Consequences of pilocarpine-induced recurrent seizures in neonatal rats

Accumulated evidence have shown that a series of morphological alternations occur in patients with epilepsy and in different epileptic animal models. Given most of animal model studies have been focused on adulthood stage, the effect of recurrent seizures to immature brain in neonatal period has not been well established. This study was designed to observe the certain morphological changes following recurrent seizures occurred in the neonatal rats. For seizure induction, neonatal Wistar rats were intraperitoneally injected with pilocarpine on postnatal day 1 (P1), P4 and P7. Rat pups were grouped and sacrificed at 1d, 7d, 14d and 42d after the last pilocarpine injection respectively. Bromodeoxyuridine (BrdU) was intraperitoneally administered 36h before the rats were sacrificed. BrdU single and double labeling with neuronal markers were used to analyze cell proliferation and differentiation. Nissl and Timm staining were performed to evaluate cell loss and mossy fiber sprouting. Rats with neonatal seizures had a significant reduction in the number of Bromodeoxyuridine-(BrdU) labeled cells in the dentate gyrus compared with the control groups when the animals were killed either 1 or 7 days after the third seizure (P<0.05) but there was no difference between two groups on P21. On the contrary, BrdU-labeled cells significantly increased in the experimental group compared with control group on P49 (P<0.05). The majority of the BrdU-labeled cells colocalized with neuronal marker-NF200 (Neurofilament-200). Nissl staining showed that there was no obvious neuronal loss after seizure induction over all different time points. Rats with the survival time of 42 days after neonatal seizures developed to increased mossy fiber sprouting in both the CA3 region and supragranular zone of the dentate gyrus compared with the control groups (P<0.05). Taken together, the present findings suggest that synaptic reorganization only occurs at the later time point following recurrent seizures in neonatal rats, and neonatal recurrent seizures can modulate neurogenesis oppositely over different time window with a down-regulation at early time and up-regulation afterwards.