Dykes R W, Craig A D
Département de Physiologie, Université de Montréal, Montreal, Quebec H3C 3J7, Canada.
J Neurophysiol. 1998 Jul;80(1):120-9. doi: 10.1152/jn.1998.80.1.120.
Both accidental and experimental lesions of the spinal cord suggest that neuronal processes occurring in the spinal cord modify the relay of information through the dorsal column-lemniscal pathway. How such interactions might occur has not been adequately explained. To address this issue, the receptive fields of mechanosensory neurons of the dorsal column nuclei were studied before and after manipulation of the spinal dorsal horn. After either a cervical or lumbar laminectomy and exposure of the dorsal column nuclei in anesthetized cats, the representation of the hindlimb or of the forelimb was defined by multiunit recordings in both the dorsal column nuclei and in the ipsilateral spinal cord. Next, a single cell was isolated in the dorsal column nuclei, and its receptive field carefully defined. Each cell could be activated by light mechanical stimuli from a well-defined cutaneous receptive field. Generally the adequate stimulus was movement of a few hairs or rapid skin indentation. Subsequently a pipette containing either lidocaine or cobalt chloride was lowered into the ipsilateral dorsal horn at the site in the somatosensory representation in the spinal cord corresponding to the receptive field of the neuron isolated in the dorsal column nuclei. Injection of several hundred nanoliters of either lidocaine or cobalt chloride into the dorsal horn produced an enlargement of the receptive field of the neuron being studied in the dorsal column nuclei. The experiment was repeated 16 times, and receptive field enlargements of 147-563% were observed in 15 cases. These data suggest that the dorsal horn exerts a tonic inhibitory control on the mechanosensory signals relayed through the dorsal column-lemniscal pathway. Because published data from other laboratories have shown that receptive field size is controlled by signals arising from the skin, we infer that the control of neuronal excitability, receptive field size and location for lemniscal neurons is determined by tonic afferent activity that is relayed through a synapse in the dorsal horn. This influence of dorsal horn neurons on the relay of mechanosensory information through the lemniscal pathways must modify our traditional views concerning the relative independence of these two systems.
脊髓的意外损伤和实验性损伤均表明，脊髓中发生的神经元活动会改变通过背柱-内侧丘系通路的信息传递。然而，这种相互作用是如何发生的，目前尚无充分解释。为解决这一问题，我们在操作脊髓背角前后，对背柱核的机械感觉神经元的感受野进行了研究。在麻醉猫中进行颈椎或腰椎椎板切除并暴露背柱核后，通过在背柱核和同侧脊髓中进行多单位记录来确定后肢或前肢的代表区。接下来，在背柱核中分离出单个细胞，并仔细确定其感受野。每个细胞都可以被来自明确界定的皮肤感受野的轻微机械刺激激活。一般来说，适宜刺激是几根毛发的移动或皮肤的快速压痕。随后，将一支装有利多卡因或氯化钴的移液管，放入脊髓体感代表区中与背柱核中分离出的神经元感受野相对应的同侧背角部位。向背角注射几百纳升的利多卡因或氯化钴，会使在背柱核中被研究的神经元的感受野扩大。该实验重复了16次，在15例中观察到感受野扩大了147% - 563%。这些数据表明，背角对通过背柱-内侧丘系通路传递的机械感觉信号施加了紧张性抑制控制。由于其他实验室发表的数据表明，感受野大小受皮肤产生的信号控制，我们推断，内侧丘系神经元的兴奋性、感受野大小和位置的控制，是由通过背角突触传递的紧张性传入活动决定的。背角神经元对通过内侧丘系通路的机械感觉信息传递的这种影响，必然会改变我们关于这两个系统相对独立性的传统观点。
