Enriched environment causes epigenetic changes in hippocampus and improves long-term cognitive function in sepsis.

Sepsis is defined as a life-threatening organ dysfunction caused by an inappropriate host response to infection. The presence of oxidative stress and inflammatory mediators in sepsis leads to dysregulated gene expression, leading to a hyperinflammatory response. Environmental conditions play an important role in various pathologies depending on the stimulus it presents. A standard environment condition (SE) may offer reduced sensory and cognitive stimulation, but an enriched environment improves spatial learning, prevents cognitive deficits induced by disease stress, and is an important modulator of epigenetic enzymes. The study evaluated the epigenetic alterations and the effects of the environmental enrichment (EE) protocol in the brain of animals submitted to sepsis by cecal ligation and perforation (CLP). Male Wistar rats were divided into sham and CLP at 24 h, 72 h, 10 days and 30 days after sepsis. Other male Wistar rats were distributed in a SE or in EE for forty-five days. Behavioral tests, analysis of epigenetic enzymes:histone acetylase (HAT), histone deacetylase (HDAC) and DNA methyltransferase (DNMT), biochemical and synaptic plasticity analyzes were performed. An increase in HDAC and DNMT activities was observed at 72 h, 10 days and 30 days. There was a positive correlation between epigenetic enzymes DNMT and HDAC 24 h, 10 days and 30 days. After EE, HDAC and DNMT enzyme activity decreased, cognitive impairment was reversed, IL1-ß levels decreased and there was an increase in PSD-95 levels in the hippocampus. Interventions in environmental conditions can modulate the outcomes of long-term cognitive consequences associated with sepsis, supporting the idea of the potential benefits of EE.

Effects of different probiotic strains B. lactis, L. rhamnosus and L. reuteri on brain-intestinal axis immunomodulation in an endotoxin-induced inflammation.

The study evaluated the effects of supplementation with three different probiotic strains Bifidobacterium lactis (LACT GB™), Lactobacillus rhamnosus (RHAM GB™) and Lactobacillus reuteri (REUT GB™) on brain-intestinal immunomodulation in an animal model of LPS-induced inflammation. Fifty mice Balb/C were distributed into five groups: control; lipopolysaccharide (LPS); LPS + B. lactis (LACT GB™); LPS + L. rhamnosus (RHAM GB™); and LPS + L. reuteri (REUT GB™). The animals were supplemented with their respective probiotic microorganisms daily, for 30 days, at a concentration of 1 × 109 CFU/animal/day. After 30 days of supplementation, animals received the inflammatory insult by LPS (15 mg/kg). Behavioral tests, oxidative stress and inflammation were performed, as well as gut and brain histology. In the behavioral test, LPS + B. lactis group was less anxious than the other groups. Serum interleukin IL-1ß and IL-6 levels increased in all groups that received the LPS insult, and there was a reduction in inflammation in the supplemented groups when compared to the LPS group in brain and gut. There is a reduction in myeloperoxidase activity and oxidative stress in groups supplemented with probiotics. In intestine histological analysis occurs damage to the tissue integrity in the LPS group, in the other hand, occurs preservation of integrity in the probiotic supplemented animals. In the brain, infiltrates of perivascular inflammatory cells can be seen in the LPS group. The three probiotic studies showed efficient immunomodulating activity and ensured integrity of the intestinal barrier function, even after the severe insult by LPS. These results show the important role of probiotics in the gut-brain axis. Graphical abstract illustratively represents the gut-brain axis and how different probiotic strains influence the immunomodulatory response releasing different pro- and anti-inflammatory cytokines, and their role in the balance of dysbiosis.

Comparative effects of fresh and sterile fecal microbiota transplantation in an experimental animal model of necrotizing enterocolitis.

