Abstracts

There is controversy as to whether early-life seizures are harmful as the immature brain is relatively resistant to seizure-induced neurodegeneration. However, abnormal migration of developing neurons or neuronal precursors may contribute to aberrant anatomical connections and increased incidence of seizures with maturation The retrograde tracer carbocyanine dye 1,1[apos]-dioctadecyl-3,3,3[apos],3[apos]-tetramethylindo-carbocyanine perchlorate (DiI) and 4-chloromethyl benzol amino tetramethyl rhodamine (CMTMR) were used to determine whether proliferating precursor cells disperse to distant limbic locations in the postnatal brain with increasing number of perinatal seizures. Immunohistochemistry with precursor neuronal and non-neuronal markers was used to identify the cell types affected. Kainic acid (KA) was administered intraperitoneally (i.p.) three times (3xKA), once on postnatal (P) days P6, P9, and P13. DiI or CMTMR was stereotaxically injected bilaterally into the dorsal ventricular zone (VZ) of P13 pups three hours after the third KA-induced seizure. Animals were sacrificed after 5 days or 45 days. In controls, diffuse labeling was observed only near the infusion site and few DiI labeled cells co-localized with nestin, an undifferentiated neural stem cell marker, at 5 and 45 days; however a few precursor-like cells lined the third ventricle at both times. In contrast, after 3xKA and 5 days and even more so after 45 days many cells migrated from the injection site and formed a chain notably into ventral cortico-amygdala and ventral hypothalamic structures. A striking overabundance of cell proliferation was observed within the third ventricle that increased with maturation. This was not observed in age-matched adults with one long episode of KA-induced status epilepticus and 5 days. Nestin and NeuN co-expressed with many immature cells labeled with DiI or CMTMR near the VZ and in distant thalamic and amygdala structures. Co-localization of the third ventricle with GFAP was also observed. Oligodendrocyte and non-neuronal cell precursor markers, vimentin, A2B5, and RIP antibodies also co-localized in either VZ, corpus collosum, thalamic or limbic structures. Co-localization suggests that a number of neural precursors originate from the VZ and may eventually differentiate into neurons in distant locations to alter appropriate target innervations and induce latent epileptic disease. Co-labeling with non-neuronal cell types suggests that early-life seizures increase ventricular astrocytosis during the course of development and simultaneously increase proliferating oligodendrocytes to contribute to previously unrecognized long-term perinatal-induced seizure pathology. (Supported by New York College of Osteopathic Medicine of NYIT and NJ Neuroscience Institute.)