Role of heme oxygenase-1 in the antidepressant-like effect of ursolic acid in the tail suspension test.

OBJECTIVES: This study investigated the involvement of heme oxygenase-1 (HO-1) in the antidepressant-like effects of ursolic acid (UA), a plant-derived compound with neuroprotective and antidepressant-like properties. METHODS: Mice received intracerebroventricular injections of zinc protoporphyrin IX (ZnPP) or cobalt protoporphyrin IX (CoPP) to inhibit or induce HO-1, respectively, together with effective (0.1 mg/kg, p.o.) or sub-effective (0.01 mg/kg, p.o.) doses of UA or fluoxetine (10 mg/kg, p.o.). Immobility time was assessed using the tail suspension test (TST) and the ambulatory behaviour with the open field test. HO-1 immunocontent was evaluated in mice hippocampus and prefrontal cortex. KEY FINDINGS: ZnPP prevented the anti-immobility effects of UA and fluoxetine. Combined treatment with a sub-effective dose of CoPP and UA synergistically exerted antidepressant-like effects in the TST. Acute administration of UA or CoPP, but not fluoxetine, increased the HO-1 immunocontent in the hippocampus. None of the treatments altered the HO-1 immunocontent in the prefrontal cortex. CONCLUSIONS: In conclusion, this work shows that increased hippocampal HO-1 content and activity mediate the antidepressant-like effect of UA in the TST.

Ursolic acid abrogates depressive-like behavior and hippocampal pro-apoptotic imbalance induced by chronic unpredictable stress.

Emerging evidence has shown that ursolic acid exerts antidepressant-like effects, however, its ability to elicit an antidepressant-like response in rodents subjected to stress model that mimics behavioral and neurochemical alterations found in depression remains to be determined. Thus, this study investigated the possible antidepressant-like effect of ursolic acid in mice subjected to chronic unpredictable stress (CUS) for 14 days, and whether this effect could be associated with the modulation of serum corticosterone levels and hippocampal Bcl-2/Bax mRNA expression. Our results indicated that CUS induced a depressive-like behavior, as demonstrated by an increase in the immobility time and latency to first grooming in the tail suspension test and splash test, respectively. Conversely, the repeated administration of ursolic acid (0.1 mg/kg, p.o.) or fluoxetine (10 mg/kg, p.o.) in the last 7 days of CUS completely prevented CUS-induced behavioral alterations, suggesting an antidepressant-like effect. Additionally, CUS significantly increased the mRNA expression of Bax (pro-apoptosis marker), but not Bcl-2 (anti-apoptosis marker) in the hippocampus. Moreover, reduced hippocampal mRNA expression of Bcl-2/Bax ratio was detected in CUS-exposed mice. Ursolic acid, but not fluoxetine, prevented CUS-induced increase in the expression of Bax, but both ursolic acid and fluoxetine prevented CUS-induced reduction on Bcl-2/Bax ratio. Furthermore, neither CUS nor treatments with ursolic acid or fluoxetine altered serum corticosterone levels. Our study unveils the ability of ursolic acid to prevent the depressive-like behavior induced by stress and the modulation of Bcl-2/Bax expression could be associated with this response.

mTORC1-dependent signaling pathway underlies the rapid effect of creatine and ketamine in the novelty-suppressed feeding test.

The development of fast-acting antidepressants is crucial considering that conventional antidepressants require a long period to elicit therapeutic effects. Creatine, an ergogenic guanidine-like compound, stands out as a candidate to exert fast antidepressant-like responses. The present study investigated whether a single dose of creatine elicits a fast response in mice submitted to the novelty-suppressed feeding (NSF) test, a paradigm that may assess depression-like and anxiety-like behaviors. Ketamine, an NMDA receptor antagonist that has rapid antidepressant effects, and conventional antidepressants were also tested. The involvement of the mTORC1 signaling pathway in the behavioral responses was also investigated. Biochemical analyses included hippocampal BDNF level (ELISA) and total and phospho-mTORC1 (Ser2448), PSD95 and synapsin immunocontent (Western Blotting). Creatine (10 mg/kg, p.o.) or ketamine (1 mg/kg, i.p.) reduced the latency to feed in the NSF test. Conversely, fluoxetine (10 mg/kg, p.o.), imipramine (1 mg/kg, p.o.) or bupropion (10 mg/kg, p.o.) did not alter this parameter. The administration of rapamycin (mTOR inhibitor, 0.2 nmol/site, i.c.v.) abolished the effects of creatine or ketamine in the NSF test. Creatine or ketamine-treated mice presented increased hippocampal BDNF level, an effect abolished by rapamycin. The hippocampal phospho-mTORC1 (Ser2448) immunocontent was increased by creatine, but not by ketamine. However, ketamine, but not creatine, increased PSD95 and synapsin immunocontent. Creatine and ketamine elicit a rapid response in the NSF test by a mechanism dependent on the mTORC1 signaling pathway.

