Nandrolone-induced aggressive behavior is associated with alterations in extracellular glutamate homeostasis in mice.

Nandrolone decanoate (ND), an anabolic androgenic steroid (AAS), induces an aggressive phenotype by mechanisms involving glutamate-induced N-methyl-d-aspartate receptor (NMDAr) hyperexcitability. The astrocytic glutamate transporters remove excessive glutamate surrounding the synapse. However, the impact of supraphysiological doses of ND on glutamate transporters activity remains elusive. We investigated whether ND-induced aggressive behavior is interconnected with GLT-1 activity, glutamate levels and abnormal NMDAr responses. Two-month-old untreated male mice (CF1, n=20) were tested for baseline aggressive behavior in the resident-intruder test. Another group of mice (n=188) was injected with ND (15mg/kg) or vehicle for 4, 11 and 19days (short-, mid- and long-term endpoints, respectively) and was evaluated in the resident-intruder test. Each endpoint was assessed for GLT-1 expression and glutamate uptake activity in the frontoparietal cortex and hippocampal tissues. Only the long-term ND endpoint significantly decreased the latency to first attack and increased the number of attacks, which was associated with decreased GLT-1 expression and glutamate uptake activity in both brain areas. These alterations may affect extracellular glutamate levels and receptor excitability. Resident males were assessed for hippocampal glutamate levels via microdialysis both prior to, and following, the introduction of intruders. Long-term ND mice displayed significant increases in the microdialysate glutamate levels only after exposure to intruders. A single intraperitoneal dose of the NMDAr antagonists, memantine or MK-801, shortly before the intruder test decreased aggressive behavior. In summary, long-term ND-induced aggressive behavior is associated with decreased extracellular glutamate clearance and NMDAr hyperexcitability, emphasizing the role of this receptor in mediating aggression mechanisms.

Long-Term Oral Administration of Capsicum baccatum Extracts Does Not Alter Behavioral, Hematological, and Metabolic Parameters in CF1 Mice.

Our group showed that crude ethanol (CE) and butanol (BUT) extracts of Capsicum baccatum presented anti-inflammatory and antioxidant properties. Furthermore, the flavonoid and total phenolic contents were positively correlated with both of these properties observed for C. baccatum extracts. The present study demonstrated that 60 days of oral administration of CE and BUT (200 mg/kg) in mice did not cause significant differences in the following parameters evaluated: hematological profile, body weight and relative weight of visceral organs, systemic lipid profile, glucose homeostasis (GTT), kidney and hepatic biochemical markers, and spontaneous locomotion and anxiety-like behavior. Altogether, these results indicate for the first time that the long-term oral administration of C. baccatum extracts does not affect specific aspects of CF1 mice physiology, suggesting their safety, building up the venue to test their efficacy in animal models underlying persistent activation of oxidative and inflammatory pathways.

Coriandrum sativum Extract Prevents Alarm Substance-Induced Fear- and Anxiety-Like Responses in Adult Zebrafish.

Anxiety disorders appear to involve distinct neurobiological mechanisms and several medications are available against this mental health problem. However, pharmacological therapeutic approaches display undesirable side effects for patients, particularly when long-term therapy is required. Some evidences have suggested that Coriandrum sativum extract (CSE) provide sedative and anxiolytic effects. We investigate if CSE could attenuate anxiety-like behaviors induced by novelty and alarm substance exposures in zebrafish. Adult zebrafish were injected with vehicle, clonazepam, or CSE (25, 50 or 100 mg/kg) and submitted to novel tank test. At the end, saline or alarm substance was added and anxiety-like responses were recorded. Twenty-four hours after, fish were submitted to the light/dark test. Novelty associated with alarm substance exposure decreased distance traveled and total time mobile in novel tank, and CSE (at 50 and 100 mg/kg) prevented these alterations similarly to clonazepam. Alarm substance reduced the time spent in white compartment (p = 0.0193 as compared with vehicle group). Clonazepam and CSE prevented this anxiogenic effect of alarm substance. CSE presents anxiolytic effects against alarm substance-induced locomotor and anxiogenic responses similarly to clonazepam. These data corroborate with the use of this plant in traditional medicine and provides a putative new pharmacological intervention for anxiety disorders.

