The Journal of Comparative Neurology

Prenatal bilateral enucleation induces cortex, which normally would have become striate cortex, to follow a default developmental pathway and to take on the cytoarchitectonic appearance of extrastriate cortex (default extrastriate cortex, Dehay et al. [1996] J. Comp. Neurol. 367:70-89). We have investigated if this manipulation influences the cortical expression of acetylcholinesterase (AChE) and cytochrome oxidase (GO). Early enucleation (before embryonic day 81; E81) had only minor effects on the distribution of AChE and CO in the striate cortex. In animals that underwent operation, the striate cortex CO blobs were significantly more closely spaced on the operculum compared with the calcarine. After early enucleation, there was a periodic distribution of CO dense patches in default extrastriate cortex. These CO patches had a center-to-center spacing that was considerably smaller than that of CO stripes in normal area V2, but was somewhat larger than that of the CO blobs in striate cortex. Although the GO stripes characteristic of normal area V2 could not be detected, there were some high-frequency CO patches, similar to those found in default extrastriate cortex. Early enucleation caused a failure to form the transient AChE bands running perpendicular to the striate border, which are normally present in the fetus and early neonate. Late enucleation did not alter AChE expression in extrastriate cortex. The relatively minor effects of early enucleation in the reduced striate cortex contrast with the changes in expression of these enzymes in extrastriate cortex, which accompany large shifts in the location of the striate border. This suggests a massive reorganisation of cortical phenotype in extrastriate cortex. a 1996 Wiley-Liss, Inc. Indexing terms: primate, plasticity, vision, striate cortex, extrastriate cortex The presence of the retinae during prenatal development is essential for the normal specification of the dimensions of monkey striate cortex (Rakic, 1988; Dehay et al., 1989, 1991, 1996; Rakic et al., 1991). Early fetal bilateral enucleation (before embryonic day 81; E81) leads to a reduction in the dimensions of area 17 which, however, retains its normal lamination. Quantitative measurements of different cortical regions have provided evidence that this large reduction of striate cortex is accompanied by an expansion of extrastriate cortex (Dehay et al., 1996). These results support the conclusion that early enucleation leads to a border shift and that cortex immediately surrounding the reduced striate cortex was destined to become striate cortex. This amounts to the respecification of a cortical area and is, therefore, of considerable theoretical interest. However, the cortex immediately surrounding the reduced striate cortex in the early enucleate has a cytoarchitecture indistinguishable from that of the extrastriate cortex in the Accepted July 12,1996. Address reprint requests to Henry Kennedy, INSERM U371,18 Av Doyen Lepine, 69675 Bron, Cedex, France. E rnail:[email protected] O 1996 WILEY-LISS, INC. ENUCLEATION AND MONKEY VISUAL CORTEX