Prophylactic effect of physical exercise on Aß1-40-induced depressive-like behavior and gut dysfunction in mice.

Alzheimer's disease (AD) is a prevalent neurodegenerative disease that is highly comorbid with depression. Gut dysfunction has been proposed as a possible risk factor for both clinical conditions. In the present study, we investigated the ability of treadmill exercise for 4 weeks (5 days/week, 40 min/day) to counteract amyloid ß1-40 peptide (Aß1-40)-induced depressive-like behavior, alterations in morphological parameters of the duodenum, and the abundance of Firmicutes and Bacteroidetes phyla. Aß1-40 administration (400 pmol/mouse, i.c.v.) increased immobility time in the tail suspension test (TST) and reduced time spent sniffing in the female urine sniffing test (FUST), indicating behavioral despair and impairment in reward-seeking behavior. These behavioral alterations, indicative of depressive-like behavior, were accompanied by reduced villus width in the duodenum. Moreover, photomicrographs obtained by transmission electron microscopy revealed abnormal epithelial microvilli in the duodenum from sedentary Aß1-40-exposed mice, characterized by shorter microvilli and heterogeneity in the length of these structures that exhibit a disordered packing. Regarding the ultrastructure of Paneth cells, Aß1-40 administration caused a reduction in the secretory granule diameter, as well as an enlarged peripheral halo. These animals also presented reduced Firmicutes and increased Bacteroidetes abundance, and increased Bacteroidetes/Firmicutes ratio. Most of the alterations observed in Aß1-40-exposed mice were prevented by the practice of physical exercise. Altogether the results provide evidence of the prophylactic effect of physical exercise on Aß1-40-induced depressive-like behavior and gut dysfunction in mice, suggesting that physical exercise could be useful for preventing depression associated with AD.

Antidepressant-like and pro-neurogenic effects of physical exercise: the putative role of FNDC5/irisin pathway.

Physical exercise has been shown to exert antidepressant effects, but the mechanisms underlying this effect are not completely elucidated. Therefore, we aimed at investigating the antidepressant, pro-neurogenic, and neuroprotective effects of physical exercise and the possible role of FNDC5/irisin for this effect. Treadmill running was used as a protocol of physical exercise (45 min/day/5 days/week for 4 weeks) in female Swiss mice. Immobility time was registered in the tail suspension test (TST) and forced swim test (FST). Immunohistochemical analyses to evaluate hippocampal cell proliferation, neuronal survival, and neuronal commitment and maturation, as well as expression of FNDC5 C-terminal fragment were performed in the entire, dorsal, and ventral dentate gyrus (DG) of the hippocampus. Fluoro-Jade B staining was performed to evaluate degenerating neurons in DG. FNDC5 C-terminal and FNDC5/irisin immunocontents were analyzed by western blot. Exposure to physical exercise reduced the immobility time both in the TST and the FST. This antidepressant-like effect was accompanied by an increase in hippocampal cell proliferation, hippocampal neuronal differentiation, and neuronal survival in the dorsal and ventral DG. Fluoro-Jade B staining was reduced in entire and dorsal DG in exercised mice. Finally, physical exercise also resulted in increased number of FNDC5-positive cells in the hippocampal DG as well as elevated FNDC5 C-terminal and FNDC5/irisin immunocontent in the entire hippocampus. The results suggest that the FNDC5 C-terminal fragment/irisin pathway may be implicated in the antidepressant-like, pro-neurogenic, and neuroprotective effects of treadmill running.

Ascorbic acid presents rapid behavioral and hippocampal synaptic plasticity effects.

