Formation of alternating tiers in the optic chiasm of the chick embryo

Drenhaus, Ulrich; Rager, Günter

doi:10.1002/ar.1092400413

Cited by 10 publications

(6 citation statements)

References 66 publications

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“…Crossing of pioneering axons at the midline was consistently observed between HH 20 and 24, whilst the second and further waves of axons were added. The asymmetry was transient and not discernible at later stages when thousands of axons are added (Drenhaus and Rager, 1994). A quantitative analysis of the data obtained at HH 20 -24 with anterograde staining is shown in Figure 2.…”

Section: Pioneering Retinofugal Axons Grow Out Asymmetricallymentioning

confidence: 99%

Potential role of Pax‐2 in retinal axon navigation through the chick optic nerve stalk and optic chiasm

et al. 2004

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The degree of fiber decussation at the optic chiasm differs between species, ranging from complete crossing in lower vertebrates to highly complex patterns of intermingling of the fibers from the two eyes seen in mammals and birds. Understanding the genetic control of fiber guidance through the chiasm is therefore important to unravel the developmental mechanisms within the visual system. Here we first report on early stages of chiasm formation, with pioneering axons from the left eye consistently arriving earlier than their counterparts from the right eye. This initial left-right asymmetry is transient and no functional significance is assigned to it yet. Secondly, we examined formation of the chiasm in relation with the expression of the transcription factor Pax-2 along the ventral eye cup and optic nerve stalk. Finally, in order to examine causal involvement of Pax-2 in chiasm formation, the gene was overexpressed along the neuraxis and in the eye cup at embryonic stages preceding the exit of axons from the eye, and hence arrival of axons at the chiasm. When studied with neuroanatomical tracing, Pax-2 overexpression resulted in visibly anomalous decussation of axons at the chiasm. A likely consequence of this perturbation was erroneous arrival of axons at the tectum, as observed by anterograde staining from the retina. These data suggest that balanced expression of Pax-2 results in the correct formation of the chick chiasm at early stages by imposing accurate pathfinding within the optic stalk and the midline.

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Section: Pioneering Retinofugal Axons Grow Out Asymmetricallymentioning

confidence: 99%

Potential role of Pax‐2 in retinal axon navigation through the chick optic nerve stalk and optic chiasm

et al. 2004

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“…In such species, including humans, several rearrangements take place at the chiasm until the final adult configuration is reached (Guillery et al, 1995). These topographic rearrangements may occur in other species with loss of retino-topic order at the chiasm such as nonprimates (Wizenmann et al, 1993;Chan and Guillery, 1994), and the chick (Halfter, 1987;Drenhaus and Rager, 1994). Evidence of chiasmal misrouting exists in human albino neonates (Apkarian et al, 1991), whereas normal humans form the so-called Wilbrand's knee (Horton, 1997), which is a loop of nasal fibers into the Figure 11.…”

Section: Topological and Quantitative Aspects Of The Projectionmentioning

confidence: 99%

“…In addition to axons that project erroneously within a particular target area, aberrant connections with "nontarget" areas have been described in the developing C NS (Innocenti, 1981;McL oon and L und, 1982;Cowan et al, 1984;O'Leary and Terashima, 1988;Nakamura and O'Leary, 1989;Simon et al, 1994). Such projections occur predominantly in areas connecting related anatomical regions, such as the decussation of retinal axons at the chiasm (Silver, 1984;Halfter, 1987;Sretavan, 1990;Drenhaus and Rager, 1994), the crossing of cortical axons at the midline (Koester and O'Leary, 1994), and the crossing of ascending spinal and descending corticospinal fibers at the level of brainstem in the pyramidal tract (for review, see O'Leary et al, 1994). Most investigations ascribe no particular function to fibers entering inappropriate pathways and nontarget areas, because most of the cells die during development.…”

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confidence: 99%

Genesis, Neurotrophin Responsiveness, and Apoptosis of a Pronounced Direct Connection between the Two Eyes of the Chick Embryo: A Natural Error or a Meaningful Developmental Event?

