Endolymphatic Potential Measured From Developing and Adult Mouse Inner Ear.

Area of Science:

• Neuroscience
• Otolaryngology
• Physiology

Background:

• The mammalian inner ear comprises the cochlea (hearing) and vestibular organ (balance), separated by distinct extracellular fluids: endolymph and perilymph.
• Stereocilia of hair cells are bathed in endolymph, crucial for mechanotransduction via the endolymphatic potential (ELP).
• Understanding ELP development is key to comprehending sensory organ maturation.

Purpose of the Study:

• To measure and compare the endolymphatic potential (ELP) in adult and neonatal mouse cochlear and vestibular endolymph.
• To determine the developmental timeline of ELP maturation in both sensory systems.
• To assess the maturation of vestibular function by correlating ELP with vestibular microphonic responses.

Main Methods:

• Electrophysiological recordings of ELP in adult and neonatal C57BL/6J mice.
• Measurement of vestibular microphonic response from saccule in neonatal mice.
• Comparative analysis of ELP across different inner ear compartments (cochlea turns, saccule, utricle, semicircular canal).

Main Results:

• Adult ELP shows significant variation: +95 mV (cochlear base), +87 mV (cochlear apex), +9 mV (saccule/utricle), and +3 mV (semicircular canal).
• Vestibular ELP matures to adult levels around postnatal day 6.
• Cochlear ELP (endocochlear potential) matures approximately 12 days later than vestibular ELP.
• Vestibular microphonic response maturation aligns with vestibular ELP maturation.

Conclusions:

• ELP is a localized potential, varying significantly even with similar endolymph composition.
• Vestibular sensory function matures substantially earlier than auditory function in mice.
• This developmental dissociation has implications for understanding sensory system maturation and potential therapeutic interventions.