A cellular mechanism for dendritic spine loss in the pilocarpine model of status epilepticus.
OBJECTIVE
Previous studies have documented a synaptic translocation of calcineurin (CaN) and increased CaN activity following status epilepticus (SE); however, the cellular effect of these changes in CaN in the pathology of SE remains to be elucidated. This study examined a CaN-dependent modification of the dendritic cytoskeleton. CaN has been shown to induce dephosphorylation of cofilin, an actin depolymerization factor. The ensuing actin depolymerization can lead to a number of physiological changes that are of interest in SE.


METHODS
SE was induced by pilocarpine injection, and seizure activity was monitored by video-EEG. Subcellular fractions were isolated by differential centrifugation. CaN activity was assayed using a paranitrophenol phosphate (pNPP) assay protocol. Cofilin phosphorylation was assessed using phosphocofilin-specific antibodies. Cofilin-actin binding was determined by coimmunoprecipitation, and actin polymerization was measured using a triton-solubilization protocol. Spines were visualized using a single-section rapid Golgi impregnation procedure.


RESULTS
The immunoreactivity of phosphocofilin decreased significantly in hippocampal and cortical synaptosomal samples after SE. SE-induced cofilin dephosphorylation could be partially blocked by the preinjection of CaN inhibitors. Cofilin activation could be further demonstrated by increased actin-cofilin binding and a significant depolymerization of neuronal actin, both of which were also blocked by CaN inhibitors. Finally, we demonstrated a CaN-dependent loss of dendritic spines histologically.


CONCLUSIONS
The data demonstrate a CaN-dependent, cellular mechanism through which prolonged seizure activity results in loss of dendritic spines via cofilin activation. Further research into this area may provide useful insights into the pathology of SE and epileptogenic mechanisms.
Kurz
Jonathan E
JE
Department of Neurology, Virginia Commonwealth University, Richmond, Virginia 23298, USA.
Moore
Bryan J
BJ
Henderson
Scott C
SC
Campbell
John N
JN
Churn
Severn B
SB
D000199:Actins / Q000378:metabolism; D000704:Analysis of Variance; D000818:Animals; D001921:Brain / Q000473:pathology / Q000648:ultrastructure*; D019703:Calcineurin / Q000378:metabolism; D003712:Dendrites / Q000187:drug effects / Q000473:pathology; D049229:Dendritic Spines / Q000187:drug effects / Q000473:pathology*; D004195:Disease Models, Animal; D051937:Dopamine and cAMP-Regulated Phosphoprotein 32 / Q000378:metabolism; D047468:Immunoprecipitation / Q000379:methods; D010766:Phosphorylation; D010862:Pilocarpine; D051381:Rats; D017207:Rats, Sprague-Dawley; D016622:Silver Staining / Q000379:methods; D013226:Status Epilepticus / Q000139:chemically induced / Q000473:pathology*; D013347:Subcellular Fractions / Q000648:ultrastructure; D013997:Time Factors
D000199:Actins; D051937:Dopamine and cAMP-Regulated Phosphoprotein 32; C497930:Ppp1r1b protein, rat; D010862:Pilocarpine; D019703:Calcineurin