Developmental inhibitory transmitter switching for GANA to glycine

为了阐明发生在脑干听觉中继核的抑制性递质转换的功能意义，我们用电生理和免疫组织化学方法检测了GABA_B受体在发育过程中的表达。GABAB受体亚基R1和R2的表达密度随着发育而降低，我们还观察到R1的表达模式从神经元到星形胶质细胞的发育变化。GABAB受体介导的突触后K~+电导在同一时期显著降低。因此，我们发现，在大鼠听力开始前后(出生后约10天)，LSO神经元中GABAB受体的表达和GABA_B受体激活的功能效应(即膜K~+电导增加)都显著减少。已知在听力开始时，LSO的抑制输入由GABA能变为甘氨酸能，我们的结果表明GABA_B受体介导的抑制也显示出发育可塑性。除了已描述的GABA_A受体介导的反应从去极化到超极化的发育变化之外，目前的数据还为GABA能神经生物学的发育变化提供了一个新的和额外的例子。

In order to elucidate the functional implication of inhibitory transmitter switching occurring at auditory relay nucleus of brain stem, we employed electrophysiological and immunohistochemical approach of GABA_B receptor expression over the developmental period. There was a concomitant developmental reduction in the density of expression of the GABAB receptor subunits, R1 and R2, and we also observed a developmental change in the expression pattern of R1 from neurons to astroglia. The GABAB receptor mediated increase in postsynaptic K^+ conductance showed a dramatic reduction over the same period. We have therefore shown that, around the onset of hearing in rats (about 10 days after birth) there is a dramatic reduction in both GABAB receptor expressions in LSO neurons and in the functional effects of GABA_B receptor activation i.e. increased membrane K^+ conductance. It is known that inhibitory input into the LSO changes from being GABAergic to being glycinergic around the onset of hearing ; our results indicate that GABA_B receptor mediated inhibition also shows developmental plasticity. In addition to the well-described developmental change of GABA_A receptor mediated responses from depolarizing to hyperpolarizing, the current data provides a novel and additional example of developmental changes in GABAergic neurobiology.