Increase of 5?-nucleotidase activity in some brain subcellular fractions after the administration of the convulsant 3-mercaptopropionic acid

Astrocytic response in hippocampus and cerebral cortex in an experimental epilepsy model

Astrocytes are very sensitive to alterations in the brain environment and respond showing a phenomenon known as astroglial reaction. S100beta is an astroglial derived neurotrophic factor, seems to be involved in neuroplasticity. The aim of this work was to study the astrocytic response in rat hippocampus and cerebral cortex after repetitive seizures induced by 3-mercaptopropionic acid (MP) administration. Immunocytochemical studies were performed to analyze GFAP and S100beta expression. Both studied areas showed hypertrophied astrocytes with enlarged processes and increased soma size. Astrocyte hyperplasia was observed only in the cerebral cortex. A significant decrease in the astrocytic S100beta immunostaining occurs after MP treatment. These results indicate that MP administration induces an astroglial reaction with reduced intracellular S100beta level. The observed reduction in astroglial S100beta could be related to the release of this factor to the extracellular space, where it may produce neurotrophic or deleterious effects accordingly to the concentration achieved. The mechanism of this remains to be elucidated.

Seizure activity produces differential changes in adenosine A1 receptors within rat hippocampus

Specific ligand binding to rat hippocampal adenosine A1 receptor after administration of the convulsant drug 3-mercaptopropionic acid (MP) was studied by means of a quantitative autoradiographic method. 2-Chloro-N6-[cyclopentyl-2,3,4,5-3H adenosine] ([3H]CCPA), a potent and selective A1 receptor ligand, was selected for binding studies. MP administration (150 mg/kg, i.p.), at seizure, caused significant increases in the following CA1 layers: pyramidal (45%), radiatum (18%) and lacunosum molecular (35%); in CA2 area, a significant decrease in stratum oriens (36%) and an increase in stratum radiatum (14%) and lacunosum molecular (33%) layers was observed. In CA3 area a rise in pyramidal (40%) and radiatum layers (26%), as well as in hillus (97%) was found. At postseizure, changes were restricted to CA1, CA2 and CA3 pyramidal layers and to CA1 lacunosum molecular layer, with increases ranging from 22 to 50%. These results show that [3H]CCPA binding is modified diversely in intrahippocampal layers and areas, thus indicating their dissimilar role in seizure activity.

Effects of an adenosine analogue administration on the striatal NMDA receptors in an experimental model of epilepsy

Specific [3H]-MK801 binding to rat NMDA receptors following the administration of the convulsant drug 3-mercaptopropionic acid (MP) and the adenosine analogue cyclopentyladenosine (CPA) was studied in striatal membrane fractions. MP administration (150 mg/kg, i.p.) caused an increase of 53% and 82% in [3H]-MK801 binding during seizure and the postseizure period respectively. Administration of CPA (2 mg/kg, i.p.) raised [3H]-MK801 binding by 72%. When CPA was administered 30 min before MP and rats sacrificed at seizure (CPA + MPc), an increase of 64%, was observed. Saturation results indicate that receptor sites increased their maximal binding capacity (Bmax) in all treatments while the apparent dissociation constant (Kd) remained unchanged. MP administration brought about an increase of 52% and 42% in [3H]-MK801 binding sites during seizure and postseizure respectively. Administration of CPA raised receptor density by 75%. When CPA was administered 30 min before MP and rats sacrificed at seizure (CPA + MPc), an increase of 62%, was observed. These results show that striatal NMDA receptors have a selective role in seizure activity in the basal ganglia and that the adenosine analogue administration may modify [3H]-MK801 binding in a way similar to that of the convulsant drug.

Striatum adenosine A2 receptors are modified during seizure: effect of cyclopentyladenosine administration

Rat CNS adenosine A2A receptors were studied after administration of the convulsant drug 3-mercaptopropionic acid (MP) and the adenosine analogue cyclopentyladenosine (CPA) by means of a quantitative autoradiographic method. Specific binding was quantified in striatum only. The highest density was found in caudate-putamen (2.50 fmol/mm2), followed by nuclei accumbens (1.85 fmol/mm2) and the lowest values in the olfactory tubercle (1.26 fmol/mm2). These differences were statistically significant. MP administration (150 mg/kg) caused significant increases (12-18%) in caudate-putamen and nuclei accumbens in both stages: seizure and postseizure and no changes in the olfactory tubercle. CPA administration (2 mg/kg) originated a rise of 16% in nuclei accumbens but no change in the other two regions. When CPA was injected 30 minutes before MP, an increase (18 to 45%) in caudate-putamen and nuclei accumbens at seizure and postseizure stages was observed. Saturation results, in striatal membrane fraction, indicate that receptor sites increased their maximal binding capacity (Bmax) while the apparent dissociation constant (Kd) remained unchanged. These results suggest the involvement of the adenosine A2A receptors in convulsant activity and that CPA administration at the dose selected brings about a rise in neuronal excitability in this area.

Regional vulnerability to oxidative stress in a model of experimental epilepsy

We evaluated oxidative stress associated with a model of experimental epilepsy. Male Wistar rats were injected i.p. with 150 mg/kg convulsant 3-mercaptopropionic acid and decapitated in two stages: during seizures or in the post-seizure period. Spontaneous chemiluminescence, levels of thiobarbituric acid reactive substances, total antioxidant capacity and antioxidant enzyme activities were measured in cerebellum, hippocampus, cerebral cortex and striatum. In animals killed at seizure, increases of 42% and 90% were observed in spontaneous chemiluminescence of cerebellum and cerebral cortex homogenates, respectively, accompanied by a 25% increase in cerebral cortex levels of thiobarbituric acid reactive substances. In the post-seizure stage, emission completely returned to control levels in cerebral cortex and partly in cerebellum, thus showing oxidative stress reversibility in time. Hippocampus and striatum seemed less vulnerable areas to oxidative damage. A 30% decrease in glutathione peroxidase activity was only observed in cerebral cortex during seizures, while catalase and superoxide dismutase remained unchanged in all four areas during either stage. Likewise, total antioxidant capacity was unaffected in any of the studied areas. It is suggested that oxidative stress in this model of epilepsy arises from an increase in oxidant species rather than from depletion of antioxidant defences.