INTRODUCTION: Necrotizing Enterocolitis (NEC) is a serious intestinal disease that affects premature neonates, causing high mortality, despite the technological development in neonatal intensive care, with antibiotics, parenteral nutrition, surgery, and advanced life support. The correction of dysbiosis with fecal microbiome transplantation (FMT) has shown beneficial effects in experimental models of the disease. The different forms of administration and conservation of FMT and mixed results depending on several factors lead to questions about the mechanism of action of FMT. This study aimed to compare the effectiveness of fresh, sterile FMT and probiotic treatment under parameters of inflammation, oxidative stress, and tissue damage in a neonatal model of NEC. METHODS: One-day-old Wistar rats were used to induce NEC model. Animals were divided in five groups: Control + saline; NEC + saline; NEC + fresh FMT; NEC + sterile FMT and NEC+ probiotics. Parameters of inflammatory response and oxidative damage were measured in the gut, brain, and serum. It was also determined gut histopathological alterations. RESULTS: Proinflammatory cytokines were increased in the NEC group, and IL-10 levels decreased in the gut, brain, and serum. Fresh and sterile FMT decreased inflammation when compared to the use of probiotics. Oxidative and histological damage to the intestine was apparent in the NEC group, and both FMT treatments had a protective effect. CONCLUSION: Fresh and sterile FMT effectively reduced the inflammatory response, oxidative damage, and histological alterations in the gut and brain compared to an experimental NEC model.

Detailed Characterization of Brain Dysfunction in a Long-Term Rodent Model of Critical Illness.

Critical illness encompasses a wide spectrum of life-threatening clinical conditions requiring intensive care. Our objective was to evaluate cognitive, inflammatory and cellular metabolism alterations in the central nervous system in an animal model of critical illness induced by zymosan. For this Wistar rats that were divided into Sham and zymosan. Zymozan was administered once intraperitoneally (30 g/100 g body weight) diluted in mineral oil. The animals were submitted to behavioral tests of octagonal maze, inhibitory avoidance and elevated plus maze. Brain structures (cortex, prefrontal and hippocampus) were removed at 24 h, 4, 7 and 15 days after zymosan administration for analysis of cytokine levels (TNF-α, IL-1b, IL-6 and IL-10), oxidative damage and oxygen consumption. Zymosan-treated animals presented mild cognitive impairment both in aversive (inhibitory avoidance) and non-aversive (octagonal maze) tasks by day 15. However, they did not show increase in anxiety (elevated-plus maze). The first neurochemical alteration found was an increase in brain pro-inflammatory cytokines (IL-1ß, IL-6 and TNF-α) at day 4th in the hippocampus. In cortex, a late (7 and 15 days) increase in TNF-α was also noted, while the anti-inflammatory cytokine IL-10 decrease from 4 to 15 days. Oxygen consumption was decreased in the hippocampus and pre-frontal, but not cortex, only at 7 days. Additionally, it was observed a late (15 days) increase in oxidative damage parameters. This characterization of brain dysfunction in rodent model of critical illness reproduces some of the alterations reported in humans such neuropsychiatric disorders, especially depression, memory loss and cognitive changes and can add to the nowadays used models.

The Protective Effect of PK-11195 on Cognitive Impairment in Rats Survived of Polymicrobial Sepsis.

Sepsis is an organ dysfunction caused by a host's unregulated response to infection, causing long-term brain dysfunction with microglial activation, the release of inflammatory components, and mitochondrial changes. Neuroinflammation can increase the expression of the 18-kD translocator protein (TSPO) in the mitochondria, leading to the activation of the microglia and the release of inflammatory components. The antagonist PK-11195 can modulate TSPO and reduce microglial activation and cognitive damage presented in an animal model of sepsis. The aim of this was to evaluate the effects of PK-11195 on long-term brain inflammation and cognitive impairment in an animal model of sepsis. Wistar rats, 60 days old, were submitted to cecal ligation and puncture (CLP) surgery, divided into groups control/saline, control/PK-11195, sepsis/saline, and sepsis/PK-11195. Immediately after surgery, the antagonist PK-11195 was administered at a dose of 3 mg/kg. Ten days after CLP surgery, the animals were submitted to behavioral tests and determination of brain inflammatory parameters. The sepsis/saline group presented cognitive damage. However, there was damage prevention in animals that received PK-11195. Besides, the sepsis increased the levels of cytokines and M1 microglia markers and caused oxidative damage. However, PK-11195 had the potential to decrease inflammation. These events show that the modulation of neuroinflammation during sepsis by PK-11195, possibly related to changes in TSPO, improves mitochondrial function in the animals' brains. In conclusion, the antagonist PK-11195 attenuated brain inflammation and prevented cognitive impairment in animals subjected to sepsis.

