the brainstem, amygdala, and hypothalamus, while its receptor (NPSR) is ubiquitously expressed in the central nervous system (CNS). Besides CNS, NPS and NPSR are also expressed in the peripheral nervous system. NPSR is a G-protein coupled receptor that primarily uses Gq and Gs signaling pathways to mediate the actions of NPS. In animal models of Parkinsonism and Alzheimer's disease, NPS exerts neuroprotective effects. NPS suppresses oxidative stress, anxiety, food intake, and pain, and promotes arousal. NPSR facilitates reward, reinforcement, and addiction-related behaviors. Genetic variation and single nucleotide polymorphism in NPSR are associated with depression, schizophrenia, rheumatoid arthritis, and asthma. NPS interacts with several neurotransmitters including glutamate, noradrenaline, serotonin, corticotropin-releasing factor, and gamma-aminobutyric acid. It also modulates the immune system via augmenting pro-inflammatory cytokines and plays an important role in the pathogenesis of rheumatoid arthritis and asthma. In the present review, we discussed the distribution profile of NPS and NPSR, signaling pathways, and their importance in the pathophysiology of various neurological disorders. We have also proposed the areas where further investigations on the NPS system are warranted.

Neuropeptide S Receptor as an Innovative Therapeutic Target for Parkinson Disease

Parkinson disease (PD) is a neurodegenerative disease mainly characterized by the loss of nigral dopaminergic neurons in the substantia nigra pars compacta. Patients suffering from PD develop severe motor dysfunctions and a myriad of non-motor symptoms. The treatment mainly consists of increasing central dopaminergic neurotransmission and alleviating motor symptoms, thus promoting severe side effects without modifying the disease’s progress. A growing body of evidence suggests a close relationship between neuropeptide S (NPS) and its receptor (NPSR) system in PD: (i) double immunofluorescence labeling studies showed that NPSR is expressed in the nigral tyrosine hydroxylase (TH)-positive neurons; (ii) central administration of NPS increases spontaneous locomotion in naïve rodents; (iii) central administration of NPS ameliorates motor and nonmotor dysfunctions in animal models of PD; (iv) microdialysis studies showed that NPS stimulates dopamine release in naïve and parkinsonian rodents; (v) central injection of NPS decreases oxidative damage to proteins and lipids in the rodent brain; and, (vi) 7 days of central administration of NPS protects from the progressive loss of nigral TH-positive cells in parkinsonian rats. Taken together, the NPS/NPSR system seems to be an emerging therapeutic strategy for alleviating motor and non-motor dysfunctions of PD and, possibly, for slowing disease progress.

Stress induces reinstatement of extinguished cocaine conditioned place preference by a sequential signaling via neuropeptide S, orexin, and endocannabinoid

Neurons containing neuropeptide S (NPS) and orexins are activated during stress. Previously, we reported that orexins released during stress, via orexin OX₁ receptors (OX₁ Rs), contribute to the reinstatement of cocaine seeking through endocannabinoid/CB₁ receptor (CB₁ R)-mediated dopaminergic disinhibition in the ventral tegmental area (VTA). Here, we further demonstrated that NPS released during stress is an up-stream activator of this orexin-endocannabinoid cascade in the VTA, leading to the reinstatement of cocaine seeking. Mice were trained to acquire cocaine conditioned place preference (CPP) by context-pairing cocaine injections followed by the extinction training with context-pairing saline injections. Interestingly, the extinguished cocaine CPP in mice was significantly reinstated by intracerebroventricular injection (i.c.v.) of NPS (1 nmol) in a manner prevented by intraperitoneal injection (i.p.) of SHA68 (50 mg/kg), an NPS receptor antagonist. This NPS-induced cocaine reinstatement was prevented by either i.p. or intra-VTA microinjection (i.vta.) of SB-334867 (15 mg/kg, i.p. or 15 nmol, i.vta.) and AM 251 (1.1 mg/kg, i.p. or 30 nmol, i.vta.), antagonists of OX₁ Rs and CB₁ Rs, respectively. Besides, NPS (1 nmol, i.c.v.) increased the number of c-Fos-containing orexin neurons in the lateral hypothalamus (LH) and increased orexin-A level in the VTA. The latter effect was blocked by SHA68. Furthermore, a 30-min restraint stress in mice reinstated extinguished cocaine CPP and was prevented by SHA68. These results suggest that NPS is released upon stress and subsequently activates LH orexin neurons to release orexins in the VTA. The released orexins then reinstate extinguished cocaine CPP via an OX₁ R- and endocannabinoid-CB₁ R-mediated signaling in the VTA.

