Lo Y J, Rao S C, Sanes D H
Center for Neural Science, New York University, New York 10003, USA.
Neuroscience. 1998 Apr;83(4):1075-84. doi: 10.1016/s0306-4522(97)00410-7.
Inhibitory synaptic transmission is of fundamental importance during the maturation of central auditory circuits, and their subsequent ability to process acoustic information. The present study investigated the manner in which inhibitory transmission regulates intracellular free calcium levels in the gerbil inferior colliculus using a brain slice preparation. Inhibitory and excitatory postsynaptic potentials were evoked by electrical stimulation of the ascending afferents at the level of the dorsal nucleus of the lateral lemniscus. Pharmacologically isolated inhibitory synaptic potentials were able to attenuate a calcium rise in collicular neurons that was generated by depolarizing current injection. In addition, GABA(A) and glycine receptor antagonists typically led to an increase of calcium in collicular neurons during electrical stimulation of the ascending afferent pathway at the level of the dorsal nucleus of the lateral lemniscus. Bath application of GABA or muscimol, a GABA(A) receptor agonist, evoked a brief hyperpolarization followed by a long-lasting depolarization in inferior colliculus neurons. This treatment also induced a transient calcium increase that correlated with the membrane depolarization phase. Baclofen, a GABA(B) receptor agonist, had no effect on either membrane potential or calcium levels. Ratiometric measures indicated that the muscimol-evoked rise in calcium was approximately 150 nM above basal levels. The muscimol-evoked responses were completely antagonized by bicuculline and attenuated by picrotoxin. Together, these results suggest that inhibitory synaptic transmission participates in the regulation of postsynaptic calcium during the developmental period. Inhibitory transmission may attenuate a calcium influx that is evoked by excitatory synapses, but it can also produce a modest influx of calcium when activated alone. These mechanisms may help to explain the influence of inhibitory transmission on the development of postsynaptic properties.
抑制性突触传递在中枢听觉回路成熟及其随后处理声学信息的能力过程中具有至关重要的意义。本研究利用脑片标本，研究了抑制性传递调节沙鼠下丘细胞内游离钙水平的方式。通过电刺激外侧丘系背核水平的上行传入纤维诱发抑制性和兴奋性突触后电位。药理学分离的抑制性突触电位能够减弱由去极化电流注入产生的丘神经元钙升高。此外，在电刺激外侧丘系背核水平的上行传入通路时，GABA(A)和甘氨酸受体拮抗剂通常会导致丘神经元钙增加。浴用GABA或GABA(A)受体激动剂蝇蕈醇，在下丘神经元中诱发短暂的超极化，随后是持久的去极化。这种处理还诱导了与膜去极化阶段相关的短暂钙增加。GABA(B)受体激动剂巴氯芬对膜电位或钙水平均无影响。比率测量表明，蝇蕈醇诱发的钙升高比基础水平高约150 nM。蝇蕈醇诱发的反应被荷包牡丹碱完全拮抗，被印防己毒素减弱。这些结果共同表明，抑制性突触传递在发育期间参与突触后钙的调节。抑制性传递可能减弱由兴奋性突触诱发的钙内流，但当单独激活时也可产生适度的钙内流。这些机制可能有助于解释抑制性传递对突触后特性发育的影响。
