Felipe Schmitz

Methylphenidate affects memory, brain-derived neurotrophic factor immunocontent and brain acetylcholinesterase activity in the rat

Methylphenidate, a psychostimulant that affects both dopaminergic and noradrenergic systems, is one of the most frequently prescribed treatments for attention-deficit hyperactivity disorder. The present study investigated the effects of chronic administration of methylphenidate to juvenile rats on spatial memory, brain-derived neurotrophic factor immunocontent and acetylcholinesterase activity in hippocampus and prefrontal cortex. Rats received intraperitoneal injections of methylphenidate (2.0mg/kg) once a day, from the 15th to the 45th day of age or an equivalent volume of 0.9% saline solution (controls). Twenty-four hours after the last injection, animals were subjected to testing in the Morris water maze. After that, animals were sacrificed and hippocampus and prefrontal cortex were dissected out for determination of brain-derived neurotrophic factor immunocontent and acetylcholinesterase activity. Chronic administration of methylphenidate provoked cognitive impairments on spatial reference and working memory tasks. A reduction on brain-derived neurotrophic factor immunocontent and increased acetylcholinesterase activity in prefrontal cortex, but not in hippocampus, of rats treated with methylphenidate were also observed. These results suggest that the deficit in spatial memory may be associated to decreased brain-derived neurotrophic factor immunocontent and increased acetylcholinesterase in prefrontal cortex of juvenile rats subjected to methylphenidate administration.

Development of an animal model for chronic mild hyperhomocysteinemia and its response to oxidative damage.

The purpose of this study was to develop a chronic chemically induced model of mild hyperhomocysteinemia in adult rats. We produced levels of Hcy in the blood (30 μM), comparable to those considered a risk factor for the development of neurological and cardiovascular diseases, by injecting homocysteine subcutaneously (0.03 μmol/g of body weight) twice a day, from the 30th to the 60th postpartum day. Controls received saline in the same volumes. Using this model, we evaluated the effect of chronic administration of homocysteine on redox status in the blood and cerebral cortex of adult rats. Reactive oxygen species and thiobarbituric acid reactive substances were significantly increased in the plasma and cerebral cortex, while nitrite levels were reduced in the cerebral cortex, but not in the plasma, of rats subjected to chronic mild hyperhomocysteinemia. Homocysteine was also seen to disrupt enzymatic and non‐enzymatic antioxidant defenses in the blood and cerebral cortex of rats. Since experimental animal models are useful for understanding the pathophysiology of human diseases, the present model of mild hyperhomocysteinemia may be useful for the investigation of additional mechanisms involved in tissue alterations caused by homocysteine.

Methylphenidate induces lipid and protein damage in prefrontal cortex, but not in cerebellum, striatum and hippocampus of juvenile rats

The use of psychostimulant methylphenidate has increased in recent years for the treatment of attention-deficit hyperactivity disorder in children and adolescents. However, the behavioral and neurochemical changes promoted by its use are not yet fully understood, particularly when used for a prolonged period during stages of brain development. Thus, the aim of this study was to determine some parameters of oxidative stress in encephalic structures of juvenile rats subjected to chronic methylphenidate treatment. Wistar rats received intraperitoneal injections of methylphenidate (2.0 mg/kg) once a day, from the 15th to the 45th day of age or an equivalent volume of 0.9% saline solution (controls). Two hours after the last injection, animals were euthanized and the encephalic structures obtained for determination of oxidative stress parameters. Results showed that methylphenidate administration increased the activities of superoxide dismutase and catalase, but did not alter the levels of reactive species, thiobarbituric acid reactive substances levels and sulfhydryl group in cerebellum of rats. In striatum and hippocampus, the methylphenidate-treated rats presented a decrease in the levels of reactive species and thiobarbituric acid reactive substances, but did not present changes in the sulfhydryl groups levels. In prefrontal cortex, methylphenidate promoted an increase in reactive species formation, SOD/CAT ratio, and increased the lipid peroxidation and protein damage. These findings suggest that the encephalic structures respond differently to methylphenidate treatment, at least, when administered chronically to young rats. Notably, the prefrontal cortex of juvenile rats showed greater sensitivity to oxidative effects promoted by methylphenidate in relation to other encephalic structures analyzed.

