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Prenatal and postnatal development of retinogeniculate and retinocollicular projections in the mouse
Insights
This study maps the development of retinal projections to the brain in mice. It details how contralateral and ipsilateral fibers grow into the dorsal lateral geniculate nucleus and superior colliculus, establishing distinct visual pathways.
Area of Science:
- Neuroscience
- Developmental Biology
- Visual System Research
Background:
- The formation of precise neural connections is crucial for sensory processing.
- Understanding retinal projection development informs studies on visual pathway organization.
Purpose of the Study:
- To investigate the developmental timeline and spatial organization of retinal projections to the dorsal lateral geniculate nucleus (dLGN) and superior colliculus (SC) in mice.
- To characterize the establishment and segregation of contralateral and ipsilateral retinal fibers during fetal and neonatal periods.
Main Methods:
- Utilized anterograde transport techniques with tritiated proline and horseradish peroxidase (HRP) in fetal and neonatal mice (C57BL/6 strain).
- Analyzed the growth patterns and density of retinal efferents in the dLGN and SC at various developmental stages (E14-P8).
Main Results:
- Contralateral retinal fibers reach the dLGN and SC by embryonic day 16.
- Ipsilateral fibers invade the dLGN and SC later, between embryonic day 18 and postnatal day 3, initially showing less dense projections.
- Distinct segregation of crossed and uncrossed retinal projections within the dLGN and SC occurs between postnatal days 4 and 8.
Conclusions:
- Retinal projections to the dLGN and SC follow a specific developmental trajectory with distinct timing for contralateral and ipsilateral inputs.
- The precise timing and spatial patterning of these projections are critical for the formation of functional visual circuits.
- The study provides a detailed map of visual pathway development, highlighting the dynamic process of fiber growth, invasion, and segregation.
Abstract:
The development of retinal projections to the dorsal lateral geniculate nucleus (dLGN) and superior colliculus (SC) has been studied in fetal and neonatal mice of the pigmented C57BL/6 strain, using the anterograde transport of tritiated proline and horseradish peroxidase (HRP). Retinal efferents are present contralaterally just beyond the chiasm at E14. By E16 they have grown into both dLGN and SC. Ipsilateral fibers are limited to the proximal optic tract at E16; their growth into dLGN and SC is delayed until E18-birth. During the first 2 postnatal days, an early population of ipsilateral fibers invades the dLGN. Most of these fibers grow in or around the medio-dorsal sector of the dLGN, i.e., the future binocular segment. Fibers are also present, but at lower densities, in the ventral half of the nucleus and thereafter become dispersed or are lost, without at any stage becoming dense. Some denser labeling is also present ipsilaterally in the outer rim of dLGN, just below the optic tract, and later disappears. On the third postnatal day, the ipsilateral fibers establish a deep and denser projection along the medial and dorsal borders of dLGN; this projection overlaps part of the crossed projection, which at this age extends to the whole nucleus. The segregation of each projection starts on the fourth postnatal day, when crossed fibers begin to disappear from the small region of uncrossed projection. This process goes on for another 4 days. During this period, the ipsilateral fibers withdraw from the deepest layer of dLGN, and their terminal density increases gradually; by the eighth postnatal day, both projections are already well separated. Dense crossed projections first appear near the surface of the SC at birth. Prior to this, retinal fibers course throughout neurons of the collicular plate and underneath the pia. The uncrossed fibers invade the SC between birth and P3. They are located preferentially in the anterior and medial aspect of the SC. Subsequently, there occurs a diminution in the laminar and tangential extent of these projections, simultaneously with an intensification of the ipsilateral input to several small, longitudinally oriented clusters located deep to the crossed projections.