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Ouabain induced seizures: site of production and response to anticonvulsants
Abstract:
Ouabain, an inhibitor of Na+ -K" -ATP'ase, has been administered intraventricularly to rats to study the effect of impairment of membrane transport mechanisms on the genesis of seizures. Running and leaping seizures occur rapidly after injection of ouabain in a low volume (10 microliter) when the maximal uptake of ouabain (39.8%) is the hippocampus. Generalized clonic-tonic seizures are induced by higher volume injections (50 microliter) associated with wider distribution of ouabain, including the cerebellum and brainstem. Ouabain was injected into cerebral cortex, caudate nucleus, dorsal hippocampus, fastigeal nucleus, ventrolateral mesencephalic reticular formation and cerebellar cortex. The cerebellar injections produced both running and leaping and generalized clonic-tonic seizures. It is suggested that this results from decreased inhibitory effect of vermal and paravermal Purkinje cells on intra-cerebellar nuclei, which alters cerebellar influence on the reticular formation and the limbic system. Diphenylhydantoin, phenobarbitone, phenacemide, carbamezepine and clonazepam but not ethosuximide are effective against generalized clonic-tonic seizures, suggesting that this is a model for "grand mal" but not "petit mal" seizure mechanisms. It is furthermore suggested that running and leaping are subcortical, probably limbic, seizures that are most relevant as a model for temporal lobe seizures.
Insights
Ouabain, a Na+-K+-ATPase inhibitor, induces distinct seizure types in rats. Hippocampal ouabain causes limbic seizures, while broader distribution, including the cerebellum, triggers generalized seizures, offering models for epilepsy research.
Area of Science:
- Neuroscience
- Pharmacology
- Epilepsy Research
Background:
- Membrane transport mechanisms are crucial for neuronal function.
- Impairment of these mechanisms can lead to neurological disorders like seizures.
- Ouabain is a specific inhibitor of the Na+-K+-ATPase pump.
Purpose of the Study:
- To investigate the effects of impaired membrane transport on seizure genesis.
- To characterize seizure types induced by intraventricular ouabain administration in rats.
- To establish a potential animal model for different epilepsy types.
Main Methods:
- Intraventricular administration of ouabain in rats at varying volumes (10 µL and 50 µL).
- Targeted injections into specific brain regions including the hippocampus, cerebellum, and brainstem.
- Evaluation of seizure phenotypes (running, leaping, generalized clonic-tonic).
- Assessment of anticonvulsant efficacy of various drugs.
Main Results:
- Low-volume ouabain (10 µL) primarily affected the hippocampus, inducing running and leaping seizures (limbic/temporal lobe model).
- High-volume ouabain (50 µL) distributed more widely, including the cerebellum, causing generalized clonic-tonic seizures (grand mal model).
- Cerebellar injections induced both seizure types.
- Generalized seizures were responsive to diphenylhydantoin, phenobarbitone, phenacemide, carbamazepine, and clonazepam, but not ethosuximide.
Conclusions:
- Ouabain-induced seizures in rats provide distinct models for temporal lobe and generalized (grand mal) epilepsy.
- Cerebellar involvement is implicated in the generation of both seizure types.
- The study highlights the role of Na+-K+-ATPase function in seizure pathophysiology.