Thanos

1999

J. Neurosci.

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Unilateral intraocular injections of either of two fluorescent carbocyanine dyes into the embryonic chick eye resulted in both retrograde staining of ganglion cells (GCs) in the eye contralateral to site of injection and anterograde labeling of axons whose cell bodies were located within the injected eye. This prominent retino-retinal projection formed by thousands of GCs having a nasal origin and temporal termination appeared at embryonic day 6 (E6), attained its maximum intensity at E13-E14, and gradually disappeared until E18. The axonal growth cones ended superficially and never penetrated deeper layers of the retina. Treatment of the projection with BDNF resulted in massive terminal branching of the axons within deeper layers of the target retina. Double injection into the eye and the isthmo-optic nucleus showed a concomitant ingrowth of axons in the contralateral retina. Individual GCs died between E9 and E13, but massive apoptotic cell death was mainly monitored at E14 and later. Disintegrated cells showed typical images of apoptosis. Because degenerating cells were prelabeled with the membranophilic fluorescent carbocyanine dye, their death allowed the concomitant visualization of phagocytosing cells, too. Radial Mü ller glia were the only class of cells observed to become phagocytotic between E9 and E16. These cells became replaced exclusively with microglial cells from E17 on. The results suggest that the topologically restricted retinoretinal projection may have some developmental significance rather than representing a massive erroneous projection. Most likely, the projection may serve as a "template" to guide centrifugal isthmo-optic axons into the retina.

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“…Similar chronotopic mapping occurs in Rhesus macaque, where the papillomacular fibers occupy the center of the optic nerve as it approaches the chiasm where these axons move to a dorsal position (Polyak, 1957) as they do in R. pipiens. The same pattern is seen in chicken, where the oldest retinal axons originating from the central retina occupy the dorsal portion of the chiasm (Drenhaus and Ranger, 1994). An additional factor may also be responsible for the particular configuration that occurs in R. pipiens.…”

Section: Discussionmentioning

confidence: 56%

“…For example, photomicrographs of the rat optic chiasm appear to indicate a laminar structure (Chan and Guillery, 1994), as do the drawings of the optic chiasm in cichlid fish (Presson et al, 1985). The strongest evidence is found in the chicken, where optic axons form a tiered structure, with alternating layers of axons from the right and left eyes (Drenhaus and Ranger, 1994). In most vertebrates, several tracts innervating multiple targets emerge from the optic chiasm.…”

Section: Discussionmentioning

confidence: 97%

Organization of retinal axons within the optic nerve, optic chiasm, and the innervation of multiple central nervous system targets Rana pipiens

1998

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Light microscopic analysis of the optic nerve, chiasm, and optic tracts of Rana pipiens after the anterograde and retrograde transport of horseradish peroxidase has shown that retinal ganglion-cell axons reach the optic nerve head in chronotopically organized fascicles that form bands across the intraocular optic nerve. These bands of fascicles are divided along the midline in a "zone of reorganization" to create two full maps of the retinal surface; however, this map is discontinuous in that nasal and temporal quadrants are adjacent to one another. In the intracranial portion of the optic nerve, axons undergo another reorganization such that peripheral retinal axons shift position and become localized laterally and ventrally, whereas centrally placed axons become localized dorsally. Within this reorganization, the nerve is reconfigured into laminae of axons, and each lamina consists of age-related axons organized into two retinal maps. In the ipsilateral chiasm, axons diverge to form three central, optic tracts: the medial optic tract, the projection to the corpus geniculatum, and the basal optic root. Ipsilateral axons leave the chiasm at the same level of the chiasm as do their contralateral counterparts. The remaining axons converge in the lateral diencephalon to form a fourth fascicle, the marginal optic tract. Thus, within the optic chiasm, a sequence of positional transformations occur that result in the formation of multiple optic pathways. The various changes in axonal trajectory always coincide with changes in the orientation of cell groups that lie within the nerve and optic chiasm.

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Formation of alternating tiers in the optic chiasm of the chick embryo

Cited by 10 publications

References 66 publications

Potential role of Pax‐2 in retinal axon navigation through the chick optic nerve stalk and optic chiasm

Potential role of Pax‐2 in retinal axon navigation through the chick optic nerve stalk and optic chiasm

Genesis, Neurotrophin Responsiveness, and Apoptosis of a Pronounced Direct Connection between the Two Eyes of the Chick Embryo: A Natural Error or a Meaningful Developmental Event?

Organization of retinal axons within the optic nerve, optic chiasm, and the innervation of multiple central nervous system targets Rana pipiens

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