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Developmental expression of glycine immunoreactivity and its colocalization with GABA in the embryonic chick
A C Berki1, M J O'Donovan, M Antal
1Department of Anatomy, University Medical School, Debrecen, Hungary.
Insights
Glycine immunoreactivity appears later than GABA in chick spinal cord development. Their combined neuron populations remain constant, with distinct distribution patterns and colocalization emerging early.
Area of Science:
- Neuroscience
- Developmental Biology
- Neurochemistry
Background:
- Glycine and gamma-aminobutyric acid (GABA) are key inhibitory neurotransmitters in the spinal cord.
- Understanding their developmental trajectories is crucial for comprehending neural circuit formation.
Purpose of the Study:
- To investigate the developmental timeline and distribution of glycine immunoreactivity in the embryonic and posthatched chick lumbosacral spinal cord.
- To compare the development of glycine- and GABA-ergic neurons to identify distinct and overlapping characteristics.
Main Methods:
- Postembedding immunocytochemical methods were employed to detect glycine immunoreactivity.
- Data on GABA-ergic neuron development from previous studies were utilized for comparative analysis.
Main Results:
- Glycine immunoreactivity was first observed at embryonic day 8 (E8), significantly later than GABA (E4).
- Glycine-positive neurons increased from E8, while GABA-positive neurons decreased in the ventral horn, maintaining a constant total inhibitory neuron population.
- Distinct spatial distributions and significant colocalization of glycine and GABA immunoreactivity were observed throughout development.
Conclusions:
- Glycine and GABA exhibit differential developmental timing and distribution patterns in the chick spinal cord.
- The balance between glycinergic and GABAergic neurons is maintained during the latter half of embryonic development.
- The study provides insights into the development of inhibitory interneurons and their roles in spinal cord function.
Abstract:
The development of immunoreactivity for the putative inhibitory amino acid neurotransmitter glycine was investigated in the embryonic and posthatched chick lumbosacral spinal cord by using postembedding immunocytochemical methods. Glycine immunoreactive perikarya were first observed at embryonic day 8 (E8) both in the dorsal and ventral gray matters. The number of immunostained neurons sharply increased by E10 and was gradually augmented further at later developmental stages. The general pattern of glycine immunoreactivity characteristic of mature animals had been achieved by E12 and was only slightly altered afterward. Most of the immunostained neurons were located in the presumptive deep dorsal horn (laminae IV-VI) and lamina VII, although glycine-immunoreactive neurons were scattered throughout the entire extent of the spinal gray matter. By using some of our previously obtained and published data concerning the development of gamma-aminobutyric acid (GABA)-ergic neurons in the embryonic chick lumbosacral spinal cord, we have compared the numbers, sizes, and distribution of glycine- and GABA-immunoreactive spinal neurons at various developmental stages and found the following marked differences in the developmental characteristics of these two populations of putative inhibitory interneurons. (i) GABA immunoreactivity was expressed very early (E4), whereas immunoreactivity for glycine appeared relatively late (E8) in embryonic development. (ii) In the ventral horn, GABA immunoreactivity declined, whereas immunoreactivity for glycine gradually increased from E8 onward in such a manner that the sum of glycinergic and GABAergic perikarya remained constant during the second half of embryonic development. (iii) Glycinergic and GABAergic neurons showed different distribution patterns in the spinal gray matter throughout the entire course of embryogenesis as well as in the posthatched animal. When investigating the colocalization of glycine and GABA immunoreactivities, perikarya immunostained for both amino acids were revealed at all developmental stages from E8 onward, and the proportions of glycine- and GABA-immunoreactive neurons that were also immunostained for the other amino acid were remarkably constant during development. The characteristic features of the development of the investigated putative inhibitory spinal interneurons are discussed and correlated with previous neuroanatomical and physiological studies.