Growing evidence has suggested that ascorbic acid may exhibit rapid anxiolytic and antidepressant-like effects. In this study the effects of a single administration of ascorbic acid (1 mg/kg, p.o.), ketamine (1 mg/kg, i.p., a fast-acting antidepressant) and fluoxetine (10 mg/kg, p.o., conventional antidepressant) were investigated on: a) behavioral performance in the novelty suppressed feeding (NSF) test; b) hippocampal synaptic protein immunocontent; c) dendritic spine density and morphology in the dorsal and ventral dentate gyrus (DG) of the hippocampus and d) hippocampal dendritic arborization. Ascorbic acid or ketamine, but not fluoxetine, decreased the latency to feed in the NSF test in mice. This effect was accompanied by increased p70S6K (Thr389) phosphorylation 1 h after ascorbic acid or ketamine treatment, although only ascorbic acid increased synapsin I immunocontent. Ketamine administration increased the dendritic spine density in the dorsal DG, but none of the treatments affected the maturation of dendritic spines in this region. In addition, both ascorbic acid and ketamine increased the dendritic spine density in the ventral DG, particularly the mature spines. Sholl analysis demonstrated no effect of any treatment on hippocampal dendritic arborization. Altogether, the results provide evidence that the behavioral and synaptic responses observed following ascorbic acid administration might occur via the upregulation of synaptic proteins, dendritic spine density, and maturation in the ventral DG, similar to ketamine. These findings contribute to understand the cellular targets implicated in its antidepressant/anxiolytic behavioral responses and support the notion that ascorbic acid may share with ketamine the ability to increase synaptic function.

Augmentation effect of ketamine by guanosine in the novelty-suppressed feeding test is dependent on mTOR signaling pathway.

The ketamine's potential for the treatment of refractory depression and anxiety has been considered one the most important discoveries in the last years, however, repeated use of ketamine is limited due to its side/adverse effects. Therefore, the search for effective augmentation strategies that may reduce ketamine doses is welcome. Therefore, this study sought to augment the effect of ketamine by guanosine in the novelty-suppressed feeding (NSF) test, a behavioral paradigm able to detect depression/anxiety-related behavior. Acute administration of guanosine (0.05 mg/kg, p.o.), similar to ketamine (1 mg/kg, i.p.), produced a rapid behavioral response in mice submitted to NSF test. Moreover, the coadministration of sub-effective doses of guanosine (0.01 mg/kg, p.o.) and ketamine (0.1 mg/kg, i.p.) was effective in mice submitted to NSF test. Subsequently, the intracellular mechanism underpinning the augmentation effect of ketamine by guanosine was investigated. Our results suggest that augmentation response of ketamine by guanosine in the NSF test probably involves the activation of mTOR signaling, since the treatment with rapamycin (0.2 nmol/site, i.c.v., a selective mTOR inhibitor) completely abolished this effect. This augmentation strategy also increased mTOR phosphorylation (Ser2448) in the hippocampus, reinforcing the role of mTOR in this augmentation response. However, no changes in the p70S6K, PSD-95, GluA1, and synapsin immunocontents were found in the hippocampus of ketamine plus guanosine-treated mice. Overall, results provide evidence that guanosine is able to augment the effect of ketamine in the NSF test via mTOR activation, a finding that might have therapeutic implications for the management of depression/anxiety.

Prophylactic effect of physical exercise on Aß1-40-induced depressive-like behavior: Role of BDNF, mTOR signaling, cell proliferation and survival in the hippocampus.

Alzheimer's disease (AD) is characterized by progressive cognitive impairments as well as non-cognitive symptoms such as depressed mood. Physical exercise has been proposed as a preventive strategy against AD and depression, an effect that may be related, at least partially, to its ability to prevent impairments on cell proliferation and neuronal survival in the hippocampus, a structure implicated in both cognition and affective behavior. Here, we investigated the ability of treadmill exercise (4 weeks) to counteract amyloid ß1-40 peptide-induced depressive-like and anxiety-like behavior in mice. Moreover, we addressed the role of the BDNF/mTOR intracellular signaling pathway as well as hippocampal cell proliferation and survival in the effects of physical exercise and/or Aß1-40. Aß1-40 administration (400 pmol/mouse, i.c.v.) increased immobility time and reduced the latency to immobility in the forced swim test, a finding indicative of depressive-like behavior. In addition, Aß1-40 administration also decreased time spent in the center of the open field and increased grooming and defecation, alterations indicative of anxiety-like behavior. These behavioral alterations were accompanied by a reduction in the levels of mature BDNF and mTOR (Ser2448) phosphorylation in the hippocampus. In addition, Aß1-40 administration reduced cell proliferation and survival in the ventral, dorsal and entire dentate gyrus of the hippocampus. Importantly, most of these behavioral, neurochemical and structural impairments induced by Aß1-40 were not observed in mice subjected to 4 weeks of treadmill exercise. These findings indicate that physical exercise has the potential to prevent the occurrence of early emotional disturbances associated with AD and this appears to be mediated, at least in part, by modulation of hippocampal BDNF and mTOR signaling as well as through promotion of cell proliferation and survival in the hippocampal DG.