The Neural Network of Neuropeptide S (NPS): Implications in Food Intake and Gastrointestinal Functions

The Neuropeptide S (NPS), a 20 amino acids peptide, is recognized as the endogenous ligand of a previously orphan G protein-coupled receptor, now termed NPS receptor (NPSR). The limited distribution of the NPS-expressing neurons in few regions of the brainstem is in contrast with the extensive expression of NPSR in the rodent central nervous system, suggesting the involvement of this receptor in several brain functions. In particular, NPS promotes locomotor activity, behavioral arousal, wakefulness, and unexpectedly, at the same time, it exerts anxiolytic-like properties. Intriguingly, the NPS system is implicated in the rewarding properties of drugs of abuse and in the regulation of food intake. Here, we focus on the anorexigenic effect of NPS, centrally injected in different brain areas, in both sated and fasted animals, fed with standard or palatable food, and, in addition, on its influence in the gastrointestinal tract. Further investigations, regarding the role of the NPS/NPSR system and its potential interaction with other neurotransmitters could be useful to understand the mechanisms underlying its action and to develop novel pharmacological tools for the treatment of aberrant feeding patterns and obesity.

Role of Neuropeptide S on Behavioural and Neurochemical Changes of an Animal Model of Attention-Deficit/Hyperactivity Disorder

Neuropeptide S (NPS) is a recently discovered peptide signalling through its receptor NPSR, which is expressed throughout the brain. Since NPSR activation increases dopaminergic transmission, we now tested if NPSR modulates behavioural and neurochemical alterations displayed by an animal model of attention-deficit/hyperactivity disorder (ADHD), Spontaneous Hypertensive Rats (SHR), compared to its control strain, Wistar Kyoto rats (WKY). NPS (0.1 and 1 nmol, intracerebroventricularly (icv)) did not modify the performance in the open field test in both strains; however, NPSR antagonism with [^tBu-d-Gly⁵]NPS (3 nmol, icv) increased, per se, the total distance travelled by WKY. In the elevated plus-maze, NPS (1 nmol, icv) increased the percentage of entries in the open arms (%EO) only in WKY, an effect prevented by pretreatment with [^tBu-d-Gly⁵]NPS (3 nmol, icv), which decreased per se the %EO in WKY and increased their number of entries in the closed arms. Immunoblotting of frontal cortical extracts showed no differences of NPSR density, although SHR had a lower NPS content than WKY. SHR showed higher activity of dopamine uptake than WKY, and NPS (1 nmol, icv) did not change this profile. Overall, the present work shows that the pattern of functioning of the NPS system is distinct in WKY and SHR, suggesting that this system may contribute to the pathophysiology of ADHD.

Neuropeptide S-initiated sequential cascade mediated by OX1, NK1, mGlu5 and CB1 receptors: a pivotal role in stress-induced analgesia

Background

Stress-induced analgesia (SIA) is an evolutionarily conserved phenomenon during stress. Neuropeptide S (NPS), orexins, substance P, glutamate and endocannabinoids are known to be involved in stress and/or SIA, however their causal links remain unclear. Here, we reveal an unprecedented sequential cascade involving these mediators in the lateral hypothalamus (LH) and ventrolateral periaqueductal gray (vlPAG) using a restraint stress-induced SIA model.

Methods

Male C57BL/6 mice of 8–12 week-old were subjected to intra-cerebroventricular (i.c.v.) and/or intra-vlPAG (i.pag.) microinjection of NPS, orexin-A or substance P alone or in combination with selective antagonists of NPS receptors (NPSRs), OX₁ receptors (OX₁Rs), NK₁ receptors (NK₁Rs), mGlu₅ receptors (mGlu₅Rs) and CB₁ receptors (CB₁Rs), respectively. Antinociceptive effects of these mediators were evaluated via the hot-plate test. SIA in mice was induced by a 30-min restraint stress. NPS levels in the LH and substance P levels in vlPAG homogenates were compared in restrained and unrestrained mice.

