Developmental changes in the distribution of retinal catecholaminergic neurones in hamsters and gerbils

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Abstract
Although Syrian hamsters and Mongolian gerbils are closely related, they have quite different patterns of retinal ganglion cell distribution and different patterns of retinal growth that produce their distributions. We have examined the morphology and distribution of catecholaminergic (CA) neurones in adult and developing retinae of these species in order to gain a more general understanding of the mechanisms producing cellular topographies in the retina. CA neurones were identified with an antibody to tyrosine hydroxylase (TH), the rate limiting enzyme in the production of catecholamines. In adult retinae of both hamsters and gerbils, most CA somata were located in the inner part of the inner nuclear layer (INL) and CA dendrites spread in a outer stratum of the inner plexiform layer (IPL). Their somata varied with retinal position, being largest in temporal and smallest in central retina. In hamsters, but not gerbils, a small number of CA interplexiform cells was also observed. In development, CA somata of hamster retinae were observed first in the middle and /or scleral regions of the cytoblast layer (CBL) at P (postnatal day) 8. By P12, CA somata were commonly located in the inner part of the INL and their dendrites spread into the outer region of the IPL. In developing gerbil retinae, CA somata were first observed at P6 in the middle of the CBL. Over subsequent days, they migrated into the inner part of the INL and spread their dendrites into the outer strata of the IPL. In both hamsters and gerbils, CA cells were initially concentrated in the superior temporal margin of the retina. In hamsters, this supero‐temporal concentration persisted until adulthood, whereas in adult gerbils, the greatest density of CA cells was found just superior to the visual streak. These distributions were distinct from those of the ganglion cells in adult and developing retinae of each species. We discuss the role of maturational expression of TH, cell death, and retinal growth in the generation of the distinct distribution of the CA cells.