The possible beneficial effects of creatine for the management of depression.

Depression, a highly prevalent neuropsychiatric disorder worldwide, causes a heavy burden for the society and is associated with suicide risk. The treatment of this disorder remains a challenge, since currently available antidepressants provide a slow and, often, incomplete response and cause several side effects that contribute to diminish the adhesion of patients to treatment. In this context, several nutraceuticals have been investigated regarding their possible beneficial effects for the management of this neuropsychiatric disorder. Creatine stands out as a supplement frequently used for ergogenic purpose, but it also is a neuroprotective compound with potential to treat or mitigate a broad range of central nervous systems diseases, including depression. This review presents preclinical and clinical evidence that creatine may exhibit antidepressant properties. The focus is given on the possible molecular mechanisms underlying its effects based on the results obtained with different animal models of depression. Finally, evidence obtained in animal models of depression addressing the possibility that creatine may produce rapid antidepressant effect, similar to ketamine, are also presented and discussed.

Subchronic administration of creatine produces antidepressant-like effect by modulating hippocampal signaling pathway mediated by FNDC5/BDNF/Akt in mice.

Creatine has been shown to play a significant role in the pathophysiology and treatment of major depressive disorder (MDD) in preclinical and clinical studies. However, the biological mechanisms underlying its antidepressant effect is still not fully elucidated. This study investigated the effect of creatine (p.o.) administered for 21 days in the behavior of mice submitted to tail suspension test (TST), a predictive test of antidepressant activity. Creatine reduced the immobility time in the TST (1-10 mg/kg), without affecting locomotor activity, a finding consistent with an antidepressant profile. Creatine administration increased the ubiquitous creatine kinase (uCK) and creatine kinase brain isoform (CK-B) mRNA in the hippocampus of mice. Taking into account that PGC-1α induces FNDC5/irisin expression mediating BDNF-dependent neuroplasticity, the effect of creatine administration (1 mg/kg, p. o.) on the hippocampal PGC-1α, FNDC5 and BDNF gene expression was investigated. Creatine treatment increased PGC-1α, FNDC5 and BDNF mRNA in the hippocampus as well as BDNF immunocontent. The involvement of BDNF downstream intracellular signaling pathway mediated by Akt, proapoptotic proteins BAX and BAD and antiapoptotic proteins Bcl2 and Bcl-xL was also investigated following creatine treatment. Creatine increased Akt phosphorylation (Ser 473), and Bcl2 mRNA and protein levels, and Bcl-xL mRNA, whereas BAD mRNA was decreased following creatine administration in the hippocampus. Altogether these results indicate that creatine antidepressant-like effect may be dependent on Akt activation and increased expression of the neuroprotective proteins in the hippocampus of mice. The obtained data reinforce the antidepressant property of creatine and highlight the role of these molecular targets in the pathophysiology of MDD.

Antidepressant effects of creatine on amyloid ß1-40-treated mice: The role of GSK-3ß/Nrf2 pathway.

