Abstracts

Intracerebral (i.c) administration of glutamate analogs (ibotenate, an NMDA and metabotropic receptor agonist or S-bromowillardiine, an AMPA/kainate agonist) to newborn mouse pups induces damage mimicking lesions observed in human pre-term and full-term neonates. The primary objective of the present study was to determine the neuroprotective properties of Topiramate (TPM) in the ibotenate or S-bromowillardiine mouse model of neonatal neuro-degeneration. Secondary aims were, to gain insight into the mechanism of neuroprotection induced by TPM.
Mouse pups were injected i.c. with 10 [micro]g ibotenate, dissolved in phosphate buffer saline (PBS) or with 15 [micro]g S-bromowillardiine dissolved in PBS. TPM was administered according to 3 different schedules : a) immediately following the i.c. injection with the excitotoxin, pups received a single intraperitoneal (i.p.) injection of TPM (1, 10 or 30 mg/kg) or of PBS; b) 60 minutes prior to the i.c. injection with the excitotoxin, pups received a single i.p. injection of TPM (10 mg/kg) or of PBS; c) one injection TPM (10 or 30 mg/kg) per day, between P5 and P10, starting immediately after the excitotoxin injection. To study transduction pathways underlying TPM-induced neuroprotection against S-bromowillardiine mediated brain lesions P5 pups were injected i.c. with one of the following drugs or combination of drugs: 15 [micro]g S-bromowillardiine alone; 15 [micro]g S-bromowillardiine + an inhibitor (0,1 [micro]g bisindolilmalmeimide I (PKC inhibitor); 1 [micro]g U-73122 (phospholipase C inhibitor); 3 [micro]g PD98059 (inhibitor MAPK); 5 [micro]g H89 (PKA inhibitor); 1 [micro]g Calmidazolium (calmodulin-dependent PK[ndash]inhibitor); 0.1[micro]g Wortmannin (phosphatidylinositol 3-OH kinase inhibitor); 0.02 [micro]g Okadaic acid (protein phosphatase 1A and 2A inhibitor). Five days following excitotoxin injection (P10), surviving pups were decapitated and brains processed for histology to determine brain lesion size.
In the ibotenate model, TPM had no detectable effect on excitotoxic cortical plate and white matter lesions. Injection of a single dose TPM immediately following S-bromowillardiine induced a dose-dependent neuroprotection of both the cortical plate and white matter lesions. Pre-treatment with 10 mg/kg TPM was significantly neuroprotective for both types of lesions while post-treatment with the same dose was did not induce a significant protection of the white matter lesion. Finally, post-treatment with 10 or 30 mg/kg TPM for 5 days induced significant neuroprotection both for the cortex and white matter ; however, the level of neuroprotection reached with this regimen was not different from the protection obtained with a single dose given immediately after the insult. TPM-induced neuroprotection against S-bromowillardiine toxicity was blocked by inhibitors of PKC, phospholipase-C and protein phosphatase.
In the S-bromowillardiine model, TPM is neuroprotective for both cortical plate and white matter.
[Supported by: a grant from Johnson [amp] Johnson Pharmaceutical Research and Development, LLC.]