Physical exercise reverses glutamate uptake and oxidative stress effects of chronic homocysteine administration in the rat

The influence of physical exercise on the effects elicited by homocysteine on glutamate uptake and some parameters of oxidative stress, namely thiobarbituric acid‐reactive substances, 2′,7′‐dichlorofluorescein (H2DCF) oxidation, as well as enzymatic antioxidant activities, superoxide dismutase, catalase and glutathione peroxidase in rat cerebral cortex were investigated. Wistar rats received subcutaneous administration of homocysteine or saline (control) from the 6th to 29th day of life. The physical exercise was performed from the 30th to 60th day of life; 12 h after the last exercise session animals were sacrificed and the cerebral cortex was dissected out. It is shown that homocysteine reduces glutamate uptake increases thiobarbituric acid‐reactive substances and disrupts enzymatic antioxidant defenses in cerebral cortex. Physical activity reversed the homocysteine effects on glutamate uptake and on antioxidant enzymes activities; although the increase in thiobarbituric acid‐reactive substances was only partially reversed by exercise. These findings allow us to suggest that physical exercise may have a protective role against homocysteine‐induced oxidative imbalance and brain damage to the glutamatergic system.

Early life adversities or high fat diet intake reduce cognitive function and alter BDNF signaling in adult rats: Interplay of these factors changes these effects.

Environmental factors, like early exposure to stressors or high caloric diets, can alter the early programming of central nervous system, leading to long‐term effects on cognitive function, increased vulnerability to cognitive decline and development of psychopathologies later in life. The interaction between these factors and their combined effects on brain structure and function are still not completely understood. In this study, we evaluated long‐term effects of social isolation in the prepubertal period, with or without chronic high fat diet access, on memory and on neurochemical markers in the prefrontal cortex of rats. We observed that early social isolation led to impairment in short‐term and working memory in adulthood, and to reductions of Na+,K+‐ATPase activity and the immunocontent of phospho‐AKT, in prefrontal cortex. Chronic exposure to a high fat diet impaired short‐term memory (object recognition), and decreased BDNF levels in that same brain area. Remarkably, the association of social isolation with chronic high fat diet rescued the memory impairment on the object recognition test, as well as the changes in BDNF levels, Na+,K+‐ATPase activity, MAPK, AKT and phospho‐AKT to levels similar to the control‐chow group. In summary, these findings showed that a brief social isolation period and access to a high fat diet during a sensitive developmental period might cause memory deficits in adulthood. On the other hand, the interplay between isolation and high fat diet access caused a different brain programming, preventing some of the effects observed when these factors are separately applied.

MK-801 alters Na + , K + -ATPase activity and oxidative status in zebrafish brain: reversal by antipsychotic drugs

Schizophrenia is a debilitating mental disorder with a global prevalence of 1% and its etiology remains poorly understood. In the current study we investigated the influence of antipsychotic drugs on the effects of MK-801 administration, which is a drug that mimics biochemical changes observed in schizophrenia, on Na+, K+-ATPase activity and some parameters of oxidative stress in zebrafish brain. Our results showed that MK-801 treatment significantly decreased Na+, K+-ATPase activity, and all antipsychotics tested prevented such effects. Acute MK-801 treatment did not alter reactive oxygen/nitrogen species by 2′7′-dichlorofluorscein (H2DCF) oxidation assay, but increased the levels of thiobarbituric acid reactive substances (TBARS), when compared with controls. Some antipsychotics such as sulpiride, olanzapine, and haloperidol prevented the increase of TBARS caused by MK-801. These findings indicate oxidative damage might be a mechanism involved in the decrease of Na+, K+-ATPase activity induced by MK-801. The parameters evaluated in this study had not yet been tested in this animal model using the MK-801, suggesting that zebrafish is an animal model that can contribute for providing information on potential treatments and disease characteristics.

Quinolinic acid neurotoxicity: Differential roles of astrocytes and microglia via FGF-2-mediated signaling in redox-linked cytoskeletal changes.

QUIN is a glutamate agonist playing a role in the misregulation of the cytoskeleton, which is associated with neurodegeneration in rats. In this study, we focused on microglial activation, FGF2/Erk signaling, gap junctions (GJs), inflammatory parameters and redox imbalance acting on cytoskeletal dynamics of the in QUIN-treated neural cells of rat striatum. FGF-2/Erk signaling was not altered in QUIN-treated primary astrocytes or neurons, however cytoskeleton was disrupted. In co-cultured astrocytes and neurons, QUIN-activated FGF2/Erk signaling prevented the cytoskeleton from remodeling. In mixed cultures (astrocyte, neuron, microglia), QUIN-induced FGF-2 increased level failed to activate Erk and promoted cytoskeletal destabilization. The effects of QUIN in mixed cultures involved redox imbalance upstream of Erk activation. Decreased connexin 43 (Cx43) immunocontent and functional GJs, was also coincident with disruption of the cytoskeleton in primary astrocytes and mixed cultures. We postulate that in interacting astrocytes and neurons the cytoskeleton is preserved against the insult of QUIN by activation of FGF-2/Erk signaling and proper cell-cell interaction through GJs. In mixed cultures, the FGF-2/Erk signaling is blocked by the redox imbalance associated with microglial activation and disturbed cell communication, disrupting the cytoskeleton. Thus, QUIN signal activates differential mechanisms that could stabilize or destabilize the cytoskeleton of striatal astrocytes and neurons in culture, and glial cells play a pivotal role in these responses preserving or disrupting a combination of signaling pathways and cell-cell interactions. Taken together, our findings shed light into the complex role of the active interaction of astrocytes, neurons and microglia in the neurotoxicity of QUIN.

