Abstract
Retinal projections to the nucleus of the optic tract (NOT) and accessory optic nuclei (AON) were studied in the postnatal hooded rat after monocular injection of cholera toxin B subunit (CTB) into the vitreous chamber of the eye. At all postnatal ages, retinal axons were labeled sensitively; they revealed dense projections to the contralateral, and sparse but distinct projections to the ipsilateral, NOT and AON. The CTB Iabeling enabled the first delineation of the complete morphology of developing retinal axons in the ipsilateral NOT and AON. From postnatal day (P) 1 to P3, axons with complex growth cones were seen, and unbranched collaterals with simple growth cones increased and extended gradually. At P6, complex growth cones disappeared while branched collaterals with simple growth cones as well as small-sized varicosities increased. By P12 (two days before eye-opening) the adult-like pattern of terminal arbors appeared. The branched collaterals with tiny, small-sized varicosities present probably represented developing synaptic boutons. At P16 (after eye opening), the pattern of terminal arbors was well developed, almost to the same extent as in the adult. By contrast, a broadly distributed, transient retinal projection around NOT and AON was gradually eliminated; it started to disappear during the first few postnatal days, and was fully retracted by the time of eye-opening time to a pattern normal for the adult.
