Figure 1.

Rearing conditions for ferrets in dark-rearing, recovery after dark-rearing, light deprivation and early eyelid opening paradigms. Each bar represents a rearing condition. Number of animals at each rearing condition is marked within each bar. The end point of bars denote the age at perfusion, except for age-matched controls, which consisted 16 ferrets that were perfused at P30, P43–46, P55–65 or older than P90. Two additional early eyelid opening littermate controls are not depicted here. L0–L30 suffixes denote the number of days of normal light exposure after dark-rearing (DR), light deprivation (LD) or early eyelid opening (EEO). Hatched area is the duration of normal rearing while eyelids are closed. Black area is the duration of dark-rearing. White area is the duration of normal (16/8hrs) light exposure before the perfusion. Normal eye opening occurs at P32 (vertical line). Critical period of layer IV plasticity, as described in earlier studies (Issa et al. 1999) is marked with gray shading. All dark-rearing/recovery animals came from three litters. Except for littermate controls for EEO cases and some adult controls that mothered the experimental litters, genetic relations of normal controls to experimental animals are not available.