Evidence that AKT and GSK-3β pathway are involved in acute hyperhomocysteinemia

Homocysteine is a neurotoxic amino acid that accumulates in several disorders including homocystinuria, neurodegenerative and neuroinflammatory diseases. In the present study we evaluated the effect of acute and chronic hyperhomocysteinemia on Akt, NF‐κB/p65, GSK‐3β, as well as Tau protein in hippocampus of rats. For acute treatment, rats received a single injection of homocysteine (0.6 μmol/g body weight) or saline (control). For chronic treatment, rats received daily subcutaneous injections of homocysteine (0.3–0.6 μmol/g body weight) or saline (control) from the 6th to the 28th days‐of‐age. One or 12 h after the last injection, rats were euthanized, the hippocampus was removed and samples were submitted to electrophoresis followed by Western blotting. Results showed that acute hyperhomocysteinemia increases Akt phosphorylation, cytosolic and nuclear immunocontent of NF‐κB/p65 subunit and Tau protein phosphorylation, but reduces GSK‐3β phosphorylation at 1 h after homocysteine injection. However, 12 h after acute hyperhomocysteinemia there is no effect on Akt and GSK‐3β phosphorylation. Furthermore, chronic hyperhomocysteinemia did not alter Akt and GSK‐3β phosphorylation at 1 h and 12 h after the last administration of this amino acid. Our data showed that Akt, NF‐κB/p65, GSK‐3β and Tau protein are activated in hippocampus of rats subjected to acute hyperhomocysteinemia, suggesting that these signaling pathways may be, at least in part, important contributors to the neuroinflammation and/or brain dysfunction observed in some hyperhomocystinuric patients.

Evaluation of Na+, K+-ATPase activity in the brain of young rats after acute administration of fenproporex

OBJECTIVES Fenproporex is an amphetamine-based anorectic which is rapidly converted into amphetamine in vivo. Na+, K+-ATPase is a membrane-bound enzyme necessary to maintain neuronal excitability. Considering that the effects of fenproporex on brain metabolism are poorly known and that Na+, K+-ATPase is essential for normal brain function, this study sought to evaluate the effect of this drug on Na+, K+-ATPase activity in the hippocampus, hypothalamus, prefrontal cortex, and striatum of young rats. METHODS Young male Wistar rats received a single injection of fenproporex (6.25, 12.5, or 25 mg/kg intraperitoneally) or polysorbate 80 (control group). Two hours after the last injection, the rats were killed by decapitation and the brain was removed for evaluation of Na+, K+-ATPase activity. RESULTS Fenproporex decreased Na+, K+-ATPase activity in the striatum of young rats at doses of 6.25, 12.5, and 25 mg/kg and increased enzyme activity in the hypothalamus at the same doses. Na+, K+-ATPase activity was not affected in the hippocampus or prefrontal cortex. CONCLUSION Fenproporex administration decreased Na+, K+-ATPase activity in the striatum even in low doses. However, in the hypothalamus, Na+, K+-ATPase activity was increased. Changes in this enzyme might be the result of the effects of fenproporex on neuronal excitability.

Intracerebroventricular D-galactose administration impairs memory and alters activity and expression of acetylcholinesterase in the rat.

Tissue accumulation of galactose is a hallmark in classical galactosemia. Cognitive deficit is a symptom of this disease which is poorly understood. The aim of this study was to investigate the effects of intracerebroventricular administration of galactose on memory (inhibitory avoidance and novel object recognition tasks) of adult rats. We also investigated the effects of galactose on acetylcholinesterase (AChE) activity, immunocontent and gene expression in hippocampus and cerebral cortex. Wistar rats received a single injection of galactose (4 mM) or saline (control). For behavioral parameters, galactose was injected 1 h or 24 h previously to the testing. For biochemical assessment, animals were decapitated 1 h, 3 h or 24 h after galactose or saline injection; hippocampus and cerebral cortex were dissected. Results showed that galactose impairs the memory formation process in aversive memory (inhibitory avoidance task) and recognition memory (novel object recognition task) in rats. The activity of AChE was increased, whereas the gene expression of this enzyme was decreased in hippocampus, but not in cerebral cortex. These findings suggest that these changes in AChE may, at least in part, to lead to memory impairment caused by galactose. Taken together, our results can help understand the etiopathology of classical galactosemia.