Ocular dominance plasticity and developmental changes of 5′-nucleotidase distributions in the kitten visual cortex

The distribution of the adenosine‐producing ecto‐enzyme 5′‐nucleotidase was investigated histochemically in the visual cortex of normally reared and monocularly deprived kittens and cats. In normally reared kittens aged between 11 to 44 days, 5′‐nucleotidase activity formed a band of intense neuropil staining throughout conical layer IV of areas 17 and 18. The other layers were almost devoid of reaction product. Between the 4th and 6th week, this band had a patchy appearance in area 17, the center‐to‐center spacing of 5′‐nucleotidase patches being approximately 1 mm. Monocular enucleation accentuated these patches of enhanced 5′‐nucleotidase activity or made them reappear at developmental stages at which they had normally faded. Simultaneous visualization of ocular dominance columns by transneuronal transport of intraocularly injected 3H‐proline showed that the patches of enhanced 5′‐nucleotidase activity coincided with the territories of afferents from the intact eye. With increasing age and normal visual development, the patches disappeared and 5′‐nucleotidase activity spread to the supra‐ and infragranular layers. The adult pattern was characterized by dense staining of all cortical laminae in both areas 17 and 18 and was established at about 8 weeks of age. At approximately 7 weeks of age, when the patches in layer IV had disappeared in the course of normal development, monocular enucleation caused a reappearance of the discontinuous pattern of 5′‐nucleotidase activity in layer IV. These results reveal a close relation between the distribution of 5′‐nucleotidase and the time course of the developmental phase during which the visual cortex is susceptible to experience‐dependent alterations. As suggested by the correlation between sites of enzyme activity and eye dominance columns, the expression of 5′‐nucleotidase patches in layer IV appears to be associated with the remodelling of ocular dominance territories that occurs both in normal development and after manipulation of afferent retinal input Thus, 5′‐nucleotidase is likely to serve a function in activity‐dependent modifications of cortical circuitry. Moreover, 5′‐nucleotidase activity is the only endogenous marker known to date that exhibits a columnar pattern in cat visual cortex.