Kotak Vibhakar C, Sanes Dan H
Center for Neural Science, New York University, 4 Washington Place, Room 809, New York, NY 10003, USA.
Biol Cybern. 2003 Nov;89(5):363-70. doi: 10.1007/s00422-003-0441-7. Epub 2003 Nov 28.
A group of central auditory neurons residing in the lateral superior olivary nucleus (LSO) responds selectively to interaural level differences and may contribute to sound localization. In this simple circuit, ipsilateral sound increases firing of LSO neurons, whereas contralateral sound inhibits the firing rate via activation of the medial nucleus of the trapezoid body (MNTB). During development, individual MNTB fibers arborize within the LSO, but they undergo a restriction of their boutons that ultimately leads to mature topography. A critical issue is whether a distinct form of inhibitory synaptic plasticity contributes to MNTB synapse elimination within LSO. Whole-cell recording from LSO neurons in brain slices from developing gerbils show robust long-term depression (LTD) of the MNTB-evoked IPSP/Cs when the MNTB was activated at a low frequency (1 Hz). These inhibitory synapses also display mixed GABA/glycinergic transmission during development, as assessed physiologically and immunohistochemically (Kotak et al. 1998). While either glycine or GABA(A) receptors could independently display inhibitory LTD, focal delivery of GABA, but not glycine, at the postsynaptic-locus induces depression. Furthermore, the GABA(B) receptor antagonist, SCH-50911, prevents GABA or synaptically induced depression. Preliminary evidence also indicated strengthening of inhibitory transmission (LTP) by a distinct pattern of inhibitory activity. These data support the idea that GABA is crucial for the expression inhibitory LTD and that this plasticity may underlie the early refinement of inhibitory synaptic connections in the LSO.
一群位于外侧上橄榄核（LSO）的中枢听觉神经元对双耳水平差异有选择性反应，可能有助于声音定位。在这个简单的回路中，同侧声音会增加LSO神经元的放电，而对侧声音则通过激活梯形体内侧核（MNTB）来抑制放电率。在发育过程中，单个MNTB纤维在LSO内形成分支，但它们的终扣会经历限制，最终形成成熟的拓扑结构。一个关键问题是，一种独特形式的抑制性突触可塑性是否有助于LSO内MNTB突触的消除。对发育中的沙鼠脑片LSO神经元进行全细胞记录显示，当MNTB以低频（1 Hz）激活时，MNTB诱发的抑制性突触后电流/复合突触后电流（IPSP/Cs）出现强烈的长时程抑制（LTD）。如通过生理学和免疫组织化学评估（Kotak等人，1998年），这些抑制性突触在发育过程中也表现出混合的GABA/甘氨酸能传递。虽然甘氨酸或GABA(A)受体都可以独立表现出抑制性LTD，但在突触后位点局部递送GABA而非甘氨酸会诱发抑制。此外，GABA(B)受体拮抗剂SCH-50911可阻止GABA或突触诱导的抑制。初步证据还表明，通过一种独特的抑制性活动模式可增强抑制性传递（LTP）。这些数据支持这样一种观点，即GABA对于抑制性LTD的表达至关重要，并且这种可塑性可能是LSO中抑制性突触连接早期精细化的基础。
