Onset coding is degraded in auditory nerve fibers from mutant mice lacking synaptic ribbons.
Synaptic ribbons, found at the presynaptic membrane of sensory cells in both ear and eye, have been implicated in the vesicle-pool dynamics of synaptic transmission. To elucidate ribbon function, we characterized the response properties of single auditory nerve fibers in mice lacking Bassoon, a scaffolding protein involved in anchoring ribbons to the membrane. In bassoon mutants, immunohistochemistry showed that fewer than 3% of the hair cells' afferent synapses retained anchored ribbons. Auditory nerve fibers from mutants had normal threshold, dynamic range, and postonset adaptation in response to tone bursts, and they were able to phase lock with normal precision to amplitude-modulated tones. However, spontaneous and sound-evoked discharge rates were reduced, and the reliability of spikes, particularly at stimulus onset, was significantly degraded as shown by an increased variance of first-spike latencies. Modeling based on in vitro studies of normal and mutant hair cells links these findings to reduced release rates at the synapse. The degradation of response reliability in these mutants suggests that the ribbon and/or Bassoon normally facilitate high rates of exocytosis and that its absence significantly compromises the temporal resolving power of the auditory system.
Eaton-Peabody Laboratory, Massachusetts Eye and Ear Infirmary, Boston, Massachusetts 02114, USA. bburan@alum.mit.edu
Bradley N
BN
Buran
Nicola
N
Strenzke
Andreas
A
Neef
Eckart D
ED
Gundelfinger
Tobias
T
Moser
M Charles
MC
Liberman
D000161:Acoustic Stimulation / Q000379:methods; D000429:Alcohol Oxidoreductases; D000818:Animals; D001304:Auditory Diseases, Central / Q000235:genetics / Q000473:pathology / Q000503:physiopathology; D001306:Auditory Pathways / Q000502:physiology / Q000503:physiopathology; D001309:Auditory Threshold / Q000502:physiology; D056970:Co-Repressor Proteins; D003056:Cochlear Nerve / Q000503:physiopathology*; D004268:DNA-Binding Proteins / Q000378:metabolism; D004195:Disease Models, Animal; D004569:Electroencephalography / Q000379:methods; D016057:Evoked Potentials, Auditory, Brain Stem / Q000235:genetics / Q000502:physiology; D006198:Hair Cells, Auditory / Q000378:metabolism / Q000648:ultrastructure; D051379:Mice; D008810:Mice, Inbred C57BL; D008818:Mice, Neurologic Mutants; D008959:Models, Neurological; D009419:Nerve Tissue Proteins / Q000235:genetics*; D017084:Otoacoustic Emissions, Spontaneous / Q000235:genetics / Q000502:physiology; D010750:Phosphoproteins / Q000378:metabolism; D011571:Psychoacoustics; D011930:Reaction Time / Q000235:genetics / Q000502:physiology; D013569:Synapses / Q000235:genetics* / Q000473:pathology*
C498441:Bsn protein, mouse; D056970:Co-Repressor Proteins; D004268:DNA-Binding Proteins; D009419:Nerve Tissue Proteins; D010750:Phosphoproteins; D000429:Alcohol Oxidoreductases; C111341:Ctbp2 protein, mouse