Results

NPS (i.c.v., but not i.pag.) induced antinociception. This effect was prevented by i.c.v. blockade of NPSRs. Substance P (i.pag.) and orexin-A (i.pag.) also induced antinociception. Substance P (i.pag.)-induced antinociception was prevented by i.pag. Blockade of NK₁Rs, mGlu₅Rs or CB₁Rs. Orexin-A (i.pag.)-induced antinociception has been shown previously to be prevented by i.pag. blockade of OX₁Rs or CB₁Rs, and here was prevented by NK₁R or mGlu₅R antagonist (i.pag.). NPS (i.c.v.)-induced antinociception was prevented by i.pag. blockade of OX₁Rs, NK₁Rs, mGlu₅Rs or CB₁Rs. SIA has been previously shown to be prevented by i.pag. blockade of OX₁Rs or CB₁Rs. Here, we found that SIA was also prevented by i.c.v. blockade of NPSRs or i.pag. blockade of NK₁Rs or mGlu₅Rs. Restrained mice had higher levels of NPS in the LH and substance P in the vlPAG than unrestrained mice.

Conclusions

These results suggest that, during stress, NPS is released and activates LH orexin neurons via NPSRs, releasing orexins in the vlPAG. Orexins then activate OX₁Rs on substance P-containing neurons in the vlPAG to release substance P that subsequently. Activates NK₁Rs on glutamatergic neurons to release glutamate. Glutamate then activates perisynaptic mGlu₅Rs to initiate the endocannabinoid retrograde inhibition of GABAergic transmission in the vlPAG, leading to analgesia.

Dopamine D1 and D2 receptors mediate neuropeptide S-induced antinociception in the mouse formalin test

Neuropeptide S (NPS) is the endogenous ligand of a G-protein coupled receptor named NPS receptor. The NPS system controls several biological functions, including anxiety, wakefulness, locomotor activity, food intake, and pain transmission. A growing body of evidence supports facilitatory effects for NPS over dopaminergic neurotransmission. The present study was aimed to investigate the role of dopamine receptors signaling in the antinociceptive effects of NPS in the mouse formalin test. The following dopamine receptor antagonists were employed: SCH 23390 (selective dopamine D₁ antagonist, 0.05 mg/kg, ip), haloperidol (non-selective dopamine D₂-like receptor antagonist; 0.03 mg/kg, ip), and sulpiride (selective dopamine D₂-like receptor antagonist; 25 mg/kg, ip). Mice were pretreated with dopamine antagonists before the supraspinal administration of NPS (0.1 nmol, icv). Morphine (5 mg/kg, sc) and indomethacin (10 mg/kg, ip) were used as positive controls to set up the experimental conditions. Morphine-induced antinociceptive effects were observed during phases 1 and 2 of the test, while indomethacin was only active at phase 2. Central NPS significantly reduced formalin-induced nociception during both phases. The systemic administration of SCH 23390 slightly blocked the effects of NPS only during phase 2. Haloperidol prevented NPS-induced antinociceptive effects. Similar to haloperidol, sulpiride also counteracted the antinociceptive effects of NPS in both phases of the formalin test. In conclusion, the present findings suggest that the analgesic effects of NPS are linked with dopaminergic neurotransmission mainly through dopamine D₂-like receptor signaling.

Central neuropeptide-S treatment improves neurofunctions of 6-OHDA-induced Parkinsonian rats