Alzheimer's disease (AD) is characterized by progressive synaptic dysfunction and neuronal lost in specific brain areas including hippocampus, resulting in memory/learning deficits and cognitive impairments. In addition, non-cognitive symptoms are reported in AD patients, such as anxiety, apathy and depressed mood. The current antidepressant drugs present reduced efficacy to improve depressive symptoms in AD patients. Here, we investigated the ability of creatine, a compound with neuroprotective and antidepressant properties, to counteract amyloid ß1-40 peptide-induced depressive-like behavior in mice. Moreover, we addressed the participation of the intracellular signaling pathway mediated by glycogen synthase kinase-3ß (GSK-3ß)/nuclear factor erythroid-2-related factor 2 (Nrf2) in the creatine effects. Aß1-40 administration (400 pmol/mouse, i.c.v.) increased the immobility time in the tail suspension test and decreased the grooming time and increased latency to grooming in the splash test, indicative of depressive-like behavior. These impairments were attenuated by creatine (0.01 and 10 mg/kg, p.o.) and fluoxetine (10 mg/kg, p.o., positive control). No significant alterations on locomotor performance were observed in the open field. Aß1-40 administration did not alter hippocampal phospho-GSK-3ß (Ser9)/total GSK-3ß, total GSK-3ß and heme oxygenase-1 (HO-1) immunocontents. However, Aß1-40-infused mice treated with creatine (0.01 mg/kg) presented increased phosphorylation of GSK-3ß(Ser9) and HO-1 immunocontent in the hippocampus. Fluoxetine per se increased GSK-3ß(Ser9) phosphorylation, but did not alter HO-1 levels. In addition, Aß1-40 administration increased hippocampal glutathione (GSH) levels as well as glutathione reductase (GR) and thioredoxin reductase (TrxR) activities, and these effects were abolished by creatine and fluoxetine. This study provides the first evidence of the antidepressive-like effects of creatine in Aß1-40-treated mice, which were accompanied by hippocampal inhibition of GSK-3ß and modulation of antioxidant defenses. These findings indicate the potential of creatine for the treatment of depression associated with AD.

Central irisin administration affords antidepressant-like effect and modulates neuroplasticity-related genes in the hippocampus and prefrontal cortex of mice.

Evidence has indicated that the practice of physical exercise has antidepressant effects that might be associated with irisin release and BDNF signaling. In this study we investigated the effects of the central administration of irisin or BDNF in predictive tests of antidepressant properties paralleled with the gene expression of peroxisome proliferator-activated receptor gamma co-activator 1α (PGC-1α), fibronectin type III domain-containing protein 5 (FNDC5) and brain-derived neurotrophic factor (BDNF) in the hippocampus and prefrontal cortex of mice. Irisin (0.5-1 ng/mouse, i.c.v.) reduced the immobility time in the tail suspension test (TST) and forced swim test (FST), without altering locomotion in the open field test (OFT). Irisin reduced the immobility time in the TST up to 6 h after its administration. Irisin administration (6 h) increased PGC-1α mRNA in the hippocampus and prefrontal cortex and reduced (1 h) PGC-1α mRNA in the prefrontal cortex. FNDC5 and BDNF mRNA expression was decreased (1 h) in both structures and remained reduced up to 6 h in the prefrontal cortex. Moreover, BDNF administered at 0.25 µg/mouse, i.c.v. (1 and 6 h before the test) reduced the immobility time in the TST. BDNF administration reduced PGC-1α mRNA in the hippocampus (6 h) and prefrontal cortex (1 and 6 h). It also increased FNDC5 mRNA expression in the hippocampus (1 and 6 h), but reduced the expression of this gene and also BDNF mRNA in the prefrontal cortex (1 and 6 h). None of the treatments altered BDNF protein levels in both structures. In conclusion, irisin presents a behavioral antidepressant profile similar to BDNF, an effect associated with the modulation of gene expression of PGC-1α, FNDC5 and BDNF, reinforcing the pivotal role of these genes in mood regulation.

Therapeutic Potential of Ursolic Acid to Manage Neurodegenerative and Psychiatric Diseases.

Ursolic acid is a pentacyclic triterpenoid found in several plants. Despite its initial use as a pharmacologically inactive emulsifier in pharmaceutical, cosmetic and food industries, several biological activities have been reported for this compound so far, including anti-tumoural, anti-diabetic, cardioprotective and hepatoprotective properties. The biological effects of ursolic acid have been evaluated in vitro, in different cell types and against several toxic insults (i.e. 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine, amyloid-ß peptides, kainic acid and others); in animal models of brain-related disorders (Alzheimer disease, Parkinson disease, depression, traumatic brain injury) and ageing; and in clinical studies with cancer patients and for muscle atrophy. Most of the protective effects of ursolic acid are related to its ability to prevent oxidative damage and excessive inflammation, common mechanisms associated with multiple brain disorders. Additionally, ursolic acid is capable of modulating the monoaminergic system, an effect that might be involved in its ability to prevent mood and cognitive dysfunctions associated with neurodegenerative and psychiatric conditions. This review presents and discusses the available evidence of the possible beneficial effects of ursolic acid for the management of neurodegenerative and psychiatric disorders. We also discuss the chemical features, major sources and potential limitations of the use of ursolic acid as a pharmacological treatment for brain-related diseases.

