Mechanisms and impact of NMDA-receptor signaling during sensory processing in an echo-locating circuit
Final Report Abstract
NMDA-R currents and information content: Within the DNLL a heterogeneity of Mg2+ sensitivities is present that is likely based on distinct subtypes expression patterns indicated by our immunofluorescence. NMDA-R currents amplify DNLL output in vitro and in vivo without affecting the temporal precision of these neurons. The reduced output, does not affect ITD sensitivity, but does change the dynamic range of ITD coding. Therefore, NMDA-R activation enhances the auditory information content in general in the DNLL without affecting binaural information specifically. NMDA currents affect excitation and inhibition integration: The interactions between excitation and inhibition were studied predominantly in vivo. We found that the length of the persistent inhibition, the stimulus outlasting suppression of activity, is sensitive to sound intensity. The intensity sensitivity of the persistent inhibition was reproduced in vitro by scaling excitatory and inhibitory synaptic conductances. Moreover using in vivo pharmacology, we could show that NMDA-R contribute to the reduction of the persistent inhibition in a response rate dependent manner. Therefore, the sound intensity dependent duration of the persistent inhibition is also adjusted by NMDA-R activation. Thus, NMDA-R activation contributes to shorten the inhibitory time course and therefore, help to overcome GABAergic inhibition. This is consistent with the low Mg2+ sensitive NMDA-R currents we have described. Using human psychophysics, we could show that sound intensity indeed shortens the localisation and detection time of two successive sound stimulations. Thus, we can hypothesize that NMDA-R signalling might adjust the time of the binaural filter in a sound intensity dependent manner. This finding allows us to speculate that NMDA-R signalling is involved in aiding the estimation of the distance of a fluctuating sound source.
Publications
- Electrogenic N-methyl-D- aspartate receptor signaling enhances binaural responses in the adult brainstem. European Journal of Neuroscience, 2018, 47, 858-865
Siveke I., Ammer J.J., Gleiss S.A., Grothe B., Leibold C., Felmy F.
(See online at https://doi.org/10.1111/ejn.13859) - A Temporal Filter for Binaural Hearing Is Dynamically Adjusted by Sound Pressure Level. Front Neural Circuits. 2019, Feb 13; 13:8
Siveke I., Lingner A., Ammer J.J., Gleiss S.A., Grothe B., Felmy F.
(See online at https://doi.org/10.3389/fncir.2019.00008) - Lateral lemniscus. The Senses, 2nd Edition, Elsevier, Volume 2, 2020, Pages 556-565 (Chapter 2.29)
Felmy F., Meyer E.M.M.
(See online at https://doi.org/10.1016/B978-0-12-809324-5.24167-9)
