Waterhouse B D, Sessler F M, Cheng J T, Woodward D J, Azizi S A, Moises H C
Department of Physiology and Biophysics, Hahnemann University, Philadelphia, PA 19102-1192.
Brain Res Bull. 1988 Sep;21(3):425-32. doi: 10.1016/0361-9230(88)90154-2.
Many previous studies have examined the effects of norepinephrine (NE) on neuronal responsiveness to synaptic inputs and putative transmitter substances and have described differential depressant actions of NE on stimulus evoked versus spontaneous discharge such that the "signal to noise" ratio of threshold responses was increased. In the present studies, similar experimental strategies employing a combination of microiontophoresis, single unit recording and afferent pathway stimulation in intact anesthetized and brain tissue slice preparations have revealed noradrenergic "gating" actions whereby weak or subthreshold synaptic stimuli can evoke threshold neuronal responses in the presence of iontophoretically applied NE or following electrical stimulation of the locus coeruleus. Overall, these results suggest that potentially threshold excitatory and inhibitory synaptic inputs may normally arrive at central neurons but appear weak or absent except during behavioral conditions favoring the synaptic release of NE. As such, these findings provide evidence that signal to noise ratio may not be the only potential modulatory action expressed by NE in noradrenergic target circuits of the mammalian brain.
许多先前的研究已经考察了去甲肾上腺素（NE）对神经元对突触输入和假定递质物质反应性的影响，并描述了NE对刺激诱发放电与自发放电的不同抑制作用，从而使阈反应的“信噪比”增加。在本研究中，在完整的麻醉动物和脑组织切片标本中，采用微离子电泳、单单位记录和传入通路刺激相结合的类似实验策略，揭示了去甲肾上腺素能的“门控”作用，即在离子电泳施加NE的情况下，或在电刺激蓝斑后，微弱或阈下突触刺激可诱发阈神经元反应。总体而言，这些结果表明，潜在的阈兴奋性和抑制性突触输入通常可能到达中枢神经元，但除了在有利于NE突触释放的行为条件下，这些输入似乎微弱或不存在。因此，这些发现提供了证据，表明信噪比可能不是NE在哺乳动物脑去甲肾上腺素能靶回路中表达的唯一潜在调节作用。
