ABSTRACT
The permanent occlusion of common carotid arteries (2VO) causes a significant reduction of cerebral blood flow (hypoperfusion) in rats and constitutes a well established experimental model to investigate neuronal damage and cognitive impairment that occurs in human ageing and Alzheimer's disease. In the present study, we evaluated two astroglial proteins--S100B and glial fibrillary acidic protein (GFAP)--in cerebral cortex and hippocampus tissue, glutamate uptake and glutamine synthetase activity in hippocampus tissue, as well as S100B in cerebrospinal fluid. Cognition, as assessed by reference and working spatial memory protocols, was also investigated. Adult male Wistar rats were submitted to 10 weeks of chronic cerebral hypoperfusion by the 2VO method. A significant increase of S100B and GFAP in hippocampus tissue was observed, as well a significant decrease in glutamate uptake. Interestingly, we observed a decrease in S100B in cerebrospinal fluid. As for the cognitive outcome, there was an impairment of both reference and working spatial memory in the water maze; positive correlation between cognitive impairment and glutamate uptake decrease was evidenced in hypoperfused rats. These data support the hypothesis that astrocytes play a crucial role in the mechanisms of experimental neurodegeneration and that hippocampal pathology arising after chronic hypoperfusion gives rise to memory deficits.
Subject(s)
Astrocytes/metabolism , Cerebral Cortex/physiopathology , Cognition Disorders/physiopathology , Gliosis/physiopathology , Hypoxia-Ischemia, Brain/physiopathology , Hypoxia-Ischemia, Brain/psychology , Animals , Astrocytes/pathology , Biomarkers/analysis , Biomarkers/metabolism , Carotid Stenosis/metabolism , Carotid Stenosis/physiopathology , Carotid Stenosis/psychology , Cerebral Cortex/metabolism , Cerebral Cortex/pathology , Cognition Disorders/etiology , Cognition Disorders/metabolism , Disease Models, Animal , Glial Fibrillary Acidic Protein/analysis , Glial Fibrillary Acidic Protein/metabolism , Gliosis/etiology , Gliosis/metabolism , Glutamate-Ammonia Ligase/metabolism , Glutamic Acid/metabolism , Hippocampus/metabolism , Hippocampus/pathology , Hippocampus/physiopathology , Hypoxia-Ischemia, Brain/metabolism , Male , Maze Learning/physiology , Memory Disorders/etiology , Memory Disorders/metabolism , Memory Disorders/physiopathology , Nerve Growth Factors/analysis , Nerve Growth Factors/metabolism , Rats , Rats, Wistar , S100 Calcium Binding Protein beta Subunit , S100 Proteins/analysis , S100 Proteins/metabolism , Synaptic Transmission/physiologyABSTRACT
1. S100B is a calcium-binding protein that acts as a neurotrophic cytokine and is expressed in the central nervous system, predominantly by astrocytes. At nanomolar concentrations, S100B stimulates neurite outgrowth and glial glutamate uptake, as well as protecting neurons against glutamate excitoxicity. 2. Peripheral S100B concentrations, particularly in the serum and cerebrospinal fluid (CSF), have been used as a parameter of glial activation or death in several physiological and pathological conditions. 3. In the present study, we investigated the effect of anaesthetics (thiopental, ketamine and halothane) on CSF concentrations of S100B, as well as a possible sex dependence, because several studies have suggested astrocytes as putative targets for oestrogen. 4. Higher levels of CSF S100B were found when rats were anaesthetized with thiopental; these levels, independently of anaesthetic, were sex dependent. Conversely, no effect of anaesthetic or sex was observed on serum concentrations of S100B. 5. The increase in CSF concentrations of S100B induced by thiopental was confirmed in non-anaesthetized neonatal rats and cortical astrocyte cultures. 6. Assuming CSF S100B as a marker of development, glial activation or even brain damage, investigations regarding the sex dependence of its concentration may be useful in gaining an understanding of sex variations in the behaviour and the pathological course of, as well as susceptibility to, many brain disorders. The findings of the present study reinforce the sex effect on synaptic plasticity and suggest a sex dependence of neural communication mediated by extracellular S100B without restricting the influence of astrocytes on the developmental phase.
