GluA2-Containing AMPA Receptors Distinguish Ribbon-Associated from Ribbonless Afferent Contacts on Rat Cochlear Hair...

Area of Science:

• Neuroscience
• Auditory system physiology
• Synaptic transmission

Background:

• Mechanosensory hair cells transmit auditory information via glutamate release at ribbon synapses.
• AMPA-type ionotropic glutamate receptors (AMPARs) mediate excitation of postsynaptic afferent neurons.
• Type II afferent neurons in the mammalian cochlea were previously thought to lack AMPARs and presynaptic ribbons at many contacts.

Purpose of the Study:

• To investigate the presence and function of AMPARs at type II afferent neuron contacts with hair cells in the rat cochlea.
• To characterize the nature of afferent contacts, including those previously described as "ribbonless".

Main Methods:

• Immunohistochemistry using antibodies against the AMPAR subunit GluA2.
• Electrophysiological recordings of synaptic currents in type II afferents.
• Analysis of postsynaptic densities using markers like PSD-95, Shank, and Homer.

Main Results:

• Antibodies to GluA2 labeled afferent contacts below both inner and outer hair cells.
• Synaptic currents in type II afferents exhibited AMPAR-specific pharmacology.
• Approximately half of the postsynaptic densities in type II afferents were associated with GluA2 or presynaptic ribbons, indicating "empty slots" at ribbonless contacts.

Conclusions:

• AMPAergic transmission is a universal mechanism used by hair cells in the cochlea.
• The findings support the existence of functional "silent" afferent contacts, expanding our understanding of auditory neurotransmission.