Effects of microbiota transplantation and the role of the vagus nerve in gut-brain axis in animals subjected to chronic mild stress.

INTRODUCTION: Currently, there is a growing emphasis on the study of intestinal signaling as an influencer in the pathophysiology of neuropsychiatric diseases, and the gut-brain axis is recognized as a communication route through endocrine, immune, and neural pathways (vagus nerve). Studies have shown that diets that modify the microbiota can reduce stress-related behavior and hypothalamic-pituitary-adrenal axis activation. Investigators have used fecal microbiota transplantation (FMT) approaches to demonstrate that stress-related microbiota composition plays a causal role in behavioral changes. AIM: We hypothesized that FMT may present immunomodulatory, biochemical, endocrine, cognitive, and behavioral benefits in stress situations and that these changes can be mediated via the vagus nerve. METHODS: Animals were subjected to a chronic mild stress (CMS) protocol. In one experiment, animals were divided into five groups: control, control + FMT, control + FMT + CMS, CMS + saline, and CMS + FMT. The animals received FMT, and behavioral tests were performed; cytokine and carbonyl levels were measured. In a second experiment, animals were submitted to vagotomy and divided into two groups: CMS + FMT and CMS + vagotomy + FMT. RESULTS: Animals submitted to the CMS protocol or that received FMT from stressed animals showed behavioral changes and changes in neuroactive substances (increased IL-6 and TNF-α levels and carbonyl proteins). The FMT of healthy donors improved the analyzed parameters. In addition, vagotomy influenced beneficial FMT results, confirmed by behavioral testing and protein carbonyl in the hippocampus. CONCLUSION: Manipulation of the microbiota reversed the behavioral and biochemical changes induced by the CMS protocol, and the vagus nerve influenced the gut-brain axis response.

Modulation of microglial phenotypes improves sepsis-induced hippocampus-dependent cognitive impairments and decreases brain inflammation in an animal model of sepsis.

BACKGROUND: In order to modulate microglial phenotypes in vivo, M1 microglia were depleted by administration of gadolinium chloride and the expression of M2 microglia was induced by IL-4 administration in an animal model of sepsis to better characterize the role of microglial phenotypes in sepsis-induced brain dysfunction. METHODS: Wistar rats were submitted to sham or cecal ligation and perforation (CLP) and treated with IL-4 or GdCl3. Animals were submitted to behavioral tests 10 days after surgery. In a separated cohort of animals at 24 h, 3 and 10 days after surgery, hippocampus was removed and cytokine levels, M1/M2 markers and CKIP-1 levels were determined. RESULTS: Modulation of microglia by IL-4 and GdCl3 was associated with an improvement in long-term cognitive impairment. When treated with IL-4 and GdCl3, the reduction of pro-inflammatory cytokines was apparent in almost all analyzed time points. Additionally, CD11b and iNOS were increased after CLP at all time points, and both IL-4 and GdCl3 treatments were able to reverse this. There was a significant decrease in CD11b gene expression in the CLP+GdCl3 group. IL-4 treatment was able to decrease iNOS expression after sepsis. Furthermore, there was an increase of CKIP-1 in the hippocampus of GdCl3 and IL-4 treated animals 10 days after CLP induction. CONCLUSIONS: GdCl3 and IL-4 are able to manipulate microglial phenotype in an animal models of sepsis, by increasing the polarization toward an M2 phenotype IL-4 and GdCl3 treatment was associated with decreased brain inflammation and functional recovery.

