Axonal inclusions in the crab Hemigrapsus nudus

Area of Science:

• Cell Biology
• Neuroscience
• Crustacean Biology

Background:

• Giant axons are crucial for rapid nerve impulse transmission in many invertebrates.
• Understanding axonal structures provides insights into neuronal function and adaptation.
• Hemigrapsus nudus, a marine crab, offers a model for studying crustacean neurobiology.

Purpose of the Study:

• To investigate the ultrastructure of intra-axonal inclusions observed in Hemigrapsus nudus.
• To determine the composition and potential origin of these unique axonal structures.
• To compare the axonal inclusions in H. nudus with those in other decapod crustaceans.

Main Methods:

• Light microscopy of living giant axons from Hemigrapsus nudus walking legs.
• Thin section electron microscopy to analyze the ultrastructure of intra-axonal inclusions.
• Comparative analysis of leg axons from various decapod crustacean species.

Main Results:

• Intra-axonal inclusions, measuring tens of micrometers long and 5 micrometers wide, were identified in H. nudus giant axons.
• These inclusions were primarily composed of mitochondria (68% by volume) and filled with light-scattering particles.
• Membrane-bounded spaces, likely smooth endoplasmic reticulum, surrounded each inclusion.
• Similar inclusions were absent in the leg axons of other examined decapod crustaceans.

Conclusions:

• Hemigrapsus nudus possesses unique, mitochondrion-rich intra-axonal inclusions within its giant axons.
• The composition suggests a significant role for mitochondria in these structures, potentially related to high energy demands.
• The presence of associated smooth endoplasmic reticulum indicates complex intracellular organization.
• These findings highlight a specialized adaptation in H. nudus neurobiology not observed in related species.