| dc.description | The visual cortex of the cat is immature at birth and requires visual experience for the development of normal anatomical and functional properties. This requirement for visual experience has been demonstrated from examination of dark-reared kittens in which the functional properties of visual cortical cells have been shown to remain at much the same level as is observed in an immature animal. Despite the severity of this deficit, remarkable recovery of function can occur following the introduction short periods of visual experience (as little as six hours). In view of the speed with which they are expressed and their potential functional role in controlling the transcription of other genes, immediate early genes (IEGs) represent part of the potential mechanisms by which visually evoked activity could be translated to rapid cellular changes. This possibility was explored in this thesis which used immunohistochemical techniques to examine the expression of the IEG, c-fos, in the visual cortex of dark-reared kittens that subsequently received short periods of visual exposure. In contrast to control animals that were not visually exposed, the visual cortex of dark-reared animals revealed high levels of Fos-like immunoreactivity, particularly after one to two hours. Fos-like immunoreactive nuclei were absent in the dorsal lateral geniculate nucleus, and in area 17, were most numerous in the extragranular layers (2, 3, and 6) but sparse in lower layer 4 and layer 5, and virtually absent from layer 1. The laminar distribution of Fos-like immunoreactive nuclei in these animals is not consistent with explanations for Fos expression that are solely activity-based. Furthermore, the substantially higher levels and different pattern of Fos-like immunoreactivity observed in normal kittens as compared to adults is consistent with the notion that Fos plays a role in, or at least is expressed in parallel with, the widespread visually induced anatomical changes during development. In the supragranular layers of the animals exposed for two hours, Fos-like immunoreactive nuclei were non-uniformly distributed in a columnar fashion that was most evident in area 17 of the kittens that were dark-reared until either three or four weeks. This pattern of Fos-like immunoreactivity appears to reveal a transiently expressed, previously unexpected form of intrinsic modular organization. The exact function of these Fos-like immunoreactive columns is unknown. However, it is evident that the columns of Fos-like immunoreactive nuclei are not eye-related as similar tangential patterns were observed in animals monocularly or binocularly exposed. The nature of the role that Fos or other IEGs play in development could, in the future, be explored by experiments that use anti-sense oligonucleotides to block the function(s) of these genes. | en_US |