Memantine mediates astrocytic activity in response to excitotoxicity induced by PP2A inhibition.

Reduced activity of protein phosphatase 2 A (PP2A) is a common feature in Alzheimer's disease (AD) and non-AD tauopathies. The administration of okadaic acid (OKA), a potent PP2A and PP1 inhibitor, is a common research tool for inducing AD-like alterations such as tau hyperphosphorylation and cognitive decline. Recently, we showed that OKA increases cerebrospinal fluid (CSF) glutamate levels, which was strongly correlated with cognitive decline. Also, we demonstrated that memantine (MN), a glutamatergic NMDAR channel blocker, was capable of preventing the increase in CSF glutamate levels and cognitive decline. Here, we aimed to analyze whether the protective effects of MN involve intrinsic astrocytic properties, particularly related to glutamate uptake and astrocytic reactivity - indexed by the expression of S100B and glial fibrillary acidic protein (GFAP). Rats received intraperitoneal injections of MN or saline over 3 consecutive days before receiving intrahippocampal infusion of OKA or saline. Afterward, they were submitted to behavioral tasks and then, euthanatized for neurochemical analysis. Here, we showed that the neuroprotective effects of MN in response to OKA neurotoxicity involve astrocytic activation. MN decreased glutamate uptake in the hippocampus and increased the release of S100B protein in the CSF in response to OKA neurotoxicity, which indicates a possible neurons-astrocyte coupling protective mechanism. These findings shed light on astrocytes as potential targets for treating neurological disorders associated with decreased PP2A activity.

Memantine decreases neuronal degeneration in young rats submitted to LiCl-pilocarpine-induced status epilepticus.

Several works have demonstrated that status epilepticus (SE) induced-neurodegeneration appears to involve an overactivation of N-methyl-d-aspartate receptors and treatment with high-affinity NMDAR antagonists is neuroprotective against this brain damage. However, these compounds display undesirable side effects for patients since they block physiological NMDA receptor dependent-activity. In this context, memantine (MN), a well tolerable low-affinity NMDAR channel blocker, will be a promising alternative, since it does not compromise the physiological role of NMDA receptors on synaptic transmission. The aim of the present study was to investigate if MN could attenuate seizure severity and neuronal cell death caused by SE induced early in life. Wistar rats (15 days old; n = 6-8 per group) received memantine (20 mg/kg i.p.) in six different treatments: 6 and 3 h before SE onset; concomitant with pilocarpine; 15min and 1h after SE onset; and four consecutive administrations (15 min, 6 h, 12 h, and 18 h) after pilocarpine injection. Neurodegeneration was quantified by fluoro-jade C staining. Treatment with memantine increase latency to SE onset only in groups treated 3 h before or concomitant with pilocarpine. In CA1 hippocampal subfield, memantine significantly reduced neurodegeneration at the following times: 3 h prior SE-onset, concomitant with pilocarpine, and 15 min after pilocarpine injection. For amygdala and thalamus, all post-SE onset treatments were able to decrease neurodegeneration. In conclusion, the present study showed that MN was neuroprotective against SE-induced neuronal death and this neuroprotection appears to be time- and region-dependent.

Changes in body composition of Wistar rats: effects of high-intensity interval training

The present study aimed to investigate the effectiveness of high-intensity interval training (HIIT) in the body composition of Wistar rats. The HIIT protocol consisted of high-intensity swimming three times a week for four weeks. There were no differences between groups as to the Lee index. However, the weights of the perigonadal (p=0.001) and retroperitoneal (p=0.026) fats were significantly different between the Control Group (CG, n=10) vs. Trained Group (TG, n=10), respectively. There was also a significant increase in the body weight of the animals in TG (16.43%) and CG (7.19%) at the end of the experiment. These findings suggested that HIIT was not sufficient to improve significantly the body composition of rats.

