Activation of NOP receptor increases vulnerability to stress: role of glucocorticoids and CRF signaling

RATIONALE

Recently, we demonstrated that the activation of the nociceptin/orphanin FQ (N/OFQ) receptor (NOP) signaling facilitates depressive-like behaviors. Additionally, literature findings support the ability of the N/OFQ-NOP system to modulate the hypothalamic-pituitary-adrenal (HPA) axis.

OBJECTIVES

Considering that dysfunctional HPA axis is strictly related to stress-induced psychopathologies, we aimed to study the role of the HPA axis in the pro-depressant effects of NOP agonists.

METHODS

Mice were treated prior to stress with the NOP agonist Ro 65-6570, and immobility time in the forced swimming task and corticosterone levels were measured. Additionally, the role of endogenous glucocorticoids and CRF was investigated using the glucocorticoid receptor antagonist mifepristone and the CRF1 antagonist antalarmin in the mediation of the effects of Ro 65-6570.

RESULTS

The NOP agonist in a dose-dependent manner further increased the immobility of mice in the second swimming session compared to vehicle. By contrast, under the same conditions, the administration of the NOP antagonist SB-612111 before stress reduced immobility, while the antidepressant nortriptyline was inactive. Concerning in-serum corticosterone in mice treated with vehicle, nortriptyline, or SB-612111, a significant decrease was observed after re-exposition to stress, but no differences were detected in Ro 65-6570-treated mice. Administration of mifepristone or antalarmin blocked the Ro 65-6570-induced increase in the immobility time in the second swimming session.

CONCLUSIONS

Present findings suggest that NOP agonists increase vulnerability to depression by hyperactivating the HPA axis and then increasing stress circulating hormones and CRF1 receptor signaling.

The alpha1A antagonist tamsulosin impairs memory acquisition, consolidation and retrieval in a novel object recognition task in mice

Tamsulosin is an α1-adrenoceptor antagonist used to treat benign prostatic hyperplasia. This drug exhibits high affinity for α1A- and α1D-adrenoceptor subtypes, which are also expressed in the brain. While dementia symptoms have been reported after administration of tamsulosin in humans, studies on its effects on the rodent brain are still rare. The present study investigated the effects of tamsulosin (and biperiden, an amnesic drug) on cognitive performance in the object recognition task (ORT). Tamsulosin (0.001-0.01 mg/kg) was orally administrated in mice at three distinct time points: pre-training, post-training and pre-test session. Tamsulosin 0.01 mg/kg impaired object recognition regardless of when it was injected, whereas at lower doses did not affect mouse performance in the ORT. Biperiden also impaired acquisition and consolidation of object recognition in mice. Furthermore, the effects of tamsulosin on locomotion, motivation and anxiety were excluded as potential confounding factors. At all doses tested, tamsulosin did not alter distance moved, time spent exploring objects in the ORT, and anxiety-related behaviors in the elevated plus-maze test. By contrast, diazepam evoked a significant reduction of anxiety-like behaviours. In conclusion, tamsulosin impaired memory acquisition, consolidation and retrieval in an object recognition task in mice, thus affecting memory performance in a non-specific phase manner. These findings contribute to our understanding of the potential adverse effects of tamsulosin, and shed light on the role played by α1-adrenoceptors, particularly α1A- subtype, in cognitive processes.

Tamsulosin facilitates depressive-like behaviors in mice: Involvement of endogenous glucocorticoids

The benign prostatic hyperplasia (BPH) is the main source of lower urinary tract symptoms. The BPH is a common age-dependent disease and tamsulosin is an α₁-adrenoceptor blocker widely prescribed for BPH. Beyond the common adverse effects of tamsulosin, increased diagnosis of dementia after prescription was observed. Importantly, a clinical study suggested that tamsulosin may exert antidepressant effects in BPH patients. Considering the expression of α₁-adrenoceptors in the brain, this study aimed to investigate the effects of tamsulosin in the forced swimming and open field tests in mice. For this, tamsulosin (0.001-1 mg/kg) was orally administered subacutely (1, 5 and 23 hr) and acutely (60 min) before tests. Mifepristone (10 mg/kg), a glucocorticoid receptor antagonist, and aminoglutethimide (10 mg/kg), a streoidogenesis inhibitor, were intraperitoneally injected before tamsulosin to investigate the role of the hypothalamic-pituitary-adrenal axis in the mediation of tamsulosin-induced effects. Subacute and acute administrations of tamsulosin increased the immobility time in the first exposition to an inescapable stressful situation. In the re-exposition to the swim task, controls displayed a natural increase in the immobility time, and the treatment with tamsulosin further increased this behavioral parameter. Tamsuslosin did not affect spontaneous locomotion neither in naïve nor in stressed mice. Our findings also showed that mifepristone and aminoglutethimide prevented the tamsulosin-induced increase in the immobility time in the first and second swimming sessions, respectively. In conclusion, tamsulosin may contribute to increased susceptibility to depressive-like behaviors, by facilitating the acquisition of a passive stress-copying strategy. These effects seem to be dependent on endogenous glucocorticoids.

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.

Nociceptin/orphanin FQ receptor system blockade as an innovative strategy for increasing resilience to stress

The ability to successfully cope with stress is known as 'resilience', and resilient individuals are less prone to develop psychopathologies. Understanding the neurobiological mechanisms of resilience may be instrumental to improve current therapies and benefit high-risk subjects. This review summarizes the complex interplay that exists between physiological and pathological responses to stressful events and the nociceptin/orphanin FQ (N/OFQ) - N/OFQ receptor (NOP) system, including: the effects of stress in regulating N/OFQ release and NOP expression; the ability of the N/OFQ-NOP system to modulate the hypothalamic-pituitary-adrenal axis; behavioral studies; and evidence in humans correlating this peptidergic system with psychopathologies. Available findings support the view that N/OFQ signaling stimulates the hypothalamic-pituitary-adrenal axis, thus increasing stress circulating hormones and corticotropin-releasing factor signaling. Additionally, activation of the NOP receptor inhibits monoamine transmission, including 5-HT, and this may contribute to maladaptive outcomes of stress. Ultimately, the N/OFQ system seems to have an important role in stress vulnerability, and blockade of NOP signaling may provide an innovative strategy for the treatment of stress related psychopathologies.

