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Nucleus Ruber of Actinopterygians.

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Area of Science:

  • Neuroscience
  • Comparative Anatomy
  • Evolutionary Biology

Background:

  • The nucleus ruber is a key center for forelimb movement control in tetrapods.
  • Homologous structures in fish may control pectoral fin movements.
  • Two distinct structures, NRg and NRnp, have been identified as potential nucleus ruber homologues in actinopterygians, causing confusion.

Purpose of the Study:

  • To determine the phylogenetic homology of the two identified actinopterygian 'nucleus ruber' structures with the tetrapod nucleus ruber.
  • To clarify the evolutionary origins of these brain nuclei in fish.

Main Methods:

  • Retrograde tracing of tegmental neurons from the spinal cord in eight actinopterygian species.
  • Analysis of brain sections (Nissl and Bodian staining) from 28 additional actinopterygian species.
  • Comparative morphological analysis of candidate rubral neurons and tracer-labeled neurons.

Main Results:

  • The Goldstein nucleus ruber (NRg) was found in all investigated actinopterygians.
  • The Nieuwenhuys and Pouwels nucleus ruber (NRnp) was absent in basal actinopterygians.
  • Phylogenetic distribution suggests NRg is the likely homologue of the tetrapod nucleus ruber.

Conclusions:

  • The NRg represents the conserved nucleus ruber across actinopterygians.
  • The NRnp is likely a derived structure that evolved later within actinopterygian evolution.
  • This study resolves the homology of nucleus ruber in fish, providing insights into motor control evolution.