Endolymph movement visualized with light sheet fluorescence microscopy in an acute hydrops model.

Area of Science:

• Inner ear fluid dynamics
• Otolaryngology
• Physiology

Background:

• Endolymphatic hydrops is a condition linked to inner ear fluid imbalance.
• Understanding endolymph dynamics is crucial for diagnosing and treating inner ear disorders.
• Current techniques for studying endolymph are limited in their ability to visualize fluid movement.

Purpose of the Study:

• To investigate endolymph dynamics in vivo using a novel injection and imaging technique.
• To visualize and quantify fluid movement within the inner ear compartments.
• To elucidate the role of the endolymphatic duct in endolymph volume regulation.

Main Methods:

• Injection of fluorescein isothiocyanate-dextran (FITC-dex) and artificial endolymph into scala media of anesthetized guinea pigs via glass micropipette.
• High-resolution 3D imaging of inner ear fluid movement using Light Sheet Fluorescence Microscopy (LSFM).
• Analysis of fluid distribution following injections of varying volumes (<2.5 μl and >2.5 μl).

Main Results:

• Endolymph moved into the utricle, semicircular canals, and endolymphatic duct/sac when >2.5 μl fluid was injected.
• No significant fluid movement into perilymphatic compartments was observed.
• FITC-dex showed remarkable uptake into the endolymphatic duct and surrounding periductal channels.

Conclusions:

• The study successfully visualized endolymph movement and distribution in vivo.
• A threshold volume of 2.5 μl is suggested for significant endolymph redistribution.
• The endolymphatic duct and its associated channels are functionally important for endolymph volume homeostasis.