EXPRESSION OF 2 FORMS OF GLUTAMIC-ACID DECARBOXYLASE (GAD67 AND GAD65) DURING POSTNATAL-DEVELOPMENT OF CAT VISUAL-CORTEX

The postnatal development of GAD67 and GAD65 protein expression and of GAD67 positive neurons and GAD65 containing axon terminals in cat vis ual cortex was studied. Western blot analysis showed that the expressi on of both GAD67 and GAD65 increased to approximately two-thirds of th e adult level during the first 5 postnatal weeks and gradually increas ed thereafter. In adult cats, immunohistochemistry showed that GABA an d GAD67 containing neurons were found in all cortical layers. Faint ce ll body staining was seen with the antibody to GAD65, but it densely l abeled puncta. In neonates, GABA and GAD67 immunoreactivity was most i ntense in two distinct bands, one superficial (Layer 1/Marginal zone), another deep (Layer VI/Subplate). Unlike in adults, GAD65 positive ce ll bodies were clearly evident in neonates and distributed similarly t o, but less frequently than, GABA and GAD67. These GAD65 positive cell s frequently had morphologies suggestive of embryonic cells and largel y disappeared in older animals. During postnatal development, the neur ochemical differentiation of GAD67 positive neurons and GAD65 positive axon terminals across visual cortical laminae followed an inside-outs ide developmental pattern, which reached adult levels after 10 weeks o f age. These results suggest that postnatal development of the visual cortical GABA system involves three distinct processes: (A) a dying of f of embryonic GABA cells which could play a role in formation of the cortical plate; (B) a period of relative quiescence of the VC GABA sys tem in the first 5 postnatal weeks which could maximize excitatory NMD A effects during the rising phase of the critical period; (C) the prol onged postnatal maturation of the adult GABA system which could be inv olved in the crystallization of adult physiological properties and the disappearance of neural plasticity. (C) 1997 Elsevier Science B.V.