Deusa Vendite

Ebselen prevents excitotoxicity provoked by glutamate in rat cerebellar granule neurons

Ebselen is a selenium compound that have glutathione peroxidase-like activity which is neuroprotective in acute stroke ischemia. The efficacy of ebselen to prevent excitotoxicity provoked by glutamate in cerebellar granule neurons was investigated at various time points and concentrations. Simultaneous addition of ebselen with glutamate decreased neuronal death and was completely reversed by 3 microM of ebselen (3 (4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide (MTT) and propidium iodide assays). However, when 1 microM of ebselen was added with glutamate and remained in the culture medium until 24 or 48 h, the neuronal survival increased to the control. The mechanism proposed for neuroprotection was the ability of ebselen to prevent lipoperoxidation provoked by glutamate. The present findings propose to amplify the use of ebselen in others neurodegenerative disorders involving glutamatergic system.

Beta-endorphin causes retrograde amnesia and is released from the rat brain by various forms of training and stimulation

The endogenous opiate peptide, beta-endorphin (0.4, 1.0, 2.0, and 10.0 μg/kg) was injected IP into rats immediately after training in a shuttle avoidance task, and its effect on memory retention was evaluated in test sessions carried out 24 h later. The drug was found to cause retrograde amnesia, the ED50 being 1.0 μg/kg. Beta-endorphin immunoreactivity was measured in the hypothalamus and rest of the brain of rats submitted to training, or test sessions of shuttle avoidance learning, pseudoconditioning in the shuttle-box, tones alone, or foot-shocks alone. After training in any of the four paradigms, there was a marked (46–60%) depletion of beta-endorphin immunoreactivity in the rest of the brain. No changes were detected in the hypothalamus or after test sessions. The loss of beta-endorphin immunoreactivity may be attributed to release of this substance caused by the stimuli used for training. From the present findings, as well as previous observations on the memory-facilitating influence of the opiate receptor antagonist, naloxone, it is concluded that there is a physiological amnesic mechanism mediated by beta-endorphin (and perhaps other opoid peptides as well), which is triggered by the non-associative factors present in the various forms of learning.

Repeated restraint stress alters hippocampal glutamate uptake and release in the rat.

Glutamatergic mechanisms are thought to be involved in stress-induced changes of brain function, especially in the hippocampus. We hypothesized that alterations caused by the hormonal changes associated with chronic and acute stress may affect glutamate uptake and release from hippocampal synaptosomes in Wistar rats. It was found that [3H]glutamate uptake and release by hippocampal nerve endings, when measured 24 h after 1 h of acute restraint, presented no significant difference. The exposure to repeated restraint stress for 40 days increased neuronal presynaptic [3H]glutamate uptake as well as basal and K+-stimulated glutamate release when measured 24 h after the last stress session. Chronic treatment also caused a significant decrease in [3H]glutamate binding to hippocampal membranes. We suggest that changes in the glutamatergic system are likely to take part in the mechanisms involved in nervous system plasticity following repeated stress exposure.

NMDA preconditioning protects against seizures and hippocampal neurotoxicity induced by quinolinic acid in mice.

Summary:  Purpose: N‐methyl d‐aspartate (NMDA) preconditioning has been used to prevent cellular death induced by glutamate or NMDA in cultured neurons. Quinolinic acid (QA)‐induced seizures are used to average NMDA receptors–evoked neurotoxicity in animal models. The purpose of this study was to investigate the potential neuroprotective effects of NMDA preconditioning against QA‐induced seizures and hippocampal damage in vivo.

Adenosine receptors co-operate with NMDA preconditioning to protect cerebellar granule cells against glutamate neurotoxicity.

