Characterization of the tetanus toxin model of refractory focal neocortical epilepsy in the rat.
OBJECTIVE
To characterize in detail a model of focal neocortical epilepsy.


METHODS
Chronic focal epilepsy was induced by injecting 25-50 ng of tetanus toxin or vehicle alone (controls) into the motor neocortex of rats. EEG activity was recorded from electrodes implanted at the injection site, along with facial muscle electromyographic (EMG) activity and behavioral monitoring intermittently for up to 5 months in some animals. Drug responsiveness was assessed by using the antiepileptic drugs (AEDs) diazepam (DZP) and phenytoin (PHT) delivered systemically, while 1,2,3,4-tetrahydro-6-nitro-2,3-dioxo-benzo[f]quinoxaline-7-sulfonamide (NBQX), a competitive antagonist at AMPA receptors, was administered directly to the brain to investigate the potential benefits of focal drug delivery.


RESULTS
Tetanus toxin induced mild behavioral seizures that persisted indefinitely in all animals. EEG spiking activity, occurring up to 80% of the time, correlated with clinical seizures consisting of interrupted behavioral activity, rhythmic bilateral facial twitching, and periods of abrupt motor arrest. Seizures were refractory to systemic administration of DZP and PHT. However, focal delivery of NBQX to the seizure site reversibly reduced EEG and behavioral seizure activity without detectable side effects.


CONCLUSIONS
This study provides a long-term detailed characterisation of the tetanus toxin model. Spontaneous, almost continuous, well-tolerated seizures occur and persist, resembling those seen in neocortical epilepsy, including cortical myoclonus and epilepsia partialis continua. The seizures appear to be similarly resistant to conventional AEDs. The consistency, frequency, and clinical similarity of the seizures to refractory epilepsy in humans make this an ideal model for investigation of both mechanisms of seizure activity and new therapeutic approaches.
Nilsen
Karen E
KE
Clinical Neurosciences (Epilepsy), Department of Cardiological Sciences, St. George's Hospital Medical School, London, England.
Walker
Matthew C
MC
Cock
Hannah R
HR
D000818:Animals; D000927:Anticonvulsants / Q000494:pharmacology; D001522:Behavior, Animal / Q000187:drug effects / Q000502:physiology; D001921:Brain / Q000187:drug effects / Q000502:physiology / Q000503:physiopathology; D003975:Diazepam / Q000494:pharmacology; D004195:Disease Models, Animal; D004569:Electroencephalography / Q000187:drug effects / Q000706:statistics & numerical data; D004576:Electromyography / Q000187:drug effects; D004828:Epilepsies, Partial / Q000139:chemically induced* / Q000175:diagnosis / Q000503:physiopathology; D005106:Exploratory Behavior / Q000187:drug effects / Q000502:physiology; D008297:Male; D009043:Motor Activity / Q000187:drug effects / Q000502:physiology; D019579:Neocortex / Q000187:drug effects / Q000503:physiopathology*; D010672:Phenytoin / Q000494:pharmacology; D011810:Quinoxalines / Q000494:pharmacology; D051381:Rats; D017207:Rats, Sprague-Dawley; D018091:Receptors, AMPA / Q000187:drug effects; D013744:Tetanus Toxin / Q000494:pharmacology
D000927:Anticonvulsants; D011810:Quinoxalines; D018091:Receptors, AMPA; D013744:Tetanus Toxin; C062865:2,3-dioxo-6-nitro-7-sulfamoylbenzo(f)quinoxaline; D010672:Phenytoin; D003975:Diazepam