Ultrastructural effects of monocular deprivation in the neuropil of nucleus rotundus in the zebra finch: a quantitative electron microscopic study.

Ultrastructural effects of monocular deprivation starting at hatching have been studied in the neuropil of nucleus rotundus, the thalamic visual relay station of the tectofugal pathway in birds. Synaptic density, presynaptic terminal size, and length of postsynaptic density (PSD) have been quantified in juvenile (20-day) and adult (100-day) zebra finches. These parameters are mature in 20-day-old zebra finches when reared under normal conditions. Alterations obtained by monocular deprivation were: The synaptic density increases by 35% in the nucleus rotundus of both sides of the brain above normal values in juvenile birds. In adult birds only the deprived side maintains this hypertrophy of synaptic density (33%), the non-deprived side returns to normal values. The presynaptic terminal size remains small in the deprived nucleus of 20-day- and 100-day-old animals, whereas the non-deprived nucleus is not affected. By the age of 20 days the length of PSD in deprived and non-deprived nuclei is not reduced as much as in normally reared zebra finches. By the age of 100 days, however, the PSDs of both sides of monocularly deprived birds show a further reduction of their median length and do not differ from PSDs of zebra finches reared under normal conditions.