Morphological, electrophysiological and biochemical changes have been shown to occur in the retina, lateral geniculate nucleus, and visual cortex of light deprived animals. We attempted to determine whether the dark-rearing of rats from birth to 15, 30 and 60 days of age alters the ability of noradrenaline (NA) 30 μM, potassium chloride (KCI) 50 μM, adenosine 30 μM and combinations of NA and KCI with adenosine to stimulate the _in vitro formation of cyclic AMP (cAMP) in visual cortical slices and, as an internal control, in frontal cortical slices. At 15 and 30 days of age there was an 11% and 2170 reduction, respectively, compared to normally reared controls, in the stimulation of cAMP formation in a 5 minute incubation with NA in both frontal and visual cortical slices. After 60 days of dark-rearing, however, this was reversed in that the NA stimulation of cAMP formation was 23% and 357» higher than controls in frontal and visual cortical slices. In frontal cortical slices of rats dark-reared for 15 and 30 days there was a significant reduction in the stimulation of cAMP formation in a 20 minute incubation with NA. No differences were observed between 30 day old experimental and control animals in studies of the accumulation of cAMP in frontal and visual cortical slices incubated for various times with KCI. The stimulation of cAMP formation induced by KCI and adenosine in a 5 minute incubation was 5770 and 397o higher, respectively, in frontal cortical slices of 60 day old experimental animals than controls while the response in visual cortical slices was unaffected. The differences found between 60 day old experimental and control animals were abolished in both visual and frontal cortical slices when adenosine was used in combination with NA or KCI. Studies of the accumulation of cAMP in slices incubated for various times with NA revealed that the effect observed in the visual cortex after 30 days of light deprivation was due to a decrease in the maximum level of cAMP reached within a 20 minute incubation period, whereas in the frontal cortex the maximum level attained within a 20 minute incubation period was unaffected. These results are discussed in terms of our present knowledge concerning supersensitivity and plasticity in the central nervous system and the role of cAMP in nerve. / Medicine, Faculty of / Biochemistry and Molecular Biology, Department of / Graduate