Effects of monocular deprivation in the nucleus rotundus of zebra finches: a Nissl and deoxyglucose study.

We evaluated in zebra finches the effects of monocular deprivation on morphological and physiological features of the nucleus rotundus, the thalamic relay station of the tectofugal pathway. In a first series of experiments neuron size and total volume were estimated in animals deprived for 20, 40 and at least 100 days and compared to values obtained from normally reared birds. Monocular closure for more than 40 days causes a marked hypertrophy in cells receiving their main input from the open eye, whereas the deprived cells are normal in size. However, with only 20 days of monocular deprivation both deprived and non-deprived rotundal neurons are larger than normal. This indicates that monocular closure has a biphasic effect: firstly, an unselective hypertrophy of deprived and non-deprived neurons, and secondly, a subsequent period of shrinkage of the deprived cells to normal values, while cells driven by the open eye remain hypertrophied. The total volume of the deprived n. rotundus turns out to be smaller in all age groups. In a second series of experiments the activity of the n. rotundus of animals monocularly deprived from birth for 100 days was investigated with the 2-deoxyglucose-method (Sokoloff et al. 1977). With binocular stimulation the activity of the deprived n. rotundus was reduced by about 40%. Depriving adult animals for 100 days does not result in asymmetric labeling of the n. rotundus. We interpretate the 2-DG data as evidence for the existence of a sensitive period for the effects of monocular deprivation. The anatomical data suggest, however, that the effects of monocular deprivation in birds are different from those observed in mammals.