N-Methyl-D-aspartate (NMDA) preconditioning is evoked by subtoxic concentrations of NMDA (50 microM), which has been shown previously to lead to transient resistance to subsequent lethal dose of glutamate or NMDA in cultured neurons. The purpose of this study was to investigate the participation of adenosine A1 and A2A receptors on NMDA preconditioning against glutamate-induced cellular damage in cerebellar granule cells. NMDA preconditioning prevented the stimulatory effect induced by glutamate on AMP hydrolysis, but not on ADP hydrolysis. The neuroprotection evoked by NMDA preconditioning against glutamate-induced cellular damage was prevented by the presence of adenosine A1 receptor antagonist, 8-cyclopentyl-1,3-dimethylxanthine (CPT, 100 nM), but not by the adenosine A2A receptors antagonist, (4-(2[7-amino-2-(2-furyl {1,2,4}-triazolo{2,3-a{1,3,5}triazian-5-yl-aminoethyl)phenol (ZM 241385, 50 nM). Interestingly, a long-term treatment with CPT or ZM 241385 alone protected cells against glutamate-induced neurotoxicity. Moreover, the functionality of adenosine A1 receptor was not affected by NMDA preconditioning, but this treatment promoted adenosine A2A receptor desensitization, measured by cAMP accumulation. Taken together, the results described herein suggest that the neuroprotection evoked by NMDA preconditioning against cellular damage elicited by glutamate occurs through mechanisms involving adenosine A2A receptors desensitization co-operating with adenosine A1 receptors activation in cerebellar granule cells.

Desensitization of adenosine A1 receptor-mediated inhibition of adenylyl cyclase in cerebellar granule cells.

Agonist-induced desensitization of adenosine A1 receptor-mediated inhibition of adenylyl cyclase has been studied in cerebellar granule cells. Exposure of cells to the adenosine A1 receptor agonist R-phenylisopropyl adenosine (R-PIA) from 2 to 48 h brings about desensitization of this signal transduction pathway. Associated with the desensitization process, a decrease in radioligand binding performed in intact cells with the adenosine A1 receptor agonist [3H]cyclohexyladenosine (CHA) has been detected. Simultaneously, an increase of adenosine A1 radioligand binding has also been detected in microsomes. A decrease in the steady-state level of α-Gi in both, plasma membrane and microsomes also has been detected during the desensitization process. These data may account for the desensitization of the inhibitory pathway of the adenylyl cyclase in cerebellar granule cells described herein. After a transient increase in adenosine A1 receptor mRNA, no changes were observed in this parameter after 12 hr of treatment with the adenosine A1 agonist R-PIA, suggesting a post-transcriptional regulation of this receptor during long-term desensitization.

Effects of chronic administration of caffeine and stress on feeding behavior of rats

Anorectic effects of caffeine are controversial in the literature, while stress and obesity are growing problems in our society. Since many stressed people are coffee drinkers, the objective of the present study was to evaluate the effect of stress and chronic administration of caffeine on feeding behavior and body weight in male and female rats. Wistar rats (both males and females) were divided into 3 groups: control (receiving water), caffeine 0.3 g/L and caffeine 1.0 g/L (in the drinking water). These groups were subdivided into non-stressed and stressed (repeated-restraint stress for 40 days). During the entire treatment, chow consumption was monitored and rats were weighed monthly. Afterwards, feeding behavior was evaluated during 3-min trials in food-deprived and ad libitum fed animals and also in repeated exposures, using palatable food (Froot Loops and Cheetos). Chronic administration of caffeine did not affect rat chow consumption or body weight gain, but diminished the consumption of both salty (Cheetos) and sweet (Froot Loops) palatable food. In the repeated trial tests, stress diminished savory snack consumption in the later exposures [I.S. Racotta, J. Leblanc, D. Richard The effect of caffeine on food intake in rats: involvement of corticotropin-releasing factor and the sympatho-adrenal system. Pharmacol Biochem Behav. 1994, 48:887-892; S.D. Comer, M. Haney, R.W. Foltin, M.W. Fischman Effects of caffeine withdrawal on humans living in a residential laboratory. Exp Clin Psychopharmacol. 1997, 5:399-403; A. Jessen, B. Buemann, S. Toubro, I.M. Skovgaard, A. Astrup The appetite-suppressant effect of nicotine is enhanced by caffeine. Diab Ob Metab. 2005, 7:327-333; J.M. Carney Effects of caffeine, theophylline and theobromine on scheduled controlled responding in rats. Br J Pharmacol. 1982, 75:451-454] and caffeine diminished consumption of both palatable foods (savory and sweet) during the early and later exposures. Most responses to caffeine were stronger in females, and stress exposure influenced the effect. Neither chronic caffeine nor stress affected adrenal weight and plasma corticosterone levels of the rats. These observations suggest that chronic caffeine consumption may have sex-specific effects on palatable food ingestion.

