Giakoumaki Stella G, Hourdaki Eugenia, Grinakis Vangelis, Theou Katerina, Bitsios Panos
Department of Psychiatry and Behavioural Sciences, Medical School, University of Crete, Heraklion, Crete, Greece.
J Psychopharmacol. 2005 Mar;19(2):139-48. doi: 10.1177/0269881105048994.
Fear (e.g. associated with the threat of an electric shock) causes an increase in initial pupil diameter (IPD) and a decrease in the amplitude of the light reflex response. There is evidence for dissociation between the two responses to threat: only the reduction in light reflex response amplitude is sensitive to the anxiolytic drug diazepam. We examined the effects of peripheral sympathetic blockade with the alpha(1)-adrenoceptor antagonist dapiprazole on both responses to threat on the basis of the hypothesis that only the response of the IPD will be affected, whereas the response of the light reflex will remain unaffected. Twelve healthy volunteers (Experiment 1) and eight healthy volunteers with smaller pupils (Experiment 2) participated in one experimental session. Dapiprazole 0.5% (two drops of 20 microl, three times) was instilled in the subjects' right or left eye while the contralateral eye was treated with placebo eye drops (artificial tear, two drops of 20 microl, three times) according to a single-blind balanced design. Pupil diameter was monitored by infrared binocular television pupillometry. At the point of maximum dapiprazole-evoked miosis, the light reflex was elicited three times in each of three Safe blocks (no possibility of electric shock), alternating with three Threat blocks (possibility of electric shock). At the end of each Safe and Threat block, subjects rated their mood and feelings on the Visual Analogue Scales. In Experiment 1, dapiprazole caused significant miosis. Threat increased subjectively rated anxiety and inhibited the light reflex. The inhibition of the light reflex was unaffected by dapiprazole. The threat-induced increase in IPD was also unaffected by dapiprazole, probably due to a ceiling effect curtailing the threat-induced increase in IPD. In the smaller pupil group in Experiment 2, where the possible contribution of a ceiling effect was minimized, dapiprazole suppressed the threat-induced increase in IPD. The inhibition of the light reflex by threat is likely to reflect central parasympathetic inhibition and is unlikely to involve the peripheral sympathetic innervation of the iris. The threat-induced increase in IPD is likely to reflect mainly central sympathetic excitation. The different central autonomic mechanisms underlying the two pupillary responses to threat may explain the dissociation between the separate effects of threat on IPD and light reflex amplitude.
恐惧（例如与电击威胁相关）会导致初始瞳孔直径（IPD）增大以及光反射反应幅度减小。有证据表明对威胁的这两种反应之间存在分离：只有光反射反应幅度的降低对抗焦虑药物地西泮敏感。基于仅IPD的反应会受到影响而光反射反应将不受影响这一假设，我们研究了用α(1)-肾上腺素能受体拮抗剂达哌唑进行外周交感神经阻滞对两种威胁反应的影响。12名健康志愿者（实验1）和8名瞳孔较小的健康志愿者（实验2）参与了一个实验环节。按照单盲平衡设计，将0.5%的达哌唑（两滴，每滴20微升，共三次）滴入受试者的右眼或左眼，而对侧眼用安慰剂眼药水（人工泪液，两滴，每滴20微升，共三次）处理。通过红外双目电视瞳孔测量法监测瞳孔直径。在达哌唑引起最大程度瞳孔缩小的时候，在三个安全时段（无电击可能性）中的每一个时段，光反射被诱发三次，与三个威胁时段（有电击可能性）交替进行。在每个安全和威胁时段结束时，受试者在视觉模拟量表上对他们的情绪和感受进行评分。在实验1中，达哌唑引起了显著的瞳孔缩小。威胁增加了主观评定的焦虑并抑制了光反射。光反射的抑制不受达哌唑影响。威胁引起的IPD增加也不受达哌唑影响，这可能是由于天花板效应限制了威胁引起的IPD增加。在实验2的较小瞳孔组中，天花板效应的可能影响被最小化，达哌唑抑制了威胁引起的IPD增加。威胁对光反射的抑制可能反映了中枢副交感神经抑制，不太可能涉及虹膜的外周交感神经支配。威胁引起的IPD增加可能主要反映中枢交感神经兴奋。对威胁的两种瞳孔反应背后不同的中枢自主神经机制可能解释了威胁对IPD和光反射幅度的单独影响之间的分离。
