Enhanced Excitability Induced by Ionizing Radiation in the Kindled Rat

Evidence derived from both clinical and experimental investigations has suggested an influence of ionizing radiation on focal epileptogenicity. To better characterize this influence we applied focal ionizing radiation to a kindled epileptic focus in the rat amygdala. The right and left basolateral a...

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Bibliographic Details
Published in:	Experimental neurology Vol. 169; no. 1; pp. 96 - 104
Main Authors:	Jenrow, K.A., Ratkewicz, A.E., Elisevich, K.V.
Format:	Journal Article
Language:	English
Published:	Amsterdam Elsevier Inc 01-05-2001 Elsevier
Subjects:	amygdala Amygdala - physiopathology Amygdala - radiation effects Animals Behavior, Animal - radiation effects Biological and medical sciences Disease Models, Animal Disease Progression Dose-Response Relationship, Radiation Electric Stimulation Electrodes, Implanted Epilepsies, Partial - physiopathology epilepsy Frontal Lobe - physiopathology Gamma Rays Headache. Facial pains. Syncopes. Epilepsia. Intracranial hypertension. Brain oedema. Cerebral palsy hyperexcitability kindling Kindling, Neurologic - radiation effects Male Medical sciences Motor Activity - radiation effects Nervous system (semeiology, syndromes) Neural Inhibition - radiation effects Neurology radiation Rats Rats, Wistar seizure Sensory Thresholds epilepsy amygdala hyperexcitability seizure radiation kindling Monthly Amygdala Rat Pathogenesis Brain stem Epilepsy Epileptic focus Frontal cortex Ionizing radiation Weekly Radiation effect Neurological disorder Status epilepticus Nervous system diseases Bipolar electrode Kindling Rodentia Single dose Excitability Cerebral disorder Vertebrata Mammalia Convulsion Animal Central nervous system disease Irradiation Clinical investigation Hippocampus
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Summary:	Evidence derived from both clinical and experimental investigations has suggested an influence of ionizing radiation on focal epileptogenicity. To better characterize this influence we applied focal ionizing radiation to a kindled epileptic focus in the rat amygdala. The right and left basolateral amygdala and right frontal cortex were implanted with concentric bipolar electrodes. Rats were kindled through a minimum of 10 stage 5 seizures by afterdischarge-threshold electrostimulation of the left amygdala, after which generalized seizure thresholds were determined prior to irradiation. The left amygdala was exposed to single-fraction central-axis doses of either 18 or 25 Gy using a beam-collimated 60Co source (1.25 MeV). Generalized seizure thresholds were then redetermined at weekly intervals for 10 weeks and at monthly intervals for an additional 3 months. We observed no significant changes in seizure threshold during the postirradiation interval; however, we did observe persistent changes in seizure dynamics manifesting within the first week postirradiation. These consisted of an increased tendency for seizure activity to propagate into brain stem circuits during the primary ictus (i.e., “running fits”) and an increased tendency for secondary convulsions to emerge postictally. These effects involving seizure dynamics have not been reported previously and appear to represent a radiation-induced disinhibition of one or more neural circuits. The disparity between these effects and earlier reports of seizure-suppressive effects resulting from analogous radiation exposures is discussed in relation to kindling and status epilepticus-induced pathogenesis within the hippocampus.
ISSN:	0014-4886 1090-2430
DOI:	10.1006/exnr.2000.7616