Structural changes in the neocortex as correlates of variations in EEG spectra and seizure susceptibility in rat brains with different degrees of dysplasia

Disturbances of the early stages of neurogenesis lead to irreversible changes in the structure of the mature brain and its functional impairment, including increased excitability, which may be the basis for drug-resistant epilepsy. The range of possible clinical symptoms is as wide as the different stages of disturbed neurogenesis may be. In this study, we used a quadruple model of brain dysplasia by comparing structural and functional disorders in animals whose neurogenesis was disturbed with a single dose of 1 Gy of gamma rays at one of the four stages of neurogenesis, that is, on days 13, 15, 17, or 19 of prenatal development. When reached adulthood, the prenatally irradiated rats received EEG teletransmitter implantation. Thereafter, pilocarpine was administered and significant differences in susceptibility to seizure behavioral symptoms were detected depending on the degree of brain dysplasia. Before, during, and after the seizures significant correlations were found between the density of parvalbumin-immunopositive neurons located in the cerebral cortex and the intensity of behavioral seizure symptoms or increases in the power of particular EEG bands. Neurons expressing calretinin or NPY showed also dysplasia-related increases without, however, correlations with parameters of seizure intensity. The results point to significant roles of parvalbumin-expressing interneurons, and also to expression of NPY-an endogenous anticonvulsant and neuroprotectant reducing susceptibility to seizures and supporting neuronal survival.