Postnatal changes in arborization patterns of murine retinocollicular axons

Abstract

The growth and arborization of murine retinocollicular axons have been studied by means of HRP axon filling during postnatal development. Transformations in arborization patterns have been correlated with changes in synaptic density in the superficial collicular neuropil and with the formation of synapses by HRP-filled axons. At all postnatal ages axons of the optic projection are fasciculated and most follow a rostrocaudally aligned path. On the day of birth the axons course through both stratum griseum superficiale (SGS) and stratum opticum (SO); during the following 4 days the axon trunks disappear from SGS and are subsequently found only in SO. From postnatal day (P) 0 to P3, the majority continue far caudally in the colliculus, giving rise to small ascending collaterals at multiple points along their course. Ultimately, usually by P3, one or two collaterals begin to branch profusely and by P5 the majority of axons give rise to a focal terminal ascending arborization. The general configuration of most arborizations at P3 approximates that of the mature axon. However, the richness of terminal branching increases from P3 through the first 2 postnatal weeks. Synaptic density is relatively low in the first postnatal week, and no synapses involving HRP-filled optic axons were identified in this interval. Subsequently, after elaboration of definitive arbors has begun, synaptogenesis in the surrounding neuropil accelerates. Synaptic density in the upper SGS approximates adult values early in the third postnatal week. By this time synaptic junctions involving the terminal arborizations of optic axons are abundant.

Growth cone morphology varies with position in the developing mouse visual pathway from retina to first targets

“…Other studies on growth cones in situ support our observations that, just outside of targets, growth cones have the elaborate form of growth cones found in decision regions (Harris et al, 1985;Mason, 1985;Nordlander, 1985;Young and Rubel, 1986), but within targets, immature axon arbors have small tapered tips or miniature growth cones (Mason, 1982(Mason, , 1985Reh and Constantine-Paton, 1985;Sakaguchi and Murphey, 1985;Sachs et al, 1986;Sretavan and Shatz, 1986). A surprising observation of the present study is that growth cones become smaller in both appropriate and inappropriate targets.…”

Requirement of Adenylate Cyclase 1 for the Ephrin-A5-Dependent Retraction of Exuberant Retinal Axons

“…Interestingly, the in vitro timing of events matches the in vivo tempo of maturation of the retinal axons. The axon exuberance of retinal axons at 4 DIV corresponds to the in vivo overgrowth of retinal axons in the SC at P1; the formation of axon branches at 8 DIV and their increased complexity at 12 DIV matches the elaboration of axon collateral branches during the first postnatal week (Sachs et al, 1986;Simon and O'Leary, 1992).…”

“…Based on morphological criteria that described the synaptogenesis in the SC (Lund and Lund, 1972;Sachs et al, 1986), we identified symmetric, asymmetric, and serial synapses in the SC (data not shown). In addition, using GFPimmunocytochemistry to label the retinal axons, retinotectal synapses were identified between the retinal axons and dendrites of collicular neurons (Fig.…”

“…Subsequently, overextended axon branches are removed, and collateral branches establish a focused and precise axon terminal arbor (Sachs et al, 1986;Simon and O'Leary, 1992). Membranebound guidance molecules ephrin-As and their EphA receptors in the retina define the target zones in the SC and are required for establishing the retinal topography along the rostrocaudal axis (Knoll and Drescher, 2002;McLaughlin et al, 2003a).…”

Topography of Auditory Nerve Projections to the Cochlear Nucleus in Cats after Neonatal Deafness and Electrical Stimulation by a Cochlear Implant

“…However, after the initial pathway formation, some sensory systems exhibit significant refinement of connections during late prenatal or early postnatal development, with projecting axons undergoing "pruning" of their axonal domains, resulting in more precise topographic maps of the afferent input (LeVay et al 1978;Cowan et al 1984;Easter et al 1985;Sachs et al 1986;, with some examples reported in the auditory system (Jackson and Parks 1982;Young and Rubel 1986;Friauf and Lohmann 1999;Leake et al 2002). As outlined in the "Introduction", some studies of visual system development have emphasized that neuronal activity plays a critical role in this topographic refinement .…”