Protective effects of fecal microbiota transplantation in sepsis are independent of the modulation of the intestinal flora.

OBJECTIVE: The aim of this study was to investigate the protective effects of probiotics and fecal transplantation on inflammatory and oxidative parameters in the intestines of two rat models of sepsis. METHODS: Rats were treated with prebiotics, probiotics, or symbiotics and exposed to lipopolysaccharide (LPS) or zymosan after 15 d to induce endotoxemia. Oxidative damage and inflammation were analyzed, and histologic examination of the intestinal tissue was performed. Fecal microbiota transplantation (FMT) was carried out in LPS- and zymosan-induced rat models of sepsis. RESULTS: Supplementation with symbiotics for 15 d effectively reduced the inflammatory parameters compared with supplementation for 7 d. Probiotics, prebiotics, and symbiotics exerted different effects on the evaluated parameters. In general, Lactobacillus rhamnosus and L. casei exerted better local protective effects. Evaluation of the role of the intestinal microbiota through FMT revealed its protective effects irrespective of the previous treatment with probiotics. CONCLUSION: Probiotic strains significantly differ among themselves and exert different effects on the host's health. Symbiotics and FMT could offer additional immunomodulatory benefits to drug therapy, thus serving as a new therapeutic alternative in pediatric patients with sepsis.

Characterization and modulation of microglial phenotypes in an animal model of severe sepsis.

We aim to characterize the kinetics of early and late microglial phenotypes after systemic inflammation in an animal model of severe sepsis and the effects of minocycline on these phenotypes. Rats were subjected to CLP, and some animals were treated with minocycline (10 ug/kg) by i.c.v. administration. Animals were killed 24 hours, 5, 10 and 30 days after sepsis induction, and serum and hippocampus were collected for subsequent analyses. Real-time PCR was performed for M1 and M2 markers. TNF-α, IL-1ß, IL-6, IL-10, CCL-22 and nitrite/nitrate levels were measured. Immunofluorescence for IBA-1, CD11b and arginase was also performed. We demonstrated that early after sepsis, there was a preponderant up-regulation of M1 markers, and this was not switched to M2 phenotype markers later on. We found that up-regulation of both M1 and M2 markers co-existed up to 30 days after sepsis induction. In addition, minocycline induced a down-regulation, predominantly, of M1 markers. Our results suggest early activation of M1 microglia that is followed by an overlap of both M1 and M2 phenotypes and that the beneficial effects of minocycline on sepsis-associated brain dysfunction may be related to its effects predominantly on the M1 phenotype.

The Role of Secretase Pathway in Long-term Brain Inflammation and Cognitive Impairment in an Animal Model of Severe Sepsis.

Inflammatory cytokines are related to impaired learning and memory processes in the central nervous system, contributing to the cognitive dysfunction present in sepsis survivors. In sepsis, brain of survivors presented increased deposition of amyloid-beta (Aß) peptide and this was associated with cognitive impairment. However, it is not known if the upregulation of secretase pathway is involved the deposition of Aß peptide and consequent development of cognitive impairment in survivors. The aim of the study is to evaluate the effects of secretase inhibitors on behavioral, Aß accumulation, and neuroinflammatory parameters in rats submitted to sepsis. Sepsis was induced by cecal ligation and perforation in Wistar rats, and the activity of alpha-, beta-, and gamma-secretases was determined in the hippocampus and prefrontal at different times. Additionally, in a different cohort of animal's epigallocatechin gallate, a beta-secretase inhibitor or a gamma-secretase inhibitor was administrated once a day for three consecutive days. Fifteen or 30 days after sepsis induction, Aß content, TNF-α, IL-1ß, and IL-6 and cognitive performance were determined. There was no increase in alpha-secretase activity. Both beta- and gamma-secretase activities increased, mainly late after sepsis. The inhibition of beta- or gamma-secretases improved cognitive performance 10 days after sepsis induction, and beta-secretase inhibition improved cognitive performance up to 30 days after sepsis induction. Furthermore, beta-secretase inhibition decreased IL-1ß and Aß brain levels. It was demonstrated that during sepsis development there was an increase in the amyloidogenic route, and the inhibition of this pathway promoted attenuation of neuroinflammation, Aß peptide content, and improvement of cognitive impairment.