Parkinson's disease (PD) is characterized by degeneration of the dopaminergic neurons in substantia nigra (SN). The motor symptoms of PD include tremor, rigidity, bradykinesia and postural impairment. In rodents, central administration of neuropeptide-S (NPS) has been shown to induce locomotor activity, dopamine release and neuronal survival by decreasing lipid peroxidation, additionally, the NPS receptor (NPSR) was detected in SN. Accumulating findings suggest that central NPS may ameliorate the parkinsonian symptoms, however, this has been explored incompletely due to the scarcity of experimental studies. Therefore, the present study was designed to test whether central NPS treatment exerts protective and/or alleviative effects on 6-OHDA-induced rat experimental PD model. Adult male Wistar rats received acute (alleviate; 10 nmol, icv) or chronic (protective; 1 nmol, icv for 7 days) NPS treatment following the central injection of 6-OHDA in medial forebrain bundle. Motor performance tests and in vivo nigral microdialysis were performed before and 7 days after the central 6-OHDA injection. The immunoreactivities for tyrosine hydroxylase (TH), NPSR, 4-hydroxynonenal (4-HNE) and c-Fos were detected by immunohistochemistry in frozen SN sections. Our double immunofluorescence labeling studies demonstrated that NPSR is present in the nigral TH-positive neurons. Central NPS injection caused a remarkable c-Fos expression in SN; whereas, no change was observed following vehicle injection. In both chronic and acute treatment groups, the 6-OHDA-induced motor dysfunction and impaired nigral dopamine release were improved significantly. However, only chronic, but not acute treatment restored the loss of nigral TH-positive cells, while decreasing the 4-HNE immunoreactivity in SN. Our findings demonstrate that central NPS treatment not only exerts a neuroprotective action on nigral dopaminergic neurons, it also improves the striatal dopaminergic signaling. Therefore, the present study candidates the NPSR agonism as a novel therapeutic approach for PD treatment.

Physiology, pharmacology, and pathophysiology of neuropeptide S receptor

Neuropeptide S receptor 1 (NPSR1), originally named G protein-coupled receptor 154 (GPR154), was deorphanized in 2002 with neuropeptide S identified as the endogenous ligand. NPSR1 is primarily expressed in bronchus, brain as well as immune cells. It regulates multiple physiological processes, including immunoregulation, locomotor activity, anxiety, arousal, learning and memory, and food intake and energy balance. SNPs of NPSR1 are significantly associated with several diseases, including asthma, anxiolytic and arousal disorders, and rheumatoid arthritis. This chapter will summarize studies on NPSR1, including its molecular structure, tissue distribution, physiology, pharmacology, and pathophysiology.

Neuropeptide S overcomes short term memory deficit induced by sleep restriction by increasing prefrontal cortex activity

Sleep restriction (SR) impairs short term memory (STM) that might be related to different processes. Neuropeptide S (NPS), an endogenous neuropeptide that improves short term memory, activates arousal and decreases anxiety is likely to counteract the SR-induced impairment of STM. The objective of the present study was to find common cerebral pathways in sleep restriction and NPS action in order to ultimately antagonize SR effect on memory. The STM was assessed using a spontaneous spatial alternation task in a T-maze. C57-Bl/6J male mice were distributed in 4 groups according to treatment (0.1nmol of NPS or vehicle intracerebroventricular injection) and to 20h-SR. Immediately after behavioural testing, regional c-fos immunohistochemistry was performed and used as a neural activation marker for spatial short term memory (prefrontal cortex, dorsal hippocampus) and emotional reactivity (basolateral amygdala and ventral hippocampus). Anxiety-like behaviour was assessed using elevated-plus maze task. Results showed that SR impaired short term memory performance and decreased neuronal activation in cingular cortex.NPS injection overcame SR-induced STM deficits and increased neuronal activation in infralimbic cortex. SR spared anxiety-like behavior in the elevated-plus maze. Neural activation in basolateral nucleus of amygdala and ventral hippocampus were not changed after SR.In conclusion, the present study shows that NPS overcomes SR-induced STM deficits by increasing prefrontal cortex activation independently of anxiety-like behaviour.

Identification of the first biased NPS receptor agonist that retains anxiolytic and memory promoting effects with reduced levels of locomotor stimulation

The neuropeptide S system has been implicated in a number of centrally mediated behaviors including memory consolidation, anxiolysis, and increased locomotor activity. Characterization of these behaviors has been primarily accomplished using the endogenous 20AA peptide (NPS) that demonstrates relatively equal potency for the calcium mobilization and cAMP second messenger pathways at human and rodent NPS receptors. This study is the first to demonstrate that truncations of the NPS peptide provides small fragments that retain significant potency only at one of two single polymorphism variants known to alter NPSR function (NPSR-107I), yet demonstrate a strong level of bias for the calcium mobilization pathway over the cAMP pathway. We have also determined that the length of the truncated peptide correlates with the degree of bias for the calcium mobilization pathway. A modified tetrapeptide analog (4) has greatly attenuated hyperlocomotor stimulation in vivo but retains activity in assays that correlate with memory consolidation and anxiolytic activity. Analog 4 also has a bias for the calcium mobilization pathway, at the human and mouse receptor. This suggests that future agonist ligands for the NPS receptor having a bias for calcium mobilization over cAMP production will function as non-stimulatory anxiolytics that augment memory formation.

