Morphological changes in leech Retzius neurons after target contact during embryogenesis

Area of Science:

• Neuroscience
• Developmental Biology
• Cell Biology

Background:

• Segmental variation in neurons offers insights into extrinsic influences on neuronal phenotype.
• Leeches possess two large serotonergic Retzius (Rz) cells per segmental ganglion.
• Most Rz cells innervate body walls, but Rz cells in ganglia 5 and 6 (Rz(5,6)) innervate reproductive tissue.

Purpose of the Study:

• To describe and quantify developmental differences between Rz(5,6) cells and other Rz cells.
• To investigate the timing and potential causes of morphological divergence in Rz cells.

Main Methods:

• Individual Rz cells were filled with Lucifer yellow or horseradish peroxidase (HRP) in adult and embryonic leeches.
• Morphological analysis focused on peripheral innervation, neuropilar arborization, and soma size.
• Temporal correlation of Rz cell process outgrowth and target tissue interaction was assessed.

Main Results:

• Rz(5,6) cell morphology was initially indistinguishable from other Rz cells during the first 72 hours of process outgrowth.
• Morphological differences emerged specifically after Rz(5,6) cell processes reached the reproductive tissue.
• This indicates a divergence from segmental homologs based on target tissue interaction.

Conclusions:

• The specific target tissue influences the final neuronal phenotype of Rz cells.
• Extrinsic factors, particularly interactions with reproductive tissue, drive the specialization of Rz(5,6) cells.
• This study highlights how environmental interactions shape neuronal development and function.