Elaine C. Gavioli

Nociceptin/orphanin FQ receptor antagonists as innovative antidepressant drugs

Nociceptin/orphanin FQ (N/OFQ) and its receptor (NOP) were identified in the mid 90s as a novel peptidergic system structurally related to opioids. A growing body of preclinical evidence suggests that blockade of NOP receptors evokes antidepressant-like actions. These have been explored using a range of compounds (peptide and non peptide antagonists), across different species (rat and mouse) and assays (behavioral despair and chronic mild stress) suggesting a robust and consistent antidepressant-like effect. Moreover, rats and mice knockout for the NOP receptor gene display an antidepressant-like phenotype in behavioral despair assays. Electrophysiological, immunohistochemical and neurochemical studies point to an important role played by monoaminergic systems, particularly 5-HTergic, in mediating the antidepressant-like properties of NOP antagonists. However other putative mechanisms of action, including modulation of the CRF system, circadian rhythm and a possible neuroendocrine-immune control might be involved. A close relationship between the N/OFQ-NOP receptor system and stress responses is well described in the literature. Stressful situations also alter endocrine, behavioral and neurochemical parameters in rats and chronic administration of a NOP antagonist restored these alterations. Interestingly, clinical findings showed that plasma N/OFQ levels were significantly altered in major and post-partum depression, and bipolar disease patients. Collectively, data in the literature support the notion that blockade of NOP receptor signaling could be a novel and interesting strategy for the development of innovative antidepressants.

Effects of long-term ovariectomy on anxiety and behavioral despair in rats.

Clinical and pre-clinical findings point to the critical role of ovarian hormones in modulating anxiety and depressive symptoms in female. However, few studies investigated the effects of long-term ovarian hormones withdrawal on animal behavior. The current study evaluated the behavioral effects of long-term ovariectomy (performed at 3 months of life) in adult (6 months old) and aged (18 months old) rats subjected to the elevated plus-maze and forced swimming tests. A substantial reduction in the time spent in open arms in adult and aged ovariectomized rats was observed compared to intact animal from the same age. A significant increase in the immobility time was observed in aged rats, ovariectomized or not, compared to adult rats. It should be noted that no alterations in the spontaneous locomotion were detected among groups. In addition, a reduction in serum concentrations of 17beta-estradiol was observed in adult ovariectomized and aged sham and ovariectomized rats compared to adult intact animals. Taken together, these findings suggest that anxiety-related behaviors were affected by ovariectomy, but not aging. However, the depressive-like behavior observed in aged rats seems to be much more influenced by senescence than ovarian hormones withdrawal. The presented results are discussed considering the effects of gradual and abrupt reduction of ovarian steroids concentrations, and the influence of aging on behavior of female rats.

Emotional behavior in middle-aged rats: Implications for geriatric psychopathologies

Clinical findings reveal that middle-aged patients are more susceptible to suffer from psychiatric disorders than older ones. However, little is known about the emotional behavior of aging rodents. This study aimed to investigate behavioral alterations in male middle-aged Wistar rats in the open-field (OF) test (at illuminated and dimly light conditions), elevated plus maze (EPM), forced swimming (FST) and inhibitory avoidance task (IA). In the EPM, middle-aged rats displayed reduced percentages of the time spent in and entries into open arms. The ambulatory activity measured in the OF under dimly light conditions was identical among groups. However, under illuminated conditions, a reduction in the number of crossings was detected in older rats, reinforcing that aged animals display a genuine anxiogenic-like phenotype. Additionally, aged rats showed an increase in the immobility time in the FST, and a reduction in the latency to step down the platform in the IA. A negative correlation was found between the immobility time and latency to step down the platform, suggesting a relationship between depressive-behavior and cognitive impairment in old rats. Altogether, male middle-aged rats are more anxious, depressed, and display aversive memory impairments. These observations contribute to investigate biological mechanisms and therapeutic interventions for geriatric anxiety and depression.

The elevated T-maze task as an animal model to simultaneously investigate the effects of drugs on long-term memory and anxiety in mice.

The elevated T-maze (ETM) is an apparatus derived from the elevated plus-maze test, which is used to evaluate anxiety. Because anxiety is a biasing factor in models of memory, this study proposed the ETM as a task for the simultaneous assessment of memory and anxiety in mice. The ETM consists of one enclosed and two open arms. The procedure is based on the avoidance of open spaces learned during training session, in which mice were exposed to the enclosed arm as many times as needed to stay 300s. In the test session, memory is assessed by re-exposing the mouse to the enclosed arm and the latency to enter an open arm was recorded. The anxiolytic diazepam (DZP; 1 or 2mg/kg) and the amnestic biperiden (BPR; 0.5, 1 or 3mg/kg) were injected at three distinct times: pre-training, post-training, and pre-test. Pre-training administration of BPR 1 and DZP 2 increased the number of trials needed to reach the avoidance criterion, suggesting a passive avoidance learning impairment. However, BPR induced hyperlocomotion, which could bias the interpretation of any BPR-induced effects during the training session. Pre-training injection of BPR did not affect the spontaneous increase in the latency to enter an open arm between trials, while DZP reduced latencies in the first three trials suggesting anxiolysis. In the test session, pre-training injection of BPR 1 and DZP 2 reduced latencies to enter an open arm, indicating memory impairment. Post-training and pre-test injection of DZP or BPR did not affect memory. In conclusion, the proposed ETM task is practical for the detection of the anxiolytic and amnesic effects of drugs.

Anxiolytic-like effect of central administration of NOP receptor antagonist UFP-101 in rats submitted to the elevated T-maze

Depression and anxiety disorders present several genetic and neurobiological similarities. Drugs with antidepressant activity are effective in the treatment of a wide spectrum of anxiety disorders. Preclinical results showed that acute and chronic treatment with the NOP antagonist [Nphe(1),Arg(14),Lys(15)]N/OFQ-NH(2) (UFP-101) produced antidepressant-like effects in rodents. Thus, the present study aimed to investigate the effect of central administration of UFP-101 on the anxiety-related behavior in rats as evaluated in the elevated T-maze (ETM) test. Our results showed that UFP-101 reduced the latency of inhibitory avoidance in the ETM, indicating an anxiolytic-like effect. The endogenous peptide N/OFQ prevented this anxiolytic-like action of UFP-101, demonstrating its modulation via central NOP receptors. However, UFP-101 failed to interfere with the latency to escape. No change was observed in locomotor activity after UFP-101 treatment, ruling out any nonspecific motor effect. In conclusion, our results showed that the central administration of UFP-101 presents an anxiolytic-like effect in rats evaluated in the ETM test, providing new insights for drug development to treat anxiety disorders targeting the N/OFQ-NOP receptor system.

The blockade of transient receptor potential ankirin 1 (TRPA1) signalling mediates antidepressant‐ and anxiolytic‐like actions in mice

Transient receptor potential vanilloid 1 (TRPV1) and TRP ankyrin 1 (TRPA1) are involved in many biological processes, including nociception and hyperalgesia. Whereas the involvement of TRPV1 in psychiatric disorders such as anxiety and depression has been reported, little is known regarding the role of TRPA1 in these 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.

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.

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.

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.