INCREASED SEROTONIN IN THE DEVELOPING SUPERIOR COLLICULUS DOES NOT ALTER THE NUMBER OR DISTRIBUTION OF RETINOTECTAL GANGLION-CELLS

Administration of a single subcutaneous dose of 5,7-dihydroxytryptamin e (5,7-DHT) to newborn hamsters results in a significant increase in t he density of serotoninergic (5-HT) fibers in the superficial layers o f the superior colliculus (SC) and marked abnormalities in both the cr ossed and uncrossed retinotectal projections when these animals reach adulthood (R. Rhoades, C. Bennett-Clarke, R. Lane, M. Leslie, and R. M ooney, 1993, J. Comp. Neurol. 334:397-409). The present study was unde rtaken to determine whether changes in the retinotectal projection of 5,7-DHT-treated animals were associated with alterations in the number or distribution of retinal ganglion cells in these animals. Nissl sta ining of retinae from normal adult and 5,7-DHT-treated hamsters reveal ed no differences between them in the number or average diameter of ce lls in the retinal ganglion cell layer. Retrograde labeling with horse radish peroxidase (HRP) demonstrated no effect of 5,7-DHT treatment on the number or distribution of ipsilaterally or contralaterally projec ting ganglion cells. Neonatal 5,7-DHT administration also had no effec t on the distribution of soma diameters for HRP-labeled retinal gangli on cells. Electron microscopic analysis demonstrated no significant di fference between the number of optic nerve fibers in the normal and 5, 7-DHT-treated hamsters. The results are consistent with the conclusion that the effect of 5,7-DHT on the retinotectal projection may primari ly be a function of this toxin, or the increase in 5-HT it induces, on the terminal arbors of retinotectal axons rather than on their parent cells. (C) 1996 Wiley-Liss, Inc.