Precise temporal processing in the gerbil auditory brainstem [Elektronische Ressource] / vorgelegt von Antje Brand

Brand Hunt, Antje

Sujets

• Biologie

Informations

• Publié par: ludwig-maximilians-universitat_munchen
• Publié le: 01 janvier 2003
• Nombre de lectures: 11
• Langue: English
• Poids de l'ouvrage: 10 Mo

Extrait

PRECISE TEMPORAL PROCESSING IN THE
GERBIL AUDITORY BRAINSTEM







Dissertation
zur Erlangung des Grades eines Doktors
der Naturwissenschaften

an der Fakultät für Biologie
der Ludwig-Maximilians-Universität München



vorgelegt von
Antje Brand


München, im Januar 2003






























1. Gutachter: PD Dr. Benedikt Grothe
2. Gutachter: Prof. Dr. Gerhard Neuweiler

eingereicht am 20. Januar 2003
Tag der mündlichen Prüfung: 14. März 2003









Nothing shocks me. I'm a scientist.
Harrison Ford, as Indiana Jones

Success is the ability to go from one
failure to another with no loss of
enthusiasm.
Sir Winston Churchill

0. Table of Contents

1. Summary / Zusammenfassung ........................................ 1
2. Introduction...................................................................... 5
2.1 The Medial Superior Olive.....................................................................5
2.1.1 Temporal processing in a spatial context..........................................5
2.1.2 The role of the MSO in sound recognition ......................................12
2.2 The Superior Paraolivary Nucleus.......................................................14
2.3 The gerbil as an animal model.............................................................16
2.4 The scope of this study .........................................................................17
3. Methods .......................................................................... 19
3.1 Stereotaxia and Surgery.......................................................................19
3.2 Neuronal Recordings...........................................................................21
3.3 Acoustic stimulation.............................................................................22
3.4 Recording Procedure
3.5 Pharmacology......................................................................................23
3.6 Data Analysis.......................................................................................24
3.7 Histology..............................................................................................25
3.7.1 Histology of HRP Injections............................................................26
3.7.2 Histology of bead injections27
3.8 MSO - Reconstruction ..........................................................................27
4. Results ............................................................................ 29
4.1 The Medial Superior Olive...................................................................29
4.1.1 Reconstruction of recording sites....................................................29
4.1.2 Spontaneous activity........................................................................33
4.1.3 Tuning characteristics.....................................................................34
4.1.4 Tonotopic Representation................................................................35
4.1.5 Response pattern.............................................................................38
4.1.6 Response latency41
4.1.7 Binaural response characteristics...................................................42
4.1.8 ITD sensitivity to low frequency pure tones ....................................43
4.1.9 Effects of glycinergic inhibition in the MSO ...................................47
4.1.9.1 General effects ............................................................................47
4.1.9.2 Glycinergic inhibition in ITD coding .........................................48
4.1.10 ITD sensitivity to high frequencies..................................................52
4.1.11 Responses to SAM ...........................................................................53
4.1.11.1 Rate-based modulation transfer functions..................................54
4.1.11.2 Vector-strength based modulation transfer functions ................55
4.1.11.3 Monaural stimulation with SAM.................................................56
4.1.12 Glycinergic inhibition and high frequency temporal processing....57
4.2 The Superior Paraolivary Nucleus.......................................................59
4.2.1 Reconstruction of recording sites....................................................59
4.2.2 Spontaneous activity........................................................................60
4.2.3 Tuning characteristics.....................................................................
Table of Contents

4.2.4 Response pattern.............................................................................61
4.2.5 Response latency63
4.2.6 Binaural response characteristics...................................................64
4.2.7 Responses to SAM ...........................................................................67
4.2.8 Pharmacology.................................................................................70
4.3 Comparison of neuronal properties in MSO and SPN.........................73
5. Discussion....................................................................... 75
5.1 The Medial Superior Olive...................................................................75
5.1.1 Localization of low frequency sounds .............................................75
5.1.1.1 Representation of auditory space ...............................................75
5.1.1.2 Comparison to other ITD studies76
5.1.1.3 Models of the representation of auditory space .........................77
5.1.1.4 Encoding of ITDs in the avian system ........................................78
5.1.2. The role of inhibition in ITD coding80
5.1.2.1 The mammalian system...............................................................80
5.1.2.2 The avian system.........................................................................84
5.1.3 High frequency temporal processing...............................................85
5.1.3.1 Temporal processing in non-spatial context...............................85
5.1.3.2 Spatial Processing of high frequency cues .................................87
5.1.4 General response characteristics....................................................88
5.1.5 Reconstruction of recording sites91
5.1.6 Technical challenges of recording from single MSO neurons ........92
5.2 The Superior Paraolivary Nucleus.......................................................94
5.2.1 Temporal processing.......................................................................94
5.2.2 Binaural ........................................................................97
5.2.3 Tonotopy and cell subsets................................................................98
6. References 99
List of Abbreviations ...........................................................116
Acknowledgements .............................................................117
Curriculum Vitae .................................................................118
2 1. 1 Summary

Sound localization and recognition are two important tasks of the auditory system.
Both require accurate processing of temporal cues.
Microsecond differences in the arrival time of a sound at the two ears (interaural time
differences, ITDs) are the main cue for localizing low frequency sound sources in space.
Traditionally, ITDs are thought to be encoded by an array of coincidence-detector
neurons, receiving excitatory inputs from the two ears via axons of variable length
(“delay lines”), aligned in a topographic map of azimuthal auditory space. Convincing
evidence for the existence of such a map in the mammalian ITD detector, the medial
superior olive (MSO) is, however, lacking. Equally undetermined is the role of a
temporally glycinergic inhibitory input to MSO neurons. Using in vivo recordings from
the MSO of the Mongolian gerbil, the present study showed that the responses of ITD-
sensitive neurons are inconsistent with the idea of a topographic map of auditory space.
Moreover, whereas the maxima of ITD functions were found to be outside, the steepest
slope was positioned in the physiologically encountered range of ITDs. Local
iontophoretic application of glycine and its antagonist strychnine revealed that precisely-
timed glycinergic inhibition plays a critical role in determining the mechanism of ITD
tuning, by shifting the slope into the physiological range of ITDs.
Natural sounds are modulated in frequency and amplitude and their recognition
depends on the analysis of, amongst others, temporal cues. The bat MSO has been
shown to be involved in filtering of sinusoidally amplitude modulated (SAM) sounds.
This observation led to the assumption that the MSO serves different functions in high
and low frequency hearing mammals, namely filtering of temporal cues in high and
sound localization in low frequency hearing animals. However, the response to
temporally structured sounds