Marcos Luiz Santos Perry

Diphenyl diselenide and diphenyl ditelluride affect the rat glutamatergic system in vitro and in vivo.

The aim of this study was to investigate the possible involvement of the glutamatergic system in the toxicity of organochalcogens, since this is an important neurotransmitter system for signal transduction and neural function. The results indicated that 100 microM diphenyl diselenide (PhSe)(2) and diphenyl ditelluride (PhTe)(2) inhibit by 50 and 70% (P<0.05), respectively, [(3)H]glutamate binding in vitro. Acute administration of 25 micromol/kg (PhSe)(2) or 3 micromol/kg (PhTe)(2) caused a significant reduction in [(3)H]glutamate (30%, P<0.05) or [(3)H]MK-801 binding (30%, P<0.05) to rat synaptic membranes. These results suggest that (PhSe)(2) and (PhTe)(2) affect, in a rather complex way, the glutamatergic system after acute in vivo exposure in rats. In vitro, total [(3)H]GMP-PNP binding was inhibited about 40% at 100 microM (PhSe)(2) and (PhTe)(2). Acute exposure in vivo to (PhSe)(2) decreased the stable [(3)H]GMP-PNP binding to 25% and (PhTe)(2) to 68% of the control value (P<0.05, for both compounds). Simultaneously, the unstable binding of [(3)H]GMP-PNP was decreased about 30 and 50% (P<0.05, for both compounds) after exposure to (PhSe)(2) and (PhTe)(2), respectively. GMP-PNP stimulated adenylate cyclase (AC) activity significantly in control animals. (PhSe)(2)- and (PhTe)(2)-treated animals increased the basal activity of this enzyme, but GMP-PNP stimulation was totally abolished. These results suggest that the toxic effects of organochalcogens could result from action at different levels of neural signal transduction pathways, possibly involving other neurotransmitters besides the 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.

Effect of various behavioral training and testing procedures on brain β-endorphin-like immunoreactivity and the possible role of β-endorphin in behavioral regulation

Beta-Endorphin-like immunoreactivity is reduced in the rat diencephalon after the animals are exposed for the first time to any of the following behavioral situations: 50 tones (habituation), 50 tone-footshock shuttle avoidance trials, one step-down inhibitory avoidance trial, simple exposure to the avoidance apparatus with no footshocks, or inescapable shock. The effect is not observed when animals are exposed to any of these situations for a second time. The reduction of brain beta-endorphin-like immunoreactivity is attributable to release and subsequent metabolism of the substance, and correlates with the novelty inherent in the diverse training or test situations. The role of beta-endorphin in behavior is discussed in the light of these and previous results which showed that it causes both retrograde amnesia and a facilitation of retrieval. The substance would appear to serve an adaptive function when animals are exposed to a new experience, by inducing a temporary forgetting of the experience together with (or leading to) a state of alertness or preparedness for what may happen next.

The role of opioid peptides in memory and learning

Evidence is discussed which points to the existence of a physiologic amnesic mechanism mediated by beta-endorphin and perhaps by other opioid peptides as well. This mechanism is triggered by various forms of training and by either painful or painless stimulation. It may operate through the inhibition of central dopaminergic and beta-adrenergic systems that modulate the memory consolidation process. This amnesic mechanism in unrelated to the regulation of pain perception, and operates at opioid peptide levels several orders of magnitude below those that are needed to cause analgesia or other effects. In addition, shuttle avoidance and habituation learning seem to be dependent on a state induced by the release of beta-endorphin. It is possible that this may be related to the amnesic properties of this substance. Therefore, it appears that the endogenous opioid peptides may exert their primary function in the modulation of memory processes.

