nitrophenols and Status-Epilepticus

This study was performed to determine the effect of prolonged status epilepticus on the activity and subcellular location of a neuronally enriched, calcium-regulated enzyme, calcineurin. Brain fractions isolated from control animals and rats subjected to pilocarpine-induced status epilepticus were subjected to differential centrifugation. Specific subcellular fractions were tested for both calcineurin activity and enzyme content. Significant, status epilepticus-induced increases in calcineurin activity were found in homogenates, nuclear fractions, and crude synaptic membrane-enriched fractions isolated from both cortex and hippocampus. Additionally, significant increases in enzyme levels were observed in crude synaptic fractions as measured by Western analysis. Immunohistochemical studies revealed a status epilepticus-induced increase in calcineurin immunoreactivity in dendritic structures of pyramidal neurons of the hippocampus. The data demonstrate a status epilepticus-induced increase in calcineurin activity and concentration in the postsynaptic region of forebrain pyramidal neurons.

Topics: Animals; Calcineurin; Calcium; Calcium Signaling; Cell Compartmentation; Cell Nucleus; Cerebral Cortex; Dendrites; Disease Models, Animal; Hippocampus; Male; Nitrophenols; Organophosphorus Compounds; Phosphorylation; Pilocarpine; Prosencephalon; Pyramidal Cells; Rats; Rats, Sprague-Dawley; Status Epilepticus; Synaptic Membranes; Synaptosomes; Up-Regulation

This study focused on the effects of status epilepticus on the activity of calcineurin, a neuronally enriched, calcium-dependent phosphatase. Calcineurin is an important modulator of many neuronal processes, including learning and memory, induction of apoptosis, receptor function and neuronal excitability. Therefore, a status epilepticus-induced alteration of the activity of this important phosphatase would have significant physiological implications. Status epilepticus was induced by pilocarpine injection and allowed to continue for 60 min. Brain region homogenates were then assayed for calcineurin activity by dephosphorylation of p-nitrophenol phosphate. A significant status epilepticus-dependent increase in both basal and Mn(2+)-dependent calcineurin activity was observed in homogenates isolated from the cortex and hippocampus, but not the cerebellum. This increase was resistant to 150 nM okadaic acid, but sensitive to 50 microM okadaic acid. The increase in basal activity was also resistant to 100 microM sodium orthovanadate. Both maximal dephosphorylation rate and substrate affinity were increased following status epilepticus. However, the increase in calcineurin activity was not found to be due to an increase in calcineurin enzyme levels. Finally, increase in calcineurin activity was found to be NMDA-receptor activation dependent. The data demonstrate that status epilepticus resulted in a significant increase in both basal and maximal calcineurin activity.

Topics: Animals; Brain; Calcineurin; Cerebral Cortex; Disease Models, Animal; Dizocilpine Maleate; Hippocampus; Kinetics; Male; Nitrophenols; Organ Specificity; Organophosphorus Compounds; Pilocarpine; Protein Tyrosine Phosphatases; Rats; Rats, Sprague-Dawley; Seizures; Status Epilepticus; Substrate Specificity