Central adenosine A1 and A2A receptors mediate the antinociceptive effects of neuropeptide S in the mouse formalin test

AIMS

The present study aimed to investigate the intraplantar (ipl) and central (icv) effects of neuropeptide S (NPS) in the formalin test and to evaluate the role of adenosine receptors, mainly A1 and A2A, in mediating such effects.

MAIN METHODS

The ipl injection of formalin was used to assess the nociceptive activity. Moreover, by pretreating mice with non-selective and selective antagonists of adenosine receptors, the effects of icv NPS on formalin-induced ongoing nociception were assessed.

KEY FINDINGS

Morphine-induced antinociceptive effects were observed during phases 1 and 2 of the test, while indomethacin was active only at the later nociceptive phase. The ipl injection of NPS (alone or combined with formalin) did not modify the nociceptive response. However, icv NPS significantly reduced formalin-induced nociception during both phases. Caffeine (3 mg/kg, ip), a non-selective adenosine receptor antagonist, prevented NPS-induced antinociceptive effects. Similar to caffeine, icv ZM241385 (0.01 nmol), an A2A receptor antagonist, prevented the antinociceptive effects of NPS. Moreover, icv DPCPX (0.001 nmol), an A1 receptor antagonist, blocked the effects of NPS only during phase 1.

SIGNIFICANCE

The above findings suggest that: (i) NPS evokes central antinociceptive effects by activating both A1 and A2A receptors during phase 1, but (ii) only the adenosine A2A receptor during phase 2 of the formalin test.

Neuropeptide S counteracts 6-OHDA-induced motor deficits in mice

Neuropeptide S (NPS) is a 20-aminoacid peptide that selectively activates a G-protein coupled receptor named NPSR. Preclinical studies have shown that NPSR activation promotes anxiolysis, hyperlocomotion, arousal and weakfullness. Previous findings suggest that dopamine neurotransmission plays a role in the actions of NPS. Based on the close relationship between dopamine and Parkinson disease (PD) and on the evidence that NPSR are expressed on brain dopaminergic nuclei, the present study investigated the effects of NPS in motor deficits induced by intracerebroventricular (icv) administration of the dopaminergic neurotoxin 6-OHDA in the mouse rotarod test. 6-OHDA injection evoked motor deficits and significantly reduced tyrosine hidroxylase (TH)-positive cells in the substantia nigra (SN) and ventral tegmental area. However, a positive correlation was found only between the motor performance of 6-OHDA-injected mice and the number of TH-positive cells in SN. The systemic administration of l-DOPA+benserazide (25+6.25 mg/kg) counteracted 6-OHDA-induced motor deficits in mice. Similar to L-DOPA, the icv injection of NPS (0.1 and 1 nmol) reversed motor deficits evoked by 6-OHDA. In conclusion, NPS attenuated 6-OHDA-induced motor impairments in mice assessed in the rota-rod test. We discussed the beneficial actions of NPS based on a putative facilitation of dopaminergic neurotransmission in the brain. Finally, these findings candidate NPSR agonists as a potential innovative treatment for PD.

The role of the neuropeptide S system in addiction: focus on its interaction with the CRF and hypocretin/orexin neurotransmission

Recent behavioral, pharmacological and molecular findings have linked the NPS system to drug dependence. Most of the evidence supports the possibility that increased NPS activity may contribute to shaping vulnerability to addiction, especially relapse. However, data suggesting that the anxiolytic-like properties of NPS may have protective effects on addiction have been also published. In addition, evidence from conditioned place preference experiments, though not unequivocal, suggests that NPS per se is devoid of motivational properties. Intriguingly, several effects of NPS on drugs of abuse appear to be mediated by downstream activation of brain corticotrophin releasing factor (CRF) and hypocretin-1/orexin-A (Hcrt-1/Ox-A) systems. The major objective of the present article is to review the existing work on NPS and addiction. Particular attention is devoted to the interpretation of findings revealing complex neuroanatomical and functional interactions between NPS, CRF, and the Hcrt-1/Ox-A systems. Original data aimed at shedding light on the role of NPS in reward processing are also shown. Finally, existing findings are discussed within the framework of addiction theories, and the potential of the NPS system as a treatment target for addiction is analyzed.

