Bhandari R N, Ogilvie J, Clarke R W
Division of Animal Physiology, School of Biological Sciences, University of Nottingham, Loughborough, UK.
Neuroscience. 1999 Apr;90(1):177-89. doi: 10.1016/s0306-4522(98)00426-6.
Noxious mechanical and chemical stimuli were applied to the toes of the left hind limb of decerebrated, spinalized rabbits and their effects on a hind limb spinal withdrawal reflex and expression of Fos-like immunoreactivity in the spinal cord were measured. The animals were prepared so as to minimize nociceptive inputs arising from surgery. A single crush stimulus applied with a pair of haemostatic forceps caused long-lasting (c. 20 min) inhibition of reflexes evoked in medial gastrocnemius motoneurons by electrical stimulation of the skin at the heel. Naloxone (0.25 mg/kg i.v.) increased reflexes to more than 1000% of pre-drug controls and reversed crush-evoked inhibition. Mustard oil applied to the toes had no consistent effects on the heel-gastrocnemius reflex before or after naloxone. Both crush and mustard oil stimuli gave rise to unilateral increases in the number of Fos-immunopositive profiles in the superficial dorsal horn of spinal segments L7 and S1. There were significantly more Fos-immunoreactive elements in the central and lateral parts of lamina I of both segments in animals receiving the crush stimulus than there were in animals receiving the mustard oil stimulus. Immunochemical localization of enkephalins in rabbit spinal cord showed a dense network of fibres and terminals in laminae I and II, accompanied by infrequent but distinctly stained neuronal cell bodies. The same pattern, with increased numbers of visible cell bodies, was seen after treatment with colchicine. The present data show that tonic and stimulus-evoked opioidergic inhibition of the heel-gastrocnemius reflex of the rabbit are not epiphenomena of surgical preparation of the hindlimb. Opioid-mediated inhibition of the heel-gastrocnemius withdrawal reflex of the rabbit was evoked by noxious mechanical but not by chemical stimulation of the toes. Of these stimuli, the former gave rise to greater activation of neurons in central and lateral lamina I of segments L7 and S1, the region of termination of afferent fibres from the heel and the location of some enkephalin-positive neuronal cell bodies. Thus, noxious mechanical stimulation of the toes elicits inhibition of the heel-gastrocnemius withdrawal reflex, probably via activation of enkephalinergic neurons in the lateral half of lamina I in the L7 and S1 segments.
将有害的机械和化学刺激施加于去大脑、脊髓横断的家兔左后肢的脚趾，并测量其对后肢脊髓退缩反射以及脊髓中Fos样免疫反应性表达的影响。对动物进行准备以尽量减少手术引起的伤害性输入。用一把止血钳施加单次挤压刺激会导致对通过电刺激足跟皮肤在腓肠肌内侧运动神经元中诱发的反射产生持久（约20分钟）的抑制。纳洛酮（0.25毫克/千克静脉注射）使反射增加至用药前对照的1000%以上，并逆转挤压诱发的抑制。在纳洛酮给药前后，将芥子油涂抹在脚趾上对足跟 - 腓肠肌反射没有一致的影响。挤压和芥子油刺激均导致L7和S1脊髓节段浅表背角中Fos免疫阳性轮廓数量单侧增加。接受挤压刺激的动物中，两个节段I层中央和外侧部分的Fos免疫反应性元素明显多于接受芥子油刺激的动物。脑啡肽在兔脊髓中的免疫化学定位显示I层和II层中有密集的纤维和终末网络，伴有不常见但染色明显的神经元细胞体。用秋水仙碱处理后可见相同模式，可见细胞体数量增加。目前的数据表明，兔足跟 - 腓肠肌反射的紧张性和刺激诱发的阿片样物质抑制不是后肢手术准备的附带现象。阿片类物质介导的兔足跟 - 腓肠肌退缩反射抑制是由有害机械刺激而非脚趾的化学刺激诱发的。在这些刺激中，前者引起L7和S1节段中央和外侧I层神经元的更大激活，该区域是来自足跟的传入纤维的终止部位以及一些脑啡肽阳性神经元细胞体的位置。因此，脚趾的有害机械刺激可能通过激活L7和S1节段I层外侧半部的脑啡肽能神经元来引发对足跟 - 腓肠肌退缩反射的抑制。