Subject(s)
Anesthetics/pharmacology , Astrocytes/drug effects , Cerebral Cortex/drug effects , Cisterna Magna/drug effects , Halothane/pharmacology , Ketamine/pharmacology , Nerve Growth Factors/cerebrospinal fluid , S100 Proteins/cerebrospinal fluid , Thiopental/pharmacology , Animals , Animals, Newborn , Astrocytes/metabolism , Cells, Cultured , Cerebral Cortex/cytology , Cerebral Cortex/metabolism , Cisterna Magna/metabolism , Female , Male , Rats , Rats, Wistar , S100 Calcium Binding Protein beta Subunit , Sex FactorsABSTRACT
Methylmercury (MeHg) is a well-known environmental pollutant toxic to the nervous tissue, particularly during development. We recently described transitory hippocampal changes in neonate rats prenatally exposed to MeHg. In this study, we evaluate oxidative stress in the hippocampus on the 1st and 30th postnatal days. Motor behavior (open-field, foot-fault and strength tests) of these animals also was studied after the 30th postnatal day. Female Wistar rats were injected with MeHg (5 mg/Hg/day) on the 12th, 13th and 14th gestational days. Biochemical parameters measured for oxidative stress were levels of the antioxidant enzymes superoxide dismutase (SOD), glutathione peroxidase (GPx) and catalase (CAT). Total antioxidant reactivity (TAR) and protein oxidation (contents of tryptophan and tyrosine) were also recorded. Our results showed low activities of antioxidant enzymes in the MeHg group at birth. SOD activity remained reduced on the 30th postnatal day. Moreover, a decrease of TAR and protein oxidation was observed only at 30 days of age. No changes were observed in the motor behavior of these animals. Although mercury content in hippocampus is present at undetectable levels at 30 days of age, we observed more persistent changes in oxidative balance. Our data confirm that mercury induces oxidative stress in hippocampus and that this alteration, particularly SOD activity, remained altered even when mercury was no longer present.
Subject(s)
Antioxidants/metabolism , Hippocampus/drug effects , Hippocampus/metabolism , Methylmercury Compounds/toxicity , Oxidative Stress/drug effects , Prenatal Exposure Delayed Effects , Age Factors , Animals , Animals, Newborn , Catalase/drug effects , Catalase/metabolism , Disease Models, Animal , Down-Regulation/drug effects , Down-Regulation/physiology , Female , Glutathione Peroxidase/drug effects , Glutathione Peroxidase/metabolism , Hippocampus/growth & development , Motor Activity/drug effects , Nerve Degeneration/chemically induced , Nerve Degeneration/enzymology , Nerve Degeneration/physiopathology , Neurotoxins/toxicity , Oxidative Stress/physiology , Pregnancy , Rats , Rats, Wistar , Superoxide Dismutase/drug effects , Superoxide Dismutase/metabolism , Tryptophan/metabolism , Tyrosine/metabolismABSTRACT
Methylmercury (MeHg), an organic methylated form of mercury, is one of the most hazardous environmental pollutants. MeHg is a potent neurotoxin, particularly during brain development. Neurotoxicity-induced by MeHg in prenatal age can cause mental disorders, cerebral palsy and seizures. We investigated cerebrospinal fluid (CSF) and brain tissue contents of S100B, a calcium binding protein produced and secreted by astrocytes, which has trophic and toxic activity on neurons depending on concentration. Pregnant rats were exposed to MeHg (5 mg/kg per day, on the 12th, 13th and 14th days of pregnancy). CSF and brain tissue (hippocampus, cerebral cortex and cerebellum) were obtained from neonate rats on 1, 15 and 30 days postnatal. MeHg accumulation was measured in brain tissue after birth and on the 30th postnatal day. An increase of CSF S100B was observed on the 15th, but not on the 30th postnatal day. Hippocampal tissue demonstrated increased S100B (and reduction in glial fibrillary acidic protein) immediately after birth, but not later. No changes in the S100B content were observed in cerebellum and cerebral cortex. No changes were observed in the spatial learning of these rats at adult age. These specific and reversible changes in the hippocampus could be related to the cognitive and epileptic disorders attributed to MeHg. Our results further indicate the glial involvement in the MeHg-induced neurotoxicity. The increment of CSF S100B in neonates exposed to MeHg reinforces the view that increased S100B is related to damage in the nervous system and that S100B could be a marker for MeHg-neurotoxicity. Although the cellular mechanism related to MeHg-induced increase in S100B content in CSF remains unknown, our results suggest the use of S100B as a peripheral marker of brain damage induced by MeHg.
