Inhibitory interneurons in focal cortical dysplasia and microdysgenesis

Abstract

Commonly identified cortical malformations in patients undergoing epilepsy surgery for intractable seizures include focal cortical dysplasia (FCD) and microdysgenesis (MD). Both are characterized by abnormalities in the cortical laminar architecture and in FCD the presence of dysplastic neurons and balloon cell glia are also observed. The aetiology and mechanisms of seizure genesis in these lesions is still questioned, as is the distinction of cellular changes that are developmental rather than a consequence of seizures. We investigated the distribution of calcium binding protein (calbindin‐CB, parvalbumin‐PV and calretinin‐CR), Neuropeptide Y and reelin positive cells in 12 cases of FCD and in 12 temporal lobectomy specimens from patients with hippocampal sclerosis with or without additional MD. The majority of FCD cases showed a reduction in PV interneurons but abnormal PV puncta around dysplastic neurons. Hypertrophic multipolar CB cells were commonly seen in FCD cases whereas smaller multipolar CB cells were present in MD. Altered NPY patterns were observed in FCD and a prominent superficial NPY plexus in some MD. Significantly higher numbers of reelin positive cells were present in layer I in MD compared with controls (P < 0.05) but were more variable in FCD with reduction of layer I reelin in some FCD cases.