Effects of neuropeptide S on seizures and oxidative damage induced by pentylenetetrazole in mice

Neuropeptide S (NPS) and its receptor were recently discovered in the central nervous system. In rodents, NPS promotes hyperlocomotion, wakefulness, anxiolysis, anorexia, and analgesia and enhances memory when injected intracerebroventricularly (i.c.v.). Herein, NPS at different doses (0.01, 0.1 and 1nmol) was i.c.v. administered in mice challenged with pentylenetetrazole (PTZ; 60mg/kg) repeatedly injected. Aiming to assess behavioral alterations and oxidative damage to macromolecules in the brain, NPS was injected 5min prior to the last dose of PTZ. The administration of NPS only at 1nmol increased the duration of seizures evoked by PTZ, without modifying frequency and latency of seizures. Biochemical analysis revealed that NPS attenuated PTZ-induced oxidative damage to proteins and lipids in the hippocampus and cerebral cortex. In contrast, the administration of NPS to PTZ-treated mice increased DNA damage in the hippocampus, but not cerebral cortex. In conclusion, this is the first evidence of the potential proconvulsive effects of NPS in mice. The protective effects of NPS against lipid and protein oxidative damage in the mouse hippocampus and cerebral cortex evoked by PTZ-induced seizures are quite unexpected. The present findings were discussed analyzing the paradoxical effects of NPS: facilitation of convulsive behavior and protection against oxidative damage to lipids and proteins.

Modification of caffeine effects on the affect-modulated startle by neuropeptide S receptor gene variation

RATIONALE/OBJECTIVES

Both the neuropeptide S (NPS) system and antagonism at the adenosine A2A receptor (e.g., by caffeine) were found to play a crucial role in the mediation of arousal and anxiety/panic in animal and human studies. Furthermore, a complex interaction of the neuropeptide S and the adenosinergic system has been suggested with administration of the adenosine A2A receptor antagonist caffeine downregulating NPS levels (Lage et al., 2006) and attenuating the stimulatory effects of NPS in rodents (Boeck et al., 2010).

METHODS

Thus, in the present study, the impact of the functional neuropeptide S receptor (NPSR) A/T (Asn(107)Ile; rs324981) variant on affect-modulated (neutral, unpleasant, and pleasant IAPS pictures) startle response depending on the administration of 300 mg caffeine citrate was investigated in a sample of 124 (m = 58, f = 66) healthy probands using a double-blind, placebo-controlled design.

RESULTS

ANOVA revealed a significant interaction between NPSR genotype, challenge condition, and picture valence. Comparing startle magnitudes upon stimulation with neutral or emotional pictures between the placebo and caffeine condition, in AA/AT non-risk genotype carriers no significant difference was discerned, while TT risk genotype carriers showed a significantly increased startle magnitude in response to neutral stimuli (p = .02) and a significantly decreased startle magnitude in response to unpleasant stimuli (p = .02) in the caffeine condition as compared to the placebo condition.

CONCLUSIONS

In summary, the present findings - extending previous evidence from rodent studies - for the first time provide support for a complex, non-linear interaction of the neuropeptide S and adenosinergic systems affecting the affect-modulated startle response as an intermediate phenotype of anxiety in humans.

