The sensitive period for the morphological effects of monocular deprivation in two nuclei of the tectofugal pathway of zebra finches

Abstract

Previous experiments with 2-deoxyglucose (2-DG) suggested the existence of a critical period for the effects of monocular deprivation in the nucleus rotundus of zebra finches. The present study concerns the time course of this sensitive period for the morphological effects of monocular deprivation in two areas of the tectofugal visual pathway of zebra finches, the nucleus rotundus of the thalamus and the telencephalic ectostriatum. Cell size and volume changes were measured in birds subjected to 40 days of unilateral eye closure starting at ages spaced regularly throughout the first 70 days of life. The results show that monocular deprivation markedly affects cell size in both areas if the treatment starts at one or 10 days posthatch. The differences between deprived and non-deprived neurons decline monotonically with increasing visual experience prior to deprivation. However, deprivation onset at day 40 again causes as severe effects as early monocular closure. Deprivation as from day 50 or later no longer leads to abnormalities. The measurements of the volume of the nucleus rotundus parallel the cell size measurements, with the exception that the second increase in sensitivity occurs with deprivation onset at day 50 instead of day 40. These data indicate that the time course of the sensitive period for the effects of monocular deprivation may be double-peaked: the sensitivity for external stimuli declines from hatch until day 30, but has another peak at 40-50 days of life. The definite end of the sensitive period, as determined with this method, can therefore be assumed to be at around day 50-60.

Post-hatch activity-dependent modulation of visual asymmetry formation in pigeons

“…Thus, the effects of monocular deprivation are not confined to the deprived brain side but affect both hemispheres. Such a bilateral deprivation effect has also been shown in zebra finches in which closure of one eye changes tectofugal cell sizes in both brain halves [14,15]. Besides, these results demonstrate that the TTX treatment did not perturb mechanisms of visual discrimination which might have been responsible for asymmetric performances.…”

“…Right eye deprivation leads to a reversal of the functional and morphological asymmetry pattern, while left-eye deprivation increases right-eye superiority [7,13]. Since it is known that monocular deprivation affects neuronal cell size in the tectofugal pathway [7,[13][14][15] and since anatomical asymmetries are present within this system, the unbalanced visual stimulation can directly influence the differentiation of the tectofugal pathway. The development of this pathway is well known to be controlled by afferent activity [16] and neurotrophic factors are key mediators of this regulation [17].…”

Development of flash-evoked responses in the ectostriatum of the zebra finch: An evoked potential and current-source-density analysis

“…Some parameters continue to change until adulthood. However, the anatomical changes after day 40 are generally not statistically significant (Herrmann & Bischof, 1986a, 1988a. In contrast, the tectofugal visual pathway does not respond to visual stimuli in the same way as in adult birds of this age.…”

“…Changeux & Danchin, 1976). In zebra finches, the size of neurons and the number of spines in the ectostriatum decrease after day 20 (Herrmann & Bischof, 1988a). This exuberant connectivity leads to a largely random distribution of current flow vectors and therefore a strong cancellation of currents (e.g.…”

“…Two main conclusions can be drawn from these data. Firstly, the morphological development of the tectofugal system is obviously complete by day 40 coinciding with the end of the sensitive phase for monocular deprivation (Herrmann & Bischof, 1988a). Secondly, the major effects of monocular deprivation are localized in the hemisphere driven by the non-deprived eye (Herrmann & Bischof, 1986a, b, c;Herrmann & Bischof, 1988e,6;Nixdorf & Bischof, 1987).…”