Corda M, Pantaleo T, Calamai F
Arch Fisiol. 1979 Jun 30;71(1-4):265-78.
The mode of action of acetylcholine (ACh) and succinylcholine (SCh) on the isolated frog's muscle spindle has been studied. Receptor afferent nervous supply was maintained; the appropriate spinal roots were dissected for stimulating motor axons and recording from sensory fibres. Excitatory effects on the afferent activity, when the receptor was held still and during stretching, were found with ACh or SCh concentrations of 10(-8) to 10(-3); 10(-6) g/ml being usually effective. These effects are similar to those obtained by stimulating fusimotor nerve fibres. The contractile activity of intrafusal muscle fibres which occurred during these effects was observed. Seldom, and only for high concentrations of ACh and SCh, a decrease in afferent activity following the excitatory effects was found. Tubocurarine chloride (10(-5)-10(04) g/ml) in the bath prevented both motor fibres and drugs effects. Sometimes slight transient excitation occurred at very high concentrations of the two tested substances; however, this effect was prevented by stronger curarization. The observed blocking effects were always reversed by removing tubocurarine from the bath. No more excitatory effects by motor fibres stimulation and by ACh and SCh action could be found after destruction of intrafusal muscle fibres, by pinching them as close as possible to the ends of the spindle. It is suggested that ACh and SCh act indirectly by causing mechanical changes in intrafusal muscle fibres, and that a direct action on sensory nerve endings, if any, cannot, by itself, increase the afferent activity of the receptor.
已对乙酰胆碱（ACh）和琥珀酰胆碱（SCh）对离体青蛙肌梭的作用方式进行了研究。维持受体传入神经供应；解剖相应的脊神经根以刺激运动轴突并记录感觉纤维的活动。当受体保持静止以及在拉伸过程中，发现ACh或SCh浓度为10（-8）至10（-3）时对传入活动有兴奋作用；10（-6）g/ml通常有效。这些作用与刺激梭内运动神经纤维所获得的作用相似。观察到在这些作用过程中梭内肌纤维的收缩活动。很少发现，而且仅在高浓度的ACh和SCh作用下，兴奋作用后传入活动会降低。浴槽中的氯化筒箭毒碱（10（-5）-10（04）g/ml）可阻止运动纤维和药物的作用。有时在两种受试物质的非常高浓度下会出现轻微的短暂兴奋；然而，更强的箭毒化可阻止这种作用。通过从浴槽中去除筒箭毒碱，观察到的阻断作用总是会逆转。在尽可能靠近肌梭末端捏断梭内肌纤维后，通过刺激运动纤维以及ACh和SCh的作用不再能发现兴奋作用。提示ACh和SCh通过引起梭内肌纤维的机械变化间接起作用，并且对感觉神经末梢的直接作用（如果有的话）本身不能增加受体的传入活动。