Effect of adenosine A2A receptor antagonist ZM241385 on amygdala-kindled seizures and progression of amygdala kindling

The purpose of this study was to evaluate the effect of adenosine A2A receptor antagonist ZM241385 on amygdala-kindled seizures and its roles in epileptogenesis. Electrodes were implanted into the right amygdala of male adult Wistar rats. Kindling was accomplished by using stimulus strength of 500 μA applied daily to the amygdala until 10 consecutive stage 5 seizues were induced. Then effect of ZM241385 was studied in fully kindled rats after intracerebroventricular administration of the drug. In addition, the effect on kindling progression was evaluated through ZM241385 injection before daily stimulation. In all experiments, behavioral changes in the rats in response to ZM241385 were monitored closely. The results showed that, in fully amygdala-kindled rats, ZM241385 (0.001-0.1 nmol/L) decreased afterdischage duration (ADD), motor seizure duration (MSD), stage 5 duration (S5D) and seizure duration (SD), but only the effect on ADD was dose-dependent. The doses of 0.001-0.1 nmol/L had no influence on stage 4 latency (S4L) and seizure stage (SS). The dosages of 0.0001 and 1 nmol/L of ZM241385 did not exert any effect on all seizure parameters. In contrast to the results in fully amygdala-kindled rats, ZM241385 (0.001-0.1 nmol/L) had minimal or no effects on the progression of amygdala-kindled seizures. We are led to the conclusion that although ZM241385 had no influence on the progression of amygdala-kindled seizures, it had potent anti-convulsant profile and little adverse effects at the dosage of 0.001-0.1 nmol/L, suggesting that the agent is effective against the amygdala-kindled seizures.

Role of the ecto-nucleotidases in the cooperative effect of adenosine and neuropeptide-S on locomotor activity in mice

Activation of adenosine receptors modifies the action of classic neurotransmitters (i.e. dopamine, glutamate and acetylcholine) and other neuromodulators, like vasoactive intestinal peptide (VIP), calcitonin gene-related peptide (CGRP) and neuropeptide S (NPS). Similarly to adenosine, NPS is involved in the regulation of stimulus and response to fear and arousal. Thus, the present study investigates the effects of NPS on locomotor activity in mice treated with or without α,β-methylene adenosine 5'-diphosphate (AOPCP), the inhibitor of ecto-5'-nucleotidase. Additionally, we evaluate the activity of ecto-5'-nucleotidase in brain slices of mice treated with or without NPS. Male adult CF-1 mice received i.c.v. NPS as 0.1 nmol injection with or without pre-treatment with 1 nmol α,β-methylene adenosine 5'-diphosphate (AOPCP), the selective inhibitor of ecto-5'-nucleotidase, to evaluate locomotor activity. In another set of experiments, mice received i.c.v. infusion of 0.1 nmol NPS to assay enzymatic activity in brain slices. The results demonstrated that the pre-treatment with AOPCP, which was inactive per se, prevented NPS-induced hyperlocomotion in mice. The dose of 0.1 nmol NPS was efficient to induce hyperlocomotion in animals during the observation period in the activity cage. Regarding enzymatic activity, i.c.v. NPS injection did not induce any significant alterations in ATP and AMP hydrolysis in striatum and hippocampus brain slices of mice. The present study shows that the hyperlocomotor effect of NPS depends on the ecto-5'-nucleotidase activity.

Microinjection of neuropeptide S into the rat ventral tegmental area induces hyperactivity and increases extracellular levels of dopamine metabolites in the nucleus accumbens shell

The newly identified neuropeptide S (NPS) is mainly expressed in a group of neurons located between the locus coeruleus and Barrington's nucleus in the brainstem. Central administration of NPS increases motor activity and wakefulness, and it decreases anxiety-like behavior and feeding. The NPS receptor (NPSR) is widely distributed in various brain regions including the ventral tegmental area (VTA). The mesolimbic dopaminergic system originates in the VTA, and activation of the system produces hypermotor activity. Therefore, we hypothesized that NPS-induced hypermotor activity might be mediated by activation of the mesolimbic dopaminergic pathway via the NPSR expressed in the VTA. Intra-VTA injection of NPS significantly and dose-dependently increased horizontal and vertical motor activity in rats, and the hyperactivity was significantly and dose-dependently inhibited by pre-administration of sulpiride, a DA D(2)-like receptor antagonist, into the shell of the nucleus accumbens (NAcSh). Intra-VTA injection of NPS also significantly increased extracellular 3,4-dihydroxy-phenyl acetic acid and homovanillic acid levels in the NAcSh of freely moving rats. These results support the idea that NPS activates the mesolimbic dopaminergic system presumably via the NPSR located in the VTA, thereby stimulating motor activity.