VISUAL-ACTIVITY IS REQUIRED TO MAINTAIN THE PHENOTYPE OF SUPRAGRANULAR NPY NEURONS IN RAT-AREA-17

Visual activity governs the functional maturation of the mammalian vis ual cortex. We report here, that visual experience is required for sta bilizing the phenotype of a subset of cortical interneurons. Neurons e xpressing neuropeptide Y mRNA (NPY neurons) display a transiently high er expression in the early postnatal visual areas 18a and 17 that is f ollowed by a phenotype restriction during the second postnatal month: about 50% of the NPY neurons in supragranular and infragranular layers of area 18a, and in infragranular layers of area 17 gradually stop th e NPY expression. In contrast, the expression remains unchanged in sup ragranular layers of area 17. Dark rearing rats iron birth to up to 10 0 days does neither prevent the developmental onset of NPY mRNA expres sion, nor does it prevent the phenotype restriction from occurring. In contrast, in dark reared animals NPY neurons in supragranular layers of area 17 now also undergo a phenotype restriction. Returning animals to light after variable periods of darkness results in an upregulatio n of NPY mRNA expression selectively in neurons in supragranular layer s of area 17. These neurons acquire a constitutive expression during t he second postnatal month. This suggests that the phenotypic specifica tion of a distinct subset of cortical interneurons is regulated by vis ual experience which thus influences on the maturation of the neuroche mical architecture of area 17.