Effects of light- and dark-rearing on the postnatal development of GABA receptor sites in the chick optic lobe.
To investigate the ability of GABA receptor sites to undergo environmental-dependent plastic changes, the postnatal developmental pattern of GABA receptors was studied under different levels of light stimulation, i.e. normal-, light- and dark-rearing. At hatching the specific binding of [3H]GABA was 1.74 +/- 0.36 pmol/optic lobe. In normally reared chicks the number of GABA binding sites showed a transient increase with the highest value at the 6th day (7.0 +/- 1.32 pmol/optic lobe). This value is higher than the one reached at the adult stage. Between the 3rd and 6th day, there was a 33.7% increase in specific [3H]GABA binding in light-reared compared with normally reared animals (P less than 0.05). In the dark-reared chicks, the specific binding was 36.4% lower than that found in normally reared (P less than 0.02). However, the changes in receptor density were transient since at the 17th day the number of GABA binding sites returned to adult levels. Scatchard analysis revealed that the differences observed in the high affinity GABA binding sites between the three groups were due to modifications in the total number of binding sites while the affinity remained unchanged. The maximal number of binding sites were: 2.71, 7.01 and 1.79 pmol/mg protein in normally, light- and dark-reared chicks, respectively; while the apparent dissociation constants were unaffected: 3.2, 3.4 and 3.6 nM, respectively. These results show that, during postnatal development, different conditions of visual experience produce synaptic changes at the molecular level. These changes probably occur within a period of high plasticity, prior to the end of a critical period.
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Instituto de Biología Celular, Facultad de Medicina, Universidad de Buenos Aires, Argentina.
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D000375:Aging / Q000378:metabolism* / Q000502:physiology; D000818:Animals; D002645:Chickens; D007700:Kinetics; D008029:Lighting; D009929:Organ Size; D011506:Proteins / Q000378:metabolism; D011963:Receptors, GABA-A / Q000378:metabolism* / Q000502:physiology; D003336:Tectum Mesencephali / Q000254:growth & development / Q000378:metabolism* / Q000502:physiology; D014795:Visual Pathways / Q000378:metabolism* / Q000502:physiology
D011506:Proteins; D011963:Receptors, GABA-A