Ursolic acid affords antidepressant-like effects in mice through the activation of PKA, PKC, CAMK-II and MEK1/2.

BACKGROUND: Ursolic acid has been shown to display antidepressant-like effects in mice through the modulation of monoaminergic systems. In this study, we sought to investigate the involvement of signaling pathways on the antidepressant-like effects of ursolic acid. METHODS: Mice were treated orally with ursolic acid (0.1mg/kg) and, 45min later they received the followings inhibitors by intracerebroventricular route: H-89 (PKA inhibitor, 1µg/mouse), KN-62 (CAMK-II inhibitor, 1µg/mouse), chelerythrine (PKC inhibitor, 1µg/mouse), U0126 (MEK1/2 inhibitor, 5µg/mouse), PD98059 (MEK1/2 inhibitor, 5µg/mouse), wortmannin (PI3K irreversible inhibitor, 0.1µg/mouse) or LY294002 (PI3K inhibitor, 10 nmol/mouse). Immobility time of mice was registered in the tail suspension test (TST). RESULTS: The anti-immobility effect of ursolic acid in the TST was abolished by the treatment of mice with H-89, KN-62, chelerythrine, U0126 or PD98059, but not with wortmannin or LY294002. CONCLUSIONS: These results suggest that activation of PKA, PKC, CAMK-II, MEK1/2 may underlie the antidepressant-like effects of ursolic acid.

Creatine Prevents Corticosterone-Induced Reduction in Hippocampal Proliferation and Differentiation: Possible Implication for Its Antidepressant Effect.

The benefits of creatine supplementation have been reported in a broad range of central nervous system diseases, including depression, although the mechanisms underlying these effects remain to be understood. In the present study, we investigated the ability of creatine to counteract the morphological and behavioral effects elicited by chronic administration of corticosterone (CORT, 20 mg/kg, p.o.) for 21 days to mice, a pharmacological model of depression that mimics exposure to stress. CORT treatment increased immobility time in the tail suspension test (TST) and forced swim test (FST), as well as latency to immobility in the FST, and decreased the sucrose consumption in the sucrose preference test (SPT). These behavioral effects were associated with decreased hippocampal cell proliferation and neuronal differentiation and increased glial fibrillary acid protein (GFAP) immunostaining (suggestive of astrogliosis) in dentate gyrus (DG) of the hippocampus. These CORT-induced alterations were abolished by treatment with either fluoxetine (a conventional antidepressant) or creatine for 21 days (both 10 mg/kg, p.o.). In addition, fluoxetine, but not creatine, was able to reverse the CORT-induced reduction in serum CORT levels. Collectively, our results suggest that creatine produces morphological alterations that contribute to the improvement of depressive-like behaviors triggered by chronic CORT administration in mice.

MPP+-Lesioned Mice: an Experimental Model of Motor, Emotional, Memory/Learning, and Striatal Neurochemical Dysfunctions.