The impact of age on long-term behavioral and neurochemical parameters in an animal model of severe sepsis.

This study aimed to evaluate behavioral and neurochemical parameters in adult (180-day-old) and young (60-day-old) rats subjected to sepsis. Sepsis was induced by cecal ligation and perforation (CLP). Thirty days after surgery, behavioral tests were performed, and the ß-amyloid content, oxidative damage, and cytokine levels were measured in the hippocampus and prefrontal cortex. In both adult and young rats, sepsis impaired the inhibitory avoidance task performance and increased immobility time in the forced swimming test. However, the adult septic rats had a higher immobility time compared to the young rats. Both sepsis and aging induced brain inflammation and oxidative damage and increased Aß content. Sepsis along with aging had additive effects on hippocampal interleukin-1 levels and prefrontal carbonyl levels. Taken together, our results suggest that age has a minor influence on brain inflammation and behavioral alterations observed in septic rats.

Microglial Cells Depletion Increases Inflammation and Modifies Microglial Phenotypes in an Animal Model of Severe Sepsis.

Sepsis-associated encephalopathy is highly prevalent and has impact both in early and late morbidity and mortality. The mechanisms by which sepsis induces brain dysfunction include neuroinflammation, disrupted blood-brain barrier, oxidative stress, and microglial activation, but the cellular and molecular mechanisms involved in these events are not completely understood. Our objective was to determine the effects of microglial depletion in the early systemic and brain inflammatory response and its impact in phenotypes expression in an animal model of sepsis. Animals were subjected to CLP, and depletion of microglial cells was accomplished by administration of (Lipo)-encapsulated clodronate and microglial repopulation by doxycycline. Clod-lip treatment was effective in decreasing microglia density in the hippocampus of animals. Pro-inflammatory cytokines were increased in the CLP+PBS, and liposomes administration increased even further these cytokines mainly 7 days, suggesting that microglial depletion exacerbates both local and systemic inflammation. In contrast, repopulation with doxycycline was able to revert the cytokine levels in both serum and cerebral structures on day 7 and 14 after repopulation. There were no differences in the correlation between M1 and M2 markers by real-time PCR, but immunohistochemistry showed significant increase in CD11b expression in CLP+PBS with greater expression in CLP + liposomes in the hippocampus. These results suggest that the depletion of microglia during severe sepsis development could be associated with early exacerbation of brain and systemic inflammation and repopulation is able to revert this condition, once a rapid neurological recovery is noticed until 7 days after sepsis.

Early Maternal Deprivation Induces Microglial Activation, Alters Glial Fibrillary Acidic Protein Immunoreactivity and Indoleamine 2,3-Dioxygenase during the Development of Offspring Rats.

