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Updated: Jun 2, 2026
Spinal Cord Transection In Xenopus laevis Tadpoles
Published on: December 10, 2021
Functional repair of transected spinal cord in embryonic chick
S J Hasan1, B H Nelson, J I Valenzuela
1Departments of Anatomy and Zoology, University of British Columbia, Vancouver, B.C. (Canada).
Insights
Chick embryo spinal cord transections before embryonic day 13 show complete anatomical and functional repair, indicating regeneration of descending spinal tracts. Later transections impair this recovery, highlighting a critical developmental window for spinal cord repair.
Area of Science:
- Developmental Neuroscience
- Neurobiology
- Regenerative Medicine
Background:
- Descending spinal tracts are crucial for motor control.
- The chick embryo provides a model to study spinal cord development and repair.
- Understanding the timing of repair capacity loss is vital for regenerative strategies.
Purpose of the Study:
- To identify the developmental stage in chick embryos when descending spinal tracts lose their capacity for anatomical and functional repair after thoracic spinal cord transection.
- To investigate the mechanisms underlying spinal cord repair in developing chicks.
Main Methods:
- Thoracic spinal cord transections and sham operations were performed on chick embryos from embryonic day (E) 3 to E14.
- Anatomical repair was assessed using retrograde tract-tracing techniques.
- Functional recovery was evaluated through behavioral observations and brainstem stimulation with electromyographic recordings.
Main Results:
- Complete anatomical and functional recovery was observed in chick embryos transected on or before E12.
- Transections performed on E13-E14 resulted in reduced anatomical labeling and impaired functional recovery.
- Regeneration of previously axotomized projections is suggested as a mechanism for repair in younger embryos.
Conclusions:
- The chick embryo's descending spinal tracts retain the capacity for significant anatomical and functional repair until embryonic day 12.
- A critical developmental window exists, after which the ability for spinal cord repair diminishes.
- Regeneration of descending supraspinal pathways likely contributes to the observed repair in early-stage embryos.
Abstract:
The purpose of this study was to determine the developmental stage of the chick embryo when descending spinal tracts lose the capacity for anatomical and functional repair after complete transection of the thoracic spinal cord. Previous studies have demonstrated that the first reticulospinal projections descend to the lumbar cord by embryonic day (E) 5. A comparison of the distribution and density of retrogradely labelled brainstem-spinal neurons in embryos versus hatchling chicks suggests that the descent of all brainstem-spinal projections is essentially complete to lumbar levels between E10 and El2. Transections and control sham operations were performed on different embryos from E3 through E14 of development. After a recovery period of 5-18 days, the extent of anatomical repair was assessed by injecting a small volume of a retrograde tract-tracing chemical into the upper lumbar spinal cord, caudal to the transection site. The brainstem nuclei were then examined for the number and distribution of retrogradely labelled brainstem-spinal neurons. In comparison to control animals, anatomical recovery appeared to be complete for embryos transected as late as E12, whereas thoracic cord transections conducted on E13-E14 resulted in reduced labelling of most brainstem-spinal nuclei. In addition, a number of E3-E6 transected embryos were allowed to hatch and with some assistance a few E7-E14 transected embryos also hatched. Functional recovery was assessed by behavioral observations and by focal electrical stimulation of brainstem locomotor regions (known to have direct projections to the lumbar spinal cord). Brainstem stimulation experiments were undertaken on transected and control embryos, either in ovo on E18-E20 or after hatching. Leg and wing muscle electromyographic recordings were used to monitor any brainstem evoked motor activity. Voluntary open-field locomotion (hatchling chicks) or brainstem evoked locomotion (embryonic or hatchling) in animals transected on or before E12 was indistinguishable from that observed in control (i.e. sham-operated or unoperated) chicks, indicating that complete functional recovery had occurred. In contrast, chicks transected on or after El3 showed reduced functional recovery. Since a previous study has shown that neurogenesis in chick brainstem-spinal neurons is complete prior to E5, the possible intrinsic neuronal mechanisms underlying the repair of descending supraspinal pathways are: (1) subsequent projections from later developing (undamaged) neurons, or (2) regrowth of previously axotomized projections (regeneration). For the E5-E12 chick embryos examined in this study, significant descending supraspinal fibers are present within the thoracic cord at the time of transection. Even if the transection is made at E12, when descending projections have completed their development to the lumbar cord, there is still a similar number and distribution of brainstem-spinal neurons labelled afterward (when compared to controls). This suggests that regeneration of previously axotomized projections may account for some of the observed anatomical and functional repair of brainstem-spinal pathways.
