Development of GABA binding sites in chick embryo optic lobe: effect of triton X-100.
The temporal course of the development of GABA receptor sites in chick optic lobe was studied as a parameter of neuronal differentiation in the central nervous system. At 10 days of incubation, specific [3H]GABA binding was of 0.08 pmol/optic lobe and increased 7-8 fold between 12 and 16 days of incubation, reaching at 16 days a value of 0.60 pmol/optic lobe. This coincides with the period of arrival of the retinal fibers to the optic lobe. After this stage, the number of GABA binding sites decreased to a value of 0.35 pmol/optic lobe at hatching. After hatching a new increase appeared which reached at 5 days post-hatching a value of 0.87 pmol/optic lobe. Scatchard analysis of the saturation binding data obtained at 16 days of incubation and at hatching revealed the presence of two binding sites: one with high affinity and the other with low affinity, while at 12 days of incubation, the earliest stage examined, only the low-affinity binding site appeared. The high-affinity binding site for [3H]GABA was inhibited by muscimol, GABA, and bicuculline (IC50: 0.006, 0.002 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 showed a marked increase in the amount of specific [3H]GABA binding after 16 days of incubation reaching a 3-fold increase at hatching. These results suggest that endogenous inhibitors of the higher affinity binding site, probably appear during this period.
Flores
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Instituto de Biología Celular, Facultad de Medicina, Universidad de Buenos Aires, Paraguay, Argentina.
Rios
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Fiszer de Plazas
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D000818:Animals; D002642:Chick Embryo / Q000187:drug effects / Q000378:metabolism*; D009419:Nerve Tissue Proteins / Q000378:metabolism; D017830:Octoxynol; D009899:Optic Lobe, Nonmammalian / Q000187:drug effects / Q000196:embryology / Q000378:metabolism*; D011092:Polyethylene Glycols / Q000494:pharmacology*; D011963:Receptors, GABA-A / Q000187:drug effects / Q000378:metabolism*
D009419:Nerve Tissue Proteins; D011963:Receptors, GABA-A; D011092:Polyethylene Glycols; D017830:Octoxynol