1998 Volume 17 Issue 3-4 Pages 3-4_97-3-4_103
Retinal degeneration characterized by photoreceptor apoptosis was induced by a single systemic administration of N-methyl-N-nitrosourea (MNU) in a variety of adult animals: rodents (mouse, rat and hamster), insectivora (shrew; Suncus murinus), and non-human primates (monkey; Macaca Fuscata). Therefore, phylogenetically, MNU-induced photoreceptor apoptosis is a universal phenomenon. However, the lesions (similar to human retinitis pigmentosa) initiated from the equatorial zone in monkeys, whereas in the other species the lesions originated from the posterior pole. After the photoreceptor cell loss, an intraretinal migration of pigment epithelial cells was seen in rats and hamsters, but as in humans, the migrated pigment epithelial cells in contact with a blood vessel was seen only in the hamsters; no pigment epithelial cell migration was seen in the mice, shrews or monkeys. Retinal dysplasia characterized by dysplastic rosettes was induced in mice treated with MNU at day 0 or 3 (the stage of retinal cell proliferation), whereas no retinal response was seen when MNU was administered at day 5 or 8 (the stage of retinal cell differentiation), and retinal degeneration occurred when MNU was administered at or over day 11 (after cellular differentiation). Thus, from the ontogenetic point of view, the MNU response was related to retinal development in that there was a critical period for the time of MNU administration for the induction of retinal lesions.
