Abstracts

Neonatal prolonged seizures may cause long term functional changes which in certain cases may increase the risk for subsequent epilepsy. Using a model of 3 episodes of neonatal kainic acid induced status epilepticus (KA-SE), we have shown that the normal GABAA receptor mediated differentiation of the substantia nigra pars reticulata (SNR) and its role in seizure control are disrupted. Here we investigate whether the 3 episodes of neonatal KA-SE also lead to long term changes in GABAA receptor subunit expression, which could alter its sensitivity to GABAAergic drugs., Male Sprague-Dawley rats were subjected to 3 daily episodes of KA-SE at postnatal days (PN) 4, 5, and 6 by intraperitoneal injections of KA (PN4: 1.25mg/kg ; PN5: 1.5 mg/kg; PN6: 2 mg/kg) and were monitored behaviorally for 6 hours daily (n=8 rats, KA456 group). Micropunches from the anterior SNR were obtained at PN30. RT-PCR using primers specific for the a1 - a6, b2, g1, g2L, delta GABAA receptor subunits, the rho1 GABAC receptor subunit, and beta-actin were performed. RT-PCR products were electrophoretically separated and compared by densitometry with the subunit expression of control PN30 male anterior SNR (n=7 rats). Results were referred to beta-actin., Control male PN30 anterior SNR expressed the following subunits: a1 [gt] b2, a5, g2L [gt] g1, a2 [gt] a3, a4, delta , rho1. The a6 subunit was not expressed, whereas low expression of rho1 was detected in 2/7 control rats. In the PN30 KA456 male rats, the following subunits were reduced compared to controls: (1) a1 subunit (P[lt] 0.05, unpaired t-test); (2) the a3 subunit was not present in 5/3 KA456 rats, whereas it was present in all studied controls (chi square P = 0.01); (3) the g1 subunit also tended to be reduced in KA456 males (unpaired t-test P=0.055). No significant changes in the other subunits were seen., The anterior SNR of PN30 control male rats had a relative dominance of benzodiazepine-sensitive subtypes, over the extrasynaptic and steroid sensitive delta-containing subtypes. The PN30 KA456 male anterior SNR had reduced expression of the a1 and a3, and showed a trend for reduced expression of the g1 subunit. These suggest that the sensitivity to certain benzodiazepine GABAA receptor agonists - ie those selective for a1, a3, and possibly g1 - may be reduced in KA456 rat anterior SNR. Since a1-selective GABAAergic drugs can mediate anticonvulsant effects through their actions on the PN30 anterior SNR, further studies are needed to test whether the reduction of a1 subunits in KA456 rats may be a mechanism of drug refractoriness to the anticonvulsant effects of certain GABAAergic drugs, especially those selectively acting on a1-containing receptors., (Supported by NIH NINDS grants NS045243 and NS20253 and a Rett Syndrome Research Foundation grant.)