The neurotoxin 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) induces motor and nonmotor dysfunctions resembling Parkinson's disease (PD); however, studies investigating the effects of 1-methyl-4-phenylpyridinium (MPP+), an active oxidative product of MPTP, are scarce. This study investigated the behavioral and striatal neurochemical changes (related to oxidative damage, glial markers, and neurotrophic factors) 24 h after intracerebroventricular administration of MPP+ (1.8-18 µg/mouse) in C57BL6 mice. MPP+ administration at high dose (18 µg/mouse) altered motor parameters, since it increased the latency to leave the first quadrant and reduced crossing, rearing, and grooming responses in the open-field test and decreased rotarod latency time. MPP+ administration at low dose (1.8 µg/mouse) caused specific nonmotor dysfunctions as it produced a depressive-like effect in the forced swim test and tail suspension test, loss of motivational and self-care behavior in the splash test, anxiety-like effect in the elevated plus maze test, and short-term memory deficit in the step-down inhibitory avoidance task, without altering ambulation. MPP+ at doses of 1.8-18 µg/mouse increased tyrosine hydroxylase (TH) immunocontent and at 18 µg/mouse increased α-synuclein and decreased parkin immunocontent. The astrocytic calcium-binding protein S100B and glial fibrillary acidic protein (GFAP)/S100B ratio was decreased following MPP+ administration (18 µg/mouse). At this highest dose, MPP+ increased the ionized calcium-binding adapter molecule 1 (Iba-1) immunocontent, suggesting microglial activation. Also, MPP+ at a dose of 18 µg/mouse increased thiobarbituric acid reactive substances (TBARS) and glutathione (GSH) levels and increased glutathione peroxidase (GPx) and hemeoxygenase-1 (HO-1) immunocontent, suggesting a significant role for oxidative stress in the MPP+-induced striatal damage. MPP+ (18 µg/mouse) also increased striatal fibroblast growth factor 2 (FGF-2) and brain-derived neurotrophic factor (BDNF) levels. Moreover, MPP+ decreased tropomyosin receptor kinase B (TrkB) immunocontent. Finally, MPP+ (1.8-18 µg/mouse) increased serum corticosterone levels and did not alter acetylcholinesterase (AChE) activity in the striatum but increased it in cerebral cortex and hippocampus. Collectively, these results indicate that MPP+ administration at low doses may be used as a model of emotional and memory/learning behavioral deficit related to PD and that MPP+ administration at high dose could be useful for analysis of striatal dysfunctions associated with motor deficits in PD.

The antidepressant-like effect of chronic guanosine treatment is associated with increased hippocampal neuronal differentiation.

Guanosine is a purine nucleoside that occurs naturally in the central nervous system, exerting trophic effects. Given its neuroprotective properties, the potential of guanosine as an antidepressant has been recently examined. Within this context, the present study sought to investigate the effects of chronic treatment with guanosine on the tail suspension test (TST), open field test and adult hippocampal neurogenesis. Swiss mice were administered guanosine for 21 days (5 mg/kg/day, p.o.) and subsequently submitted to the TST and open-field test. Following behavioural testing, animals were killed and the brains were processed for immunohistochemical analyses of hippocampal cell proliferation and neuronal differentiation. Animals treated with guanosine showed a reduction in immobility time in the TST without alterations in locomotor activity, confirming the antidepressant-like effect of this compound. Quantitative microscopic analysis did not reveal significant alterations in the numbers of Ki-67- and proliferating cell nuclear antigen (PCNA)-positive cells in the hippocampal dentate gyrus (DG) of guanosine-treated mice. However, guanosine treatment resulted in a significant increase in the number of immature neurons, as assessed by immunohistochemistry for the neurogenic differentiation protein. Interestingly, this effect was localized to the ventral hippocampal DG, a functionally distinct region of this structure known to regulate emotional and motivational behaviours. Taken together, our results suggest that the antidepressant-like effect of chronic guanosine treatment is associated with an increase in neuronal differentiation, reinforcing the notion that this nucleoside may be an endogenous mood modulator.

Involvement of PI3K/Akt Signaling Pathway and Its Downstream Intracellular Targets in the Antidepressant-Like Effect of Creatine.

Creatine has been proposed to exert beneficial effects in the management of depression, but the cell signaling pathways implicated in its antidepressant effects are not well established. This study investigated the involvement of PI3K/Akt signaling pathway and its downstream intracellular targets in the antidepressant-like effect of creatine. The acute treatment of mice with creatine (1 mg/kg, po) increased the Akt and P70S6K phosphorylation, and HO-1, GPx and PSD95 immunocontents. The pretreatment of mice with LY294002 (10 nmol/mouse, icv, PI3K inhibitor), wortmannin (0.1 µg/mouse, icv, PI3K inhibitor), ZnPP (10 µg/mouse, icv, HO-1 inhibitor), or rapamycin (0.2 nmol/mouse, icv, mTOR inhibitor) prevented the antidepressant-like effect of creatine (1 mg/kg, po) in the TST. In addition, the administration of subeffective dose of either the selective GSK3 inhibitor AR-A014418 (0.01 µg/mouse, icv), the nonselective GSK3 inhibitor lithium chloride (10 mg/kg, po), or the HO-1 inductor CoPP (0.01 µg/mouse, icv), in combination with a subeffective dose of creatine (0.01 mg/kg, po) reduced the immobility time in the TST as compared with either drug alone. No treatment caused significant changes in the locomotor activity of mice. These results indicate that the antidepressant-like effect of creatine in the TST depends on the activation of Akt, Nrf2/HO-1, GPx, and mTOR, and GSK3 inhibition.

