Substantial reduction of cortical noradrenaline by lesions of adrenergic pathway does not prevent effects of monocular deprivation.

We tested the theory that depletion of noradrenaline reduces the plasticity of the visual cortex in kittens by using another method of depletion. Lesions were made in the lateral hypothalamus to interrupt fibers in the dorsal noradrenergic bundle going from the locus ceruleus to the telencephalon. The lesions were induced at approximately 3 1/2 weeks of age in kittens; approximately 2 weeks later one eye was sutured shut, and about 10 days after that cells were recorded in the visual cortex. The location of the lesions was verified histologically, and the effect of the lesions was verified by noradrenaline analyses (high pressure liquid chromatography-electrochemistry) of samples from the visual cortex. The noradrenaline content of the visual cortex was reduced by 70 to 90%. However, the majority of cells recorded in the visual cortex could not be driven through the eye that had been sutured closed. The ocular dominance histograms for cells in the visual cortex were indistinguishable from those of kittens that were monocularly deprived for a similar period in the "critical period" and that had normal amounts of noradrenaline in their visual cortex. Therefore, we conclude that reduction of the noradrenaline content of the visual cortex by 70 to 90% is insufficient, by itself, to prevent the physiological changes that occur in the visual cortex after monocular deprivation.