Modification of [3H]MK801 binding to rat brain NMDA receptors after the administration of a convulsant drug and an adenosine analogue: a quantitative autoradiographic study

Specific [3H]MK801 binding to rat brain NMDA receptors after the administration of the convulsant drug 3-mercaptopropionic acid (MP) and the adenosine analogue cyclopentyladenosine (CPA) was studied by means of a quantitative autoradiographic method. MP administration (150 mg/kg, i.p.) caused significant decreases in [3H]MK801 binding in several hippocampus subareas and layers, mainly in CA1 and CA3 at seizure (11-27%) and postseizure (8-16%) and in cerebral occipital cortex at seizure (18-22%). In nucleus accumbens, a rise was observed at postseizure (44%) and a tendency to increase at seizure (24%). CPA (2mg/kg, i.p.) decreased ligand binding in hippocampus (CAI, CA2, CA3) (17-22%) and in occipital cerebral cortex (18-24%). When CPA was administered 30 minutes before MP (which delayed seizure onset) and rats were sacrificed at seizure, decreases in [3H]MK801 binding in several layers of CA1 and CA3 of hippocampus (11-27%) and in CA1, CA2, CA3 (24-35%) after CPA+MP postseizure, and an increase in CA2 after CPA and CPA+MP postseizure (20-34%), were observed. A drop was found in the occipital subarea (18-24%) after CPA and in the frontal and occipital subarea after CPA+MP postseizure (24-34%) while no changes were observed in any treatment involving the other cerebral cortex regions, thalamic nuclei, caudate putamen and olfactory tubercle. These results show that [3H]MK801 binding changes according to drug treatment and the area being studied, thus indicating a different role in seizure activity.

CNS adenosine A1 receptors are altered after the administration of convulsant 3-mercaptopropionic acid and cyclopentyladenosine: an autoradiographic study

Rat CNS adenosine A1 receptors were studied by quantitative autoradiography after the administration of convulsant 3-mercaptopropionic acid (MP) and an adenosine analogue cyclopentyladenosine (CPA), using 2-chloro-N6-[cyclopentyl-2,3,4,5-3H adenosine]-([3H]CCPA) as radioactive ligand. Specific binding was quantified in hippocampus, cerebellum, cerebral cortex, thalamic nuclei, superior colliculus and striatum, and the highest densities were found in CA1, CA2, and CA3 hippocampus subareas and the lowest levels in superior colliculus and striatum. MP administration (150 mg/kg, i.p.) produced significant increases in [3H]CCPA binding in CA1 subarea at seizure (15%) and postseizure (21%) and in CA2 at seizure (15%) but a tendency to decrease in dentate gyrus. There was an increase in cerebellum at seizure (18%) but no significant changes in the other studied regions. CPA injection (2 mg/kg, i.p.) enhanced [3H]CCPA binding in CA1 and CA2 areas (17-18%) but not in CA3 area of the hippocampus. When CPA was administered before MP, which delayed seizure onset, an increase in [3H]CCPA binding in CA1 hippocampus subarea (19%) and cerebellum (28%) was also observed. Results showed that the administration of convulsant MP and adenosine analogue CPA exerts differential effects on adenosine A1 receptors in CNS areas; hippocampus is the most affected area with all treatments, specially CA1 subarea, supporting an essential role in convulsant activity as well as in seizure prevention.

Area-specific modification of acetylcholinesterase activity following 3-mercaptopropionic acid-induced seizures

Acetylcholinesterase activity (AChE) was assayed in rat CNS membrane fractions after administration of the convulsant 3-mercaptopropionic acid (150 mg/kg, ip). In comparison with saline-injected controls, total AChE activity decreased 12-20% in striatum and cerebellum during seizure and postseizure but failed to change in cerebral cortex. Specific AChE activity, assayed in the presence of 10(-4) M ethopropazine (a butyrylcholinesterase inhibitor), decreased 15-25% in striatum and cerebellum, increased 20-45% in hippocampus, but remained unchanged in cerebral cortex. Saline injection alone increased AChE activity in striatum (68%) and cerebellum (36%) but failed to modify enzyme activity in hippocampus and cerebral cortex. To conclude, AChE sensitivity to convulsant and saline administration is tissue-specific and not restricted to cholinergic areas.

A study of 5'-nucleotidase activity in subcellular fractions of rat cerebellum after the administration of the convulsant 3-mercaptopropionic acid

The activity of 5'-nucleotidase in cerebellum subcellular fractions after the administration of the convulsant 3-mercaptopropionic acid was studied. This membrane enzyme presented an increase in its activity in certain fractions containing nerve endings and microsomes (Mic20, Mic100) in seizure and postseizure periods. 5'-nucleotidase activity in nuclear and myelin fractions did not show differences between the control and treated fractions. On the other hand, a decreased activity in the crude mitochondrial fraction and in a nuclear subfraction was found. It is suggested that the changes in the enzyme activity in some cerebellum fractions might be related to structural alterations previously observed in this laboratory and with the anticonvulsant actions of adenosine.