Time course of oxidative events in the hippocampus following intracerebroventricular infusion of quinolinic acid in mice.

The excitotoxicity induced by QA has been related to its ability to increase free radical content and oxidative stress. In order to investigate the time course of toxicity and oxidative profile in the mice hippocampus following seizures induced by QA infusion (36.8 nM, i.c.v.), we evaluated the cellular damage (PI uptake assay), content of ROS formation (DCF assay) and the total radical antioxidant potential (TRAP) and reactivity (TAR) levels. The present results showed that a cellular damage occurred as early as 4 h after QA infusion coincident with an increase in the ROS contents, which returned to control levels after 24 h, while the cellular damage persisted for 72 h. There was a marked increased in the total antioxidant capacity at 8 h after QA infusion in both reactivity and potential levels. By 72 h post-treatment, the TRAP levels decreased, but the TAR levels remained augmented. Therefore, the delayed and persistent increase in the antioxidant capacity after QA insult may be a cellular adaptative response, probably contributing to decrease the ROS levels in order to prevent the spreading of the cellular damage. Therefore, the increase in the QA level in the brain ventricle may induce oxidative stress, which is followed by a persistent response in the antioxidant system in the hippocampus. The present study may, therefore, contribute to elucidate the mechanism of the brain dysfunction in patients with several neurological disorders involving elevation of QA in the CSF.

The effect of unpredictable chronic mild stress on depressive-like behavior and on hippocampal A1 and striatal A2A adenosine receptors

This study examined the effects of two chronic stress regimens upon depressive-like behavior, A(1) and A(2A) adenosine receptor binding and immunocontent. Male rats were subjected to unpredictable chronic mild stress (UCMS) or to chronic restraint stress (CRS) for 40 days. Subsequently, depressive-like behaviors (forced swimming and consumption of sucrose) were evaluated, and A(1) adenosine or A(2A) adenosine receptors were examined in the hippocampus or striatum, respectively. UCMS animals demonstrated depressive-related behaviors (decrease in sucrose consumption and increased immobility in the forced swimming test). This group also presented increased A(1) adenosine receptor binding and immunoreactivity in hippocampus, as well as increased striatal A(2A) adenosine receptor binding in the striatum, without alteration in immunoreactivity. Conversely, the chronic restraint stress group displayed only an increase in A(1) adenosine receptor binding and no alteration in the other parameters evaluated. We suggest that the alteration in adenosine receptors, particularly the upregulation of striatal A(2A) adenosine receptors following UCMS, could be associated with depressive-related behavior.

Phosphorylation of glial fibrillary acidic protein is stimulated by glutamate via NMDA receptors in cortical microslices and in mixed neuronal/glial cell cultures prepared from the cerebellum

In previous work we showed that phosphorylation of glial fibrillary acidic protein (GFAP), an astrocyte marker, is increased by glutamate in hippocampal slices from immature rats via a type II metabotropic receptor. In the present work we show that glutamate also stimulates GFAP phosphorylation in microslices prepared from immature cerebellar cortex, but by a different receptor mechanism from that observed in the hippocampus. Thus, in cerebellar microslices, NMDA consistently stimulated GFAP phosphorylation, whereas no effect of metabotropic or non-NMDA ionotropic agonists was observed. Glutamate and NMDA also stimulated GFAP phosphorylation in mixed neuronal/glial cell cultures from the cerebellum, although no effect of these agonists was observed in primary cultures of cerebellar astrocytes. In both models, the effects of glutamate and NMDA were dependent on external Ca(2+), were reversed by the NMDA receptor antagonist AP5 and were not blocked by tetrodotoxin. In the slice study the effect of NMDA was confined to a period starting with the first detectable expression of GFAP at 10 days and finishing at 16 days postnatal, as previously observed with metabotropic agonists in hippocampal slices. This period in the rat corresponds to the start of synaptogenesis when astrocyte hypertrophy is occurring. The results are discussed in the light of information in the literature on the occurrence of functional NMDA receptor subunits in glia.