Altered distribution of inhibitory interneurons in polymicrogyria

There is a high incidence of epilepsy in patients with polymicrogyria; however, the epileptogenic mechanisms are largely unknown. The density of parvalbumin-immunoreactive interneurons was evaluated in an experimental model of polymicrogyria, in order to assess the potential changes in the development of one population of inhibitory interneurons. Newborn hamsters received an intracerebral injection of ibotenate, and all injected animals showed abnormal cortical layers characterized by one or two microgyrus in the fronto-parietal cortex. A quantitative analysis revealed that the ratios of parvalbumin-immunoreactive neurons in total neurons were significantly reduced in the medial paramicrogyral area, and in the medial and central parts of microgyrus in comparison to that in the lateral part of microgyrus (P < 0.01). The lateral paramicrogyral area had the greatest number of parvalbumin-immunoreactive neurons, which was increased significantly in comparison to that in the control cortex (P < 0.01). We suggest that the callosal, thalamic and intracortical afferents to the microgyrus and paramicrogyral area may induce a remarkable imbalance between the excitatory and inhibitory activities of the cortical structures, associated with the epileptogenic mechanism in polymicrogyria.