Effect of acute and repeated restraint stress on glucose oxidation to CO2 in hippocampal and cerebral cortex slices

It has been suggested that glucocorticoids released during stress might impair neuronal function by decreasing glucose uptake by hippocampal neurons. Previous work has demonstrated that glucose uptake is reduced in hippocampal and cerebral cortex slices 24 h after exposure to acute stress, while no effect was observed after repeated stress. Here, we report the effect of acute and repeated restraint stress on glucose oxidation to CO2 in hippocampal and cerebral cortex slices and on plasma glucose and corticosterone levels. Male adult Wistar rats were exposed to restraint 1 h/day for 50 days in the chronic model. In the acute model there was a single exposure. Immediately or 24 h after stress, the animals were sacrificed and the hippocampus and cerebral cortex were dissected, sliced, and incubated with Krebs buffer, pH 7.4, containing 5 mM glucose and 0.2 microCi D-[U-14C] glucose. CO2 production from glucose was estimated. Trunk blood was also collected, and both corticosterone and glucose were measured. The results showed that corticosterone levels after exposure to acute restraint were increased, but the increase was smaller when the animals were submitted to repeated stress. Blood glucose levels increased after both acute and repeated stress. However, glucose utilization, measured as CO2 production in hippocampal and cerebral cortex slices, was the same in stressed and control groups under conditions of both acute and chronic stress. We conclude that, although stress may induce a decrease in glucose uptake, this effect is not sufficient to affect the energy metabolism of these cells.

Effect of protein malnutrition on redox state of the hippocampus of rat

The protein malnutrition is a worldwide problem, affecting mainly newborns and children of developing countries. This deficiency reaches the brain in the most critical period of the development. Various consequences are related to this insult, such as memory disturbance, learning, and behavioral impairment. Protein content of the diet plays an important role on antioxidant mechanisms. This study observed the effects of protein malnutrition on rat hippocampus redox state. Wistar rats were separate in four groups, receiving different diets: first group with 25% casein, protein deficient group with 8% casein, and the same two groups supplemented with methionine (0.15%). Diets were isocaloric and were administered since the prenatal period up to the sacrifice. Rats were decapitated at 21 or 75 days old and hippocampus were isolated for measuring the lipoperoxidation by TBARS method, protein oxidative damage by carbonyl (DNPH) levels, and the activities of antioxidant enzymes superoxide dismutase (SOD) and catalase (CAT). There was significant alterations in the activities of the enzyme SOD, lipoperoxidation, and protein oxidation in hippocampus of 21 and 75 day-old rats fed with 25% of protein with methionine and the groups fed with low levels of protein (8%) both supplemented or not with methionine. Our data suggest that both the content of protein in the diet and the essential amino acid methionine may alter the antioxidant system and the redox state of the brain.

Inhibition of brain energy metabolism by the branched-chain amino acids accumulating in maple syrup urine disease.

In the present work we investigated the in vitro effect of the branched-chain amino acids (BCAA) accumulating in maple syrup urine disease (MSUD) on some parameters of energy metabolism in cerebral cortex of rats. 14CO2 production from [1-14C]acetate, [1-5-14C]citrate and [U-14C]glucose, as well as glucose uptake by the brain were evaluated by incubating cortical prisms from 30-day-old rats in the absence (controls) or presence of leucine (Leu), valine (Val) or isoleucine (Ile). All amino acids significantly reduced 14CO2 production by around 20–55%, in contrast to glucose utilization, which was significantly increased by up to 90%. Furthermore, Leu significantly inhibited the activity of the respiratory chain complex IV, whereas Val and Ile markedly inhibited complexes II–III, III and IV by up to 40%. We also observed that trolox (α-tocopherol) and creatine totally prevented the inhibitory effects provoked by the BCAA on the respiratory chain complex activities, suggesting that free radicals were involved in these effects. The results indicate that the major metabolites accumulating in MSUD disturb brain aerobic metabolism by compromising the citric acid cycle and the electron flow through the respiratory chain. We presume that these findings may be of relevance to the understanding of the pathophysiology of the neurological dysfunction of MSUD patients.

