Reliability of synaptic transmission at the synapses of Held in vivo under acoustic stimulation.
BACKGROUND
The giant synapses of Held play an important role in high-fidelity auditory processing and provide a model system for synaptic transmission at central synapses. Whether transmission of action potentials can fail at these synapses has been investigated in recent studies. At the endbulbs of Held in the anteroventral cochlear nucleus (AVCN) a consistent picture emerged, whereas at the calyx of Held in the medial nucleus of the trapezoid body (MNTB) results on the reliability of transmission remain inconsistent. In vivo this discrepancy could be due to the difficulty in identifying failures of transmission.


RESULTS
We introduce a novel method for detecting unreliable transmission in vivo. Based on the temporal relationship between a cells' waveform and other potentials in the recordings, a statistical test is developed that provides a balanced decision between the presence and the absence of failures. Its performance is quantified using simulated voltage recordings and found to exhibit a high level of accuracy. The method was applied to extracellular recordings from the synapses of Held in vivo. At the calyces of Held failures of transmission were found only rarely. By contrast, at the endbulbs of Held in the AVCN failures were found under spontaneous, excited, and suppressed conditions. In accordance with previous studies, failures occurred most abundantly in the suppressed condition, suggesting a role for inhibition.


CONCLUSIONS
Under the investigated activity conditions/anesthesia, transmission seems to remain largely unimpeded in the MNTB, whereas in the AVCN the occurrence of failures is related to inhibition and could be the basis/result of computational mechanisms for temporal processing. More generally, our approach provides a formal tool for studying the reliability of transmission with high statistical accuracy under typical in vivo recording conditions.
Max Planck Institute for Mathematics in the Sciences, Leipzig, Germany.
Bernhard
B
Englitz
Sandra
S
Tolnai
Marei
M
Typlt
Jürgen
J
Jost
Rudolf
R
Rübsamen
D000161:Acoustic Stimulation / Q000379:methods*; D000200:Action Potentials / Q000502:physiology; D000818:Animals; D001306:Auditory Pathways / Q000502:physiology; D017626:Cochlear Nucleus / Q000502:physiology*; D003198:Computer Simulation; D004594:Electrophysiology / Q000379:methods; D019706:Excitatory Postsynaptic Potentials / Q000502:physiology; D005849:Gerbillinae; D009433:Neural Inhibition / Q000502:physiology; D009474:Neurons / Q000502:physiology; D015203:Reproducibility of Results; D013569:Synapses / Q000502:physiology; D009435:Synaptic Transmission / Q000502:physiology*