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Published on: December 19, 2017
Development of Light-activated Pupilloconstriction in Rats as Mediated by Normal and Transplanted Retinae
J. D. Radel1, S. Das, R. D. Lund
1Department of Neurobiology, Anatomy and Cell Science, University of Pittsburgh School of Medicine, Pittsburgh, PA 15261, USA.
Insights
Pupil constriction to light develops with retinal maturation in rats. Transplanted retinae show delayed responses, indicating the retina itself limits light-activated pupilloconstriction development.
Area of Science:
- Neuroscience
- Developmental Biology
- Ophthalmology
Background:
- The pupilloconstriction response to light is crucial for visual function.
- Understanding the developmental timeline and underlying mechanisms of this response is essential.
Purpose of the Study:
- To investigate the relationship between retinal maturation and the development of pupilloconstriction in rats.
- To determine if the retina or central pathways limit the expression of light-activated pupilloconstriction.
Main Methods:
- Studied pupillary responses in normal rats from postnatal day 7 to 14.
- Utilized intracranial retinal transplants in newborn rats to assess developmental timing.
- Correlated pupillary response development with anatomical changes in the retina.
Main Results:
- Pupillary response to light first appeared around postnatal days 7-9 in normal rats, improving by week 2.
- Response onset correlated with synaptic contact formation; improved responses correlated with photoreceptor maturation.
- Transplanted retinae showed delayed pupillary responses, proportional to developmental disparity.
Conclusions:
- Retinal maturation is a key factor in the development of light-activated pupilloconstriction.
- The retina contains intrinsic limitations for the expression of this response, not central nuclei or output pathways.
Abstract:
The relationship between the development of the pupilloconstriction response to changes in light levels and retinal maturation was studied in normal rats and rats that had received intracranial retinal transplants at birth. A pupillary response to light was first observed between postnatal days 7 and 9 in normal rats, and was typically of small amplitude and sluggish. By the time the eyelids first open, 2 weeks after birth, the pupillary response had improved to near adult levels. The inception of the pupillary response correlates with the first appearance of conventional synaptic contacts in the inner and outer plexiform layers of the retina, while improved responses correlate with maturation of photoreceptor outer segments and formation of synaptic ribbons in the inner plexiform layer. When embryonic retinae were transplanted to intracranial locations in newborn hosts and the transplants later illuminated as the host matured, the onset of a pupillary response to transplant illumination was delayed in proportion to the developmental disparity between the transplant and the host. The pattern of anatomical development in transplanted retinae was also similar, but delayed in time, compared to normal retinae. This indicates that the limiting factors for expression of light-activated pupilloconstriction exist within the retina, rather than being intrinsic to the central nuclei or to the output pathway subserving the response.
