Ernest Gallo Clinic and Research Center, University of California, San Francisco, Emeryville, California 94608, USA.
J Neurosci. 2010 Jun 16;30(24):8229-33. doi: 10.1523/JNEUROSCI.1754-10.2010.
Coincident signaling by dopamine and glutamate is thought to be crucial for a variety of motivated behaviors. Previous work has suggested that some midbrain dopamine neurons are themselves capable of glutamate corelease, but this phenomenon remains poorly understood. Here, we expressed the light-activated cation channel Channelrhodopsin-2 (ChR2) in genetically defined midbrain dopamine neurons to stimulate exocytosis specifically from dopaminergic terminals in both the nucleus accumbens (NAc) shell and dorsal striatum of brain slices from adult mice. Optical activation resulted in robust glutamate-mediated EPSCs in all medium spiny neurons examined in the NAc shell. In contrast, optically evoked glutamatergic currents were nearly undetectable in the dorsal striatum. Further, we used a conditional knock-out mouse lacking vesicular glutamate transporter 2 (VGLUT2) specifically in dopamine neurons to determine whether VGLUT2 is required for the exocytotic release of glutamate from dopamine neurons. Our data show that conditional knock-out completely abolished all optically evoked glutamate release. These results provide definitive physiological evidence for VGLUT2-mediated glutamate release by mature dopamine neurons projecting to the NAc shell, but not to the dorsal striatum. Thus, the unique ability of NAc-projecting dopamine neurons to synchronously activate both dopamine and glutamate receptors may have crucial implications for the ability to respond to motivationally significant stimuli.
多巴胺和谷氨酸的共信号传递被认为对各种动机行为至关重要。先前的工作表明,一些中脑多巴胺神经元本身能够共释放谷氨酸,但这种现象仍知之甚少。在这里,我们在遗传定义的中脑多巴胺神经元中表达了光激活阳离子通道 Channelrhodopsin-2(ChR2),以刺激来自成年小鼠脑切片中伏隔核壳(NAc 壳)和背侧纹状体的多巴胺能末梢的胞吐作用。光激活导致 NAc 壳中所有检查的中间棘神经元中均产生强大的谷氨酸介导的 EPSC。相比之下,在背侧纹状体中,光诱发的谷氨酸电流几乎无法检测到。此外,我们使用在多巴胺神经元中特异性缺失囊泡谷氨酸转运体 2(VGLUT2)的条件敲除小鼠来确定 VGLUT2 是否是多巴胺神经元从突触小泡中释放谷氨酸所必需的。我们的数据表明,条件敲除完全消除了所有光诱发的谷氨酸释放。这些结果为 VGLUT2 介导的投射到 NAc 壳的成熟多巴胺神经元的谷氨酸释放提供了明确的生理证据,但不会投射到背侧纹状体。因此,NAc 投射多巴胺神经元同步激活多巴胺和谷氨酸受体的独特能力可能对响应动机重要刺激的能力具有重要意义。