Postnatal dendritic maturation of alpha and beta ganglion cells in cat retina

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Abstract
Of the 3 anatomically defined classes of ganglion cell in adult cat retina, the alpha and beta cells are the most well documented, thus providing a basis of comparison for developing ganglion cells. Alpha and beta ganglion cells in cat retinae at various ages from birth (P0) to adult were intracellularly injected with Lucifer yellow. At all ages, both cell types strongly resembled their adult counterparts. However, transient developmental characteristics established their immaturity. These features included spiny protuberances and “rings” along the dendritic surface that were no longer detectable after 3 weeks of age. In a small proportion of both inner and outer stratifying alpha ganglion cells, there was aberrant dendritic arborization. However, by P5 there was no remaining evidence of this deviant stratification pattern and all alpha and beta cells displayed the adult pattern of unistratification (present among the majority of these cells from birth). For both alpha and beta cells, the area of greatest development was the retinal periphery. In this region alpha cell dendritic trees continued to grow until 3 weeks postnatally, when they approached the adult dendritic field size; around this time, the major period of beta cell dendritic expansion began. From birth to adulthood, the distance between alpha cell dendritic branching points increased, while the number of nodes and tips decreased with age. The temporal disparity between alpha and beta cell dendritic expansion suggests that postnatal dendritic development involves an active process of growth, rather than merely passive stretching.