Neurotransmitters also appear to play a role in migration, especially GABA and dopamine. While migrating internruons express GABAA and GABAB receptors, reducing GABA levels leads to a decrease in the number of interneurons that cross into the cortical wall. In addition, migrating interneurons also have D1 and D2 dopamine receptors. Whereas D1 nulls show decreased ability to migrate, D2 knockoutss are show an increased propensity to migration. This suggests that D1 and D2 normally function to promote or inhibit, respectively, cortical interneuron migration.
Why are there two mechanisms of migration? Radial migration produces a one to one mapping between the originating location in the embryonic brain and the final destination in the cortex. Tangential migration does not depend on physical pathways established by RGCs and thus allows neurons from a given region to be distributed to multiple cortical regions in a one-to-many pattern. This may allow for an increase in the complexity of the cortical circuitry.
Cellular and molecular mechanisms controlling the migration of neocortical interneurons \cite{Mar_n_2013}
we have discovered that the leading process of migrating neurons has relatively distinct morphologies in different classes of neurons, probably reflecting their adaptation to specific microenvoronments. In contrast to the simplicity of the single leading process reported for radially migrating pyramidal cells, tangentially migrating neurons display very elaborated leading process morphologies.
In these cells, leading process branches are stabilized or retracted in binary decisions that determine the direction followed by the nucleus during nucleokinesis and this process is intimately linked to their directional guidance.