title: The calyx of Held develops adult-like dynamics and reliability by hearing onset in the mouse in vivo.
abstract: The development of the auditory system has received increasing attention since the mechanisms of patterned, spontaneous activity in prehearing mammals were discovered. This early activity originates in the cochlea and is assumed to be of importance for the establishment and refinement of synaptic connections in the auditory system. In the present study we investigate synaptic transmission and its interplay with spontaneous discharges in the developing auditory system. We used the calyx of Held as a model system, where this question can be investigated in vivo over a broad range of ages [postnatal day 8 (P8)-P28]. To precisely quantify the timing and reliability of synaptic transmission, we developed a novel fitting approach which decomposes the extracellularly recorded signal into its presynaptic and postsynaptic components. In prehearing mice, we found signal transmission to be unreliable, with high variability in the transmission delay and in the amplitude of postsynaptic components. These timing and amplitude changes were strongly correlated with the preceding activity. Around hearing onset (P12-P14), the properties of signal transmission converged to the adult-like state which was characterized by high transmission reliability as well as high consistency in timing and amplitude. Although activity-dependent depression was still found in action potentials, EPSP depression no longer played a prominent role. In conclusion, the maturation of synaptic transmission at the calyx of Held seems to be precisely timed to achieve its adult potential by the time acoustically evoked signal processing commences.
authors.affiliation: Faculty of Biosciences, Pharmacy and Psychology, University of Leipzig, 04103 Leipzig, Germany.
authors.forename: Mandy
authors.initials: M
authors.lastname: Sonntag
authors.forename: Bernhard
authors.initials: B
authors.lastname: Englitz
authors.forename: Marei
authors.initials: M
authors.lastname: Typlt
authors.forename: Rudolf
authors.initials: R
authors.lastname: Rübsamen
mesh_terms: D000161:Acoustic Stimulation; D000200:Action Potentials / Q000502:physiology; D000818:Animals; D001306:Auditory Pathways / Q000502:physiology*; D001933:Brain Stem / Q000502:physiology*; D004594:Electrophysiology; D005072:Evoked Potentials, Auditory / Q000502:physiology; D005260:Female; D006309:Hearing / Q000502:physiology*; D008297:Male; D051379:Mice; D013569:Synapses / Q000502:physiology*; D009435:Synaptic Transmission / Q000502:physiology*