Investigating Neotenic and Metamorphic Axolotl Brain Complexity: A Stereological and Immunohistochemical Perspective.

Area of Science:

• Neuroscience
• Developmental Biology
• Regenerative Medicine

Background:

• Tetrapods exhibit variable regenerative capacities, with amphibians showing high potential and humans limited potential.
• Ependymoglia cells in the brain's ventricular region possess stem cell properties and proliferate during damage and homeostasis.

Purpose of the Study:

• To investigate cellular and structural changes in the axolotl central nervous system during metamorphosis.
• To assess alterations in neurons and glia, including ependymoglia cells, following the transition from aquatic to terrestrial life.

Main Methods:

• Stereological analysis and immunohistochemistry were employed to examine brain tissue.
• Light and electron microscopy were used to assess morphological and ultrastructural changes in neurons and glia.
• Proliferation indices and NeuN expression were quantified.

Main Results:

• No significant difference in total telencephalon neuron numbers was found between neotenic and metamorphic axolotls.
• Metamorphic axolotls showed significantly higher proliferation indices and NeuN-positive cells.
• Ultrastructural analysis revealed chromatin reorganization in neurons (euchromatic to heterochromatic) and altered myelin sheath organization post-metamorphosis. Secretory sacs were observed on ependymoglia cells.

Conclusions:

• Axolotl metamorphosis induces substantial neuronal and glial remodeling in the central nervous system.
• Changes in chromatin organization and myelin structure suggest dynamic neuronal adaptation.
• The study highlights the complex cellular dynamics during amphibian metamorphosis and provides a basis for understanding CNS plasticity.