Hyperpalatable Diet and Physical Exercise Modulate the Expression of the Glial Monocarboxylate Transporters MCT1 and 4.

Hyperpalatable diets (HP) impair brain metabolism, and regular physical exercise has an apparent opposite effect. Here, we combined a prior long-term exposure to HP diet followed by physical exercise and evaluated the impact on some neuroenergetic components and on cognitive performance. We assessed the extracellular lactate concentration, expression of monocarboxylate transporters (MCTs), pyruvate dehydrogenase (PDH), and mitochondrial function in the hippocampus. Male C57BL/6J mice were fed 4 months with HP or a control diet. Subsequently, they were divided in the following groups: control diet sedentary (CDS), control diet exercise (CDE), HP diet sedentary (HPS), and HP diet exercise (HPE) (n = 15 per group) and were engaged for an additional 30-day period of voluntary exercise and HP diet. Relative to the control situation, exercise increased MCT1, MCT4, and PDH protein levels, while the HP diet increased MCT1 and MCT4 protein levels. The production of hydrogen peroxide (H2O2) and the mitochondrial membrane potential (∆Ñ°m) stimulated by succinate in hippocampal homogenates were not significantly different between groups. ADP phosphorylation and the maximal respiratory rate induced by FCCP showed similar responses between groups, implying a normal mitochondrial function. Also, extracellular brain lactate levels were increased in the HPE group compared to other groups soon after performing the Y-maze task. However, such enhanced lactate levels were not associated with improved memory performance. In summary, hippocampal protein expression levels of MCT1 and 4 were increased by physical exercise and HP diet, whereas PDH was only increased by exercise. These observations indicate that a hippocampal metabolic reprogramming takes place in response to these environmental factors.

Brain Insulin Administration Triggers Distinct Cognitive and Neurotrophic Responses in Young and Aged Rats.

Aging is a major risk factor for cognitive deficits and neurodegenerative disorders, and impaired brain insulin receptor (IR) signaling is mechanistically linked to these abnormalities. The main goal of this study was to investigate whether brain insulin infusions improve spatial memory in aged and young rats. Aged (24 months) and young (4 months) male Wistar rats were intracerebroventricularly injected with insulin (20 mU) or vehicle for five consecutive days. The animals were then assessed for spatial memory using a Morris water maze. Insulin increased memory performance in young rats, but not in aged rats. Thus, we searched for cellular and molecular mechanisms that might account for this distinct memory response. In contrast with our expectation, insulin treatment increased the proliferative activity in aged rats, but not in young rats, implying that neurogenesis-related effects do not explain the lack of insulin effects on memory in aged rats. Furthermore, the expression levels of the IR and downstream signaling proteins such as GSK3-ß, mTOR, and presynaptic protein synaptophysin were increased in aged rats in response to insulin. Interestingly, insulin treatment increased the expression of the brain-derived neurotrophic factor (BDNF) and tropomyosin receptor kinase B (TrkB) receptors in the hippocampus of young rats, but not of aged rats. Our data therefore indicate that aged rats can have normal IR downstream protein expression but failed to mount a BDNF response after challenge in a spatial memory test. In contrast, young rats showed insulin-mediated TrkB/BDNF response, which paralleled with improved memory performance.

Corrigendum: Long-term NMDAR antagonism correlates reduced astrocytic glutamate uptake with anxiety-like phenotype.

[This corrects the article on p. 219 in vol. 9, PMID: 26089779.].

A new device for step-down inhibitory avoidance task--effects of low and high frequency in a novel device for passive inhibitory avoidance task that avoids bioimpedance variations.

