Loss of synapses in the entorhinal-dentate gyrus pathway following repeated induction of electroshock seizures in the rat.
The goal of this study was to answer the question of whether repeated administration of electroconvulsive shock (ECS) seizures causes structural changes in the entorhinal-dentate projection system, whose neurons are known to be particularly vulnerable to seizure activity. Adult rats were administered six ECS seizures, the first five of which were spaced by 24-hr intervals, whereas the last two were only 2 hr apart. Stereological approaches were employed to compare the total neuronal and synaptic numbers in sham- and ECS-treated rats. Golgi-stained material was used to analyze dendritic arborizations of the dentate gyrus granule cells. Treatment with ECS produced loss of neurons in the entorhinal layer III and in the hilus of the dentate gyrus. The number of neurons in the entorhinal layer II, which provides the major source of dentate afferents, and in the granular layer of the dentate gyrus, known to receive entorhinal projections, remained unchanged. Despite this, the number of synapses established between the entorhinal layer II neurons and their targets, dentate granule cells, was reduced in ECS-treated rats. In addition, administration of ECS seizures produced atrophic changes in the dendritic arbors of dentate granule cells. The total volumes of entorhinal layers II, III, and V-VI were also found to be reduced in ECS-treated rats. By showing that treatment with ECS leads to partial disconnection of the entorhinal cortex and dentate gyrus, these findings shed new light on cellular processes that may underlie structural and functional brain changes induced by brief, generalized seizures.
Cardoso
Armando
A
Department of Anatomy, Porto Medical School, Porto, Portugal.
Assunção
Marco
M
Andrade
José P
JP
Pereira
Pedro A
PA
Madeira
M Dulce
MD
Paula-Barbosa
Manuel M
MM
Lukoyanov
Nikolai V
NV
D000818:Animals; D002452:Cell Count; D018891:Dentate Gyrus / Q000473:pathology* / Q000528:radiation effects; D004597:Electroshock / Q000009:adverse effects*; D018728:Entorhinal Cortex / Q000473:pathology* / Q000528:radiation effects; D008297:Male; D046529:Microscopy, Electron, Transmission / Q000379:methods; D019599:Mossy Fibers, Hippocampal / Q000473:pathology / Q000648:ultrastructure; D009434:Neural Pathways / Q000473:pathology / Q000528:radiation effects; D009474:Neurons / Q000473:pathology* / Q000648:ultrastructure; D051381:Rats; D017208:Rats, Wistar; D012640:Seizures / Q000209:etiology* / Q000473:pathology*; D016622:Silver Staining / Q000379:methods; D013569:Synapses / Q000473:pathology* / Q000528:radiation effects / Q000648:ultrastructure; D013997:Time Factors