Photoreceptor degeneration and synaptogenesis in retinal‐degenerative (rd) mice

Abstract

The influence of photoreceptor degeneration upon synaptogenesis in the photoreceptor terminal of developing retinae of rd mice (C3H/HeJ and C57BL rd le) is outlined and compared to the sequential development of the photoreceptor terminals of the retinae of normal mice. The initial phases of synaptogenesis in the photoreceptor terminal of the rd retina appear normal during the first postnatal week. Appositional contacts form between the photoreceptor terminal and neuronal processes before invagination of horizontal processes occurs to form a dyad configuration. A virtual absence of triad configurations in the photoreceptor terminal suggests that synaptogenesis is arrested in the photoreceptor terminal of the rd retina between the 7th and 10th day, at which time the central (bipolar) process normally invaginates into the photoreceptor terminal. During this period, photoreceptor cell death proceeds rapidly but few signs of degeneration are apparent. It is suggested that the inherited abnormality influences the maturation of bipolar cells more than that of horizontal cells. The b‐wave component of the electroretinogram (ERG) of the immature rd retina is discussed in terms of photoreceptor/bipolar cell synaptic contacts.