Maternal deprivation (MD) induces behavioral changes and impacts brain circuits that could be associated with the pathophysiology of depression. This study investigated the markers of microglia and astrocyte activation as well as indoleamine 2,3-dioxygenase (IDO) expression in developmental programming after early life MD (on postnatal days (PNDs) 20, 30, 40, and 60). On PND 60, the rats that were subjected to MD displayed depressive-like behavior. On PND 10, it was found that there was a decrease in the level of glial fibrillary acidic protein (GFAP) immunopositive cells, a decrease in the level of IDO expression, and an increase in the level of Iba-1 (microglial marker) in the hippocampus of rats that were subjected to MD. On PND 20, levels of GFAP were also found to have decreased in the hippocampus, and there was an increase in the level of Iba-1 in the hippocampus. AIF-1 (microglial marker) expression was observed in the PFC following MD. On PND 30, the levels of Iba-1 remained elevated. On PND 40, the levels of GFAP were found to have increased in the hippocampus of rats that were subjected to MD. On PND 60, the levels of GFAP and AIF-1 remained elevated following MD. These results suggest that early life stress induces negative developmental programming in rats, as demonstrated by depressive-like behavior in adult life. Moreover, MD increases microglial activation in both early and late developmental phases. The levels of GFAP and IDO decreased in the early stages but were found to be higher in later developmental periods. These findings suggest that MD could differentially affect the expression of the IDO enzyme, astrocytes, and microglial activation depending on the neurodevelopmental period. The onset of an inflammatory state from resident brain cells could be associated with the activation of the kynurenine pathway and the development of depressive behavior in adulthood.

Anxious phenotype potentiates damage in peripheral organs of animals submitted to sepsis / Fenótipo ansioso potencializa danos em órgãos periféricos de animais submetidos à sepse

Introduction: Anxiety and sepsis are important public health problems that present high morbidity, mortality and significant economic repercussions. The present study investigated the presence of oxidative damage in peripheral organs in two lines of animals that are bred for high and low freezing responses to contextual cues that are previously associated with foot shock (Carioca High-conditioned Freezing [CHF] and Carioca Low-conditioned Freezing [CLF]) associated to sepsis. Methods: Animals were subject to sepsis by the cecal ligation and perforation (CLP) or sham operated. 24 hours and 10 days after sepsis animals were euthanized and removed adrenal, kidney, lung, serum, heart for the determination of carbonyl protein levels and adrenal for check weight this structure. Results: Sepsis increased oxidative damage in different systemic organs, included serum. There wasn't a significant increase in protein carbonyls in heart and kidney. Anxious phenotype potentiates this damage. Conclusion: These findings suggest that an anxious phenotype plus sepsis may induce more pronounced organs damage, and promote more alterations in the HPA axis. These findings may help to explain, at least in part, the common point of the mechanisms involved with the pathophysiology of sepsis and anxiety.

Introdução: Ansiedade e sepse são importantes problemas de saúde pública que apresentam alta morbidade, mortalidade e repercussões econômicas significativas. O presente estudo investigou a presença de dano oxidativo em órgãos periféricos em duas linhagens de animais criados para respostas de alta (CHF) e baixa (CLF) ansiedade associado a sepse. Métodos: Os animais foram submetidos a sham (controle) ou sepse por ligação e perfuração cecal (CLP). 24 horas e 10 dias após a sepse os animais foram eutanasiados e estruturas foram removidas: adrenal, rim, pulmão, soro e coração para a determinação dos níveis de proteínas carboniladas e adrenal para verificação do peso dessa estrutura. Resultados: A sepse aumentou o dano oxidativo em diferentes órgãos sistêmicos, incluindo o soro. Não houve um aumento significativo de proteínas carbonilas no coração e nos rins. Fenótipo ansioso potencializa esse dano. Conclusão: Esses achados sugerem que um fenótipo ansioso associado a sepse pode induzir dano mais pronunciado aos órgãos e promover mais alterações no eixo HPA. Esses achados podem ajudar a explicar, pelo menos em parte, o ponto comum dos mecanismos envolvidos na fisiopatologia da sepse e da ansiedade.

ω-3 and folic acid act against depressive-like behavior and oxidative damage in the brain of rats subjected to early- or late-life stress.

