Synaptic changes underlying the strengthening of GABA/glycinergic connections in the developing lateral superior olive

• Published in: Neuroscience Vol. 171; no. 3; pp. 924 - 933
• Main Authors: Kim, G, Kandler, K
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier Ltd 15.12.2010; Elsevier
• Subjects: Acoustic Stimulation - methods; Animals; Animals, Newborn; auditory; Biological and medical sciences; Cochlear Nucleus - physiology; Cochlear Nucleus - secretion; Fundamental and applied biological sciences. Psychology; gamma-Aminobutyric Acid - metabolism; gamma-Aminobutyric Acid - secretion; Glycine - metabolism; Glycine - secretion; inhibitory; Mice; Mice, 129 Strain; Neural Pathways - physiology; Neural Pathways - secretion; Neurology; Olivary Nucleus - cytology; Olivary Nucleus - growth & development; Olivary Nucleus - metabolism; Organ Culture Techniques - methods; Pons - cytology; Pons - growth & development; Pons - metabolism; refinement; sound localization; Synaptic Transmission - physiology; Vertebrates: nervous system and sense organs; miniature PSCs; PPRs; paired pulse ratios; mPSCs; PPD; inhibitory; LSO; MNTB; postsynaptic currents; lateral superior olive; CV; sound localization; auditory; PSCs; paired pulse depression; refinement; coefficient of variation; medial nucleus of the trapezoid body; Stimulus localization; Neurotransmitter; Development; GABA; Lateral superior olivary nucleus
• ISSN: 0306-4522; 1873-7544
• DOI: 10.1016/j.neuroscience.2010.09.054

Abstract Before hearing onset, the topographic organization of the auditory GABA/glycinergic pathway from the medial nucleus of the trapezoid body (MNTB) to the lateral superior olive (LSO) is refined by synaptic silencing and strengthening. The synaptic mechanisms underlying the developmental strengthening of maintained MNTB-LSO connections are unknown. Here we address this question using whole-cell recordings from LSO neurons in slices prepared from prehearing mice. Minimal and maximal stimulation techniques demonstrated that during the first two postnatal weeks, individual LSO neurons lose about 55% of their initial presynaptic MNTB partners while maintained single-fiber connections become about 14-fold stronger. Analysis of MNTB-evoked miniature events indicates that this strengthening is accompanied by a 2-fold increase in quantal amplitude. Strengthening is not caused by an increase in the probability of release because paired pulse ratios (PPRs) increased from 0.7 in newborn animals to 0.9 around hearing onset, indicating a developmental decrease rather than increase in release probability. In addition, a possible soma-dendritic relocation of MNTB input seems unlikely to underlie their strengthening as indicated by analysis of the rise times of synaptic currents. Taken together, we conclude that the developmental strengthening of MNTB-LSO connections is achieved by a 2-fold increase in quantal size and an 8-fold increase in quantal content.