Differential activation of the cortical visual areas in visually deprived rats.

The distribution of Fos-like protein, suggested to be a sensitive marker for neuronal activity, was studied in the visual cortex of 60 days old rats which were either blind congenitally and had their eyelids remained closed, or were born normally in terms of their visual apparatus but were dark reared, or were dark reared and exposed to light shortly before sacrifice, or were normal and reared in normal ambient light. Regardless of the primary cause, light deprivation produced a striking increase in Fos immunoreactivity, mainly in visual areas 17 and 18 a, with Fos-positive cells predominantly located in laminae IV and VI. Exposure of dark reared rats to ambient light further enhanced Fos immunoreactivity but it did not change the distribution pattern of Fos-immunoreactive neurons.