Creatine, Similar to Ketamine, Counteracts Depressive-Like Behavior Induced by Corticosterone via PI3K/Akt/mTOR Pathway.

Ketamine has emerged as a novel strategy to treat refractory depression, producing rapid remission, but elicits some side effects that limit its use. In an attempt to investigate a safer compound that may afford an antidepressant effect similar to ketamine, this study examined the effects of the ergogenic compound creatine in a model of depression, and the involvement of phosphatidylinositol-3-kinase/protein kinase B/mammalian target of rapamycin (PI3K/Akt/mTOR) pathway in its effect. In order to induce a depressive-like behavior, mice were administered with corticosterone (20 mg/kg, per os (p.o.)) for 21 days. This treatment increased immobility time in the tail suspension test (TST), an effect abolished by a single administration of creatine (10 mg/kg, p.o.) or ketamine (1 mg/kg, i.p.), but not by fluoxetine (10 mg/kg, p.o., conventional antidepressant). Treatment of mice with wortmannin (PI3K inhibitor, 0.1 µg/site, intracerebroventricular (i.c.v.)) or rapamycin (mTOR inhibitor, 0.2 nmol/site, i.c.v.) abolished the anti-immobility effect of creatine and ketamine. None of the treatments affected locomotor activity of mice. The immunocontents of p-mTOR, p-p70S6 kinase (p70S6K), and postsynaptic density-95 protein (PSD95) were increased by creatine and ketamine in corticosterone or vehicle-treated mice. Moreover, corticosterone-treated mice presented a decreased hippocampal brain-derived neurotrophic factor (BDNF) level, an effect abolished by creatine or ketamine. Altogether, the results indicate that creatine shares with ketamine the ability to acutely reverse the corticosterone-induced depressive-like behavior by a mechanism dependent on PI3K/AKT/mTOR pathway, and modulation of the synaptic protein PSD95 as well as BDNF in the hippocampus, indicating the relevance of targeting these proteins for the management of depressive disorders. Moreover, we suggest that creatine should be further investigated as a possible fast-acting antidepressant.

Creatine, similarly to ketamine, affords antidepressant-like effects in the tail suspension test via adenosine A1 and A2A receptor activation.

The benefits of creatine supplementation have been reported in a broad range of central nervous systems diseases, including depression. A previous study from our group demonstrated that creatine produces an antidepressant-like effect in the tail suspension test (TST), a predictive model of antidepressant activity. Since depression is associated with a dysfunction of the adenosinergic system, we investigated the involvement of adenosine A1 and A2A receptors in the antidepressant-like effect of creatine in the TST. The anti-immobility effect of creatine (1 mg/kg, po) or ketamine (a fast-acting antidepressant, 1 mg/kg, ip) in the TST was prevented by pretreatment of mice with caffeine (3 mg/kg, ip, nonselective adenosine receptor antagonist), 8-cyclopentyl-1,3-dipropylxanthine (DPCPX) (2 mg/kg, ip, selective adenosine A1 receptor antagonist), and 4-(2-[7-amino-2-{2-furyl}{1,2,4}triazolo-{2,3-a}{1,3,5}triazin-5-yl-amino]ethyl)-phenol (ZM241385) (1 mg/kg, ip, selective adenosine A2A receptor antagonist). In addition, the combined administration of subeffective doses of creatine and adenosine (0.1 mg/kg, ip, nonselective adenosine receptor agonist) or inosine (0.1 mg/kg, ip, nucleoside formed by the breakdown of adenosine) reduced immobility time in the TST. Moreover, the administration of subeffective doses of creatine or ketamine combined with N-6-cyclohexyladenosine (CHA) (0.05 mg/kg, ip, selective adenosine A1 receptor agonist), N-6-[2-(3,5-dimethoxyphenyl)-2-(methylphenyl)ethyl]adenosine (DPMA) (0.1 mg/kg, ip, selective adenosine A2A receptor agonist), or dipyridamole (0.1 µg/mouse, icv, adenosine transporter inhibitor) produced a synergistic antidepressant-like effect in the TST. These results indicate that creatine, similarly to ketamine, exhibits antidepressant-like effect in the TST probably mediated by the activation of both adenosine A1 and A2A receptors, further reinforcing the potential of targeting the purinergic system to the management of mood disorders.