Exercise Increases Insulin Signaling in the Hippocampus: Physiological Effects and Pharmacological Impact of Intracerebroventricular Insulin Administration in Mice

Increasing evidence indicates that physical exercise induces adaptations at the cellular, molecular, and systemic levels that positively affect the brain. Insulin plays important functional roles within the brain that are mediated by insulin‐receptor (IR) signaling. In the hippocampus, insulin improves synaptic plasticity, memory formation, and learning via direct modulation of GABAergic and glutamatergic receptors. Separately, physical exercise and central insulin administration exert relevant roles in cognitive function. We here use CF1 mice to investigate (i) the effects of voluntary exercise on hippocampal insulin signaling and memory performance and (ii) whether central insulin administration alters the effects of exercise on hippocampal insulin signaling and memory performance. Adult mice performed 30 days of voluntary exercise on running wheel and afterward both, sedentary and exercised groups, received intracerebroventricular (icv) injection of saline or insulin (0.5–5 mU). Memory performance was assessed using the inhibitory avoidance and water maze tasks. Hippocampal tissue was measured for [U‐14C] glucose oxidation and the immunocontent of insulin receptor/signaling (IR, pTyr, pAktser473). Additionally, the phosphorylation of the glutamate NMDA receptor NR2B subunit and the capacity of glutamate uptake were measured, and immunohistochemistry was used to determine glial reactivity. Exercise significantly increased insulin peripheral sensitivity, spatial learning, and hippocampal IR/pTyrIR/pAktser473 immunocontent. Glucose oxidation, glutamate uptake, and astrocyte number also increased relative to the sedentary group. In both memory tasks, 5 mU icv insulin produced amnesia but only in exercised animals. This amnesia was associated a rapid (15 min) and persistent (24 h) increase in hippocampal pNR2B immunocontent that paralleled the increase in glial reactivity. In conclusion, physical exercise thus increased hippocampal insulin signaling and improved water maze performance. Overstimulation of insulin signaling in exercised animals, however, via icv administration impaired behavioral performance. This effect was likely the result of aberrant phosphorylation of the NR2B subunit.

Effects of Undernutrition on Glutamatergic Parameters in Rat Brain

Early restriction of nutrients during the perinatal period has marked repercussions on CNS ontogeny, Leading to impaired functions. This study investigated the effects of pre- and postnatal (up to 75 days) undernutrition (diet: 8% protein; normonourished group: 25% protein) on some glutamatergic and behavioral parameters of rats. Undernutrition reduced: (i) seizures caused by ICV quinolinic acid (QA) administration; (ii) Na-independent [3H]glutamate binding in cell plasma membranes of cerebral cortex, and (ii) basal [3H]glutamate release from synaptosomal preparation. Behavioral parameters related to locomotion, anxiety, or memory were not affected. These results indicate that our model of undernutrition decreased the sensitivity to QA as convulsing agent and point to some putative glutamatergic parameters involved in this effect.

Serum and liver lipids in rats and chicks fed with diets containing different oils.

OBJECTIVES Because dietary fat composition is determinant for serum cholesterol level, which is related to cardiovascular disease, we evaluated the effects of diets containing saturated (coconut oil) or polyunsaturated fatty acids (soybean oil) supplemented or not with dietary cholesterol on serum and liver lipid composition in two animal species. METHODS Male Wistar rats (21 d old) were assigned to one of seven groups and fed with commercial diet or diets containing 5% or 20% soybean oil or 20% coconut oil with or without 1% cholesterol. Chicks were assigned to one of four groups and fed with diets containing 15% soybean oil or 15% coconut oil with or without 1% cholesterol. RESULTS In rats, the accumulations of hepatic cholesterol and triacylglycerols were higher in the group fed 20% soybean oil and 1% cholesterol than in the group fed 20% coconut fat and 1% cholesterol. The highest serum levels of cholesterol and triacylglycerols were observed in the group fed coconut oil and cholesterol, compared with the group fed soybean oil and cholesterol. Triacylglycerol, high-density lipoprotein, and total cholesterol serum levels increased with diet containing coconut oil and cholesterol. In chicks, the highest hepatic cholesterol accumulation occurred in the group fed 15% coconut fat and 1% cholesterol. Total and high-density lipoprotein cholesterol levels increased with diet containing coconut oil and cholesterol, although none of these diets modified serum triacylglycerol levels. CONCLUSIONS The type of experimental animal model and the diet composition influence lipid metabolism.