MORPHOLOGICAL AND GABA-IMMUNOREACTIVE DEVELOPMENT OF THE EMBRYONIC CHICK TELENCEPHALON

The development of neurons utilizing gamma-aminobutyric acid (GABAergi c neurons) in prosencephalon and telencephalon from chicken embryonic days 4-14 (E4-E14) was studied by means of immunohistochemistry, Furth ermore, routine histology and transmission electron microscopy, respec tively, were performed in order to study the morphological development in the designated area. The main finding is that development of GABAe rgic neurons in the chick telencephalon is rapid; the GABA neurons are appearing in bulk at day 8, being ''overexpressed'' at days 10-11, de creasing in numbers thereafter and achieving mature morphology on day 14, which is considerably faster than in the rodent. Morphological ana lysis revealed that the prosencephalon mainly consisted of a thin laye r of undifferentiated neuroblasts in the E4 embryo. By E6, the prosenc ephalon had increased in thickness and occasional cells outside the ne uroepithelium showed a more mature morphology with a few cells weakly staining positive for GABA. At E8, the prospective granular and subven tricular layers had developed. At E14, the appearance of the telenceph alon is approximating that of the adult since both ependymal cells and morphologically mature neurons can be seen.