Increased seizure susceptibility and up-regulation of nNOS expression in hippocampus following recurrent early-life seizures in rats

Abstract

This study aimed to determine the long-term change of seizure susceptibility and the role of nNOS on brain development following recurrent early-life seizures in rats. Video-EEG recordings were conducted between postnatal days 50 and 60. Alterations in seizure susceptibility were assayed on day 22 or 50 using the flurothyl method. Changes in nNOS expression were determined by quantitative immunoblotting on day 50. On average, rats had 8.4+/-2.7 seizures during 10 daily 1 hr behavioral monitoring sessions. As adults (days 50-60), all rats displayed interictal spikes in the hippocampus and/or overlying cortex. Brief electrographic seizures were recorded in only one of five animals. Rats appeared to progress from a period of marked seizure susceptibility (day 22) to one of lessened seizure susceptibility (day 50). Up-regulation of nNOS expression following early-life recurrent seizures was observed on day 50. In conclusion, these data suggested that recurrent early-life seizures had the long-term effects on seizure susceptibility late in life and up-regulatory nNOS expression on the hippocampus during brain development, and nNOS appeared to contribute to the persistent changes in seizure susceptibility, and epileptogenesis.

Keywords: Early-life; Epileptogenesis; Hippocampus; Rat; Recurrent Seizures; Seizure Susceptibility; nNOS.

Fig. 1

Behavioral monitoring of seizures in infant rats. Average seizures during the 10 hr of observation (one hour/1 day for 10 days); 8.4±2.73, Seizure frequency peaks; within 24-48 hr. WRS, wild running seizure; TNTX, tetanus toxin.

Fig. 2

Vedeo-EEG monitoring on day 50-60. (A) Recordings from 3 control rats display no epileptiform activity. (B, C) Video EEG recordings from 5 rats that had experienced recurrent seizures in early-life; all displayed frequent interictal spikes in the hippocampus and/or neocortex but only 1 had electrographic seizures (B). This rat had brief electrographic events that had no behavioral accompaniments. Vertical arrows (↑) indicate an interictal spike. R, right; L, left; H, hippocampus; O, occiput; C, cortex; NC, normal control; TNTX, tetanus toxin.

Fig. 3

Changes in seizure susceptibility between on day 22 and 50. (A) A marked increase in seizure susceptibility is observed on day 22, when compared to litter mate controls. (B) A small (15%) but significant decrease in the time to onset of seizures is observed on day 50. NC, normal control; SC, saline control; TNTX, tetanus toxin injected.

Fig. 4

Expression of nNOS level in the hippocampal subfield, CA1, CA3, and dentate gyrus of the right hippocampus on day 45 following recurrent seizures on day 10. Distinctively, the significant up-regulation of nNOS is revealed in the CA1 and CA3 subfields of the hippocampus. However, there is statistically no change in nNOS expression level in the dentate gyrus. NC, normal control; SC, saline control; TNTX, tetanus toxin injected; DG, dentate gyrus.