BACKGROUND: Step-down inhibitory avoidance task has been widely used to evaluate aversive memory, but crucial parameters inherent to traditional devices that may influence the behavior analysis (as stimulus frequency, animal's bioimpedance) are frequently neglected. NEW METHOD: We developed a new device for step-down inhibitory avoidance task by modifying the shape and distribution of the stainless steel bars in the box floor where the stimuli are applied. The bars are 2 mm wide, with rectangular shape, arranged in pairs at intervals of 1cm from the next pairs. Each pair makes an electrical dipole where the polarity inverts after each pulse. This device also presents a component that acquires and records the exact current received by the animal foot and precisely controls the frequency of stimulus applied during the entire experiment. RESULT: Different from conventional devices, this new apparatus increases the contact surface with bars and animal's paws, allowing the electric current pass through the animal's paws only, drastically reducing the influence of animal's bioimpedance. The analysis of recorded data showed that the current received by the animal was practically the same as applied, independent of the animal's body composition. Importantly, the aversive memory was observed at specific stimuli intensity and frequency (0.35 or 0.5 mA at 62 and 125 Hz but not at 0.20 mA or 20 Hz). Moreover, with this device it was possible to observe the well-known step-down inhibitory avoidance task memory impairment induced by guanosine. CONCLUSION: This new device offers a substantial improvement for behavioral analysis in step-down inhibitory avoidance task and allows us to precisely compare data from different animals with distinct body composition.

Long-term NMDAR antagonism correlates reduced astrocytic glutamate uptake with anxiety-like phenotype.

The role of glutamate N-methyl-D-aspartate receptor (NMDAR) hypofunction has been extensively studied in schizophrenia; however, less is known about its role in anxiety disorders. Recently, it was demonstrated that astrocytic GLT-1 blockade leads to an anxiety-like phenotype. Although astrocytes are capable of modulating NMDAR activity through glutamate uptake transporters, the relationship between astrocytic glutamate uptake and the development of an anxiety phenotype remains poorly explored. Here, we aimed to investigative whether long-term antagonism of NMDAR impacts anxiety-related behaviors and astrocytic glutamate uptake. Memantine, an NMDAR antagonist, was administered daily for 24 days to healthy adult CF-1 mice by oral gavage at doses of 5, 10, or 20 mg/kg. The mice were submitted to a sequential battery of behavioral tests (open field, light-dark box and elevated plus-maze tests). We then evaluated glutamate uptake activity and the immunocontents of glutamate transporters in the frontoparietal cortex and hippocampus. Our results demonstrated that long-term administration of memantine induces anxiety-like behavior in mice in the light-dark box and elevated plus-maze paradigms. Additionally, the administration of memantine decreased glutamate uptake activity in both the frontoparietal cortex and hippocampus without altering the immunocontent of either GLT-1 or GLAST. Remarkably, the memantine-induced reduction in glutamate uptake was correlated with enhancement of an anxiety-like phenotype. In conclusion, long-term NMDAR antagonism with memantine induces anxiety-like behavior that is associated with reduced glutamate uptake activity but that is not dependent on GLT-1 or GLAST protein expression. Our study suggests that NMDAR and glutamate uptake hypofunction may contribute to the development of conditions that fall within the category of anxiety disorders.

Caffeine consumption prevents memory impairment, neuronal damage, and adenosine A2A receptors upregulation in the hippocampus of a rat model of sporadic dementia.

Intracerebroventricular (icv) streptozotocin (STZ) administration induces pathological and behavioral alterations similar to those observed in Alzheimer's disease (AD) and is thus considered an experimental model of sporadic AD. Since caffeine (an adenosine receptor antagonist) and selective antagonists of adenosine A2A receptors modify the course of memory impairment in different amyloid-ß-based experimental models of AD, we now tested the impact of caffeine on STZ-induced dementia and associated neurodegeneration in the hippocampus as well as on the expression and density of adenosine receptors. Adult male rats received a bilateral infusion of saline or STZ (3 mg/kg, icv), which triggered memory deficits after four weeks, as gauged by impaired object recognition memory. This was accompanied by a reduced NeuN immunoreactivity in the hippocampal CA1 region and an increased expression and density of adenosine A2A receptors (A2AR), but not A1R, in the hippocampus. Caffeine consumption (1 g/L in the drinking water starting 2 weeks before the STZ challenge) prevented the STZ-induced memory impairment and neurodegeneration as well as the upregulation of A2AR. These findings provide the first demonstration that caffeine prevents sporadic dementia and implicate the control of central A2AR as its likely mechanism of action.

