Neocortical VIP neurons are increased in the hemisphere containing focal cerebrocortical microdysgenesis in New Zealand Black mice.

Twenty to forty percent of New Zealand Black mice, a strain that develops severe autoimmune disease and learning deficits, exhibit focal unilateral collections of ectopic neurons and glia in layer I of the neocortex with underlying laminar dysplasia. This type of anomaly traditionally has been considered to represent disordered neuronal migration. In an attempt to further characterize these abnormalities, we compared counts of immunohistochemically-stained VIP-neurons in cortical regions containing ectopias and in adjacent cortex to homologous regions of the opposite hemisphere. There was an overall increase in the number of these neurons in the hemisphere containing the ectopias, which resulted from an increase in the number of VIP neurons both in the column of cortex within and underlying the ectopias and in the medially adjoining columns. We concluded that the presence of ectopias in the cerebral cortex not only represent abnormal migration, but also an increase in the number of at least one subset of neurons.