Mechanisms underlying action of neurotrophic factors on postsynaptic glutamate and GABA receptors

先前我们发现脑源性神经营养因子（BDNF）以活动依赖的方式从突触前位点释放，并作用于突触后神经元。在本研究中，我们试图观察BDNF在谷氨酸能兴奋性突触和gaba能抑制性突触中的作用是否不同，并进一步阐明这种作用的机制。我们得到了以下结果。利用绿色荧光蛋白（GFP）小鼠和BDNF敲除小鼠的混合神经元培养制剂，我们探讨了突触前BDNF对突触后神经元的作用。我们发现突触前BDNF促进突触后gaba能神经元的树突发育。在胶质微岛培养的gabaergy神经元中，研究了外源性BDNF对gabaergy突触的作用，完全排除了BDNF对兴奋性突触的影响。我们发现BDNF增加了gaba能突触的活跃数量。研究了内源性BDNF在敲除BDNF和野生型小鼠桶状皮质谷氨酸能突触发育中的作用。我们发现，仅由NMDA受体组成的沉默突触在BDNF敲除小鼠中异常增加，这可以通过外源性BDNF修复。外源性BDNF对gaba能神经元兴奋性突触作用的研究尚未见报道。我们通过使用GAD67-GFP敲入小鼠来解决这个问题，在小鼠中gaba能神经元很容易被识别。我们发现BDNF严重抑制gaba能神经元兴奋性突触的功能。

Previously we found that brain-derived neurotrophic factor (BDNF) is released from presynaptic sites in an activity-dependent manner and acts on postsynaptic neurons. In this study we attempted to see whether actions of BDNF are different between glutamatergic excitatory synapses and GABAergic inhibitory synapses, and further to elucidate mechanisms underlying such actions. We obtained the following results.1.Using mixed neuron culture preparations obtained from green fluorescence protein (GFP) mice and BDNF knockout mice, we explored what actions presynaptic BDNF exerts on postsynaptic neurons. We found that presynaptic BDNF promotes dendritic development of postsynaptic GABAergic neurons.2.Actions of exogenous BDNF on GABAergic synapses were investigated in solitary GABAergic neurons cultured on glial microisland to completely exclude possible involvement of excitatory synapses from the observed effects of BDNF. We found that BDNF increased the number of active GABAergic synapses.3.Roles of endogenous BDNF in development of glutamatergic synapses were investigated in barrel cortex of BDNF knockout and wild type mice. We found that silent synapses, which consist only of NMDA receptors, are abnormally increased in BDNF knockout mice, and this is rescued by exogenously applied BDNF.4.Actions of exogenous BDNF on excitatory synapses on GABAergic neurons were not studied previously. We addressed this issue by using GAD67-GFP knock-in mice, in which GABAergic neurons are easily identified. We found that BDNF acutely depressed function of excitatory synapses to GABAergic neurons.