Pretreatment with memantine prevents Alzheimer-like alterations induced by intrahippocampal okadaic acid administration in rats.

Cerebral okadaic acid (OA) administration induces Alzheimer's disease (AD)-like phenotype in rats. Alterations in glutamate levels associated with hyperactivation of cyclin dependent kinase 5 (Cdk5) signaling pathway downstream Tau phosphorylation may participate in the genesis of this pathological phenotype. Here, we examined the efficacy of memantine (MN) pretreatment on reducing OA-induced AD-like phenotypes in rats. Wistar rats were given daily intraperitoneal injections of MN for 3 days and then given an intrahippocampal infusion of OA. Animals were divided into four groups: control (CO), MN, OA and MN/OA. Spontaneous locomotion and spatial memory performance were assessed by open field and Morris water maze respectively. Additionally, we measured glutamate levels in the cerebrospinal fluid (CSF) and the immunocontent of Cdk5, p35, p25 and phosphorylated Tau (pTauSer199/202) in the hippocampus. Spontaneous locomotion did not differ between groups. The OA group showed a significant decrease in spatial memory performance compared to all groups. The OA infusion also increased CSF glutamate levels and the immunocontents of Cdk5, p25 and pTauSer199/202 in the hippocampus. Conversely, pretreatment with MN prevented OA-induced spatial memory deficits and the increment of CSF glutamate level; which paralleled with normal immunocontents of Cdk5, p25 and pTau- Ser199/202 proteins. There were positive correlations between spatial memory performance and the neurochemical parameters. In summary, pretreatment with MN prevents spatial memory deficits induced by intrahippocampal OA administration in rats. The prevention of increase CSF glutamate levels, along with the reduced hippocampal phosphorylation of TauSer199/202 by Cdk5/p25 signaling pathway, are the mechanisms proposed to participate in the prophylactic effects of MN in this AD-like model.

Physical exercise exacerbates memory deficits induced by intracerebroventricular STZ but improves insulin regulation of H2O2 production in mice synaptosomes.

Insulin brain resistant state is associated with cognitive deficits and Alzheimer's disease by mechanisms that may involve mitochondrial damage and oxidative stress. Conversely, physical exercise improves cognitive function and brain insulin signaling. The intracerebroventricular (i.c.v.) administration of streptozotocin (STZ) in rodents is an established model of insulin-resistant brain state. This study evaluates the effects of physical exercise on memory performance of i.c.v., STZ-treated mice(1 and 3 mg/kg) and whether insulin (50 and 100 ng/ml) modulates mitochondrial H2O2 generation in synaptosomes. S100B levels and SOD and CAT activities were assessed as markers of brain damage caused by STZ. Sedentary and exercise vehicle-treated mice demonstrated similar performance in object recognition memory task. In the water maze test, exercise vehicle-treated mice showed improvement performance in the acquisition and retrieval phases. The administration of STZ (1 mg/kg) before thirty days of voluntary physical exercise protocol impaired recognition and spatial memory only in exercised mice, whereas STZ (3 mg/kg) impaired the performance of sedentary and exercise groups. Moreover, STZ (3 mg/kg) increased hippocampal S100B levels in both groups and SOD/CAT ratio in the sedentary animals. Insulin decreased synaptosomal H2O2 production in exercised compared to sedentary mice; however, both STZ doses abolished this effect. Normal brain insulin signaling is mechanistically involved in the improvement of cognitive function induced by exercise through the regulation of mitochondrial H2O2 production. However, a prior blockade of brain insulin signaling with STZ abolished the benefits of exercise on memory performance and mitochondrial H2O2 regulation.

Distinctive effects of unpredictable subchronic stress on memory, serum corticosterone and hippocampal BDNF levels in high and low exploratory mice.