Blockade of nociceptin/orphanin FQ signaling facilitates an active copying strategy due to acute and repeated stressful stimuli in mice

The role of stress in the etiology of depression has been largely reported. In this line, exogenous glucocorticoids are employed to mimic the influence of stress on the development of depression. The N/OFQ-NOP receptor system has been implicated in the modulation of stress and emotional behaviors. In fact, the blockade of NOP receptors induces antidepressant effects and increases resilience to acute stress. This study investigated the effects of the NOP receptor blockade on dexamethasone-treated mice exposed to acute and prolonged swimming stress. Swiss and NOP(+/+) and NOP(−/−) mice were treated with dexamethasone, and the protective effects of the NOP antagonist SB-612111 (10 mg/kg, ip) or imipramine (20 mg/kg, ip) were investigated in three swimming sessions. The re-exposure to swim stress increased immobility time in Swiss and NOP(+/+), but not in NOP(−/−) mice. Acute and repeated dexamethasone administration induced a further increase in the immobility time, and facilitated body weight loss in Swiss mice. Single administration of SB-612111, but not imipramine, prevented swimming stress- and dexamethasone-induced increase in the immobility time. Repeated administrations of SB-612111 prevented the deleterious effects of 5 days of dexamethasone treatment. Imipramine also partially prevented the effects of repeated glucocorticoid administration on the immobility time, but did not affect the body weight loss. NOP(−/−) mice were more resistant than NOP(+/+) mice to inescapable swimming stress, but not dexamethasone-induced increase in the immobility time and body weight loss. In conclusion, the blockade of the NOP receptor facilitates an active stress copying response and attenuates body weight loss due to repeated stress.

Effects of non-peptide nociceptin/orphanin FQ receptor ligands on methylphenidate-induced hyperactivity in mice: Implications for bipolar disorders

Bipolar disorder is a psychiatric pathology characterized by biphasic mood episodes of mania or hypomania and depression. The pharmacotherapy of bipolar disorder has significant adverse effects impairing treatment adherence and patient quality of life. The N/OFQ-NOP receptor system has been widely implicated with mood disorders. Clinical and preclinical findings suggest antidepressants actions for NOP antagonists. More recently, the administration of NOP agonists has shown to promote depressant states. The present study aimed to investigate the effects of non-peptide NOP ligands in methylphenidate-induced manic-like behavior in mice. The NOP agonist Ro 65-6570 (0.01-1 mg/kg, ip), at the higher dose, did not affect spontaneous locomotion per se, but prevented the methylphenidate (10 mg/kg, sc)-induced hyperlocomotion. The NOP partial agonist AT-090 (0.001-0.03 mg/kg, ip) and the NOP antagonist SB-612111 (1-10 mg/kg, ip) did not significantly affect the psychostimulant-induced hyperactivity. Experiments performed with mice lacking the NOP receptor (NOP(-/-)) demonstrated that the treatment with methylphenidate induced similar hyperlocomotion in NOP(-/-) and NOP(+/+) mice. In conclusion, these findings suggest a potential role for NOP agonists in the prevention of manic states, especially by counteracting the hyperactivity symptom of bipolar patients. However, more studies are necessary in order to evaluate these compounds in other features of bipolar disorder.

Prenatal restraint stress impairs recognition memory in adult male and female offspring

OBJECTIVE

Accumulating evidence from preclinical and clinical studies indicates that prenatal exposure to stress impairs the development of the offspring brain and facilitates the emergence of mental illness. This study aims to describe the impact of prenatal restraint stress on cognition and exploration to an unfamiliar environment at adulthood in an outbred strain of mice.

METHODS

Late pregnant mice were exposed to restraint stress and adult offspring (60 days of age) behaviours were assessed in the object recognition task and open field test.

FINDINGS

Prenatal stress (PNS) impaired new object recognition in male and female mice. Importantly, the learning deficits in female PNS mice were linked to their estrous cycle. Actually, PNS females in metestrus/diestrus but not in proestrus/estrus phases displayed recognition deficits compared to controls. Concerning locomotion in an unfamiliar environment, male but not female PNS mice displayed significant increase, but showed no differences in the distance travelled within the centre zone of the arena.

CONCLUSION

Present findings support the view that maternal restraint-stress during late pregnancy impairs recognition memory in both male and female offspring, and in females, this cognitive deficit is dependent on the estrous cycle phase. Ultimately, these data reinforce that PNS is an aetiological component of psychiatric disorders associated with memory deficits.

Modulation of the NOP receptor signaling affects resilience to acute stress

BACKGROUND

The peptide nociceptin/orphanin FQ (N/OFQ) and its receptor (NOP) are implicated in the modulation of emotional states. Previous human and rodent findings support NOP antagonists as antidepressants. However, the role played by the N/OFQ-NOP receptor system in resilience to stress is unclear.

AIMS

The present study investigated the effects of activation or blockade of NOP receptor signaling before exposure to acute stress.

METHODS

The behavioral effects of the administration before stress of the NOP agonists Ro 65-6570 (0.01-1 mg/kg) and MCOPPB (0.1-10 mg/kg), and the NOP antagonist SB-612111 (1-10 mg/kg) were assessed in mice exposed to inescapable electric footshock and forced swim as stressors. The behavioral phenotype of mice lacking the NOP receptor (NOP(-/-)) exposed to inescapable electric footshock was also investigated.

RESULTS

The activation of NOP receptor signaling with the agonists increased the percentage of mice developing helpless behavior and facilitated immobile posture. In contrast, the blockade of NOP receptor reduced the acquisition of depressive-like phenotypes, and similar resistance to develop helpless behaviors was observed in NOP(-/-) mice. Under the same stressful conditions, the antidepressant nortriptyline (20 mg/kg) did not change the acquisition of helpless behavior and immobile posture.

CONCLUSIONS

These findings support the view that NOP activation during acute stress facilitates the development of depressive-related behaviors, whereas NOP blockade has a protective outcome. This study showed for first time that NOP antagonists are worthy of investigation as preemptive treatments in patients with severe risk factors for depression.

Venlafaxine and nortriptyline reverse acute dexamethasone-induced depressive-like behaviors in male and female mice

Major depression can be triggered by stressful events that promote deregulation of the hypothalamic-pituitary-adrenal axis response and, in some circumstances, persistent elevation of circulating glucocorticoid levels. Animal models are widely used to investigate the mechanisms responsible for the etiology and treatment of major depression. However, to mimic the dysfunction of the hypothalamic-pituitary-adrenal axis in rodents, animals should be exposed to sustained physical and psychological stressful situations. These animal models of depression are labor intensive and impact individual animals differently. Aiming to add evidence for a new acute neuroendocrine model of depression, male and female mice were treated with a single administration of dexamethasone, and behavioral effects were evaluated in the presence and absence of the antidepressants nortriptyline and venlafaxine. Male and female Swiss mice were treated with dexamethasone (0.07 mg/kg, subcutaneously) and the mouse behavior was assessed in the tail suspension and open field tests at 4 h, 24 h, and 7 days after administration. Dexamethasone induced depressogenic-like states in both sexes at 4 and 24 h after injection. Additionally, acute dexamethasone increased latency to body fur licking, thus corroborating the depressive-like behavior. The treatment with nortriptyline and venlafaxine (both at 30 mg/kg, intraperitoneally) blocked dexamethasone-induced increase in the immobility time and the latency to self-care. In conclusion, the present findings suggest that a single administration of dexamethasone induces depressive-like states in male and female mice, and these behavioral alterations are counteracted by conventional antidepressants. Ultimately, these data provide new evidence for an acute neuroendocrine model of depression. (PsycINFO Database Record (c) 2019 APA, all rights reserved).

