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Raphe-spinal neurons display an age-dependent differential capacity for neurite outgrowth compared to other
J F Borisoff1, D M Pataky, C B McBride
1Collaboration On Repair Discoveries (CORD), University of British Columbia, Vancouver, British Columbia, V6T 1Z4, Canada.
Insights
Spinal cord regeneration in chicks is possible before embryonic day 13, but not after. This study shows that young brainstem neurons can regrow, while mature neurons have limited regenerative capacity, depending on their type.
Area of Science:
- Neuroscience
- Developmental Biology
- Regenerative Medicine
Background:
- Functional regeneration of brainstem-spinal pathways in chicks is observed before embryonic day (E) 13, but is lost after this developmental stage.
- This loss of regenerative capacity may be due to inhibitory extrinsic factors or intrinsic neuronal limitations.
- Understanding these age-dependent changes is crucial for developing therapeutic strategies for spinal cord injury.
Purpose of the Study:
- To investigate the in vitro neurite outgrowth capacity of different brainstem-spinal projection neuron populations from young (E8) and mature (E17) chick embryos.
- To determine if neuronal age and phenotype influence the ability of these neurons to regenerate.
Main Methods:
- Brainstem-spinal projection neurons were retrogradely labeled using DiI dye in ovo.
- Brainstem explants from young (E8) and mature (E17) embryos were cultured in serum-free media on laminin substrates.
- Neurite outgrowth was assessed by observing DiI redistribution in regenerating processes.
Main Results:
- At E8, all studied brainstem-spinal neuron populations (rubro-, reticulo-, vestibulo-, and raphe-spinal) exhibited robust neurite outgrowth.
- At E17, only raphe-spinal neurons showed significant neurite outgrowth.
- Raphe-spinal neuron outgrowth was associated with 5-hydroxy-tryptamine immunoreactivity.
Conclusions:
- Neurite outgrowth from brainstem-spinal neurons in vitro is dependent on both the age of the neuron and its specific phenotype.
- The developing chick brainstem exhibits a transition from a regenerative to a non-regenerative state, influenced by neuronal intrinsic properties.
- These findings highlight the importance of developmental timing and neuronal identity in spinal cord regeneration research.
Abstract:
Functional regeneration of brainstem-spinal pathways occurs in the developing chick when the spinal cord is severed prior to embryonic day (E) 13. Functional spinal cord regeneration is not observed in animals injured after E13. This developmental transition from a permissive to a restrictive repair period may be due to the formation of an extrinsic inhibitory environment preventing axonal growth, and/or an intrinsic inability of mature neurons to regenerate. Here, we investigated the capacity of specific populations of brainstem-spinal projection neurons to regrow neurites in vitro from young (E8) versus mature (E17) brainstem explants. A crystal of carbocyanine dye (DiI) was implanted in ovo into the E5 cervical spinal cord to retrogradely label brainstem-spinal projection neurons. Three or 12 days later, discrete regions of the brainstem containing DiI-labeled neurons were dissected to produce explant cultures grown in serum-free media on laminin substrates. The subsequent redistribution of DiI into regenerating processes permitted the study of in vitro neurite outgrowth from identified brainstem-spinal neurons. When explanted on E8, i.e., an age when brainstem-spinal neurons are normally elongating through the spinal cord and are capable of in vivo functional regeneration, robust neurite outgrowth was observed from all brainstem populations, including rubro-, reticulo-, vestibulo-, and raphe-spinal neurons. In contrast, when explanted on E17, robust neurite outgrowth was seen only from raphe-spinal neurons. Neurite outgrowth from raphe-spinal neurons was 5-hydroxy-tryptamine immunoreactive. This study demonstrates that in growth factor-free environments with permissive growth substrates, neurite outgrowth from brainstem-spinal neurons is dependent on both neuronal age and phenotype.