OBJECTIVES: To investigate the antidepressant and antioxidant effects of omega-3, folic acid and n-acetylcysteine (NAC) in rats which were subjected to early or late life stress. METHODS: Early stress was induced through maternal deprivation (MD), while late life stress was induced using the chronic mild stress (CMS) protocol. Young rats which were subjected to MD and the adult rats which were subjected to CMS were treated with omega-3 fatty acids (0.72 g/kg), NAC (20 mg/kg) or folic acid (50 mg/kg) once/day, for a period of 20 days. Then, the animals' immobility times were evaluated using the forced swimming test. Oxidative stress parameters were evaluated in the brain. RESULTS: Depressive-like behavior induced by CMS was prevented by NAC and folic acid, and depressive-like behavior induced by MD was prevented by NAC, folic acid and omega-3. NAC, folic acid and omega-3 were able to exert antioxidant effects in the brain of rats subjected to CMS or MD. These preventive treatments decreased the levels of protein carbonylation and lipid peroxidation, and also decreased the concentrations of nitrite/nitrate and reduced the activity of myeloperoxidase activity in the rat brain which was induced by CMS or MD. NAC, folic acid and omega-3 increased superoxide dismutase and catalase activities in the rat brain subjected to early or late life stress. CONCLUSIONS: NAC, omega-3 and folic acid may present interesting lines of treatment based on their antioxidant properties, which cause an inhibition of behavioral and brain changes that occur from stressful life events.

The additive effect of aging on sepsis-induced cognitive impairment and neuroinflammation.

Systemic inflammation is emerging as a significant driver of cognitive decline in the aged and vulnerable brain. In sepsis survivors animals low-grade brain inflammation occurs, suggesting that sepsis is able to induce in microglia a primed-like state. The purpose of this study is to analyze the role of sepsis-induced brain inflammation in the progression of the physiological process of brain aging. Wistar rats 2month-old were subjected to sepsis and 60 and 90days after were submitted to the new object recognition test and brain was removed to the determination of cytokines, myeloperoxidase (MPO) activity, amyloid-beta peptide (Aß) and immunohistochemistry markers of microglial activation. In the hippocampus, from 60 to 90days there was an increase in TNF-α and IL-1ß levels in septic animals. This also occurred to the levels of IL-1ß and IL-6 in the prefrontal cortex. This was associated with persistent increased in microglial activation and Aß levels. In conclusion, neuroinflammation is persistent after sepsis and this could burst the usual inflammation that occurs during brain aging.

Effects of ketamine administration on mTOR and reticulum stress signaling pathways in the brain after the infusion of rapamycin into prefrontal cortex.

Recent studies show that activation of the mTOR signaling pathway is required for the rapid antidepressant actions of glutamate N-methyl-D-aspartate (NMDA) receptor antagonists. A relationship between mTOR kinase and the endoplasmic reticulum (ER) stress pathway, also known as the unfolded protein response (UPR) has been shown. We evaluate the effects of ketamine administration on the mTOR signaling pathway and proteins of UPR in the prefrontal cortex (PFC), hippocampus, amygdala and nucleus accumbens, after the inhibiton of mTOR signaling in the PFC. Male adult Wistar rats received pharmacological mTOR inhibitor, rapamycin (0.2 nmol), or vehicle into the PFC and then a single dose of ketamine (15 mg/kg, i.p.). The immunocontent of mTOR, eukaryotic initiation factor 4E-binding protein 1 (4E-BP1), eukaryotic elongation factor 2 kinase (eEF2K) homologous protein (CHOP), PKR-like ER kinase (PERK) and inositol-requiring enzyme 1 (IRE1) - alpha were determined in the brain. The mTOR levels were reduced in the rapamycin group treated with saline and ketamine in the PFC; p4EBP1 levels were reduced in the rapamycin group treated with ketamine in the PFC and nucleus accumbens; the levels of peEF2K were increased in the PFC in the vehicle group treated with ketamine and reduced in the rapamycin group treated with ketamine. The PERK and IRE1-alpha levels were decreased in the PFC in the rapamycin group treated with ketamine. Our results suggest that mTOR signaling inhibition by rapamycin could be involved, at least in part, with the mechanism of action of ketamine; and the ketamine antidepressant on ER stress pathway could be also mediated by mTOR signaling pathway in certain brain structures.