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.

NOP agonist action of cebranopadol counteracts its liability to promote physical dependence

Cebranopadol is a mixed NOP/opioid receptor agonist currently under development as innovative analgesic. In this study the liability of cebranopadol to produce opioid-type physical dependence has been evaluated in comparison with morphine in wild type mice and in mice knockout for the NOP receptor gene (NOP(-/-)). Mice were treated twice a day for 5 days with increasing doses of cebranopadol or morphine (cumulative doses 10.2 and 255 mg/kg, respectively) and the number of jumping in response to naloxone 10 mg/kg were measured after 2 h from the last injection. In wild type mice naloxone evoked a similar withdrawal jumping behavior in animal pretreated with morphine or cebranopadol. In NOP(-/-) mice morphine treatment produced the same signs of withdrawal as in NOP(+/+) animals, while cebranopadol treatment elicited a stronger withdrawal syndrome in NOP(-/-) than of NOP(+/+) mice. These results demonstrated that the activation of the NOP receptor reduces the liability of cebranopadol to produce opioid-like physical dependence. Thus, the simultaneous activation of NOP and opioid receptors can be an effective pharmacological strategy to counteract physical dependence to opioid drugs.

Nociceptin/orphanin FQ receptor agonists increase aggressiveness in the mouse resident-intruder test

Aggressive behaviors can be considered symptoms of bipolar disorder, schizophrenia, post-traumatic stress, intermittent explosive, and personality disorders. Nociceptin/orphanin FQ (N/OFQ) is a peptide acting as endogenous ligand of the NOP receptor. Preclinical and clinical findings suggest the NOP receptor as an innovative target for the treatment of psychopathologies, such as anxiety, depression, and drug abuse. This study investigated the effects of NOP ligands and the behavioral phenotype of mice lacking the NOP receptor in an animal model of aggressiveness, the resident-intruder test. Mood stabilizers, such as valproate, lithium, and carbamazepine reduced aggressive behaviors of resident mice, while diazepam was inactive. In contrast, para-chlorophenylalanine (PCPA), an inhibitor of 5-HT synthesis, increased aggressiveness in mice. Similar to PCPA, the treatment with the NOP agonists Ro 65-6570 and AT-090 also increased aggressive behaviors. The systemic administration of the NOP antagonist SB-612111 did not modify the behavior of resident mice, but it prevented the aggressive behavior of Ro 65-6570. NOP receptor knockout mice did not display any behavioral difference compared to wild-type animals in the resident-intruder test. None of the treatments affected non-agonistic behaviors and spontaneous locomotion. In conclusion, NOP receptor agonists increased aggressiveness, while the pharmacological and genetic blockade of NOP receptor signaling did not modify agonistic behaviors. Ultimately, the aggressive profile of action of NOP agonists should be taken into account in the development of innovative psychiatric drugs targeting the NOP receptor.

NOP agonists prevent the antidepressant-like effects of nortriptyline and fluoxetine but not R-ketamine

RATIONALE

Nociceptin/orphanin FQ (N/OFQ) is the endogenous ligand of a Gi protein-coupled receptor named NOP. Both N/OFQ and NOP receptor are widely expressed in brain areas involved in the control of emotional processes. Clinical and preclinical studies support antidepressant effects due to the blockade of NOP receptor signaling. By contrast, NOP receptor activation did not evoke any change in behavioral despair tests.

OBJECTIVES

The present study aimed to investigate the effects of the co-administration of NOP agonists and classic antidepressant drugs in the forced swimming test (FST) and learned helplessness model (LH) in mice.

METHODS

Male Swiss mice were co-administered with NOP agonists (N/OFQ and Ro 65-6570) and antidepressants (nortriptyline, fluoxetine, and R-ketamine) or SB-612111 (NOP antagonist) and the behavioral effects were assessed in the FST and LH tests.

RESULTS

Fluoxetine, nortriptyline, R-ketamine and the NOP antagonist SB-612111 displayed antidepressant-like effects in the FST. The administration of the NOP agonists N/OFQ and Ro 65-6570 did not induce any behavioral change. However, co-administration of NOP agonists blocked the antidepressant effects of SB-612111, fluoxetine, and nortriptyline, but not R-ketamine in the FST. Similarly, in the LH, the systemic injection of SB-612111, nortriptyline, and R-ketamine reversed helplessness. The co-administration of Ro 65-6570 blocked the antidepressant-like effects of SB-612111 and nortriptyline, but not R-ketamine.

CONCLUSIONS

NOP receptor activation inhibits the acute antidepressant effects of nortriptyline and fluoxetine, but not R-ketamine. The present findings contribute to further understand the role played by the N/OFQ-NOP receptor system in regulating mood states.

Craving espresso: the dialetics in classifying caffeine as an abuse drug

Caffeine is the most consumed psychoactive substance in the world; in general, it is not associated to potentially harmful effects. Nevertheless, few studies were performed attempting to investigate the caffeine addiction. The present review was mainly aimed to answer the following question: is caffeine an abuse drug? To adress this point, the effects of caffeine in preclinical and clinical studies were summarized and critically analyzed taking account the abuse disorders described in the Diagnostic and Statistical Manual of Mental Disorders (DSM-V). We concluded that the diagnostic criteria evidenced on DSM-V to intoxication-continued use and abstinence are not well supported by clinical studies. The fact that diagnostic criteria is not widely supported by preclinical or clinical studies may be due specially to a controversy in its exactly mechanism of action: recent literature point to an indirect, rather than direct modulation of dopamine receptors, and auto-limitant consumption due to adverse sensations in high doses. On the other hand, it reports clear withdrawal-related symptoms. Thus, based on a classical action on reward system, caffeine only partially fits its mechanism of action as an abuse drug, especially because previous research does not report a clear effect of dopaminergic activity enhance on nucleus accumbens; despite this, there are reports concerning dopaminergic modulation by caffeine on the striatum. However, based on human and animal research, caffeine withdrawal evokes signals and symptoms, which are relevant enough to include this substance among the drugs of abuse.

NOP Ligands for the Treatment of Anxiety and Mood Disorders

Many studies point toward the nociceptin/orphanin FQ (N/OFQ) and the N/OFQ peptide receptor (NOP) as targets for the development of innovative drugs for treating anxiety- and mood-related disorders. Evidence supports the view that the activation of NOP receptors with agonists elicits anxiolytic-like effects, while its blockade with NOP antagonists promotes antidepressant-like actions in rodents. Genetic studies showed that NOP receptor knockout mice display an antidepressant-like phenotype, and NOP antagonists are inactive in these animals. In contrast, the genetic blockade of NOP receptor signaling generally displays an increase of anxiety states in the elevated plus-maze test. In this chapter we summarized the most relevant findings of NOP receptor ligands in the modulation of anxiety and mood disorders, and the putative mechanisms of action are discussed.

