Smith A T, Baker-Short C M
Vision Research Unit, School of Psychology, University of Wales College of Cardiff, Wales.
Vis Neurosci. 1993 Nov-Dec;10(6):1073-9. doi: 10.1017/s095252380001018x.
Two basic types of cholinergic receptor have been identified in nervous systems: nicotinic and muscarinic. In the mammalian visual system, the balance of evidence suggests that nicotinic activity is associated primarily with transmission and processing of information while muscarinic activity reflects modulatory influences arising in the brainstem and basal forebrain. We have measured contrast sensitivity functions using a two-alternative forced-choice procedure in young human volunteers with and without administration of nicotine (1.5 mg by buccal absorption) or the muscarinic antagonist scopolamine (1.2 mg orally). Scopolamine elevates contrast-detection thresholds uniformly at all spatial frequencies, consistent with blocking of a nonspecific arousal system. Nicotine, in contrast, improves sensitivity at low spatial frequencies (below about 4 cycle/deg); at higher spatial frequencies sensitivity is, if anything, impaired. Using counterphase gratings, we find that scopolamine elevates thresholds uniformly at all temporal frequencies. Nicotine lowers thresholds at high but not low temporal frequencies. The results obtained with nicotine suggest that contrast sensitivity reflects the activity of two mechanisms, or sets of spatiotemporal filters, that are pharmacologically distinct, the contrast sensitivity function reflecting the envelope of their sensitivities.
烟碱型和毒蕈碱型。在哺乳动物视觉系统中，现有证据表明，烟碱型活动主要与信息的传递和处理相关，而毒蕈碱型活动则反映了源自脑干和基底前脑的调节性影响。我们在年轻人类志愿者中使用二项必选法测量了对比敏感度函数，这些志愿者分别在给予尼古丁（经颊吸收1.5毫克）或毒蕈碱拮抗剂东莨菪碱（口服1.2毫克）前后进行测量。东莨菪碱在所有空间频率下均一致提高对比检测阈值，这与阻断非特异性唤醒系统相符。相比之下，尼古丁提高了低空间频率（低于约4周/度）下的敏感度；在较高空间频率下，敏感度反而受损。使用反相光栅，我们发现东莨菪碱在所有时间频率下均一致提高阈值。尼古丁降低了高时间频率而非低时间频率下的阈值。尼古丁的实验结果表明，对比敏感度反映了两种机制或时空滤波器组的活动，它们在药理学上是不同的，对比敏感度函数反映了它们敏感度的包络线。
