The plastic response to monocular deprivation persists in kitten visual cortex after chronic depletion of norepinephrine

In order to clarify the role of norepinephrine (NE) in visual cortical plasticity, we monocularly deprived kittens that had received systemic injections of the neurotoxin 6-hydroxydopamine (6-OHDA) shortly after birth. We found, using high pressure liquid chromatography, that this means of drug treatment produces a permanent and substantial reduction in the level of cortical NE as compared with littermate controls. Nonetheless, single unit recording in area 17 of these kittens revealed no difference in the cortical response to monocular deprivation: both drug-treated and control kittens displayed large ocular dominance shifts to the open eye. Because local depletion of NE by intracortical 6-OHDA in kittens can prevent the expected ocular dominance shift after short-term monocular deprivation, we propose that neocortex has the capacity to compensate for chronic depletion of NE in a way which allows for the possibility of plastic changes.