Peptide welding technology - A simple strategy for generating innovative ligands for G protein coupled receptors

Based on their high selectivity of action and low toxicity, naturally occurring peptides have great potential in terms of drug development. However, the pharmacokinetic properties of peptides, in particular their half life, are poor. Among different strategies developed for reducing susceptibility to peptidases, and thus increasing the duration of action of peptides, the generation of branched peptides has been described. However, the synthesis and purification of branched peptides are extremely complicated thus limiting their druggability. Here we present a novel and facile synthesis of tetrabranched peptides acting as GPCR ligands and their in vitro and vivo pharmacological characterization. Tetrabranched derivatives of nociceptin/orphanin FQ (N/OFQ), N/OFQ related peptides, opioid peptides, tachykinins, and neuropeptide S were generated with the strategy named peptide welding technology (PWT) and characterized by high yield and purity of the desired final product. In general, PWT derivatives displayed a pharmacological profile similar to that of the natural sequence in terms of affinity, pharmacological activity, potency, and selectivity of action in vitro. More importantly, in vivo studies demonstrated that PWT peptides are characterized by increased potency associated with long lasting duration of action. In conclusion, PWT derivatives of biologically active peptides can be viewed as innovative pharmacological tools for investigating those conditions and states in which selective and prolonged receptor stimulation promotes beneficial effects.

Monoaminergic neurotransmission is mediating the antidepressant-like effects of Passiflora edulis Sims fo. edulis

The genus Passiflora is popularly used to treat anxiety. Recent studies showed antidepressant-like effects of two varieties of P. edulis (edulis and flavicarpa) in mice. However, the mechanisms of antidepressant actions are still unknown. Here, the effects of P. edulis fo. edulis aqueous extract (AE, 100-300mg/kg, po), and ethyl acetate (AcOEt, 25-50mg/kg, po), butanol (BuOH, 25-50mg/kg, po) and residual aqueous (25-100mg/kg, po) fractions were investigated in the mouse forced swimming test. In addition, the involvement of monoamines in the P. edulis fractions-induced antidepressant actions was approached. HPLC analyses showed that AcOEt and BuOH, but not residual, fractions shared with AE the main peaks between 25 and 70min (UV 340nm), which are suggestive of flavonoids. Nortriptyline and fluoxetine reduced the immobility time and similar results were observed for AE, AcOEt and BuOH but not residual fractions. PCPA (inhibitor of 5-HT synthesis), AMPT (inhibitor of catecholamine synthesis) and sulpiride (selective D2 receptor antagonist), but not DSP-4 (noradrenergic neurotoxin), blocked the antidepressant actions of AcOEt and BuOH. In conclusion, AcOEt and BuOH fractions shared with AE similar phytochemical composition and antidepressant actions. Preserved 5-HT and dopamine transmissions were required for the antidepressant effects of P. edulis fractions.

Topiramate reduces basal anxiety and relieves ethanol withdrawal-induced anxious behaviors in male rats

Anxiety disorders are associated with increased impairments in psychosocial functioning, work productivity and health-related quality of life. In addition, anxiety is a common symptom of ethanol withdrawal and it strongly contributes to relapse. Benzodiazepines are frequently prescribed for relief of anxiety and ethanol withdrawal symptoms but considerable side effects, such sedation, tolerance and dependence, are observed during treatment. Therefore, better drugs are needed for the treatment of anxiety states. The purpose of this study was to investigate whether topiramate would reduce basal levels of anxiety and ethanol-withdrawn induced anxiety in male rats; the elevated plus maze (EPM) was used as an animal model of anxiety. In Experiment 1, topiramate (0, 10, and 40 mg/kg, i.g.) and diazepam (1 mg/kg, i.p.) was acutely and repeatedly administered to naive rats. In Experiments 2 and 3, topiramate (0 or 40 mg/kg, i.g.) was acutely and chronically administered in early (72 hr after ethanol removal) and protracted (21 days after ethanol removal) ethanol-withdrawn rats, respectively. Acute and repeated topiramate treatment induced anxiolytic-like effects in naive rats. Early ethanol withdrawal increased anxiety, and acute topiramate administration counteracted the anxiogenic-like effects of ethanol removal. Protracted withdrawal did not produce lasting changes in anxiety but topiramate was equally effective at reducing anxiety in ethanol-withdrawn and control animals. Importantly, no signs of tolerance to the anxiolytic effects of topiramate were observed. In conclusion, these data support a role for topiramate in the treatment of basal levels of anxiety and ethanol withdrawal-induced anxiety. (PsycINFO Database Record

In vitro functional characterization of novel nociceptin/orphanin FQ receptor agonists in recombinant and native preparations

Nociceptin/Orphanin FQ (N/OFQ) regulates several biological functions via selective activation of the N/OFQ receptor (NOP). In this study novel nonpeptide NOP ligands were characterized in vitro in receptor binding and [³⁵S]GTPγS stimulated binding in membranes of cells expressing human NOP and classical opioid receptors, calcium mobilization assay in cells coexpressing the receptors and chimeric G proteins, bioluminescence resonance energy transfer (BRET) based assay for studying NOP receptor interaction with G protein and arrestin, the electrically stimulated mouse vas deferens and the mouse colon bioassays. The action of the AT compounds were compared with standard NOP agonists (N/OFQ and Ro 65-6570) and the NOP selective antagonist SB-612111. AT compounds displayed high NOP affinity and behaved as NOP agonists in all the functional assays consistently showing the following rank order of potency AT-127≥AT-090≥AT-035>AT-004= AT-001. AT compounds behaved as NOP full agonists in the calcium mobilization and mouse colon assays and as partial agonists in the [³⁵S]GTPγS and BRET assays. Interestingly AT-090 and AT-127, contrary to standard nonpeptide agonists that display G protein biased agonism, behaved as an unbiased agonists. AT-090 and AT-127 displayed higher NOP selectivity than Ro 65-6570 at native mouse receptors. AT-090 and AT-127 might be useful pharmacological tools for investigating the therapeutic potential of NOP partial agonists.

Short term, low dose fluoxetine blocks estrous cycle-linked changes in responsiveness to diazepam in female rats

Anxiety behavior in female Wistar rats was assessed at different stages of the estrous cycle using the elevated plus maze (EPM). No differences were observed at any cycle stage. Pretreatment with diazepam (1 mg kg(-1) intraperitoneal (i.p.)) 30 min before testing produced an anxiolytic effect (significant increase in percentage of time in the open arms compared to control group in the same cycle phase) in animals in proestrus, estrus, and early diestrus but had no effect in rats in late diestrus. Locomotor activity (total arm entries) was unchanged at any cycle phase. When rats in the late diestrus phase were pretreated with the selective serotonin reuptake inhibitor fluoxetine (1.75 mg kg(-1) i.p. on the afternoon of early diestrus and again in the morning of late diestrus) diazepam produced an anxiolytic effect (increase percentage time in the open arms). This dose is sufficient to raise brain allopregnanolone concentration without affecting 5-hydroxytryptamine (5-HT) systems. We propose that insensitivity to diazepam in late diestrus is due to increased expression of benzodiazepine insensitive α4 subunit-containing gamma-aminobutyric acid A (GABAA) receptors triggered by a sharp decrease in brain allopregnanolone concentration. Pretreatment with fluoxetine to raise brain allopregnanolone concentration during late diestrus prevents the withdrawal effect.

