Thyroid hormone controls the timing of cochlear ribbon synapse maturation

Area of Science:

• Neuroscience
• Developmental Biology
• Otolaryngology

Background:

• Ribbon synapses in cochlear hair cells undergo significant pruning and maturation before hearing onset.
• Thyroid hormone (TH) is known to be crucial for this developmental process, but its precise mechanisms remain unclear.

Purpose of the Study:

• To investigate the role of thyroid hormone receptor alpha (Thrα) and thyroid hormone in the development and maturation of ribbon synapses in the cochlea.
• To elucidate the mechanisms by which thyroid hormone regulates synaptic pruning and migration during postnatal development.

Main Methods:

• Utilized Pax8 gene knockout mice to induce hypothyroidism and study its effects on synaptic development.
• Administered liothyronine sodium (T3) to induce hyperthyroidism in mice.
• Performed spatiotemporal analysis of ribbon synapse distribution and maturation in the cochlea.

Main Results:

• Thyroid hormone receptor α (Thrα) is expressed in the cochlear sensory epithelium and spiral ganglion neurons.
• Hypothyroidism (Pax8 knockout) significantly delays ribbon synapse pruning and migration in developing mouse cochleas.
• Postnatal hyperthyroidism accelerates ribbon synapse pruning without impacting auditory function.

Conclusions:

• Thyroid hormone regulates the timing of cochlear ribbon synapse maturation, affecting both pruning and migration.
• The findings suggest TH is a timing cue rather than a determinant factor in synapse development.
• This research provides insights into the hormonal regulation of auditory system development.