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Ontogenesis of GABA receptor sites in chick embryo cerebellum
Insights
GABA receptor sites in chick embryo cerebellum develop alongside synaptic junctions. Binding affinity increases significantly from incubation to hatching, reaching adult levels at birth.
Area of Science:
- Neuroscience
- Developmental Biology
- Biochemistry
Background:
- GABAergic neurotransmission is crucial for cerebellar function.
- Understanding the development of GABA receptors is key to comprehending cerebellar maturation.
Purpose of the Study:
- To investigate the developmental timeline of GABA receptor sites in the chick embryo cerebellum.
- To correlate GABA receptor development with synaptogenesis.
Main Methods:
- Quantification of specific [3H]GABA binding at different embryonic stages.
- Scatchard analysis to characterize binding sites at birth.
- Inhibition studies using GABAergic ligands and Triton X-100 treatment.
Main Results:
- Specific [3H]GABA binding increased 3-fold between 15 days of incubation and hatching, reaching adult levels by birth.
- Two binding sites for [3H]GABA were identified at birth (KdS 40 and 174 nM).
- High-affinity binding was inhibited by muscimol, GABA, imidazoleacetic acid, and bicuculline, consistent with synaptic GABA receptors.
Conclusions:
- GABA receptor development in the chick cerebellum parallels the formation of synaptic junctions.
- The emergence of GABA-modulin, which inhibits GABA binding, also occurs during this developmental period.
Abstract:
The time-course of the development of GABA receptor sites in chick embryo cerebellum was correlated with the appearance of synaptic junctions in the cerebellar cortex. At 13 days of incubation, the earliest stage examined, specific [3H]GABA binding was only 19% of that found in cerebella of adult chicks. Between 15 days of incubation and hatching, specific [3H]GABA binding increased 3-fold, already reaching at birth adult values. During this period the number of synaptic junctions also increased. Scatchard analysis of the binding data obtained at birth revealed two binding sites of KdS 40 and 174 nM and a maximal number of binding sites (n) of about 1.6 and 4.0 pmol/mg protein, respectively. The high-affinity binding site for [3H]GABA was inhibited by muscimol, GABA, imidazoleacetic acid and bicuculline (IC50: 0.007, 0.020, 0.1 and 10 microM, respectively). These values correspond to the potencies shown by those compounds in the binding to the synaptic GABA receptor. Treatment of the synaptic membranes with Triton X-100 enhanced [3H]GABA binding depending on the developmental stage studied, suggesting that GABA-modulin that inhibits the binding also appears during that period.