Antidepressant activity of nociceptin/orphanin FQ receptor antagonists in the mouse learned helplessness

RATIONALE

Pharmacological and genetic evidence support antidepressant-like effects elicited by the blockade of the NOP receptor. The learned helplessness (LH) model employs uncontrollable and unpredictable electric footshocks as a stressor stimulus to induce a depressive-like phenotype that can be reversed by classical antidepressants.

OBJECTIVES

The present study aimed to evaluate the action of NOP receptor antagonists in helpless mice.

METHODS

Male Swiss mice were subjected to the three steps of the LH paradigm (i.e., (1) induction, (2) screening, and (3) test). Only helpless animals were subjected to the test session. During the test session, animals were placed in the electrified chamber and the latency to escape after the footshock and the frequency of escape failures were recorded. The effect of the following treatments administered before the test session were evaluated: nortriptyline (30 mg/kg, ip, 60 min), fluoxetine (30 mg/kg, ip, four consecutive days of treatment), and NOP antagonists SB-612111 (1-10 mg/kg, ip, 30 min) and UFP-101 (1-10 nmol, icv, 5 min). To rule out possible biases, the effects of treatments on controllable stressful and non stressful situations were assessed.

RESULTS

In helpless mice, nortriptyline, fluoxetine, UFP-101 (3-10 nmol), and SB-612111 (3-10 mg/kg) significantly reduced escape latencies and escape failures. No effects of drug treatments were observed in mice subjected to the controllable electric footshocks and non stressful situations.

CONCLUSIONS

Acute treatment with NOP antagonists reversed helplessness similarly to the classical antidepressants. These findings support the proposal that NOP receptor antagonists are worthy of development as innovative antidepressant drugs.

Lithium and valproate prevent methylphenidate-induced mania-like behaviors in the hole board test

Manic bipolar is diagnosed by psychomotor agitation, increased goal-directed activity, insomnia, grandiosity, excessive speech, and risky behavior. Animal studies aimed to modeling mania are commonly based in psychostimulants-induced hyperlocomotion. The exploration of other behaviors related with mania is mandatory to investigate this phase of bipolar disorder in animals. In this study, the hole board apparatus was suggested for evaluating mania-like behaviors induced by the psychostimulant methylphenidate. The treatment with methylphenidate (10mg/kg, ip) increased locomotion in the open field test. The pretreatment with lithium (50mg/kg, ip) and valproate (400mg/kg, ip) significantly prevented the hyperlocomotion. In the hole-board test, methylphenidate increased interactions with the central and peripheral holes and the exploration of central areas. Lithium was more effective than valproate in preventing all the behavioral manifestations induced by the psychostimulant. These findings were discussed based on the ability of methylphenidate-treated mice mimicking two symptoms of mania in the hole board test: goal-directed action and risk-taking behavior. In conclusion, the results point to a new approach to study mania through the hole board apparatus. The hole board test appears to be a sensitive assay to detect the efficacy of antimanic drugs.

Beta-arrestin 2 rather than G protein efficacy determines the anxiolytic-versus antidepressant-like effects of nociceptin/orphanin FQ receptor ligands

BACKGROUND AND PURPOSE

Nociceptin/orphanin FQ (N/OFQ) receptor (NOP) agonists produce anxiolytic-like effects in rodents while antagonists promote antidepressant-like effects. The aim of this study was to investigate the effect on anxiety and depression of NOP receptor partial agonists such as the peptides [F/G]N/OFQ(1-13)NH2 and UFP-113 and the non-peptide AT-090.

EXPERIMENTAL APPROACH

In vitro AT-090, UFP-113, and [F/G]N/OFQ(1-13)NH2 were tested for their ability to promote NOP/G-protein and NOP/β-arrestin 2 interaction, using a bioluminescence resonance energy transfer assay. In vivo, they were tested in mice in the elevated plus maze (EPM) and in the forced swim (FST) tests. NOP partial agonists effects were systematically compared to those of full agonists (N/OFQ and Ro 65-6570) and antagonists (UFP-101 and SB-612111).

KEY RESULTS

In vitro, AT-090, UFP-113, and [F/G]N/OFQ(1-13)NH2 promoted NOP/G protein interaction, with maximal effects lower than those evoked by N/OFQ and Ro 65-6570. AT-090 behaved as a NOP partial agonist also in inducing β-arrestin 2 recruitment, while UFP-113 and [F/G]N/OFQ(1-13)NH2 were inactive in this assay. In vivo, AT-090 induced anxiolytic-like effects in the EPM but was inactive in the FST. Opposite results were obtained with UFP-113 and [F/G]N/OFQ(1-13)NH2.

CONCLUSIONS AND IMPLICATIONS

NOP ligands producing similar effects on NOP/G protein interaction (partial agonism) but showing different effects on β-arrestin 2 recruitment (partial agonism vs antagonism) elicited different actions on anxiety and mood. These results suggest that the action of a NOP ligand on emotional states is better predicted based on its β-arrestin 2 rather than G-protein efficacy.

Neurological disease in human and canine leishmaniasis--clinical features and immunopathogenesis

Leishmaniasis is a vectorborne disease caused by Leishmania protozoa, which is a major health problem and a neglected disease common in many regions of the world. Leishmania is an intracellular parasite transmitted by sand flies that causes clinical manifestations ranging from a severe and potentially fatal disease named visceral leishmaniasis to less severe but in many cases disfiguring diseases that mainly affect the skin or mucosal tissues, known as cutaneous leishmaniasis. Despite the detection of Leishmania parasites in the brain and cerebrospinal fluid of human patients and dogs, epidemiological data, as well as information about the mechanisms of central and peripheral nervous system alterations, are poorly described. This review is focused on the current knowledge about the neurological manifestations and immunopathogenic mechanisms in human patients and animals infected with Leishmania.

