engleski

Tangentional migration in the human telencephalon during midestation: A Golgi study

Telencephalic GABA-ergic interneurons are very heterogeneous population that differs by their morphology, neurochemical contents, specificity of their connections and their physiological properties. In rodent all hippocampal and almost all cortical GABA-ergic interneurons are generated in the ventral (basal, subcortical) proliferative zones, the ganglionic eminence, and migrate tangentially to their target regions. Evolution of the cortex increased extremely the distance that interneurons have to pass, so in human fetuses migration of interneurons becomes extremely complex and more vulnerable event then in any other species. This might explain why disturbances of the GABA-ergic network are found in majority of neurological and psychiatric disorders. To study migrational routes of prospective GABA-ergic interneurons we describe spatial and temporal patterns of tangentionaly and nonradialy migrating like cells on frontal sectioned slices of the human fetal brain in period from 13.5 to 22 weeks of gestation using Stensaas modification of the Golgi-Del Rio Hortega method. This material was obtained from the Zagreb Neuroembryological Collection. Tangentional and nonradial migrating cells have oval, up to 10 microns in length, cell body with one process. In the ganglionic eminence many cells in the stream lack, or have shorter process, as the cell body was smaller. Through all stages examined, we found densely packed tangentionally oriented (in parallel with ventricular surface) migrating like cells that form a continuous stream through whole subventricular zone of the ganglionic eminence. This stream continues on the ventral and dorsal border of ganglionic eminence to upper subventricular and lower intermediate zone of the telencephalic anlage. This stream could be followed to the most medial located telencephalic parts, but their density decreased. There were individual cells leaving it, more on some specific position: (1) many individual cells leave ganglionic eminence and enter directly to striatum ; (2) on the dorsal emerge from ganglionic eminence, group of cells change their direction in the way to cortex ; (3) on the level of olfactory tubercule a ventral stream is divided on two parts: one continuing to medial located septal region, and another continuing to olfactory tract. However, many tangentionaly and nonradialy oriented migratory like cells were observed in all other fetal layers, with respect to ventricular zone in the early stages analyzed. The density of tangetionaly migrating cells was highest in the oldest stage analyzed and the thickness of the stream has also increased. However, in opposite to earlier stages density of nonradialy migrating neurons in other cortical layers, principally subplate, has decreased. This might be explained by dilution regarding huge increase in volume of the subplate through this period. Increase in number of tangentionaly migrating like cells up to second half of gestation becomes more important in the view that radial migration has decreased substantionaly. This suggests that intensive production of interneurons continued into the second half of gestation, while the production of projection neurons is decreasing rapidly. So, the final establishment of cortical circuitry seems mostly to be connected with formation of inhibitory elements.

interneurons; GABA; epilepsy

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