Stress affects learning and memory processes and sensitivity to stress greatly varies between individuals. We studied behavioral and neurobiological effects of unpredictable subchronic stress (USCS) in two behavioral extremes of mice from the same strain (CF1) selected by their exploratory behavior of the central arena of an open field. The top and bottom 25% explorers were classified as low exploratory (LE) and high exploratory (HE) mice, respectively. The open field task, the novel object recognition task (NOR), sucrose intake and tail suspension task were evaluated in LE and HE groups exposed to USCS for two weeks or control conditions. Also serum corticosterone and hippocampal BDNF and S100B levels were analyzed. Both stressed groups exhibited less exploratory activity when submitted to USCS, but their difference in exploratory behavior remained. This short stress protocol did not induce changes in sucrose intake or immobility in the tail suspension task. Also, LE mice exhibited impaired NOR performance after USCS, whereas HE mice changed their pattern of exploration towards less exploration of the familiar object. HE had lower corticosterone levels than LE mice, but corticosterone levels increased after stress only in HE mice. Hippocampal BDNF in LE was lower than in HE but decreased after USCS only in HE mice, whereas S100B levels were not different between groups and did not change with USCS. In conclusion, our results suggest that individual differences in exploratory behavior in rodents from the same strain influence cognitive and biochemical response to stress.

Enriched environment effects on behavior, memory and BDNF in low and high exploratory mice.

Environmental enrichment (EE) has been largely used to investigate behavioral modifications and neuroplasticity in the adult brain both in normal and pathological conditions. The interaction between individual behavioral traits with EE responsiveness has not been investigated within the same strain. By using two extremes of CF1 mice that differ by their exploratory behavior in the Open Field (OF) task (Kazlauckas V, 2005), denominated as Low (LE) and High (HE) Exploratory Mice, the present study evaluated if EE during adulthood could modify the putative differences between LE and HE mice on exploratory behavior, memory performance and hippocampal BDNF levels. To this end, we investigated the effect of adult LE and HE mice after 2 months of enriched or standard housing conditions on the open field, on novel object recognition, on the inhibitory avoidance task and on hippocampal BDNF immunocontent. LE showed low exploratory behavior, less retention in the inhibitory avoidance and lower hippocampal BDNF levels. EE enhanced exploratory behavior, memory performance and hippocampal BDNF levels both in LE and HE mice. Importantly, the general profile of LE mice submitted to EE was similar to HE mice housed in standard conditions. These results show that internalized behavior of LE mice can be significantly modified by exposure to an enriched environment even during adulthood. These observations may contribute to investigate biological mechanisms and therapeutical interventions for individuals with internalized psychiatric disorders.

Electrophysiological effects of guanosine and MK-801 in a quinolinic acid-induced seizure model.

Quinolinic acid (QA) is an N-methyl-D-aspartate receptor agonist that also promotes glutamate release and inhibits glutamate uptake by astrocytes. QA is used in experimental models of seizures studying the effects of overstimulation of the glutamatergic system. The guanine-based purines (GBPs), including the nucleoside guanosine, have been shown to modulate the glutamatergic system when administered extracellularly. GBPs were shown to inhibit the binding of glutamate and analogs, to be neuroprotective under excitotoxic conditions, as well as anticonvulsant against seizures induced by glutamatergic agents, including QA-induced seizure. In this work, we studied the electrophysiological effects of guanosine against QA-induced epileptiform activity in rats at the macroscopic cortical level, as inferred by electroencephalogram (EEG) signals recorded at the epidural surface. We found that QA disrupts a prominent basal theta (4-10 Hz) activity during peri-ictal periods and also promotes a relative increase in gamma (20-50 Hz) oscillations. Guanosine, when successfully preventing seizures, counteracted both these spectral changes. MK-801, an NMDA-antagonist used as positive control, was also able counteract the decrease in theta power; however, we observed an increase in the power of gamma oscillations in rats concurrently treated with MK-801 and QA. Given the distinct spectral signatures, these results suggest that guanosine and MK-801 prevent QA-induced seizures by different network mechanisms.