Zhang S Q, Butler J M, Cole D F
Exp Eye Res. 1984 Feb;38(2):153-63. doi: 10.1016/0014-4835(84)90099-x.
Electrical field stimulation produced contractions of the rabbit isolated iris sphincter muscle which were completely blocked by tetrodotoxin (10(-6) M). Low frequency (0.16-5 Hz) responses were atropine-resistant, but were prevented by sensory (trigeminal) denervation, and were considered to be owing to antidromic stimulation of sensory nerves. Higher frequency (10-40 Hz) responses were apparently unaffected by atropine alone (3 X 10(-7) M) and unaltered by sensory denervation, but were completely blocked by a combination of both. Thus at higher frequencies both cholinergic and sensory nerves would seem to be activated. Capsaicin-induced contraction of the isolated iris sphincter muscle, previously shown to be dependent upon an intact and functional sensory nerve supply, was not suppressed by atropine (3 X 10(-7) M) or by tetrodotoxin (10-6 M). Capsaicin therefore, although acting via sensory nerves, does not seem to require axonal conduction or Na+ flux to produce a response. This pain-producing substance may therefore act directly on sensory elements to release a mediator without requiring excitation of adjacent fibres by axon reflex. Contractile responses to capsaicin and also to low-frequency electrical stimulation were partially inhibited by morphine (5 X 10(-5) M), which in contrast had no effect on responses to carbachol or to substance P. Thus, at the peripheral as at the central endings of these bipolar primary afferent fibres, morphine may inhibit the release of the putative mediator.
电场刺激可使兔离体虹膜括约肌产生收缩，这种收缩可被河豚毒素（10⁻⁶ M）完全阻断。低频（0.16 - 5 Hz）反应对阿托品有抗性，但可通过感觉（三叉神经）去神经支配来预防，被认为是由于感觉神经的逆向刺激所致。高频（10 - 40 Hz）反应单独使用阿托品（3×10⁻⁷ M）时显然不受影响，感觉去神经支配也不会改变，但两者联合使用时则完全被阻断。因此，在较高频率下，胆碱能神经和感觉神经似乎都会被激活。辣椒素诱导的离体虹膜括约肌收缩，先前已证明依赖于完整且功能正常的感觉神经供应，不受阿托品（3×10⁻⁷ M）或河豚毒素（10⁻⁶ M）的抑制。因此，辣椒素虽然通过感觉神经起作用，但似乎不需要轴突传导或钠离子通量来产生反应。这种致痛物质可能因此直接作用于感觉元件以释放介质，而不需要通过轴突反射激发相邻纤维。对辣椒素以及低频电刺激的收缩反应被吗啡（5×10⁻⁵ M）部分抑制，相比之下，吗啡对卡巴胆碱或P物质的反应没有影响。因此，在这些双极初级传入纤维的外周和中枢末梢，吗啡可能抑制假定介质的释放。
