TRANSIENT INTRA-AREAL AXONS IN DEVELOPING CAT VISUAL-CORTEX

Transient axons reaching the medialmost part of area 17 were demonstra ted with anterogradely transported biocytin injected in the dorsal par t of the lateral gyrus in kittens during the first and second postnata l weeks. The axons decreased in number during the third postnatal week and were only exceptionally found thereafter. Computer-aided reconstr uctions from serial sections demonstrated axons with different degrees of complexity. The most complex ones were found at postnatal days 7-9 and were characterized by multiple branches terminating with growth c ones in the white matter. Characteristically, endings of axons that en tered the cortex remained confined to the infragranular layers V and V I. A few axons entered the supragranular layers. Transient axons termi nated with different endings, which may indicate different stages of m aturation. A few, possibly permanent, axons were still found in the me dial part of area 17 at the end of the first, and during the second po stnatal months; they arborized widely in the infragranular layers, and modestly or not at all supragranularly.