, 2011). These studies suggest that specific classes of interneurons derive from distinct regions of the subpallium to later colonize multiple cortical structures. Fast-spiking interneurons are a clear example of this circumstance. Transplantation and genetic fate-mapping studies have shown that selleck screening library the MGE is the origin of fast-spiking interneurons found in the amygdala, striatum,
piriform cortex, hippocampus, and neocortex (Marín et al., 2000, Pleasure et al., 2000, Tricoire et al., 2011, Wichterle et al., 2001 and Xu et al., 2008). Several lines of evidence suggest that distinct pools of progenitor cells within the MGE are specified to produce interneurons for each of these telencephalic structures. For instance, striatal and cortical interneurons seem to derive from different progenitor pools within the MGE (Flandin et al., 2010). Consistent with this notion, striatal and cortical interneurons are specified to reach their targets by expressing different complements of guidance receptors (Marín et al., 2001, Nóbrega-Pereira et al., 2008 and van den Berghe et al., 2013). In addition, the hippocampus contains certain classes of interneurons that do not seem to have a clear homolog in the neocortex, such as PV+/SST+ bistratified cells (Buhl et al., 1994). Similarly, VIP+
interneurons populate the cortex and the hippocampus but are absent from the striatum. Thus, it is conceivable that different pools of progenitor cells within the subpallium are specified to generate interneurons Pexidartinib concentration that see more migrate to specific subdivisions of the telencephalon (i.e., striatum, amygdala, neocortex, hippocampus). Does the same rule apply for different neocortical regions? If this were the case, then one would expect to observe a topographical relationship between the origin of a specific class of interneurons within the subpallium and their final distribution in the neocortex. Transplantation experiments in
slices have shown that the mediolateral distribution of GABAergic interneurons in the neocortex is not topographically related to their birthplace. So, irrespective of the site of origin in the MGE, interneurons tend to colonize the neocortex following a lateral to medial progression (Lourenço et al., 2012), in parallel to the normal maturation gradient of pyramidal cells (Bayer and Altman, 1987). Consistent with this notion, PV+ interneurons within the same layer are, on average, younger in the lateral third of the somatosensory cortex than in the medial third (Rymar and Sadikot, 2007). The mechanisms that control the regional distribution of neocortical interneurons are presently unclear, but several lines of evidence suggest that this process is related to the transition of interneuron migration from tangential to radial or, more precisely, to its timing (Figure 2).