cytochalasin-d and Brain-Ischemia

The fungal toxin cytochalasin D as well as endogenous gelsolin depolymerize filamentous actin which may induce dynamic uncoupling of membrane ion channels. In vitro application of cytochalasin D reduced NMDA-induced [(3)H]noradrenaline release from mouse brain neocortical slices by 38%. In gsn deficient neocortical synaptosomes [Ca(2+)](i) increase in response to K(+) (30 mM) depolarization was 33% higher than in wild-type. After transient focal cerebral ischemia K(+)-induced [Ca(2+)](i) increase in neocortical synaptosomes was 56% lower than in synaptosomes prepared from the non-ischemic contralateral hemisphere. After in vivo pretreatment with cytochalasin D 10 min before MCA occlusion K(+)-induced [Ca(2+)](i) increase in synaptosomes in vitro prepared 1 h after reperfusion from the ischemic hemisphere was only 25% lower than in contralateral synaptosomes, while cytochalasin D pretreatment in vivo did not reduce K(+)-induced [Ca(2+)](i) increase in vitro. Hence, presynaptic Ca(2+) influx and subsequently neuronal vulnerability are attenuated by increased and are aggravated by decreased F-actin depolymerization.

Topics: Adrenergic alpha-Agonists; Animals; Biological Transport; Brain Ischemia; Calcium; Cerebral Cortex; Cytochalasin D; Cytoskeleton; Gelsolin; In Vitro Techniques; Mice; Mice, Inbred C57BL; N-Methylaspartate; Norepinephrine; Nucleic Acid Synthesis Inhibitors; Potassium; Synaptosomes; Tritium

Applying the recently developed DNA array technique to a murine stroke model, we found that the gene coding for RhoB, a member of the family of GTPases that regulate a variety of signal transduction pathways, is upregulated in ischemia-damaged neurons. RhoB immunoreactivity precedes DNA single-strand breaks and heralds the evolving infarct, making it an early predictor of neuronal death. Expression of RhoB colocalized with drastic rearrangement of the actin cytoarchitecture indicates a role for Rho in postischemic morphological changes. Apoptosis in a murine hippocampal cell line was also associated with an early increase in RhoB protein. Activation of caspase-3, a crucial step in apoptosis, could be inhibited by cytochalasin D, a substance that counteracts the actin-modulating activity of Rho GTPases, indicating that Rho proteins may have impact on injury-initiated neuronal signal transduction. Our findings make Rho GTPases potential targets for the development of drugs aimed at limiting neuronal death following brain damage.

Topics: Actin Cytoskeleton; Animals; Apoptosis; Brain Infarction; Brain Ischemia; Caspase 3; Caspases; Cells, Cultured; Cytochalasin D; Disease Models, Animal; DNA Damage; DNA, Single-Stranded; Gene Expression; Hippocampus; Immunohistochemistry; Mice; Mice, Inbred C57BL; Nerve Degeneration; Neurons; Oligonucleotide Array Sequence Analysis; Predictive Value of Tests; Reperfusion Injury; rhoB GTP-Binding Protein; RNA, Messenger; Time Factors; Up-Regulation