Effects of intracortical infusion of 6-hydroxydopamine on the response of kitten visual cortex to monocular deprivation

Summary

Between 4 and 10 weeks of age 10 normally reared kittens were bilaterally implanted with osmotic minipumps. The visual cortex of one hemisphere was infused with 4 mM 6-hydroxydopamine while the other hemisphere received only a vehicle solution. The pumps delivered the solutions at 1 μl/h for one week concurrent with monocular deprivation. Subsequent electrophysiological recording was performed blind and revealed a marked effect of the 6-OHDA treatment: while most cells in the control hemisphere were primarily activated by stimulation of the non-deprived eye, cells in the 6-OHDA-treated hemisphere were significantly more binocular. High pressure liquid chromatography revealed that the loss of normal ocular dominance plasticity in 6-OHDA-infused hemispheres was always accompanied by at least a 50% decrease in cortical norepinephrine levels and a smaller decrease in dopamine levels. Furthermore, there appeared to be a positive correlation of the degree of ocular dominance shift and the relative amount of norepinephrine present. These results are consistent with the hypothesis that catecholamines, especially norepinephrine, are normally required for ocular dominance plasticity during the critical period in kittens.