ABSTRACT
PURPOSE: This study was conducted to characterize the early cellular changes in CaM kinase II activity that occur during the induction of status epilepticus (SE). METHODS: The pilocarpine model of SE was characterized both behaviorally and electrographically. At specific time points after the first discrete seizure, specific brain regions were isolated for biochemical study. Phosphate incorporation into a CaM kinase II-specific substrate, autocamtide III, was used to determine kinase activity. RESULTS: After the development of SE, the data show an immediate inhibition of both cortical and hippocampal CaM kinase II activity in homogenate, but a delayed inhibition in synaptic kinase activity. The maintenance of synaptic kinase activity was due to a translocation of CaM kinase II protein to the synapse. However, despite the translocation of functional kinase, CaM kinase II activity was not maintained, membrane potential was not restored, and the newly translocated CaM kinase II did not terminate the SE event. Unlike the homogenate samples, in the crude synaptoplasmic membrane (SPM) subcellular fractions, a positive correlation is found between the duration of SE and the inhibition of CaM kinase II activity in both the cortex and hippocampus. CONCLUSIONS: The data support the hypothesis that alterations of CaM kinase II activity are involved in the early events of SE pathology.
Subject(s)
Calcium-Calmodulin-Dependent Protein Kinases/metabolism , Cerebral Cortex/enzymology , Hippocampus/enzymology , Muscarinic Agonists/pharmacology , Pilocarpine/pharmacology , Status Epilepticus/chemically induced , Status Epilepticus/enzymology , Animals , Behavior, Animal/drug effects , Behavior, Animal/physiology , Brain Mapping , Calcium-Calmodulin-Dependent Protein Kinase Type 2 , Calcium-Calmodulin-Dependent Protein Kinases/antagonists & inhibitors , Cerebral Cortex/metabolism , Disease Models, Animal , Electroencephalography , Enzyme Inhibitors/pharmacology , Hippocampus/metabolism , Male , Membrane Potentials/drug effects , Membrane Potentials/physiology , Peptides/metabolism , Rats , Rats, Wistar , Status Epilepticus/metabolism , Subcellular Fractions/drug effects , Subcellular Fractions/enzymology , Synapses/enzymology , Time Factors , Tissue DistributionABSTRACT
This study was conducted to characterize the post-pubertal developmental aspects on seizure susceptibility and severity as well as calcium/calmodulin protein kinase type II (CaM kinase II) activity in status epilepticus (SE). Thirty- to ninety-day-old rats, in 10-day increments, were studied. This corresponds to a developmental age group that has not received thorough attention. The pilocarpine model of SE was characterized both behaviorally and electrographically. Seven criteria were analyzed for electrographical characterization: seizure severity, SE susceptibility, the average number of discrete seizures, average time until first seizure, average time to SE, average time from first discrete seizure to SE, and death. After 1 h of SE, specific brain regions were isolated for biochemical study. Phosphate incorporation into a CaM kinase II-specific substrate, autocamtide III, was used to determine kinase activity. There was no developmental effect on the average number of discrete seizures, average time until first seizure, average time to SE, average time from first discrete seizure to SE, and death; however, there was a significant effect on SE probability and seizure severity. Once SE was expressed, all animals showed a decrease in both cortical and hippocampal CaM kinase II activities. Conversely, seizure activity in the absence of SE did not result in a decrease in CaM kinase II activity. The data suggest that there is a gradual age-dependent modulation of SE susceptibility and seizure severity within the developmental stages studied. Additionally, once status epilepticus is observed at any age, there is a corresponding SE-induced inhibition of CaM kinase II.
