engleski

Protracted development of ganglionic eminence in the monkey and human brain

Previous studies have demonstrated that in primates, cortical GABAergic neurons (cxGABAn) are first generated exclusively by the ganglionic eminence (GE), resembling spatial pattern in origin of cxGABAn in rodents. Then, during the second trimester of gestation cxGABAn are massively produced in the newly evolved outer subventricular zone of the pallium. This massive production of cxGABAn by pallium progenitors reported in primates could be an evolutionary answer to provide cxGABAn to a complex and expanded cortex. How the GE contribute to cxGABAn production during this second trimester of gestation remains to be established. For this purpose we investigate the development of the primate GE during the stage when pallial production of cxGABAn occurs. Our data indicate that there is no decrease in the proliferative capability of the GE up to midgestation both in human and monkey when cxGABAn are generated in the pallium. In the rhesus monkey no decrease was observed in a stream of GAD65-containing tangentially migrating cells arising from the GE up to the embryonic day (E)75. In addition, a pool of GAD/Ki65 labeled progenitors was still observed in the GE. Golgi impregnated sections from human fetuses aged 22-26 post- conceptual week (pcw), illustrated clearly streams of densely packed cells leaving the GE toward the dorsal telencephalon. At 32-36 pcw streams of migratory-like cells extended in ventro-dorsal direction from the GE at the position of cortico-striatal border. At this developmental stage, the GE displayed decreased size but was still clearly distinguishable. Many of these nonradially oriented migratory cells leaving the GE were labeled for MAP-2 and calretinin. These data suggests that the GE conserves its proliferative properties to generate cxGABAn during pallial production of cxGABAn. Furthermore, the GE reaches a maximum peak of cxGABAn production at the beginning of the second half of gestation, when the vast majority of principal cortical glutamatergic neurons have already been generated. In keeping with this observation, volumetric analyses of GE from in vivo MRI images of 15 human fetuses aged 13-32 pcw demonstrates a maximum size of the GE around 18-20 pcw and persistence of GE through the entire third trimester of gestation. These data suggest a protracted period for cxGABAn production from the GE in human fetuses. Therefore, a pallial production but also subpallial protracted neurogenesis are a hallmark of cxGABAn development in primates.

GABA; ganglionic eminence; primate

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