Blockade of nociceptin/orphanin FQ receptor signaling reverses LPS-induced depressive-like behavior in mice

Nociceptin/orphanin FQ is the natural ligand of a Gi-protein coupled receptor named NOP. This peptidergic system is involved in the regulation of mood states and inflammatory responses. The present study aimed to investigate the consequences of blocking NOP signaling in lipopolysaccharide (LPS)-induced sickness and depressive-like behaviors in mice. LPS 0.8mg/kg, ip, significantly induced sickness signs such as weight loss, decrease of water and food intake and depressive-like behavior in the tail suspension test. Nortriptyline (ip, 60min prior the test) reversed the LPS-induced depressive states. The NOP receptor antagonist SB-612111, 30min prior LPS, did not modify LPS-induced sickness signs and depressive-like behavior. However, when injected 24h after LPS, NOP antagonists (UFP-101, icv, and SB-612111, ip) significantly reversed the mood effects of LPS. LPS evoked similar sickness signs and significantly increased tumor necrosis factor-α (TNF-α) and interleukin-6 (IL-6) plasma levels 6h post-injection in wild-type ((NOP(+/+)) and NOP knockout ((NOP(-/-)) mice. However, LPS treatment elicited depressive-like effects in NOP(+/+) but not in NOP(-/-) mice. In conclusion, the pharmacological and genetic blockade of NOP signaling does not affect LPS evoked sickness signs while reversing depressive-like behavior.

Neuropeptide S reduces mouse aggressiveness in the resident/intruder test through selective activation of the neuropeptide S receptor

Neuropeptide S (NPS) regulates various biological functions by selectively activating the NPS receptor (NPSR). In particular NPS evokes robust anxiolytic-like effects in rodents together with a stimulant and arousal promoting action. The aim of the study was to investigate the effects of NPS on the aggressiveness of mice subjected to the resident/intruder test. Moreover the putative role played by the endogenous NPS/NPSR system in regulating mice aggressiveness was investigating using mice lacking the NPSR receptor (NPSR(-/-)) and the NPSR selective antagonists [(t)Bu-D-Gly(5)]NPS and SHA 68. NPS (0.01-1 nmol, icv) reduced, in a dose dependent manner, both the time that resident mice spent attacking the intruder mice and their number of attacks, producing pharmacological effects similar to those elicited by the standard anti-aggressive drug valproate (300 mg/kg, ip). This NPS effect was evident in NPSR wild type (NPSR(+/+)) mice but completely disappeared in NPSR(-/-) mice. Moreover, NPSR(-/-) mice displayed a significantly higher time spent attacking than NPSR(+/+) mice. [(t)Bu-D-Gly(5)]NPS (10 nmol, icv) did not change the behavior of mice in the resident/intruder test but completely counteracted NPS effects. SHA 68 (50 mg/kg, ip) was inactive per se and against NPS. In conclusion, this study demonstrated that NPS produces anti-aggressive effects in mice through the selective activation of NPSR and that the endogenous NPS/NPSR system can exert a role in the control of aggressiveness levels under the present experimental conditions.

Nitroprusside single-dose prevents the psychosis-like behavior induced by ketamine in rats for up to one week

Recently, we found a rapid and long-lasting improvement of symptoms in schizophrenic patients on antipsychotics after a single four-hour infusion of sodium nitroprusside (SNP), a nitric oxide (NO) donor with a short half-life. This improvement persisted for up to 4weeks. Because these patients remained on antipsychotics after infusion of SNP was finished, the question arises about whether this improvement was due to SNP itself. We have now investigated whether SNP, alone, can produce preventive antipsychotic effects in rats treated with ketamine (KET). 56 adult rats divided into 7 groups were infused with SNP 4mg/kg, KET 25mg/kg, or saline as follows: group1 - saline, group2 - SNP, group3 - KET, group4 - KET 12h after SNP, group5 - KET 1day after SNP, group6 - KET 2days after SNP, and group7 - KET 1week after SNP. The animals were filmed in an open field arena for 30min and the videos were later analyzed by ANY-Maze software to measure activity and stereotypy. SNP significantly prevented the emergence of hyperactivity induced by KET when it was administered for up to 1week before KET, and prevented the emergence of stereotypies when it was administered for up to 1day before KET. These findings in rats, which have an even faster metabolic rate than humans, suggest that the long-lasting effects observed in our clinical trial with SNP in humans could have been due to SNP itself, and indicate for the first time that SNP may present preventive antipsychotic effects.

Nociceptin/orphanin FQ-NOP receptor system in inflammatory and immune-mediated diseases

The neuropeptide nociceptin/orphanin FQ (N/OFQ) is the endogenous ligand of the G-protein-coupled receptor NOP. Cells from the immune system express the precursor preproN/OFQ and the NOP receptor, as well as secrete N/OFQ. The activation of the N/OFQ-NOP pathway can regulate inflammatory and immune responses. Several immune activities, including leukocyte migration, cytokine and chemokine production, and lymphocytes proliferation are influenced by NOP activation. It was demonstrated that cytokines and other stimuli such as Toll-like receptor agonist (e.g., lipopolysaccharide) induce N/OFQ production by cells from innate and adaptive immune response. In this context, N/OFQ could modulate the outcome of inflammatory diseases, such as sepsis and immune-mediated pathologies by mechanisms not clearly elucidated. In fact, clinical studies revealed increased levels of N/OFQ under sepsis, arthritis, and Parkinson's disease. Preclinical and clinical studies pointed to the blockade of NOP receptor signaling as successful strategy for the treatment of inflammatory diseases. This review is focused on experimental and clinical data that suggest the participation of N/OFQ-NOP receptor activation in the modulation of the immune response, highlighting the immunomodulatory potential of NOP antagonists in the inflammatory and immunological disturbances.

Nociceptin/orphanin FQ induces simultaneously anxiolytic and amnesic effects in the mouse elevated T-maze task

Studies have shown a close relationship between anxiety and aversive memory processing, but few animal models are suitable for investigating the effects of a given compound on anxiety and memory simultaneously. A growing body of evidence suggests anxiolytic and amnesic effects of nociceptin/orphanin FQ (N/OFQ). The mouse elevated T-maze (ETM) has been shown to detect the effects of drugs on anxiety and memory at the same time. In this study, the effects of intracerebroventricular N/OFQ injected before or immediately after training session were assessed in the ETM task. When pretraining injected, N/OFQ 0.1 nmol significantly decreased the latency to enter an open arm in the training session compared to control, which is suggestive of anxiolysis. In addition, N/OFQ (0.1 and 1 nmol) significantly reduced the latency to enter an open arm during the test session compared to control, thus suggesting memory impairments. However, when N/OFQ was administered posttraining, it did not affect memory retrieval. No alterations in locomotion were detected in N/OFQ-treated mice in the open field test. In conclusion, these findings are discussed considering the simultaneous anxiolytic and amnesic effects of N/OFQ.

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.

