title: Early postnatal development of spontaneous and acoustically evoked discharge activity of principal cells of the medial nucleus of the trapezoid body: an in vivo study in mice.
abstract: The calyx of Held synapse in the medial nucleus of the trapezoid body of the auditory brainstem has become an established in vitro model to study the development of fast glutamatergic transmission in the mammalian brain. However, we still lack in vivo data at this synapse on the maturation of spontaneous and sound-evoked discharge activity before and during the early phase of acoustically evoked signal processing (i.e., before and after hearing onset). Here we report in vivo single-unit recordings in mice from postnatal day 8 (P8) to P28 with a specific focus on developmental changes around hearing onset (P12). Data were obtained from two mouse strains commonly used in brain slice recordings: CBA/J and C57BL/6J. Spontaneous discharge rates progressively increased from P8 to P13, initially showing bursting patterns and large coefficients of variation (CVs), which changed to more continuous and random discharge activity accompanied by gradual decrease of CV around hearing onset. From P12 on, sound-evoked activity yielded phasic-tonic discharge patterns with discharge rates increasing up to P28. Response thresholds and shapes of tuning curves were adult-like by P14. A gradual shortening in response latencies was observed up to P18. The three-dimensional tonotopic organization of the medial nucleus of the trapezoid body yielded a high-to-low frequency gradient along the mediolateral and dorsoventral but not in the rostrocaudal axes. These data emphasize that models of signal transmission at the calyx of Held based on in vitro data have to take developmental changes in firing rates and response latencies up to the fourth postnatal week into account.
authors.affiliation: Faculty of Bioscience, Pharmacy, and Psychology, University of Leipzig, Leipzig, Germany.
authors.forename: Mandy
authors.initials: M
authors.lastname: Sonntag
authors.forename: Bernhard
authors.initials: B
authors.lastname: Englitz
authors.forename: Cornelia
authors.initials: C
authors.lastname: Kopp-Scheinpflug
authors.forename: Rudolf
authors.initials: R
authors.lastname: Rübsamen
mesh_terms: D000161:Acoustic Stimulation; D000200:Action Potentials; D000375:Aging / Q000502:physiology; D000704:Analysis of Variance; D000818:Animals; D000831:Animals, Newborn; D001307:Auditory Perception / Q000502:physiology; D001309:Auditory Threshold / Q000502:physiology; D016057:Evoked Potentials, Auditory, Brain Stem; D051379:Mice; D008810:Mice, Inbred C57BL; D008808:Mice, Inbred CBA; D008839:Microelectrodes; D009474:Neurons / Q000502:physiology*; D009847:Olivary Nucleus / Q000033:anatomy & histology / Q000254:growth & development* / Q000502:physiology*; D011930:Reaction Time; D013569:Synapses / Q000502:physiology; D009435:Synaptic Transmission / Q000502:physiology; D013997:Time Factors