Abstracts

RATIONALE: F-actin filaments are intimately involved in both controlling dendritic spine shapes and in the attachment of glutamate receptors and interacting postsynaptic proteins. Excessive glutamate excitatory activity induces F-actin depolymerization in dendritic spines. However, F-actin disruption and the consequential dendritic spine loss is generally supposed to be an effect of epileptic seizures, not a cause. We have previously shown that direct disruption of F-actin filaments with single perfusions of latrunculin A induces long-term changes in neuronal excitability as measured by picrotoxin seizure thresholds [1]. On these basis, we have studied, for the first time in living animals, the effect of repeated perfusions of latrunculin A and jasplakinolide.
METHODS: Latrunculin A affects actin polymerization by the formation of a 1:1 molar complex with G-actin, causing net actin depolymerization [2]. Jasplakinolide induces in vivo monomeric actin polymerization into amorphous masses, preventing the normal use of actin monomers by the neuron [3]. In order to study their effect on neuronal excitability, both substances were dissolved in ringer fluid (2, 4 and 6 [mu]g/ml) and perfused into the rat hippocampus during 8 hours for several consecutive days using a CMA/120 microdialysis system for freely moving animals and CMA/12 microdialysis probes, with continuous EEG and videotape recording. Control EEG monitoring was performed at least twice a week on each animal during the following six months.
RESULTS: Repeated perfusions of both latrunculin A and jasplakinolide induced epileptic seizures during days of perfusion 2 to 4. During the 6 months following administration, sporadic seizures were observed in 80% of the animals (0.4[plusminus]0.3 seizures/month for latrunculin A; 1.7[plusminus]1.3 for jasplakinolide). Seizures were more frequent from the 2nd to the 6th month after latrunculin A or jasplakinolide administration. Seizure duration and severity varied among animals, however, partial seizures were observed more frequently.
CONCLUSIONS: In vitro studies show that latrunculin A induces a loss of dendritic spines and glutamate receptor reorganization. Both are features found in patients with chronic focal epilepsy [4]. Our results indicate that direct F-actin disruption may be a good new experimental model of chronic epilepsy and epileptogenesis.
REFERENCES:
[1] Sierra-Paredes et al., Epilepsia 41, suppl 7, 23 (2000)
[2] Spector et al., D. Cell. Motil. Cytoskeleton 13, 127-144 (1989)
[3] Bubb et al., J. Biol. Chem. 275, 5163-5170 (2000)
[4] Multani et al., Epilepsia 35, 728-736 (1994)
Support: Supported by Grant XUGA PGIDT00PXI20807PR from Xunta de Galicia, Galicia, Spain.