Evaluation of the effect of acute sibutramine in female rats in the elevated T-maze and elevated plus-maze tests

Sibutramine is a serotonin and norepinephrine reuptake inhibitor indicated for the treatment of obesity. A pre-clinical study showed that acute administration of sibutramine promoted anxiolytic- and panicolytic-like effects in male rats. However, in clinical reports, sibutramine favoured the onset of panic attacks in women. In this study, the effect of sibutramine on experimental anxiety in females and the relevance of different oestrous cycle phases for this effect were analysed. In experiment 1, both male and female rats were submitted to acute intraperitoneal injection of sibutramine or vehicle 30 min. before testing in the elevated T-maze (ETM) and in the open-field test (OF). Females in the pro-oestrus (P), oestrus (E), early dioestrus (ED) and late dioestrus (LD) phases were tested in the ETM and OF (experiment 2) or in the elevated plus-maze (EPM) 30 min. after the injection of sibutramine. Sibutramine impaired the escape response in the ETM in both males and females. This effect was observed for P, E and ED, but not for LD females. Sibutramine altered neither the inhibitory avoidance in the ETM nor the behaviour of females in the EPM. Thus, sibutramine promoted a panicolytic-like effect in female rats cycling at P, E and ED, but not in the LD phase and did not alter behaviours related to anxiety in both ETM and EPM. Considering that pre-clinical studies aiming the screening of anxiolytic drugs employ male rodents, data here obtained reinforce the importance of better understanding the effects of drugs in females.

Anxiogenic-like profile of Wistar adult rats based on the pilocarpine model: an animal model for trait anxiety?

RATIONALE

There is extensive evidence indicating the influence of seizures on emotional responses observed in human and animals, but so far few studies are focusing on the behavioral profile of animals that do not have seizures despite being treated with convulsant agents.

OBJECTIVES

We aimed to establish the behavioral profile, biochemical, and electrographic features of rats submitted to the pilocarpine model of temporal lobe epilepsy

METHODS

Rats treated with pilocarpine (20 to 350 mg/kg, i.p.) that did not develop status epilepticus or spontaneous recurrent seizures were evaluated 1 month later in the elevated plus maze (EPM), T-maze (ETM), open-field (OF), and step-down avoidance tests. Electroencephalographic (EEG), glutamate uptake, and hippocampal neuronal death assays were also performed

RESULTS

Pilocarpine (150 or 350 mg/kg) promoted anxiogenic-like effects in rats evaluated in the EPM, ETM, and OF tests, whereas only the highest dose evoked spike-wave discharges during EEG recordings. Hippocampal theta rhythm was increased by pilocarpine 150 or 350 mg/kg and only the highest dose reduced the L-[(3)H]-glutamate uptake and cell viability on hippocampal slices.

CONCLUSIONS

Subconvulsant doses of pilocarpine promote long-lasting alterations on neural circuitry, reflected by an increased theta activity in the hippocampus and an anxiety-like profile of rats evaluated 1 month after the treatment which is independent of seizure occurrence and is not related to changes in glutamate uptake or hippocampal damage. These results prompt us to suggest that a systemic administration of subconvulsant doses of pilocarpine could be useful as a new tool to model trait anxiety in rats.

NOP Receptor Ligands as Potential Agents for Inflammatory and Autoimmune Diseases

Nociceptin/orphanin FQ (N/OFQ) is a seventeen-amino acid peptide that is the endogenous ligand of a G-protein-coupled receptor (NOP). Various immune cells express the precursor protein and secrete N/OFQ as well as display binding sites for this peptide. The functional capacity of NOP receptor was demonstrated in vitro and in vivo studies by the ability of N/OFQ to induce chemotaxis of immune cells, to regulate the expression of cytokines and other inflammatory mediators, and to control cellular and humoral immunity. In this context, N/OFQ could modulate the outcome of some inflammatory diseases, such as sepsis and autoimmune pathologies by mechanisms not clearly elucidated yet. In fact, human body fluid revealed increased levels of N/OFQ under sepsis, arthritis, and Parkinson's diagnose. Preclinical studies pointed to the blockade of NOP receptor signaling as successful in treating these experimental conditions. Further preclinical and clinical studies are required to investigate the potential of NOP ligands in treating inflammatory diseases.

Lithium attenuates behavioral and biochemical effects of neuropeptide S in mice

Neuropeptide S (NPS) and its receptor NPSR comprise a recently deorphaned G-protein-coupled receptor system. There is a body of evidence suggesting the involvement of NPS in wakefulness, anxiety, locomotor activity and oxidative stress damage. Considering that mood stabilizers block the stimulatory effect of psychostimulants in rodents, the present study aimed to investigate the effects of the pretreatment with lithium and valproate on the hyperlocomotion evoked by NPS. Another relevant action induced by lithium and valproate is the neuroprotection against oxidative stress. Thus, aiming to get further information about the mechanisms of action of NPS, herein we evaluated the effects of NPS, lithium and valproate, and the combination of them on oxidative stress damage. Behavioral studies revealed that the pretreatment with lithium (100 mg/kg, i.p.) and valproate (200 mg/kg, i.p.) prevented hyperlocomotion evoked by NPS 0.1 nmol. Importantly, the dose of valproate used in this study reduced mouse locomotion, although it did not reach the statistical significance. Biochemical analyses showed that lithium attenuated thiobarbituric reactive species (TBARS) formation in the striatum, cerebellum and hippocampus. NPS per se reduced TBARS levels only in the hippocampus. Valproate did not significantly affect TBARS levels in the brain. However, the combination of mood stabilizers and NPS blocked, instead of potentiate, the neuroprotective effects of each one. No relevant alterations were observed in carbonylated proteins after all treatments. Altogether, the present findings suggested that mainly the mood stabilizer lithium evoked antagonistic effects on the mediation of hyperlocomotion and protection against lipid peroxidation induced by NPS.

Increased oxidative stress in submitochondrial particles into the brain of rats submitted to the chronic mild stress paradigm

Major depression is a common, serious and recurrent disorder, characterized by symptoms at the psychological, behavioral and physiological levels. Recent studies have suggested that reactive oxygen species (ROS) may play a role in the pathophysiology of bipolar disorder. The chronic mild stress (CMS) rat model has been used as an animal model of depression, since it induces some symptoms of a major depressive episode in humans (i.e. anhedonia). We investigated behavioral, physiological and neurochemical aspects of rats exposed for 40 days to CMS. Sweet food consumption, locomotor activity and body weight were assessed in stressed and control rats. We also investigated the potential involvement of ROS in the CMS model. Superoxide generation in submitochondrial particles from the rat hippocampus, prefrontal cortex and cortex was measured through superoxide-dependent oxidation of epinephrine to adrenochrome in a submitochondrial extract. We report that sweet food intake was reduced in rats subjected to CMS compared to controls. Further, CMS animals failed to gain body weight compared with non-stressed rats. Locomotor activity was not affected in stressed rats. An increase in superoxide production was detected in all brain structures analyzed. However, thiobarbituric acid reactive substances were increased only in cortex. In conclusion, these observations support the view that the CMS model of depression mimics alterations observed in depressed patients. The model affords a useful system in which to test the hypothesis that altered brain energy metabolism is associated with neuropsychiatric disorders.

Ketamine treatment reverses behavioral and physiological alterations induced by chronic mild stress in rats

Several studies have supported the idea that ionotropic glutamate N-methyl-d-aspartate receptor (NMDA) is an important player in the etiology of psychopathologies, such as anxiety disorders and major depression. Additionally, studies have shown that ketamine induces antidepressant effects in humans as well as in rodents subjected to animal models of depression. In this context, the present study was aimed to evaluate behavioral and physiological effects of acute and chronic administration of ketamine, a NMDA receptor antagonist, in rats exposed to chronic mild stress (CMS). After 40 days of CMS, rats were treated with ketamine (15 mg/kg) and sweet food consumption, body and adrenal gland weight, corticosterone and adrenocorticotropic (ACTH) hormone levels, and hippocampal BDNF protein levels were assessed. Our findings demonstrated that CMS evoked anhedonia, induced hypertrophy of adrenal gland, impaired gain of body weight and increased corticosterone and ACTH circulating levels in rats. Acute and chronic treatment with ketamine reversed the increase in adrenal gland weight, promoted regain of body weight, and normalized corticosterone and ACTH circulating levels. Repeated, but not acute, administration of ketamine reversed anhedonia-like behavior, although the treatment with ketamine per se increased sweet food consumption in non-stressed rats. Finally, acute and chronic ketamine treatment did not alter hippocampal BDNF protein levels in stressed rats. In conclusion, these findings support the idea of a putative role of NMDA receptors in mood-related symptoms, and rapid and robust effects of ketamine in reverting mainly physiological alterations induced by chronic mild stressful situations in rats.

Chronic mild stress paradigm reduces sweet food intake in rats without affecting brain derived neurotrophic factor protein levels

Major depression is a common, serious and recurrent disorder that affects 17-20% of the population of the world. The chronic mild stress (CMS) model has been used as an animal model of depression but reflect anhedonia in animals. Present study investigated behavioral, physiological and neurochemical aspects of rats exposed to a CMS procedure. The consumption of sweet food, locomotor activity, body and adrenal gland weight, BDNF protein levels evaluated in hippocampus, cerebrospinal fluid and serum were assessed in rats. Our findings demonstrated decreased in sweet food intake, increase of adrenal gland weight and a decrease of body weight and no changes were observed in BDNF protein levels in serum, cerebrospinal fluid and hippocampus in rats subjected to CMS procedure. Indeed, locomotor activity was not significantly affected. In conclusion, these data reveal that BDNF protein levels were not significantly correlated with the decrease of sweet food consumption observed in CMS exposed animals.

Further studies on the pharmacological features of the nociceptin/orphanin FQ receptor ligand ZP120

ZP120 is a nociceptin/orphanin FQ (N/OFQ) peptide receptor (NOP) ligand. In previous studies, the effects of ZP120 were found to be sensitive to J-113397 in mouse tissues while resistant to UFP-101 in rat tissues. The aim of this study was to further investigate the ZP120 pharmacological profile using mouse and rat preparations, J-113397 and UFP-101, as well as NOP receptor knockout (NOP(-/-)) mice. Electrically stimulated mouse and rat vas deferens were used to characterize the pharmacology of ZP120 in vitro. For in vivo studies the tail-withdrawal assay was performed in wild type (NOP(+/+)) and NOP knockout (NOP(-/-)) mice. In the mouse and rat vas deferens ZP120 mimicked the effects of N/OFQ showing higher potency but lower maximal effects. In both preparations, J-113397 antagonized N/OFQ and ZP120 effects showing similar pK(B) values ( approximately 7.8). UFP-101 antagonized the actions of N/OFQ (pK(B) values approximately 7.3) but did not modify the effects of ZP120. The inhibitory effects of N/OFQ and ZP120 were no longer evident in vas deferens tissues taken from NOP(-/-) mice. In NOP(+/+) mice subjected to the tail-withdrawal assay, ZP120 (1 nmol) mimicked the pronociceptive action of N/OFQ (10 nmol), producing longer lasting effects. The effects of both peptides were absent in NOP(-/-) animals. The NOP receptor ligand ZP120 is a high potency NOP selective partial agonist able to evoke long-lasting effects; its diverse antagonist sensitivity in comparison with N/OFQ may derive from different modality of binding to the NOP receptor.

Effects of chronic mild stress on the oxidative parameters in the rat brain

Major depression is characterized for symptoms at the psychological, behavioral and physiological levels. The chronic mild stress model has been used as an animal model of depression. The consumption of sweet food, locomotor activity, body weight, lipid and protein oxidation levels and superoxide dismutase and catalase activities in the rat hippocampus, prefrontal cortex and cortex were assessed in rats exposed to chronic mild stress. Our findings demonstrated a decrease on sweet food intake, no effect on locomotor activity, lack of body weight gain, increase in protein (prefrontal, hippocampus, striatum and cortex) and lipidic peroxidation (cerebellum and striatum), and an increase in catalase (cerebellum, hippocampus, striatum, cortex) and a decrease in superoxide dismutase activity (prefrontal, hippocampus, striatum and cortex) in stressed rats. In conclusion, our results support the idea that stress produces oxidants and an imbalance between superoxide dismutase and catalase activities that contributes to stress-related diseases, such as depression.

GABA(A) signalling is involved in N/OFQ anxiolytic-like effects but not in nocistatin anxiogenic-like action as evaluated in the mouse elevated plus maze

Nociceptin/orphanin FQ (N/OFQ) and nocistatin are two neuropeptides originated from the same precursor prepronociceptin/orphanin FQ (ppN/OFQ). N/OFQ is the endogenous ligand of the NOP receptor, while the target of action of nocistatin is still unknown. N/OFQ modulates various biological functions, including anxiety. Conversely, nocistatin either behaves as a functional N/OFQ antagonist or evokes per se effects opposite to those of N/OFQ. Here we investigated the interaction between the anxiolytic-like effects of N/OFQ and the anxiogenic-like action of nocistatin with those evoked by GABA(A) receptor ligands in the mouse elevated plus maze. The anxiogenic-like effects of the GABA(A) receptor antagonist pentylenetetrazol (20mg/kg; intraperitoneal, i.p.) were abolished by the co-treatment with N/OFQ (10pmol; intracerebroventricular, i.c.v.) while potentiated by the administration of nocistatin (0.01pmol; i.c.v.). The anxiolytic-like effects of the benzodiazepine receptor agonist diazepam (0.75mg/kg, i.p.) were reversed by nocistatin (0.1pmol; i.c.v.), whereas signs of sedation were observed when mice were co-treated with diazepam and N/OFQ (3pmol). Interesting enough, the i.p. treatment with flumazenil (1mg/kg) blocked the anxiolytic-like effects of N/OFQ (10pmol; i.c.v.), but not the anxiogenic effect elicited by nocistatin. Collectively, our findings suggest that the effects on anxiety elicited by pentylenetetrazol and diazepam can be counteracted or potentiated in the presence of N/OFQ and nocistatin. In addition, the effects on anxiety of N/OFQ, but not nocistatin, appear to be dependent on the benzodiazepine site of the GABA(A) receptor.